tunnel backfill knowledge: Topics by WorldWideScience.org

Sample records for tunnel backfill knowledge

Backfilling of deposition tunnels: Use of bentonite pellets

International Nuclear Information System (INIS)

Dixon, David; Sanden, Torbjoern; Jonsson, Esther; Hansen, Johanna

2011-02-01

The state of knowledge related to use of bentonite pellets as part of backfill or other gap filling components in repository applications is reviewed. How the pellets interact with adjacent sealing materials and the surrounding rock mass is a critical aspect in determining backfill behaviour. The key features and processes that determine how the pellet component of the KBS-3V deposition tunnel backfill will behave are discussed and recommendations related to what additional information needs to be developed are provided. Experiences related to pellet material composition, size, shape, placement options and more importantly, the density to which they can be placed all indicate that there are significant limitations to the achievable as-placed density of bentonite pellet fill. Low as-placed density of the pellet fill component of the backfill is potentially problematic as the outermost regions of tunnel backfill will be the first region of the backfill to be contacted by water entering the tunnels. It is also through this region that initial water movement along the length of the deposition tunnels will occur. This will greatly influence the operations in a tunnel, especially with respect to situations where water is exiting the downstream face of still open deposition tunnels. Pellet-filled regions are also sensitive to groundwater salinity, susceptible to development of piping features and subsequent mechanical erosion by through flowing water, particularly in the period preceding deposition tunnel closure. A review of the experiences of various organisations considering use of bentonite-pellet materials as part of buffer or backfill barriers is provided in this document. From this information, potential options and limitations to use of pellets or pellet-granule mixtures in backfill are identified. Of particular importance is identification of the apparent upper-limits of dry density to which such materials can to be placed in the field. These bounds will
Backfilling of deposition tunnels: Use of bentonite pellets

Energy Technology Data Exchange (ETDEWEB)

Dixon, David (Atomic Energy of Canada Limited (Canada)); Sanden, Torbjoern (Clay Technology AB (Sweden)); Jonsson, Esther (Swedish Nuclear Fuel and Waste Mangaement Co. (Sweden)); Hansen, Johanna (Posiva Oy (Finland))

2011-02-15

The state of knowledge related to use of bentonite pellets as part of backfill or other gap filling components in repository applications is reviewed. How the pellets interact with adjacent sealing materials and the surrounding rock mass is a critical aspect in determining backfill behaviour. The key features and processes that determine how the pellet component of the KBS-3V deposition tunnel backfill will behave are discussed and recommendations related to what additional information needs to be developed are provided. Experiences related to pellet material composition, size, shape, placement options and more importantly, the density to which they can be placed all indicate that there are significant limitations to the achievable as-placed density of bentonite pellet fill. Low as-placed density of the pellet fill component of the backfill is potentially problematic as the outermost regions of tunnel backfill will be the first region of the backfill to be contacted by water entering the tunnels. It is also through this region that initial water movement along the length of the deposition tunnels will occur. This will greatly influence the operations in a tunnel, especially with respect to situations where water is exiting the downstream face of still open deposition tunnels. Pellet-filled regions are also sensitive to groundwater salinity, susceptible to development of piping features and subsequent mechanical erosion by through flowing water, particularly in the period preceding deposition tunnel closure. A review of the experiences of various organisations considering use of bentonite-pellet materials as part of buffer or backfill barriers is provided in this document. From this information, potential options and limitations to use of pellets or pellet-granule mixtures in backfill are identified. Of particular importance is identification of the apparent upper-limits of dry density to which such materials can to be placed in the field. These bounds will
Flow and solute transport in backfilled tunnel and collapsed backfill - possible extension of Comp32

International Nuclear Information System (INIS)

Neretnieks, Ivars

2006-09-01

In the Swedish deep geological final repository for spent fuel the tunnels will be filled with a backfill with low permeability. However, some flow may take place in the backfill. Nuclides released from a leaking canister could diffuse up to the flowing water in the backfill and be transported downstream in the tunnel. At an intersection of the tunnel with a fracture zone the contaminated water might flow out into the zone.This report addresses the transport mechanisms and rate of transport from a leaking canister up through the buffer and backfill in the deposition hole, further into the backfill in the tunnel and the transport along the tunnel. Spreading by diffusion in the buffer and backfill as well as retardation of sorbing nuclides is accounted for.The transport mechanisms and rates of transport are described and some simple models with analytical solutions are used to quantify the processes. These simple solutions are used to gain insights into when different transport mechanisms are important. The simple solutions are used to simulate a base case example where a non-sorbing nuclide (iodide) and a sorbing nuclide (radium) move in the backfill by diffusion and by advective flow. The simple sample calculations show that it would take thousands of years for iodide to move 20 m along the tunnel and that a release pulse would spread out considerably over time. The sorbing nuclide 226 Ra with a half life of 1,600 years would be strongly retarded by sorption and would decay to insignificance during its migration along the tunnel. The consequences of a collapse of backfill leaving a channel above the backfill is also studied by a simple analytical model that accounts for water flowing in the collapsed part of the backfill at the ceiling of the tunnel. A nuclide that diffuses up to the flowing channel will flow with the ('rapidly' flowing) water but will be retarded by diffusion down into the backfill again. This down diffusion retards the nuclide migration
Flow and solute transport in backfilled tunnel and collapsed backfill - possible extension of Comp32

Energy Technology Data Exchange (ETDEWEB)

Neretnieks, Ivars [Royal Inst. of Technology, Stockholm (Sweden). Dept. of Chemical Engineering and Technology

2006-09-15

In the Swedish deep geological final repository for spent fuel the tunnels will be filled with a backfill with low permeability. However, some flow may take place in the backfill. Nuclides released from a leaking canister could diffuse up to the flowing water in the backfill and be transported downstream in the tunnel. At an intersection of the tunnel with a fracture zone the contaminated water might flow out into the zone.This report addresses the transport mechanisms and rate of transport from a leaking canister up through the buffer and backfill in the deposition hole, further into the backfill in the tunnel and the transport along the tunnel. Spreading by diffusion in the buffer and backfill as well as retardation of sorbing nuclides is accounted for.The transport mechanisms and rates of transport are described and some simple models with analytical solutions are used to quantify the processes. These simple solutions are used to gain insights into when different transport mechanisms are important. The simple solutions are used to simulate a base case example where a non-sorbing nuclide (iodide) and a sorbing nuclide (radium) move in the backfill by diffusion and by advective flow. The simple sample calculations show that it would take thousands of years for iodide to move 20 m along the tunnel and that a release pulse would spread out considerably over time. The sorbing nuclide {sup 226}Ra with a half life of 1,600 years would be strongly retarded by sorption and would decay to insignificance during its migration along the tunnel. The consequences of a collapse of backfill leaving a channel above the backfill is also studied by a simple analytical model that accounts for water flowing in the collapsed part of the backfill at the ceiling of the tunnel. A nuclide that diffuses up to the flowing channel will flow with the ('rapidly' flowing) water but will be retarded by diffusion down into the backfill again. This down diffusion retards the nuclide
Backfilling of deposition tunnels, block alternative

International Nuclear Information System (INIS)

Keto, P.; Roennqvist, P.-E.

2007-03-01

This report presents a preliminary process description of backfilling the deposition tunnels with pre-compacted blocks consisting of a mixture of bentonite and ballast (30:70). The process was modified for the Finnish KBS-3V type repository assuming that the amount of spent fuel canisters disposed of yearly is 40. Backfilling blocks (400 x 300 x 300 mm) are prepared in a block production plant with a hydraulic press with an estimated production capacity of 840 blocks per day. Some of the blocks are modified further to fit the profile of the tunnel roof. Prior to the installation of the blocks, the deposition tunnel floor is levelled with a mixture of bentonite and ballast (15:85). The blocks are placed in the tunnel with a modified reach truck. Centrifugal pellet throwing equipment is used to fill the gap between the blocks and the rock surface with bentonite pellets. Based on a preliminary assessment, the average dry density achieved with block backfill is sufficient to fulfil the criteria set for the backfill in order to ensure long-term safety and radiation protection. However, there are uncertainties concerning saturation, homogenisation, erosion, piping and self-healing of the block backfill that need to be studied further with laboratory and field tests. In addition, development efforts and testing concerning block manufacturing and installation are required to verify the technical feasibility of the concept. (orig.)
Development of a tunnel backfilling concept for nuclear waste disposal

International Nuclear Information System (INIS)

Gunnarsson, D.; Borgesson, L.

2003-01-01

In the main concept for disposal of the Swedish Nuclear Waste (KBS-3V) it is vital that the drifts can be backfilled with sufficiently good material at high density to fulfill the following requirements: - to obstruct upwards swelling of bentonite from the deposition holes, - to prevent or restrict the water flow in the tunnel and around the canister, - to resist chemical conversion for a long period of time, - not to cause any significant chemical conversion of the buffer surrounding the canister. Investigations and tests of backfill material and techniques have been running in the Swedish underground laboratory, Aspo HRL, since 1996. In the first test, Field Test of Tunnel Backfilling, the objectives were to test the manufacturing of backfill material, to develop and test a backfilling technique and to investigate what densities could be achieved with different backfill materials in the field. Horizontal layers were applied and compacted by a roller in 0.2 m thick layers to 1.5 m from the floor. The rest of the tunnel was backfilled with inclined layers. Five different backfill materials were tested; TBM-muck, TBM-muck crushed to a maximum grain size of 20 mm and crushed TBM-muck mixed with 10, 20 and 30% MX-80 bentonite. The main conclusions from these tests were that the technique for manufacturing backfill material and for backfilling the tunnel were suitable but that the horizontal backfill layers were sensitive to wet conditions, that the backfilling equipment needed to be improved to better reach the areas close to the rock walls and roof and that the durability of the equipment needed to be improved. For the continued development for the Backfill and Plug Test and the Prototype Repository it was decided that the backfilling should be made with inclined layers in the entire cross section of the tunnel in order to decrease the sensitivity to water inflow. The backfilling equipment was improved; two new compactors, the so-called slope compactor and the so
Development of a tunnel backfilling concept for nuclear waste disposal

Energy Technology Data Exchange (ETDEWEB)

Gunnarsson, D.; Borgesson, L. [Clay Technology AB, Ideon, Lund (Sweden)

2003-07-01

In the main concept for disposal of the Swedish Nuclear Waste (KBS-3V) it is vital that the drifts can be backfilled with sufficiently good material at high density to fulfill the following requirements: - to obstruct upwards swelling of bentonite from the deposition holes, - to prevent or restrict the water flow in the tunnel and around the canister, - to resist chemical conversion for a long period of time, - not to cause any significant chemical conversion of the buffer surrounding the canister. Investigations and tests of backfill material and techniques have been running in the Swedish underground laboratory, Aspo HRL, since 1996. In the first test, Field Test of Tunnel Backfilling, the objectives were to test the manufacturing of backfill material, to develop and test a backfilling technique and to investigate what densities could be achieved with different backfill materials in the field. Horizontal layers were applied and compacted by a roller in 0.2 m thick layers to 1.5 m from the floor. The rest of the tunnel was backfilled with inclined layers. Five different backfill materials were tested; TBM-muck, TBM-muck crushed to a maximum grain size of 20 mm and crushed TBM-muck mixed with 10, 20 and 30% MX-80 bentonite. The main conclusions from these tests were that the technique for manufacturing backfill material and for backfilling the tunnel were suitable but that the horizontal backfill layers were sensitive to wet conditions, that the backfilling equipment needed to be improved to better reach the areas close to the rock walls and roof and that the durability of the equipment needed to be improved. For the continued development for the Backfill and Plug Test and the Prototype Repository it was decided that the backfilling should be made with inclined layers in the entire cross section of the tunnel in order to decrease the sensitivity to water inflow. The backfilling equipment was improved; two new compactors, the so-called slope compactor and the so
Tunnel backfill erosion by dilute water

International Nuclear Information System (INIS)

Olin, M.

2014-03-01

The goal was to estimate smectite release from tunnel backfill due to dilute groundwater pulse during post glacial conditions. The plan was to apply VTT's two different implementations (BESW D and BESW S ) of well-known model of Neretnieks et al. (2009). It appeared difficult to produce repeatable results using this model in COMSOL 4.2 environment, therefore a semi-analytical approximate approach was applied, which enabled to take into account both different geometry and smectite content in tunnel backfill as compared to buffer case. The results are quite similar to buffer results due to the decreasing effect of smaller smectite content and the increasing effect of larger radius. (orig.)
Tunnel backfill erosion by dilute water

Energy Technology Data Exchange (ETDEWEB)

Olin, M. [VTT Technical Research Centre of Finland, Espoo (Finland)

2014-03-15

The goal was to estimate smectite release from tunnel backfill due to dilute groundwater pulse during post glacial conditions. The plan was to apply VTT's two different implementations (BESW{sub D} and BESW{sub S}) of well-known model of Neretnieks et al. (2009). It appeared difficult to produce repeatable results using this model in COMSOL 4.2 environment, therefore a semi-analytical approximate approach was applied, which enabled to take into account both different geometry and smectite content in tunnel backfill as compared to buffer case. The results are quite similar to buffer results due to the decreasing effect of smaller smectite content and the increasing effect of larger radius. (orig.)
Backfilling of deposition tunnels, in situ alternative

International Nuclear Information System (INIS)

Keto, P.

2007-04-01

The backfilling process described in this report is based on in situ compaction of a mixture of bentonite and ballast (30:70) into the deposition tunnel. This method has been tested in practice in various field tests by SKB, most recently in the Prototype repository test performed at Aespoe HRL. The backfill mixture is prepared above ground and transported to the repository level with a tank truck. The material is compacted into layers with an inclination of 35 deg C and a thickness of approximately 20 cm. The compaction is performed with a vibratory plate attached to a boom of an excavator. In order to keep up with the required canister installation rate determined for the Finnish repository, at least 13 layers need to be compacted daily. This means working in 2-3 shifts on the working days that are available for backfilling operations. The dry densities achieved in field tests for the wall/roof section of the backfill have been insufficient compared with the dry density criteria set for the backfill. In theory, it may be possible to reach dry densities that fulfil the criteria, although with a relatively small safety margin. Another open issue is whether the mixture of bentonite and ballast has sufficient self-healing ability to seal-off erosion channels after the tunnels have been closed and the backfill has reached full saturation. (orig.)
Effect of localized water uptake on backfill hydration and water movement in a backfilled tunnel: half-scale tests at Aespoe Bentonite Laboratory

Energy Technology Data Exchange (ETDEWEB)

Dixon, D. [Atomic Energy of Canada Limited, Chalk River (Canada); Jonsson, E. [Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden); Hansen, J. [Posiva Oy, Olkiluoto (Finland); Hedin, M. [Aangpannefoereningen, Stockholm (Sweden); Ramqvist, G. [Eltekno AB, Figeholm (Sweden)

2011-04-15

The report describes the outcome of the work within the project 'SU508.20 Impact of water inflow in deposition tunnels'. Project decision SKB doc 1178871 Version 3.0. Two activity plans have been used for the field work: AP TD SU50820-09-019 and AP TD SU 50820-09-071. SKB and Posiva have been examining those processes that may have particularly strong effects on the evolution of a newly backfilled deposition tunnel in a KBS-3V repository. These assessments have involved the conduct of increasingly large and complex laboratory tests and simulations of a backfilled tunnel section. In this series of four tests, the effect of water inflow into a backfilled tunnel section via an intersecting fracture feature was evaluated. The tests included the monitoring of mock-ups where water entered via the simulated fractures as well as evaluation of what the effect of isolated tunnel sections caused by localized water inflow would have on subsequent evolution of these isolated sections. It was found that even a slowly seeping fracture can have a substantial effect on the backfill evolution as it will cause development of a gasket-like feature that effectively cuts of air and water movement from inner to outer regions of the backfilled tunnel. Water entering via these fractures will ultimately move out of the tunnel via a single discrete flow path, in a manner similar to what was observed in previous 1/2-scale and smaller simulations. If the low-rate of water inflow from fracture is the only source of water inflow to the tunnel this will result in hydraulic behaviour similar to that observed for a single inflow point in previous tests. The presence of a fracture feature will however result in a larger proportion of water uptake by the process of suction than might occur in a point inflow situation and hence a more uniform water distribution will be present in the pellet fill. This also results in a greater tendency for water to be absorbed into the adjacent block fill
Effect of localized water uptake on backfill hydration and water movement in a backfilled tunnel: half-scale tests at Aespoe Bentonite Laboratory

International Nuclear Information System (INIS)

Dixon, D.; Jonsson, E.; Hansen, J.; Hedin, M.; Ramqvist, G.

2011-04-01

The report describes the outcome of the work within the project 'SU508.20 Impact of water inflow in deposition tunnels'. Project decision SKB doc 1178871 Version 3.0. Two activity plans have been used for the field work: AP TD SU50820-09-019 and AP TD SU 50820-09-071. SKB and Posiva have been examining those processes that may have particularly strong effects on the evolution of a newly backfilled deposition tunnel in a KBS-3V repository. These assessments have involved the conduct of increasingly large and complex laboratory tests and simulations of a backfilled tunnel section. In this series of four tests, the effect of water inflow into a backfilled tunnel section via an intersecting fracture feature was evaluated. The tests included the monitoring of mock-ups where water entered via the simulated fractures as well as evaluation of what the effect of isolated tunnel sections caused by localized water inflow would have on subsequent evolution of these isolated sections. It was found that even a slowly seeping fracture can have a substantial effect on the backfill evolution as it will cause development of a gasket-like feature that effectively cuts of air and water movement from inner to outer regions of the backfilled tunnel. Water entering via these fractures will ultimately move out of the tunnel via a single discrete flow path, in a manner similar to what was observed in previous 1/2-scale and smaller simulations. If the low-rate of water inflow from fracture is the only source of water inflow to the tunnel this will result in hydraulic behaviour similar to that observed for a single inflow point in previous tests. The presence of a fracture feature will however result in a larger proportion of water uptake by the process of suction than might occur in a point inflow situation and hence a more uniform water distribution will be present in the pellet fill. This also results in a greater tendency for water to be absorbed into the adjacent block fill material and
Design, production and initial state of the backfill and plug in deposition tunnels

Energy Technology Data Exchange (ETDEWEB)

Boerjesson, Lennart; Gunnarsson, David; Johannesson, Lars-Erik; Jonsson, Esther

2010-12-15

The report is included in a set of Production reports, presenting how the KBS-3 repository is designed, produced and inspected. The set of reports is included in the safety report for the KBS-3 repository and repository facility. The report provides input on the initial state of the backfill and plug in deposition tunnels for the assessment of the long-term safety, SR-Site. The initial state refers to the properties of the engineered barriers once they have been finally placed in the KBS-3 repository and will not be further handled within the repository facility. In addition, the report provides input to the operational safety report, SR-Operation, on how the backfill and plug shall be handled and installed. The report presents the design premises and reference designs of the backfill and plug in deposition tunnels and verifies their conformity to the design premises. It also describes the production of the backfill from excavation and delivery of backfill material to installation in the deposition tunnel, and gives an outline of the installation of the plug. Finally, the initial states of the backfill and plug and their conformity to the reference designs and design premises are presented
Piping and erosion in buffer and backfill materials. Current knowledge

International Nuclear Information System (INIS)

Boergesson, Lennart; Sanden, Torbjoern

2006-09-01

The water inflow into the deposition holes and tunnels in a repository will mainly take place through fractures in the rock and will lead to that the buffer and backfill will be wetted and homogenised. But in general the buffer and backfill cannot absorb all water that runs through a fracture, which leads to that a water pressure will be generated in the fracture when the inflow is hindered. If the counter pressure and strength of the buffer or backfill is insufficiently high, piping and subsequent erosion may take place. The processes and consequences of piping and erosion have been studied in some projects and several laboratory test series in different scales have been carried through. This brief report describes these tests and the results and conclusions that have emerged. The knowledge of piping and erosion is insufficient today and additional studies are needed and running
Deep repository - engineered barrier systems. Assessment of backfill materials and methods for deposition tunnels

International Nuclear Information System (INIS)

Gunnarsson, D.; Moren, L.; Sellin, P; Keto, P.

2007-09-01

The main objectives of this report are to: (1) present density criteria considering deposition tunnels for the investigated backfill materials, (2) evaluate what densities can be achieved with the suggested backfill methods, (3) compare the density criteria to achievable densities, (4) based on this comparison evaluate the safety margin for the combinations of backfill materials and methods and, (5) make recommendations for further investigations and development work. The backfilling methods considered in this report are compaction of backfill material in situ in the tunnel and placement of pre-compacted blocks and pellets. The materials investigated in the second phase of the SKB-Posiva backfilling programme can be divided into three main categories: (1) Bentonite clays: two high-grade Na-bentonites from Wyoming (MX-80 and SPV200), one low-grade bentonite from Kutch (India Asha 2 0), and one high- and one low-grade Ca-bentonite from Milos (Deponite CA-N and Milos backfill). The highgrade bentonites are used in different bentonite-ballast mixtures. (2) Smectite-rich mixed-layer clays: one from Dnesice-Plzensko Jih (DPJ) located in the Czech Republic and one from Northern Germany (Friedland clay). (3) Mixtures of bentonite and ballast: Mixtures consisting of high-grade bentonite (30, 40 and 50 w-%) and crushed rock with different type of grain size distribution or sand. The general conclusion from the comparison between estimated achievable densities and the density criteria is that placing pre-compacted blocks of swelling clay or 50/50 mixture and pellets in the tunnel results in the highest safety margin. (orig.)
Backfilling of KBS-3V deposition tunnels - possibilities and limitations

International Nuclear Information System (INIS)

Wimelius, Hans; Pusch, Roland

2008-12-01

By definition for the SKB repository concept, the backfill of KBS-3V deposition tunnels must be so designed that transport of dissolved matter is controlled by diffusion and not by advective water flow. This requires that the hydraulic conductivity of the backfill does not exceed about E-10 m/s. The backfilling materials also have to adequately resist compression caused by upward expansion of the buffer. It must also exert an effective pressure of at least 100 kPa on the rock in order to provide support to the rock and minimize spalling of the rock. These criteria are fulfilled by several approaches and options for backfill materials, placed and compacted layer wise or in the form of blocks of compacted clay powder. Based on the experience from comprehensive lab studies and considering practical issues, SKB has selected a concept where the major part of the backfill consists of stacked blocks that are surrounded by clay pellets. Using this concept a basis for a detailed evaluation, a study of three different techniques for placing the blocks has been undertaken. The three block placement techniques examined are the 'Block', 'Robot', and 'Module' methods. They involve different block sizes and techniques for handling and placing the blocks but the same way of preparing the foundation bed of the blocks and placing the pellet filling. The blasted tunnels have a varying cross section, caused by the orientation of the blast-holes. This requires that a varying fraction of blocks be installed in the backfilling along the blasted tunnel interval if sufficiently high density and low hydraulic conductivity is to be achieved. The efficiency of filling will depend on the type of clay used in the blocks. For example, using Friedland clay for block preparation, the filling efficiency must be 80% while it can be reduced to 60% if more smectite-rich clay is used. The use of a clay with high smectite content increases margins and is concluded to be superior from emplacement point
Tests to determine water uptake behaviour of tunnel backfill

Energy Technology Data Exchange (ETDEWEB)

Dixon, David (Atomic Energy of Canada Limited (AECL) (Canada)); Anttila, S.; Viitanen, M. (Poeyry InfRa Oy (Finland)); Keto, Paula (Saanio and Riekkola Oy, Helsinki (Finland))

2008-12-15

A series of 27 large-scale tests have been completed at the 420 level of SKB's Aespoe Hard Rock Laboratory. These tests have examined the influence of natural Aespoe fracture zone water on the movement of water into and through assemblies of Friedland clay blocks and bentonite pellets/ granules. These tests have established the manner in which groundwater may influence backfill and backfilling operations at the repository-scale. Tests have established that it is critical to provide a clay block backfilling system with lateral support and confinement as quickly as possible following block installation. Exposure of the blocks to even low rates of water ingress can result in rapid loss of block cohesion and subsequent slumping of the block materials into the spaces between the blocks and the tunnel walls. Installation of granular or pelletized bentonite clay between the blocks and the walls resulted in a system that was generally stable and not prone to unacceptable short-term strains as water entered. Inflow of water into a backfilled volume does not result in uniform wetting of the pellet/granule filled volume and as a result there is the potential for rapid movement of water from the point(s) of ingress to the downstream face of the backfill. Depending on the inflow rate and flow path(s) developed this flow can be via discrete flow channels that are essentially non-erosive or else they can develop highly erosive flow paths through the clay block materials. Erosion generally tends to be highest in the period immediately following first water exit from the backfill and then decreases as preferential flow paths develop to channel the water directly through the backfill, bypassing large volumes of unsaturated backfill. At the scale examined in this study inflow rates of 0.1 l/min or less do not tend to be immediately problematic when the source is 0.6 m distant from the downstream face of the backfill. At larger scales or longer distances from the working face, it
Tests to determine water uptake behaviour of tunnel backfill

International Nuclear Information System (INIS)

Dixon, David; Anttila, S.; Viitanen, M.; Keto, Paula

2008-12-01

A series of 27 large-scale tests have been completed at the 420 level of SKB's Aespoe Hard Rock Laboratory. These tests have examined the influence of natural Aespoe fracture zone water on the movement of water into and through assemblies of Friedland clay blocks and bentonite pellets/ granules. These tests have established the manner in which groundwater may influence backfill and backfilling operations at the repository-scale. Tests have established that it is critical to provide a clay block backfilling system with lateral support and confinement as quickly as possible following block installation. Exposure of the blocks to even low rates of water ingress can result in rapid loss of block cohesion and subsequent slumping of the block materials into the spaces between the blocks and the tunnel walls. Installation of granular or pelletized bentonite clay between the blocks and the walls resulted in a system that was generally stable and not prone to unacceptable short-term strains as water entered. Inflow of water into a backfilled volume does not result in uniform wetting of the pellet/granule filled volume and as a result there is the potential for rapid movement of water from the point(s) of ingress to the downstream face of the backfill. Depending on the inflow rate and flow path(s) developed this flow can be via discrete flow channels that are essentially non-erosive or else they can develop highly erosive flow paths through the clay block materials. Erosion generally tends to be highest in the period immediately following first water exit from the backfill and then decreases as preferential flow paths develop to channel the water directly through the backfill, bypassing large volumes of unsaturated backfill. At the scale examined in this study inflow rates of 0.1 l/min or less do not tend to be immediately problematic when the source is 0.6 m distant from the downstream face of the backfill. At larger scales or longer distances from the working face, it is
Backfill design 2012

International Nuclear Information System (INIS)

Autio, J.; Hassan, M. M.; Karttunen, P.; Keto, P.

2013-12-01

This report describes both the concept and the detailed design of backfilling in KBS-3V deposition tunnels. The purpose of the backfill is to keep the buffer in place, maintain favourable and predictable conditions for the buffer and the canister, and also favourable rock mechanical, hydrological and geochemical conditions in the near-field and to retard the transport of released radionuclides in case of canister failure. In addition to the description of the overall backfill design, detailed designs for the components of the backfill (foundation, block and pellet fill) are provided in this report. The deposition tunnel end plug design is not presented in this document. In the backfill design, the deposition tunnels are to be filled with a foundation layer material, precompacted clay blocks and extruded bentonite pellets. The foundation layer consists of Milos bentonite granules, which are compacted in situ in order to level the deposition tunnel floor, providing an even and stable base for the block filling. On the foundation layer, a rigid assemblage of overlapping layers of pre-compacted blocks made of Friedland clay are installed. The void space between the blocks and the rock wall is filled with extruded pellets made of bentonite similar to raw material of Cebogel QSE product. (orig.)
Deep repository - engineered barrier systems. Assessment of backfill materials and methods for deposition tunnels

International Nuclear Information System (INIS)

Gunnarsson, David; Moren, Lena; Sellin, Patrik; Keto, Paula

2006-09-01

The main objectives of this report are to: 1) present density criteria considering deposition tunnels for the investigated backfill materials, 2) evaluate what densities can be achieved with the suggested backfill methods, 3) compare the density criteria to achievable densities, 4) based on this comparison evaluate the safety margin for the combinations of backfill materials and methods and, 5) make recommendations for further investigations and development work. The backfilling methods considered in this report are compaction of backfill material in situ in the tunnel and placement of pre-compacted blocks and pellets. The materials investigated in the second phase of the SKB-Posiva backfilling project can be divided into three main categories: 1. Bentonite clays: two high-grade Na-bentonites from Wyoming (MX-80 and SPV200), one low-grade bentonite from Kutch (India Asha 230), and one high and one low-grade Ca-bentonite from Milos (Deponite CA-N and Milos backfill). The high-grade bentonites are used in different bentonite-ballast mixtures. 2. Smectite-rich mixed-layer clays: one from Dnesice-Plzensko Jih (DPJ) located in the Czech Republic and one from Northern Germany (Friedland clay). Mixtures of bentonite and ballast: Mixtures consisting of high-grade bentonite (0, 40 and 50 w-%) and crushed rock with different type of grain size distribution or sand. The relationships between dry densities and hydraulic conductivity, swelling pressure and compressibility in saturated state for these materials were investigated. Most of the tests were performed with a groundwater salinity of 3.5%. This salinity is comparable to sea water and can be expected to be at the high end of salinities occurring during the assessment period. The purpose of the investigations was to determine the dry densities required to meet the function indicator criteria. These densities are referred to as the density criteria. However throughout the assessment period a loss of material and thus

Deep repository - engineered barrier systems. Assessment of backfill materials and methods for deposition tunnels

Energy Technology Data Exchange (ETDEWEB)

Gunnarsson, David; Moren, Lena; Sellin, Patrik [Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden); Keto, Paula [Saanio and Riekkola Oy, Helsinki (Finland)

2006-09-15

The main objectives of this report are to: 1) present density criteria considering deposition tunnels for the investigated backfill materials, 2) evaluate what densities can be achieved with the suggested backfill methods, 3) compare the density criteria to achievable densities, 4) based on this comparison evaluate the safety margin for the combinations of backfill materials and methods and, 5) make recommendations for further investigations and development work. The backfilling methods considered in this report are compaction of backfill material in situ in the tunnel and placement of pre-compacted blocks and pellets. The materials investigated in the second phase of the SKB-Posiva backfilling project can be divided into three main categories: 1. Bentonite clays: two high-grade Na-bentonites from Wyoming (MX-80 and SPV200), one low-grade bentonite from Kutch (India Asha 230), and one high and one low-grade Ca-bentonite from Milos (Deponite CA-N and Milos backfill). The high-grade bentonites are used in different bentonite-ballast mixtures. 2. Smectite-rich mixed-layer clays: one from Dnesice-Plzensko Jih (DPJ) located in the Czech Republic and one from Northern Germany (Friedland clay). Mixtures of bentonite and ballast: Mixtures consisting of high-grade bentonite (0, 40 and 50 w-%) and crushed rock with different type of grain size distribution or sand. The relationships between dry densities and hydraulic conductivity, swelling pressure and compressibility in saturated state for these materials were investigated. Most of the tests were performed with a groundwater salinity of 3.5%. This salinity is comparable to sea water and can be expected to be at the high end of salinities occurring during the assessment period. The purpose of the investigations was to determine the dry densities required to meet the function indicator criteria. These densities are referred to as the density criteria. However throughout the assessment period a loss of material and thus
Backfilling of KBS-3V deposition tunnels - possibilities and limitations

Energy Technology Data Exchange (ETDEWEB)

Wimelius, Hans (Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden)); Pusch, Roland (Geodevelopment International AB, Lund (Sweden))

2008-12-15

By definition for the SKB repository concept, the backfill of KBS-3V deposition tunnels must be so designed that transport of dissolved matter is controlled by diffusion and not by advective water flow. This requires that the hydraulic conductivity of the backfill does not exceed about E-10 m/s. The backfilling materials also have to adequately resist compression caused by upward expansion of the buffer. It must also exert an effective pressure of at least 100 kPa on the rock in order to provide support to the rock and minimize spalling of the rock. These criteria are fulfilled by several approaches and options for backfill materials, placed and compacted layer wise or in the form of blocks of compacted clay powder. Based on the experience from comprehensive lab studies and considering practical issues, SKB has selected a concept where the major part of the backfill consists of stacked blocks that are surrounded by clay pellets. Using this concept a basis for a detailed evaluation, a study of three different techniques for placing the blocks has been undertaken. The three block placement techniques examined are the 'Block', 'Robot', and 'Module' methods. They involve different block sizes and techniques for handling and placing the blocks but the same way of preparing the foundation bed of the blocks and placing the pellet filling. The blasted tunnels have a varying cross section, caused by the orientation of the blast-holes. This requires that a varying fraction of blocks be installed in the backfilling along the blasted tunnel interval if sufficiently high density and low hydraulic conductivity is to be achieved. The efficiency of filling will depend on the type of clay used in the blocks. For example, using Friedland clay for block preparation, the filling efficiency must be 80% while it can be reduced to 60% if more smectite-rich clay is used. The use of a clay with high smectite content increases margins and is concluded to be
Backfilling and closure of the deep repository. Assessment of backfill concepts

International Nuclear Information System (INIS)

Gunnarsson, David; Boergesson, Lennart; Keto, Paula; Tolppanen, Pasi; Hansen, Johanna

2004-06-01

This report presents the results from work made in Phase 1 of the joint SKB-Posiva project 'Backfilling and Closure of the Deep Repository' aiming at selecting and developing materials and techniques for backfilling and closure of a KBS-3 type repository for spent nuclear fuel. The aim of phase 1, performed as a desk study, was to describe the potential of the suggested backfill concepts in terms of meeting SKB and Posiva requirements, select the most promising ones for further investigation, and to describe methods that can be used for determining the performance of the concepts. The backfilling concepts described in this report differ from each other with respect to backfill materials and installation techniques. The concepts studied are the following: Concept A: Compaction of a mixture of bentonite and crushed rock in the tunnel. Concept B: Compaction of natural clay with swelling ability in the tunnel. Concept C: Compaction of non-swelling soil type in the tunnel combined with application of pre-compacted bentonite blocks at the roof. Concept D: Placement of pre-compacted blocks; a number of materials are considered. Concept E: Combination of sections consisting of a) crushed rock compacted in the tunnel and b) pre-compacted bentonite blocks. The bentonite sections are installed regularly above every disposal hole. Concept F: Combination of sections consisting of a) crushed rock compacted in the tunnel and b) pre-compacted bentonite blocks. The distance between the bentonite sections is adapted to the local geology and hydrology.The assessment of the concepts is based on performance requirements set for the backfill in the deposition tunnels for providing a stable and safe environment for the bentonite buffer and canister for the repository service time. In order to do this, the backfill should follow certain guidelines, 'design criteria' concerning compressibility, hydraulic conductivity, swelling ability, long-term stability, effects on the barriers and
Backfilling and closure of the deep repository. Assessment of backfill concepts

Energy Technology Data Exchange (ETDEWEB)

Gunnarsson, David; Boergesson, Lennart [Clay Technology AB, Lund (Sweden); Keto, Paula [Saanio Riekkola Oy (Finland); Tolppanen, Pasi [Jaakko Poeyry Infra (Finland); Hansen, Johanna [Posiva Oy, Helsinki (Finland)

2004-06-01

This report presents the results from work made in Phase 1 of the joint SKB-Posiva project 'Backfilling and Closure of the Deep Repository' aiming at selecting and developing materials and techniques for backfilling and closure of a KBS-3 type repository for spent nuclear fuel. The aim of phase 1, performed as a desk study, was to describe the potential of the suggested backfill concepts in terms of meeting SKB and Posiva requirements, select the most promising ones for further investigation, and to describe methods that can be used for determining the performance of the concepts. The backfilling concepts described in this report differ from each other with respect to backfill materials and installation techniques. The concepts studied are the following: Concept A: Compaction of a mixture of bentonite and crushed rock in the tunnel. Concept B: Compaction of natural clay with swelling ability in the tunnel. Concept C: Compaction of non-swelling soil type in the tunnel combined with application of pre-compacted bentonite blocks at the roof. Concept D: Placement of pre-compacted blocks; a number of materials are considered. Concept E: Combination of sections consisting of a) crushed rock compacted in the tunnel and b) pre-compacted bentonite blocks. The bentonite sections are installed regularly above every disposal hole. Concept F: Combination of sections consisting of a) crushed rock compacted in the tunnel and b) pre-compacted bentonite blocks. The distance between the bentonite sections is adapted to the local geology and hydrology.The assessment of the concepts is based on performance requirements set for the backfill in the deposition tunnels for providing a stable and safe environment for the bentonite buffer and canister for the repository service time. In order to do this, the backfill should follow certain guidelines, 'design criteria' concerning compressibility, hydraulic conductivity, swelling ability, long-term stability, effects on
Installation of the backfill and plug test

International Nuclear Information System (INIS)

Gunnarsson, D.; Borgesson, L.; Hokmark, H.; Hohannesson, L.E.; Sanden, T.

2003-01-01

The Backfill and Plug Test is a full scale test of backfill material, backfilling technique and a tunnel plug. The main objectives of the Backfill and Plug Test are: - to develop and test different materials and compaction techniques for backfilling of tunnels excavated by blasting; - to test the function of the backfill and its interaction with the surrounding rock in a tunnel excavated by blasting; - to develop technique for building tunnel plugs and to test the function. The installation was made in the Swedish underground laboratory, Aspo HRL, during 1999. The inner part of the tunnel is not used for the test but was filled with drainage material. The test volume, which is about 28 m long, can be divided into the following three parts: - the inner part filled with backfill containing 30% bentonite; - the outer part filled with backfill without bentonite and bentonite blocks and pellets at the roof; - the plug. Permeable layers divide the test volume into 11 test sections. The permeable layers are used for increasing the water saturation rate in the backfill and for applying hydraulic gradients between the layers for studying the flow of water in the backfill and in the near field rock. The permeable layers were installed every 2.2 m and each layer is divided into three units in order to separately measure the flow close to the roof, in the central areas of the tunnel and close to the floor. The outer part ends with a wall of prefabricated concrete beams that were used for temporary support of the backfill during the casting of the plug. The upper volume close to the plug is filled with bentonite pellets and blocks consisting of 20% bentonite and 80% sand. The backfill is instrumented with 34 pore water pressure cells, 21 total pressure cells, 57 sensors for monitoring the water saturation and 13 gauges for measuring the local hydraulic conductivity. The water pressures in the permeable mats are measured in all sections. Four pressure cylinders, 2 in the roof
Water uptake by and movement through a Backfilled KBS-3V deposition tunnel: results of large-scale simulations

International Nuclear Information System (INIS)

Dixon, D.A.; Ramqvist, G.; Jonsson, E.; Gunnarsson, D.; Hansen, J.

2010-01-01

Document available in extended abstract form only. Posiva and SKB initiated a joint programme BACLO (Backfilling and Closure of the Deep repository) in 2003 with the aim to develop methods and clay-based materials for backfilling the deposition tunnels of a repository utilizing the KBS-3V deposition concept. This paper summarises the results obtained in intermediate and large-scale simulations to evaluate water movement into and through backfill consisting of bentonite pellets and pre-compacted clay blocks. The main objectives of Baclo Phase III were related to examining backfill materials, deposition concepts and their importance to the clay-block and pellet backfilling concept. Bench-scale studies produced a large body of information on how various processes (e.g. water inflow, piping, erosion, self-healing, homogenisation and interaction between backfill and buffer), might affect the hydro-mechanical evolution of backfill components. The tests described in this paper examined the movement of water into and through assemblies of clay blocks and bentonite pellets/granules and represent a substantial up-scaling and inclusion of parameters that more closely simulate a field situation. In total, 27 intermediate-scale tests have been completed and 18 large-scale tests (∼ 1/2-tunnel cross-section) will be completed at SKB's Aespoe HRL by mid 2010. At intermediate-scale, point inflow rates ranging from 0.01 to 1.0 l/min were applied to block - dry pellet assemblies and water movement into and through the system was monitored. Tests determined that it is critical to provide clay blocks with lateral support and confinement as quickly as possible following block installation. Exposure of the blocks to even low rates of water ingress can result in rapid loss of block cohesion and subsequent slumping of the block materials into the spaces between the blocks and the tunnel walls. Installation of granular or pelletized bentonite clay between the blocks and the walls
Assessment of backfill design for KBS-3V repository

International Nuclear Information System (INIS)

Keto, Paula; Dixon, David; Jonsson, Esther; Gunnarsson, David; Boergesson, Lennart; Hansen, Johanna

2009-12-01

Posiva and SKB initiated a joint programme BACLO (Backfilling and Closure of the Deep repository) in 2003 with the aim to develop methods and materials for backfilling of deposition tunnels. This report summarises the work done in the third and final phase of the BACLO programme. The main objective of this phase was to study how the various processes active during backfill installation and saturation as well as technical constraints affect its design basis. The work focused on the performance and technical feasibility of a block backfill concept, which calls for filling the majority of the tunnel volume with pre-compacted backfill blocks and the remaining volume with bentonite pellets. Several backfill composition alternatives were chosen for study and they consisted of clay materials with differing amounts of swelling minerals. A large body of information was gained on the effect of different processes on the performance of these backfill options, e.g. water inflow, piping, erosion, self-healing, homogenisation and interaction between backfill and buffer in various laboratory and small-scale field tests. More practical tests included e.g. studies how the blocks and pellets could be installed to the deposition tunnel. Based on the new information on the effect of the processes investigated and the estimated achievable block filling degree and backfill density, recommendations were made concerning material selection, backfill layout and technical issues. In addition, issues requiring further attention to verify the long-term performance of the proposed backfill concept are identified and listed
Assessment of backfill design for KBS-3V repository

Energy Technology Data Exchange (ETDEWEB)

Keto, Paula (B+tech, Eurajoki (Finland)); Dixon, David (AECL, Harwell (United Kingdom)); Jonsson, Esther; Gunnarsson, David (Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden)); Boergesson, Lennart (Clay Technology AB, Lund (Sweden)); Hansen, Johanna (Posiva (Finland))

2009-12-15

Posiva and SKB initiated a joint programme BACLO (Backfilling and Closure of the Deep repository) in 2003 with the aim to develop methods and materials for backfilling of deposition tunnels. This report summarises the work done in the third and final phase of the BACLO programme. The main objective of this phase was to study how the various processes active during backfill installation and saturation as well as technical constraints affect its design basis. The work focused on the performance and technical feasibility of a block backfill concept, which calls for filling the majority of the tunnel volume with pre-compacted backfill blocks and the remaining volume with bentonite pellets. Several backfill composition alternatives were chosen for study and they consisted of clay materials with differing amounts of swelling minerals. A large body of information was gained on the effect of different processes on the performance of these backfill options, e.g. water inflow, piping, erosion, self-healing, homogenisation and interaction between backfill and buffer in various laboratory and small-scale field tests. More practical tests included e.g. studies how the blocks and pellets could be installed to the deposition tunnel. Based on the new information on the effect of the processes investigated and the estimated achievable block filling degree and backfill density, recommendations were made concerning material selection, backfill layout and technical issues. In addition, issues requiring further attention to verify the long-term performance of the proposed backfill concept are identified and listed
Backfilling and sealing of tunnels, shafts and boreholes. Volume 2: Appendices

International Nuclear Information System (INIS)

Studer, J.; Ammann, W.; Meier, P.; Mueller, Ch.; Glauser, E.

1984-12-01

The present report is a synthesis of the state of knowledge regarding backfilling and sealing of nuclear waste repositories. It is based on an evaluation of both the general and special publications concerning this problem (articles in scientific journals, research reports, conference papers and textbooks) and represents the state of knowledge up to summer 1984. In addition, it contains an outlook on the continuing work. This will serve to broaden the scientific base and to achieve the technical as well as economical optimization. The report consists of two volumes: Volume 1 Main Part, Volume 2 Appendices. Starting with the functions of backfilling and sealing in the safety concept assessment criteria and from these, taking into consideration the given conditions in the project 'Gewaehr 1985' ('Guarantee'), the requirements for the backfilling and sealing materials are formulated. The properties of several materials under consideration are discussed in the Appendix together with a detailed description of the most important of these materials. The reasons are given for the choice of the proposed materials for the project 'Gewaehr 1985'. Alternative backfilling and sealing concepts for repositories Type B and Type C are presented and reasons are given for the selected variants for the project 'Gewaehr 1985'. Chapter 10 represents a review of the report. This report is intended as a reference work for the corresponding chapters in the NGB reports (cf. /NGB 85-03, 1985/, /NGB 85-06, 1985/). (author)
Performance of concrete backfilling materials for shafts and tunnels in rock formations

International Nuclear Information System (INIS)

Storer, G.; Mistry, N.; Galliara, J.

1985-10-01

This report (Part 2) describes the mathematical modelling studies carried out within a research project into the performance of concrete backfilling materials for shafts and tunnels comprising a hard rock geological disposal repository for High Level, Heat Generating Wastes (HLW/HGW) or Intermediate Level Wastes (ILW) with long lived isotopes. A complementary volume (Part 1) describes laboratory research studies into the development, manufacture and testing of a pre-placed aggregate concrete (PAC). The ongoing objective is to demonstrate that concrete will serve as a beneficial engineered barrier, part of a multi-barrier system, in isolating potentially harmful radionuclides from the biosphere. The report recognises that the backfill cannot be considered in isolation and that there are many interactions between the primary repository elements of host rock, waste and backfill. The interactions considered include mechanical, thermal, creep and moisture movement. Analyses were carried out using the ADINA finite element system, by programmed analytical formulae and using the TEMPOR program (for thermally driven moisture migration in concrete). The emphasis has been directed at establishing basic mathematical approaches to the understanding and quantification of the phenomena involved and applying them to simplified and idealised repository scenarios. The methods devised lay foundations for future work on more defined disposal scenarios. (author)
BACEKO II. Flow-through, open-front and saturation tests of pre-compacted backfill blocks in a quarter-scale test tunnel

International Nuclear Information System (INIS)

Keski-Kuha, E.; Nemlander, R.; Koho, P.

2013-11-01

The series of tests performed in BACEKO II project examined three different block materials for potential use in backfilling the repository; Friedland clay, 40/60-mixture of bentonite (40 %) and crushed rock (60 %) and Milos B clay in conjunction with pellet materials Cebogel QSE and Milos B clay. The testing program consisted of 9 tests, that continued the 1/4-scale tests executed in BACEKO 2008. The block backfilling degree of the 1/4-scale test tunnels was 73.8 % which was consistent with the material ratios associated with filling a repository tunnel having a 10 % over-excavation ratio. Some of these tests were conducted using a restraint installed at the front face of the setup and open-front tests were subsequently added in order to establish the time span which an open backfill front can remain stable should an interruption in the backfilling process occur. Additionally one flow-through test with higher salinity water (7 % TDS versus the 3,5 % TDS used in all other tests), was performed for an assembly constructed using Friedland clay. The rate of test assembly, consumption of materials and achieved densities were all monitored. During the tests, the erosion rates, progression of saturation and development of total pressure were monitored. In disassembling the tests, samples were collected for gravimetric water content measurement, the erosion pathways were identified and the sections were photographed with an infrared camera to illustrate the moister areas in the backfill. The greatest amounts of eroded material were observed in open-front tests where exiting water removed clay from the face of the backfill and formed a deepening channel in the block backfill. The open-front tests remained stable only until the outflow emerged. The properties of the pellet layer depend on the as-placed conditions which were operatordependant and also affect the outflow times. There was not much difference in the amount of erosion observed for the different block materials
Assessment of backfill design for a KBS-3V repository: the BACLO program

International Nuclear Information System (INIS)

Jonsson, E.; Gunnarsson, D.; Hansen, J.; Keto, P.; Dixon, D.A.; Boergesson, L.

2010-01-01

Document available in extended abstract form only. Posiva and SKB initiated a joint programme BACLO (Backfilling and Closure of the Deep repository) in 2003 with the aim to develop methods and clay-based materials for backfilling the deposition tunnels of a repository utilizing the KBS-3V deposition concept. This paper summarises the work done in the third and final phase of the BACLO programme (2006-2008). The main objectives of this work were to examine backfill materials, deposition concepts and their importance to the clay-based block and pellet backfilling concept. Baclo Phase III was primarily intended to address the following four items: 1. evaluate options for design of block and pellet/granule materials for use in backfilling and in so doing provide a basis for selecting backfill materials; 2. provide a basis for recommending reference design(s) for backfilling through evaluation of materials, environmental processes and technical constraints likely to be encountered in a repository; 3. analyze how the potentially critical processes taking place during the installation and saturation phase affect the performance of the backfill and consequently the design basis for the backfill; and 4. evaluate how water will move through backfilled volumes and generally identify under what conditions water management will become an operational issue; and identify needs for further investigations and technical development. To address these objectives, studies were undertaken to examine how the various processes active during backfill installation and saturation as well as technical constraints affect its design basis. The work focused on the performance and technical feasibility of a block backfill concept, which calls for filling the majority of the tunnel volume with pre-compacted, clay-based backfill blocks and the remaining volume with bentonite pellets. Several backfill composition alternatives were chosen for study and they consisted of clay materials with differing
Evaluation of a new method to estimate the hydration time of the tunnel backfill

Energy Technology Data Exchange (ETDEWEB)

Svensson, Urban (Computer-aided Fluid Engineering AB, Lyckeby (Sweden))

2010-12-15

A safety assessment of a repository requires that all stages (excavation, waste emplacement, etc) of a repository are analysed and understood. In this report the time after the waste emplacement will be in focus. One important issue during this phase is the saturation of the tunnel backfill. After the installation of the backfill, 30-50% of the pore space is filled with air; this volume will eventually be filled with water and it is the time scale for this hydration process that needs to be estimated. A method to estimate the hydration time of a repository has been suggested and evaluated. The key idea in the suggested method is to 'create' the volume initially filled with air by the use of the specific storage term and hence be able to stay within the single phase framework. A series of test cases, defined and simulated in /Boergesson et al. 2006/, are used to demonstrate and evaluate the method. Encouraging results have been obtained. It is also shown that the simulation model can be applied to a real world case
Deep repository - Engineered barrier system. Erosion and sealing processes in tunnel backfill materials investigated in laboratory

Energy Technology Data Exchange (ETDEWEB)

Sanden, Torbjoern; Boergesson, Lennart; Dueck, Ann; Goudarzi, Reza; Loennqvist, Margareta (Clay Technology AB, Lund (Sweden))

2008-12-15

SKB in Sweden and Posiva in Finland are developing and plan to implement similar disposal concepts for the final disposal of spent nuclear fuel. Co-operation and joint development work between Posiva and SKB with the overall objective to develop backfill concepts and techniques for sealing and closure of the repository have been going on for several years. The investigation described in this report is intended to acquire more knowledge regarding the behavior of some of the candidate backfilling materials. Blocks made of three different materials (Friedland clay, Asha 230 or a bentonite/ballast 30/70 mixture) as well as different bentonite pellets have been examined. The backfill materials will be exposed to an environment simulating that in a tunnel, with high relative humidity and water inflow from the rock. The processes and properties investigated are: 1. Erosion properties of blocks and pellets (Friedland blocks, MX-80 pellets, Cebogel QSE pellets, Minelco and Friedland granules). 2. Displacements of blocks after emplacement in a deposition drift (Blocks of Friedland, Asha 230 and Mixture 30/70). 3. The ability of these materials to seal a leaking in-situ cast plug cement/rock but also other fractures in the rock (MX-80 pellets). 4. The self healing ability after a piping scenario (Blocks of Friedland, Asha 230 Mixture 30/70 and also MX-80 pellets). 5. Swelling and cracking of the compacted backfill blocks caused by relative humidity. The erosion properties of Friedland blocks were also investigated in Phase 2 of the joint SKBPosiva project 'Backfilling and Closure of the Deep Repository, BACLO, which included laboratory scale experiments. In this phase of the project (3) some completing tests were performed with new blocks produced for different field tests. These blocks had a lower density than intended and this has an influence on the erosion properties measured. The erosion properties of MX-80 pellets were also investigated earlier in the project but
Use of Gap-fills in the Buffer and Backfill of an HLW Repository

Energy Technology Data Exchange (ETDEWEB)

Lee, Jae Owan; Lee, Min Soo; Choi, Heui Joo [KAERI, Daejeon (Korea, Republic of)

2016-05-15

The buffer and backfill are significant barrier components of the repository. They play the roles of preventing the inflow of groundwater from the surrounding rock, retarding the release of radionuclides from the waste, supporting disposal container against external impacts, and discharging decay heat from the waste. When the buffer and backfill are installed for the HLW repository, there may be gaps between the container and buffer and between the backfill and the wall of disposal tunnels, respectively. These gaps occur because spaces are allowed for ease of the installation of the buffer and backfill in excavated deposition boreholes and disposal tunnels. If the gaps are left without any sealing as they are, however, the buffer and backfill can't accomplish their functions as the barrier components. This paper reviews the gap-fill concepts of the developed foreign countries, and then suggests a gap-fill concept which is applicable for the KRS. The gap-fill is suggested to employ bentonite- based materials with a type of pellet, granule, and pellet-granule mixture. The roller compression method and extrusion-cutting method are applicable for the fabrication of the bentonite pellets which can have the high density and the required amount for use to the buffer and backfill. For the installation of the gap-fill, the pouring and then pressing method and the shotcrete- blowing method are preferable for the gap of the deposition borehole and the gap of the disposal tunnel, respectively.
The feasibility of Backfilling a Repository of Spent Fuel: An Assessment of Recent Developments by SKB

International Nuclear Information System (INIS)

Bennett, David

2010-12-01

In the Review Statement and Evaluation of SKB's RDandD programme 2007 (SKI Report 2008:48E), the former Swedish Nuclear Power Inspectorate (SKI) commented that considerable work remained to be done for knowledge of both practical management issues on backfilling and analysis of long-term backfill evolution to reach the same level as for the canister and the buffer. SKI considered that the backfill material had not been thoroughly reported in the RDandD programme. More concrete plans were also needed relating to large-scale demonstration experiments to investigate the performance of the backfill in as realistic conditions as possible. In the spring of 2009, noting that SKB had changed its concept for backfilling several times over the last few years, and after having visited SKB's most recent backfilling trials at Aespoe, both SSM and SSM's expert group BRITE had strong concerns regarding SKB's programme for backfilling the repository tunnels. Although the BRITE expert group has been keeping a watching brief over SKB's development work on backfilling, SSM has not undertaken a systematic assessment of SKB's work in this area since the SR-Can Safety Report was reviewed in 2006. Dr David Bennett, a member and secretary of the BRITE expert group, was asked to do such an assessment. This report describes the assessment results
The feasibility of Backfilling a Repository of Spent Fuel: An Assessment of Recent Developments by SKB

Energy Technology Data Exchange (ETDEWEB)

Bennett, David (TerraSalus Limited, Rutland (United Kingdom))

2010-12-15

In the Review Statement and Evaluation of SKB's RDandD programme 2007 (SKI Report 2008:48E), the former Swedish Nuclear Power Inspectorate (SKI) commented that considerable work remained to be done for knowledge of both practical management issues on backfilling and analysis of long-term backfill evolution to reach the same level as for the canister and the buffer. SKI considered that the backfill material had not been thoroughly reported in the RDandD programme. More concrete plans were also needed relating to large-scale demonstration experiments to investigate the performance of the backfill in as realistic conditions as possible. In the spring of 2009, noting that SKB had changed its concept for backfilling several times over the last few years, and after having visited SKB's most recent backfilling trials at Aespoe, both SSM and SSM's expert group BRITE had strong concerns regarding SKB's programme for backfilling the repository tunnels. Although the BRITE expert group has been keeping a watching brief over SKB's development work on backfilling, SSM has not undertaken a systematic assessment of SKB's work in this area since the SR-Can Safety Report was reviewed in 2006. Dr David Bennett, a member and secretary of the BRITE expert group, was asked to do such an assessment. This report describes the assessment results
Basic experimental study on the backfilling material under saline seawater condition

International Nuclear Information System (INIS)

Kikuchi, Hirohito; Tanai, Kenji; Sugita, Yutaka

2003-11-01

In geological disposal of high-level radioactive waste, closure of repository is the technique of filling clearance using the backfilling material to preserve barrier performance of the engineered barrier system. The required performances of the backfilling material are clearance filling, low permeability and swelling pressure and stiffness. The expecting behaviors of the backfilling material are very complex which are decrease of section area of the tunnel due to creep displacement, decrease of performance of bentonite due to alteration of the concrete lining and so on. And ideal assessment of the clearance filling performance in the backfilled tunnel will be performed considering the coupled behaviors described above. However, there is not enough data to explain the expecting behaviors, and mechanisms of the coupled behaviors are not clarified yet. Therefore, the clearance filling performance of backfilling material was selected first. In this study, the clearance filling performance was tested using the clearance considering only decrease of the volume of the concrete lining due to alteration of the concrete. Basic examination of the backfilling material was performed, which focused on the feasibility of the backfilling material described in the H12 report and the adequate bentonite/sand mixture to obtain conservative filling clearance performance. Results of the examination showed, under test conditions that 30% of the volume of concrete lining decreases due to alteration and such volume become clearance between the backfilling material and concrete lining, in distilled water condition, the specification (bentonite/sand mixture) of the backfilling material described in H12 report almost filled the clearance. However, in saline seawater, 50% and more bentonite was required to fill the clearance. Since this examination fixed the clearance, water stopping performance will be examined in next phase. Through the saline seawater examination, the basic clearance
Managing the risks of the backfill production line from material acquisition to installation

International Nuclear Information System (INIS)

Kiviranta, Leena; Kumpulainen, Sirpa; Keto, Paula; Autio, Jorma; Siivonen, Markku; Koho, Petri

2012-01-01

Document available in extended abstract form only. The tunnel backfill of Finnish KBS-3V type repository for spent nuclear fuel consists of foundation layer that is installed at site, pre-compacted backfill blocks that fill most of the tunnel and bentonite pellets to fill the gap between blocks and tunnel wall. In order to ensure the quality, availability, and timely delivery of backfill materials and components, and further to ensure the fulfillment of the requirements and specifications set for backfilling of deposition tunnels, the backfill production line was explored step-by-step, and risks related were defined and analyzed. The work described in this paper was initiated by Posiva Oy and is reported in Keto et al. (2012). The first part of the backfill production line is described in Figure 1 for Friedland clay that is designed to be used for the backfill blocks. It consists of excavation, processing and delivery of materials to backfill production facility. Second part of the production line consists of manufacturing of the backfill components, and the third part is the installation. A preliminary risk assessment was done in 2011 for the acquisition of Friedland clay and manufacturing and installation of foundation layer, blocks and pellets. The critical points of the production line were determined using a material flow description where risk is defined as a probability of something unwanted to happen times the severity of the consequences. Risk analysis was performed by going through the whole backfill production line step by step and analyzing all the incidents, which have occurred (or might occur) during the backfilling operations. A risk number from 1 to 25 was given to each step of the chain depending on how long delay the problem causes and how often it occurs. Low risk was the target for each step of the chain, medium risk was considered tolerable, for high risks management actions to decrease the risk number were considered and extremely high risks
The Buffer and Backfill Handbook. Part 2: Materials and techniques

International Nuclear Information System (INIS)

Pusch, Roland

2001-12-01

Improved technology and prospection yielding more pure and homogeneous raw materials for preparing buffers and backfills will ultimately outdate the clays and ballast materials described in the present part of the Handbook. It describes experimentally investigated materials of potential use in repositories but other, more suitable materials will replace them in the future. The Handbook will hence have to be reviewed regularly, making room for superior materials in future, upgraded Handbook versions. Buffer is the term for dense clay used for embedment of canisters with highly radioactive waste, while backfill is soil used for filling tunnels and shafts in repositories. Examples of soil materials of potential use as buffers and backfills in repositories of KBS-3 type are described in this part of the Handbook. They are: smectitic clay materials intended for preparation of buffers (canister-embedding clay) and used as clay component in artificially prepared tunnel and shaft backfills consisting of mixtures of clay and ballast. Ballast materials intended for backfilling of tunnels and shafts and used as components of artificially prepared backfills. Smectitic natural clay soils intended for use as buffers and backfills. Very fine-grained smectite clay used as grout for sealing rock fractures. In this part of the Handbook for Buffers and Backfills, description of various candidate materials will be made with respect to their mineral composition and physical properties, with respect to the groundwater chemistry that can be expected in a deep repository in Swedish bedrock. Chapter 3 deals with smectitic clay materials intended for embedment of heat-producing canisters with highly radioactive waste. Focus is on the nature of the buffer constituents, i. e. the smectite content, the non-expanding clay minerals colloidal and the accessory non-clay minerals as well as amorphous matter and organic substances. The dominant part of the chapter describes the occurrence and origin

The Buffer and Backfill Handbook. Part 2: Materials and techniques

Energy Technology Data Exchange (ETDEWEB)

Pusch, Roland [Geodevelopment AB, Lund (Sweden)

2001-12-01

Improved technology and prospection yielding more pure and homogeneous raw materials for preparing buffers and backfills will ultimately outdate the clays and ballast materials described in the present part of the Handbook. It describes experimentally investigated materials of potential use in repositories but other, more suitable materials will replace them in the future. The Handbook will hence have to be reviewed regularly, making room for superior materials in future, upgraded Handbook versions. Buffer is the term for dense clay used for embedment of canisters with highly radioactive waste, while backfill is soil used for filling tunnels and shafts in repositories. Examples of soil materials of potential use as buffers and backfills in repositories of KBS-3 type are described in this part of the Handbook. They are: smectitic clay materials intended for preparation of buffers (canister-embedding clay) and used as clay component in artificially prepared tunnel and shaft backfills consisting of mixtures of clay and ballast. Ballast materials intended for backfilling of tunnels and shafts and used as components of artificially prepared backfills. Smectitic natural clay soils intended for use as buffers and backfills. Very fine-grained smectite clay used as grout for sealing rock fractures. In this part of the Handbook for Buffers and Backfills, description of various candidate materials will be made with respect to their mineral composition and physical properties, with respect to the groundwater chemistry that can be expected in a deep repository in Swedish bedrock. Chapter 3 deals with smectitic clay materials intended for embedment of heat-producing canisters with highly radioactive waste. Focus is on the nature of the buffer constituents, i. e. the smectite content, the non-expanding clay minerals colloidal and the accessory non-clay minerals as well as amorphous matter and organic substances. The dominant part of the chapter describes the occurrence and origin
Characterization of backfill mortars used in different tunnels in Spain

Directory of Open Access Journals (Sweden)

Cavalaro, S.

2013-03-01

Full Text Available The main objective of this paper is to compare typical backfill mortars used in Spanish tunnels to fill the annular void left between the lining and the ground by the TBM. Initially, a new experimental program is outlined using material corresponding to 6 mixes from 4 tunnels. The results obtained indicate a considerable difference in the density and in the rheological properties of the mixes tested. According to the estimations performed, this leads to a difference of up to 67% on the potency required from the pumps to inject the material. Furthermore, a correlation between the fine content and the rheological properties of the mix was observed. This correlation may be a practical tool to control and modify the performance of the mortars directly in the worksite.

El objetivo principal del presente estudio es llevar a cabo la comparación de las dosificaciones de mortero de relleno empleadas en algunos de los grandes túneles españoles para rellenar el hueco anular dejado entre el terreno y el extradós de las dovelas. Inicialmente se hace una nueva propuesta experimental usando la composición y los materiales correspondientes a 6 dosificaciones usadas en 4 túneles. Los resultados obtenidos indican diferencias significativas en cuanto a la densidad, a la consistencia y a las propiedades reológicas. De acuerdo con las estimaciones realizadas, ello se traduce en diferencias de hasta un 67% en la potencia requerida del sistema de bombas de la tuneladora para inyectar el material. Por otro lado, se refleja una correlación entre el contenido de finos de la mezcla y las propiedades reológicas. Esa correlación puede servir para controlar y modificar dichas propiedades de manera fácil y rápida a pie de obra.
Water saturation phase of the buffer and backfill in the KBS-3V concept. Special emphasis given to the influence of the backfill on the wetting of the buffer

International Nuclear Information System (INIS)

Boergesson, Lennart; Faelth, Billy; Hernelind, Jan

2006-08-01

The wetting and rate of saturation of the buffer and backfill materials in a KBS- V repository from the rock fractures and the rock matrix have been investigated by a large number of different finite element models and calculations. For most models the FE-code ABAQUS has been used but for investigation of the influence of trapped air in the backfill FE-code Code Bright was used. Both codes include completely coupled THM models, which have been used, but for some calculations it has been sufficient to limit the models to only use the hydraulic or thermohydraulic parts of the models. The following analyses have been made: 1. The influence of the backfill properties and wetting conditions on the water saturation phase of the buffer has been investigated with the old FEM-model used in earlier wetting calculations for SR-97. The old calculations have been updated regarding the influence of the backfill. The model is 2-dimensional with axial symmetry around the axis of the deposition hole. These calculations show that there is strong influence of wetting from the backfill if the rock is rather dry (K rock = 10 -13 m/s), while the influence is low if the rock is rather wet (K rock = 10 -12 m/s). At K rock = 10 -13 m/s the time to saturation decreases with a factor 2 in the absence of fractures and with a factor 1.5 with two fractures intersecting the hole when water is supplied from the backfill (30/70) compared to when no water is available. A completely dry rock yields very long time to saturation and of course decisive influence of the water supply from the backfill. If water is freely available at a water pressure of 5 MPa in the backfill it takes 250-500 years to reach full saturation of the buffer. If the water available in the backfill is limited to the initial amount (completely dry rock also around the tunnel and thus no addition of water from the rock in the tunnel) it will take several thousands years to reach some kind of equilibrium with a degree of
Water saturation phase of the buffer and backfill in the KBS-3V concept. Special emphasis given to the influence of the backfill on the wetting of the buffer

Energy Technology Data Exchange (ETDEWEB)

Boergesson, Lennart; Faelth, Billy [Clay Technology AB, Lund (Sweden); Hernelind, Jan [5T Engineering AB, Vaesteraas (Sweden)

2006-08-15

The wetting and rate of saturation of the buffer and backfill materials in a KBS- V repository from the rock fractures and the rock matrix have been investigated by a large number of different finite element models and calculations. For most models the FE-code ABAQUS has been used but for investigation of the influence of trapped air in the backfill FE-code Code Bright was used. Both codes include completely coupled THM models, which have been used, but for some calculations it has been sufficient to limit the models to only use the hydraulic or thermohydraulic parts of the models. The following analyses have been made: 1. The influence of the backfill properties and wetting conditions on the water saturation phase of the buffer has been investigated with the old FEM-model used in earlier wetting calculations for SR-97. The old calculations have been updated regarding the influence of the backfill. The model is 2-dimensional with axial symmetry around the axis of the deposition hole. These calculations show that there is strong influence of wetting from the backfill if the rock is rather dry (K{sub rock} = 10{sup -13} m/s), while the influence is low if the rock is rather wet (K{sub rock} = 10{sup -12} m/s). At K{sub rock} = 10{sup -13} m/s the time to saturation decreases with a factor 2 in the absence of fractures and with a factor 1.5 with two fractures intersecting the hole when water is supplied from the backfill (30/70) compared to when no water is available. A completely dry rock yields very long time to saturation and of course decisive influence of the water supply from the backfill. If water is freely available at a water pressure of 5 MPa in the backfill it takes 250-500 years to reach full saturation of the buffer. If the water available in the backfill is limited to the initial amount (completely dry rock also around the tunnel and thus no addition of water from the rock in the tunnel) it will take several thousands years to reach some kind of
Mechanical interaction buffer/backfill. Finite element calculations of the upward swelling of the buffer against both dry and saturated backfill

Energy Technology Data Exchange (ETDEWEB)

Boergesson, Lennart (Clay Technology AB, Lund (Sweden)); Hernelind, Jan (5T-Engineering AB, Vaesteraas (Sweden))

2009-10-15

The mechanical interaction between the buffer material in the deposition hole and the backfill material in the deposition tunnel is an important process in the safety assessment since the primary function of the backfill is to keep the buffer in place and not allow it to expand too much and thereby loose too much of its density and barrier properties. In order to study the upwards swelling of the buffer and the subsequent density reduction a number of finite element calculations have been performed. The calculations have been done with the FE-program Abaqus with 3D-models of a deposition hole and the deposition tunnel. In order to refine the modelling only the two extreme cases of completely un-wetted (dry) and completely water saturated (wet) backfill have been modelled. For the wet case the influence of different factors has been studied while only one calculation of the dry case has been done. The calculated upwards swelling of the buffer varied between 2 and 15 cm for the different wet cases while it was about 10 cm for the dry case. In the wet reference case the E-modulus of the block and pellets fillings was 50 MPa and 3.24 MPa respectively, the friction angle between the buffer and the rock and canister was 8.7 deg and there were no swelling pressure from the backfill. There is a strong influence of the friction angle on both the upwards swelling and the canister heave. The friction is important for preventing especially canister displacements. The unrealistic case of no friction yielded strong unacceptable influence on the buffer with an upwards swelling of 15 cm and a strong heave of 5 cm of the canister. The influence of the backfill stiffness is as expected strong. Both buffer swelling and canister heave are twice as large at the E-modulus E = 25 MPa than at the E-modulus E = 100 MPa. The influence of the stiffness of the pellets filling is not strong since there are no pellets on the floor in the model used. The influence of the swelling pressure of the
Mechanical interaction buffer/backfill. Finite element calculations of the upward swelling of the buffer against both dry and saturated backfill

International Nuclear Information System (INIS)

Boergesson, Lennart; Hernelind, Jan

2009-10-01

The mechanical interaction between the buffer material in the deposition hole and the backfill material in the deposition tunnel is an important process in the safety assessment since the primary function of the backfill is to keep the buffer in place and not allow it to expand too much and thereby loose too much of its density and barrier properties. In order to study the upwards swelling of the buffer and the subsequent density reduction a number of finite element calculations have been performed. The calculations have been done with the FE-program Abaqus with 3D-models of a deposition hole and the deposition tunnel. In order to refine the modelling only the two extreme cases of completely un-wetted (dry) and completely water saturated (wet) backfill have been modelled. For the wet case the influence of different factors has been studied while only one calculation of the dry case has been done. The calculated upwards swelling of the buffer varied between 2 and 15 cm for the different wet cases while it was about 10 cm for the dry case. In the wet reference case the E-modulus of the block and pellets fillings was 50 MPa and 3.24 MPa respectively, the friction angle between the buffer and the rock and canister was 8.7 deg and there were no swelling pressure from the backfill. There is a strong influence of the friction angle on both the upwards swelling and the canister heave. The friction is important for preventing especially canister displacements. The unrealistic case of no friction yielded strong unacceptable influence on the buffer with an upwards swelling of 15 cm and a strong heave of 5 cm of the canister. The influence of the backfill stiffness is as expected strong. Both buffer swelling and canister heave are twice as large at the E-modulus E = 25 MPa than at the E-modulus E = 100 MPa. The influence of the stiffness of the pellets filling is not strong since there are no pellets on the floor in the model used. The influence of the swelling pressure of the
Status of assessment tools on the performance guarantee contents of backfill, bulkhead, tunnel and pit

International Nuclear Information System (INIS)

Kawakami, Susumu; Fujita, Tomoo; Yui, Mikazu

2006-03-01

In order to contribute to the safety standards and guidelines which a regulator will decide, a state-of-the-art assessment method is investigated and summarized in tables about performance guarantee contents of backfill, bulkhead, tunnel (access, main, connecting, disposal) and disposal pit. In addition, examples of assessment tools are described. In this report, summary of (1) basic properties of bentonite, including swelling, mechanical and hydraulic properties, (2) long-term behavior of bentonite, including extrusion/erosion into host rock, and alteration, (3) effect of high pH plume from cementitious material and (4) mechanical stability of the near-field is described. Check points, assessment methods for (based on the data obtained from the experimental results, the estimation value obtained from empirical equations and database, and the modeling calculations) and latest results of these R and D programs were also summarized. (author)
Backfilling techniques and materials in underground excavations: Potential alternative backfill materials in use in Posiva's spent fuel repository concept

International Nuclear Information System (INIS)

Dixon, D.A.; Keto, P.

2009-05-01

A variety of geologic media options have been proposed as being suitable for safely and permanently disposing of spent nuclear fuel or fuel reprocessing wastes. In Finland the concept selected is construction of a deep repository in crystalline rock (Posiva 1999, 2006; SKB 1999), likely at the Olkiluoto site (Posiva 2006). Should that site prove suitable, excavation of tunnels and several vertical shafts will be necessary. These excavations will need to be backfilled and sealed as emplacement operations are completed and eventually all of the openings will need to be backfilled and sealed. Clay-based materials were selected after extensive review of materials options and the potential for practical implementation in a repository and work over a 30+ year period has led to the development of a number of workable clay-based backfilling options, although discussion persists as to the most suitable clay materials and placement technologies to use. As part of the continuous process of re-evaluating backfilling options in order to provide the best options possible, placement methods and materials that have been given less attention have been revisited. Primary among options that were and continue to be evaluated as a potential backfill are cementitious materials. These materials were included in the list of candidate materials initially screened in the late 1970's for use in repository backfilling. Conventional cement-based materials were quickly identified as having some serious technical limitations with respect their ability to fulfil the identified requirements of backfill. Concerns related to their ability to achieve the performance criteria defined for backfill resulted in their exclusion from large-scale use as backfill in a repository. Development of new, less chemically aggressive cementitious materials and installation technologies has resulted in their re-evaluation. Concrete and cementitious materials have and are being developed that have chemical, durability
Effects of grouting, shotcreting and concrete leachates on backfill geochemistry

Energy Technology Data Exchange (ETDEWEB)

Luna, Miguel; Arcos, David; Duro, Lara [Enviros Consulting, Valldoreix, Barc elona (Spain)

2007-11-15

The use of concrete to seal open fractures (grouting) and to impermeabilise the deposition tunnels (shotcreting) has been envisaged in the construction of a high level nuclear waste (HLNW) repository according to SKB designs. Nevertheless, the geochemical effect of using concrete in the repository is not fully understood. Concrete degradation due to the interaction with groundwater can affect the performance of other repository barriers, such as the backfill material used for sealing the deposition tunnels. One of the main effects of concrete degradation is the generation of alkaline plumes. For this reason, SKB is currently planning to use a type of concrete whose degradation result in lower pH values than those developed with Ordinary Portland Cement (OPC). In order to assess the long-term geochemical effect of including low-pH concrete elements in a HLNW repository, we performed a 2D reactive-transport model of a backfilled deposition tunnel that intersects a hydraulic conductive fracture which has been partially grouted. An additional case has been modelled where part of the deposition tunnel walls were covered with a shotcrete layer. The modelling results predict the development of a high-alkalinity plume, larger in the case of considering a grouted fracture, accompanied by the precipitation of CSH-phases in the fracture. However, the effect on the backfill material is only significant if concrete is in contact with the backfill (shotcrete case). In order to conduct these models, and considering that at the beginning of the present work there was not a specific composition for such a low-pH concrete, its composition has been assumed in order to meet the expected geochemical evolution of concrete degradation according to SKB expectations. This is a pH of pore water of around 11 and the degradation of CSH phases resulting in a source for Ca and Si into the system. For this reason, jennite and tobermorite have been selected, although it is known that jennite is
Effects of grouting, shotcreting and concrete leachates on backfill geochemistry

International Nuclear Information System (INIS)

Luna, Miguel; Arcos, David; Duro, Lara

2007-11-01

The use of concrete to seal open fractures (grouting) and to impermeabilise the deposition tunnels (shotcreting) has been envisaged in the construction of a high level nuclear waste (HLNW) repository according to SKB designs. Nevertheless, the geochemical effect of using concrete in the repository is not fully understood. Concrete degradation due to the interaction with groundwater can affect the performance of other repository barriers, such as the backfill material used for sealing the deposition tunnels. One of the main effects of concrete degradation is the generation of alkaline plumes. For this reason, SKB is currently planning to use a type of concrete whose degradation result in lower pH values than those developed with Ordinary Portland Cement (OPC). In order to assess the long-term geochemical effect of including low-pH concrete elements in a HLNW repository, we performed a 2D reactive-transport model of a backfilled deposition tunnel that intersects a hydraulic conductive fracture which has been partially grouted. An additional case has been modelled where part of the deposition tunnel walls were covered with a shotcrete layer. The modelling results predict the development of a high-alkalinity plume, larger in the case of considering a grouted fracture, accompanied by the precipitation of CSH-phases in the fracture. However, the effect on the backfill material is only significant if concrete is in contact with the backfill (shotcrete case). In order to conduct these models, and considering that at the beginning of the present work there was not a specific composition for such a low-pH concrete, its composition has been assumed in order to meet the expected geochemical evolution of concrete degradation according to SKB expectations. This is a pH of pore water of around 11 and the degradation of CSH phases resulting in a source for Ca and Si into the system. For this reason, jennite and tobermorite have been selected, although it is known that jennite is
Assessment of the oxygen consumption in the backfill. Geochemical modelling in a saturated backfill

International Nuclear Information System (INIS)

Grandia, Fidel; Domenech, Cristina; Arcos, David; Duro, Lara

2006-11-01

The consumption of oxygen in the deep disposal is a major concern due to the ability of this element to corrode the canisters where high level nuclear wastes (HLNW) are disposed. The anoxic conditions initially present in a deep geologic environment are disturbed by the excavation of the repository facilities. After sealing the deposition holes and tunnels using clay-based materials, oxygen remains dissolved in porewater or as a gas phase in the unsaturated pores. The main mechanisms of oxygen depletion that can be considered in the backfill materials are: (1) diffusion into the surrounding rock and (2) kinetic reactions with accessory minerals and organic matter existing in the backfill. In this report, a set of numerical simulations are carried out in one and two dimensions in order to test the effect on the oxygen concentration in the pore water of all these mechanisms. The backfill considered is a 0/70 mixture of MX-80 bentonite and crushed material from the excavation itself. In addition to organic matter, the solid phases with reducing capacity in the backfill are Fe(II)-bearing minerals: pyrite (FeS 2 ) and siderite (FeCO) (as accessory minerals in the bentonite) and Fe-biotite (from the crushed granite). In the simulations, other chemical processes like cation exchange and surface complexation onto clay surfaces, and thermodynamic equilibrium with calcite, gypsum and quartz are considered. Initial composition of porewater is obtained by equilibrating the Forsmark groundwater with the backfill material. The 1D simulation consists of a number of cells with no reactive minerals or organic matter representing granite. The central cell, however, contains oxygen and reactive minerals resembling a backfill. Oxygen is allowed to move only by diffusion. The 2D model simulates the interaction with a backfill of a granitic groundwater flowing through a fracture. Like in the 1D model, the backfill contains oxygen and reactive solids. The results are very similar in
Assessment of the oxygen consumption in the backfill. Geochemical modelling in a saturated backfill

Energy Technology Data Exchange (ETDEWEB)

Grandia, Fidel; Domenech, Cristina; Arcos, David; Duro, Lara [Enviros Spain S.L., Barcelona (Spain)

2006-11-15

The consumption of oxygen in the deep disposal is a major concern due to the ability of this element to corrode the canisters where high level nuclear wastes (HLNW) are disposed. The anoxic conditions initially present in a deep geologic environment are disturbed by the excavation of the repository facilities. After sealing the deposition holes and tunnels using clay-based materials, oxygen remains dissolved in porewater or as a gas phase in the unsaturated pores. The main mechanisms of oxygen depletion that can be considered in the backfill materials are: (1) diffusion into the surrounding rock and (2) kinetic reactions with accessory minerals and organic matter existing in the backfill. In this report, a set of numerical simulations are carried out in one and two dimensions in order to test the effect on the oxygen concentration in the pore water of all these mechanisms. The backfill considered is a 0/70 mixture of MX-80 bentonite and crushed material from the excavation itself. In addition to organic matter, the solid phases with reducing capacity in the backfill are Fe(II)-bearing minerals: pyrite (FeS{sub 2}) and siderite (FeCO) (as accessory minerals in the bentonite) and Fe-biotite (from the crushed granite). In the simulations, other chemical processes like cation exchange and surface complexation onto clay surfaces, and thermodynamic equilibrium with calcite, gypsum and quartz are considered. Initial composition of porewater is obtained by equilibrating the Forsmark groundwater with the backfill material. The 1D simulation consists of a number of cells with no reactive minerals or organic matter representing granite. The central cell, however, contains oxygen and reactive minerals resembling a backfill. Oxygen is allowed to move only by diffusion. The 2D model simulates the interaction with a backfill of a granitic groundwater flowing through a fracture. Like in the 1D model, the backfill contains oxygen and reactive solids. The results are very similar in
Development and validation of a CFD model predicting the backfill process of a nuclear waste gallery

International Nuclear Information System (INIS)

Gopala, Vinay Ramohalli; Lycklama a Nijeholt, Jan-Aiso; Bakker, Paul; Haverkate, Benno

2011-01-01

Research highlights: → This work presents the CFD simulation of the backfill process of Supercontainers with nuclear waste emplaced in a disposal gallery. → The cement-based material used for backfill is grout and the flow of grout is modelled as a Bingham fluid. → The model is verified against an analytical solution and validated against the flowability tests for concrete. → Comparison between backfill plexiglas experiment and simulation shows a distinct difference in the filling pattern. → The numerical model needs to be further developed to include segregation effects and thixotropic behavior of grout. - Abstract: Nuclear waste material may be stored in underground tunnels for long term storage. The example treated in this article is based on the current Belgian disposal concept for High-Level Waste (HLW), in which the nuclear waste material is packed in concrete shielded packages, called Supercontainers, which are inserted into these tunnels. After placement of the packages in the underground tunnels, the remaining voids between the packages and the tunnel lining is filled-up with a cement-based material called grout in order to encase the stored containers into the underground spacing. This encasement of the stored containers inside the tunnels is known as the backfill process. A good backfill process is necessary to stabilize the waste gallery against ground settlements. A numerical model to simulate the backfill process can help to improve and optimize the process by ensuring a homogeneous filling with no air voids and also optimization of the injection positions to achieve a homogeneous filling. The objective of the present work is to develop such a numerical code that can predict the backfill process well and validate the model against the available experiments and analytical solutions. In the present work the rheology of Grout is modelled as a Bingham fluid which is implemented in OpenFOAM - a finite volume-based open source computational fluid
Buffer, backfill and closure process report for the safety assessment SR-Site

International Nuclear Information System (INIS)

Sellin, Patrik

2010-11-01

This report gives an account of how processes in buffer, deposition tunnel backfill and the closure important for the long-term evolution of a KBS-3 repository for spent nuclear fuel, will be documented in the safety assessment SR-Site
Buffer, backfill and closure process report for the safety assessment SR-Site

Energy Technology Data Exchange (ETDEWEB)

Sellin, Patrik (ed.)

2010-11-15

This report gives an account of how processes in buffer, deposition tunnel backfill and the closure important for the long-term evolution of a KBS-3 repository for spent nuclear fuel, will be documented in the safety assessment SR-Site
2D and 3D finite element analysis of buffer-backfill interaction

International Nuclear Information System (INIS)

Leoni, M.

2013-08-01

Methods for backfilling and sealing of disposal tunnels in an underground repository for spent nuclear fuel are studied in cooperation between Finland (Posiva Oy) and Sweden (Svensk Kaernbraenslehantering AB, SKB) in 'BAckfilling and CLOsure of the deep repository' (Baclo) programme. Baclo phase III included modelling task force SP1: Finite element modelling of deformation of the backfill due to swelling of the buffer. The objective of the finite element modelling of the backfill was to study the interaction between the buffer and backfilling. The calculations aimed to find out how large deformations can happen in the buffer-backfill interface causing loosening of the buffer bentonite above the canister. The criterion used was that the saturated density of the buffer right above the canister should be higher than 1990 kg/m 3 . This report presents the results of finite element numerical analyses carried out by Wesi Geotecnica Srl. The modelling calculations were conducted with the so-called OL1-2 deposition tunnel geometry (Juvankoski 2009). Several parameters have been considered, varying from geometry variations to different mechanical constitutive models for different components of the model. In all analyses it has been assumed that the buffer material is fully saturated, thus exerting the isotropic swelling pressure estimated in the range 7 MPa .. 15 MPa, against a fully-dry backfill, which is no doubt the 'worst case scenario' with the highest risk to lead in decrease in dry density of the buffer. Friedland clay has been considered for backfill blocks and 30/70 mixture for foundation bed on which backfill blocks are installed. Preliminarily, finite element analyses have been performed with newly released PLAXIS 2D 2010 within the assumption of axial symmetry, the purpose of this first set of calculations being the evaluation of most relevant parameters influencing the deformations of buffer material. Hence, full 3D calculations have been performed with PLAXIS
Bentonite as backfill in a final repository for high-level waste: chemical aspects

International Nuclear Information System (INIS)

Grauer, R.

1986-01-01

The present Nagra concept for disposal of high-level waste foresees emplacing the steel containers enclosing the borosilicate glass in tunnels at a depth of 1000 to 1500 m. These tunnels are to be backfilled with bentonite. Bentonites are suitable as a backfill due to their swelling capability, their low hydraulic conductivity and their sorption properties. This report is restricted to chemical aspects of the backfill material: swelling capability, sorption properties and long-term stability. Under repository conditions, the swelling of monmorillonite upon water inflow is primarily innercrystalline. Cation adsorption, which is important for nuclide retention in the repository, can be described by appropriate models. It can be concluded from natural analogue studies and from laboratory experiments that the properties of the backfill material will not alter significantly over a periode of 10/sup 6/ years. Nevertheless in the long term, the formulation of mixed-layer illite/monmorillonite cannot be ruled out. Such mixed-layer clays still have good swelling and sorption properties. Given the quantity ratios foreseen, no adverse changes due to radioactive decay are to be expected. The interaction between the bentonite and the container corrosion products must, in the absence of literature data, be investigated experimentally. The type of reaction products expected (iron-containing clay minerals) and the high bentonite/iron ratio lead to the conclusion that the function of the backfill need not be impaired by these processes. Because of its better stability, a calcium bentonite is preferable to the sodium variant. A low iron content is desirable because, under reducing conditions, the surface charge of the montorillonite is increased by reduction of iron(III). Organic and sulphidic contaminants should also be kept to a minimum
Preliminary results from water content and density measurements of the backfill and buffer in the prototype repository at Aespoe HRL

International Nuclear Information System (INIS)

Johannesson, Lars-Erik; Grahm, Paer; Hagman, Patrik

2012-01-01

Document available in extended abstract form only. Since 2001 the Prototype Repository at Aespoe Hard Rock Laboratory has been carried out as a large-scale experimental installation of the KBS-3 Swedish/Finnish concept for final disposal of spent nuclear fuel. The Prototype Repository consists of a total of six full-scale deposition holes with a centre distance of 6 m, located in a TBM tunnel at a depth of 450 m. Each deposition hole is fitted with a full-scale bentonite buffer, consisting of altogether 14 blocks and a full-scale canister, Figure 1. The canisters are equipped with heaters to simulate the heat from spent nuclear fuel. There are two sections of the installation; The inner section (I) consisting of four deposition holes (no. 1-4) with buffer and canister, and the outer section (II) consisting of two deposition holes (no. 5-6). The deposition tunnel is filled with a mixture of crushed rock and bentonite (30% of bentonite). A massive concrete plug, designed to withstand full water and swelling pressures, separates the test area from the open tunnel system and a second plug separates the two sections. This layout provides two more or less independent test sections. The outer section was opened and retrieved during 2011. The backfill was excavated with a back-hoe loader in layers of two metres. Samples were taken in these layers with the object of determining density and water content. Important items of the backfill to examine were the contact between backfill and the tunnel wall and the contact between the buffer and backfill in the deposition holes. The water content of the backfill was determined by drying samples in an oven at a temperature of 105 C for 24 h and the density was determined by weighting the sample both in air and merged into paraffin oil with known density. Altogether more than 900 tons of backfill material was excavated from the tunnel and more than 1100 samples, distributed over 11 sections, were taken for determining the water
Effect of the mineral precipitation-dissolution at tunnel walls during the operational and post-operational phases

Energy Technology Data Exchange (ETDEWEB)

Domenech, Cristina; Arcos, David; Duro, Lara; Grandia, Fidel [Enviros Consul ting, Valldoreix, Barcelona (Spain)

2007-11-15

The extent of reversibility of the geochemical conditions disturbed during the construction and operational phases is of importance in order to assess the chemical evolution of the repository system. In this regard, it is essential to have a deep understanding of the chemical status of the repository system at closure in order to describe its immediate geochemical evolution beyond this point. This project assesses the dissolution and precipitation of minerals due to the interaction with groundwater in the deposition tunnel wall-rock during the operational phase (prior to tunnel backfilling) and during the saturation phase, also considering the effect on the backfill material. We have performed a 2D model in which a fracture intersecting the main tunnel has been considered. The project has been developed in two consecutive stages. The first stage simulates the precipitation and dissolution of minerals in the tunnel wall rock during the operational phase (100 years after excavation) when the tunnel is empty and filled with air. During this stage, water flows through fractures into the tunnel. The results of the model suggest that the interaction between groundwater, fracture-filling minerals, and atmospheric O{sub 2}(g) and CO{sub 2}(g) present in the tunnel leads to the precipitation of secondary minerals (calcite and iron(III) oxy-hydroxide) that do not significantly affect the porosity of the area surrounding the tunnel. The second stage starts after the operational phase, once the tunnel is backfilled, and simulates the interaction of groundwater with fracture-filling minerals and the backfill material. The model implemented assumes that the backfill is already water saturated and that water flows following the regional head gradient. Moreover, it also assumes that O2(g) is still present in the tunnel wall, as a result of the operational phase disturbances. The results show that oxygen will oxidise pyrite in the backfill and promote the precipitation of Fe
Thermal simulation of drift emplacement. Geotechnical and geophysical investigations in and around backfilled galleries

International Nuclear Information System (INIS)

Schneefub, J.U.; Gommlich, G.E.

1988-01-01

The concept for the direct disposal of spent fuel in rock salt foresees the emplacement of large waste canisters on the floor of a disposal gallery. Subsequent to emplacement the drift is backfilled with salt grit. In a demonstration test six cylindrical containments are to be emplaced within distances of 3 m from each other in two parallel galleries of 14 m 2 , separated by a pillar of 10 m thickness. They will be heated up by a power output of approx. 1 kW/m to 200 degree C surface temperature by electrical heaters. The thermal and mechanical response of the salt rock and the backfilling to the artificial heating is to be investigated as follows: (1) measurement of the temperature field at the contained surface, in the backfill and in the rock salt; (2) deformation measurements of the salt rock around the heated drifts; (3) measurements of tunnel convergence in heated and unheated sections; (4) compaction measurements of the backfilling in heated and unheated areas; (5) measurement of rock stresses in areas very close to the galleries; and (6) pressure measurements in the backfilling, between backfilling and rock, and between backfilling and containers. The rock burst monitoring system of the Asse salt mine will be expanded to this special field of the mine to detect seismic events due to thermomechanical effects. Another seismoacoustic system will be installed to observe the compaction of the backfilling. This system must be calibrated for the relation between the density and velocities of seismic waves. It is planned to monitor the density by gamma-gamma log measurements. The changes in overall density during the entire experiment will be observed by gravimeter measurements of high precision

Particle-scale Analysis of Key Technologies on Cut-and-over Tunnel in Slope Engineering

Directory of Open Access Journals (Sweden)

J.H. Yang

2014-08-01

Full Text Available When the shallow tunnel is constructed on the slope terrain in the mountains, there are the potential risks such as landslide induced by cutting the slope and the non-compacted backfill material during the construction of the cut-andcover tunnel. In order to solve these problems, based on a practical engineering, the optimized construction plans of the cut-and-cover tunnel were analyzed by particle flow code (PFC, the key parts of the open-cut construction were identified, and the anti-slide piles countermeasures were proposed. Furthermore, the grouting reinforcement process for the non-compacted backfill material around the shallow tunnel was simulated by PFC, and the variation characteristics of the porosity and grouting pressure were revealed as well. The results are of great value to the similar engineering.
Status of Sandia backfill-getter development studies

International Nuclear Information System (INIS)

Molecke, M.A.; Nowak, E.J.

1980-01-01

In this paper, specific functions desired of the backfill as well as various recent experimental studies, results, and current plans for further studies, and modeling of the backfill's effectiveness for delaying radionuclide release are presented. Experimental studies and results are as follows: smectite swelling clay, bentonite, has been selected as a major component in the backfill because of its favorable properties in contact with salt and brine solution; sorptive properties for Pu and Am in batch and column-type experiments are being measured; various materials such as synthetic zeolites, titanates, and charcoal show promise for sorbing fission products in brine; mechanisms of backfill alteration or degradation which may cause the backfill barrier to lose some of its chemical and physical effectiveness is being investigated, with pH, Eh, temperature, pressure, radiation, and backfill-getter overall composition as parameters of interest; hydrothermal backfill-brine reactions have been studied experimentally; geotechnical measurements on bentonite and bentonite-sand mixtures have yielded brine and water permeabilities in the microdarcy range; and engineering-scale work on backfill emplacement forms and techniques to be used in a repository is under investigation, and will culminate with an actual demonstration of backfill emplacement in a field test
Effect of Initial Backfill Temperature on the Deformation Behavior of Early Age Cemented Paste Backfill That Contains Sodium Silicate

Directory of Open Access Journals (Sweden)

Aixiang Wu

2016-01-01

Full Text Available Enhancing the knowledge on the deformation behavior of cemented paste backfill (CPB in terms of stress-strain relations and modulus of elasticity is significant for economic and safety reasons. In this paper, the effect of the initial backfill temperature on the CPB’s stress-strain behavior and modulus of elasticity is investigated. Results show that the stress-strain relationship and the modulus of elasticity behavior of CPB are significantly affected by the curing time and initial temperature of CPB. Additionally, the relationship between the modulus of elasticity and unconfined compressive strength (UCS and the degree of hydration was evaluated and discussed. The increase of UCS and hydration degree leads to an increase in the modulus of elasticity, which is not significantly affected by the initial temperature.
Buffer and backfill process report for the safety assessment SR-Can

Energy Technology Data Exchange (ETDEWEB)

Sellin, Patrik (comp.)

2006-09-15

This document compiles information on processes in the buffer and deposition tunnel backfill relevant for long-term safety of a KBS-repository. It supports the safety assessment SR-Can, which is a preparatory step for a safety assessment that will support the licence application for a final repository in Sweden. The purpose of the process reports is to document the scientific knowledge of the processes to a level required for an adequate treatment of the processes in the safety assessment. The documentation is not exhaustive from a scientific point of view, since such a treatment is neither necessary for the purposes of the safety assessment nor possible within the scope of an assessment. However, it must be sufficiently detailed to motivate, by arguments founded on scientific understanding, the treatment of each process in the safety assessment. The purpose is further to determine how to handle each process in the safety assessment at an appropriate degree of detail, and to demonstrate how uncertainties are taken care of, given the suggested handling.
Buffer and backfill process report for the safety assessment SR-Can

International Nuclear Information System (INIS)

Sellin, Patrik

2006-09-01

This document compiles information on processes in the buffer and deposition tunnel backfill relevant for long-term safety of a KBS-repository. It supports the safety assessment SR-Can, which is a preparatory step for a safety assessment that will support the licence application for a final repository in Sweden. The purpose of the process reports is to document the scientific knowledge of the processes to a level required for an adequate treatment of the processes in the safety assessment. The documentation is not exhaustive from a scientific point of view, since such a treatment is neither necessary for the purposes of the safety assessment nor possible within the scope of an assessment. However, it must be sufficiently detailed to motivate, by arguments founded on scientific understanding, the treatment of each process in the safety assessment. The purpose is further to determine how to handle each process in the safety assessment at an appropriate degree of detail, and to demonstrate how uncertainties are taken care of, given the suggested handling
Deep repository - engineered barrier systems. Half scale tests to examine water uptake by bentonite pellets in a block-pellet backfill system

International Nuclear Information System (INIS)

Dixon, David; Lundin, Cecilia; Oertendahl, Ellinor; Hedin, Mikael; Ramqvist, Gunnar

2008-12-01

In order to examine the behaviour of water entering a section of tunnel that had recently been backfilled using a combination of bentonite pellets and compacted, smectitic clay blocks, a series of large-scale tests have been completed. These tests, done at a scale of approximately 0.5 that of an emplacement tunnel were completed in a mock-up constructed in the Buffer Laboratory at SKB's Aespoe Hard Rock Laboratory. A total of 12 tests, undertaken under well controlled conditions were completed, examining the effects of inflow rate, inflow location and time on assemblies of blocks and pellets. Water was supplied to the assembly at rates ranging from 0.1 to 2.5 l/min and the time for water exit, the exit location, potential for erosion of backfill, the rate of water uptake and resistance of the assembly to water influx were all monitored for periods of 3 to 7 days. The testing time was selected to simulate a reasonable duration for unanticipated backfilling interruption. Longer durations were not necessary and risked both the stability of the system and the loss of the early stage conditions through progression of swelling and homogenization. Testing determined that initial water movement through backfill is largely controlled by the pellets. Water influx of up to 30 l/h at a single location was diverted by the pellets forming essentially horizontal flow channels (pipes) along the chamber wall - pellet interface. These piping features directed the majority of the incoming water around the backfill and towards the unconfined downstream face of the assembly. The time required for the water to exit the assembly was dependant on a combination of inflow rate and distance that it needed to travel. Water typically exited the face of the backfill at well-defined location(s) and once established, these features remained for the duration of the test. The exiting water typically carried only limited eroded material but could cause some disruption of the downstream face of the
Deep repository - engineered barrier systems. Half scale tests to examine water uptake by bentonite pellets in a block-pellet backfill system

Energy Technology Data Exchange (ETDEWEB)

Dixon, David (Atomic Energy of Canada Limited (AECL) (Canada)); Lundin, Cecilia (Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden)); Oertendahl, Ellinor (NCC (Sweden)); Hedin, Mikael (Aangpannefoereningen, Stockholm (Sweden)); Ramqvist, Gunnar (Eltekno AB (Sweden))

2008-12-15

In order to examine the behaviour of water entering a section of tunnel that had recently been backfilled using a combination of bentonite pellets and compacted, smectitic clay blocks, a series of large-scale tests have been completed. These tests, done at a scale of approximately 0.5 that of an emplacement tunnel were completed in a mock-up constructed in the Buffer Laboratory at SKB's Aespoe Hard Rock Laboratory. A total of 12 tests, undertaken under well controlled conditions were completed, examining the effects of inflow rate, inflow location and time on assemblies of blocks and pellets. Water was supplied to the assembly at rates ranging from 0.1 to 2.5 l/min and the time for water exit, the exit location, potential for erosion of backfill, the rate of water uptake and resistance of the assembly to water influx were all monitored for periods of 3 to 7 days. The testing time was selected to simulate a reasonable duration for unanticipated backfilling interruption. Longer durations were not necessary and risked both the stability of the system and the loss of the early stage conditions through progression of swelling and homogenization. Testing determined that initial water movement through backfill is largely controlled by the pellets. Water influx of up to 30 l/h at a single location was diverted by the pellets forming essentially horizontal flow channels (pipes) along the chamber wall - pellet interface. These piping features directed the majority of the incoming water around the backfill and towards the unconfined downstream face of the assembly. The time required for the water to exit the assembly was dependant on a combination of inflow rate and distance that it needed to travel. Water typically exited the face of the backfill at well-defined location(s) and once established, these features remained for the duration of the test. The exiting water typically carried only limited eroded material but could cause some disruption of the downstream face of
A multiphysics-viscoplastic cap model for simulating blast response of cemented tailings backfill

Directory of Open Access Journals (Sweden)

Gongda Lu

2017-06-01

Full Text Available Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill, an evolutive porous medium used in underground mine cavities, very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing process. In fact, there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine exploitations. In this study, a coupled thermo-hydro-mechanical-chemical (THMC-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading. A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal, hydraulic, mechanical and chemical factors. Then, the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus, in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast loading. All of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill (CPB properties in the curing process. Thus, the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of concern. The validation results of the proposed model indicate a good agreement between the experimental and the simulated results. The authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting, and also to practical risk management of backfill structures associated with such a dynamic condition.
Principle plug design for deposition tunnels

International Nuclear Information System (INIS)

Haaramo, M.; Lehtonen, A.

2009-06-01

This report examines the plug structures to be built in the deposition tunnels of the repository. The deposition tunnels located below the depth of 400 metres have been used as input data. Each plug consists of a massive concrete structure. The planned maximum pressure acting on the plug is 7.5 MPa. It consists of 4.5 MPa of groundwater pressure and 3 MPa of swelling pressure of the backfill. Five different plug types have been examined. Two of them (butt and irregular plug) turned out to be difficult from the point of view of other works in the central and deposition tunnels. One type (straight plug) requires a lot of construction material. Wedge-shaped and dome plugs have been examined more carefully. The wedge shaped plug has advantageous properties in comparison with the dome plug, such as a three dimensional state of stress, the wedging effect which increases strength as pressure increases and larger tolerances for the excavation of the slot. Leakage water has a longer path through the wedge shaped plug than through the dome plug. Pressure load affects the wedge shaped plug, creating normal stresses, which are compressive along each coordinate axis. The long-term rise in temperature in the deposition tunnels can produce high extra stresses in all the plug alternatives. These stresses make it necessary to increase the strength of the concrete or the distance between the plug and the nearest deposition hole. The stability effects of different plug distances and deposition tunnel orientations have been examined. The plug does not significantly affect stresses in the surrounding bedrock or the stability of the bedrock. Stresses caused by excavation and temperature rise are decisive factors. A groundwater chloride content of 0-3% in the environment of the repository is used as input data. It affects the tightness of the concrete and the quality of the cement. Cement has to be sulphate resistant with a low pH value. Low pH results in the weakening of the corrosion
Final report of the drive of the TASS-tunnel; Slutrapport fraan drivningen av TASS-tunneln

Energy Technology Data Exchange (ETDEWEB)

Karlzen, Rickard; Johansson, Emmeli (Svensk Kaernbraenslehantering AB (Sweden))

2010-05-15

controlling documents has given continuous improvements. The knowledge of the aim for the project and the achievements of those involved have played an important role in detecting, documenting and handling of aberrations. In the purchasing of the contractor a strong emphasis were placed on the knowledge and skills of the management and workers together with the quality of equipment and machinery for tunnelling. This has given good dividends and improved the quality of work performed considerably. The contract in its entirety, including how its aim has been passed on into the practical work, gave the client the ability to control the execution and the contractor the opportunity to complete a quality-assured work without conflicts regarding compensation. This has been a major contributing factor to the good cooperation. When the client takes a more distinct performance responsibility, the role of the entire organization is changing. Among other things are the demands increasing on the availability in quickly maintaining the communication between the client and the contactor in the field and that all understand and accept the client's intentions in the instructions given. The work to achieve a good tunnel contour has been very successful and the contour encounters the controlling requirements of the production line of the backfilling method. The average over break in the tunnel was approximately 16% with small amounts of under break. The area variations of the tunnel shows that the tunnel area never reaches the theoretical area and the largest area is reached approximately 0,7 m before the border of the next round. The introduction of electronic detonators improved the tunnel contour and increased the proportion of visible drill holes. The average amount of visible drill holes identified in the tunnel contour was 78%. With the drilling pattern that were used and the introduction of electronic detonators it has been possible to use contour explosives in the tunnel floor
Backfilling and closure of the deep repository. Phase 3 - pilot tests to verify engineering feasibility. Geotechnical investigations made on unsaturated backfill materials

International Nuclear Information System (INIS)

Johannesson, Lars-Erik

2008-12-01

The investigations described in this report is a part of the third phase of the joint SKB-Posiva project 'Backfilling and Closure of the Deep Repository, BACLO'. The overall objective of the BACLO project is to develop backfilling concept for the deep repository that can be configured to meet SKB's and Posiva's requirements in the chosen repository sites. The project was divided into four phases, of which two have already been performed. The second phase of the BACLO project consisted of laboratory tests and deepened analyses of the investigated backfill materials and methods and resulted in recommendation to focus on the development and testing of the block placement concept with three alternative backfill materials. The third phase investigations comprise of laboratory and large-scale experiments aiming at testing the engineering feasibility of the concept. In addition, how site-specific constraints, backfilling method and materials affect the long-term functions of the barriers will be described and analysed in order to set design specifications for the backfill. The third phase of the BACLO project is divided into several subprojects. The work described in this report belongs to subproject 1 concerning processes during installation and saturation of the backfill that may affect the long-term function of the bentonite buffer and the backfill itself. One of the main functions of backfill is to restrict buffer expansion which can lead to decrease in buffer density in the deposition hole. The criterion used as a basis for the Baclo investigations was that the buffer density at saturation should not be below 1,950 kg/m 3 at the level of the canister. The same criterion was applied for the work described in this report. The upward swelling of the buffer and the enclosed compression of the backfill was first studied assuming that both the buffer and the backfill were saturated. The main objective of this work was to study a case where the buffer is fully saturated
Backfilling and closure of the deep repository. Phase 3 - pilot tests to verify engineering feasibility. Geotechnical investigations made on unsaturated backfill materials

Energy Technology Data Exchange (ETDEWEB)

Johannesson, Lars-Erik (Clay Technology AB, Lund (Sweden))

2008-12-15

The investigations described in this report is a part of the third phase of the joint SKB-Posiva project 'Backfilling and Closure of the Deep Repository, BACLO'. The overall objective of the BACLO project is to develop backfilling concept for the deep repository that can be configured to meet SKB's and Posiva's requirements in the chosen repository sites. The project was divided into four phases, of which two have already been performed. The second phase of the BACLO project consisted of laboratory tests and deepened analyses of the investigated backfill materials and methods and resulted in recommendation to focus on the development and testing of the block placement concept with three alternative backfill materials. The third phase investigations comprise of laboratory and large-scale experiments aiming at testing the engineering feasibility of the concept. In addition, how site-specific constraints, backfilling method and materials affect the long-term functions of the barriers will be described and analysed in order to set design specifications for the backfill. The third phase of the BACLO project is divided into several subprojects. The work described in this report belongs to subproject 1 concerning processes during installation and saturation of the backfill that may affect the long-term function of the bentonite buffer and the backfill itself. One of the main functions of backfill is to restrict buffer expansion which can lead to decrease in buffer density in the deposition hole. The criterion used as a basis for the Baclo investigations was that the buffer density at saturation should not be below 1,950 kg/m3 at the level of the canister. The same criterion was applied for the work described in this report. The upward swelling of the buffer and the enclosed compression of the backfill was first studied assuming that both the buffer and the backfill were saturated. The main objective of this work was to study a case where the buffer is
The influence of backfill on seismicity

CSIR Research Space (South Africa)

Hemp, DA

1990-09-01

Full Text Available , that the seismicity has been reduced in areas where backfill had been placed. A factor complicating the evaluation of backfill on seismicity is the effect of geological structures on seismicity....
Backfilling with Fairness and Slack for Parallel Job Scheduling

International Nuclear Information System (INIS)

Sodan, Angela C; Wei Jin

2010-01-01

Parallel job scheduling typically combines a basic policy like FCFS with backfilling, i.e. moving jobs to an earlier than their regular scheduling position if they do not delay the jobs ahead in the queue according to the rules of the backfilling approach applied. Commonly used are conservative and easy backfilling which either have worse response times but better predictability or better response times and poor predictability. The paper proposes a relaxation of conservative backfilling by permitting to shift jobs within certain constraints to backfill more jobs and reduce fragmentation and subsequently obtain better response times. At the same time, deviation from fairness is kept low and predictability remains high. The results of the experimentation evaluation show that the goals are met, with response-time performance lying as expected between conservative and easy backfilling.
Backfilling with Fairness and Slack for Parallel Job Scheduling

Energy Technology Data Exchange (ETDEWEB)

Sodan, Angela C; Wei Jin, E-mail: acsodan@uwindsor.ca [University of Windsor, Computer Science, Windsor, Ontario (Canada)

2010-11-01

Parallel job scheduling typically combines a basic policy like FCFS with backfilling, i.e. moving jobs to an earlier than their regular scheduling position if they do not delay the jobs ahead in the queue according to the rules of the backfilling approach applied. Commonly used are conservative and easy backfilling which either have worse response times but better predictability or better response times and poor predictability. The paper proposes a relaxation of conservative backfilling by permitting to shift jobs within certain constraints to backfill more jobs and reduce fragmentation and subsequently obtain better response times. At the same time, deviation from fairness is kept low and predictability remains high. The results of the experimentation evaluation show that the goals are met, with response-time performance lying as expected between conservative and easy backfilling.
Migration of radionuclides through backfill in a nuclear waste repository

International Nuclear Information System (INIS)

Lung, H.

1986-01-01

Four models are analyzed to predict the performance of a backfill layer as part of the waste package emplacement in a nuclear waste repository. The corresponding computer code for each model is also developed. The time-dependent mass transfer analysis on a spherical waste-backfill geometry indicates that the radioactive decay effect can enhance the mass transfer rate from the backfill instead of reducing it. The analysis yields the breakthrough time of the backfill layer, which in turn characterizes the backfill performance. A non-linear (Langmuir) sorption isotherm is used to describe the sorption saturation in the backfill. The steady state mass transport analysis through a prolate spheroidal waste-backfill geometry shows that a simple formula can be used to calculate the individual resistances to mass transport in backfill and in host rock. A general, non-recursive analytical solution is derived for a radioactive decay chain of arbitrary length in either a finite or a semi-infinite medium. Numerical examples are given for different boundary conditions and for different decay chains. The results justify that for a backfill layer made of low permeability material, a zero water velocity can be used in the backfill analysis. It is also shown that under normal repository conditions, the mass transfer rate from the backfill is quite small. For the daughter member with a smaller retardation coefficient than that of the mother nuclide, such as 226 Ra in the 234 U → 230 Th → 226 Ra chain, an interior maximum in the concentration profile appears in the backfill. This phenomenon can be seen only in a chain calculation
Colonization of compacted backfill materials by microorganisms

Energy Technology Data Exchange (ETDEWEB)

Lucht, L.M.; Stroes-Gascoyne, S.; Miller, S.H.; Hamon, C.J.; Dixon, D.A

1997-11-01

Experiments were carried out to investigate the occurrence of pore clogging in backfill by bacterial activity. Four differently prepared and treated backfill materials were used to determine the effects of the quality and preparation method of the backfill materials on the occurrence of pore clogging. The backfills were compacted in permeameters which were infused with either groundwater or sterile distilled water. A constant pressure was applied to increase the rate of saturation. Results showed different inflow rates for the four materials despite the use of the same packing method for each specimen, the same dry density for each backfill and indications of similar initial pore volumes. These differences were likely caused by the fact that the two slowest-flowing permeameters contained a mixture of Na-bentonite and illitic shale simulating a glacial lake clay. Hydraulic conductivities measured ranged from 5 x 10{sup -11} m/s to 5 x 10{sup -12} m/s for the backfills containing glacial lake clay and 4 x 10{sup -12} m/s to 9 s 10{sup -13} m/s for the backfills containing a mixture of Na-bentonite and illitic shale. Weekly samples of outflow from the permeameters were analyzed microbially. Aerobic heterotrophs were low initially but stabilized around 10{sup 6} to 10{sup 7} colony forming units (CFU)/mL after about one week. Anaerobic heterotrophs stabilized at around 10{sup 2} to 10{sup 3} CFU/mL. Sulphate-reducing bacteria (SRB) were measured by the most probable number (MPN) method. Results showed low initial numbers but they stabilized around 10{sup 4} MPN/mL after one to two months. No significant numbers of aerobic or anaerobic sulphur oxidizing bacteria were found. Enumeration of methanogens indicated that they were generally present in the permeameters that contained non-autoclaved backfill. Results are partially inconclusive because of the lack of confirmation of methane gas present in the headspace of part of the MPN culture tubes. Microbial pore clogging
Colonization of compacted backfill materials by microorganisms

International Nuclear Information System (INIS)

Lucht, L.M.; Stroes-Gascoyne, S.; Miller, S.H.; Hamon, C.J.; Dixon, D.A.

1997-11-01

Experiments were carried out to investigate the occurrence of pore clogging in backfill by bacterial activity. Four differently prepared and treated backfill materials were used to determine the effects of the quality and preparation method of the backfill materials on the occurrence of pore clogging. The backfills were compacted in permeameters which were infused with either groundwater or sterile distilled water. A constant pressure was applied to increase the rate of saturation. Results showed different inflow rates for the four materials despite the use of the same packing method for each specimen, the same dry density for each backfill and indications of similar initial pore volumes. These differences were likely caused by the fact that the two slowest-flowing permeameters contained a mixture of Na-bentonite and illitic shale simulating a glacial lake clay. Hydraulic conductivities measured ranged from 5 x 10 -11 m/s to 5 x 10 -12 m/s for the backfills containing glacial lake clay and 4 x 10 -12 m/s to 9 s 10 -13 m/s for the backfills containing a mixture of Na-bentonite and illitic shale. Weekly samples of outflow from the permeameters were analyzed microbially. Aerobic heterotrophs were low initially but stabilized around 10 6 to 10 7 colony forming units (CFU)/mL after about one week. Anaerobic heterotrophs stabilized at around 10 2 to 10 3 CFU/mL. Sulphate-reducing bacteria (SRB) were measured by the most probable number (MPN) method. Results showed low initial numbers but they stabilized around 10 4 MPN/mL after one to two months. No significant numbers of aerobic or anaerobic sulphur oxidizing bacteria were found. Enumeration of methanogens indicated that they were generally present in the permeameters that contained non-autoclaved backfill. Results are partially inconclusive because of the lack of confirmation of methane gas present in the headspace of part of the MPN culture tubes. Microbial pore clogging was not evident for the two fastest
Implementation of Paste Backfill Mining Technology in Chinese Coal Mines

Science.gov (United States)

Chang, Qingliang; Zhou, Huaqiang; Bai, Jianbiao

2014-01-01

Implementation of clean mining technology at coal mines is crucial to protect the environment and maintain balance among energy resources, consumption, and ecology. After reviewing present coal clean mining technology, we introduce the technology principles and technological process of paste backfill mining in coal mines and discuss the components and features of backfill materials, the constitution of the backfill system, and the backfill process. Specific implementation of this technology and its application are analyzed for paste backfill mining in Daizhuang Coal Mine; a practical implementation shows that paste backfill mining can improve the safety and excavation rate of coal mining, which can effectively resolve surface subsidence problems caused by underground mining activities, by utilizing solid waste such as coal gangues as a resource. Therefore, paste backfill mining is an effective clean coal mining technology, which has widespread application. PMID:25258737
The stochastic nuclide transport model for buffer/backfill materials

International Nuclear Information System (INIS)

Ma Liping; Han Yongguo

2014-01-01

Currently, study on nuclide migration law in geological disposal repository of high level waste is assumed buffer/backfill layer to be continuous medium, utilized the continuity equation, equation of state, the equations of motion, etc, formed a set of theory and method to estimate nuclide concentration distribution in buffer/backfill layer, and provided an important basis for nuclide migration rules of repository. However, it is necessary to study the buffer/backfill layer microstructure and subtly describe the pore structure and fracture system of the buffer/backfill layer, and reflect the changes in connectivity and in different directions of the buffer/backfill layer. Through using random field theory, the nuclide transport for the buffer/backfill layer in geological disposal repository of nuclear waste is described in the paper. This paper mainly includes that, t represents the time, ξ t ⊂ Z d = d represents the integer lattice, Z represents collectivity integers, d = l, 2, 3, for instance, d = 2, Z d = {(m, n) : m, n ∈ Z} the state point of ξ t is typically considered to be occupied by the nuclide concentration values of the buffer/backfill layer, ξ t also represents random set in the diagram of two dimensional integer lattice, namely, t ∈ [0, T], {ξ t ,0 ≤ t ≤ ⊂ T} Consequently, according to the stochastic process obtained above, the changes of the nuclide concentration values of the buffer/backfill layer or the buffer/backfill laboratory materials in the repository with the time can be known. (authors)

Scoping calculations for canister-tunnel migration of corrodants, oxidants and radionuclides

International Nuclear Information System (INIS)

Shaw, W.; Worth, D.

1992-03-01

This report presents the mathematical models and results obtained for a set of scooping calculations which estimate the possible extent of the vertical migration of canister corrodants, oxidants (forming a redox front) and radionuclides between a copper canister containing spent nuclear fuel, and an overlying emplacement tunnel. The KBS-3 concept for the disposal of spent nuclear fuel is copper canisters, vertically emplaced in deposition holes bored in the floor of a tunnel, situated deep underground. The deposition holes are filled with a buffer of bentonite and the tunnel is backfilled with a mixture of sand and bentonite. (au)
Discussion on sealing performance required in disposal system. Hydraulic analysis of tunnel intersections

International Nuclear Information System (INIS)

Sugita, Yutaka; Takahashi, Yoshiaki; Uragami, Manabu; Kitayama, Kazumi; Fujita, Tomoo; Kawakami, Susumu; Yui, Mikazu; Umeki, Hiroyuki; Miyamoto, Yoichi

2005-09-01

The sealing performance of a repository must be considered in the safety assessment of the geological disposal system of the high-level radioactive waste. NUMO and JNC established 'Technical Commission on Sealing Technology of Repository' based on the cooperation agreement. The objectives of this commission are to present the concept on the sealing performance required in the disposal system and to develop the direction for future R and D programme for design requirements of closure components (backfilling material, clay plug, etc.) in the presented concept. In the first phase of this commission, the current status of domestic and international sealing technologies were reviewed; and repository components and repository environments were summarized subsequently, the hydraulic analysis of tunnel intersections, where a main tunnel and a disposal tunnel in a disposal panel meet, were performed, considering components in and around the engineered barrier system (EBS). Since all tunnels are connected in the underground facility, understanding the hydraulic behaviour of tunnel intersections is an important issue to estimate migration of radionuclides from the EBS and to evaluate the required sealing performance in the disposal system. In the analytical results, it was found that the direction of hydraulic gradient, hydraulic conductivities of concrete and backfilling materials and the position of clay plug had impact on flow condition around the EBS. (author)
Creep consolidation of nuclear depository backfill materials

International Nuclear Information System (INIS)

Butcher, B.M.

1980-10-01

Evaluation of the effects of backfilling nuclear waste repository rooms is an important aspect of waste repository design. Consolidation of the porous backfill takes place as the room closes with time, causing the supporting stress exerted by the backfill against the intact rock to increase. Estimation of the rate of backfill consolidation is required for closure rate predictions and should be possible if the creep law for the solid constituent is known. A simple theory describing consolidation with a spherical void model is derived to illustrate this relationship. Although the present form of the theory assumes a homogeneous isotropic incompressible material atypical of most rocks, it may be applicable to rock salt, which exhibits considerable plasticity under confined pressure. Application of the theory is illustrated assuming a simple steady-state creep law, to show that the consolidation rate depends on the externally applied stress, temperature, and porosity
Filling of recovered mining areas using solidifying backfill

Directory of Open Access Journals (Sweden)

Zeman Róbert

2001-12-01

Full Text Available The aim of this article is to explore the possibilities for filling recovered mining areas using solidifying backfill .The article describes the preparation of the backfill (backfill formulation with an eventual application using low quality sands, wastes from treatment plants and ash from power plants etc now to transport it as well as its application in practice. Advantageous and disadvantageous of this method are also mentioned.Several factors must be taken info consideration during the preparation process of the backfill mixture. Firstly, the quantities of each individual component must be constantly regulated. Secondly, the properties of each component must be respected. In addition, the needs of the pipeline transport system and the specific conditions of the recovered area to be filled must also be considered.Hydraulic transport and pneumo-hydraulic pipeline transport are used for handling the backfill. Pumps for transporting the solidifying backfill have to carry out demanding tasks.Due to the physical-mechanical properties of the backfill, only highly powerful pumps can be considered. Piston type pumps such as Abel Simplex and Duplex pumps with capacities of up to 100 m3.h-1 and operating pressures of up to 16 MPa would be suitable.This method has been applied abroad for different purposes. For example, solid backfill was used in the Hamr mine during exploitation of uranium using the room-and-pillar system mining method.In the OstravaKarvina Coal field, backfill was used in decontamination work, filling areas in a zone of dangerous deformations and for creating a dividing stratum during thick seam mining.Research info the use of solidifying backfill was also done in the Walsum mine in Germany. The aim of this research was:- to investigate the possibilities of filling a collapsing area in a working face using a solidifying mixture of power plant ash and water,- to verify whether towing pipelines proposed by the DMT corporation would be
Uranium mill tailings backfill management. Final report

International Nuclear Information System (INIS)

Thomson, B.M.; Heggen, R.J.

1984-01-01

Backfilling, the disposal of spent uranium mill tailings in empty mine stopes, has been practiced in the Grants Mineral Belt of New Mexico for nearly 20 years. The principal objective of backfilling is the prevention of roof collapse and hydraulic connection with overlying aquifers, increasing mine dewatering requirements. Backfilling is accomplished by gravity feed of a slurry of sand-fraction tailings and treated mine water into the slope. The effects of backfilling on surface discharge of mine wastewater are negligible due to the small fraction of the total flow represented by slurry decant. Furthermore, quality of the decant is not significantly below that of other mine waters. Groundwater effects of backfilling may be classified as short-term (while the mine is operational) and long-term (after dewatering operations have been terminated). Short-term effects are insignificant because of rapid and continuous flow to the mine sump. Long-term effects on aquifer water quality are predicted to be minimal due to (1) the small amount of slurry liquor present after drainage, (2) the precipitation of SO 4 and CO 3 phases, and (3) the reestablishment of reducing conditions and subsequent precipitation of major contaminants including U, As, Mo, Se, and V. 28 references, 19 figures, 9 tables
Exchangeability of bentonite buffer and backfill materials

Energy Technology Data Exchange (ETDEWEB)

Savage, D. [Savage Earth Associates Ltd, Bournemouth (United Kingdom); Arthur, R. [Intera Inc, Ottawa, ON, (Canada); Luukkonen, A.

2012-08-15

Clay-based buffer and tunnel backfill materials are important barriers in the KBS-3 repository concept for final disposal of spent nuclear fuel in Finland. One issue that is relevant to material properties is the degree to which different bentonite compositions can be regarded as interchangeable. In Posiva's current repository design, the reference bentonite composition is MX-80, a sodium montmorillonite dominated clay. Posiva would like to be able to use bentonite with Ca-montmorillonite as the dominant clay mineral. However, at this stage, it is not clear what supporting data need to be acquired/defined to be able to place the state of knowledge of Ca-bentonite at the same level as that of Na-bentonite. In this report, the concept of bentonite exchangeability has been evaluated through consideration of how bentonite behaviour may be affected in six key performance-relevant properties, namely (1) mineralogical composition and availability of materials, (2) hydraulic conductivity, (3) mechanical and rheological properties, (4) long-term alteration, (5) colloidal properties, and (6) swelling pressure. The report evaluates implications for both buffer and backfill. Summary conclusions are drawn from these sections to suggest how bentonite exchangeability may be addressed in regulatory assessments of engineered barrier design for a future geological repository for spent fuel in Finland. Some important conclusions are: (a) There are some fundamental differences between Ca- and Na-bentonites such as colloidal behaviour, pore structure and long-term alteration that could affect the exchangeability of these materials as buffer or backfill materials and which should be further evaluated; (b) Additional experimental data are desirable for some issues such as long-term alteration, hydraulic properties and swelling behaviour, (c) The minor mineral content of bentonites is very variable, both between different bentonites and within the same bentonite type, it is not clear
Electrical resisitivity of mechancially stablized earth wall backfill

Science.gov (United States)

Snapp, Michael; Tucker-Kulesza, Stacey; Koehn, Weston

2017-06-01

Mechanically stabilized earth (MSE) retaining walls utilized in transportation projects are typically backfilled with coarse aggregate. One of the current testing procedures to select backfill material for construction of MSE walls is the American Association of State Highway and Transportation Officials standard T 288: ;Standard Method of Test for Determining Minimum Laboratory Soil Resistivity.; T 288 is designed to test a soil sample's electrical resistivity which correlates to its corrosive potential. The test is run on soil material passing the No. 10 sieve and believed to be inappropriate for coarse aggregate. Therefore, researchers have proposed new methods to measure the electrical resistivity of coarse aggregate samples in the laboratory. There is a need to verify that the proposed methods yield results representative of the in situ conditions; however, no in situ measurement of the electrical resistivity of MSE wall backfill is established. Electrical resistivity tomography (ERT) provides a two-dimensional (2D) profile of the bulk resistivity of backfill material in situ. The objective of this study was to characterize bulk resistivity of in-place MSE wall backfill aggregate using ERT. Five MSE walls were tested via ERT to determine the bulk resistivity of the backfill. Three of the walls were reinforced with polymeric geogrid, one wall was reinforced with metallic strips, and one wall was a gravity retaining wall with no reinforcement. Variability of the measured resistivity distribution within the backfill may be a result of non-uniform particle sizes, thoroughness of compaction, and the presence of water. A quantitative post processing algorithm was developed to calculate mean bulk resistivity of in-situ backfill. Recommendations of the study were that the ERT data be used to verify proposed testing methods for coarse aggregate that are designed to yield data representative of in situ conditions. A preliminary analysis suggests that ERT may be utilized
Investigation of stress in a circular tunnel due to overburden and thermal loading of horizontally placed 21 PWR multi purpose canisters

International Nuclear Information System (INIS)

Kandalaft-Ladkany, N.; Wyman, R.V.

1994-01-01

The drift of a High Level Nuclear Waste (HLNW) Repository were subjected to 2-D thermal loading resulting from the horizontal emplacement of 125 Ton Multi-Purpose Canisters (MPC). Ten 2-D temperature profiles, resulting from 57 Kw/acre and 114 Kw/acre thermal loading conditions, were used in a finite element analysis of the drift; in which a quadrant of the drift and surrounding rock ±100m above and below the drift were modeled. Our analysis shows that the 114 Kw/acre thermal loading results in compressive stresses around the drift, 60 years after emplacement, that exceed the unconfined compressive strength of the TSW tuff analyzed. Stresses resulting from a 57 Kw/acre thermal loading are within the acceptable limit in tunnel rock. A parametric analysis of the invert backfill material showed that Young's modulus for the invert backfill should closely match that of the surrounding unconfined rock in the tunnel in order to prevent an unacceptable stress rise in both rock and backfill
Jetting and flooding of granular backfill materials : [summary].

Science.gov (United States)

2015-03-01

Granular backfill materials on highway projects are often compacted by mechanical methods. : This requires the contractor to place backfill material into loose lifts of varying thickness : and use compaction equipment to reduce air voids and increase...
Research of Cemented Paste Backfill in Offshore Environments

Science.gov (United States)

Wang, Kun; Yang, Peng; Lyu, Wensheng; Lin, Zhixiang

2018-01-01

To promote comprehensive utilization of mine waste tailings and control ground pressure, filling mine stopes with cement paste backfill (CPB) is becoming the most widely used and applicable method in contemporary underground mining. However, many urgent new problems have arisen during the exploitation in offshore mines owing to the complex geohydrology conditions. A series of rheological, settling and mechanical tests were carried out to study the influences of bittern ions on CPB properties in offshore mining. The results showed that: (1) the bittern ion compositions and concentrations of backfill water sampled in mine filling station were similar to seawater. Backfill water mixed CPB slurry with its higher viscosity coefficient was adverse to pipeline gravity transporting; (2) Bleeding rate of backfill water mixed slurry was lower than that prepared with tap water at each cement-tailings ratio; (3) The UCS values of backfill water mixed samples were higher at early curing ages (3d, 7d) and then became lower after longer curing time at 14d and 28d. Therefore, for mine production practice, the offshore environments can have adverse effects on the pipeline gravity transporting and have positive effects on stope dewatering process and early-age strength growth.
Stability of reinforced cemented backfills

International Nuclear Information System (INIS)

Mitchell, R.J.; Stone, D.M.

1987-01-01

Mining with backfill has been the subject of several international meetings in recent years and a considerable research effort is being applied to improve both mining economics and ore recovery by using backfill for ground support. Classified mill tailings sands are the most commonly used backfill material but these fine sands must be stabilized before full ore pillar recovery can be achieved. Normal portland cement is generally used for stabilization but the high cost of cement prohibits high cement usage. This paper considers the use of reinforcements in cemented fill to reduce the cement usage. It is concluded that strong cemented layers at typical spacings of about 3 meters in a low cement content bulk fill can reinforce the fill and reduce the overall cement usage. Fibre reinforcements introduced into strong layers or into bulk fills are also known to be effective in reducing cement usage. Some development work is needed to produce the ideal type of anchored fibre in order to realize economic gains from fibre-reinforced fills
Deformation Monitoring of the Spallation Neutron Source (SNS) Tunnels

CERN Document Server

Error, J J; Fazekas, J J; Helus, S A; Maines, J R

2005-01-01

The SNS Project is a 1.4 MW accelerator-based neutron source located at Oak Ridge National Laboratory in Oak Ridge, Tennessee. For shielding purposes, a 17 foot berm of native soil has been constructed on top of the accelerator tunnel system. This backfill has caused ongoing settlement of the tunnels. The settlement has been monitored by the SNS Survey and Alignment Group at regular intervals, in order to discover the patterns of deformation, and to determine when the tunnels will be stable enough for precise alignment of beam line components. The latest monitoring results indicate that the settlement rate has significantly decreased. This paper discusses the techniques and instrumentation of the monitoring surveys, and provides an analysis of the results.
Application of Paste Backfill in Underground Coal Fires

Science.gov (United States)

Masniyom, M.; Drebenstedt, C.

2009-04-01

Coal fires are known from different coalfields worldwide. China, India, USA, Australia, Indonesia and South Africa are the main countries affected by coal fires. The fires is thermally intensive and cause numerous sinkholes, large-scale subsidence, air pollution, global warming, loss of mining productivity and increasing safety risk. The Wuda Inner Mongolia coalfield has been selected as a possible test area for paste backfill. The traditional methods, executed by fire fighting teams, by covering the coalfire areas with soil, blasting burning coal outcrops and injecting water in the subsurface fire pockets are continuously improved and extended. Initiatives to introduce modern techniques, such as backfill placement at fracture and borehole, to cool down the burning coal and cut off the air supply. This study is to investigate backfill materials and techniques suited for underground coal fires. Laboratory tests were carried out on physical, chemical and mechanical properties of different backfill materials and mixtures thereof. Special attention was paid to materials generated as by-products and other cheaply available materials e.g. fly ash from power plants. There is a good chance that one of the different material mixtures investigated can be used as a technically and economically viable backfill for underground coal fires.
Tire Shred Backfill in Mechanically Stabilized Earth Wall Applications

OpenAIRE

Balunaini, Umashankar; Yoon, Sungmin; Prezzi, Monica; Salgado, Rodrigo

2009-01-01

Tire shred-soil mixture backfill for use in mechanically stabilized earth (MSE) walls has several advantages over traditional backfill materials: 1) good drainage, 2) high shear strength, 3) low compacted unit weight and 4) low lateral pressure exerted on retaining structures. This work presents the results of laboratory tests performed on tire shred-sand mixtures focusing on determining the properties required for their use as backfill in MSE wall applications. Three sizes of tire shreds are...
Evaluation for swelling characteristics of buffer and backfill materials for high-level nuclear waste disposal. Influence of sand-bentonite content and cation compositions in bentonite

International Nuclear Information System (INIS)

Komine, Hideo; Ogata, Nobuhide

1999-01-01

Compacted bentonite and sand-bentonite mixture are attracting greater attention as buffer and backfill materials for disposal pits and access tunnels in the underground facilities for repositories of high-level nuclear waste. Buffer and backfill materials must have the swelling characteristics and are expected to fill up the space between these materials and surrounding ground by swelling. This role is called as 'Self-sealing'. To design the specifications, such as dry density, bentonite content and size, of buffer and backfill materials for the disposal facilities of high-level nuclear wastes described above, we must evaluate the swelling characteristics of compacted bentonite and sand-bentonite mixtures. For this purpose, this study proposed the evaluation formula for swelling characteristics of buffer and backfill materials containing bentonite. This study derived new equations for evaluating the relationship between the swelling deformation of compacted bentonite and sand-bentonite mixtures, and the swelling behavior of montmorillonite minerals, which are swelling clay minerals. This study also proposed new equations for evaluating the ion compositions of bentonite, ion concentration of pore water and the specific surface of bentonite, which significantly influence the swelling characteristics of buffer and backfill materials. The evaluation formula proposed in this study is presented by combining the above-mentioned new equations with theoretical equations, of which are the Gouy-Chapman diffuse double layer theory and the van der Waals force, of repulsive and attractive forces of montmorillonite minerals. (author)
Study on HDPE Mixed with Sand as Backfilled Material on Retaining Structure

Science.gov (United States)

Talib, Z. A.

2018-04-01

The failure of the retaining wall is closely related to backfill material. Granular soils such as sand and gravel are most suitable backfill material because of its drainage properties. However two basic materials are quite heavy and contribute high amount of lateral loads. This study was to determine the effectiveness High Density Polyethylene (HDPE) as a backfill material. HDPE has a lighter weight compare to the sand. It makes HDPE has potential to be used as backfill material. The objective of this study is to identify the most effective percentage of HDPE to replace sand as a backfill material. The percentage of HDPE used in this study was 20%, 30%, 50%, 75% and also 100%. Testing involved in this study were sieve analysis test, constant head permeability test, direct shear test and relative density test. The result shows that the HDPE can be used as backfilled material and save the cost of backfill material
The in-situ experiment for performance confirmation of engineered barrier system at Horonobe Underground Research Laboratory. Examination of backfill material using muck from URL construction

International Nuclear Information System (INIS)

Nakayama, Masashi; Ohno, Hirokazu; Tanai, Kenji; Fujita, Tomoo; Sugita, Yutaka

2016-06-01

The Horonobe Underground Research Laboratory (URL) Project has being pursued by Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host sedimentary formation at Horonobe, northern Hokkaido. The URL Project consists of two major research areas, “Geoscientific Research” and “Research and Development on Geological Disposal Technologies”, and proceeds in three overlapping phases, “Phase I: Surface-based investigations”, “Phase II: Investigations during tunnel excavation” and “Phase III: Investigations in the underground facilities”, over a period of around 20 years. Phase III investigation was started in 2010 fiscal year. The in-situ experiment for performance confirmation of engineered barrier system (EBS experiment) was prepared from 2013 to 2014 fiscal year at G.L.-350m gallery (Niche No.4), and heating by electric heater in simulated overpack started in January, 2015. One of objectives of the experiment is acquiring data concerned with Thermal – Hydrological – Mechanical – Chemical (THMC) coupled behavior. These data will be used in order to confirm the performance of engineered barrier system. In EBS experiment, the backfill material using mixture of bentonite and muck from Horonobe URL construction was used for backfilling a part of Niche No.4. This report shows the results of properties of the backfill material, confirmation test of compaction method and making backfill material block, and so on. From these results, it was confirmed that the backfill material would satisfy target value of the permeability and the swelling pressure. (author)
Cementitious backfill in mining

Energy Technology Data Exchange (ETDEWEB)

Taute, A; Spice, J; Wingrove, A C [Van Niekerk, Kleyn Edwards (South Africa)

1993-03-01

This article describes the need for increased usage of backfill material in mining and presents some of the considerations for use of cemented materials. Laboratory test results obtained using a variety of cementitious binders and mine tailings are presented. 3 figs., 1 tab.
30 CFR 816.105 - Backfilling and grading: Thick overburden.

Science.gov (United States)

2010-07-01

... 30 Mineral Resources 3 2010-07-01 2010-07-01 false Backfilling and grading: Thick overburden. 816...-SURFACE MINING ACTIVITIES § 816.105 Backfilling and grading: Thick overburden. (a) Definition. Thick... surrounding terrain. (b) Performance standards. Where thick overburden occurs within the permit area, the...
A historical review of Waste Isolation Pilot Plant backfill development

International Nuclear Information System (INIS)

Krumhansl, James L.; Molecke, Martin A.; Papenguth, Hans W.; Brush, Laurence H.

2000-01-01

Backfills have been part of Sandia National Laboratories' [Sandia's] Waste Isolation Pilot Plant [WIPP] designs for over twenty years. Historically, backfill research at Sandia has depended heavily on the changing mission of the WIPP facility. Early testing considered heat producing, high level, wastes. Bentonite/sand/salt mixtures were evaluated and studies focused on developing materials that would retard brine ingress, sorb radionuclides, and withstand elevated temperatures. The present-day backfill consists of pure MgO [magnesium oxide] in a pelletized form and is directed at treating the relatively low contamination level, non-heat producing, wastes actually being disposed of in the WIPP. Its introduction was motivated by the need to scavenging CO 2 [carbon dioxide] from decaying organic components in the waste. However, other benefits, such as a substantial desiccating capacity, are also being evaluated. The MgO backfill also fulfills a statutory requirement for assurance measures beyond those needed to demonstrate compliance with the US Environmental Protection Agency [EPA] regulatory release limits. However, even without a backfill, the WIPP repository design still operates within EPA regulatory release limits

Backfill formulations for a nuclear fuel waste disposal vault

International Nuclear Information System (INIS)

Yong, R.N.; Boonsinsuk, P.; Wong, G.; Ming, X.D.; Caporuscio, F.; Lytle, P.

1987-01-01

Atomic Energy of Canada Limited and Ontario Hydro are studying the concept of disposing of nuclear fuel wastes in a vault within the Canadian Shield. After nuclear waste containers have been emplaced in a vault, the vault will have to be backfilled permanently. A suitable backfill material should have low hydraulic conductivity and high radionuclide sorption capacity. The research was done with a goal of recommending a specification for formulating this backfill material. This report suggests that such a backfill material should be a mixture of coarse aggregates and swelling clay. Actual trial mixtures were prepared using crushed granite and natural Lake Agassiz clay. Various trial mixtures were subjected to constant-head permeability tests. The results indicate that the hydraulic conductivity of the aggregate-clay mixtures could be close to those of the clay (by itself) when the clay content was in the range of 25% or more. The resulting hydraulic conductivity of about 10 -10 m/s is considered to be low, especially since the maximum grain size is 19.1 mm. Selected mixtures were evaluated for free swell and swelling pressure, both of which increased with increasing clay content. When the clay content was 25%, the free swell was about 4%, compared with 6% for the 100% clay. The corresponding swelling pressure was about 16 kPa - in comparison to 48 kPa for the 100% clay. These results indicate that the proposed backfill material should contain about 25% clay, with a maximum grain size of 19.1 mm. The selected mixture was also tested to evaluate the effects of mixing methods, load-carrying capacity and compaction techniques suitable for the underground vault conditions. The proposed backfill material appeared to perform satisfactorily according to the criteria demanded. The backfill material proposed was further tested for its behaviour during water intake. The unsaturated hydraulic conductivity was found to be approximately 10 -10 m/s and the swelling pressure was
BACCHUS 2: an in situ backfill hydration experiment for model validation

International Nuclear Information System (INIS)

Volckaert, G.; Bernier, F.; Alonso, E.; Gens, A.

1995-01-01

The BACCHUS 2 experiment is an in situ backfill hydration test performed in the HADES underground research facility situated in the plastic Boom clay layer at 220 m depth. The experiment aims at the optimization and demonstration of an installation procedure for a clay based backfill material. The instrumentation has been optimized in such a way that the results of the experiments can be used for the validation of hydro-mechanical codes such a NOSAT developed at the University of Catalunya Spain (UPC). The experimental set-up consists in a bottom flange and a central filter around which the backfill material was applied. The backfill material consist of a mixture of high density clay pellets and clay powder. The experimental set-up and its instrumentation are described in detail. The results of the hydro-mechanical characterization of the backfill material is summarized. (authors). 8 refs., 16 figs., 1 tab
Ion-exchange equilibria and diffusion in engineered backfill

International Nuclear Information System (INIS)

Soudek, A.; Jahnke, F.M.; Radke, C.J.

1984-01-01

Engineered backfill can add confidence to confinement times of high-level nuclear waste stored in geologic media. This paper discusses the design and operation of a unique radial-flow diffusion cell to determine ion migration rates in backfill material under realistic repository conditions. New experimental results were reported for diffusion of CsCl in a background of NaCl into compacted bentonite and bentonite/quartz mixtures. Representation of the measured diffusion rates by the traditional, homogeneous porous-medium model significantly underestimates cesium penetration distances into the backfill. Surface diffusion is suggested as an additional mechanism by which cations transport in swollen montmorillonite; the surface diffusion coefficients for cesium is determined to be approximately 10 -7 cm 2 /s. An electrostatic site-binding model is developed for ion-exchange equilibria on montmorillonite clay. The effect of pH, ionic strength, and specific adsorption are evaluated and compared favorably to new, experimental exchange isotherms measured on disaggregated clay. The electrostatic site-binding model permits a prediction of the influence of backfill compaction on K/sub d/ values. We find that for strongly adsorbing cations, compactions has little effect. However, anions exhibit significant Donnan exclusion with clay compaction. 40 references, 12 figures
EFFECTS OF THE BACK-FILLING TO THE STABILITY OF A CAISSON

Science.gov (United States)

Kikuchi, Yoshiaki; Shinsha, Hiroshi; Kawamura, Kensuke; Eguchi, Shinya

The back-filling improves the stability of a caisson used for breakwater against wave force. But, the extent of the improvement of the stability is affected by the interaction among the back-filling and the caisson and the foundation. A series of the model loading experiments was carried out to clarify the effects of the interaction to the stability. In this series of experiments, horizontal static load was applied to the model caisson having back-filling. Sliding failure surface was estimated from the deformation of rubble mound and back-filling. Passive earth pressure by back-filling calculated by wedge theory was compared with the experimental results. New stability evaluation method considering circular arc failure mode was developed and evaluated its validity. Followings are main conclusions in this research; 1) Increment of stability of a caisson against wave force can be estimated from wedge theory. 2) Both sliding and bearing capacity stability were considered in one time using newly developed evaluation method considering circular arc failure mode.
Preparation for YMP backfill activities

International Nuclear Information System (INIS)

Conca, J.

1998-01-01

Yucca Mountain activities for FY 1999 are anticipated to require specific information on the chemical and physical properties of the candidate getter materials and other backfill components necessary for defensible modeling of the source term, and possible controlling of the source term. There should be three tasks to this activity: at the end of this report is a draft test plan reflecting the present funding anticipated, the other tasks may be added as funding becomes available. (Task 1) The immobilization capacity of the getter materials for specific radionuclides. This task will primarily include column sorption tests of getter materials with solutions spiked with radionuclides. The getter materials will include Apatite II, MgO (with NaPO 4 plus Ba,SrCO 3 and soluble sulfate, with and without Apatite II), Gibbsite/Boehmite, and Hematite. Radionuclides will include Pu, U, Np, Am, Ra, Tc, and Th. Experiments will be performed under various anticipated repository conditions and with anticipated solution compositions. Occasional batch tests will be used to obtain specific K d s and other thermodynamic data. Solid and liquid analyses will be needed for characterization of the effluent concentrations from the columns to assess performance and for use in geochemical modeling. (Task 2) Intrinsic stability of the getter materials under repository conditions. The use of any candidate getter material will depend upon its anticipated lifetime in the backfill environment. Literature search for any existing data will be performed and augmented by solubility experiments on the getter materials. This is especially important for the reactive materials such as MgO and the soluble sulfates and phosphates that may be a limited lifetime in the backfill. It is also necessary to decide how much getter material to emplace. (Task 3) Diffusion of radionuclides across a Richards Barrier. The Richards Barrier, if emplaced, will act as a hydraulic diversion barrier for the diversion of
Physical response of backfill materials to mineralogical changes in a basalt environment

International Nuclear Information System (INIS)

Couture, R.A.; Seitz, M.G.

1983-01-01

Backfill materials surrounding waste canisters in a high-level nuclear waste repository are capable of ensuring very slow flow of groundwater past the canisters, and thereby increase the safety of the repository. However, in the design of a repository it will be necessary to allow for possible changes in the backfill. In this experimental program, changes in permeability, swelling behavior, and plastic behavior of the backfill at the temperatures, pressures, and radiation levels expected in a repository are investigated. The emphasis is on investigation of relevant phenomena and evaluation of experimental procedures for use in licensing procedures. The permeability of a slightly compacted sand-clay mixture containing 25% bentonite, with a dry bulk density of 1.59 g/cm 3 , was determined to be 0.9 x 10 -18 m 2 in liquid water at 25 and 200 0 C, respectively. This is sufficiently low to demonstrate the potential effectiveness of proposed materials. In practice, fractures in the host rock may form short circuits around the backfill, so an even lower flow rate is probable. However, alteration by any of several mechanisms is expected to change the properties of the backfill. Crushed basalt plus bentonite is a leading candidate backfill for a basalt repository. Experiments show that basalt reacts with groundwater vapor or with liquid groundwater producing smectites, zeolites, silica, and other products that may be either beneficial or detrimental to the long-term performance of the backfill. Concentration of groundwater salts in the backfill by evaporation would cause immediate, but possibly reversible, reduction of the swelling abaility of bentonite. Moreover, under some circumstances, gamma radiolysis of moist air in the backfill could produce up to 0.5 mole of nitric acid or ammonia per liter of pore space. 27 references, 7 figures, 4 tables
M4FT-16LL080303052-State of Knowledge for Colloid Facilitated Radionuclide Transport and Update on Actinide Diffusion in Bentonite Backfill

Energy Technology Data Exchange (ETDEWEB)

Zavarin, Mavrik [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Glenn T. Seaborg Inst.. Physical and Life Sciences; Joseph, C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Glenn T. Seaborg Inst.. Physical and Life Sciences

2016-08-16

This progress report (Level 4 Milestone Number M4FT-16LL080303052) summarizes research conducted at Lawrence Livermore National Laboratory (LLNL) within the Crystalline Disposal R&D Activity Number FT-16LL080303051 and Crystalline International Collaborations Activity Number FT-16LL080303061. The focus of this research is the interaction of radionuclides with Engineered Barrier System (EBS) and host rock materials at various physico-chemical conditions relevant to subsurface repository environments. They include both chemical and physical processes such as solubility, sorption, and diffusion. The colloid-facilitated transport effort focused on preparation of a draft manuscript summarizing the state of knowledge and parameterization of colloid-facilitated transport mechanisms in support of reactive transport and performance assessment models for generic crystalline repositories. This draft manuscript is being submitted as a level 3 milestone with LANL as the primary author. LLNL’s contribution to that effort is summarized only briefly in the present report. A manuscript summarizing long-term U(VI) diffusion experiments through bentonite backfill material was recently accepted for publication; the contents of that manuscript are summarized in the present report. The Np(IV) diffusion experiments were started mid-year and are ongoing. The completion of these experiments is planned for early FY17. Our progress in quantifying Np(IV) diffusion in bentonite backfill is summarized in the present report. Our involvement with the NEA TDB project was summarized in a recent Argillite Disposal activity report. It is not included in this report.
Some characteristics of potential backfill materials

International Nuclear Information System (INIS)

Simpson, D.R.

1983-05-01

A backfill material is one of the multiple barriers that may be involved in the disposal of nuclear waste. Such backfill should be a desiccant with the hydrous product having acceptable stability; it should sorb any released radioisotopes, and it should reseal any breached site. The backfill must also have acceptable thermal conductivity. This report presents data on the rate of hydration and the nature of the product of reaction of some candidate backfill materials with water and with brine. Thermal conductivity data is reported for both the reactants and the products. Granular MgO at 150 0 C completely hydrates in less than 10 hours. At 60 0 C and 20 0 C, such extensive hydration requires about 100 and 1000 hours, respectively. The product of the reaction is stable to more than 300 0 C. A doped discalcium silicate was less reactive and the product contains less water of crystallization than the MgO. The reaction product of dicalcium silicate is cementous, but it has low thermal stability. Bentonite readily reacts with water and expands. The reaction product has the properties of vermiculite, which indicates that magnesium ions have diffused into the bentonite structure and are not simply adsorbed on the surface. If bentonite is emplaced in a saline environment, the properties of vermiculite, the reaction product, should also be considered. The thermal conductivity of MgO, discalcium silicate, and bentonite is primarily dependent on the porosity of the sample. A slight increase in thermal conductivity was found with increased temperature, in contrast to most rocks. If the conductive data for the different materials is equated to the same porosity, MgO has the superior thermal conductivity compared to bentonite or discalcium silicate
Studies of the behaviour of backfill taking into account the interaction between rock and backfill, and other sealing components at a salina repository

International Nuclear Information System (INIS)

Diekmann, N.; Stuehrenberg, D.

1991-09-01

According to the present planning level of the designed Gorleben repository, the salt produced by opening up cavities for ultimate disposal will be used as salt fines for backfilling residual cavities after radioactive waste emplacement. The essential function properties of the backfill - compaction and permeability - were studied for salt fines, and the results achieved were discussed. (BBR) [de
Experimental Evaluation of Backfill in Scour Holes Around Offshore Monopiles

DEFF Research Database (Denmark)

Sørensen, Søren Peder Hyldal; Ibsen, Lars Bo; Frigaard, Peter

2010-01-01

be to allow the forming of a scour hole and hereby design the monopile with a larger penetration depth. The depth of the scour hole will change over time as the scour depth will increasewhen currents are dominating and backfilling of the scour hole will take placewhenwaves are dominating. Several researchers...... of the foundation for fatigue. A backfill test has been performed in the LargeWave Channel (GWK) of the Coastal Research Centre (FZK) in Hannover.The relative density of the backfilled soil material has based on soil samples and CPT measurements been determined to be in the range of 60–80%. The normalized time...
Optimum permeability for a cement based backfill material

International Nuclear Information System (INIS)

Jacobs, F.; Wittmann, F.H.; Iriya, K.

1989-01-01

In Switzerland it is planned to dispose low- and intermediate radioactive waste (LLW/ILW) in an underground repository. Between the materials present in a repository different chemical reactions may occur. Due to radiolytic decomposition, microbiological degradation and corrosion gas (mainly hydrogen) may be produced. The release of gas can cause the build-up of pressure in the cavern and finally lead to the formation of cracks and/or serious damage in the concrete structure or host rock. Through cracks a contamination of the groundwater and the biosphere could be possible. This investigation develops a suitable cement based material which can be used as backfill for the repository. Besides other aspects mentioned later a suitable backfill material has to be characterized by a certain minimum gas permeability and a as low as possible hydraulic conductivity. On the one hand gas permeability is necessary to release gas overpressure and on the other hand a low hydraulic conductivity should prevent leaching of backfill materials and contamination of the environment
SEEPAGE/BACKFILL INTERACTIONS

International Nuclear Information System (INIS)

Mariner, P.

2000-01-01

As directed by written development plan (CRWMS M andO 1999a), a sub-model of seepage/backfill interactions is developed and presented in this document to support the Engineered Barrier System (EBS) Physical and Chemical Environment Model. The purpose of this analysis is to assist Performance Assessment Operations (PAO) and the Engineered Barrier Performance Department in modeling the geochemical environment within a repository drift. In this analysis, a conceptual model is developed to provide PAO a more detailed and complete in-drift geochemical model abstraction and to answer the key technical issues (KTI) raised in the NRC Issue Resolution Status Report (IRSR) for the Evolution of the Near Field Environment (NFE) Revision 2 (NRC 1999). The development plan calls for a sub-model that evaluates the effect on water chemistry of chemical reactions between water that enters the drift and backfill materials in the drift. The development plan specifically requests an evaluation of the following important chemical reaction processes: dissolution-precipitation, aqueous complexation, and oxidation-reduction. The development plan also requests the evaluation of the effects of varying seepage and drainage fluxes, varying temperature, and varying evaporation and condensation fluxes. Many of these effects are evaluated in a separate Analysis/Model Report (AMR), ''Precipitates Salts Analysis AMR'' (CRWMS M andO 2000), so the results of that AMR are referenced throughout this AMR
SEEPAGE/BACKFILL INTERACTIONS

Energy Technology Data Exchange (ETDEWEB)

P. Mariner

2000-04-14

As directed by written development plan (CRWMS M&O 1999a), a sub-model of seepage/backfill interactions is developed and presented in this document to support the Engineered Barrier System (EBS) Physical and Chemical Environment Model. The purpose of this analysis is to assist Performance Assessment Operations (PAO) and the Engineered Barrier Performance Department in modeling the geochemical environment within a repository drift. In this analysis, a conceptual model is developed to provide PAO a more detailed and complete in-drift geochemical model abstraction and to answer the key technical issues (KTI) raised in the NRC Issue Resolution Status Report (IRSR) for the Evolution of the Near Field Environment (NFE) Revision 2 (NRC 1999). The development plan calls for a sub-model that evaluates the effect on water chemistry of chemical reactions between water that enters the drift and backfill materials in the drift. The development plan specifically requests an evaluation of the following important chemical reaction processes: dissolution-precipitation, aqueous complexation, and oxidation-reduction. The development plan also requests the evaluation of the effects of varying seepage and drainage fluxes, varying temperature, and varying evaporation and condensation fluxes. Many of these effects are evaluated in a separate Analysis/Model Report (AMR), ''Precipitates Salts Analysis AMR'' (CRWMS M&O 2000), so the results of that AMR are referenced throughout this AMR.
Relative Density of Backfilled Soil Material around Monopiles for Offshore Wind Turbines

DEFF Research Database (Denmark)

Sørensen, Søren Peder Hyldal; Ibsen, Lars Bo; Frigaard, Peter

2012-01-01

The relative density of backfilled soil material around offshore monopiles is assessed through experimental testing in the Large Wave Channel (GWK) of the Coastal Research Centre (FZK) in Hannover. The relative density of the backfill material was found to vary between 65 and 80 %. The dependency...... of the relative density of backfill on the maximum pile bending moment is assessed through three-dimensional numerical modeling of a monopile foundation located at the offshore wind farm at Horns Reef, Denmark....
On the risk of liquefaction of buffer and backfill

Energy Technology Data Exchange (ETDEWEB)

Pusch, R. [Geodevelopment AB, Lund (Sweden)

2000-10-01

The necessary prerequisites for liquefaction of buffers and backfills in a KBS-3 repository exist but the stress conditions and intended densities practically eliminate the risk of liquefaction for single earthquakes with magnitudes up to M=8 and normal duration. For buffers rich in expandable minerals it would be possible to reduce the density at water saturation to 1,700 - 1,800 kg/m{sup 3} or even less without any significant risk of liquefaction, while the density at saturation of backfills with 10 - 15% expandable clay should not be reduced to less than about 1,900 kg/m{sup 3}. Since the proposed densities of both buffers and backfills will significantly exceed these minimum values it is concluded that there is no risk of liquefaction of the engineered soil barriers in a KBS-3 repository even for very significant earthquakes.
On the risk of liquefaction of buffer and backfill

International Nuclear Information System (INIS)

Pusch, R.

2000-10-01

The necessary prerequisites for liquefaction of buffers and backfills in a KBS-3 repository exist but the stress conditions and intended densities practically eliminate the risk of liquefaction for single earthquakes with magnitudes up to M=8 and normal duration. For buffers rich in expandable minerals it would be possible to reduce the density at water saturation to 1,700 - 1,800 kg/m 3 or even less without any significant risk of liquefaction, while the density at saturation of backfills with 10 - 15% expandable clay should not be reduced to less than about 1,900 kg/m 3 . Since the proposed densities of both buffers and backfills will significantly exceed these minimum values it is concluded that there is no risk of liquefaction of the engineered soil barriers in a KBS-3 repository even for very significant earthquakes
Deformation Monitoring of Waste-Rock-Backfilled Mining Gob for Ground Control.

Science.gov (United States)

Zhao, Tongbin; Zhang, Yubao; Zhang, Zhenyu; Li, Zhanhai; Ma, Shuqi

2017-05-05

Backfill mining is an effective option to mitigate ground subsidence, especially for mining under surface infrastructure, such as buildings, dams, rivers and railways. To evaluate its performance, continual long-term field monitoring of the deformation of backfilled gob is important to satisfy strict public scrutiny. Based on industrial Ethernet, a real-time monitoring system was established to monitor the deformation of waste-rock-backfilled gob at -700 m depth in the Tangshan coal mine, Hebei Province, China. The designed deformation sensors, based on a resistance transducer mechanism, were placed vertically between the roof and floor. Stress sensors were installed above square steel plates that were anchored to the floor strata. Meanwhile, data cables were protected by steel tubes in case of damage. The developed system continually harvested field data for three months. The results show that industrial Ethernet technology can be reliably used for long-term data transmission in complicated underground mining conditions. The monitoring reveals that the roof subsidence of the backfilled gob area can be categorized into four phases. The bearing load of the backfill developed gradually and simultaneously with the deformation of the roof strata, and started to be almost invariable when the mining face passed 97 m.
Numerical simulation of wave-induced scour and backfilling processes beneath submarine pipelines

DEFF Research Database (Denmark)

Fuhrman, David R.; Baykal, Cüneyt; Sumer, B. Mutlu

2014-01-01

A fully-coupled hydrodynamic/morphodynamic numerical model is presented and utilized for the simulation of wave-induced scour and backfilling processes beneath submarine pipelines. The model is based on solutions to Reynolds-averaged Navier–Stokes equations, coupled with k−ω turbulence closure......≤30 demonstrate reasonable match with previous experiments, both in terms of the equilibrium scour depth as well as the scour time scale. Wave-induced backfilling processes are additionally studied by subjecting initial conditions taken from scour simulations with larger KC to new wave climates...... characterized by lower KC values. The simulations considered demonstrate the ability of the model to predict backfilling toward expected equilibrium scour depths based on the new wave climate, in line with experimental expectations. The simulated backfilling process is characterized by two stages: (1...
Low-pH concrete plug for sealing the KBS-3V deposition tunnels

International Nuclear Information System (INIS)

Malm, Richard

2012-01-01

In SKB's main alternative for final repository of radioactive material, KBS-3V, the backfilled deposition tunnels will be separated from the remaining tunnel system with concrete plugs. These concrete plugs will be designed for a life span of 100 years and their function shall maintain until the transport tunnels outside the plug are backfilled and the natural geohydrological conditions have been restored. The purpose of this report is to document the results and the evaluation from this project and motivate the choice of the most appropriate design for closing the deposition tunnels in the spent fuel repository. The purpose has also been to investigate and present the loads acting on the plug system and determine the load capacity of the concrete plug. This report is the result of a project conducted between 2009-01-01 - 2010-12-31 and the project group has made its assessment based on the conditions and requirements that are present today. The entire design of the plug system is part of this project, where the plug system consists of a filter, a bentonite seal and a cast-in-place concrete plug. Two different conceptual design alternatives for the concrete plug have been studied in this report, one long tapered plug and one dome shaped plug. The results in this report focus on the choice of the conceptual design for the concrete plug and its possibility to assist the entire plug system to satisfy its requirements. It is a complicated task to dispose the radioactive waste and it sets high technical requirements on the design and the production of the backfill and the closing of the deposition tunnels. The aim of this project is to design and develop a plug system suitable for production. This is done by the means of numerical calculations and analyses. The primary function of the concrete plug is to act as a resistance to the external loads originated from the axial expansion of the backfill and the water pressure. However, the entire plug system has a requirement
Low-pH concrete plug for sealing the KBS-3V deposition tunnels

Energy Technology Data Exchange (ETDEWEB)

Malm, Richard (Vattenfall Power Consultant AB (Sweden))

2012-01-15

In SKB's main alternative for final repository of radioactive material, KBS-3V, the backfilled deposition tunnels will be separated from the remaining tunnel system with concrete plugs. These concrete plugs will be designed for a life span of 100 years and their function shall maintain until the transport tunnels outside the plug are backfilled and the natural geohydrological conditions have been restored. The purpose of this report is to document the results and the evaluation from this project and motivate the choice of the most appropriate design for closing the deposition tunnels in the spent fuel repository. The purpose has also been to investigate and present the loads acting on the plug system and determine the load capacity of the concrete plug. This report is the result of a project conducted between 2009-01-01 - 2010-12-31 and the project group has made its assessment based on the conditions and requirements that are present today. The entire design of the plug system is part of this project, where the plug system consists of a filter, a bentonite seal and a cast-in-place concrete plug. Two different conceptual design alternatives for the concrete plug have been studied in this report, one long tapered plug and one dome shaped plug. The results in this report focus on the choice of the conceptual design for the concrete plug and its possibility to assist the entire plug system to satisfy its requirements. It is a complicated task to dispose the radioactive waste and it sets high technical requirements on the design and the production of the backfill and the closing of the deposition tunnels. The aim of this project is to design and develop a plug system suitable for production. This is done by the means of numerical calculations and analyses. The primary function of the concrete plug is to act as a resistance to the external loads originated from the axial expansion of the backfill and the water pressure. However, the entire plug system has a

Time effects of water drainage from deposited back-fill

International Nuclear Information System (INIS)

Baranski, L.A.

1976-01-01

Time effects of water drainage from deposited back-fill in mine excavations are considered. The time dependence of drainage from the deposited material was determined from ''in situ'' measurements with the aid of radioisotope gauges. The measurements were performed for given drainage conditions and practically constant grain size composition. It was found that in a few hours after the end of the back-filling operation the mechanical properties of the deposited material are practically constant. (author)
Ocean disposal of heat generating radioactive waste backfilling requirements

International Nuclear Information System (INIS)

1986-07-01

This report describes the backfilling requirements arising from the disposal of HGW in deep ocean sediments. The two disposal options considered are the drilled emplacement method and the free fall penetrator method. The materials best suited for filling the voids in the two options are reviewed. Candidate materials are selected following a study of the property requirements of each backfill. Placement methods for the candidate materials, as well as the means available for verifying the quality of the filling, are presented. Finally, an assessment of the overall feasibility of each placement method is given. The main conclusion is that, although the proposed methods are feasible, further work is necessary to test in inactive trials each of the proposed filling methods. Moreover, it is difficult to envisage how two of the backfilling operations in drilled emplacement option can be verified by non destructive methods. (author)
Analysis of factors affecting the stability of backfill materials

International Nuclear Information System (INIS)

Peacor, D.R.; Essene, E.J.; Lee, J.H.; Kuo, L.C.

1984-01-01

Storage of high-level nuclear waste in subsurface repositories involves a backfill material as a physical/chemical barrier between the solid waste canisters and host rock. Chemical, structural, and textural changes due to hydrothermal reaction may degrade the backfill performance over the life of the repository. In order to evaluate the potential for such changes, we have: (1) carried out hydrothermal experiments on candidate backfill materials (smectite, illite, basalt) under conditions analogous to those at the repository, (2) performed a complete characterization of these materials before and after hydrothermal treatment using EMPA, XRD, SEM/EDS, and, especially, STEM/AEM techniques, and (3) reviewed and analyzed geologic systems which are analogous to the backfill systems. These serve as natural experimental systems with ages up to many tens of millions of years. The Umtanum basalt contains up to 25% of immiscible, two-phase glasses and late opal and nontronite in fractures. These materials are especially subject to solution effects and the glass may provide K to groundwater. The kinetics of the smectite to illite and illite to muscovite transitions are primarily controlled by Al/Si diffusion which is sluggish, rather than by rapid alkali ion diffusion. Thus, even though smectite (bentonite), mixed-layer illite/smectite and illite are all metastable phases transitional to muscovite plus other phases, reactions occur so slowly that these phases are retained even within a geologic time scale for temperatures of approximately 150, 200 and 300 0 C, respectively. A high ratio of Ca/K (perhaps supplied by solution of calcite) inhibits the transitions. If clay layers are compacted to form a continuous matrix, water may be prevented from penetrating the backfill and promoting the clay mineral transition
Settlement in backfill pipelines: its causes and a novel online detection method

CSIR Research Space (South Africa)

Goosen, P

2011-03-01

Full Text Available always be determined reliably. This paper addresses what are considered to be the dominant parameters affecting backfill pipeline blockages. In particular, backfills with low water content and high cement content may undergo significant rheological...
Engineering solution for the backfilling and sealing of radioactive waste repositories

International Nuclear Information System (INIS)

Jorda, M.; Gouvenot, D.; Bonne, A.; Lees, T.P.; Schmidt, M.

1990-01-01

To ensure the safety of radioactive waste deep disposal, backfilling and sealing materials (engineered barriers) have to be used to fill residual voids. For granite medium, stress is put on emplacement techniques for cement- and clay-based materials, including in-situ validation. For clay medium, mined repository and deep boreholes drilled from the surface are considered. In the case of the first solution, the thermomechanical behaviour of a clay backfill is studied. In the same way, backfill made of excavated crushed salt is considered and thermomechanical properties evaluated by means of laboratory tests and in-situ experiments. Finally, basic works on quality assurance procedures and historic concretes behaviour are reported
Cemented Backfilling Technology of Paste-Like Based on Aeolian Sand and Tailings

Directory of Open Access Journals (Sweden)

Qinli Zhang

2016-12-01

Full Text Available Aeolian sand, tailings, and #32.5 Portland cement were used to produce backfilling aggregate, and physicochemical evaluations and proportioning tests were conducted. It is revealed that a mixture of aeolian sand and tailings can be used as a backfilling aggregate for the complementarities of their physicochemical properties; e.g., high Al2O3 content in the aeolian sand and CaO content in the tailings, coarse particles of aeolian sand and fine particles of tailings, etc. In addition, the optimal backfilling aggregate was shown to have a mass fraction of 72%–74%, a cement–sand ratio of 1:8, and an aeolian sand proportion of 25%. Furthermore, viscometer tests were used to analyze the rheological characteristics, and the slurry in these optimized proportions exhibited shear thinning phenomena with an initial yield stress, which belongs to paste-like—a cemented backfilling slurry with a higher mass fraction than a two-phase flow and better flowability than a paste slurry. Finally, the application of this backfilling technology shows that it can not only realize safe mining, but also bring huge economic benefits, and has some constructive guidance for environmental protection.
Disposal of coal combustion wastes in the hydraulic backfill process

Science.gov (United States)

Pierzyna, Piotr

2017-11-01

This article presents the results of studies regarding the physical properties of selected combustion by-products (CCPs) currently produced in the energy production industry. These properties have been compared with the requirements of the technologies applied in the Polish underground mines. The article gives special consideration to the application of the products in the hydraulic backfill technology. The possibility of using bottom-ashes and slags was considered. The amount of CCPs disposed in Polish hard coal mines is approximately 1.1 million Mg and the tendency is decreasing. In the past two years, approximately 100-150 thousand Mg of CCPs was used in the hydraulic backfill technology. The percentage of the fraction smaller than 0.1 mm is determining for the possibility of using a given type of CCPs in the backfill material. This practically excludes the possibility of using any fly ashes in that technology. In slags from conventional boilers and bottom ashes from fluidized bed boilers the fraction below 0.1 mm constitutes 25% of the total at maximum, which allows for their use in the materials used in hydraulic backfill as a component comprising from 30% to 60%, respectively. Slags (10 01 01) are characterized by the lack of bonding properties, which, in case of open backfill systems that are exposed to atmospheric conditions, constitutes an advantage in comparison to bottom ashes (10 01 24), which in turn definitely exhibit bonding properties. The solution of the problem of using bottom ashes is their supply and application on a current basis.
Research on backfilling and sealing of Rooms and Galleries in a repository in salt

International Nuclear Information System (INIS)

Glaess, F.; Kappei, G.; Schmidt, M.W.; Schwieger, K; Starke, C.; Taubert, E.; Wallmueller, R.; Walter, F.

1992-01-01

The multibarrier concept for the final disposal of radioactive wastes comprises backfilling and sealing of the mine in order to guarantee a safe enclosure of the waste. To provide for these properties, soil mechanical laboratory as well as geotechnical in situ measurements were carried out at the Asse mine. The soil mechanical investigations were performed on salt grit and precompacted backfilling material of different grain-size distribution and clay admixtures. They showed a significant dependence upon permeability and compression velocity of the type and quantity of clay used. A favourable grain-size distribution of the salt results in an acceleration of its compaction ability. Besides the investigation on a laboratory scale, first conclusions were obtained on the long-term in situ behaviour of backfilled chambers and seals and their corresponding geomechanical interaction with the surrounding rock. The geotechnical in situ stress and deformation measurements in an approximately 27.000 m 3 large chamber have so far shown no supporting effect against the surrounding rock four years after backfilling. A compaction of up to 3% of the backfill was registered. In situ measurements as well as laboratory tests on drilling cores from 60 years old backfill showed porosities of approximately 7% and a compaction effect of the backfill from the wall, decreasing towards the centre of the chamber due to the converging rock. 108 figs., 8 refs., 24 tabs
Numerical modelling approach for mine backfill

Indian Academy of Sciences (India)

Muhammad Zaka Emad

2017-07-24

Jul 24, 2017 ... conditions. This paper discusses a numerical modelling strategy for modelling mine backfill material. The .... placed in an ore pass that leads the ore to the ore bin and crusher, from ... 1 year, depending on the mine plan.
Evaluation of low-pH cement degradation in tunnel plugs and bottom plate systems in the frame of SR-Site

International Nuclear Information System (INIS)

Grandia, Fidel; Galindez, Juan-Manuel; Molinero, Jorge; Arcos, David

2010-09-01

Low-pH concrete plugs are going to be used during the backfilling of depositional tunnels of the high-level nuclear waste repository. The stability of these plugs, however, is thought to be affected by water-concrete interaction that may lead to cement degradation and dissolution. Alkaline plumes derived from such a degradation could jeopardize the chemical stability of the clay material in the backfill due to the enhanced dissolution kinetics under high-pH solutions. In this study, the cement durability of concrete plugs to be used in the repository is numerically evaluated by performing reactive transport simulations based on the geochemical degradation of the cement compounds, mainly calcium silicate hydrates (CSH). The implementation of degradation process into the geochemical model is based on a solid solution approach for CSH alteration. The numerical model also takes into account the dependency of transport properties (e.g. molecular diffusion coefficient) with the changes in porosity due to mineral precipitation-dissolution. The simulations predict that the effect of low-pH concrete alteration on the stability of backfill materials would be low. The main process governing geochemistry in the backfill-concrete boundary would be the quick loss of porosity due to ettringite precipitation. The very high molar volume of this mineral enhances the rate of clogging. The ettringite formation is mainly driven by the high sulphate concentration in the backfill porewater, which in turn is controlled by the equilibrium with gypsum in the backfill. The release and diffusion of calcium (from CSH replacement) and Al (from katoite dissolution) from concrete causes ettringite precipitation at the concrete-backfill boundary. The loss of porosity dramatically reduces solute diffusion and, consequently, the backfill-concrete system remains almost invariably for hundreds of years
Evaluation of low-pH cement degradation in tunnel plugs and bottom plate systems in the frame of SR-Site

Energy Technology Data Exchange (ETDEWEB)

Grandia, Fidel; Galindez, Juan-Manuel; Molinero, Jorge; Arcos, David (Amphos XXI Consulting S.L., Barcelona (Spain))

2010-09-15

Low-pH concrete plugs are going to be used during the backfilling of depositional tunnels of the high-level nuclear waste repository. The stability of these plugs, however, is thought to be affected by water-concrete interaction that may lead to cement degradation and dissolution. Alkaline plumes derived from such a degradation could jeopardize the chemical stability of the clay material in the backfill due to the enhanced dissolution kinetics under high-pH solutions. In this study, the cement durability of concrete plugs to be used in the repository is numerically evaluated by performing reactive transport simulations based on the geochemical degradation of the cement compounds, mainly calcium silicate hydrates (CSH). The implementation of degradation process into the geochemical model is based on a solid solution approach for CSH alteration. The numerical model also takes into account the dependency of transport properties (e.g. molecular diffusion coefficient) with the changes in porosity due to mineral precipitation-dissolution. The simulations predict that the effect of low-pH concrete alteration on the stability of backfill materials would be low. The main process governing geochemistry in the backfill-concrete boundary would be the quick loss of porosity due to ettringite precipitation. The very high molar volume of this mineral enhances the rate of clogging. The ettringite formation is mainly driven by the high sulphate concentration in the backfill porewater, which in turn is controlled by the equilibrium with gypsum in the backfill. The release and diffusion of calcium (from CSH replacement) and Al (from katoite dissolution) from concrete causes ettringite precipitation at the concrete-backfill boundary. The loss of porosity dramatically reduces solute diffusion and, consequently, the backfill-concrete system remains almost invariably for hundreds of years
Backfilling behavior of a mixed aggregate based on construction waste and ultrafine tailings.

Science.gov (United States)

Chen, Qiusong; Zhang, Qinli; Xiao, Chongchun; Chen, Xin

2017-01-01

To study the possibility of utilizing mixed construction waste and ultrafine tailings (CW&UT) as a backfilling aggregate that can be placed underground in a mine, physicochemical evaluation, proportioning strength tests, and pumpability experiments were conducted. It was revealed that mixed CW&UT can be used as a backfilling aggregate due to the complementarities of their physicochemical properties. In addition, as the results of the proportioning strength tests show, the compressive strength of a cemented CW&UT backfilling specimen cured for 28 days, with a mass fraction of 72-74%, a cement-sand ratio of 1:12, and a CW proportion of 30%, is higher than 1.0 MPa, which meets the safety requirements and economic consideration of backfilling technology in many underground metal mines, and can also be enhanced with an increase in the cement-sand ratio. The results of the pumpability experiments show that cemented backfilling slurry based on CW&UT can be transported to the stope underground with a common filling pump, with a 16.6 MPa maximum pressure, with the condition that the time of emergency shut-down is less than approximately 20 min. All in all, the research to utilize mixed CW&UT as a backfilling aggregate can not only provide a way to dispose of CW&UT but also will bring large economic benefits and can provide constructive guidance for environmental protection.
THM modelling of buffer, backfill and other system components. Critical processes and scenarios

International Nuclear Information System (INIS)

Aakesson, Mattias; Kristensson, Ola; Boergesson, Lennart; Dueck, Ann; Hernelind, Jan

2010-03-01

A number of critical thermo-hydro-mechanical processes and scenarios for the buffer, tunnel backfill and other filling components in the repository have been identified. These processes and scenarios representing different aspects of the repository evolution have been pinpointed and modelled. In total, 22 cases have been modelled. Most cases have been analysed with finite element (FE) calculations, using primarily the two codes Abaqus and Code B right. For some cases analytical methods have been used either to supplement the FE calculations or due to that the scenario has a character that makes it unsuitable or very difficult to use the FE method. Material models and element models and choice of parameters as well as presumptions have been stated for all modelling cases. In addition, the results have been analysed and conclusions drawn for each case. The uncertainties have also been analysed. Besides the information given for all cases studied, the codes and material models have been described in a separate so called data report
THM modelling of buffer, backfill and other system components. Critical processes and scenarios

Energy Technology Data Exchange (ETDEWEB)

Aakesson, Mattias; Kristensson, Ola; Boergesson, Lennart; Dueck, Ann (Clay Technology AB, Lund (Sweden)); Hernelind, Jan (5T-Engineering AB, Vaesteraas (Sweden))

2010-03-15

A number of critical thermo-hydro-mechanical processes and scenarios for the buffer, tunnel backfill and other filling components in the repository have been identified. These processes and scenarios representing different aspects of the repository evolution have been pinpointed and modelled. In total, 22 cases have been modelled. Most cases have been analysed with finite element (FE) calculations, using primarily the two codes Abaqus and Code-Bright. For some cases analytical methods have been used either to supplement the FE calculations or due to that the scenario has a character that makes it unsuitable or very difficult to use the FE method. Material models and element models and choice of parameters as well as presumptions have been stated for all modelling cases. In addition, the results have been analysed and conclusions drawn for each case. The uncertainties have also been analysed. Besides the information given for all cases studied, the codes and material models have been described in a separate so called data report
Vault-Scale Modelling of pH Buffering Capacity in Crushed Granite Backfills

International Nuclear Information System (INIS)

Benbow, Steven; Savage, David; Robinson, Peter; Watson, Sarah

2004-04-01

Some engineered barrier designs for geological repositories for radioactive wastes rely upon the use of cement as chemical conditioning agents for the wastes. Although the hyper alkaline pore fluids characteristic of cements may have a positive effect upon near-field performance, their migration into the geosphere poses problems regarding potentially deleterious interactions along groundwater flow paths, e.g. change of sorption or matrix diffusion properties of the host rock. To counteract these potential effects, SKB has developed the concept of a gravel backfill for its SFL 3-5 repository, where it is anticipated that the gravel would act as a 'sacrificial' reactive barrier between cement conditioned wastes and the geosphere. This role is dependent upon the reaction of silicate and aluminosilicate minerals in the gravel through hydroxyl ion-catalysed mineral dissolution reactions and the associated precipitation of hydroxyl ion bearing solids, such as calcium silicate hydrates. This barrier concept has been evaluated by the simulation of groundwater flow and chemical reaction of cement pore fluid through a realistic backfill geometry and various potential groundwater flow scenarios. Potential groundwater flow conditions through gravel backfill for the SFL 3-5 repository concept were modelled in 3D using MODFLOW. The regional groundwater flow field was assumed to be horizontal and its interaction with a homogeneous backfill of dimensions in accordance with published designs for the SKB SFL 3-5 repository, with uniform physical and hydraulic properties was investigated. The host rock also had uniform properties, except where simulations explicitly represented transmissive features. Calculations of cement pore fluid migration and reaction with backfill were carried out using Raiden2, a fully-coupled reaction-transport simulator. Flow fields generated in 3D with MODFLOW were converted to 2D 'slices' for reaction-transport calculations. The backfill was assumed to
Evaluation of engineering aspects of backfill placement for high level nuclear waste (HLW) deep geologic repositories

International Nuclear Information System (INIS)

Roberds, W.; Kleppe, J.; Gonano, L.

1984-04-01

This report includes the identification and subjective evaluation of alternative schemes for backfilling around waste packages and within emplacement rooms. The aspects of backfilling specifically considered in this study include construction and testing; costs have not been considered. However, because construction and testing are simply implementation and verification of design, a design basis for backfill is required. A generic basis has been developed for this study by first identifying qualitative performance objectives for backfill and then weighting each with respect to its potential influence on achieving the repository system performance objectives. Alternative backfill materials and additives have been identified and evaluated with respect to the perceived extent to which each combination can be expected to achieve the backfill design basis. Several distinctly different combinations of materials and additives which are perceived to have the highest potential for achieving the backfill design basis have been selected for further study. These combinations include zeolite/clinoptilolite, bentonite, muck, and muck mixed with bentonite. Feasible alternative construction and testing procedures for each selected combination have been discussed. Recommendations have been made regarding appropriate backfill schemes for hard rock (i.e., basalt at Hanford, Washington, tuff at Nevada Test Site, and generic granite) and salt (i.e., domal salt on the Gulf Coast and generic bedded salt). 27 references, 8 figures, 31 tables
New Knowledge of tunneling from photonic experiments

International Nuclear Information System (INIS)

Nimtz, G.

1997-01-01

Photonic experiments have shown, that the propagation of evanescent (tunneling) modes can proceed at speeds faster than the velocity of light in vacuum (superluminal). The superluminal velocities include signal and energy propagation. The analogy between the classical Helmholtz equation and the quantum mechanical Schroedinger equation was quantitatively proved in classical photonic experiments. The Hartman effect, i.e. the prediction that the tunneling time is independent of the barrier length was for the first time evidenced in a photonic analogous tunneling experiment by Enders and Nimtz. It is also shown, that the resonant state life time is not determined by the barrier traversal time. For electronic tunneling devices it follows, that the quantum mechanical phase time calculations indeed deliver the relevant intrinsic tunneling time and consequently allow to predict the dynamical specification of a device. The present theoretical descriptions of the propagation of evanescent modes is not fully compatible with the experimental situation. Superluminal signal and energy transport has been measured, and this has to be properly analyzed. May the advanced field solutions help to obtain a satisfactory theoretical description of the recent experimental results of the propagation of evanescent modes? (author)
Evaluating the methodology and performance of jetting and flooding of granular backfill materials.

Science.gov (United States)

2014-11-01

Compaction of backfill in confined spaces on highway projects is often performed with small vibratory plates, based : solely on the experience of the contractor, leading to inadequate compaction. As a result, the backfill is prone to : erosion and of...
Uniaxial backfill block compaction

International Nuclear Information System (INIS)

Koskinen, V.

2012-05-01

The main parts of the project were: to make a literature survey of the previous uniaxial compaction experiments; do uniaxial compaction tests in laboratory scale; and do industrial scale production tests. Object of the project was to sort out the different factors affecting the quality assurance chain of the backfill block uniaxial production and solve a material sticking to mould problem which appeared during manufacturing the blocks of bentonite and cruched rock mixture. The effect of mineralogical and chemical composition on the long term functionality of the backfill was excluded from the project. However, the used smectite-rich clays have been tested for mineralogical consistency. These tests were done in B and Tech OY according their SOPs. The objective of the Laboratory scale tests was to find right material- and compaction parameters for the industrial scale tests. Direct comparison between the laboratory scale tests and industrial scale tests is not possible because the mould geometry and compaction speed has a big influence for the compaction process. For this reason the selected material parameters were also affected by the previous compaction experiments. The industrial scale tests were done in summer of 2010 in southern Sweden. Blocks were done with uniaxial compaction. A 40 tons of the mixture of bentonite and crushed rock blocks and almost 50 tons of Friedland-clay blocks were compacted. (orig.)
Investigations on backfilling and sealing of chambers and shafts in a final salt repository

International Nuclear Information System (INIS)

Glaess, F.; Kappei, G.; Schmidt, M.W.; Schwieger, K.; Starke, C.; Taubert, E.; Wallmueller, R.; Walter, F.; Tischle, N.R.; Haensel, W.; Meyer, T.

1991-03-01

Soil mechanical laboratory investigations as well as geotechnical in situ measurements were carried out. The laboratory tests provided important information on the material behaviour of selected backfill and sealing materials. Initial conclusions on the long-term behaviour of backfill and seals as well as on their interaction with the rock were gained with the results of in situ measurements in backfilled chambers and seals and in the surrounding rock of the Asse salt mine. (orig./DG) [de

The backfilling and sealing of radioactive waste repositories. V. 2. Figure - Tables - Appendices

International Nuclear Information System (INIS)

1984-01-01

The two volumes of this report present a review study about backfilling and sealing of radioactive waste repositories in granites, argillaceous and salt formations. Volume 2 contains all the figures, table and appendices A detailed account of candidate backfill materials is given in a standardized format
Transport of soluble species in backfill and rock

International Nuclear Information System (INIS)

Chambre, P.L.; Lee, W.W.L.; Light, W.B.; Pigford, T.H.

1992-03-01

In this report we study the release and transport of soluble species from spent nuclear fuel. By soluble species we mean a fraction of certain fission product species. Our previously developed methods for calculating release rates of solubility-limited species need to be revised for these soluble species. Here we provide methods of calculating release rates of soluble species directly into rock and into backfill and then into rock. Section 2 gives a brief discussion of the physics of fission products dissolution from U0 2 spent fuel. Section 3 presents the mathematics for calculating release rates of soluble species into backfill and then into rock. The calculation of release rates directly into rock is a special case. Section 4 presents numerical illustrations of the analytic results
Backfill barriers for nuclear waste repositories in salt

Energy Technology Data Exchange (ETDEWEB)

Nowak, E J; Odoj, R; Merz, E [eds.

1981-06-01

Backfill materials were evaluated for containment of radionuclides, chemical modification of brine, and sensitivity to hydrothermal conditions. Experimental conditions were relevant to nuclear waste isolation in bedded salt. They were based on geologic conditions at the site of the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico, USA. Conclusions are: backfill mixtures surrounding the waste form and canister can provide a neutral or slightly acidic, potentially reducing environment, prevent convective aqueous flow, and act as an effective radionuclide migration barrier; bentonite is likely to remain hydrothermally stable but potentially sensitive to waste package interactions which could alter the pH, the ratio of dissolved ions, or the sorption properties of radionuclide species; effects of irradiation from high level waste should be investigated.
Colloids in the mortar backfill of a cementitious repository for radioactive waste

International Nuclear Information System (INIS)

Wieland, E.; Spieler, P.

1999-01-01

Colloids are present in groundwater aquifers and water-permeable engineered barrier systems and may facilitate the migration of radionuclides. A careful evaluation of colloid concentrations is required to assess the potential effect of colloids on nuclide migration and, consequently, on the safety of a repository for radioactive waste. A highly permeable mortar is foreseen to be used as backfill for the engineered barrier of the Swiss repository for low- and intermediate-level waste (L/ILW). The backfill is considered to be a chemical environment with a potential for colloid generation and, due to its high porosity, for colloid mobility. In this contribution a novel in-house built particle counting device is described, and measurements of colloid concentrations in the pore water of backfill mortar are presented. (author)
Influence of regional support systems (pillars and backfill) on local areas and internal support requirements adjacent to that regional support.

CSIR Research Space (South Africa)

Squelch, AP

2001-11-01

Full Text Available was observed of backfill creating worse hangingwall conditions; instead it was observed that poor backfill placement was associated with the less favourable hangingwall conditions. • Generally, well placed backfill improves conditions in face areas... if it is kept close to the face and conventionally designed working area support that fits in well with the backfilling/mining cycle is implemented. Conversely, quality is not assured if backfill is not well placed. Also large fill-to-face distances...
DEM Analysis of Backfilled Walls Subjected to Active Translation Mode

Directory of Open Access Journals (Sweden)

Mohammad Hossein Khosravi

2017-12-01

Full Text Available In this paper, the problem of a retaining wall under active translation mode is investigated numerically. To this end, a series of numerical models is conducted using the discrete element code, PFC2D. The backfill soil is simulated by an assembly of separate cohesionless circular particles. Backfill soil was prepared by pouring soil particles from a specific height under gravity force and giving them enough time for appropriate settlement. Different heights of retaining walls are simulated and the lateral earth pressure on the wall is observed under both at-rest and active conditions. Numerical results compared with predictions from some analytical methods and measurements from physical models. The active state of earth pressure is defined as the earth pressure distribution corresponding to the values of wall displacement where the failure zone in the backfill is fully developed. The numerical results showed that the fully active state of earth pressure occurred at a wall displacement corresponding to the strains required for reaching the critical state in biaxial compressive tests.
Preliminary on-surface experiments for backfilling a HLW repository: the ESDRED project

International Nuclear Information System (INIS)

Bastiaens, W.

2007-01-01

ESDRED is a technological integrated project within the context of the Sixth Framework Program of EURATOM. The project aims to demonstrate the technical feasibility at an industrial scale of specific technologies related to the construction, operation and closure of a deep geological repository for spent fuel and long-lived radioactive waste. The Belgian design for high level waste disposal is based on the so-called Supercontainer concept. Within this concept, the waste is encased in a carbon steel overpack, which is consequently fitted into a 70 cm thick concrete shell, in its turn enveloped by a stainless steel liner. A Supercontainer measures about 2 m in diameter. In the design of the repository, the Supercontainers will be emplaced, one after the other, in disposal galleries. The space between the Supercontainers and the gallery lining needs to be filled up with a solid material. The most essential function of this component, referred to as backfill, is to prevent a collapse of the gallery. A secondary function is to limit the presence of free oxygen, to limit corrosion. In the ESDRED project EIG EURIDICE, together with SCK-CEN and ONDRAF/NIRAS, investigates technologies to apply the backfill. Two options to apply the backfill were investigated within the ESDRED project: fill the gap with a granular material and backfill the gap with a grout. The prime operational target will be to achieve a 100 percent filling of the gap. A wide variety of materials was tested. A number of considerations regarding long-term safety and operational feasibility impose constraints on the backfill component:it should preserve the corrosion-protective environment established by the Supercontainer; it should not act as a thermal isolator; it should not introduce organic materials that can give rise to the formation of migration-enhancing complexes between radionuclides and soluble organic compounds; it should be feasible to construct at a sufficiently high rate; the strength of the
Field and laboratory investigations on pavement backfilling material for micro-trenching in cold regions

Directory of Open Access Journals (Sweden)

Leila Hashemian

2017-07-01

Full Text Available Micro-trenching is an innovative utility installation method that involves creating a narrow trench to place cable or conduit in the road pavement. Compared to other installation methods, micro-trenching provides minimal disturbance to the community and surrounding environment. Despite the advantages of micro-trenching, it is not widely accepted by municipalities because of its potential to damage the existing pavement. Quality of backfilling is an important factor in long-term sustainability of the micro-trench, particularly in cold regions. This paper investigates the performance of two typical micro-trench backfilling methods in cold climates by studying a pilot project in a parking lot in Edmonton, Alberta, followed by a laboratory evaluation of the material used. For this purpose, the installations were monitored through ground-penetrating radar, optical time-domain reflectometer, and visual observations for three years. The monitoring results revealed that conduit had significant vertical movement inside the trench; several premature failures were also observed in the backfilling material. Laboratory investigation showed that the backfilling material did not meet the criteria for use in cold climates, and micro-trench performance could be enhanced using alternative materials. Keywords: Micro-trench, Pavement backfilling material, Fiber optic installation, Ground-penetrating radar
Federal Republic of Germany/backfilling and sealing program - outline

International Nuclear Information System (INIS)

Kappei, G.

1986-01-01

After 1978 the Asse salt mine was used exclusively for research work which serves to make available scientific and technical data for the planning, construction and operation of repositories for radioactive wastes. This presentation delineates the advantages of the geological formation rock salt with a view to the final disposal of radioactive wastes subsequent to a short description of the 'Waste Management Concept' of the Federal Republic of Germany. The individual components of the internationally accepted 'Multiple Barrier System' are described, while the technical barriers 'backfilling and sealing' are subject of special consideration. A general formulation of the requirements and objectives of each specific component in the backfilling and sealing system is presented. (orig./DG)
Simulation of water recovery and its effect on settlement of open-cut coal mine back-fill

International Nuclear Information System (INIS)

Naderian, A.R.; Williams, D.J.

1996-01-01

Open-cut coal mine back-fill usually undergoes significant settlement due to inundation by surface water infiltration and groundwater rise. The rate and magnitude of inundation settlement is difficult to predict and quantify due to the large number of contributing factors. Consequently, none of the available settlement models and theories has been able to successfully describe the inundation settlement occurring in back-filled open-cut coal mines. A combination of laboratory and numerical simulation of settlement is a valuable means of estimating the inundation settlement of back-fill. The settlements predicted by this simulation are in good agreement with previous observations of inundation settlement in open-cut coal mine back-fill. 11 refs., 14 figs., 1 tab
Performance Comparison between Neutralization Tailings and Flotation Tailings Used for Backfill Mix and Mechanism Analysis

OpenAIRE

Han, Bin; Sun, Wei; Yu, Shaofeng; Liu, Chao; Yao, Song; Wu, Jianxun

2016-01-01

A comparison test of different tailings used for underground backfill was conducted, using neutralized tailings from BIOX and flotation tailings of Jinfeng Mine. Laboratory comparison test results show that, with neutralized tailings, when the cement dosage is at 19%, backfill UCS after 7 days, 14 days, and 28 days are 105%–163%, 80%–102%, and 33%–43%, respectively, which are higher than those of flotation tailings. When the cement dosage is at 12%, backfill UCS after 7 days, 14 days, and 28 ...
The advantages of a salt/bentonite backfill for Waste Isolation Pilot Plant disposal rooms

International Nuclear Information System (INIS)

Butcher, B.M.; Novak, C.F.; Jercinovic, M.

1991-04-01

A 70/30 wt% salt/bentonite mixture is shown to be preferable to pure crushed salt as backfill for disposal rooms in the Waste Isolation Pilot Plant (WIPP). This report discusses several selection criteria used to arrive at this conclusion: the need for low permeability and porosity after closure, chemical stability with the surroundings, adequate strength to avoid shear erosion from human intrusion, ease of emplacement, and sorption potential for brine and radionuclides. Both salt and salt/bentonite are expected to consolidate to a final state of impermeability (i.e., ≤ 10 -18 m 2 ) adequate for satisfying federal nuclear regulations. Any advantage of the salt/bentonite mixture is dependent upon bentonite's potential for sorbing brine and radionuclides. Estimates suggest that bentonite's sorption potential for water in brine is much less than for pure water. While no credit is presently taken for brine sorption in salt/bentonite backfill, the possibility that some amount of inflowing brine would be chemically bound is considered likely. Bentonite may also sorb much of the plutonium, americium, and neptunium within the disposal room inventory. Sorption would be effective only if a major portion of the backfill is in contact with radioactive brine. Brine flow from the waste out through highly localized channels in the backfill would negate sorption effectiveness. Although the sorption potentials of bentonite for both brine and radionuclides are not ideal, they are distinctly beneficial. Furthermore, no detrimental aspects of adding bentonite to the salt as a backfill have been identified. These two observations are the major reasons for selecting salt/bentonite as a backfill within the WIPP. 39 refs., 16 figs., 6 tabs
Comments on US approach to backfilling: Thermochemical characterization of crushed salt

International Nuclear Information System (INIS)

Smith, S.; Hume, H.

1988-01-01

From recent studies and calculations, it has become apparent that expected brine in a United States salt repository would not seriously detract from the usefulness of rock salt as backfill. It also has been shown that adding clay to the salt might add to the pressure on the emplaced waste packages. Nevertheless, the Salt Repository Project has planned to evaluate a betonite/salt mixture during the next few years. The following items have also been discussed: advantages of backfilling, variables affecting crushed salt behavior, and the general approach to a preliminary testing program
Investigating industrial investigation: examining the impact of a priori knowledge and tunnel vision education.

Science.gov (United States)

Maclean, Carla L; Brimacombe, C A Elizabeth; Lindsay, D Stephen

2013-12-01

The current study addressed tunnel vision in industrial incident investigation by experimentally testing how a priori information and a human bias (generated via the fundamental attribution error or correspondence bias) affected participants' investigative behavior as well as the effectiveness of a debiasing intervention. Undergraduates and professional investigators engaged in a simulated industrial investigation exercise. We found that participants' judgments were biased by knowledge about the safety history of either a worker or piece of equipment and that a human bias was evident in participants' decision making. However, bias was successfully reduced with "tunnel vision education." Professional investigators demonstrated a greater sophistication in their investigative decision making compared to undergraduates. The similarities and differences between these two populations are discussed. (c) 2013 APA, all rights reserved
Characterisation of bentonites from Kutch, India and Milos, Greece - some candidate tunnel back-fill materials?

International Nuclear Information System (INIS)

Olsson, Siv; Karnland, Ola

2009-12-01

During the past decades comprehensive investigations have been made on bentonite clays in order to find optimal components of the multi-barrier system of repositories for radioactive waste. The present study gives a mineralogical characterisation of some selected bentonites, in order to supply some of the necessary background data on the bentonites for evaluating their potential as tunnel back-fill materials. Two bentonites from the island of Milos, Greece (Milos BF 04 and BF 08), and two bentonites from Kutch, India (Kutch BF 04 and BF 08) were analysed for their grain size distribution, cation exchange properties and chemical composition. The mineralogical composition was determined by X-ray diffraction analysis and evaluated quantitatively by use of the Siroquant software. Both the bulk bentonite and the 63 μm. The bentonite is distinguished by a high content of dolomite and calcite, which make up almost 25% of the bulk sample. The major accessory minerals are K-feldspars and plagioclase, whereas the content of sulphur-bearing minerals is very low (0.06% total S). Smectite makes up around 60% of the bulk sample, which has a CEC value of 73 meq/100 g. The pool of interlayer cations has a composition Mg>Ca>>Na>>K. The X-ray diffraction characteristics and the high potassium content (1.03% K 2 O) of the Na>Mg>>K. The 2 O) which indicates that also this smectite may be interstratified with a few percent illitic layers. Based on the charge distribution the smectite should be classified as montmorillonite but in this case Fe predominates over Mg in the octahedral sheet. The structural formula suggests that this smectite has the lowest total layer charge of the smectites examined. Kutch BF 04 contains essentially no particles >63 μm. The bentonite has a high content of titanium and iron-rich accessory minerals, such as anatase, magnetite, hematite and goethite. Other accessory minerals of significance are feldspars and quartz, whereas the content of sulphur
The backfilling and sealing of radioactive waste repositories. V. 1. Text - Reference - List of symbols

International Nuclear Information System (INIS)

1984-01-01

The report is in two volumes: Volume 1 contains the main text, the references and a list of symbols, and Volume 2, all the figues, tables and appendices. In Volume 1, backfilling and sealing is considered in relation to the geological, physical and chemical environments. There follows a detailed evaluation of the role and performance of the backfilling and sealing system in terms of thermal, hydraulic, chemical buffering, radionuclide retention, mechanical properties and behaviour as well as longevity. The results of the listing, screening and classification of a comprehensive range of candidate backfill materials are summarized. The different candidate materials are examined
Mill tailings based composites as paste backfill in mines of U-bearing dolomitic limestone ore

Directory of Open Access Journals (Sweden)

Sandeep Panchal

2018-04-01

Full Text Available This paper elaborates on the development of paste backfill using mill tailings generated during the processing of a uranium ore deposit hosted in dolomitic limestone. The tailings have been characterized in terms of the physical, chemical and mineralogical properties. Time-dependent rheological behaviors and geotechnical properties of cemented paste backfill (CPB are also determined. The studies show that the mill tailing has the potential to form paste and the CPB has adequate strength to provide support to mine pillars, roofs, and walls. Keywords: Mining engineering, Uranium ore deposit, Tailings, Cemented paste backfill (CPB, Rheology, Compressive strength
Underground Cemented Backfill, a Design Procedure for an Integrated Mining Waste Management.

Directory of Open Access Journals (Sweden)

Abdelhadi KHALDOUN

2018-01-01

Full Text Available From several case studies around the world, it is well known that the binder represents the major part of backfilling operation cost. Therefore, in the case of Imiter operation, research were mainly focused on the optimization of binder content. To this end, the definition of the physical and chemical properties of the future formula ingredients, specifically: tailings, waste material and hydraulic binder, was necessary. Analytical verifications were conducted to predict the UCB mechanical strength according to the defined underground functions and delivery network. Experimental testing, including: uniaxial compression, Immediate Bearing Index (IBI and slump test, were then conducted to evaluate the possibility of reaching the required strength with the selected materials. The obtained results show that the tailings and mining wastes can be used as backfilling material with a specific binder content depending on each underground application. The followed approach can be applied for a prefeasibility evaluation for a backfilling facility.
Performance Comparison between Neutralization Tailings and Flotation Tailings Used for Backfill Mix and Mechanism Analysis

Directory of Open Access Journals (Sweden)

Bin Han

2016-01-01

Full Text Available A comparison test of different tailings used for underground backfill was conducted, using neutralized tailings from BIOX and flotation tailings of Jinfeng Mine. Laboratory comparison test results show that, with neutralized tailings, when the cement dosage is at 19%, backfill UCS after 7 days, 14 days, and 28 days are 105%–163%, 80%–102%, and 33%–43%, respectively, which are higher than those of flotation tailings. When the cement dosage is at 12%, backfill UCS after 7 days, 14 days, and 28 days are 58%–77%, 50%–60%, and 28%–51%, respectively, which are higher than those of flotation tailings. Slurry fluidity of neutralized tailings is lower than that of flotation tailings, while, in these two tailings, the difference of slump and diffusivity values is less than 6%, which is not a significant difference in slurry fluidity. The reason for neutralized tailings showing higher UCS is as follows: during backfill curing, neutralization tailings produce abundant crystals of CaSO4·2H2O in interlaced structure which helps in combining aggregates closely; CaSO4·2H2O hydrates with C3A C4AF contained in the cement and forms clavate cement bacillus which works as a micro reinforcing steel bar. The test proved that neutralized tailings are more optimal for backfilling.
Prediction of unsaturated flow and water backfill during infiltration in layered soils

Science.gov (United States)

Cui, Guotao; Zhu, Jianting

2018-02-01

We develop a new analytical infiltration model to determine water flow dynamics around layer interfaces during infiltration process in layered soils. The model mainly involves the analytical solutions to quadratic equations to determine the flux rates around the interfaces. Active water content profile behind the wetting front is developed based on the solution of steady state flow to dynamically update active parameters in sharp wetting front infiltration equations and to predict unsaturated flow in coarse layers before the front reaches an impeding fine layer. The effect of water backfill to saturate the coarse layers after the wetting front encounters the impeding fine layer is analytically expressed based on the active water content profiles. Comparison to the numerical solutions of the Richards equation shows that the new model can well capture water dynamics in relation to the arrangement of soil layers. The steady state active water content profile can be used to predict the saturation state of all layers when the wetting front first passes through these layers during the unsteady infiltration process. Water backfill effect may occur when the unsaturated wetting front encounters a fine layer underlying a coarse layer. Sensitivity analysis shows that saturated hydraulic conductivity is the parameter dictating the occurrence of unsaturated flow and water backfill and can be used to represent the coarseness of soil layers. Water backfill effect occurs in coarse layers between upper and lower fine layers when the lower layer is not significantly coarser than the upper layer.

Geotechnical investigations on backfill materials in the Asse salt mine

International Nuclear Information System (INIS)

Kappei, G.

1986-01-01

The compression behaviour of rock salt grit is being investigated by compression tests at the Asse salt mine. The various test parameters are introduced and their results are discussed. The permeability of rock salt grit with saturated NaCl-brine in dependency upon the grain size and compactness, resp. the porosity, is being determined at the Asse salt mine. The test equipment and the results determined here are shown. In addition to laboratory tests, geotechnical investigations are taking place in a carnallitic chamber of the Asse salt mine which had been backfilled in earlier years. They chiefly concern measurements of the deformation rates in drifts - which were mined between the chambers in remaining pillars - as well as horizontal deformation measurements in the backfilling. (orig./DG)
Stress Ratios in Entire Mine Stopes with Cohesionless Backfill: A Numerical Study

Directory of Open Access Journals (Sweden)

Pengyu Yang

2017-10-01

Full Text Available Evaluation of stress states in backfilled mine stopes (or similar openings, using arching theory, can be largely impacted by the value selected for the earth pressure coefficient, K = σ′h/σ′v. Recently, the current study’s authors addressed the debate about the value of K near the opening center, based on Rankine’s active coefficient (Ka and at-rest coefficient (K0. Here, stress ratios in vertical backfilled stopes are numerically assessed (in two dimension, 2D, considering both the independent and related backfill internal friction angle (ϕ′ and Poisson’s ratio (ν. Emphasis is placed on the backfill state near stope walls, where local rotation of stresses occurs, so the coefficient (K and principal stress ratio, Kps (= σ′3/σ′1, should be distinguished. Parametric analyses indicate that values of K and Kps depend on the position and the relationship between ϕ′ and ν. Near the opening center, K (= Kps is close to Ka when ν or ϕ′ is below a critical value; otherwise the value approaches K0, defined from ν. Near both walls, Kps is always close to Ka, while K is near K0 for related ν − ϕ′ cases and depends on their respective values for independent ν and ϕ′. Additional simulations conducted with interface elements indicate that the stress ratios near the opening center line are insensitive to interface roughness and are almost identical to values obtained without interfaces, but the stress ratios near walls may change for less rough or smooth interfaces.
Backfilling of a Scour Hole around a Pile in Waves and Current

DEFF Research Database (Denmark)

Sumer, B. Mutlu; Petersen, Thor Ugelvig; Locatelli, Luca

2013-01-01

This paper presents the results of an experimental investigation of the backfilling of scour holes around circular piles. Scour holes around a pile are generated either by a current or a wave. Subsequently, the flow climate is changed from current to wave, combined waves and current, or wave...... around the pile for the same wave (or combined waves and current) climate. The time scale of backfilling has been determined as a function of three parameters, namely, (1) the Keulegan-Carpenter number of the initial wave or current (which generates the initial scour hole); (2) that of the subsequent...
Humidity dependence of molecular tunnel junctions with an AlOx/COOH- interface

Science.gov (United States)

Zhang, Xiaohang; McGill, Stephen; Xiong, Peng

2006-03-01

We have studied the electron transport in planar tunneling junctions with aluminum oxide and an organic self-assembled monolayer (SAM) as the tunnel barrier. The structure of the junctions is Al/AlOx/SAM/(Au, Pb) with a junction area of ˜ 0.4mm^2. The organic molecules investigated include mercaptohexadecanoic acid (MHA), hexadecanoic acid (HDA), and octadecyltrichlorosilane (OTS); all of which form ordered SAMs on top of aluminum oxide. The use of a superconducting electrode (Al) enables us to determine unambiguously that these are high-quality tunnel junctions. For junctions incorporating MHA, the transport behavior is found to be strongly humidity dependent. The resistance of these junctions drops more than 50% when placed in dry nitrogen and recovers when returned into the ambient. The same drop also occurs when the sample is placed into a vacuum, and backfilling the vacuum with either dry N2 or O2 has negligible effect on the resistance. For comparison, junctions with HDA show the same humidity dependence, while OTS samples do not. Since both MHA and HDA have carboxylic groups and OTS does not, the results suggest that water molecules at the AlOx/COOH- interface play the central role in the observed behavior. Inelastic tunneling spectroscopy (IETS) has also been performed to understand the role of water. This work was supported by a FSU Research Foundation PEG grant.
Numerical calculation of backfilling of scour holes

DEFF Research Database (Denmark)

Sumer, B. Mutlu; Baykal, Cüneyt; Fuhrman, David R.

2014-01-01

A fully-coupled hydrodynamic and morphologic CFD model is presented for simulating backfilling processes around structures. The hydrodynamic model is based on Reynolds-averaged Navier-Stokes equations, coupled with two-equation k-ω turbulence closure. The sediment transport model consists of sepa...... of structures: piles, and pipelines. Initial scour holes are generated by the same model. The numerical results appear to be in accord with the existing experimental information....
The chemistry of blended cements and backfills intended for use in radioactive waste disposal

International Nuclear Information System (INIS)

Glasser, F.; Tyrer, M.; Quillin, K.

1999-01-01

This project was initiated by Her Majesty's Inspectorate of Pollution (HMIP) at the time when UK NIREX had announced its intention to develop a repository for low and intermediate level nuclear waste in the vicinity of Sellafield. In this repository setting, two main barriers existed to the return of radio-isotopes to the biosphere: the natural, or geologic and hydrogeologic barriers, and the man-made barriers. These latter comprise relatively short-lived containers as well as an engineered backfill. The backfill was designed to condition a high pH in the repository, thereby lowering the solubility of many long-lived radionuclides yet not confine gases, which might be generated from chemical and radioactive waste within the repository vault. The Environment Agency for England and Wales had already taken independent steps to examine the suitability of alkaline backfills, based on Portland cement, limestone flour and Ca(OH) 2 , for the man-made barriers. Preliminary data on post-closure repository performance assessment at Sellafield suggested the importance of two additional factors which had not hitherto been considered in assessments: (i) temperature: Inclusion of heat generating waste could drive temperatures up to ∼80 deg. C in the post closure phase; (ii) salinity of deep groundwater: Much previous work has been done in initially-pure water but borehole analyses indicated high salinity at depth. Other potential deep repositories could also be saline. These impacts were likely to occur together throughout much of the post-closure phase: backfills were likely to be in prolonged contact with hot, saline groundwater. Previous studies demonstrated that cements achieve their performance by a sacrificial action. It is however essential that the cementitious materials should not dissolve too rapidly if prolonged backfill performance lifetimes are to be achieved. By dissolving cement backfills condition permeating water to a high pH and thereby lower the solubilities
The tunnel sealing experiment: The construction and performance of full scale clay and concrete bulkheads at elevated pressure and temperature

International Nuclear Information System (INIS)

Martino, J.B.; Dixon, D.A.; Vignal, B.; Fujita, T.

2006-01-01

Concepts for deep geologic disposal of radioactive waste, as proposed by many international organizations, include bulkheads or plugs in the shaft, or at the entrances to disposal rooms, or both. The seals are primarily to prevent groundwater transport of radioisotopes along underground openings but also provide a measure of security by restricting tunnel access. The safety of the respective disposal systems relies on the combined performance of the natural barriers (host rock) and engineered barriers (the waste form, the waste container, the buffer barrier, the room, tunnel and shaft backfill and sealing materials). To understand the functionality of these systems it is important to study them in whole or in part at full scale. One such study was the Tunnel Sealing Experiment (TSX), a full-scale tunnel seal component study. The TSX showed it is possible to construct tunnel seals that limit axial flow under high hydraulic gradient and elevated temperature. The clay and concrete bulkheads had seepage rates of 1 mL/min and 10 mL/min at ambient temperature. Elevated temperatures caused a further decrease in seepage past the concrete bulkhead to approximately 2-3 mL/min. (author)
Paste backfill of shallow mine workings for land reclamation in Canmore, Alberta

International Nuclear Information System (INIS)

Predika, R.; Beattie, A.; Beddoes, R.

2008-01-01

The coal mining history in Canmore, Alberta was presented along with reclamation activities that mine regulators carried out following closure of the mines after nearly 100 years of underground mining. The 7 seams that were mined commercially extend over distances of a few hundred feet and have been displaced by faults. Voids and collapsed rubble in shallow underground workings pose a risk of potential ground subsidence that can affect the stability of surface structures and infrastructure, including the planned development of the proposed Three Sisters Mountain Village on land above the abandoned mines. The village includes plans for 10,000 residential homes, 2 golf courses, and a resource centre. A mine works mitigation program involved drilling primary injection boreholes on a 15 m grid pattern to map the constraint zones in order to gain a better perspective of the subsidence issues as well as the effects of subsidence on structural stress and public safety. When determining mitigation criteria, various land uses and ranges of subsidence hazards were considered to be compatible with each land use. A paste backfill composed of aggregate from a locally available till overburden site was mixed with cement and injected into the void spaces. This paper described the cemented paste backfill injection method; confirmatory methods; maximum volume and pressure criteria; survey for ground uplift; and borehole camera and manual checks for cemented paste backfill in adjacent boreholes. Quality control testing was carried out by means of slump tests. It was concluded that cemented paste backfill mix could be used successfully to stabilize abandoned mine workings for land recovery. 8 refs., 5 tabs., 7 figs
Tests for evaluation of pellets as foundation bed material KBP1003 - ASKAR

International Nuclear Information System (INIS)

Johnsson, Anna

2011-12-01

The reference design for the backfill of deposition tunnels, described in SKB (2010), include bentonite blocks, bentonite pellets and a foundation bed of bentonite pellets or granulate. The tunnel floor needs to be flat and have sufficient bearing capacity to make it possible to stack the backfill blocks according to the reference design. To achieve a flat foundation the tunnel floor will be covered with a bed of pellets or granulate made of bentonite clay. The bed can be either compacted or non compacted. Bed tests have been performed as a part of the project KBP1003 DP1 Design, which is a subproject of KBP1003 ASKAR. The main objectives for KBP1003 DP1 is to define all requirements for the backfill and its production and installation prior to start of the large scale tests, based on given perquisites. KBP1003 is based on the reference design for the backfill of deposition tunnels which was developed in 2010 (SKB 2010). The concept for installation and block design has been further developed during the project. A new dimension of the backfill blocks has been developed; the chosen dimension makes it possible to gain overlapping joints between the blocks by block stacking. The further developed concept is hereinafter referred to as the ASKAR-concept. The purpose of the performed bed tests was to define the bed requirements in the backfill installation to enable stable stacking of backfill blocks. The tests included stacking of blocks on different bed materials, on blasted and wire sawn floor, with and without concurrent water inflow. The bed tests was subdivided into four main parts: - block stacking on different bed compositions - block stacking on bed during water inflow - block stacking in a realistic test tunnel - block stacking on the upper part of the deposition hole and bevel
Tests for evaluation of pellets as foundation bed material KBP1003 - ASKAR

Energy Technology Data Exchange (ETDEWEB)

Johnsson, Anna (ES-Konsult AB (Sweden))

2011-12-15

The reference design for the backfill of deposition tunnels, described in SKB (2010), include bentonite blocks, bentonite pellets and a foundation bed of bentonite pellets or granulate. The tunnel floor needs to be flat and have sufficient bearing capacity to make it possible to stack the backfill blocks according to the reference design. To achieve a flat foundation the tunnel floor will be covered with a bed of pellets or granulate made of bentonite clay. The bed can be either compacted or non compacted. Bed tests have been performed as a part of the project KBP1003 DP1 Design, which is a subproject of KBP1003 ASKAR. The main objectives for KBP1003 DP1 is to define all requirements for the backfill and its production and installation prior to start of the large scale tests, based on given perquisites. KBP1003 is based on the reference design for the backfill of deposition tunnels which was developed in 2010 (SKB 2010). The concept for installation and block design has been further developed during the project. A new dimension of the backfill blocks has been developed; the chosen dimension makes it possible to gain overlapping joints between the blocks by block stacking. The further developed concept is hereinafter referred to as the ASKAR-concept. The purpose of the performed bed tests was to define the bed requirements in the backfill installation to enable stable stacking of backfill blocks. The tests included stacking of blocks on different bed materials, on blasted and wire sawn floor, with and without concurrent water inflow. The bed tests was subdivided into four main parts: - block stacking on different bed compositions - block stacking on bed during water inflow - block stacking in a realistic test tunnel - block stacking on the upper part of the deposition hole and bevel
Maximum support resistance with steel arch backfilling

Energy Technology Data Exchange (ETDEWEB)

1983-01-01

A system of backfilling for roadway arch supports to replace timber and debris lagging is described. Produced in West Germany, it is known as the Bullflex system and consists of 23 cm diameter woven textile tubing which is inflated with a pumpable hydraulically-setting filler of the type normally used in mines. The tube is placed between the back of the support units and the rock face and creates an early-stage interlocking effect.
An Investigation of the Uniaxial Compressive Strength of a Cemented Hydraulic Backfill Made of Alluvial Sand

Directory of Open Access Journals (Sweden)

Guangsheng Liu

2017-01-01

Full Text Available Backfill is commonly used in underground mines. The quality control of the backfill is a key step to ensure it meets the designed strength requirement. This is done through sample collection from the underground environment, followed by uniaxial compression tests to obtain the Uniaxial Compressive Strength (UCS in the laboratory. When the cylindrical cemented backfill samples are axially loaded to failure, several failure modes can be observed and mainly classified into diagonal shear failure and axial split failure. To date, the UCS obtained by these two failure modes are considered to be the same with no distinction between them. In this paper, an analysis of the UCS results obtained on a cemented hydraulic backfill made of alluvial sand at a Canadian underground mine over the course of more than three years is presented. The results show that the UCS values obtained by diagonal shear failure are generally higher than those obtained by axial split failure for samples with the same recipe and curing time. This highlights the importance of making a distinction between the UCS values obtained by the two different modes of failure. Their difference in failure mechanism is explained. Further investigations on the sources of the data dispersion tend to indicate that the UCS obtained by laboratory tests following the current practice may not be representative of the in-situ strength distribution in the underground stopes due to segregation in cemented hydraulic backfill.
Efficacy of backfilling and other engineered barriers in a radioactive waste repository in salt

International Nuclear Information System (INIS)

Claiborne, H.C.

1982-09-01

In the United States, investigation of potential host geologic formations was expanded in 1975 to include hard rocks. Potential groundwater intrusion is leading to very conservative and expensive waste package designs. Recent studies have concluded that incentives for engineered barriers and 1000-year canisters probably do not exist for reasonable breach scenarios. The assumption that multibarriers will significantly increase the safety margin is also questioned. Use of a bentonite backfill for surrounding a canister of exotic materials was developed in Sweden and is being considered in the US. The expectation that bentonite will remain essentially unchanged for hundreds of years for US repository designs may be unrealistic. In addition, thick bentonite backfills will increase the canister surface temperature and add much more water around the canister. The use of desiccant materials, such as CaO or MgO, for backfilling seems to be a better method of protecting the canister. An argument can also be made for not using backfill material in salt repositories since the 30-cm-thick space will provide for hole closure for many years and will promote heat transfer via natural convection. It is concluded that expensive safety systems are being considered for repository designs that do not necessarily increase the safety margin. It is recommended that the safety systems for waste repositories in different geologic media be addressed individually and that cost-benefit analyses be performed
Backfill barriers for nuclear waste repositories in salt

Energy Technology Data Exchange (ETDEWEB)

Nowak, E J; Odoj, R; Merz, E [eds.

1981-06-01

Backfill mixtures surrounding the waste form and canister can provide a neutral or slightly acidic, potentially reducing environment, prevent convective aqueous flow, and act as an effective radionuclide migration barrier. Bentonite is likely to remain hydrothermally stable but potentially sensitive to waste package interactions which could alter the pH, the ratio of dissolved wires, or the sorption properties of radionuclide species.
Hydraulic properties of buffer and backfill materials for high-level nuclear waste disposal

International Nuclear Information System (INIS)

Komine, Hideo; Ogata, Nobuhide

2001-01-01

The design and development of buffer and backfill materials, which fill up the disposal facility, are important for developing the technology of high-level nuclear wastes disposal. The compacted bentonite and sand-bentonite mixture are attracting greater attention as buffer and backfill materials because they have impermeable and swelling properties. This study investigated the hydraulic-conductivities at the different sand-bentonite mass ratio and dry density, which are the specifications of material, by the experimental works. This study also obtained the experimental data of hydraulic conductivities of the materials for 120 days at the farthest, and the permeability changes before and after swelling. Furthermore, this study proposed the evaluation method for hydraulic conductivity using the parameter 'Swelling volumetric strain of montmorillonite', which was proposed by the author. The evaluation method can obtain the hydraulic conductivity of buffer and backfill materials at various dry densities and bentonite contents. Therefore, the evaluation method can be used for designing the bentonite content and compaction density from the viewpoint of 'impermeability'. (author)
Experimental Study of the Development of Scour and Backfilling

DEFF Research Database (Denmark)

Hartvig, Peres Akrawi; Thomsen, Jess Mccann; Frigaard, Peter

2010-01-01

This paper deals with the development of scour holes in time and space around individual offshore monopiles. It is based on physical flume tests of a model-scale pile subjected to current and/or irregular water waves. The main focus is on backfilling, i.e. the wave-induced or current...
Applications of a computer model to the analysis of rock-backfill interaction in pillar recovery operations

Energy Technology Data Exchange (ETDEWEB)

Sinclair, T. J.E. [Dames and Moore, London, England, United Kingdom; Shillabeer, J. H. [Dames and Moore, Toronto (Canada); Herget, G. [CANMET, Ottawa (Canada)

1980-05-15

This paper describes the application of a computer model to the analysis of backfill stability in pillar recovery operations with particular reference to two case studies. An explicit finite difference computer program was developed for the purpose of modelling the three-dimensional interaction of rock and backfill in underground excavations. Of particular interest was the mechanics of stress transfer from the rock mass to the pillars and then the backfill. The need, therefore, for a model to allow for the three-dimensional effects and the sequence of operations is evident. The paper gives a brief description of the computer program, descriptions of the mines, the sequences of operations and how they were modelled, and the results of the analyses in graphical form. For both case studies, failure of the backfill was predicted at certain stages. Subsequent reports from the mines indicate that such failures did not occur at the relevant stage. The paper discusses the validity of the model and concludes that the approach accurately represents the principles of rock mechanics in cut-and-fill mining and that further research should be directed towards determining the input parameters to an equal degree of sophistication.
Backfill composition for secondary barriers in nuclear waste repositories

Science.gov (United States)

Beall, Gary W.; Allard, Bert M.

1982-01-01

A backfill composition for sorbing and retaining hazardous elements of nuclear wastes comprises 50-70% by weight of quartz, 10-30% by weight of montmorillonite, 1-10% by weight of phosphate mineral, 1-10% by weight of ferrous mineral, 1-10% by weight of sulfate mineral and 1-10% by weight of attapulgite.
Fat metaplasia and backfill are key intermediaries in the development of sacroiliac joint ankylosis in patients with ankylosing spondylitis

DEFF Research Database (Denmark)

Maksymowych, Walter P; Wichuk, Stephanie; Chiowchanwisawakit, Praveena

2014-01-01

step in this pathway. METHODS: We used the Spondyloarthritis Research Consortium of Canada (SPARCC) SI structural lesion score (SSS) method to assess fat metaplasia, erosions, backfill, and ankylosis on MRIs of the SI joints in 147 patients with AS monitored for 2 years. Univariate and multivariate...... regression analyses focused first on identifying significant MRI predictors of new backfill and fat metaplasia. We then assessed the role of backfill and fat metaplasia in the development of new ankylosis. All analyses were adjusted for demographic features, treatment, and baseline and 2-year change in SSS...
Ground motion studies in a backfilled stope at West Driefontein

CSIR Research Space (South Africa)

Goldbach, OD

1991-10-01

Full Text Available This report looks at the ground motion from 24 small magnitude seismic events recorded at various points inside a backfilled stope. The in-stope ground motion is compared to that recorded at an off-reef site. The seismic events are analysed...

Backfilling of trenches exposed to waves

DEFF Research Database (Denmark)

Hjelmager Jensen, Jacob; Fredsøe, Jørgen

1997-01-01

This paper treats the numerical prediction of initial and long-term morphology of small pipeline trenches. For this purpose a refined flow and sediment transport description is applied such that the entire mathematical problem is formulated and solved on a curvilinear grid using a k - ε turbulence......-closure. The backfilling process of trenches exposed to either waves or a steady current is of importance in relation to the implementation of pipelines in the marine environment. With respect to the sedimentation of trenches, the non-dimensional Trench-Keulegan-Carpenter number, KC = a/L, where a is the excursion length...
The Buffer and Backfill Handbook. Part 3: Models for calculation of processes and behaviour

Energy Technology Data Exchange (ETDEWEB)

Pusch, Roland [Geodevelopment AB, Lund (Sweden)

2003-01-15

The present document collects conceptual and mathematical models that have been proposed for describing the performance of buffers and backfills and processes in them that are related to their function under repository conditions. As in the preceding parts the following types of sealing components are defined. By definition, the buffer shall be so composed that radionuclide transport in the clay-based barriers takes place by diffusion and not by water flow, which makes it important to predict the extent and rate of diffusive transport of such elements through the buffer. It depends strongly on the density and homogeneity of the buffer, which in turn depend on the maturation rate and the ultimate degree of homogeneity of the buffer. They are influenced by the temperature and temperature gradient that exist in the initial phase of water saturation, in which the hydraulic interaction with the near field rock is also important. Design of suitable buffer and backfills hence requires that their performance can be quantified, which requires that the various processes can be modeled conceptually and expressed in mathematical form. Based on the present knowledge this can only be made for some of the involved mechanisms and for coupled processes there is still a very limited number of mathematically expressed computational codes. The models referred to here are conceptual in the first place, defining the respective processes and material property parameters. The quick development of computational tools, numerical as well as analytical, makes it irrelevant to give detailed descriptions of them, while the various assumptions on which they are based - especially the conceptual models - have been considered in some detail. The models of practical use are only described in general terms and examples at the end of the respective chapter illustrate how they can be utilized. A very important fact is that transport and rheological processes in a repository are hardly ever of simple
Development of backfill material as an engineered barrier in the waste package system. Interim topical report

International Nuclear Information System (INIS)

Wheelwright, E.J.; Hodges, F.N.; Bray, L.A.; Westsik, J.H. Jr.; Lester, D.H.; Nakai, T.L.; Spaeth, M.E.; Stula, R.T.

1981-09-01

A backfill barrier, emplaced between the containerized waste and the host rock, can both protect the other engineered barriers and act as a primary barrier to the release of radionuclides from the waste package. Attributes that a backfill should provide in order to carry out its required function have been identified. Primary attributes are those that have a direct effect upon the release and transport of radionuclides from the waste package. Supportive attributes do not directly affect radionuclide release but are necessary to support the primary attributes. The primary attributes, in order of importance, are: minimize (retard or exclude) the migration of ground water between the host rock and the waste canister system; retard the migration of selected chemical species (corrosive species and radionuclides) in the ground water; control the Eh and pH of the ground water within the waste-package environment. The supportive attributes are: self-seal any cracks or discontinuities in the backfill or interfacing host geology; retain performance properties at all repository temperatures; retain peformance properties during and after receiving repository levels of gamma radiation; conduct heat from the canister system to the host geology; retain mechanical properties and provide resistance to applied mechanical forces; retain morphological stability and compatibility with structural barriers and with the host geology for required period of time. Screening and selection of candidate backfill materials has resulted in a preliminary list of materials for testing. Primary emphasis has been placed on sodium and calcium bentonites and zeolites used in conjunction with quartz sand or crushed host rock. Preliminary laboratory studies have concentrated on permeability, sorption, swelling pressure, and compaction properties of candidate backfill materials
Properties of Shredded Roof Membrane–Sand Mixture and Its Application as Retaining Wall Backfill under Static and Earthquake Loads

Directory of Open Access Journals (Sweden)

Bennett Livingston

2017-04-01

Full Text Available About 20 billion square feet of Ethylene Propylene Diene Monomer (EPDM rubber is installed on roofs in the United States and most of them will be reaching the end of their lifespan soon. The purpose of this study is to investigate potential reuses of this rubber in Civil Engineering projects rather than disposing it into landfills. First, laboratory tests were performed on various shredded rubber-sand mixtures to quantify the basic geotechnical engineering properties. The laboratory test results show that the shredded rubber-sand mixture is lightweight with good drainage properties and has shear strength parameters comparable to sand. This indicates that the rubber-sand mixture has potential to be used for retaining wall backfill and many other projects. To assess the economic advantage of using shredded rubber-sand mixtures as a lightweight backfill for retaining walls subjected to static and earthquake loadings, geotechnical designs of a 6 m tall gravity cantilever retaining wall were performed. The computed volume of concrete to build the structural components and volume of backfill material were compared with those of conventional sand backfill. Results show significant reductions in the volume of concrete and backfill material in both static and earthquake loading conditions when the portion of shredded rubber increased in the mixture.
Radon emanation from backfilled mill tailings in underground uranium mine.

Science.gov (United States)

Sahu, Patitapaban; Mishra, Devi Prasad; Panigrahi, Durga Charan; Jha, Vivekananda; Patnaik, R Lokeswara; Sethy, Narendra Kumar

2014-04-01

Coarser mill tailings used as backfill to stabilize the stoped out areas in underground uranium mines is a potential source of radon contamination. This paper presents the quantitative assessment of radon emanation from the backfilled tailings in Jaduguda mine, India using a cylindrical accumulator. Some of the important parameters such as (226)Ra activity concentration, bulk density, bulk porosity, moisture content and radon emanation factor of the tailings affecting radon emanation were determined in the laboratory. The study revealed that the radon emanation rate of the tailings varied in the range of 0.12-7.03 Bq m(-2) s(-1) with geometric mean of 1.01 Bq m(-2) s(-1) and geometric standard deviation of 3.39. An increase in radon emanation rate was noticed up to a moisture saturation of 0.09 in the tailings, after which the emanation rate gradually started declining with saturation due to low diffusion coefficient of radon in the saturated tailings. Radon emanation factor of the tailings varied in the range of 0.08-0.23 with the mean value of 0.21. The emanation factor of the tailings with moisture saturation level over 0.09 was found to be about three times higher than that of the absolutely dry tailings. The empirical relationship obtained between (222)Rn emanation rate and (226)Ra activity concentration of the tailings indicated a significant positive linear correlation (r = 0.95, p < 0.001). This relationship may be useful for quick prediction of radon emanation rate from the backfill material of similar nature. Copyright © 2014 Elsevier Ltd. All rights reserved.
BENTONITE-QUARTZ SAND AS THE BACKFILL MATERIALS ON THE RADIOACTIVE WASTE REPOSITORY

Directory of Open Access Journals (Sweden)

Raharjo Raharjo

2010-06-01

Full Text Available An investigation of the contribution of quartz sand in the bentonite mixture as the backfill materials on the shallow land burial of radioactive waste has been done. The experiment objective is to determine the effect of quartz sand in a bentonite mixture with bentonite particle sizes of -20+40, -40+60, and -60+80 mesh on the retardation factor and the uranium dispersion in the simulation of uranium migration in the backfill materials. The experiment was carried out by the fixed bed method in the column filled by the bentonite mixture with a bentonite-to-quartz sand weight percent ratio of 0/100, 25/75, 50/50, 75/25, and 100/0 on the water saturated condition flown by uranyl nitrate solution at concentration (Co of 500 ppm. The concentration of uranium in the effluents in interval 15 minutes represented as Ct was analyzed by spectrophotometer, then using Co and Ct, retardation factor (R and dispersivity ( were determined. The experiment data showed that the bentonite of -60+80 mesh and the quartz sand of -20+40 mesh on bentonite-to-quartz sand with weight percent ratio of 50/50 gave the highest retardation factor and dispersivity of 18.37 and 0.0363 cm, respectively. Keywords: bentonite, quartz sand, backfill materials, radioactive waste
Evaluation of the effect of sodium silicate addition to mine backfill, Gelfill − Part 1

Directory of Open Access Journals (Sweden)

M. Kermani

2015-06-01

Full Text Available In this paper, the mechanical properties of sodium silicate-fortified backfill, called Gelfill, were investigated by conducting a series of laboratory experiments. Two configurations were tested, i.e. Gelfill and cemented hydraulic fill (CHF. The Gelfill has an alkali activator such as sodium silicate in its materials in addition to primary materials of mine backfill which are tailings, water and binders. Large numbers of samples of Gelfill and CHF with various mixture designs were cast and cured for over 28 d. The mechanical properties of samples were investigated using uniaxial compression test, and the results were compared with those of reference samples made without sodium silicate. The test results indicated that the addition of an appropriate amount of an alkali activator such as sodium silicate can enhance the mechanical (uniaxial compressive strength and physical (water retention properties of backfill. The microstructure analysis conducted by mercury intrusion porosimetry (MIP revealed that the addition of sodium silicate can modify the pore size distribution and total porosity of Gelfill, which can contribute to the better mechanical properties of Gelfill. It was also shown that the time and rate of drainage in the Gelfill specimens are less than those in CHF specimens made without sodium silicate. Finally, the study showed that the addition of sodium silicate can reduce the required setting time of mine backfill, which can contribute to increase mine production in accordance with the mine safety.
Analysis on Filling Ratio and Shield Supporting Pressure for Overburden Movement Control in Coal Mining with Compacted Backfilling

Directory of Open Access Journals (Sweden)

Yanli Huang

2016-12-01

Full Text Available Since the weight of overburden is sustained by both the backfill body and the unmined solid coal in coal mining with compacted backfilling (CMCB panels, the stress and deformation characteristics of the surrounding rocks in coal mining are radically changed. The overburden movement control mechanism by coordinating with backfill body and shield in CMCB was studied systematically in this paper. Based on the analysis of deformational and structural characteristics of surrounding rock in CMCB panels, the methods of theoretical analysis, numerical simulation and engineering test are employed. The results show that the fracture of the main roof is mainly controlled by the filling ratio φ and is non-correlated to the shield supporting pressure p. However, p has a significant control effect on the deflection of roof within the shield canopy length, and adversely affects the filling ratio. With the increase of the filling ratio of the gob, the maximum sagging of the immediate and the main roofs, the peak front and the influence range of the abutment pressures are gradually reduced. Correspondingly, the stable period of internal pressure of backfill body in the gob is shortened. Engineering practice shows that the sagging of the gob roof, the distribution of the abutment pressure, the distribution of the internal pressure in the backfill body, and the ground surface sagging results obtained by the in-situ measurement are approximately corresponding to the theoretical analysis and numerical simulation results.
The simplified convergence rate calculation for salt grit backfilled caverns in rock salt

International Nuclear Information System (INIS)

Navarro, Martin

2013-03-01

Within the research and development project 3609R03210 of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, different methods were investigated, which are used for the simplified calculation of convergence rates for mining cavities in salt rock that have been backfilled with crushed salt. The work concentrates on the approach of Stelte and on further developments based on this approach. The work focuses on the physical background of the approaches. Model specific limitations are discussed and possibilities for further development are pointed out. Further on, an alternative approach is presented, which implements independent material laws for the convergence of the mining cavity and the compaction of the crushed salt backfill.
Current status of preparing buffer/backfill block in HLW disposal abroad

International Nuclear Information System (INIS)

Yan Ming; Wang Xuewen; Zhang Huyuan

2014-01-01

There is an urgent need for China to commence the full-scale compaction test, resolving the preparation problem for buffer/backfill blocks when underground research laboratory project is planned for High Level Radioactive Waste (HLW) disposal. The foreign countries have some research about the preparation of buffer/backfill blocks in engineered barrier systems. The foreign research shows that installation of clay blocks with sector shape at waste pollution area is a feasible engineering method. Compacted clay blocks need to be cured in a cabinet with controlled temperature and humidity to avoid desiccation and surface powdering. A freeze mixing method, mixing powdered-ice and cooled bentonite, can be operated more easily and obtain more uniform hydration than the traditional mixing of water and bentonite. It is helpful to review and adsorb the foreign research results for the design of full-scale test of bentonite compaction. (authors)
Using prior risk-related knowledge to support risk management decisions: lessons learnt from a tunneling project.

Science.gov (United States)

Cárdenas, Ibsen Chivatá; Al-Jibouri, Saad S H; Halman, Johannes I M; van de Linde, Wim; Kaalberg, Frank

2014-10-01

The authors of this article have developed six probabilistic causal models for critical risks in tunnel works. The details of the models' development and evaluation were reported in two earlier publications of this journal. Accordingly, as a remaining step, this article is focused on the investigation into the use of these models in a real case study project. The use of the models is challenging given the need to provide information on risks that usually are both project and context dependent. The latter is of particular concern in underground construction projects. Tunnel risks are the consequences of interactions between site- and project-specific factors. Large variations and uncertainties in ground conditions as well as project singularities give rise to particular risk factors with very specific impacts. These circumstances mean that existing risk information, gathered from previous projects, is extremely difficult to use in other projects. This article considers these issues and addresses the extent to which prior risk-related knowledge, in the form of causal models, as the models developed for the investigation, can be used to provide useful risk information for the case study project. The identification and characterization of the causes and conditions that lead to failures and their interactions as well as their associated probabilistic information is assumed to be risk-related knowledge in this article. It is shown that, irrespective of existing constraints on using information and knowledge from past experiences, construction risk-related knowledge can be transferred and used from project to project in the form of comprehensive models based on probabilistic-causal relationships. The article also shows that the developed models provide guidance as to the use of specific remedial measures by means of the identification of critical risk factors, and therefore they support risk management decisions. Similarly, a number of limitations of the models are
Radial diffusion of radiocaesium and radioiodide through cementitious backfill

Science.gov (United States)

Felipe-Sotelo, M.; Hinchliff, J.; Drury, D.; Evans, N. D. M.; Williams, S.; Read, D.

The function of the backfill material in a geological disposal facility (GDF) is to chemically condition the environment of the near field and thereby chemically retard the transport of the radionuclides present in the waste. This function of the backfill material is usually referred to as chemical containment. Diffusion experiments are being carried out over periods up to four years to assess the diffusion of Cs, Ni, Eu, Th, U and I (as I-) through Nirex Reference Vault Backfill (NRVB). The method uses cylinders of NRVB (40 mm diameter, 40-45 mm height) which can be doped via a central well with the radionuclides of interest. Diffusion occurs radially into a surrounding solution already pre-equilibrated with the cement. This paper shows the results obtained during the first two years for experiments undertaken using 137Cs and 125I- tracers with and without carrier. Comparison is made to tritiated water under identical experimental conditions. Breakthrough of Cs and I- occurred within the first week of the experiments, reaching steady state in the surrounding solution after 20-50 days. The maximum concentrations expected from the original inventories based on a simple dilution calculation have not been reached, indicating that retention in the matrix has occurred; ranging from 10% to 40% for Cs, and up to 50% for I-. Corresponding experiments using a solution containing cellulose degradation products (CDP) showed an increased diffusion for both Cs and I. Migration profiles have been obtained and the relative retention of each radionuclide has been confirmed using digital autoradiography. The results indicate that, for both isotopes, migration occurs through the cement matrix rather than through microfissures. However, whereas Cs is homogeneously distributed within the blocks, there is evidence of zones of preferential I- accumulation even where concentrations in solution have reached steady state. Transport modelling using GoldSim has replicated experimental
Assessment of (222)Rn emanation from ore body and backfill tailings in low-grade underground uranium mine.

Science.gov (United States)

Mishra, Devi Prasad; Sahu, Patitapaban; Panigrahi, Durga Charan; Jha, Vivekanand; Patnaik, R Lokeswara

2014-02-01

This paper presents a comparative study of (222)Rn emanation from the ore and backfill tailings in an underground uranium mine located at Jaduguda, India. The effects of surface area, porosity, (226)Ra and moisture contents on (222)Rn emanation rate were examined. The study revealed that the bulk porosity of backfill tailings is more than two orders of magnitude than that of the ore. The geometric mean radon emanation rates from the ore body and backfill tailings were found to be 10.01 × 10(-3) and 1.03 Bq m(-2) s(-1), respectively. Significant positive linear correlations between (222)Rn emanation rate and the (226)Ra content of ore and tailings were observed. For normalised (226)Ra content, the (222)Rn emanation rate from tailings was found to be 283 times higher than the ore due to higher bulk porosity and surface area. The relative radon emanation from the tailings with moisture fraction of 0.14 was found to be 2.4 times higher than the oven-dried tailings. The study suggested that the mill tailings used as a backfill material significantly contributes to radon emanation as compared to the ore body itself and the (226)Ra content and bulk porosity are the dominant factors for radon emanation into the mine atmosphere.
Investigation of Rock Mass Stability Around the Tunnels in an Underground Mine in USA Using Three-Dimensional Numerical Modeling

Science.gov (United States)

Xing, Yan; Kulatilake, P. H. S. W.; Sandbak, L. A.

2018-02-01

The stability of the rock mass around the tunnels in an underground mine was investigated using the distinct element method. A three-dimensional model was developed based on the available geological, geotechnical, and mine construction information. It incorporates a complex lithological system, persistent and non-persistent faults, and a complex tunnel system including backfilled tunnels. The strain-softening constitutive model was applied for the rock masses. The rock mass properties were estimated using the Hoek-Brown equations based on the intact rock properties and the RMR values. The fault material behavior was modeled using the continuously yielding joint model. Sequential construction and rock supporting procedures were simulated based on the way they progressed in the mine. Stress analyses were performed to study the effect of the horizontal in situ stresses and the variability of rock mass properties on tunnel stability, and to evaluate the effectiveness of rock supports. The rock mass behavior was assessed using the stresses, failure zones, deformations around the tunnels, and the fault shear displacement vectors. The safety of rock supports was quantified using the bond shear and bolt tensile failures. Results show that the major fault and weak interlayer have distinct influences on the displacements and stresses around the tunnels. Comparison between the numerical modeling results and the field measurements indicated the cases with the average rock mass properties, and the K 0 values between 0.5 and 1.25 provide satisfactory agreement with the field measurements.
Refinement of Foam Backfill Technology for Expedient Airfield Damage Repair; Phase 2: Development of Prototype Foam Dispensing Equipment and Improved Tactics, Techniques and Procedures

Science.gov (United States)

2017-12-01

ER D C TR -1 7- 14 U.S. Air Force Rapid Airfield Damage Repair Modernization Program Refinement of Foam Backfill Technology for...Backfill Technology for Expedient Airfield Damage Repair Phase II: Development of Prototype Foam Dispensing Equipment and Improved Tactics...procedures (TTPs) for rapid airfield damage repair (RADR) using foam backfill technology . Three different prototype foam dispensing systems were
Results of a backfill monitoring programme at Vaal Reefs 5 Shaft

CSIR Research Space (South Africa)

Squelch, AP

1990-08-01

Full Text Available This report documents the results of the in situ measurements carried out in the 68-52 stope at Vaal Reefs 5 Shaft. The in situ stress-strain behaviour of classified tailing backfill has been measured in panel P3. There is good agreement between...
Use of Cemented Super-Fine Unclassified Tailings Backfill for Control of Subsidence

Directory of Open Access Journals (Sweden)

Lei Yang

2017-11-01

Full Text Available Known for its advantages in preventing geological and environmental hazards, cemented paste backfill (CPB has become a topic of interest for scientists and mining engineers in recent decades. This paper presents the results of a study on the use of cemented super-fine tailings backfill (CSUTB in an underground mine for control of surface subsidence. An analytical solution is developed based on the available model to calculate the required strength of backfill when in contact with non-cemented tailings (NCT. The effect of solid contents on the rheological properties of CSUTB is investigated. A reasonable mix proportion (RMP of CSUTB is determined for Zhongguan Iron Mine (ZGIM based on laboratory experiments. The validity of RMP in surface subsidence control is verified by a 3D numerical model. The obtained results show that CSUTB requires higher strength when in contact with NCT than when in contact with orebody. Rheological characteristics, e.g., slump, fluidity, and bleeding rate of fresh CSUTB, decrease with higher solids content, of which values with a certain solids content can be determined by quadratic polynomial regression equations. RMP with a cement to tailings (c/t ratio of 1:10 and a solids content of 70% is recommended for ZGIM, as it shows favorable mechanical and rheological abilities. The deformation parameters (curvature, inclination, and horizontal deformation rate obtained from numerical modeling are acceptable and lower than critical values, meaning CSUTB can feasibly be used with RMP in subsidence control.
DISPERSION AND SORPTION CHARACTERISTICS OF URANIUM IN THE ZEOLITE-QUARTZ MIXTURE AS BACKFILL MATERIAL IN THE RADIOACTIVE WASTE REPOSITORY

Directory of Open Access Journals (Sweden)

Herry Poernomo

2010-06-01

Full Text Available The experiment of sorption and dispersion characteristics of uranium in the zeolite-quartz mixture as candidate of raw material of backfill material in the radioactive waste repository has been performed. The objective is to know the effect of zeolite and quartz grain size on the zeolite-to-quartz weight ratio that gives porosity (ε, permeability (K, and dispersivity (α of uranium in the zeolite-quartz mixture as backfill material. The experiment was carried out by fixed bed method in the column filled by the zeolite-quartz mixture with zeolite-to-quartz weight percent ratio of 100/0, 80/20, 60/40, 40/60, 20/80, 0/100 wt. % in the water saturated condition flowed by uranyl nitrate solution of 500 ppm concentration (Co as uranium simulation which was leached from immobilized radioactive waste in the repository. The concentration of uranium in the effluents represented as Ct were analyzed by spectrophotometer Corning Colorimeter 253 every 15 minutes, then using Co and Ct uranium dispersivity (α in the backfill material was determined. The experiment data shown that 0.196 mm particle size of zeolite and 0.116 mm particle size of quartz on the zeolite-to-quartz weight ratio of 60/40 wt. % with ε = 0.678, K = 3.345x10-4 cm/second, and α = 0.759 cm can be proposed as candidate of raw material of backfill material in the radioactive waste repository. Keywords: backfill material, quartz, radioactive waste, zeolite
Experimental investigation of the long term dissolution properties of a cement-based vault backfill

International Nuclear Information System (INIS)

Butcher, E.J.; Borwick, J.; Thorburn, A.A.; Williams, S.J.

2012-01-01

One concept for the long-term management of packages of intermediate-level radioactive waste (ILW) is to place them in underground vaults in a Geological Disposal Facility (GDF). After the packaged waste is placed in the vault it is planned to fill the space around the waste packages with a cement-based backfill prior to closure of the facility. The currently specified backfill is the NRVB (Nirex Reference Vault Backfill), composed of a blend of Portland cement, limestone flour and hydrated lime. Leaching trials are ongoing at the UK National Nuclear Laboratory (NNL) to investigate the dissolution of NRVB until pH values typical of calcium carbonate are achieved. The objective of this work is to determine the buffering capacity of samples of the NRVB, and to allow the sequential release of the alkalinity from the intact samples to be monitored. Leaching is being performed utilising three leachants: deionised water and two saline solutions. Trials have been performed in duplicate for each leachant to allow an initial assessment to be made of the reproducibility of the data produced. In order to simulate the conditions expected in the GDF the approach being used in the trials is a flow through experiment utilising a flexible wall permeameter, within a 35 deg temperature-controlled cell
Use of inorganic sorbents for treatment of liquid radioactive waste and backfill of underground repositories

International Nuclear Information System (INIS)

1992-11-01

This document presents the results of a four year Co-ordinated Research Programme (CRP) on the ''Use of Inorganic Sorbents for Treatment of Liquid Radioactive Waste and Backfill of Underground Repositories'' (1987-1991). Many countries have research programmes aiming at developing processes which would provide efficient and safe concentration of radionuclides in waste streams into solid materials which could then be reliably immobilized into forms suitable for long term storage or disposal. Use of inorganic sorbents for this purpose is very attractive because of their resistance to radiation and chemical attack, strong affinity for one or more radionuclides, their compatibility with likely immobilization matrices and their availability at low cost. According to the fundamental multibarrier concept for disposal of radioactive waste, backfill material is one of the important engineered barriers. Inorganic materials such as clays, naturally occurring zeolites (clinoptilolite, modenite and chabasite) are promising backfill materials. Research in technical uses of inorganic material applications was covered within the framework of the Co-ordinated Research Programme reported in this technical document. Final contributions by participants at the last Research Co-ordination Meeting held in Rez, Czechoslovakia, from 4 to 8 November 1991, are presented here. Refs, figs and tabs

Experimental studies on the inventory of cement-derived colloids in the pore water of a cementitious backfill material

International Nuclear Information System (INIS)

Wieland, E.

2001-06-01

The potential role of near-field colloids for the colloid-facilitated migration of radionuclides has stimulated investigations concerning the generation and presence of colloids in the near-field of a repository for low- and intermediate level waste (L/ILW). The highly gas permeable mortar (Nagra designation: mortar M1) is currently favoured as backfill material for the engineered barrier of the planned Swiss L/ILW repository. The cementitious backfill is considered to be a chemical environment with some potential for colloid generation. In a series of batch-style laboratory experiments the physico-chemical processes controlling the inventory of colloids in cement pore water of the backfill were assessed for chemical conditions prevailing in the initial stage of the cement degradation. In these experiments, backfill mortar M1 or quartz, respectively, which may be used as aggregate material for the backfill, were immersed in artificial cement pore water (a NaOH/KOH rich cement fluid). Colloid concentrations in the cement pore water were recorded as a function of time for different experimental settings. The results indicate that a colloid-colloid interaction process (coagulation) controlled the colloid inventory. The mass concentration of dispersed colloids was found to be typically lower than 0.02 ppm in undisturbed batch systems. An upper-bound value was estimated to be 0.1 ppm taking into account uncertainties on the measurements. To assess the potential for colloid generation in a dynamic system, colloid concentrations were determined in the pore water of a column filled with backfill mortar. The chemical conditions established in the mortar column corresponded to conditions observed in the second stage of the cement degradation (a Ca(OH) 2 - controlled cement system). In this dynamic system, the upper-bound value for the colloid mass concentration was estimated to be 0.1 ppm. Implications for radionuclide mobility were deduced taking into account the
Study on box shield tunneling method in trial field operation; Box shield koho jissho seko ni kansuru kosatsu

Energy Technology Data Exchange (ETDEWEB)

Tada, K.; Taniguchi, T. [Toda Corp., Tokyo, (Japan); Furukawa, K.; Nakagawa, K. [Yamaguchi University, Yamaguchi (Japan). Faculty of Engineering

1997-03-20

This paper describes a rectangular section shield tunneling method as a part of developments of non-circular section shield tunneling methods. The non-circular shield is drawing attention because of need of excavation in small land available in urban areas and between congested existing structures, as well as reduction in the excavated soil amount. A full-scale machine was fabricated to perform a natural ground excavation experiment. The cutter units comprising two each of drum cutters and ring cutters were arranged above and below, by which two tunnels of 40 m long with a cross section of 2.85 m {times} 2.85 m were excavated. The natural ground was supported safely by holding mud water pressures at cutting points constant, thus stability of the cutting points was ensured. Back-filling has made complete filling of tail void (clearance between a segment and the ground) possible, resulting in suppression in conditional change of the surrounding ground. Attitude control has been performed properly as a result of correct selection of shield jacks and use of deflection jacks. Broken-type over-cutters were used to have constructed tunnels with curve radius of 80 and 100 m with high accuracy. Thrust and propulsion speed of the shield do not differ from those of circular shields. Possibilities of this construction method were verified. 8 refs., 26 figs., 2 tabs.
Bentonite as a backfill material for shallow land repositories

International Nuclear Information System (INIS)

Yalmali, V.S.; Deshingkar, D.S.

2001-01-01

Two commercially available indigenous bentonite samples were evaluated for their cesium and strontium sorption properties in distilled water and surface water. By converting them into sodium form, the distribution coefficients for both cesium (I) and strontium (II) increased. Sodium bentonite was recommended because of high sorption capacity for Cs(I), Mg(II) and Sr(II) for use as backfill material in shallow land repositories where cement waste form containing Cs, Sr and Be wastes are disposed. (author)
Conceptual design for relocation of the underground monitoring systems to ground surface

International Nuclear Information System (INIS)

Toya, Naruhisa; Ogawa, Ken; Iwatsuki, Teruki; Ohnuki, Kenji

2015-09-01

One of the major subjects of the ongoing geoscientific research program, the Mizunami Underground Research Laboratory (MIU) Project in the Tono area, central Japan, is accumulation of knowledge on a recovery of the geological environment during and after the facility closure. Then it is necessary to plan the observation system which can be use of after the backfill of research tunnels. The main purpose of this report is contribution to the detailed design for relocation of the underground monitoring systems to ground surface. We discussed the restriction and requirement for the underground monitoring systems which can be use of after the backfill. Furthermore, we made the conceptual design for relocation of the current underground monitoring systems to ground surface. (author)
Flowable Backfill Materials from Bottom Ash for Underground Pipeline

Directory of Open Access Journals (Sweden)

Kyung-Joong Lee

2014-04-01

Full Text Available The purpose of this study was to investigate the relationship between strength and strain in manufacturing controlled low strength materials to recycle incineration bottom ash. Laboratory tests for controlled low strength materials with bottom ash and recycled in-situ soil have been carried out. The optimum mixing ratios were 25%–45% of in-situ soil, 30% of bottom ash, 10%–20% of fly ash, 0%–3% of crumb rubber, 3% of cement, and 22% of water. Each mixture satisfied the standard specifications: a minimum 20 cm of flowability and 127 kPa of unconfined compressive strength. The average secant modulus (E50 was (0.07–0.08 qu. The ranges of the internal friction angle and cohesion for mixtures were 36.5°–46.6° and 49.1–180 kPa, respectively. The pH of all of the mixtures was over 12, which is strongly alkaline. Small-scale chamber tests for controlled low strength materials with bottom ash and recycled in-situ soil have been carried out. Vertical deflection of 0.88–2.41 mm and horizontal deflection of 0.83–3.72 mm were measured during backfilling. The vertical and horizontal deflections of controlled low strength materials were smaller than that of sand backfill.
Characterisation of bentonites from Kutch, India and Milos, Greece - some candidate tunnel back-fill materials?

Energy Technology Data Exchange (ETDEWEB)

Olsson, Siv; Karnland, Ola (Clay Technology AB, Lund (Sweden))

2009-12-15

During the past decades comprehensive investigations have been made on bentonite clays in order to find optimal components of the multi-barrier system of repositories for radioactive waste. The present study gives a mineralogical characterisation of some selected bentonites, in order to supply some of the necessary background data on the bentonites for evaluating their potential as tunnel back-fill materials. Two bentonites from the island of Milos, Greece (Milos BF 04 and BF 08), and two bentonites from Kutch, India (Kutch BF 04 and BF 08) were analysed for their grain size distribution, cation exchange properties and chemical composition. The mineralogical composition was determined by X-ray diffraction analysis and evaluated quantitatively by use of the Siroquant software. Both the bulk bentonite and the <1mum fraction were analyzed when relevant. Prior to the chemical analyses the <1 mum fractions were converted to homo-ionic clays and purified by dialysis. The chemical data were used for calculating the structural formula of the smectites. Milos BF 04 contains ca. 10% particles >63 mum. The bentonite is distinguished by a high content of dolomite and calcite, which make up almost 25% of the bulk sample. The major accessory minerals are K-feldspars and plagioclase, whereas the content of sulphur-bearing minerals is very low (0.06% total S). Smectite makes up around 60% of the bulk sample, which has a CEC value of 73 meq/100 g. The pool of interlayer cations has a composition Mg>Ca>>Na>>K. The X-ray diffraction characteristics and the high potassium content (1.03% K{sub 2}O) of the <1 mum fraction suggest that the smectite is interstratified with ca. 10% illitic layers. Based on the charge distribution the smectite should be classified as montmorillonite and according to the structural formula, Mg predominates over Fe in the octahedral sheet. However, remnants of Mg-carbonates, if present, may be a source of error in the formula calculation. Milos BF 08 has a
Experimental studies on the inventory of cement-derived colloids in the pore water of a cementitious backfill material

Energy Technology Data Exchange (ETDEWEB)

Wieland, E

2001-06-01

The potential role of near-field colloids for the colloid-facilitated migration of radionuclides has stimulated investigations concerning the generation and presence of colloids in the near-field of a repository for low- and intermediate level waste (L/ILW). The highly gas permeable mortar (Nagra designation: mortar M1) is currently favoured as backfill material for the engineered barrier of the planned Swiss L/ILW repository. The cementitious backfill is considered to be a chemical environment with some potential for colloid generation. In a series of batch-style laboratory experiments the physico-chemical processes controlling the inventory of colloids in cement pore water of the backfill were assessed for chemical conditions prevailing in the initial stage of the cement degradation. In these experiments, backfill mortar M1 or quartz, respectively, which may be used as aggregate material for the backfill, were immersed in artificial cement pore water (a NaOH/KOH rich cement fluid). Colloid concentrations in the cement pore water were recorded as a function of time for different experimental settings. The results indicate that a colloid-colloid interaction process (coagulation) controlled the colloid inventory. The mass concentration of dispersed colloids was found to be typically lower than 0.02 ppm in undisturbed batch systems. An upper-bound value was estimated to be 0.1 ppm taking into account uncertainties on the measurements. To assess the potential for colloid generation in a dynamic system, colloid concentrations were determined in the pore water of a column filled with backfill mortar. The chemical conditions established in the mortar column corresponded to conditions observed in the second stage of the cement degradation (a Ca(OH){sub 2{sup -}} controlled cement system). In this dynamic system, the upper-bound value for the colloid mass concentration was estimated to be 0.1 ppm. Implications for radionuclide mobility were deduced taking into account the
Performance of concrete backfilling materials for shafts and tunnels in rock formations. Volume 1: concrete selection and properties

International Nuclear Information System (INIS)

Casson, R.B.J.; Davies, I.L.

1986-01-01

Preplaced Aggregate Concrete (PAC) consists of graded coarse aggregate, immobilised by cementitious grout injected into the voids. PAC can be considered as a suitable backfill material for mined radioactive waste repositories. PAC is also reported to be amenable to mechanical/remote placement and have usefully improved properties when compared with conventionally placed concretes. In particular reduced shrinkage and heat cycle during cement hydration, higher densities and improved plant economics are claimed. This study attempts to establish the validity of these claims both from reported experience and by practical demonstration through experimentation. A literature study supported the claims made for the PAC system but all reported experiences recorded the use of organic admixtures (workability aids, retarders etc). Because of the lack of long term durability data on such admixtures, especially in a radiation environnement, it was decided to prepare a sample of PAC without organic admixtures. Considerable experimental difficulties were encountered in obtaining a satisfactory quality for test specimens. The necessary grout fluidity was only achieved by the inclusion of bentonite. The test data collected indicates that the PAC system employed did not improve mechanical properties compared with conventional concretes. This is attributed to the non-usage of organic admixtures to achieve the expected performance. Further research on low permeability concretes would require the use of organic admixtures. The effect of radiation on these materials, and their leaching rate needs to be quantified
Application of mine water leaching protocol on coal fly ash to assess leaching characteristics for suitability as a mine backfill material.

Science.gov (United States)

Madzivire, Godfrey; Ramasenya, Koena; Tlowana, Supi; Coetzee, Henk; Vadapalli, Viswanath R K

2018-04-16

Over the years, coal mining in the Mpumalanga Province of South Africa has negatively affected the environment by causing pollution of water resources, land subsidence and spontaneous coal combustion. Previous studies show that in-situ treatment of acid mine drainage (AMD) using coal fly ash (CFA) from local power stations was possible and sludge recovered out of such treatment can be used to backfill mines. In this article, the authors have attempted to understand the leaching characteristics of CFA when placed underground as a backfill material using the mine water leaching protocol (MWLP). The results show that the migration of contaminants between the coal fly ash and the AMD in the mine voids depends on the pH and quality of the mine water. While backfilling mine voids with CFA can neutralize and scavenge between 50% and 95% of certain environmentally sensitive elements from AMD such as Fe, Al, Zn, Cu, Ni, Co and Mn. At this moment, it is also important to point out that certain scavenged/removed contaminants from the AMD during initial phases of backfilling can be remobilized by the influx of acidic water into the mine voids. It has therefore been concluded that, while CFA can be used to backfill mine voids, the influx of fresh acidic mine water should be avoided to minimize the remobilization of trapped contaminants such as Fe, Al, Mn and As. However, the pozzolanic material resulting from the CFA-AMD interaction could prevent such influx.
Investigations of excavated clay-stone as backfill/seal material

International Nuclear Information System (INIS)

Zhang, Chun-Liang

2012-01-01

Document available in extended abstract form only. Crushed clay-stone produced by excavation activities of repository drifts has been investigated as backfill/seal material at the GRS laboratory. The raw aggregate with coarse grains is considered to be used for backfilling the repository openings and, in mixture with bentonite, for sealing the boreholes, drifts and shafts. The GRS research programme focused on characterizing the thermo-hydro-mechanical properties of the excavated Callovo-Oxfordian clay-stone (COX) and the clay-stone-bentonite mixtures, including mechanical compaction, gas and water permeability as function of porosity, water retention and saturation, swelling capacity, and thermal properties of the materials. The most important results are presented in this paper. Figure 1 shows the compaction and permeability behaviour of the excavated clay-stone with grains up to a size of 32 mm. The results were obtained on large samples of 280 mm diameter and 680 mm height under quasi-hydrostatic compression. The porosity and permeability decrease with increasing load. The porosity-mean stress relation is non-linear and may be expressed by an exponential function. The backfill becomes stiffer at low porosities and can sustain certain deviatoric loads. At porosity of ∼21 %, the strength is characterized by an inherent cohesion of 3.7 MPa and an internal friction angle of 12 deg.. Additionally, the compaction is also dependent on time or loading rate, water content, and temperature. The compaction of the porous backfill material leads to a reduction in permeability. The measured gas permeability decreases much faster at low porosities below ∼25 %. The gas permeability at porosity of ∼20 % becomes as low as that of 10 -20 - 10 -21 m 2 for the intact clay rock. This is probably due to disconnection of the pore network during the compaction. As sealing material, powdered COX clay-stone was mixed with MX80 bentonite powder in different ratios and compacted to
Aespoe Hard Rock Laboratory. Backfill and Plug test. Hydraulic testing of core drilled boreholes in the ZEDEX drift

Energy Technology Data Exchange (ETDEWEB)

Ludvigson, Jan-Erik; Nordqvist, Rune; Ekman, Lennart; Hansson, Kent (GEOSIGMA AB, Uppsala (Sweden))

2009-07-01

The present report documents the performance and results of hydraulic testing in selected core boreholes in the Zedex drift. The holes will be used as rock instrumentation boreholes during the Backfill and Plug Test at Aespoe HRL. The testing involves both 1 m long boreholes with 56 mm diameter as well as longer boreholes c. 5 m, 8 m and 25 m long with 56 mm or 76 mm diameter. Only single-hole tests were performed. The tests were carried out as short-time constant head injection tests since all boreholes tested (except one) were non-flowing before tests. The injection phase was followed by a pressure recovery phase. Furthermore, the tests were carried out as single-packer tests. A specially designed test system was used for the tests. The main evaluation of the tests was performed on data from the recovery phase by a new approach based on a non-linear regression technique combined with a flow simulation model (SUTRA). The tests in the 1 m-holes (testing the interval c. 0.3-0.7 m in the rock perpendicular to the tunnel face) show that the hydraulic conductivity of the superficial rock around the Zedex drift in general is low. However, during testing in some boreholes, visible leakage in the rock occurred through superficial fractures into the tunnel. These fractures were mainly located in the floor of the Zedex drift and are probably blast-induced. These fractures have a high hydraulic conductivity. The tests in the longer boreholes show that the hydraulic conductivity further into the rock in general is below c. 1x10-10 m/s. Increased hydraulic conductivity (c.1.5x10-8 m/s) was only observed in the flowing borehole KXZSD8HL.
Sorption of cesium and strontium from concentrated brines by backfill barrier materials

International Nuclear Information System (INIS)

Winslow, C.D.

1981-03-01

The sorption of radionuclides from potentially intruding groundwater at a nuclear waste repository is a major chemical function of backfill barriers. In this study, various materials (including clays, zeolites and an inorganic ion exchanger) were screened for the sorption of the fission products cesium and strontium in concentrated brines. Representative brines A and B for the Waste Isolation Pilot Plant (WIPP), a proposed radioactive waste repository and test facility in bedded salt were used. Sorption properties were quantified using empirical distribution coefficients, k/sub d/. Of the materials examined, sodium titanate had the highest k/sub d/ for the sorption of Sr(II) in both brine A (k/sub d/ = 125 ml/g) and brine B(k/sub d/ = 500 to 600 ml/g). A mordenite-type zeolite was the most effective getter for Cs(I) in brine A (k/sub d = 27 ml/g), while illite yielded the highest k/sub d/ for Cs(I) in brine B (k/sub d/ = 115 ml/g). The relative merit of these k/sub d/ values is evaluated in terms of calculated estimates of breakthrough times for a backfill barrier containing the getter. Results show that a backfill mixture containing these getters is potentially an effective barrier to the migration of Sr(II) and Cs(I), although further study (especially for the sorption of cesium from brine A) is recommended. Initial mechanistic studies revealed competing ion effects which would support an ion exchange mechanism. K/sub d/'s were constant over a Sr(II) concentration range of 10 -11 to 10 -5 M and a Cs(I) concentration range of 10 -8 to 10 -5 M, supporting the choice of a linear sorption isotherm as a model for the results. Constant batch composition was shown to be attained within one week
Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Guenter; Muenzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

2011-01-01

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: → Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. → Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. → Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. → Limitation indicates that Al-Ox layer is causing incoherent tunneling.
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FLEXIBLE BURIED PIPE DEFORMATION BEHAVIOR UNDER VARIOUS BACKFILL CONDITIONS

Directory of Open Access Journals (Sweden)

Niyazi Uğur TERZİ

2009-01-01

Full Text Available Deformation characteristics of polyethylene based flexible pipes are different than rigid pipes such as concrete and iron pipes. Deflection patterns and stress-strain behaviors of flexible pipes have strict relation between the engineering properties of backfill and its settlement method. In this study, deformation behavior of a 100 mm HDPE flexible pipe under vertical loads is investigated in laboratory conditions. Steel test box, pressurized membrane, raining system, linear position transducers and strain gauge rosettes are used in the laboratory tests. In order to analyze the buried pipe performance; Masada Derivation Formula which is mostly used by designers is employed. According to the test and mathematical studies, it is understood that relative density of backfill and its settlement method is a considerable effect on buried pipe performance and Masada Derivation method is very efficient for predicting the pipe performance.
Solubility constraints affecting the migration of selenium through the cementitious backfill of a geological disposal facility

Energy Technology Data Exchange (ETDEWEB)

Felipe-Sotelo, M., E-mail: m.felipe-sotelo@lboro.ac.uk; Hinchliff, J.; Evans, N.D.M.; Read, D.

2016-03-15

Highlights: • The availability of Ca controls the concentration of SeO{sub 3}{sup 2−} in solution. • Cellulose degradation products increase the solubility of SeO{sub 3}{sup 2−} at alkaline pH. • Selenite diffuses faster through the backfill NRVB than through fly ash cements. - Abstract: This work presents the study of the solubility of selenium under cementitious conditions and its diffusion, as SeO{sub 3}{sup 2−}, through monolithic cement samples. The solubility studies were carried out under alkaline conditions similar to those anticipated in the near-field of a cement-based repository for low- and intermediate-level radioactive waste. Experiments were conducted in NaOH solution, 95%-saturated Ca(OH){sub 2}, water equilibrated with a potential backfill material (Nirex reference vault backfill, NRVB) and in solutions containing cellulose degradation products, with and without reducing agents. The highest selenium concentrations were found in NaOH solution. In the calcium-containing solutions, analysis of the precipitates suggests that the solubility controlling phase is Ca{sub 2}SeO{sub 3}(OH){sub 2}·2H{sub 2}O, which appears as euhedral rhombic crystals. The presence of cellulose degradation products caused an increase in selenium concentration, possibly due to competitive complexation, thereby, limiting the amount of calcium available for precipitation. Iron coupons had a minor effect on selenium solubility in contrast to Na{sub 2}S{sub 2}O{sub 4}, suggesting that effective reduction of Se(IV) occurs only at E{sub h} values below −300 mV. Radial through-diffusion experiments on NRVB and in a fly ash cement showed no evidence of selenium breakthrough after one year. However, autoradiography of the exposed surfaces indicated that some migration had occurred and that selenium was more mobile in the higher porosity backfill than in the fly ash cement.
A mathematical model of the behaviour of concrete backfill in an underground radioactive-waste repository

International Nuclear Information System (INIS)

Mistry, N.S.; Carlton, D.; Storer, G.

1992-01-01

This report concerns the mathematical modelling by the finite element method of the behaviour of concrete, one of the candidate materials for use in the backfilling and scaling of underground repositories for radioactive waste. In order to act as an assured physical barrier to ground water migration in the vicinity of the waste packages, a concrete backfill must remain intact and free from cracks. One of the risk periods during which mass concrete is susceptible to cracking is during the early days after casting when concrete undergoes rapid changes in internal temperatures and mechanical properties, including, most obviously, strength. Existing commercially available finite element codes do not have a model for concrete that can adequately represent these early age characteristics. The present study, therefore, is predominantly concerned with the development of a mathematical model for use within the ADINA finite element code to predict the time-dependent performance of concrete as a backfilling and sealing material. The evaluation of creep and shrinkage strains is based on the CEB-FIP Model Code together with Illston's approach to delayed and transitional thermal strains. The finite element material model developed is general and could be applied to various types of structure and loading. The model accounts for the ageing of concrete, multi-axial creep and creep recovery, the effect of external environmental humidity and changing internal temperatures. 32 refs., 31 figs., 1 tab
Reactive transport predictions for an Olkiluoto. Final repository tunnel unit

International Nuclear Information System (INIS)

Luukkonen, A.; Nordman, H.

2007-09-01

repository level. Calculations also predict the conversion of Na-montmorillonite to mixed (Na,Ca)-montmorillonite within the tunnel unit in 10,000-20,000 years from the start of the repository operations. This mineralogical change as well as salinity changes of infiltrating groundwater should affect the engineered barrier swelling pressures. However, pressure changes are not estimated in this study. However, there are significant uncertainties included in the calculations. The future climatic and geological events are likely not completely understood. Groundwater flow/diffusion rates within the backfilled tunnel are uncertain. Changes in material properties (homogeneity, alteration) with time should be estimated as well. (orig.)
Consequences of using crushed crystalline rock as ballast in KBS-3 tunnels instead of rounded quartz particles

Energy Technology Data Exchange (ETDEWEB)

Push, R [Clay Technology AB (Sweden)

1995-02-01

The basic question has been whether such replacement alters the hydraulic conductivity and compressibility as well as expandability and also if the physical and chemical stabilities are altered. The key factor is the microstructural constitution of the bentonite/ballast mixtures, which is primarily controlled by the grain size distribution of the ballast. The compact ability of backfills with quartz sand (SB) is higher than that of backfills with crushed rock as ballast (RB). The physical stability of RB backfills in terms of piping and erosion resistance will be somewhat lower than that of SB backfills. The chemical stability is practically independent of whether the ballast is pure quartz or rock with K-bearing minerals because the temperature in the backfill will be too low to yield significant smectite to illite conversion in the short heating period. In order to reach the same densities of SB and RB backfills, which turn out to give fairly similar physical properties, the latter backfills need more effective compaction or, alternatively, a higher bentonite content. It is estimated that if the bentonite content in RB backfills is not increased while the density is enhanced to what is achievable, these backfills will serve equally well as SB backfills with the densities implied by the basic KBS-3 concept. 23 refs, 27 figs, 7 tabs.
Consequences of using crushed crystalline rock as ballast in KBS-3 tunnels instead of rounded quartz particles

International Nuclear Information System (INIS)

Push, R.

1995-02-01

The basic question has been whether such replacement alters the hydraulic conductivity and compressibility as well as expandability and also if the physical and chemical stabilities are altered. The key factor is the microstructural constitution of the bentonite/ballast mixtures, which is primarily controlled by the grain size distribution of the ballast. The compact ability of backfills with quartz sand (SB) is higher than that of backfills with crushed rock as ballast (RB). The physical stability of RB backfills in terms of piping and erosion resistance will be somewhat lower than that of SB backfills. The chemical stability is practically independent of whether the ballast is pure quartz or rock with K-bearing minerals because the temperature in the backfill will be too low to yield significant smectite to illite conversion in the short heating period. In order to reach the same densities of SB and RB backfills, which turn out to give fairly similar physical properties, the latter backfills need more effective compaction or, alternatively, a higher bentonite content. It is estimated that if the bentonite content in RB backfills is not increased while the density is enhanced to what is achievable, these backfills will serve equally well as SB backfills with the densities implied by the basic KBS-3 concept. 23 refs, 27 figs, 7 tabs
A hierarchical network modeling method for railway tunnels safety assessment

Science.gov (United States)

Zhou, Jin; Xu, Weixiang; Guo, Xin; Liu, Xumin

2017-02-01

Using network theory to model risk-related knowledge on accidents is regarded as potential very helpful in risk management. A large amount of defects detection data for railway tunnels is collected in autumn every year in China. It is extremely important to discover the regularities knowledge in database. In this paper, based on network theories and by using data mining techniques, a new method is proposed for mining risk-related regularities to support risk management in railway tunnel projects. A hierarchical network (HN) model which takes into account the tunnel structures, tunnel defects, potential failures and accidents is established. An improved Apriori algorithm is designed to rapidly and effectively mine correlations between tunnel structures and tunnel defects. Then an algorithm is presented in order to mine the risk-related regularities table (RRT) from the frequent patterns. At last, a safety assessment method is proposed by consideration of actual defects and possible risks of defects gained from the RRT. This method cannot only generate the quantitative risk results but also reveal the key defects and critical risks of defects. This paper is further development on accident causation network modeling methods which can provide guidance for specific maintenance measure.

Recycled Asphalt Pavement and Crushed Concrete Backfill: State-of-the-Art Review and Material Characterization

Science.gov (United States)

2001-10-01

This report describes research results from the first year of a three-year study focused on the use of recycled asphalt pavement (RAP) and crushed concrete (CC) as backfill for mechanically stabilized earth (MSE) walls.
Quantum tunneling of Bose-Einstein condensates in optical lattices

CERN Document Server

Fan Wen Bin

2003-01-01

In quantum tunneling a particle with energy E can pass through a high potential barrier V(>E) due to the wave character of the particle. Bose-Einstein condensates can display very strong tunneling depending on the structure of the trap, which may be a double-well or optical lattices. The employed for the first time to our knowledge the periodic instanton method to investigate tunneling of Bose-Einstein condensates in optical lattices. The results show that there are two kinds of tunneling in this system, Landau-Zener tunneling between extended states of the system and Wannier-Stark tunneling between localized states of the system, and that the latter is 1000 times faster than the former. The also obtain the total decay rate for a wide range of temperature, including classical thermal activation, thermally assisted tunneling and quantum tunneling. The results agree with experimental data in references. Finally, the propose an experimental protocol to observe this new phenomenon in future experiments
The Beginner's Guide to Wind Tunnels with TunnelSim and TunnelSys

Science.gov (United States)

Benson, Thomas J.; Galica, Carol A.; Vila, Anthony J.

2010-01-01

The Beginner's Guide to Wind Tunnels is a Web-based, on-line textbook that explains and demonstrates the history, physics, and mathematics involved with wind tunnels and wind tunnel testing. The Web site contains several interactive computer programs to demonstrate scientific principles. TunnelSim is an interactive, educational computer program that demonstrates basic wind tunnel design and operation. TunnelSim is a Java (Sun Microsystems Inc.) applet that solves the continuity and Bernoulli equations to determine the velocity and pressure throughout a tunnel design. TunnelSys is a group of Java applications that mimic wind tunnel testing techniques. Using TunnelSys, a team of students designs, tests, and post-processes the data for a virtual, low speed, and aircraft wing.
Determination of the in situ modulus of the rockmass by the use of backfill measurements

CSIR Research Space (South Africa)

Gurtunca, RG

1991-03-01

Full Text Available In situ measurements and numerical modelling based on elastic theory showed that backfill stresses are considerably higher than originally thought. This has led to a change in understanding of rockmass behaviour. After describing previous work...
Study on the properties of Gaomiaozi bentonite as the buffer/backfilling materials for HLW disposal

International Nuclear Information System (INIS)

Liu Xiaodong; Luo Taian; Zhu Guoping; Chen Qingchun

2007-12-01

Systematic studies including mineral composition and structure, physico- chemical properties and thermal properties have been conducted on Gaomiaozi bentonite, Xinghe County, Inner Mongolia Autonomous Region. The compaction characteristics of bentonite and the influence of additive to bentonite have been discussed. The analysis of mineral composition and structure show that the bentonite ores are dominated by montmorillonite. Preliminary studies of the characteristics of ores indicated that No-type bentonite from the deposit has good absorption, excellent swelling and high cation exchangeability. The compressibility of bentonite will be improved by adding the additives such as quartz sand. The studies indicated that the characteristics of Gaomiaozi bentonite can satisfy the requirement of buffer/backfilling materials for HLW repository and the ores can be selected as the preferential candidate to provide buffer/backfill- ing materials for HLW repository in China. (authors)
Study on the properties of Gaomiaozi bentonite as the buffer/backfilling materials for HLW disposal

Energy Technology Data Exchange (ETDEWEB)

Xiaodong, Liu [East China Inst. of Technology, Fuzhou (China); [Key Laboratory of Nuclear Resources and Environment of Ministry of Education, Fuzhou (China); Taian, Luo; Guoping, Zhu; Qingchun, Chen [East China Inst. of Technology, Fuzhou (China)

2007-12-15

Systematic studies including mineral composition and structure, physico- chemical properties and thermal properties have been conducted on Gaomiaozi bentonite, Xinghe County, Inner Mongolia Autonomous Region. The compaction characteristics of bentonite and the influence of additive to bentonite have been discussed. The analysis of mineral composition and structure show that the bentonite ores are dominated by montmorillonite. Preliminary studies of the characteristics of ores indicated that No-type bentonite from the deposit has good absorption, excellent swelling and high cation exchangeability. The compressibility of bentonite will be improved by adding the additives such as quartz sand. The studies indicated that the characteristics of Gaomiaozi bentonite can satisfy the requirement of buffer/backfilling materials for HLW repository and the ores can be selected as the preferential candidate to provide buffer/backfill- ing materials for HLW repository in China. (authors)
bentonite-sand mixture as new backfill/buffer material

International Nuclear Information System (INIS)

Cui Suli; Liu Jisheng; Zhang Huyuan; Liang Jian

2008-01-01

The mixture of bentonite and quartz sand is suggested as a new backfill/buffer material for geological disposal of HLW. To improve the further design of underground laboratory and in-situ industrial construction test, the optimization of sand addition to bentonite is focused at present research stage. Based on summarizing the research results abroad, laboratory tests were conducted on the mixture of GMZ001 bentonite and quartz sand, such as compaction test and swelling tests etc. Test data shows that GMZ bentonite-sand mixture exhibits a favorite compaction with a 30% sand addition, a highest swelling pressure with a 20% sand addition, and a decreasing plasticity with increases in sand addition and pore liquid concentration. (authors)
The Community project on engineering aspects of backfilling and sealing of radioactive waste repositories

International Nuclear Information System (INIS)

Lake, L.M.; Bennett, A.

1987-01-01

This report summarizes the work carried out under CEC contracts about engineering aspects of backfilling and sealing of radioactive waste repositories, for the time period 1983-84. It complements a previous report (ref. EUR 9283) on the same topic, this latter covering the period 1980-82
Utilization of Foaming Technology in Cemented Paste Backfill of High-Mud Superfine Unclassified Tailings

Directory of Open Access Journals (Sweden)

Jian-wen Zhao

2017-01-01

Full Text Available Due to high-mud content in superfine unclassified tailings (SUT, the viscosity of cemented paste backfill (CPB is high and its pipeline transportation properties are poor. Foaming technology was introduced to prepare a new three-phase flow backfill (TFB using a foaming machine. Then the rheological parameters of TFB with different bubble ratio were measured and their pipeline transportation properties were simulated by Fluent. Besides, the simulation results were further verified by a semi-industrial loop test. The results indicate that the optimum ratio of TFB is a cement-sand ratio of 1 : 8, mass concentration of 70%, and bubble ratio of 20%. Compared with CPB, the decrease of bleeding rate, viscosity, and resistance loss of TFB is 27%, 25%, and 30%, respectively. Therefore, foaming technology is an innovative and feasible solution for high-mud CPB in reducing viscosity, decreasing resistance loss, and improving pipeline transporting efficiency.
Properties of backfilling material for solidifying miscellaneous waste using recycled cement from waste concrete

International Nuclear Information System (INIS)

Matsuda, Atsuo; Yamamoto, Kazuo; Konishi, Masao; Iwamoto, Yoshiaki; Yoshikane, Toru; Koie, Toshio; Nakashima, Yoshio.

1997-01-01

A large reduction of total radioactive waste is expected, if recycled cement from the waste concrete of decommissioned nuclear power plants would be able to be used the material for backfilling mortar among the miscellaneous waste. In this paper, we discuss the hydration, strength and consistency of recycled cement compared with normal portland cement. The strength of recycled cement mortar is lower than that of normal portland cement mortar on the same water to cement ratio. It is possible to obtain the required strength to reduce the water to cement ratio by using of high range water-reducing AE agent. According to reducing of water to cement ratio, the P-type funnel time of mortar increase with the increase of its viscosity. However, in new method of self-compactability for backfilling mortar, it became evident that there was no difference between the recycled cement and normal portland cement on the self-compactability. (author)
Retention Capability of Local Backfill Materials 1-Simulated Disposal Environment

International Nuclear Information System (INIS)

Ghattas, N.K.; Eskander, S.B.; El-Adham, K.A.; Mahmoud, N.S.

2001-01-01

In Egypt, a shallow ground disposal facility was the chosen option for the disposal of low and and intermediate radioactive wastes. The impact of the waste disposal facility on the environment depends on the nature of the barriers, which intend to limit and control contaminant migration. Owing to their physical, chemical and mechanical characteristics. Local soil materials were studied to illustrate the role of the back fill as part of an optimized safety multi-barrier system, which can provide the required level of protection of the environment and meet economic and regulatory requirements. A theoretical model was proposed to calculate the transport phenomena through the backfill materials. The credibility and validity of the proposed model was checked by the experimental results obtained from a three-arms arrangement system. The obtained data for the distribution coefficient (K d ) and the apparent diffusion coefficient (D a ) were in good agreement with those previously obtained in the literatures. Taking in consideration the prevailing initial conditions, the data calculated by the theoretical model applied show a reasonable agreement with the results obtained from experimental work. Prediction of radioactive cesium migration through the backfill materials using the proposed model was performed as a function of distance. The results obtained show that after 100 years, a fraction not exceeding 1E-9 of the original activity could be detected at 1m distance away from the waste material
Understanding the Alteration of Bentonite Backfill Using Coupled THMC Modeling for a Long Term Heater Test at the Grimsel Underground Research Lab

Science.gov (United States)

Birkholzer, J. T.; Zheng, L.; Xu, H.; Rutqvist, J.

2017-12-01

Compacted bentonite is commonly used as backfill material in emplacement tunnels of nuclear waste repositories because of its low permeability, high swelling pressure, and retardation capacity of radionuclide. To assess whether this backfill material can maintain these favorable features when undergoing heating from the waste package and hydration from the host rock, we need a thorough understanding of the thermal, hydrological, mechanical, and chemical evolution of bentonite under disposal conditions. Dedicated field tests integrated with THMC modeling provide an effective way to deepen such understanding. Here, we present coupled THMC models for an in situ heater test which was conducted at the Grimsel Test Site in Switzerland for 18 years. The comprehensive monitoring data obtained in the test provide a unique opportunity to evaluate bentonite integrity and test coupled THMC models. We developed a modeling strategy where conceptual model complexity is increased gradually by adding/testing processes such as Non-Darcian flow, enhanced vapor diffusion, thermal osmosis and different constitutive relationships for permeability/porosity changes due to swelling. The final THMC model explains well all the THM data and the concentration profiles of conservative chemical species. Over the course of modeling the in situ test, we learned that (1) including Non-Darcian flow into the model leads to a significant underestimation of hydration rate of bentonite, (2) chemical data provide an important additional piece of information for calibrating a THM model; (3) key processes needed to reproduce the data include vapor diffusion, as well as porosity and permeability changes due to swelling and thermal osmosis; (4) the concentration profiles of cations (calcium, potassium, magnesium and sodium) were largely shaped by transport processes despite their concentration levels being affected by mineral dissolution/precipitation and cation exchange. The concentration profiles of p
DUSCOBS - a depleted-uranium silicate backfill for transport, storage, and disposal of spent nuclear fuel

International Nuclear Information System (INIS)

Forsberg, C.W.; Pope, R.B.; Ashline, R.C.; DeHart, M.D.; Childs, K.W.; Tang, J.S.

1995-01-01

A Depleted Uranium Silicate COntainer Backfill System (DUSCOBS) is proposed that would use small, isotopically-depleted uranium silicate glass beads as a backfill material inside storage, transport, and repository waste packages containing spent nuclear fuel (SNF). The uranium silicate glass beads would fill all void space inside the package including the coolant channels inside SNF assemblies. Based on preliminary analysis, the following benefits have been identified. DUSCOBS improves repository waste package performance by three mechanisms. First, it reduces the radionuclide releases from SNF when water enters the waste package by creating a local uranium silicate saturated groundwater environment that suppresses (1) the dissolution and/or transformation of uranium dioxide fuel pellets and, hence, (2) the release of radionuclides incorporated into the SNF pellets. Second, the potential for long-term nuclear criticality is reduced by isotopic exchange of enriched uranium in SNF with the depleted uranium (DU) in the glass. Third, the backfill reduces radiation interactions between SNF and the local environment (package and local geology) and thus reduces generation of hydrogen, acids, and other chemicals that degrade the waste package system. In addition, the DUSCOBS improves the integrity of the package by acting as a packing material and ensures criticality control for the package during SNF storage and transport. Finally, DUSCOBS provides a potential method to dispose of significant quantities of excess DU from uranium enrichment plants at potential economic savings. DUSCOBS is a new concept. Consequently, the concept has not been optimized or demonstrated in laboratory experiments
Effects of water inflow and early water uptake on buffer and backfill materials in a KBS-3V repository

International Nuclear Information System (INIS)

Boergesson, L.; Sanden, T.; Dueck, A.; Nilsson, U.; Goudarzi, R.; Andersson, L.; Jensen, V.

2012-01-01

Document available in extended abstract form only. Bentonite is an excellent sealing material when it has reached full water saturation and swelling pressure. However, bentonite is not good for sealing inflowing water from fractures with potential to build high water pressure. It cannot stop inflow of water at the depth of a repository. The water inflow into the pellets filled slots in the deposition holes and the tunnels in a KBS-3V repository is expected to continue until these slots are water filled and the water flow stopped by an end plug. Then the water pressure gradient is transferred from the fracture/bentonite interface to the plug and the bentonite will have time to homogenize and seal. This scenario leads to a number of processes that can either be harmful to the bentonite or affect the water saturation and homogenization evolution. Last year a project (EVA) started in order to investigate the processes involved by this early water inflow. The project aims at developing a model for the processes piping, erosion, water filling of pellets filled slots, early water absorption and resulting water pressure increase against the plug. The project studies the effects of water inflow in deposition holes and deposition tunnels and the emergence of piping and erosion during installation and wetting of the buffer and backfill until all slots and the pellet fillings have been water filled and piping and erosion have ceased. The project includes laboratory tests of nine different processes and modeling. The laboratory program includes tests of the following processes: 1. Erosion; 2. Piping; 3. Water flow in pellet filled slots; 4. Sealing ability of bentonite; 5. Water absorption of the bentonite blocks; 6. Formation of water or gel pockets in a pellet filled slot; 7. Formation and outflow of bentonite gel; 8. Self-sealing of cracks by eroding water; 9. Buffer swelling before placement of backfill. The laboratory tests are ongoing and preliminary results and
The behaviour of cemented backfill and the surrounding rockmass at western deep levels south mine

CSIR Research Space (South Africa)

York, G

1992-11-01

Full Text Available Cemented backfill is used at Western Deep Mine as local and regional support areas of high stopping width. The in situ performance is reported and compared to laboratory tests. A back analysis was carried out to obtain a more accurate value...
Optimization of backfill pellet properties AASKAR DP2 - Laboratory tests

Energy Technology Data Exchange (ETDEWEB)

Andersson, Linus; Sanden, Torbjoern [Clay Technology AB, Lund (Sweden)

2012-12-15

Bentonite pellets are planned to be used as a part of the backfill in the Swedish spent nuclear fuel deep repository concept KBS-3. This report describes testing and evaluation of different backfill pellet candidates. The work completed included testing of both pellet material and pellet type. The materials tested were sourced from India (ASHA), Greece (IBECO, 2 products) and Wyoming USA (MX-80 clay). The majority of the tests were completed on the ASHA clay as well as the IBECO-RWC-BF products, with only limited testing of the others. The pellets tested were manufactured using both extrusion and roller compaction techniques and had different sizes and geometries. The following tests have been performed and are presented in this report: 1. General tests. Water content, bulk density and dry density have been determined for both the pellet filling and the individual pellets. The compressibility of the pellet filling was tested with CRS-tests and the strength of the individual pellets was tested with a special compression test. The water content varied from 11.3% to 18.7% and was highest for the extruded pellets. The dry density was somewhat higher for the roller-compacted pellets and their compressibility was lower. The strength of the individual pellets was generally higher for the extruded pellets. 2. Erosion. The pellet filling will be exposed to groundwater inflow when installed in the tunnel. This flow could possibly cause significant erosion on the pellet filling. Erosion tests have been performed with comparisons in erosion resistance made on the various material- and pellet-types. The influence of variations in water salinity and flow rates was also tested. The IBECO extruded 6- and 10- mm diameter rods and the compacted Posiva spec.-A pellet filling seem to have the lowest tendency to erode. It is also the IBECO extruded pellet filling that withstands variations in water salinity and flow rates best. 3. Water storing capacity. The pellet filling
The influence of the presence of sulphate on methanogenesis in the backfill of a Canadian nuclear fuel waste disposal vault: a laboratory study

International Nuclear Information System (INIS)

Sheppard, M.I.; Stroes-Gascoyne, S.; Motycka, M.; Haveman, S.A.

1997-09-01

Microbial gas production in the clay-based buffer and backfill materials of a nuclear waste disposal vault could produce gas bubbles or a separate gas phase, depending on quantities produced and the kinetics of the process. Gas production may affect the performance of the clay-based barriers. Results from previous laboratory experiments suggested that the presence of backfill or backfill clay prevented methane production in groundwater systems, likely because of inherently high sulphate concentrations in the clay. The work presented here shows that methane production in groundwater/clay systems is possible, but only at sulphate concentrations <35 mg/L. Sulphate concentrations in laboratory systems were lowered by the addition of Ba, and also by natural (microbiological or chemical) processes occurring over time (almost 700 d). Nutrient additions (acetate, diesel fuel) appeared to increase the magnitude of methane production but not necessarily speed the onset of methanogenesis. A high pH did not reduce or enhance methanogenesis, and the role of Fe in creating suitable conditions was not clear. Methane production rates in laboratory systems containing groundwater and backfill or backfill clay ranged from 0.1 to 0.125 mole%/d. In the presence of Ba-acetate, a rate as high as 0.7 mole%/d was observed. It is recommended that all microbial gas production experiments be continued for an adequate period of time, because of the considerable time required to develop suitable conditions for methanogenesis in laboratory systems. Methane production rates in water-limited clay environments, such as those expected in a nuclear fuel waste disposal vault, are needed as well as modelling of methane production for incorporation into vault performance optimization and safety assessments. (author)
Thermo-Hydraulic Modelling of Buffer and Backfill

International Nuclear Information System (INIS)

Pintado, X.; Rautioaho, E.

2013-09-01

The temporal evolution of saturation, liquid pressure and temperature in the components of the engineered barrier system was studied using numerical methods. A set of laboratory tests was conducted to calibrate the parameters employed in the models. The modelling consisted of thermal, hydraulic and thermo-hydraulic analysis in which the significant thermo-hydraulic processes, parameters and features were identified. CODE B RIGHT was used for the finite element modelling and supplementary calculations were conducted with analytical methods. The main objective in this report is to improve understanding of the thermo-hydraulic processes and material properties that affect buffer behaviour in the Olkiluoto repository and to determine the parametric requirements of models for the accurate prediction of this behaviour. The analyses consisted of evaluating the influence of initial canister temperature and gaps in the buffer, and the role played by fractures and the rock mass located between fractures in supplying water for buffer and backfill saturation. In the thermo-hydraulic analysis, the primary processes examined were the effects of buffer drying near the canister on temperature evolution and the manner in which heat flow affects the buffer saturation process. Uncertainties in parameters and variations in the boundary conditions, modelling geometry and thermo-hydraulic phenomena were assessed with a sensitivity analysis. The material parameters, constitutive models, and assumptions made were carefully selected for all the modelling cases. The reference parameters selected for the simulations were compared and evaluated against laboratory measurements. The modelling results highlight the importance of understanding groundwater flow through the rock mass and from fractures in the rock in order to achieve reliable predictions regarding buffer saturation, since saturation times could range from a few years to tens of thousands of years depending on the hydrogeological
Principles of electron tunneling spectroscopy

CERN Document Server

Wolf, E L

2012-01-01

Electron tunnelling spectroscopy as a research tool has strongly advanced understanding of superconductivity. This book explains the physics and instrumentation behind the advances illustrated in beautiful images of atoms, rings of atoms and exotic states in high temperature superconductors, and summarizes the state of knowledge that has resulted.
Presentation of Austrians recommended dispersion model for tunnel portals

Energy Technology Data Exchange (ETDEWEB)

Oettl, D.; Sturm, P.; Almbauer, R. [Inst. for Internal Combustion Engines and Thermodynamics, Graz Univ. of Technology (Austria)

2004-07-01

Street tunnels in cities are often suggested as solution to avoid daily congestions but also to prevent residential areas from high noise and air pollution emissions. In case of longitudinal ventilated tunnels high pollution levels may occur in the vicinity of the portals. The dispersion of pollutants from tunnel portals is considered to differ significantly from those of other sources, such as line or point sources. To the best of the authors knowledge, there exist currently two distinct dispersion models, which are especially designed to treat dispersion from tunnel portals. Okamoto et al proposed a diagnostic wind field model, where the dispersion is modelled using a Taylor-Galerkin-Forester filter method. Oettl et al. developed a Lagrangian-type model (GRAL TM 3.5=Graz Lagrangian model Tunnel Module version 3.5), which is briefly described in the next section. (orig.)

Tunneling technologies for the collider ring tunnels

International Nuclear Information System (INIS)

Frobenius, P.

1989-01-01

The Texas site chosen for the Superconducting Super Collider has been studied, and it has been determined that proven, conventional technology and accepted engineering practice are suitable for constructing the collider tunnels. The Texas National Research Laboratory Commission report recommended that two types of tunneling machines be used for construction of the tunnels: a conventional hard rock tunnel boring machine (TBM) for the Austin chalk and a double shielded, rotary TBM for the Taylor marl. Since the tunneling machines usually set the pace for the project, efficient planning, operation, and coordination of the tunneling system components will be critical to the schedule and cost of the project. During design, tunneling rate prediction should be refined by focusing on the development of an effective tunneling system and evaluating its capacity to meet or exceed the required schedules. 8 refs., 13 figs
Preparation of fly ash-granulated blast furnace slag-carbide slag binder and application in total tailings paste backfill

Science.gov (United States)

Li, Chao; Hao, Ya-fei; Zhao, Feng-qing

2018-03-01

Based on activation and synergistic effect among various materials, a low-cost mine backfill cementing material, FGC binder, was prepared by using fly ash, granulated blast-furnace slag (GBFS), carbide slag and composite activator. The proper proportioning of FGC binder is obtained by response surface experiment optimization method: fly ash 62 %, GBFS 20 %, carbide slag 8 % and compound activators 10 %. Adjusting the material ratio obtains different cementing material which could satisfy requirements of different mined-out areas. With the mass ratio of cementing material and tailings 1:4∼1:8, the concentration of total solid 70 %, the compressive strength values of total tailings filling body at 28 d reaches 1.64∼4.14 MPa, and the backfilling cost is 20 % lower than using OPC cement.
The influence of the presence of sulphate on methanogenesis in the backfill of a Canadian nuclear fuel waste disposal vault: a laboratory study

Energy Technology Data Exchange (ETDEWEB)

Sheppard, M I; Stroes-Gascoyne, S; Motycka, M; Haveman, S A

1997-09-01

Microbial gas production in the clay-based buffer and backfill materials of a nuclear waste disposal vault could produce gas bubbles or a separate gas phase, depending on quantities produced and the kinetics of the process. Gas production may affect the performance of the clay-based barriers. Results from previous laboratory experiments suggested that the presence of backfill or backfill clay prevented methane production in groundwater systems, likely because of inherently high sulphate concentrations in the clay. The work presented here shows that methane production in groundwater/clay systems is possible, but only at sulphate concentrations <35 mg/L. Sulphate concentrations in laboratory systems were lowered by the addition of Ba, and also by natural (microbiological or chemical) processes occurring over time (almost 700 d). Nutrient additions (acetate, diesel fuel) appeared to increase the magnitude of methane production but not necessarily speed the onset of methanogenesis. A high pH did not reduce or enhance methanogenesis, and the role of Fe in creating suitable conditions was not clear. Methane production rates in laboratory systems containing groundwater and backfill or backfill clay ranged from 0.1 to 0.125 mole%/d. In the presence of Ba-acetate, a rate as high as 0.7 mole%/d was observed. It is recommended that all microbial gas production experiments be continued for an adequate period of time, because of the considerable time required to develop suitable conditions for methanogenesis in laboratory systems. Methane production rates in water-limited clay environments, such as those expected in a nuclear fuel waste disposal vault, are needed as well as modelling of methane production for incorporation into vault performance optimization and safety assessments. (author) 30 refs., 6 tabs., 27 figs.
Lidars for Wind Tunnels - an IRPWind Joint Experiment Project

DEFF Research Database (Denmark)

Sjöholm, Mikael; Vignaroli, Andrea; Angelou, Nikolas

2017-01-01

Measurement campaigns with continuous-wave Doppler Lidars (Light detection and ranging) developed at DTU Wind Energy in Denmark were performed in two very different wind tunnels. Firstly, a measurement campaign in a small icing wind tunnel chamber at VTT in Finland was performed with high frequency...... used in blind test comparisons for wind turbine wake modelers. These Lidar measurement activities constitute the Joint Experiment Project” L4WT - Lidars for Wind Tunnels, with applications to wakes and atmospheric icing in a prospective Nordic Network” with the aim of gaining and sharing knowledge...... about possibilities and limitations with lidar instrumentation in wind tunnels, which was funded by the IRPWind project within the community of the European Energy Research Alliance (EERA) Joint Programme on Wind Energy....
ENGINEERING GEOLOGY PROPERTIES OF 'KONJSKO' TUNNEL

Directory of Open Access Journals (Sweden)

Ivan Grabovac

2004-12-01

Full Text Available Investigation works for the design of the Konjsko Tunnel with two pipes, part of the Split-Zagreb Motorway, provided relevant data on rock mass and soil properties for construction of the prognose engineering-geological longitudinal sections. West tunnel portals are situated in tectonically deformed and partly dynamically metamorphosed Eocene flysch marls, while east ones are located in Senonian limestones. There is an overthrust contact between flysch marls and limestones. With the beginning of the excavations, rock mass characteristics were regularly registered after each blasting and actual longitudinal engineering-geological cross-sections were constructed as well as cross-sections of the excavation face. There were some differences between prognosticated and registered sections since it was infeasible to accurately determine the dip of the overthrust plane that was at shallow depth below the tunnel grade line and also due to the occurrence of transversal faults that intersected the overthrust. Data collected before and during the tunnel construction complemented the knowledge on geological structure of the surroundings and physical-mechanical characteristics of strata (the paper is published in Croatian.
Fire Resistant Panels for the Tunnel Linings

Directory of Open Access Journals (Sweden)

Gravit Marina

2016-01-01

Full Text Available Presents the results of studies of innovative materials in the field of experimental and theoretical research fire resistance fireproof panels Pyro-Safe Aestuver T. Owing to the assembly simplicity, materials cheapness, high ecological standard, recycling, reuse potential, are benefit. Research work is running to improve the knowledge about fireproof panels Pyro-Safe Aestuver T for tunnel lining, its basic performance, its long term behavior and in particular also its fire proof for example when used for the lining of road tunnels.
Concepts for backfilling and sealing of shafts

International Nuclear Information System (INIS)

Pierau, B.

1990-01-01

The disposal site is situated at a depth of 1000 to 1200 meters. It is covered by very thick cretatious mudstone layers forming the main barrier against the spread of radioactively contaminated water into the biosphere. Because of the excavation works and the resulting stress redistributions, the material surrounding the shafts is probably broken up, which leads to increased permeability in comparison with the intact rock. It is planned to backfill the shafts with an insoluble mineral mixture including a fine fraction necessary to achieve the sealing required. The joints and cracks in the brocken-up surrounding material are believed to be sealed by themselves due to swelling of the mudstone. Some strata of the mudstone contain more than 20% of smektite, a swelling clay mineral. Those regions, where the broken-up zone cannot be considered sure to self-seal due to swelling, are planned to be sealed by pressure grouting using clay suspension. (orig./HP) [de
SR-Site Data report. THM modelling of buffer, backfill and other system components

Energy Technology Data Exchange (ETDEWEB)

Aakesson, Mattias; Boergesson, Lennart; Kristensson, Ola (Clay Technology AB, Lund (Sweden))

2010-03-15

This report is a supplement to the SR-Site data report. Based on the issues raised in the Process reports concerning THM processes in buffer, backfill and other system components, 22 modelling tasks have been identified, representing different aspects of the repository evolution. The purpose of this data report is to provide parameter values for the materials included in these tasks. Two codes, Code{_}Bright and Abaqus, have been employed for the tasks. The data qualification has focused on the bentonite material for buffer, backfill and the seals for tunnel plugs and bore-holes. All these system components have been treated as if they were based on MX-80 bentonite. The sources of information and documentation of the data qualification for the parameters for MX-80 have been listed. A substantial part of the refinement, especially concerning parameters used for Code{_}Bright, is presented in the report. The data qualification has been performed through a motivated and transparent chain; from measurements, via evaluations, to parameter determinations. The measured data was selected to be as recent, traceable and independent as possible. The data sets from this process are thus regarded to be qualified. The conditions for which the data is supplied, the conceptual uncertainties, the spatial and temporal variability and correlations are briefly presented and discussed. A more detailed discussion concerning the data uncertainty due to precision, bias and representativity is presented for measurements of swelling pressure, hydraulic conductivity, shear strength, retention properties and thermal conductivity. The results from the data qualification are presented as a detailed evaluation of measured data. In order to strengthen the relevance of the parameter values and to confirm previously used relations, either newer or independent measurements have been taken into account in the parameter value evaluation. Previously used relations for swelling pressure, hydraulic
SR-Site Data report. THM modelling of buffer, backfill and other system components

International Nuclear Information System (INIS)

Aakesson, Mattias; Boergesson, Lennart; Kristensson, Ola

2010-03-01

This report is a supplement to the SR-Site data report. Based on the issues raised in the Process reports concerning THM processes in buffer, backfill and other system components, 22 modelling tasks have been identified, representing different aspects of the repository evolution. The purpose of this data report is to provide parameter values for the materials included in these tasks. Two codes, Code B right and Abaqus, have been employed for the tasks. The data qualification has focused on the bentonite material for buffer, backfill and the seals for tunnel plugs and bore-holes. All these system components have been treated as if they were based on MX-80 bentonite. The sources of information and documentation of the data qualification for the parameters for MX-80 have been listed. A substantial part of the refinement, especially concerning parameters used for Code B right, is presented in the report. The data qualification has been performed through a motivated and transparent chain; from measurements, via evaluations, to parameter determinations. The measured data was selected to be as recent, traceable and independent as possible. The data sets from this process are thus regarded to be qualified. The conditions for which the data is supplied, the conceptual uncertainties, the spatial and temporal variability and correlations are briefly presented and discussed. A more detailed discussion concerning the data uncertainty due to precision, bias and representativity is presented for measurements of swelling pressure, hydraulic conductivity, shear strength, retention properties and thermal conductivity. The results from the data qualification are presented as a detailed evaluation of measured data. In order to strengthen the relevance of the parameter values and to confirm previously used relations, either newer or independent measurements have been taken into account in the parameter value evaluation. Previously used relations for swelling pressure, hydraulic
Tibial tunnel and pretibial cysts following ACL graft reconstruction: MR imaging diagnosis

Energy Technology Data Exchange (ETDEWEB)

Ghazikhanian, Varand [Brigham and Women' s Hospital, Musculoskeletal Imaging and Intervention, Department of Radiology, Boston, MA (United States); Beltran, Javier [Maimonides Medical Center, Brooklyn, NY (United States); Nikac, Violeta [Maimonides Medical Center, Department of Radiology, Brooklyn, NY (United States); Bencardino, Jenny T. [NYU Hospital for Joint Diseases, New York, NY (United States); Feldman, Marina

2012-11-15

Tunnel cyst formation is a rare complication after anterior cruciate ligament reconstruction, usually occurring 1-5 years post-operatively, which may occasionally be symptomatic. There are multiple proposed theories regarding the etiology of tunnel cysts. Theories include necrosis, foreign-body reaction, lack of complete graft osteo-integration, and intravasation of articular fluid. It is important to know if the tunnel cysts are communicating or not communicating with the joint, as surgical management may be different. Imaging characteristics on magnetic resonance images (MRI) include tibial tunnel widening, multilocular or unilocular cyst formation in the graft or tibial tunnel, with possible extension into the pretibial space, intercondylar notch, and/or popliteal fossa. The MR imaging differential diagnosis of tibial tunnel cysts includes infection, foreign-body granuloma, or tibial screw extrusion. Importantly, to the best of our knowledge, graft failure or instability has not been reported in association with tibial tunnel cysts. (orig.)
Mechanical and thermo-mechanical analyses of the tapered plug for plugging of deposition tunnels. A feasibility study

Energy Technology Data Exchange (ETDEWEB)

Faelth, Billy (Clay Technology AB, Lund (Sweden)); Gatter, Patrik (Vattenfall Power Consultant AB, Stockholm (Sweden))

2009-09-15

This report presents results from a study that was carried out in order to examine the applicability of the tapered plug concept for plugging of deposition tunnels in the deep repository for spent nuclear fuel. The report presents results from mechanical and thermo-mechanical models of the tapered plug. The models were analyzed with 3DEC. The models included a portion of a deposition tunnel and its intersection with a main tunnel. In the deposition tunnel, a tapered concrete plug was installed. The plug was subjected to the combined load from the swelling backfill material and from pore pressure inside the deposition tunnel. The thermo-mechanical effects due to the heat generation in the spent fuel were also included in the analyses. Generic material parameter values for the concrete were used. The following items were studied: - Stresses and displacements in the plug. - Shear stresses and shear displacements in the rock-concrete interface. - Stress additions in the rock due to the loads. The sensitivity of the results to changes of constitutive models, to changes of the plug geometry and to pore water pressure in the rock-concrete interface was examined. The results indicate that the displacements in the plug will be within reasonable ranges but the stresses may locally be high enough that they exceed acceptable levels. However, they can be reduced by choice of advantageous plug geometry and by having a good rock-concrete bond. The results also show that the stress additions in the rock due to the thermal load may yield stresses that locally exceed the spalling strength of the rock. At most locations, however, the rock stresses will amount at lower levels. It was concluded that, with choice of an appropriate design, the tapered plug seems to be an applicable concept for plugging of deposition tunnels. It was also concluded that further studies of the tapered plug concept should use material properties parameter values for low-pH concrete. Further, they should also
Radionuclide sorption and migration studies of getters for backfill barriers

International Nuclear Information System (INIS)

Nowak, E.J.

1980-07-01

Bentonite and hectorite clay minerals were chosen for study and development as potential backfill materials for testing in the proposed Waste Isolation Pilot Plant (WIPP), a radioactive waste repository and test facility in bedded salt. This choice of materials was based on initial screening results which are presented and on the predicted physical properties of these materials. These properties were verified experimentally in concentrated brines specific to the WIPP site. Distribution coefficients, K/sub d/, were calculated from batch sorption measurements on bentonite and hectorite in the nearly saturated brines A and B. The resulting K/sub d/ values were in the range of (1 to 5) x 10 3 ml/g for europium; (2 to 40) x 10 3 ml/g for plutonium(IV); and (4 to 16) x 10 3 ml/g for americium(III). A silica- and calcite-containing sand mixed with bentonite and hectorite acted as a sorber of americium(III) but was merely an inert diluent for plutonium(IV). Pertechnetate anions (TcO 4 - ) sorbed on activated charcoal with K/sub d/ values in the range of (0.2 to 0.4) x 10 3 ml/g. Pertechnetate, cesium, and strontium ions in brine were not sorbed appreciably by bentonite or hectorite. Although experimental evidence is given for a possible role of solubility in the sorption of europium on getters, other data presented here and evidence from the literature are inconsistent with a simple single reaction sorption mechanism. It is concluded that a backfill containing bentonite on hectorite and activated charcoal is potentially an effective barrier to the migration of Eu(III), Pu(IV), and Am(III) cations and, with further development, to the migration of TcO 4 - anions as well
Use of the mixture of clay and crushed rock as a backfill material for low and intermediate level radioactive waste repository. Appendix 10: Republic of Korea

International Nuclear Information System (INIS)

Cho, W.J.; Lee, J.O.; Hahn, P.S.; Chun, K.S.

2001-01-01

At the time of the CRP, a repository for low and intermediate level radioactive wastes arising from nuclear power plant operation and radioisotope application in the Republic of Korea was to be constructed in the bedrock below ground surface. As the intermediate level waste cavern would contain the major part of radionuclide inventory in the cavern, the radionuclide release from the intermediate level waste cavern was therefore important from the viewpoint of disposal facility performance. The then current design concept suggested that the intermediate level waste would be emplaced into the compartment made of reinforced concrete, and the space between the concrete wall and cavern surface would be backfilled with a clay-based material. As compacted clay-based materials have a low hydraulic conductivity and the hydraulic gradient in a disposal cavern was expected to be relatively low, molecular diffusion was considered to be the principal mechanism by which radionuclides would migrate through the backfill. The mixture of calcium bentonite and crushed rock was being suggested as a candidate backfill material. This appendix summarises the KAERI research activities on the evaluation of hydraulic conductivity, radionuclide diffusion coefficient, and mechanical properties of the candidate clay-based backfill material for the intermediate level waste cavern
Evaluation of pre-jamming indication parameter during blind backfilling technique

Directory of Open Access Journals (Sweden)

Susmita Panda

2016-01-01

Full Text Available Hydraulic blind backfilling is used to reduce subsidence problems above old underground water-logged coal mines. This paper describes experimental research on a fully transparent model of a straight underground mine gallery. An automatic data acquisition system was installed in the model to continuously record the sand and water flowrates along with the inlet pressure of the slurry near the model's inlet. Pressure signature graphs and pressure loss curves with bed advancement under different flow conditions are examined. Pressure signature analyses for various flowrates and sand slurry concentrations are conducted to evaluate a pre-jamming indication parameter, which could be used to indicate the arrival of the final stage of filling.
Evaluation of backfill materials for a shallow-depth repository

International Nuclear Information System (INIS)

Buckley, L.P.; Arbique, G.M.; Tosello, N.B.; Woods, B.L.

1986-11-01

The focus of laboratory research effort on the disposal of low- and intermediate-level radioactive waste is to determine what conditions will dominate and which engineered barriers will be most effective for the retention of radionuclides. Initial studies have concentrated on the evaluation of a flooded repository and the assessment of backfill materials suitable for the adsorption of radioactivity, yet permeable enough to allow excess water to pass through the repository and into the underlying water table. Both physical and adsorption studies have been performed. Based on these preliminary experiments, it is felt that a mixture of 10 wt% clay and the remainder sand would satisfy the above criteria. Since both are available within the Ottawa Valley, they also have the added advantage of being more cost effective to use than imported materials
Retardation of uranium and thorium by a cementitious backfill developed for radioactive waste disposal.

Science.gov (United States)

Felipe-Sotelo, M; Hinchliff, J; Field, L P; Milodowski, A E; Preedy, O; Read, D

2017-07-01

The solubility of uranium and thorium has been measured under the conditions anticipated in a cementitious, geological disposal facility for low and intermediate level radioactive waste. Similar solubilities were obtained for thorium in all media, comprising NaOH, Ca(OH) 2 and water equilibrated with a cement designed as repository backfill (NRVB, Nirex Reference Vault Backfill). In contrast, the solubility of U(VI) was one order of magnitude higher in NaOH than in the remaining solutions. The presence of cellulose degradation products (CDP) results in a comparable solubility increase for both elements. Extended X-ray Absorption Fine Structure (EXAFS) data suggest that the solubility-limiting phase for uranium corresponds to a becquerelite-type solid whereas thermodynamic modelling predicts a poorly crystalline, hydrated calcium uranate phase. The solubility-limiting phase for thorium was ThO 2 of intermediate crystallinity. No breakthrough of either uranium or thorium was observed in diffusion experiments involving NRVB after three years. Nevertheless, backscattering electron microscopy and microfocus X-ray fluorescence confirmed that uranium had penetrated about 40 μm into the cement, implying active diffusion governed by slow dissolution-precipitation kinetics. Precise identification of the uranium solid proved difficult, displaying characteristics of both calcium uranate and becquerelite. Copyright © 2017 Elsevier Ltd. All rights reserved.
Field and laboratory investigations on pavement backfilling material for micro-trenching in cold regions

OpenAIRE

Leila Hashemian; Mohammad Rezaei; Alireza Bayat

2017-01-01

Micro-trenching is an innovative utility installation method that involves creating a narrow trench to place cable or conduit in the road pavement. Compared to other installation methods, micro-trenching provides minimal disturbance to the community and surrounding environment. Despite the advantages of micro-trenching, it is not widely accepted by municipalities because of its potential to damage the existing pavement. Quality of backfilling is an important factor in long-term sustainability...
Backfilling with mixtures of bentonite/ballast materials or natural smectitic clay?

International Nuclear Information System (INIS)

Pusch, R.

1998-10-01

Comparison of the performance of backfills of mixed MX-80 and crushed rock ballast, and a natural smectitic clay, represented by the German Friedland clay, shows that the latter performs better than mixtures with up to 30 % MX-80. Considering cost, Friedland clay prepared to yield air-dry powder grains is cheaper than mixtures of 30 % MX-80 and crushed ballast. Both technically and economically it appears that the Friedland clay is a competitive alternative to mixtures of 30 % MX-80 and crushed ballast. However, it remains to be demonstrated on a full scale that Friedland clay ground to a suitable grain size distribution can be acceptably compacted on site
Thermo-mechanical analysis for determining the optimum design of a deposition hole using FLAC3D

International Nuclear Information System (INIS)

Kwon, Sang Ki; Park, Jeong Hwa; Choi, Jong Won; Kang, Chul Hyung

2002-01-01

In this study, the vertical location of canister in a deposition hole was determined from the thermo-mechanical coupling analysis using the three-dimensional finite difference code, FLAC3D. A FISH program was made and used for the modeling for different conditions. The following conclusions could be drawn from the study. (1) The canister moves downward initially, but moves upward with time due to the thermal expansion of buffer. (2) The tunnel floor above the deposition hole remains elastic until 100 years after the emplacement of the canister if the top buffer thickness is more than 1.5 m. (3) It was found that the peak temperature decreases with the increase of the buffer and backfill thickness, when backfilling is done immediately after the emplacement. (4) Without swelling pressure, the maximum tensile stress is up to 18 MPa at 100 days after the emplacement. Since the swelling pressure from the buffer confines the thermal expansion of the canister, the mechanical stability of canister is improved with the swelling pressure. (5) When the air temperature in the tunnels is maintained at 27 .deg. C by ventilation, the peak temperature with delayed backfilling for 50 years is about 75 .deg. while it is over 90 .deg. with immediately backfilling. (6) The buffer and backfill thickness above the canister in a deposition hole should be at least 2 m based on literature review and the computer simulations
Preliminary design of the repository. Stage 2

International Nuclear Information System (INIS)

Saanio, T.; Kirkkomaeki, T.; Keto, P.; Kukkola, T.; Raiko, H.

2007-04-01

Spent nuclear fuel from Finnish nuclear power plants will be disposed of in deep bedrock in Olkiluoto, Eurajoki. The repository is planned to be excavated at a depth of 400 - 500 metres. Access routes to the repository include a 1:10 inclined access tunnel, and vertical shafts. The fuel is encapsulated in the encapsulation plant above ground and transferred to the repository in the canister lift. Deposition tunnels, central tunnels and technical rooms are excavated at the disposal level. The canisters are deposited in deposition holes that are covered with bentonite blocks. The deposition holes are bored in the floors of the deposition tunnels. The central tunnel system consists of two parallel central tunnels that are inter-connected at certain distances. Two parallel central tunnels improve the fire safety of the rooms and also allow flexible backfilling and closing of the deposition tunnels in stages at the operational phase of the repository. An underground rock characterization facility, ONKALO, is excavated at the disposal level to support and confirm investigations carried out from above ground. ONKALO is designed so that it can later serve as part of the repository. ONKALO excavations were started in 2004. The repository will be excavated in the 2010s and operation will start in 2020. The fifth nuclear power unit makes the operational phase of the repository very long. Parts of the repository will be excavated and closed over the long operational period. The repository can be constructed at one or several levels. The one-storey alternative is the so-called reference alternative in this preliminary design report. The two-storey alternative is also taken into account in the ONKALO designs. The preliminary designs of the repository are presented as located in Olkiluoto. The location of the repository will be revised when more information on the bedrock has been gained. More detailed data of the circumstances will be obtained from above ground investigations

Preliminary design of the repository, stage 2

International Nuclear Information System (INIS)

Saanio, T.; Kirkkomaeki, T.; Keto, P.; Kukkola, T.; Raiko, H.

2007-01-01

Spent nuclear fuel from Finnish nuclear power plants will be disposed of in deep bedrock in Olkiluoto, Eurajoki. The repository is planned to be excavated at a depth of 400 - 500 metres. Access routes to the repository include a 1:10 inclined access tunnel, and vertical shafts. The fuel is encapsulated in the encapsulation plant above ground and transferred to the repository in the canister lift. Deposition tunnels, central tunnels and technical rooms are excavated at the disposal level. The canisters are deposited in deposition holes that are covered with bentonite blocks. The deposition holes are bored in the floors of the deposition tunnels. The central tunnel system consists of two parallel central tunnels that are inter-connected at certain distances. Two parallel central tunnels improve the fire safety of the rooms and also allow flexible backfilling and closing of the deposition tunnels in stages at the operational phase of the repository. An underground rock characterization facility, ONKALO, is excavated at the disposal level to support and confirm investigations carried out from above ground. ONKALO is designed so that it can later serve as part of the repository. ONKALO excavations were started in 2004. The repository will be excavated in the 2010s and operation will start in 2020. The fifth nuclear power unit makes the operational phase of the repository very long. Parts of the repository will be excavated and closed over the long operational period. The repository can be constructed at one or several levels. The one-storey alternative is the so-called reference alternative in this preliminary design report. The two-storey alternative is also taken into account in the ONKALO designs. The preliminary designs of the repository are presented as located in Olkiluoto. The location of the repository will be revised when more information on the bedrock has been gained. More detailed data of the circumstances will be obtained from above ground investigations
Tunnel - history of

International Nuclear Information System (INIS)

1998-11-01

This book introduces history of tunnel in ancient times, the middle ages and modern times, survey of tunnel and classification of bedrock like environment survey of position, survey of the ground, design of tunnel on basic thing of the design, and design of tunnel of bedrock, analysis of stability of tunnel and application of the data, construction of tunnel like lattice girder and steel fiber reinforced shot crete, and maintenance control and repair of tunnel.
Typical Underwater Tunnels in the Mainland of China and Related Tunneling Technologies

Directory of Open Access Journals (Sweden)

Kairong Hong

2017-12-01

Full Text Available In the past decades, many underwater tunnels have been constructed in the mainland of China, and great progress has been made in related tunneling technologies. This paper presents the history and state of the art of underwater tunnels in the mainland of China in terms of shield-bored tunnels, drill-and-blast tunnels, and immersed tunnels. Typical underwater tunnels of these types in the mainland of China are described, along with innovative technologies regarding comprehensive geological prediction, grouting-based consolidation, the design and construction of large cross-sectional tunnels with shallow cover in weak strata, cutting tool replacement under limited drainage and reduced pressure conditions, the detection and treatment of boulders, the construction of underwater tunnels in areas with high seismic intensity, and the treatment of serious sedimentation in a foundation channel of immersed tunnels. Some suggestions are made regarding the three potential great strait-crossing tunnels—the Qiongzhou Strait-Crossing Tunnel, Bohai Strait-Crossing Tunnel, and Taiwan Strait-Crossing Tunnel—and issues related to these great strait-crossing tunnels that need further study are proposed. Keywords: Underwater tunnel, Strait-crossing tunnel, Shield-bored tunnel, Immersed tunnel, Drill and blast
Manufacturing and performance of customized pellets used for buffer and backfill sealing in nuclear waste containment

International Nuclear Information System (INIS)

Holt, Erika; Marjavaara, Pieti; Man, Alex; Kim, Chang-Seok; Dixon, David

2012-01-01

Document available in extended abstract form only. Bentonite pellets are proposed for use in filling gaps between highly compacted bentonite and the surrounding rock walls. Previous studies typically focused on using commercially available bentonite pellets with good performance results typically being achieved but no comprehensive evaluations were undertaken. This paper summarizes the results of two recent studies completed on gap filling materials and customized pellets that were intended to see to what degree improvement of the pellet materials and placement density could be achieved and what this would mean to system behaviour. Although the joint project covered a wide range of potential materials and sealing applications, in this presentation, the focus is on the use of bentonite filling material in the outer gap between the rock surface and large highly-compacted bentonite buffer blocks used in Posiva's Reference vertical deposition design. The gap between the deposition hole's wall and the buffer is 50 mm, which should be filled with material prior to tunnel backfilling. The required dry density of the outer gap filling is 920 kg/m 3 , with an average buffer dry density of 1600 kg/m 3 at 100% saturation. At these densities, the thermal, hydraulic and mechanical behaviour of the system meet the requirements set for them. In the first part of this study, various types of commercially-available bentonite granular materials were used alone or in combination with finer material. Different placement methods were used to fill vertical gaps of either 25 or 35 mm width in a small-scale experimental mock-up. The sizes of the rectangular gap mock-up elements used in these tests were approximately 1 m in height and 2 m long. The results from the small scale tests suggest that all the filling materials and methods used during the test would achieve as-placed dry density of 800-1200 kg/m 3 , depending on material and placement method used. The lowest values were noted
Direct, coherent and incoherent intermediate state tunneling and scanning tunnel microscopy (STM)

International Nuclear Information System (INIS)

Halbritter, J.

1997-01-01

Theory and experiment in tunneling are still qualitative in nature, which hold true also for the latest developments in direct-, resonant-, coherent- and incoherent-tunneling. Those tunnel processes have recently branched out of the field of ''solid state tunnel junctions'' into the fields of scanning tunnel microscopy (STM), single electron tunneling (SET) and semiconducting resonant tunnel structures (RTS). All these fields have promoted the understanding of tunneling in different ways reaching from the effect of coherence, of incoherence and of charging in tunneling, to spin flip or inelastic effects. STM allows not only the accurate measurements of the tunnel current and its voltage dependence but, more importantly, the easy quantification via the (quantum) tunnel channel conductance and the distance dependence. This new degree of freedom entering exponentially the tunnel current allows an unique identification of individual tunnel channels and their quantification. In STM measurements large tunnel currents are observed for large distances d > 1 nm explainable by intermediate state tunneling. Direct tunneling with its reduced tunnel time and reduced off-site Coulomb charging bridges distances below 1 nm, only. The effective charge transfer process with its larger off-site and on-site charging at intermediate states dominates tunnel transfer in STM, biology and chemistry over distances in the nm-range. Intermediates state tunneling becomes variable range hopping conduction for distances larger than d > 2 nm, for larger densities of intermediate states n 1 (ε) and for larger temperatures T or voltages U, still allowing high resolution imaging
Initial field testing definition of subsurface sealing and backfilling tests in unsaturated tuff

International Nuclear Information System (INIS)

Fernandez, J.A.; Case, J.B.; Tyburski, J.R.

1993-05-01

This report contains an initial definition of the field tests proposed for the Yucca Mountain Project repository sealing program. The tests are intended to resolve various performance and emplacement concerns. Examples of concerns to be addressed include achieving selected hydrologic and structural requirements for seals, removing portions of the shaft liner, excavating keyways, emplacing cementitious and earthen seals, reducing the impact of fines on the hydraulic conductivity of fractures, efficient grouting of fracture zones, sealing of exploratory boreholes, and controlling the flow of water by using engineered designs. Ten discrete tests are proposed to address these and other concerns. These tests are divided into two groups: Seal component tests and performance confirmation tests. The seal component tests are thorough small-scale in situ tests, the intermediate-scale borehole seal tests, the fracture grouting tests, the surface backfill tests, and the grouted rock mass tests. The seal system tests are the seepage control tests, the backfill tests, the bulkhead test in the Calico Hills unit, the large-scale shaft seal and shaft fill tests, and the remote borehole sealing tests. The tests are proposed to be performed in six discrete areas, including welded and non-welded environments, primarily located outside the potential repository area. The final selection of sealing tests will depend on the nature of the geologic and hydrologic conditions encountered during the development of the Exploratory Studies Facility and detailed numerical analyses. Tests are likely to be performed both before and after License Application
SORPTION AND DISPERSION OF STRONTIUM RADIONUCLIDE IN THE BENTONITE-QUARTZ-CLAY AS BACKFILL MATERIAL CANDIDATE ON RADIOACTIVE WASTE REPOSITORY

Directory of Open Access Journals (Sweden)

Herry Poernomo

2010-12-01

Full Text Available The experiment of sorption and dispersion characteristics of strontium in the mixture of bentonite-quartz, clay-quartz, bentonite-clay-quartz as candidate of raw material for backfill material in the radioactive waste repository has been performed. The objective of this research is to know the grain size effect of bentonite, clay, and quartz on the weight percent ratio of bentonite to quartz, clay to quartz, bentonite to clay to-quartz can be gives physical characteristics of best such as bulk density (rb, effective porosity (e, permeability (K, best sorption characteristic such as distribution coefficient (Kd, and best dispersion characteristics such as dispersivity (a and effective dispersion coefficient (De of strontium in the backfill material candidate. The experiment was carried out in the column filled by the mixture of bentonite-quartz, clay-quartz, bentonite-clay-quartz with the weight percent ratio of bentonite to quartz, clay to quartz, bentonite to clay to quartz of 100/0, 80/20, 60/40, 40/60, 20/80, 0/100 respectively at saturated condition of water, then flowed 0.1 N Sr(NO32 as buffer solution with tracer of 0.05 Ci/cm3 90Sr as strontium radionuclide simulation was leached from immobilized radioactive waste in the radioactive waste repository. The concentration of 90Sr in the effluents represented as Ct were analyzed by Ortec b counter every 30 min, then by using profile concentration of Co and Ct, values of Kd, a and De of 90Sr in the backfill material was determined. The experiment data showed that the best results were -80+120 mesh grain size of bentonite, clay, quartz respectively on the weight percent ratio of bentonite to clay to quartz of 70/10/20 with physical characteristics of rb = 0.658 g/cm3, e = 0.666 cm3/cm3, and K = 1.680x10-2 cm/sec, sorption characteristic of Kd = 46.108 cm3/g, dispersion characteristics of a = 5.443 cm, and De = 1.808x10-03 cm2/sec can be proposed as candidate of raw material of backfill material
Basic characteristic test of buffer/backfill material under Horonobe groundwater condition

International Nuclear Information System (INIS)

Kikuchi, Hirohito; Tanai, Kenji

2005-02-01

By the second progress report (H12) on research and development for the geological disposal of high-level radioactive waste (HLW) in Japan, Japan Nuclear Cycle Development Institute (JNC) extended the data base of basic properties of compacted bentonite which were mainly obtained by using distilled water as test fluid. This report presents influence of Horonobe groundwater on the basic properties of buffer and backfill material. The Horonobe groundwater is a type of saline groundwater. The groundwater was sampled at GL-300 m or deeper by using bore hole HDB-6 of the underground laboratory of Horonobe site. In addition, basic properties are also obtained by using distilled water, synthetic seawater, and NaCl solution. Experimental results are as follows; 1) Swelling characteristics, hydraulic characteristics and mechanical characteristics of the buffer material and backfill material decrease by the influence of saline water. The relationship between effective clay density and swelling stress is described by the following equation. σ = exp (2.5786ρ b 3 - 12.238ρ b 2 + 21.818ρ b - 14.035) where σ is swelling stress [MPa], ρ b is effective clay density [Mg/m 3 ]. The relationship between effective clay density and intrinsic permeability is described by the following equation. κ = exp (-41.466 + 4.316ρ b - 4.069ρ b 2 ) where κ is intrinsic permeability [m 2 ], ρ b is effective clay density [Mg/m 3 ]. The relationship between effective clay density and unconfined compressive strength is described by the following equation. qu = 1.4 x 10 -4 exp (5.637ρ b ) where qu is unconfined compressive strength [MPa], ρ b is effective clay density [Mg/m 3 ]. 2) Saline water doesn't influence the thermal characteristic of the buffer material. The thermal conductivity and specific heat are derived by using the relationship that was obtained so far. (author)
Backfilling with mixtures of bentonite/ballast materials or natural smectitic clay?

Energy Technology Data Exchange (ETDEWEB)

Pusch, R. [Geodevelopment AB, (Sweden)

1998-10-01

Comparison of the performance of backfills of mixed MX-80 and crushed rock ballast, and a natural smectitic clay, represented by the German Friedland clay, shows that the latter performs better than mixtures with up to 30 % MX-80. Considering cost, Friedland clay prepared to yield air-dry powder grains is cheaper than mixtures of 30 % MX-80 and crushed ballast. Both technically and economically it appears that the Friedland clay is a competitive alternative to mixtures of 30 % MX-80 and crushed ballast. However, it remains to be demonstrated on a full scale that Friedland clay ground to a suitable grain size distribution can be acceptably compacted on site 14 refs, 32 figs, 6 tabs
Low pH self compacting concrete for deposition tunnel plugs

International Nuclear Information System (INIS)

Vogt, Carsten; Lagerblad, Bjoern; Wallin, Kjell; Baldy, Franziska; Jonasson, Jan-Erik

2009-04-01

The temporary plugs in the entrance of the deposition tunnel have three purposes, i.e. to bring about a water pressure in the deposition holes as quickly as possible in order to facilitate the wetting of the buffer, to reduce the groundwater's pressure gradient in the backfill so that piping is prevented, and to keep the backfill in place during the operating phase until the main tunnel has been backfilled. In the repository concept, low-pH-concrete shall be used instead of conventional concrete. A low-pH concrete is a concrete with a leachate pH below 11, which is lower than in normal concrete (pH > 12.5). The low-pH concrete developed is achieved by replacing 40% by weight of the cement with silica fume. According to the current understanding, low-pH concrete should not disturb the function of the bentonite. This is accomplished by avoiding the development of a high-pH leachate by replacing leachable calcium compounds with silica in the low-pH-concrete. There are different demands on the concrete in fresh and hardened state in order to fulfil its purpose. The geometry of the plug requires the fresh concrete to be self-compacting. The method of placement requires that the fresh concrete keeps its self-compacting properties for at least two hours. All components of the mix design must be commercially available and it must be possible to produce the concrete in a normal concrete factory. The concrete shall release low exothermic heat during curing. The volume changes of the young and mature concrete shall be minimised. The properties of the young and mature concrete need to be quantified in order to design and construct the plugs so that they fulfil the intended purpose. Low-pH concrete with self-compacting properties has been developed and is presented in the report. The low-pH SCC (Self-Compacting Concrete) contains ordinary Portland cement, densified silica fume, limestone filler, super plasticizer, high quality natural fine aggregates and average quality crushed
Low pH self compacting concrete for deposition tunnel plugs

Energy Technology Data Exchange (ETDEWEB)

Vogt, Carsten; Lagerblad, Bjoern; Wallin, Kjell; Baldy, Franziska (Swedish Cement and Concrete Research Institute, Stockholm (Sweden)); Jonasson, Jan-Erik (Luleaa Univ. of Technology, Luleaa (Sweden))

2009-04-15

The temporary plugs in the entrance of the deposition tunnel have three purposes, i.e. to bring about a water pressure in the deposition holes as quickly as possible in order to facilitate the wetting of the buffer, to reduce the groundwater's pressure gradient in the backfill so that piping is prevented, and to keep the backfill in place during the operating phase until the main tunnel has been backfilled. In the repository concept, low-pH-concrete shall be used instead of conventional concrete. A low-pH concrete is a concrete with a leachate pH below 11, which is lower than in normal concrete (pH > 12.5). The low-pH concrete developed is achieved by replacing 40% by weight of the cement with silica fume. According to the current understanding, low-pH concrete should not disturb the function of the bentonite. This is accomplished by avoiding the development of a high-pH leachate by replacing leachable calcium compounds with silica in the low-pH-concrete. There are different demands on the concrete in fresh and hardened state in order to fulfil its purpose. The geometry of the plug requires the fresh concrete to be self-compacting. The method of placement requires that the fresh concrete keeps its self-compacting properties for at least two hours. All components of the mix design must be commercially available and it must be possible to produce the concrete in a normal concrete factory. The concrete shall release low exothermic heat during curing. The volume changes of the young and mature concrete shall be minimised. The properties of the young and mature concrete need to be quantified in order to design and construct the plugs so that they fulfil the intended purpose. Low-pH concrete with self-compacting properties has been developed and is presented in the report. The low-pH SCC (Self-Compacting Concrete) contains ordinary Portland cement, densified silica fume, limestone filler, super plasticizer, high quality natural fine aggregates and average quality
Monitoring pilot projects on bored tunnelling : The Second Heinenoord Tunnel and the Botlek Rail Tunnel

NARCIS (Netherlands)

Bakker, K.J.; De Boer, F.; Admiraal, J.B.M.; Van Jaarsveld, E.P.

1999-01-01

Two pilot projects for bored tunnelling in soft soil have been undertaken in the Netherlands. The monitoring was commissioned under the authority of the Centre for Underground Construction (COB). A description of the research related to the Second Heinenoord Tunnel and the Botlek Rail Tunnel will be
BEHAVIOUR OF BACKFILL MATERIALS FOR ELECTRICAL GROUNDING SYSTEMS UNDER HIGH VOLTAGE CONDITIONS

Directory of Open Access Journals (Sweden)

S. C. LIM

2015-06-01

Full Text Available Backfill materials like Bentonite and cement are effective in lowering grounding resistance of electrodes for a considerable period. During lightning, switching impulses and earth fault occurrences in medium and high voltage networks, the grounding system needs to handle extremely high currents either for a short duration or prolonged period respectively. This paper investigates the behaviour of bentonite, cement and sand under impulse and alternating high voltage (50Hz conditions. Fulguritic-formation was observed in all materials under alternating high voltage. The findings reveal that performance of grounding systems under high voltage conditions may significantly change from the outcomes anticipated at design stage.
The solubility of nickel and its migration through the cementitious backfill of a geological disposal facility for nuclear waste.

Science.gov (United States)

Felipe-Sotelo, M; Hinchliff, J; Field, L P; Milodowski, A E; Holt, J D; Taylor, S E; Read, D

2016-08-15

This work describes the solubility of nickel under the alkaline conditions anticipated in the near field of a cementitious repository for intermediate level nuclear waste. The measured solubility of Ni in 95%-saturated Ca(OH)2 solution is similar to values obtained in water equilibrated with a bespoke cementitious backfill material, on the order of 5×10(-7)M. Solubility in 0.02M NaOH is one order of magnitude lower. For all solutions, the solubility limiting phase is Ni(OH)2; powder X-ray diffraction and scanning transmission electron microscopy indicate that differences in crystallinity are the likely cause of the lower solubility observed in NaOH. The presence of cellulose degradation products causes an increase in the solubility of Ni by approximately one order of magnitude. The organic compounds significantly increase the rate of Ni transport under advective conditions and show measurable diffusive transport through intact monoliths of the cementitious backfill material. Copyright © 2016 Elsevier B.V. All rights reserved.
A study of the operational logistics in the disposal plant for spent nuclear fuel

International Nuclear Information System (INIS)

Sylvaenne, O.; Kaskinen, T.; Kuussaari, P.

2003-02-01

The final disposal plant for spent nuclear fuel comprises an encapsulation facility that will be built on the surface, other support activities above ground, and a repository that will be constructed deep in the bedrock. This report analyses the final repository operational logistics. The desktop research report is compiled of data taken from several existing planning reports covering the planning periods 1997-2002. The logistics specialised description of the final repository considers most areas in the daily operation of the facility. Among these are: Disposal tunnel excavation; construction and transports; Tunnel preparation for canisters; Reception of spent nuclear fuel transport casks; Encapsulation process; Preparation of bentonite blocks for canister holes, block laying; Final disposal of canisters; and Preparation of backfilling material and backfilling. The transport and handling volumes have certain cycles. Rock will be excavated during one contiguous period in 3 years, backfilling takes two weeks in a month and the deposition of canisters also two weeks. Thus the material flows vary greatly due to their cyclical nature. The transport and handling volumes are considerable, by far largest single item being excavated rock with about 5000 annual truck loads during the active excavation period, backfilling is about 1300 loads yearly at a steady pace. The report covers and summarises material flows, handling methods and equipment, buffering, storage and transports. It suggests some changes to operational procedures. Proposals have been made as to the location of the encapsulation facility and the methods of material transport. The logistical 'hot' issues, entry of the main transport ramp, rock field, rock crushing process, bentonite storage, bentonite brick production and backfiller production are all proposed to be located close to each other to minimise driving distance. It has also been proposed that the bentonite block buffer should rather be located at
Active Thrust on an Inclined Retaining Wall with Inclined Cohesionless Backfill due to Surcharge Effect

OpenAIRE

Dewaikar, D. M.; Pandey, S. R.; Dixit, Jagabandhu

2012-01-01

A method based on the application of Kötter’s equation is proposed for the complete analysis of active thrust on an inclined wall with inclined cohesionless backfill under surcharge effect. Coulomb’s failure mechanism is considered in the analysis. The point of application of active thrust is determined from the condition of moment equilibrium. The coefficient of active pressure and the point of application of the active thrust are computed and presented in nondimensional form. One distinguis...
In-vehicle nitrogen dioxide concentrations in road tunnels

Science.gov (United States)

Martin, Ashley N.; Boulter, Paul G.; Roddis, Damon; McDonough, Liza; Patterson, Michael; Rodriguez del Barco, Marina; Mattes, Andrew; Knibbs, Luke D.

2016-11-01

There is a lack of knowledge regarding in-vehicle concentrations of nitrogen dioxide (NO2) during transit through road tunnels in urban environments. Furthermore, previous studies have tended to involve a single vehicle and the range of in-vehicle NO2 concentrations that vehicle occupants may be exposed to is not well defined. This study describes simultaneous measurements of in-vehicle and outside-vehicle NO2 concentrations on a route through Sydney, Australia that included several major tunnels, minor tunnels and busy surface roads. Tests were conducted on nine passenger vehicles to assess how vehicle characteristics and ventilation settings affected in-vehicle NO2 concentrations and the in-vehicle-to-outside vehicle (I/O) concentration ratio. NO2 was measured directly using a cavity attenuated phase shift (CAPS) technique that gave a high temporal and spatial resolution. In the major tunnels, transit-average in-vehicle NO2 concentrations were lower than outside-vehicle concentrations for all vehicles with cabin air recirculation either on or off. However, markedly lower I/O ratios were obtained with recirculation on (0.08-0.36), suggesting that vehicle occupants can significantly lower their exposure to NO2 in tunnels by switching recirculation on. The highest mean I/O ratios for NO2 were measured in older vehicles (0.35-0.36), which is attributed to older vehicles having higher air exchange rates. The results from this study can be used to inform the design and operation of future road tunnels and modelling of personal exposure to NO2.
Backfilling and sealing of repositories and access shafts and galleries in clay, granite and salt formations

International Nuclear Information System (INIS)

Lake, L.M.; Davies, I.L.; Gera, F.; Jorda, M.; McEwen, T.; Neerdael, B.; Schmidt, M.W.

1985-01-01

The paper summarizes the work carried out under ten Commission contracts in the field of backfilling and sealing radioactive waste repositories. It covers theoretical, laboratory and field trials and experiments involving three potential host types, namely clay, salt and hard rock. It concludes that maximum opportunity should be taken over the next 15 to 25 years with a view to obtaining first hand experience in real ground with real wastes
Tunnel magnetoresistance in asymmetric double-barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Useinov, N.Kh.; Petukhov, D.A.; Tagirov, L.R.

2015-01-01

The spin-polarized tunnel conductance and tunnel magnetoresistance (TMR) through a planar asymmetric double-barrier magnetic tunnel junction (DBMTJ) have been calculated using quasi-classical model. In DBMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. The transmission coefficients of an electron to pass through the barriers have been calculated in terms of quantum mechanics. The dependencies of tunnel conductance and TMR on the applied voltage have been calculated in case of non-resonant transmission. Estimated in the framework of our model, the difference between the spin-channels conductances at low voltages was found relatively large. This gives rise to very high magnitude of TMR. - Highlights: • The spin-polarized conductance through the junction is calculated. • Dependencies of the tunnel conductance vs applied bias are shown. • Bias voltage dependence of tunnel magnetoresistance for the structure is shown
Laboratory determination of migration of Eu(III) in compacted bentonite–sand mixtures as buffer/backfill material for high-level waste disposal

International Nuclear Information System (INIS)

Zhou, Lang; Zhang, Huyuan; Yan, Ming; Chen, Hang; Zhang, Ming

2013-01-01

For the safety assessment of geological disposal of high-level radioactive waste (HLW), the migration of Eu(III) through compacted bentonite–sand mixtures was measured under expected repository conditions. Under the evaluated conditions, advection and dispersion is the dominant migration mechanism. The role of sorption on the retardation of migration was also evaluated. The hydraulic conductivities of compacted bentonite–sand mixtures were K=2.07×10 −10 –5.23×10 −10 cm/s, The sorption and diffusion of Eu(III) were examined using a flexible wall permeameter for a solute concentration of 2.0×10 −5 mol/l. The effective diffusion coefficients and apparent diffusion coefficients of Eu(III) in compacted bentonite–sand mixtures were in the range of 1.62×10 –12 –4.87×10 –12 m 2 /s, 1.44×10 –14 –9.41×10 –14 m 2 /s, respectively, which has a very important significance to forecast the relationship between migration length of Eu(III) in buffer/backfill material and time and provide a reference for the design of buffer/backfill material for HLW disposal in China. - Highlights: • The migration progress of Eu(III) in compacted bentonite–sand mixtures was researched. • The hydraulic conductivity of cominpacted bentonite–sand mixtures was measured. • The migration length of Eu(III) in buffer/backfill material after a certain period of time was forecasted

Testing the frost resistance of backfilling materials for geothermal heat probes; Pruefung der Frostbestaendigkeit von Verfuellmassen fuer Erdwaermesonden

Energy Technology Data Exchange (ETDEWEB)

Mueller, Tobias; Schnell, Kurt [HDG Umwelttechnik GmbH, Kisslegg (Germany)

2011-07-01

Groundwater protection, general operational safety and the reliable operation over many years are the key factors in the use of geothermal probes. Backfilling materials with which probes are pressed in the hole meet these requirements. For several years, manufacturers and researchers devote a great attention to the issue of an adequate freeze-thaw resistance of these components.
Sandstone uranium deposits of Meghalaya: natural analogues for radionuclide migration and backfill material in geological repository for high level radioactive waste disposal

International Nuclear Information System (INIS)

Bajpai, R.K.; Narayan, P.K.

2008-01-01

Sandstone uranium deposits serve as potential natural analogue to demonstrate safety offered by geological media against possible release of nuclear waste from their confinement and migration towards biosphere. In this study, available database on geochemical aspects of Domisiat uranium deposit of Meghalaya has been evaluated to highlight the behavior of radionuclides of concern over long term in a geological repository. Constituents like actinides (U and Th), fission products and RE elements are adequately retained in clays and organic matters associated with these sandstone deposits. The study also highlights the possibility of utilization of lean ore discarded during mining and milling as backfill material in far field areas and optimizing near field buffers/backfills in a geological repository located in granitic rocks in depth range of 400-500m. (author)
Study of Scanning Tunneling Microscope control electronics

International Nuclear Information System (INIS)

Oliva, A.J.; Pancarobo, M.; Denisenko, N.; Aguilar, M.; Rejon, V.; Pena, J.L.

1994-01-01

A theoretical study of Scanning Tunneling Microscope control electronics is made. The knowledge of its behaviour allows us to determine accurately the region where the unstable operation could effect the measurements, and also to set the optimal working parameters. Each feedback circuitry compound is discussed as well as their mutual interaction. Different working conditions analysis and results are presented. (Author) 12 refs
Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

Energy Technology Data Exchange (ETDEWEB)

Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P. [Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau 91767 (France); Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Xavier, S. [Thales Research and Technology, 1 avenue Augustin Fresnel, Palaiseau 91767 (France)

2016-03-07

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.
Variability in ACL tunnel placement: observational clinical study of surgeon ACL tunnel variability.

Science.gov (United States)

Wolf, Brian R; Ramme, Austin J; Wright, Rick W; Brophy, Robert H; McCarty, Eric C; Vidal, Armando R; Parker, Richard D; Andrish, Jack T; Amendola, Annunziato

2013-06-01

Multicenter and multisurgeon cohort studies on anterior cruciate ligament (ACL) reconstruction are becoming more common. Minimal information exists on intersurgeon and intrasurgeon variability in ACL tunnel placement. Purpose/ The purpose of this study was to analyze intersurgeon and intrasurgeon variability in ACL tunnel placement in a series of The Multicenter Orthopaedic Outcomes Network (MOON) ACL reconstruction patients and in a clinical cohort of ACL reconstruction patients. The hypothesis was that there would be minimal variability between surgeons in ACL tunnel placement. Cross-sectional study; Level of evidence, 3. Seventy-eight patients who underwent ACL reconstruction by 8 surgeons had postoperative imaging with computed tomography, and ACL tunnel location and angulation were analyzed using 3-dimensional surface processing and measurement. Intersurgeon and intrasurgeon variability in ACL tunnel placement was analyzed. For intersurgeon variability, the range in mean ACL femoral tunnel depth between surgeons was 22%. For femoral tunnel height, there was a 19% range. Tibial tunnel location from anterior to posterior on the plateau had a 16% range in mean results. There was only a small range of 4% for mean tibial tunnel location from the medial to lateral dimension. For intrasurgeon variability, femoral tunnel depth demonstrated the largest ranges, and tibial tunnel location from medial to lateral on the plateau demonstrated the least variability. Overall, surgeons were relatively consistent within their own cases. Using applied measurement criteria, 85% of femoral tunnels and 90% of tibial tunnels fell within applied literature-based guidelines. Ninety-one percent of the axes of the femoral tunnels fell within the boundaries of the femoral footprint. The data demonstrate that surgeons performing ACL reconstructions are relatively consistent between each other. There is, however, variability of average tunnel placement up to 22% of mean condylar depth
Interaction between groundwater and TBM (Tunnel Boring Machine) excavated tunnels

OpenAIRE

Font Capó, Jordi

2012-01-01

A number of problems, e.g. sudden inflows are encountered during tunneling under the piezometric level, especially when the excavation crosses high transmissivity areas. These inflows may drag materials when the tunnel crosses low competent layers, resulting in subsidence, chimney formation and collapses. Moreover, inflows can lead to a decrease in head level because of aquifer drainage. Tunnels can be drilled by a tunnel boring machine (TBM) to minimize inflows and groundwater impacts, restr...
Tunnel conductance of Watson-Crick nucleoside-base pairs from telegraph noise

International Nuclear Information System (INIS)

Chang Shuai; He Jin; Lin Lisha; Zhang Peiming; Liang Feng; Huang Shuo; Lindsay, Stuart; Young, Michael

2009-01-01

The use of tunneling signals to sequence DNA is presently hampered by the small tunnel conductance of a junction spanning an entire DNA molecule. The design of a readout system that uses a shorter tunneling path requires knowledge of the absolute conductance across base pairs. We have exploited the stochastic switching of hydrogen-bonded DNA base-nucleoside pairs trapped in a tunnel junction to determine the conductance of individual molecular pairs. This conductance is found to be sensitive to the geometry of the junction, but a subset of the data appears to come from unstrained molecular pairs. The conductances determined from these pairs are within a factor of two of the predictions of density functional calculations. The experimental data reproduces the counterintuitive theoretical prediction that guanine-deoxycytidine pairs (3 H-bonds) have a smaller conductance than adenine-thymine pairs (2 H-bonds). A bimodal distribution of switching lifetimes shows that both H-bonds and molecule-metal contacts break.
Repository for spent nuclear fuel. Plant description layout D - Forsmark; Slutfoervarsanlaeggning foer anvaent kaernbraensle. Anlaeggningsbeskrivning layout D - Forsmark

Energy Technology Data Exchange (ETDEWEB)

2010-07-15

This document describes the final repository for spent nuclear fuel, SFK, which is located at Forsmark, in Oesthammar. The bedrock at the site is part of a so-called tectonic lens, in which the rock composition is relatively homogeneous and less deformed than outside the lens. The bedrock consists mainly of granite with high quartz content and good thermal conductivity. The central parts above ground are grouped in an operations area, located at the Soederviken on the south side of the intake duct for cooling water for nuclear power plant. Operating area is divided into an internal, secured portion, where the canisters of fuel are handled and there are links to the underground part, and a outer part, where the buffer, backfill and sealing used in the repository's barriers are produced. The above-ground part of the plant and also include storage of excavated rock, ventilation stations, and supplies of bentonite. The underground portion consists of a central area and a storage area. Caverns of the central area contain features for the underground operation. It communicates with the internal operating range above ground via a spiral ramp and several shafts. The ramp used to transport capsules of spent fuel and other heavy or bulky transport. The shafts are used to transport rock, buffer, backfill and staff, as well as for ventilation. The largest part of the space below ground is the repository where the canisters with the spent fuel are disposed. The capsules are deposited in vertical holes in the tunnels. When the deposit in a tunnel is complete, the tunnel is re-filled. The two main activities underground is rock work and disposal work, which are conducted separately from each other. Rock works covers all steps required to excavate tunnels and drill deposition holes, as well as to make temporary installations in the tunnels. To the landfill works count, besides the deposit of the capsule, the placement of the bentonite buffer in the deposition hole and
Repository for spent nuclear fuel. Plant description layout D - Forsmark

International Nuclear Information System (INIS)

2010-07-01

This document describes the final repository for spent nuclear fuel, SFK, which is located at Forsmark, in Oesthammar. The bedrock at the site is part of a so-called tectonic lens, in which the rock composition is relatively homogeneous and less deformed than outside the lens. The bedrock consists mainly of granite with high quartz content and good thermal conductivity. The central parts above ground are grouped in an operations area, located at the Soederviken on the south side of the intake duct for cooling water for nuclear power plant. Operating area is divided into an internal, secured portion, where the canisters of fuel are handled and there are links to the underground part, and a outer part, where the buffer, backfill and sealing used in the repository's barriers are produced. The above-ground part of the plant and also include storage of excavated rock, ventilation stations, and supplies of bentonite. The underground portion consists of a central area and a storage area. Caverns of the central area contain features for the underground operation. It communicates with the internal operating range above ground via a spiral ramp and several shafts. The ramp used to transport capsules of spent fuel and other heavy or bulky transport. The shafts are used to transport rock, buffer, backfill and staff, as well as for ventilation. The largest part of the space below ground is the repository where the canisters with the spent fuel are disposed. The capsules are deposited in vertical holes in the tunnels. When the deposit in a tunnel is complete, the tunnel is re-filled. The two main activities underground is rock work and disposal work, which are conducted separately from each other. Rock works covers all steps required to excavate tunnels and drill deposition holes, as well as to make temporary installations in the tunnels. To the landfill works count, besides the deposit of the capsule, the placement of the bentonite buffer in the deposition hole and backfilling
Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

International Nuclear Information System (INIS)

Parui, Subir; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger; Bedoya-Pinto, Amilcar; Sun, Xiangnan; Casanova, Fèlix; Hueso, Luis E.

2016-01-01

The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al 2 O 3 /NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.
Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Parui, Subir, E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Bedoya-Pinto, Amilcar [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Max Planck Institute of Microstructure Physics, D-06120 Halle (Germany); Sun, Xiangnan [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); National Center for Nanoscience and Technology, 100190 Beijing (China); Casanova, Fèlix; Hueso, Luis E., E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

2016-08-01

The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al{sub 2}O{sub 3}/NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.
Carpal Tunnel Syndrome

Science.gov (United States)

... a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ... three times more likely to have carpal tunnel syndrome than men. Early diagnosis and treatment are important ...
Theory of superconducting tunneling without the tunneling Hamiltonian

International Nuclear Information System (INIS)

Arnold, G.B.

1987-01-01

When a tunneling barrier is nearly transparent, the standard tunneling (or transfer) Hamiltonian approximation fails. The author describes the theory which is necessary for calculating the tunneling current in these cases, and illustrate it by comparing theory and experiment on superconductor/insulator/superconductor (SIS) junctions have ultra-thin tunnel barriers. This theory accurately explains the subgap structure which appears in the dynamical resistance of such SIS junctions, including many observed details which no previous theory has reproduced. The expression for the current through an SIS junction with an ultrathin barrier is given by I(t) = Re{Sigma/sub n/ J/sub n/ (omega/sub o/)e/sup in omega/o/sup t/} where omega/sub o/ = 2eV/h is the Josephson frequency, V is the bias voltage, and the J/sub n/ are voltage dependent coefficients, one for each positive or negative integer, n, and n=0. The relative sign of the terms involving cos(n omega/sub o/t) and sin(n omega/sub o/t) agrees with experiment, in contrast to previous theories of Josephson tunneling
Tunneling works. Tunnel koji

Energy Technology Data Exchange (ETDEWEB)

Higo, M [Hazam Gumi, Ltd., Tokyo (Japan)

1991-10-25

A mountain tunneling method for rock-beds used to be applied mainly to construction works in the mountains under few restrictions by environmental problems. However, construction works near residential sreas have been increasing. There are such enviromental problems due to tunneling works as vibration, noise, lowering of ground-water level, and influences on other structures. This report mainly describes the measurement examples of vibration and noise accompanied with blasting and the effects of the measures to lessen such influences. When the tunneling works for the railroad was carried out on the natural ground mainly composed of basalt, vibration of the test blasting was measured at three stations with piezoelectric accelerometers. Then, ordinary blasting, mutistage blasting, and ABM blasting methods were used properly besed on the above results, and only a few complaints were made. In the different works, normal noise and low-frequency sound were mesured at 22 stations around the pit mouth. As countermeasures for noise, sound-proof sheets, walls, and single and double doors were installed and foundto be effective. 1 ref., 6 figs., 1 tab.
Project ANSICHT. Final repository concept and backfilling and sealing concept for the final repository site model SUeD; Projekt ANSICHT. Endlagerkonzept sowie Verfuell- und Verschlusskonzept fuer das Endlagerstandortmodell SUeD. Technischer Bericht

Energy Technology Data Exchange (ETDEWEB)

Jobmann, Michael; Lommerzheim, Andree

2015-08-03

In the frame of ANSICHT the methodology for the demonstration of safe enclosure for high-level heat generating radioactive wastes is described. The report is based on the safety requirements for final repository concepts and shows a first backfilling and sealing concept that was developed for the final repository site model SUeD. The final repository model SUeD is based on a horizontal line storage concept, the Gorleben (VSG) and ERATO container concept and the mine layout were adopted and adapted to the given conditions. The backfill and sealing concept includes migration barriers, line closures and shaft closures in the frame of a redundant and diverse enclosure system. For all technical and geotechnical barrier components the long-term functional requirements were defined. The backfilling concept of underground cavities considers the variety of possible cavities in the line and infrastructure areas.
Tunneling junction as an open system. Normal tunneling

International Nuclear Information System (INIS)

Ono, Y.

1978-01-01

The method of the tunneling Hamiltonian is reformulated in the case of normal tunneling by introducing two independent particle baths. Due to the baths, it becomes possible to realize a final stationary state where the electron numbers of the two electrodes in the tunneling system are maintained constant and where there exists a stationary current. The effect of the bath-system couplings on the current-voltage characteristics of the junction is discussed in relation to the usual expression of the current as a function of voltage. (Auth.)
Tunneling time, exit time and exit momentum in strong field tunnel ionization

International Nuclear Information System (INIS)

Teeny, Nicolas

2016-01-01

Tunnel ionization belongs to the fundamental processes of atomic physics. It is still an open question when does the electron tunnel ionize and how long is the duration of tunneling. In this work we solve the time-dependent Schroedinger equation in one and two dimensions and use ab initio quantum calculations in order to answer these questions. Additionally, we determine the exit momentum of the tunnel ionized electron from first principles. We find out results that are different from the assumptions of the commonly employed two-step model, which assumes that the electron ionizes at the instant of electric field maximum with a zero momentum. After determining the quantum final momentum distribution of tunnel ionized electrons we show that the two-step model fails to predict the correct final momentum. Accordingly we suggest how to correct the two-step model. Furthermore, we determine the instant at which tunnel ionization starts, which turns out to be different from the instant usually assumed. From determining the instant at which it is most probable for the electron to enter the tunneling barrier and the instant at which it exits we determine the most probable time spent under the barrier. Moreover, we apply a quantum clock approach in order to determine the duration of tunnel ionization. From the quantum clock we determine an average tunneling time which is different in magnitude and origin with respect to the most probable tunneling time. By defining a probability distribution of tunneling times using virtual detectors we relate both methods and explain the apparent discrepancy. The results found have in general an effect on the interpretation of experiments that measure the spectra of tunnel ionized electrons, and specifically on the calibration of the so called attoclock experiments, because models with imprecise assumptions are usually employed in order to interpret experimental results.
Tunneling time, exit time and exit momentum in strong field tunnel ionization

Energy Technology Data Exchange (ETDEWEB)

Teeny, Nicolas

2016-10-18

Tunnel ionization belongs to the fundamental processes of atomic physics. It is still an open question when does the electron tunnel ionize and how long is the duration of tunneling. In this work we solve the time-dependent Schroedinger equation in one and two dimensions and use ab initio quantum calculations in order to answer these questions. Additionally, we determine the exit momentum of the tunnel ionized electron from first principles. We find out results that are different from the assumptions of the commonly employed two-step model, which assumes that the electron ionizes at the instant of electric field maximum with a zero momentum. After determining the quantum final momentum distribution of tunnel ionized electrons we show that the two-step model fails to predict the correct final momentum. Accordingly we suggest how to correct the two-step model. Furthermore, we determine the instant at which tunnel ionization starts, which turns out to be different from the instant usually assumed. From determining the instant at which it is most probable for the electron to enter the tunneling barrier and the instant at which it exits we determine the most probable time spent under the barrier. Moreover, we apply a quantum clock approach in order to determine the duration of tunnel ionization. From the quantum clock we determine an average tunneling time which is different in magnitude and origin with respect to the most probable tunneling time. By defining a probability distribution of tunneling times using virtual detectors we relate both methods and explain the apparent discrepancy. The results found have in general an effect on the interpretation of experiments that measure the spectra of tunnel ionized electrons, and specifically on the calibration of the so called attoclock experiments, because models with imprecise assumptions are usually employed in order to interpret experimental results.
Quantum theory of tunneling

CERN Document Server

Razavy, Mohsen

2014-01-01

In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...
Thermo-mechanical effects from a KBS-3 type repository. Performance of pillars between repository tunnels

International Nuclear Information System (INIS)

Hakami, E.; Olofsson, Stig-Olof

2000-03-01

The aim of this study has been to investigate how the rock mass, in the near field of a KBS-3 type repository, will be affected by the excavation of tunnels and deposition holes and the thermal load from the deposited waste. The three-dimensional finite difference program FLAC 3D was used to perform numerical simulation of the rock mass behaviour. The rock mass was modelled as a homogeneous and isotropic continuum. The initial area heat intensity of the repository was assumed to be 10 W/m 2 in all models. The results show that in the middle of the pillar between the repository tunnels the temperature reaches a maximum of about 70 deg C after 55 years of deposition. The extent of areas where the rock is predicted to yield depends on the assumed quality of the rock mass and the initial in-situ stress field. The volume of yielded rock reaches a maximum after about 200 years after deposition. For a rock mass with internal friction angle of 45 deg and cohesion of 5 MPa (using a Mohr-Coulomb material model), the extent of yielded rock is limited to about 1.5 m behind the excavation periphery. The largest rock displacements are found in the tunnel floor at the upper part of the deposition holes. Tension and shear failure in the periphery of the excavations is predicted to occur during the rock excavation, with a depth extension depending on the magnitude and orientation of the in-situ stresses, as well as on the rock mass quality. Both the excavation effects and the then-no-mechanical effects are smallest when the major principal stress is oriented parallel with the deposition tunnels. The maximum convergence between tunnel walls was calculated to occur after 200 years and be about 9 mm, in the model assuming a rock mass with 5 MPa cohesion, 45 deg internal friction angle and maximum horizontal stress perpendicular to the tunnel. In this study confining effects from the buffer and backfill material was neglected. The effective stress concept was used in most of the models

Performance of backfill materials in near surface disposal facilities for low and intermediate level radwaste. Appendix 4: China (a)

International Nuclear Information System (INIS)

Cunli, G.; Yawen, H.; Zhiwen, F.; Anxi, C.; Xiuzhen, L.; Jinsheng, Z.

2001-01-01

Full text: Backfill material is an important component of a multi-barriered disposal facility for low and intermediate level radioactive waste. This appendix describes the work concerning 'performance study on engineering materials of shallow land disposal of low and intermediate level radwaste'. At the time of the CRP, China had planned to establish five regional disposal sites for low-and-intermediate level radioactive waste. According to the potential distribution of these sites, forty-three sampling points were selected through information survey and table discussion. After field survey and screening, eight of them were selected for further studies in laboratory. Basic physical and chemical properties of each sample were measured in laboratory. The results indicate that no one of the samples can individually function as the backfill material in a multi-barriered near surface facility. Then nine additives for adsorption modification were tested using a static method. Further adsorption tests were conducted: three additives screened out in previous experiment were evaluated using the static method. Results obtained show that the Kd values of mixtures of 90% NW-3 and 10% BC for Co-60, Cs-134 and Sr-85, compared with those of 100% NW-3, are 4.8, 4.6 and 4.7 times higher, respectively. Effects of contact time, pH of tracer solutions and radionuclide concentrations of tracer solutions on Kd values of three samples, NW-3, BC and 90% NW-3 with 10% BC, were also be evaluated using the static method. Column tests were performed to evaluate migration of Co-60, Cs-134 and Sr-85 in NW-3 columns with different densities. The column tests were carried out for 210 days. However, no breakthrough was obtained. Long term performance of backfill materials was assessed through natural analogue. We compared Chinese ancient tombs with near-surface low and intermediate level radioactive waste (LILW) disposal facilities. Both were designed based upon multi-barrier principle. Then three
Reuse of Cement Kiln Dust for backfilling and CO2 carbonation

Directory of Open Access Journals (Sweden)

Lutyński Marcin

2017-01-01

Full Text Available The study aims to investigate possible alternative paths of reusing Cement Kiln Dust in mining technologies or as mineral sorbent for CO2 capture. Properties of CKD and bottom slag slurry were assessed and these were ia.: chemical composition, compressive strength and excess water content. Results show that CKD/bottom slag slurry mixed in the proportion of 25%/75% can be used as a backfill material if concentration of contaminants in the leaching tests is at the acceptable level. Second part of the study was devoted to the assessment of CKD as a sorbent in Calcium looping technologies or for mineral carbonation. TGA and DSC study shows that the rate of CO2 capture (carbonation is determined by the free CaO content. The highest carbonation rate was within the temperature range of 600-800°C.
Development of rock segment for reduction of amount of cement use

International Nuclear Information System (INIS)

Tada, Hiroyuki; Kumasaka, Hiroo; Saito, Akira; Nakaya, Atsushi; Ishii, Takashi; Sanada, Masanori; Noguchi, Akira; Kishi, Hirokazu; Nakama, Shigeo; Fujita, Tomoo

2013-01-01

The authors have been developing methods for constructing tunnels using the minimum quantities of cement-type support materials in high-level radioactive waste disposal facilities and advancing research and development about the technical formation of rock segment using low alkali mortar. In this study, the mechanical characteristic values concerning the rock segment and backfill materials were examined. The stability analysis of drift supported by the rock segment and backfilling with gravel were performed. Technical formation and effectiveness of the support planned for further reduction in cement influence was confirmed from the study result. (author)
Spin-dependent tunnelling in magnetic tunnel junctions

International Nuclear Information System (INIS)

Tsymbal, Evgeny Y; Mryasov, Oleg N; LeClair, Patrick R

2003-01-01

The phenomenon of electron tunnelling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent tunnelling (SDT) in magnetic tunnel junctions (MTJs) has recently aroused enormous interest and has developed in a vigorous field of research. The large tunnelling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible applications in non-volatile random-access memories and next-generation magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of SDT. In this review article we present an overview of this field of research. We discuss various factors that control the spin polarization and magnetoresistance in MTJs. Starting from early experiments on SDT and their interpretation, we consider thereafter recent experiments and models which highlight the role of the electronic structure of the ferromagnets, the insulating layer, and the ferromagnet/insulator interfaces. We also discuss the role of disorder in the barrier and in the ferromagnetic electrodes and their influence on TMR. (topical review)
Crushed aggregate-betonite mixtures as backfill material for the Finnish repositories of low- and intermediate-level radioactive wastes

International Nuclear Information System (INIS)

Holopainen, P.; Pirhonen, V.; Snellman, M.

1984-03-01

Backfill materials consisting of three components: crushed rock aggregate, finely ground rock aggregate and bentonite (3 to 2 per cent of weight) were studied. The production and installation procedures of the material were evaluated. Laboratory tests were made to determine the hydraulic conductivity and swelling potential of the materials. Chemical tests were made on the different materials and groundwaters. Mineralogical changes of the clay fraction were estimated. (author)
Tunnel fire dynamics

CERN Document Server

Ingason, Haukur; Lönnermark, Anders

2015-01-01

This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.
Proton tunneling in solids

Energy Technology Data Exchange (ETDEWEB)

Kondo, J.

1998-10-01

The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)
Proton tunneling in solids

International Nuclear Information System (INIS)

Kondo, J.

1998-01-01

The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)
Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope

International Nuclear Information System (INIS)

Naaman, O.; Teizer, W.; Dynes, R. C.

2001-01-01

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50--300 k Omega. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory
The ISI Tunnel

Science.gov (United States)

1993-10-01

DP /etc/tunnelvisa p zephyr dark -star TCP /etc/tunnelvisa p zephyr dak’star ICMP /etc/tunnelvisa p zephyr quark MDP /etc/tunnelvisa p zephyr quark ...drax-net-yp 128.9.32.2 1 route add quark -net-yp 128.9.32.3 1 route add vlsi-net-yp 128.9.32.4 1 route add darkstar-net-yp 128.9.32.3 1 route add rocky...TCP /etc/tunnel-visa p zephyr quark ICMP /etc/tunnel-visa p zephyr drax tTI)P /etc/tunnel-visa p zephyr drax TCP /etc/tunnel_visa p zephyr drax ICMP
Porewater salinity and the development of swelling pressure in bentonite-based buffer and backfill materials

Energy Technology Data Exchange (ETDEWEB)

Dixon, D.A. [Atomic Energy of Canada Limited (Canada)

2000-06-01

At the depths proposed for a nuclear fuel waste repository, it is likely that saline groundwater conditions will be encountered in the granitic rocks of Finland and Canada. The potential for saline groundwater to influence of the ability of bentonite-based buffer and backfilling materials to swell and thereby generate swelling pressure has been reviewed. Based on the data collected from existing literature, it would appear that porewater salinities as high as 100 g/l will not compromise the ability of confined, bentonite-based materials to develop a swelling pressure of at least 100 kPa on its confinement, provided the effective clay dry density (ECDD), exceeds approximately 0.9 Mg/m{sup 3}. At densities less than approximately 0.9 Mg/m{sup 3} the swelling pressure of bentonite-based materials may be reduced and become sensitive to salt concentration. The influence of porewater salinity on swelling pressure can be compared on the basis of the ECDD required to develop 100 kPa of swelling pressure. In order to generate 100 kPa of swelling pressure an ECDD of approximately 0.7 Mg/m{sup 3} is required to be present under fresh water or brackish porewater conditions. This density would need to be increased to approximately 0.9 Mg/m{sup 3} where the groundwater conditions were saline. The impact that groundwater salinity will have on density specifications for buffer and backfilling materials are discussed with reference to the nuclear fuel waste disposal concepts of Finland and Canada. (orig.)
Resonant tunnel magnetoresistance in a double magnetic tunnel junction

KAUST Repository

Useinov, Arthur; Useinov, Niazbeck Kh H; Tagirov, Lenar R.; Kosel, Jü rgen

2011-01-01

We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FML/I/FMW/I/FMR, where the magnetization of the middle ferromagnetic metal layer FMW can
Tunneling through landsliding zone; Jisuberi chitainai no tunnel seko

Energy Technology Data Exchange (ETDEWEB)

Konbu, A; Hatabu, K; Kano, T [Tekken Corp., Tokyo (Japan)

1994-08-01

At the new tunnel construction site of the Shirakata tunnel on the Obama line in Yamaguchi Prefecture, a landsliding occurred at about 60 meters to the upper portion obliquely to the right hand side of the shaft when the excavation progressed to about 10 meters from the starting side. The landslide caused displacement at the shaft opening and change in the supports. As a result of the re-investigation, it was confirmed that the slide face went through the tunnel cross section. The measures taken were removal of the upper soil and an adoption of the all ground fastening (AGF) method (injection type long tip fastening method) as an auxiliary construction to stop loosening of the natural ground associated with the tunnel excavation. The result was a completion of tunneling the landsliding zone without a problem. This paper reports the AGF method adopted in the above construction, together with the construction works and natural ground conditions. The AGF method is about the same as the pipe roof method with regard to the natural ground accepting mechanism and the materials used. The difference is building an improved body in a limited area in the natural ground around the steel pipes by injecting the fixing material. The use of this method caused no problems in subsidence and displacement in the surrounding ground, and completed the tunneling construction without an unusual event. 1 ref., 7 figs., 2 tabs.
Design and construction issues associated with sealing of a repository in salt

International Nuclear Information System (INIS)

Cook, R.

1991-01-01

The isolation of radioactive wastes in geologic repositories requires that man-made penetrations such as shafts, tunnels and boreholes are adequately sealed. This paper presents the current design and construction issues for sealing a repository in salt and outlines some proposed solutions. The sealing components include shaft seals, tunnel seals, panel seals, and disposal room backfill. The performance requirements and construction constraints determine the types of materials selected and their necessary properties. The current issues of interest include: (1) selection of materials for rigid bulkheads used to promote recovery of the disturbed zone permeability; (2) the selection of bulkhead geometry to cutoff flow through more permeable zones, or zones where recovery of the backfill properties occurs more slowly or not at all; and (3) the interaction of fluids with hazardous wastes with brine and, subsequently, with seal materials that might affect seal material longevity. 19 refs., 5 figs., 1 tab
Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

International Nuclear Information System (INIS)

Gajewski, Krzysztof; Piasecki, Tomasz; Kopiec, Daniel; Gotszalk, Teodor

2017-01-01

Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown. (paper)
Fabrication of magnetic tunnel junctions with a single-crystalline LiF tunnel barrier

Science.gov (United States)

Krishna Narayananellore, Sai; Doko, Naoki; Matsuo, Norihiro; Saito, Hidekazu; Yuasa, Shinji

2018-04-01

We fabricated Fe/LiF/Fe magnetic tunnel junctions (MTJs) by molecular beam epitaxy on a MgO(001) substrate, where LiF is an insulating tunnel barrier with the same crystal structure as MgO (rock-salt type). Crystallographical studies such as transmission electron microscopy and nanobeam electron diffraction observations revealed that the LiF tunnel barrier is single-crystalline and has a LiF(001)[100] ∥ bottom Fe(001)[110] crystal orientation, which is constructed in the same manner as MgO(001) on Fe(001). Also, the in-plane lattice mismatch between the LiF tunnel barrier and the Fe bottom electrode was estimated to be small (about 0.5%). Despite such advantages for the tunnel barrier of the MTJ, the observed tunnel magnetoresistance (MR) ratio was low (˜6% at 20 K) and showed a significant decrease with increasing temperature (˜1% at room temperature). The results imply that indirect tunneling and/or thermally excited carriers in the LiF tunnel barrier, in which the current basically is not spin-polarized, play a major role in electrical transport in the MTJ.
Dessicant materials screening for backfill in a salt repository

International Nuclear Information System (INIS)

Simpson, D.R.

1980-10-01

Maintaining an anhydrous environment around nuclear waste stored in a salt repository is a concern which can be alleviated by using a desiccant material for backfilling. Such a desiccant should desiccate a brine yet be non deliquescent, the hydrated product should have moderate thermal stability, and the desiccant should have a high capacity and be readily available. From a literature search MgO and CaO were identified for detailed study. These oxides, and an intimate mixture of the two obtained by calcining dolomite, were used in experiments to further determine their suitability. They proved to be excellent desiccants with a high water capacity. The hydrates of both have moderate thermal stability and a high water content. Both MgO and CaO react in an alkaline chloride brine forming oxychloride compounds with different waters of crystallization. Some of these compounds are the Sorel Cements. CaO hydrates to Ca(OH) 2 which carbonates with CO 2 in air to form CaCO 3 and release the hydrated water. Thus the intimate mixture of CaO and MgO from calcined dolomite may serve as a desiccant and remove CO 2 from the repository atmosphere
Dessicant materials screening for backfill in a salt repository

Energy Technology Data Exchange (ETDEWEB)

Simpson, D.R.

1980-10-01

Maintaining an anhydrous environment around nuclear waste stored in a salt repository is a concern which can be alleviated by using a desiccant material for backfilling. Such a desiccant should desiccate a brine yet be non deliquescent, the hydrated product should have moderate thermal stability, and the desiccant should have a high capacity and be readily available. From a literature search MgO and CaO were identified for detailed study. These oxides, and an intimate mixture of the two obtained by calcining dolomite, were used in experiments to further determine their suitability. They proved to be excellent desiccants with a high water capacity. The hydrates of both have moderate thermal stability and a high water content. Both MgO and CaO react in an alkaline chloride brine forming oxychloride compounds with different waters of crystallization. Some of these compounds are the Sorel Cements. CaO hydrates to Ca(OH)/sub 2/ which carbonates with CO/sub 2/ in air to form CaCO/sub 3/ and release the hydrated water. Thus the intimate mixture of CaO and MgO from calcined dolomite may serve as a desiccant and remove CO/sub 2/ from the repository atmosphere.
A new approach for helium backfilling and leak testing seal-welded capsules in a hot cell

International Nuclear Information System (INIS)

Strasslsund, E.K.; Berger, D.N.

1992-05-01

Gamma irradiation sources containing radioactive 137 Cesium Chloride are being produced at the US Department of Energy's Hanford Site as part of a Westinghouse Hanford company/Pacific Northwest Laboratory cooperative program. New equipment was developed to leak test the double-encapsulated sources in a hot cell. The equipment, which includes a helium backfill chamber and end cap press , a vacuum chamber, and a helium mass spectrometer, has provided technicians with the capability to detect leaks in sealed sources as small as 1. 0x10 -7 atm cm 3 /S helium
Effects of water inflow into a deposition hole - Influence of pellets type and of buffer block manufacturing technique

Energy Technology Data Exchange (ETDEWEB)

Johannesson, Lars-Erik; Jense, Viktor [Clay Technology AB, Lund (Sweden)

2012-10-15

During the installation of buffer and canister in a deposition hole a number of different problems can arise. The problems are mainly connected to water flow from fractures in the rock into the deposition hole. According to the reference design for the KBS-3V concept, the buffer is protected with a special sheet made of rubber during the installation phase. This protection sheet will at some stage be removed and the outer gap between the buffer blocks and the rock surface will be filled with bentonite pellets. The interaction of buffer blocks and pellets have previously been investigated. The focuses of those studies were the following processes: 1. Erosion. Erosion of bentonite from the deposition hole up into the tunnel backfill material. This process will continue until a tunnel plug has been installed and the backfill is saturated. 2. Heave. Early wetting of the pellets filling may cause a heave of the buffer blocks into the backfill that will decrease the density of the buffer. The laboratory tests presented in this study are complementing previous investigations by focusing on how the choice of manufacturing process for the bentonite blocks (isostatic or uniaxial compaction) and pellets (roller compaction or extrusion) are affecting erosion and the heaving effect.

Effects of water inflow into a deposition hole - Influence of pellets type and of buffer block manufacturing technique

International Nuclear Information System (INIS)

Johannesson, Lars-Erik; Jense, Viktor

2012-10-01

During the installation of buffer and canister in a deposition hole a number of different problems can arise. The problems are mainly connected to water flow from fractures in the rock into the deposition hole. According to the reference design for the KBS-3V concept, the buffer is protected with a special sheet made of rubber during the installation phase. This protection sheet will at some stage be removed and the outer gap between the buffer blocks and the rock surface will be filled with bentonite pellets. The interaction of buffer blocks and pellets have previously been investigated. The focuses of those studies were the following processes: 1. Erosion. Erosion of bentonite from the deposition hole up into the tunnel backfill material. This process will continue until a tunnel plug has been installed and the backfill is saturated. 2. Heave. Early wetting of the pellets filling may cause a heave of the buffer blocks into the backfill that will decrease the density of the buffer. The laboratory tests presented in this study are complementing previous investigations by focusing on how the choice of manufacturing process for the bentonite blocks (isostatic or uniaxial compaction) and pellets (roller compaction or extrusion) are affecting erosion and the heaving effect
Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

NARCIS (Netherlands)

Jansen, R.; Lodder, J.C.

2000-01-01

Resonant tunneling through states in the barrier of a magnetic tunnel junction has been analyzed theoretically for the case of a spin-polarized density of barrier states. It is shown that for highly spin-polarized barrier states, the magnetoresistance due to resonant tunneling is enhanced compared
Quantum tunneling time

International Nuclear Information System (INIS)

Wang, Z.S.; Lai, C.H.; Oh, C.H.; Kwek, L.C.

2004-01-01

We present a calculation of quantum tunneling time based on the transition duration of wave peak from one side of a barrier to the other. In our formulation, the tunneling time comprises a real and an imaginary part. The real part is an extension of the phase tunneling time with quantum corrections whereas the imaginary time is associated with energy derivatives of the probability amplitudes
The Effects of High Salinity Groundwater on the Performance of Clay Barriers

International Nuclear Information System (INIS)

Savage, David

2005-08-01

Potential changes in groundwater chemistry during the operational or post-closure periods of the Swedish repository for spent fuel could affect the performance of both the bentonite buffer and repository backfill. For example, the up-coning of saline groundwater could lead to decreased swelling pressures in both the bentonite buffer and tunnel backfills, and could also induce 'piping'. SKB is considering these issues as part of its 'SR-Can' safety assessment. This report reviews evidence for the behaviour of swelling clays in groundwaters of varying salinity with special relevance to the SKB programme. Smectite clays can absorb water into clay inter-layers with the most important parameters being: the surface density of charge of the clay; the charge and solvation behaviour of the inter-layer ions; and the electrolyte concentration or activity of water. Two categories of swelling are generally observed: innercrystalline swelling caused by the hydration of the exchangeable cations in the dry clay; and osmotic swelling, resulting from concentration gradients in ion concentrations between clay surfaces and pore water. Several models exist to interpret and predict the swelling behaviour of clays. SKB currently prefer an interpretation of clay swelling pressure where clay particles are viewed as 'macro-ions' and the entire clay-water system can be considered as a 'polyelectrolyte'. SKB use the term 'Donnan exclusion' to estimate the amount of introduced ions into the clay and hence the amount of reduced swelling pressure due to contact with a saline solution. Donnan exclusion is the process whereby the migration of anions through the narrow aqueous film surrounding clay platelets is restricted due to the repulsion by the negative charge of the clay platelets. SKB's experimental work shows that: There is an exponential relation between swelling pressure and mean basal interlamellar spacing of the clay. Ions from the external electrolyte solution enter the clay volume
The Effects of High Salinity Groundwater on the Performance of Clay Barriers

Energy Technology Data Exchange (ETDEWEB)

Savage, David [Quintessa Ltd., Nottingham (United Kingdom)

2005-07-01

Potential changes in groundwater chemistry during the operational or post-closure periods of the Swedish repository for spent fuel could affect the performance of both the bentonite buffer and repository backfill. For example, the up-coning of saline groundwater could lead to decreased swelling pressures in both the bentonite buffer and tunnel backfills, and could also induce 'piping'. SKB is considering these issues as part of its 'SR-Can' safety assessment. This report reviews evidence for the behaviour of swelling clays in groundwaters of varying salinity with special relevance to the SKB programme. Smectite clays can absorb water into clay inter-layers with the most important parameters being: the surface density of charge of the clay; the charge and solvation behaviour of the inter-layer ions; and the electrolyte concentration or activity of water. Two categories of swelling are generally observed: innercrystalline swelling caused by the hydration of the exchangeable cations in the dry clay; and osmotic swelling, resulting from concentration gradients in ion concentrations between clay surfaces and pore water. Several models exist to interpret and predict the swelling behaviour of clays. SKB currently prefer an interpretation of clay swelling pressure where clay particles are viewed as 'macro-ions' and the entire clay-water system can be considered as a 'polyelectrolyte'. SKB use the term 'Donnan exclusion' to estimate the amount of introduced ions into the clay and hence the amount of reduced swelling pressure due to contact with a saline solution. Donnan exclusion is the process whereby the migration of anions through the narrow aqueous film surrounding clay platelets is restricted due to the repulsion by the negative charge of the clay platelets. SKB's experimental work shows that: There is an exponential relation between swelling pressure and mean basal interlamellar spacing of the clay. Ions from the
Tarsal tunnel disease and talocalcaneal coalition: MRI features

Energy Technology Data Exchange (ETDEWEB)

FitzGerald Alaia, Erin; Rosenberg, Zehava Sadka; Bencardino, Jenny T.; Ciavarra, Gina A.; Petchprapa, Catherine N. [New York University Langone Medical Center, New York, NY (United States); Rossi, Ignacio [New York University Langone Medical Center, New York, NY (United States); Centro de Diagnostico Dr. Enrique Rossi, Buenos Aires (Argentina)

2016-11-15

To assess, utilizing MRI, tarsal tunnel disease in patients with talocalcaneal coalitions. To the best of our knowledge, this has only anecdotally been described before. Sixty-seven ankle MRIs with talocalcaneal coalition were retrospectively reviewed for disease of tendons and nerves of the tarsal tunnel. Interobserver variability in diagnosing tendon disease was performed in 30 of the 67 cases. Tarsal tunnel nerves were also evaluated in a control group of 20 consecutive ankle MRIs. Entrapment of the flexor hallucis longus tendon (FHL) by osseous excrescences was seen in 14 of 67 cases (21 %). Attenuation, split tearing, tenosynovitis, or tendinosis of the FHL was present in 26 cases (39 %). Attenuation or tenosynovitis was seen in the flexor digitorum longus tendon (FDL) in 18 cases (27 %). Tenosynovitis or split tearing of the posterior tibial tendon (PT) was present in nine cases (13 %). Interobserver variability ranged from 100 % to slight depending on the tendon and type of disease. Intense increased signal and caliber of the medial plantar nerve (MPN), indicative of neuritis, was seen in 6 of the 67 cases (9 %). Mildly increased T2 signal of the MPN was seen in 15 (22 %) and in 14 (70 %) of the control group. Talocalcaneal coalitions may be associated with tarsal tunnel soft tissue abnormalities affecting, in decreasing order, the FHL, FDL, and PT tendons, as well as the MPN. This information should be provided to the referring physician in order to guide treatment and improve post-surgical outcome. (orig.)
Tarsal tunnel disease and talocalcaneal coalition: MRI features

International Nuclear Information System (INIS)

FitzGerald Alaia, Erin; Rosenberg, Zehava Sadka; Bencardino, Jenny T.; Ciavarra, Gina A.; Petchprapa, Catherine N.; Rossi, Ignacio

2016-01-01

To assess, utilizing MRI, tarsal tunnel disease in patients with talocalcaneal coalitions. To the best of our knowledge, this has only anecdotally been described before. Sixty-seven ankle MRIs with talocalcaneal coalition were retrospectively reviewed for disease of tendons and nerves of the tarsal tunnel. Interobserver variability in diagnosing tendon disease was performed in 30 of the 67 cases. Tarsal tunnel nerves were also evaluated in a control group of 20 consecutive ankle MRIs. Entrapment of the flexor hallucis longus tendon (FHL) by osseous excrescences was seen in 14 of 67 cases (21 %). Attenuation, split tearing, tenosynovitis, or tendinosis of the FHL was present in 26 cases (39 %). Attenuation or tenosynovitis was seen in the flexor digitorum longus tendon (FDL) in 18 cases (27 %). Tenosynovitis or split tearing of the posterior tibial tendon (PT) was present in nine cases (13 %). Interobserver variability ranged from 100 % to slight depending on the tendon and type of disease. Intense increased signal and caliber of the medial plantar nerve (MPN), indicative of neuritis, was seen in 6 of the 67 cases (9 %). Mildly increased T2 signal of the MPN was seen in 15 (22 %) and in 14 (70 %) of the control group. Talocalcaneal coalitions may be associated with tarsal tunnel soft tissue abnormalities affecting, in decreasing order, the FHL, FDL, and PT tendons, as well as the MPN. This information should be provided to the referring physician in order to guide treatment and improve post-surgical outcome. (orig.)
Measuring fire size in tunnels

International Nuclear Information System (INIS)

Guo, Xiaoping; Zhang, Qihui

2013-01-01

A new measure of fire size Q′ has been introduced in longitudinally ventilated tunnel as the ratio of flame height to the height of tunnel. The analysis in this article has shown that Q′ controls both the critical velocity and the maximum ceiling temperature in the tunnel. Before the fire flame reaches tunnel ceiling (Q′ 1.0), Fr approaches a constant value. This is also a well-known phenomenon in large tunnel fires. Tunnel ceiling temperature shows the opposite trend. Before the fire flame reaches the ceiling, it increases very slowly with the fire size. Once the flame has hit the ceiling of tunnel, temperature rises rapidly with Q′. The good agreement between the current prediction and three different sets of experimental data has demonstrated that the theory has correctly modelled the relation among the heat release rate of fire, ventilation flow and the height of tunnel. From design point of view, the theoretical maximum of critical velocity for a given tunnel can help to prevent oversized ventilation system. -- Highlights: • Fire sizing is an important safety measure in tunnel design. • New measure of fire size a function of HRR of fire, tunnel height and ventilation. • The measure can identify large and small fires. • The characteristics of different fire are consistent with observation in real fires
Microwave-induced co-tunneling in single electron tunneling transistors

DEFF Research Database (Denmark)

Ejrnaes, M.; Savolainen, M.; Manscher, M.

2002-01-01

on rubber bellows. Cross-talk was minimized by using individual coaxial lines between the sample and the room temperature electronics: The co-tunneling experiments were performed at zero DC bias current by measuring the voltage response to a very small amplitude 2 Hz current modulation with the gate voltage......The influence of microwaves on the co-tunneling in single electron tunneling transistors has been investigated as function of frequency and power in the temperature range from 150 to 500 mK. All 20 low frequency connections and the RF line were filtered, and the whole cryostat was suspended...
Influence of trap-assisted tunneling on trap-assisted tunneling current in double gate tunnel field-effect transistor

International Nuclear Information System (INIS)

Jiang Zhi; Zhuang Yi-Qi; Li Cong; Wang Ping; Liu Yu-Qi

2016-01-01

Trap-assisted tunneling (TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor (TFET). In this paper, we assess subthreshold performance of double gate TFET (DG-TFET) through a band-to-band tunneling (BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile (D it ) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current. (paper)
The carpal tunnel syndrome in children.

Science.gov (United States)

Leti Acciaro, A; Pilla, F; Faldini, C; Adani, R

2017-12-21

Carpal tunnel syndrome (CTS) in children represents a complex challenge for the hand surgeon because of its rarity, poor patient cooperation, frequently associated malformation syndromes and mental retard, atypical symptoms and nuanced and poor sensitivity of instrumental tests. The most frequently associated causes with the CTS in children are rare congenital malformations and diseases, requiring an overall assessment of the young patient and a high degree of suspicion for the potentially associated canalicular syndrome. On the other hand, the associated syndromes may be the main ally for a diagnosis that starts from the knowledge of the literature and the surgeon's suspicion by observing the child wailing. Early diagnosis and decompression treatment is mandatory. The authors report a case series of 26 children and analyze the etiology and diagnostic algorithms. Patient assessment was based on complete clinical examination and medical history collection of these young patients with the involvement of the family and educators. In all 26 patients treated, along an average period of 23 months (minimum 12, maximum 30), no signs of recurrence or persistence of median nerve disturbances were recorded. In conclusion, we believe that anamnesis, a careful physical examination and analysis of instrumental examinations, should be accompanied by a thorough knowledge of rare diseases in the context of congenital malformations. The carpal tunnel syndrome, while well known and treated by each orthopedic surgeon, reveals a mysterious aspect in the context of the "fabulous" world of childhood illnesses, even more difficult than rare congenital diseases.
Engineered Barrier System - Long-term Stability of Buffer and Backfill. Synthesis and extended abstracts

Energy Technology Data Exchange (ETDEWEB)

Apted, Mick; Arthur, Randy [Monitor Scientific LLC, Denver, CO (United States); Savage, Dave [Quintessa Ltd., Nottingham (GB)] (eds.)

2005-09-15

SKI is preparing to review the license applications being developed by the Swedish Nuclear Fuel and Waste Management Company (SKB) for an encapsulation plant and a deep repository for the geological disposal of spent nuclear fuel. As part of its preparation, SKI is conducting a series of technical workshops on key aspects of the Engineered Barrier System (EBS) of the repository. This workshop concerns the longterm stability of the buffer and the backfill. Previous workshops have addressed the overall concept for long-term integrity of the EBS, the manufacturing, testing and QA of the EBS and the performance confirmation for the EBS. The goal of this work is to achieve a comprehensive overview of all aspects of SKB's EBS work prior to the handling of forthcoming license applications. The reports from the EBS workshops will be used as one important basis in future review work. The workshops involve the gathering of a sufficient number of independent experts in different subjects of relevance to the particular aspect of EBS. A workshop starts with presentations and discussions among these experts. Following this, SKB presents recent results and responds to questions as part of an informal hearing. Finally, the independent experts and the SKI staff examine the SKB responses from different viewpoints. This report aims to summarise the issues discussed at the buffer and backfill workshop and to extract the essential viewpoints that have been expressed. The report is not a comprehensive record of the discussions and individual statements made by workshop participants should be regarded as opinions rather than proven facts. This reports includes apart from the workshop synthesis, questions to SKB identified prior or during the workshop, and extended abstracts for introductory presentations.
Engineered Barrier System - Long-term Stability of Buffer and Backfill. Synthesis and extended abstracts

International Nuclear Information System (INIS)

Apted, Mick; Arthur, Randy; Savage, Dave

2005-09-01

SKI is preparing to review the license applications being developed by the Swedish Nuclear Fuel and Waste Management Company (SKB) for an encapsulation plant and a deep repository for the geological disposal of spent nuclear fuel. As part of its preparation, SKI is conducting a series of technical workshops on key aspects of the Engineered Barrier System (EBS) of the repository. This workshop concerns the longterm stability of the buffer and the backfill. Previous workshops have addressed the overall concept for long-term integrity of the EBS, the manufacturing, testing and QA of the EBS and the performance confirmation for the EBS. The goal of this work is to achieve a comprehensive overview of all aspects of SKB's EBS work prior to the handling of forthcoming license applications. The reports from the EBS workshops will be used as one important basis in future review work. The workshops involve the gathering of a sufficient number of independent experts in different subjects of relevance to the particular aspect of EBS. A workshop starts with presentations and discussions among these experts. Following this, SKB presents recent results and responds to questions as part of an informal hearing. Finally, the independent experts and the SKI staff examine the SKB responses from different viewpoints. This report aims to summarise the issues discussed at the buffer and backfill workshop and to extract the essential viewpoints that have been expressed. The report is not a comprehensive record of the discussions and individual statements made by workshop participants should be regarded as opinions rather than proven facts. This reports includes apart from the workshop synthesis, questions to SKB identified prior or during the workshop, and extended abstracts for introductory presentations
Thermovoltages in vacuum tunneling investigated by scanning tunneling microscopy

OpenAIRE

Hoffmann, D. H.; Rettenberger, Armin; Grand, Jean Yves; Läuger, K.; Leiderer, Paul; Dransfeld, Klaus; Möller, Rolf

1995-01-01

By heating the tunneling tip of a scanning tunneling microscope the thermoelectric properties of a variable vacuum barrier have been investigated. The lateral variation of the observed thermovoltage will be discussed for polycrystalline gold, stepped surfaces of silver, as well as for copper islands on silver.
Contact-metamorphic illitization and related consequences for the functioning of backfill barriers in high level radioactive waste repositories (South Africa)

International Nuclear Information System (INIS)

Buehmann, C.

2000-01-01

A clay barrier, consisting of smectite, is common to most disposal designs for HLW repositories. Concerns are that elevated temperatures and long time periods may alter the two properties, the barrier is employed: a high swelling as well as cation exchange capacity (CEC). A ''natural analogue'' approach has therefore been attempted to predict smectite characteristics and stability in relation to time/temperature. The following investigations were performed in order to determine changes in swelling capacity and CEC: (1) Conversion of smectite to other clay minerals. (2) Changes in the layer charge characteristics of the clay minerals. (3) Swelling potential measurements of the smectitic interlayer. Smectite was thermally unstable and transformed into illite via illite/smectite interstratifications (I/S) and chlorite at temperature exceeding about 100 deg. C. The swelling potential was directly related to the proportion of smectite. As a conclusion it can be stated that elevated temperatures (> 70 deg. C) result in the transformation of smectite into illite. For backfill purposes it is recommended that the clay content in the backfill barrier should be as high as technically possible and that mixing the bentonite with K-bearing minerals (granite) should be avoided. (author)
Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

International Nuclear Information System (INIS)

Cleland, A.N.

1991-04-01

Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q ∼ 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement
About tunnelling times

International Nuclear Information System (INIS)

Olkhovsky, V.S.; Recami, E.

1991-08-01

In this paper, first we critically analyse the main theoretical definitions and calculations of the sub-barrier tunnelling and reflection times. Secondly, we propose a new, physically sensible definition of such durations, on the basis of a recent general formalism (already tested for other types of quantum collisions). At last, we discuss some results regarding temporal evolution of the tunnelling processes, and in particular the ''particle'' speed during tunnelling. (author). 36 refs, 1 fig
Review of the sorption of radionuclides on the bedrock of Haestholmen and on construction and backfill materials of a final repository for reactor wastes

International Nuclear Information System (INIS)

Kulmala, S.; Hakanen, M.

1992-10-01

Imatran Voima Oy (IVO) has plans to build a final repository for reactor wastes in the bedrock of the nuclear power plant site at Haestholmen, Loviisa. This report summarizes the sorption studies of radionuclides in Finnish bedrock performed at the Department of Radiochemistry, University of Helsinki. The values of mass distribution ratios, K d , and surface distribution ratios, K a ; of carbon, calsium, Zirconium, niobium, cobalt, nickel, strontium, cesium, uranium, plutonium, americium, thorium, chlorine, iodine and technetium are surveyed. Special attention is paid to the sorption data for construction and backfill materials of rector waste repository and the bedrock of Haestholmen. Safety assessment of a repository includes calculations of migration of the waste element in construction materials and backfill in the nearfield and in bedrock. Retardation by sorption of waste nuclides compared to groundwater flow is described by using distribution ratios between solid materials and water. (orig.)
Tunneling current between graphene layers

OpenAIRE

Poklonski, Nikolai A.; Siahlo, Andrei I.; Vyrko, Sergey A.; Popov, Andrey M.; Lozovik, Yurii E.

2013-01-01

The physical model that allows to calculate the values of the tunneling current be-tween graphene layers is proposed. The tunneling current according to the pro-posed model is proportional to the area of tunneling transition. The calculated value of tunneling conductivity is in qualitative agreement with experimental data.
Backfill barriers: the use of engineered barriers based on geologic materials to assure isolation of radioactive wastes in a repository

International Nuclear Information System (INIS)

Apps, J.A.; Cook, N.G.W.

1981-06-01

A preliminary assessment is made to show that canisters fabricated of nickel-iron alloys, and surrounded by a suitable backfill, may produce an engineered barrier where the canister material is thermodynamically stable with respect to its environment. As similar conditions exist in nature, the performance of such systems as barriers to isolate radionuclides can be predicted over very long periods, of the order of 10 6 years

Single Electron Tunneling

International Nuclear Information System (INIS)

Ruggiero, Steven T.

2005-01-01

Financial support for this project has led to advances in the science of single-electron phenomena. Our group reported the first observation of the so-called ''Coulomb Staircase'', which was produced by tunneling into ultra-small metal particles. This work showed well-defined tunneling voltage steps of width e/C and height e/RC, demonstrating tunneling quantized on the single-electron level. This work was published in a now well-cited Physical Review Letter. Single-electron physics is now a major sub-field of condensed-matter physics, and fundamental work in the area continues to be conducted by tunneling in ultra-small metal particles. In addition, there are now single-electron transistors that add a controlling gate to modulate the charge on ultra-small photolithographically defined capacitive elements. Single-electron transistors are now at the heart of at least one experimental quantum-computer element, and single-electron transistor pumps may soon be used to define fundamental quantities such as the farad (capacitance) and the ampere (current). Novel computer technology based on single-electron quantum dots is also being developed. In related work, our group played the leading role in the explanation of experimental results observed during the initial phases of tunneling experiments with the high-temperature superconductors. When so-called ''multiple-gap'' tunneling was reported, the phenomenon was correctly identified by our group as single-electron tunneling in small grains in the material. The main focus throughout this project has been to explore single electron phenomena both in traditional tunneling formats of the type metal/insulator/particles/insulator/metal and using scanning tunneling microscopy to probe few-particle systems. This has been done under varying conditions of temperature, applied magnetic field, and with different materials systems. These have included metals, semi-metals, and superconductors. Amongst a number of results, we have
Drill and blast tunnelling; Konvensjonell drift av tunneler

Energy Technology Data Exchange (ETDEWEB)

Roenn, Paal-Egil

1997-12-31

This thesis treats drill and blast tunnelling. The rapid technological advance necessitates revised and updated design criteria, quality requirements and quality control. In situ blast experiments were carried out in order to test new methods and improve the basis for calculation and design. The main topics of the experiments were (1) longer rounds and increased drillhole diameter, (2) emulsion slurry as explosives in tunnelling, and (3) electronic detonators in contour blasting. The experiments show that it is technically feasible to blast rounds of up to 8.6 m length. Using current technology, the economical optimum round length is substantially shorter. Dust, low visibility, noise and toxic fumes are occupational environmental strains for the tunnel workers. Several of the environmental factors are strongly influenced by the type of explosives used. For example, emulsion slurry resulted in 4 to 5 times better visibility than Anolit and the concentration of respirable dust and total dust was reduced by 30-50 %. Electronic detonators were tested and found to give a higher percentage of remaining drillholes in the contour than Nonel detonators. The thesis includes a chapter on economic design of hydropower tunnels. 42 refs., 83 figs., 45 tabs.
Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

KAUST Repository

Useinov, A. N.

2011-08-24

We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.
Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

KAUST Repository

Useinov, A. N.; Kosel, Jü rgen; Useinov, N. Kh.; Tagirov, L. R.

2011-01-01

We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.
Quantum size effects on spin-tunneling time in a magnetic resonant tunneling diode

OpenAIRE

Saffarzadeh, Alireza; Daqiq, Reza

2009-01-01

We study theoretically the quantum size effects of a magnetic resonant tunneling diode (RTD) with a (Zn,Mn)Se dilute magnetic semiconductor layer on the spin-tunneling time and the spin polarization of the electrons. The results show that the spin-tunneling times may oscillate and a great difference between the tunneling time of the electrons with opposite spin directions can be obtained depending on the system parameters. We also study the effect of structural asymmetry which is related to t...
Influence of trap-assisted tunneling on trap-assisted tunneling current in double gate tunnel field-effect transistor

Science.gov (United States)

Zhi, Jiang; Yi-Qi, Zhuang; Cong, Li; Ping, Wang; Yu-Qi, Liu

2016-02-01

Trap-assisted tunneling (TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor (TFET). In this paper, we assess subthreshold performance of double gate TFET (DG-TFET) through a band-to-band tunneling (BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile (Dit) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current. Project supported by the National Natural Science Foundation of China (Grant Nos. 61574109 and 61204092).
Study of tunneling transport in Si-based tunnel field-effect transistors with ON current enhancement utilizing isoelectronic trap

Science.gov (United States)

Mori, Takahiro; Morita, Yukinori; Miyata, Noriyuki; Migita, Shinji; Fukuda, Koichi; Mizubayashi, Wataru; Masahara, Meishoku; Yasuda, Tetsuji; Ota, Hiroyuki

2015-02-01

The temperature dependence of the tunneling transport characteristics of Si diodes with an isoelectronic impurity has been investigated in order to clarify the mechanism of the ON-current enhancement in Si-based tunnel field-effect transistors (TFETs) utilizing an isoelectronic trap (IET). The Al-N complex impurity was utilized for IET formation. We observed three types of tunneling current components in the diodes: indirect band-to-band tunneling (BTBT), trap-assisted tunneling (TAT), and thermally inactive tunneling. The indirect BTBT and TAT current components can be distinguished with the plot described in this paper. The thermally inactive tunneling current probably originated from tunneling consisting of two paths: tunneling between the valence band and the IET trap and tunneling between the IET trap and the conduction band. The probability of thermally inactive tunneling with the Al-N IET state is higher than the others. Utilization of the thermally inactive tunneling current has a significant effect in enhancing the driving current of Si-based TFETs.
Failure of MPC overpack and inner container under corrosion and mechanical stresses in a backfilled drift

International Nuclear Information System (INIS)

Ladkany, S.G.; Rajagopalan, R.

1995-01-01

The thickness and time at failure of the 100mm thick overpack and the 9.5mm thick inner container of a Multi-purpose canister have been assessed due to loads resulting from temperature, overburden, backfill pressure and seismic loads. Critical stresses at various reduced thicknesses, resulting from pitting corrosion over the years of emplacement, have been evaluated using Finite element analysis. Both simple and continuous support conditions of the overpack have been considered in the analysis. The anticipated failure time due to corrosion of overpack and inner container is further reduced due to overburden, self and seismic loads
Electrical installations of the Channel tunnel; Installations electriques du Tunnel sous la Manche

Energy Technology Data Exchange (ETDEWEB)

Kersabiec, G. de [Eurotunnel, Folkestone (United Kingdom)

2002-08-01

Like an underground factory, the railway and auxiliary equipments of the Channel tunnel between France and UK, need a reliable and redundant power supply with a high quality maintenance. This article presents: the design criteria of the power distribution systems, the installation itself and the organisation of its exploitation: 1 - transportation system of the Channel tunnel (loads to supply, exploitation imperatives, fundamental criteria); 2 - external power sources (connection to the UK and French grids, values used by the national grids); 3 - exploitation criteria, tunnel design; 4 - description (main UK and French power stations, 25 kV traction network, 21 kV distribution network, tunnels, lighting in railway tunnels, supply of terminals, earthing network); 5 - exploitation; 6 - maintenance and quality. (J.S.)
Heavy-Atom Tunneling Calculations in Thirteen Organic Reactions: Tunneling Contributions are Substantial, and Bell's Formula Closely Approximates Multidimensional Tunneling at ≥250 K.

Science.gov (United States)

Doubleday, Charles; Armas, Randy; Walker, Dana; Cosgriff, Christopher V; Greer, Edyta M

2017-10-09

Multidimensional tunneling calculations are carried out for 13 reactions, to test the scope of heavy-atom tunneling in organic chemistry, and to check the accuracy of one-dimensional tunneling models. The reactions include pericyclic, cycloaromatization, radical cyclization and ring opening, and S N 2. When compared at the temperatures that give the same effective rate constant of 3×10 -5 s -1 , tunneling accounts for 25-95 % of the rate in 8 of the 13 reactions. Values of transmission coefficients predicted by Bell's formula, κ Bell , agree well with multidimensional tunneling (canonical variational transition state theory with small curvature tunneling), κ SCT . Mean unsigned deviations of κ Bell vs. κ SCT are 0.08, 0.04, 0.02 at 250, 300 and 400 K. This suggests that κ Bell is a useful first choice for predicting transmission coefficients in heavy-atom tunnelling. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Remaining porosity and permeability of compacted crushed rock salt backfill in a HLW repository. Final report

Energy Technology Data Exchange (ETDEWEB)

Jobmann, M.; Mueller, C.; Schirmer, S.

2015-11-15

The safe containment of radioactive waste is to be ensured by the geotechnical barriers in combination with the containment-providing rock zone (CRZ). The latter is a key element of the recently developed concept of demonstrating the integrity of the geologic barrier (Krone et al., 2013). As stipulated in the safety requirements of the regulating body the CRZ has to have strong barrier properties, and evidence needs to be provided that it retains its integrity throughout the reference period (BMU, 2010). The underground openings excavated in the rock salt will close over time due to the creep properties of the rock salt. This process causes deformations in the surrounding rock salt, which leads to a change in stress state in the virgin rock and may impair the integrity of the containment-providing rock zone. In order to limit the effects of these processes, all underground openings will be backfilled with crushed salt. Immediately after backfilling, the crushed salt will have an initial porosity of approx. 35%, which - over time - will be reduced to very low values due to the creep properties of the rock salt. The supporting pressure that builds up in the crushed salt with increasing compaction slows down the creeping of the salt. Major influencing factors are the temperature (with higher temperatures accelerating the salt creeping) and the moisture of the salt, which - due to the related decrease in the resistance of the crushed salt - facilitates its compaction. The phenomenology of these processes and dependencies is understood to a wide extent. This project investigated the duration until compaction is completed and when and under what circumstances the crushed salt will have the sealing properties necessary to ensure safe containment. Thermo-hydro-mechanical (THM) processes play a crucial role in determining whether solutions which might enter the mine could reach the radioactive waste. This includes changes in material behaviour due to a partial or complete
Sodium Silicate Gel Effect on Cemented Tailing Backfill That Contains Lead-Zinc Smelting Slag at Early Ages

OpenAIRE

Guo, Lijie; Li, Wenchen; Yang, Xiaocong; Xu, Wenyuan

2018-01-01

This paper presents the results of an experimental study on the priming effect of sodium silicate gel (SS) on cemented tailing backfill (CTB) that contains lead-zinc smelting slag. CTB and cemented paste (CP) containing lead-zinc smelting slag samples with SS of 0 and 0.4% of the mass of the slag were prepared and cured at 20°C for 1, 3, 7, and 28 days. Mechanical test and pore structure analyses were performed on the studied CTB samples, microstructural analyses (X-ray diffraction analysis a...
Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

International Nuclear Information System (INIS)

Cleland, A.N.

1991-01-01

Experiments investigated the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very-small-capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson-phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters. The experiments on small-capacitance tunnel junctions extend the measurements on the large-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wave function has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias
Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope.

Science.gov (United States)

Nazin, G V; Wu, S W; Ho, W

2005-06-21

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.
Design of the disposal facility 2012

International Nuclear Information System (INIS)

Saanio, T.; Ikonen, A.; Keto, P.; Kirkkomaeki, T.; Kukkola, T.; Nieminen, J.; Raiko, H.

2013-11-01

The spent nuclear fuel accumulated from the nuclear power plants in Olkiluoto in Eurajoki and in Haestholmen in Loviisa will be disposed of in Olkiluoto. A facility complex will be constructed at Olkiluoto, and it will include two nuclear waste facilities according to Government Degree 736/2008. The nuclear waste facilities are an encapsulation plant, constructed to encapsulate spent nuclear fuel and a disposal facility consisting of an underground repository and other underground rooms and above ground service spaces. The repository is planned to be excavated to a depth of 400 - 450 meters. Access routes to the disposal facility are an inclined access tunnel and vertical shafts. The encapsulated fuel is transferred to the disposal facility in the canister lift. The canisters are transferred from the technical rooms to the disposal area via central tunnel and deposited in the deposition holes which are bored in the floors of the deposition tunnels and are lined beforehand with compacted bentonite blocks. Two parallel central tunnels connect all the deposition tunnels and these central tunnels are inter-connected at regular intervals. The solution improves the fire safety of the underground rooms and allows flexible backfilling and closing of the deposition tunnels in stages during the operational phase of the repository. An underground rock characterization facility, ONKALO, is excavated at the disposal level. ONKALO is designed and constructed so that it can later serve as part of the repository. The goal is that the first part of the disposal facility will be constructed under the building permit phase in the 2010's and operations will start in the 2020's. The fuel from 4 operating reactors as well the fuel from the fifth nuclear power plant under construction, has been taken into account in designing the disposal facility. According to the information from TVO and Fortum, the amount of the spent nuclear fuel is 5,440 tU. The disposal facility is being excavated
Vacuum phonon tunneling.

Science.gov (United States)

Altfeder, Igor; Voevodin, Andrey A; Roy, Ajit K

2010-10-15

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.
Breaking through the tranfer tunnel

CERN Document Server

Laurent Guiraud

2001-01-01

This image shows the tunnel boring machine breaking through the transfer tunnel into the LHC tunnel. Proton beams will be transferred from the SPS pre-accelerator to the LHC at 450 GeV through two specially constructed transfer tunnels. From left to right: LHC Project Director, Lyn Evans; CERN Director-General (at the time), Luciano Maiani, and Director for Accelerators, Kurt Hubner.
New Tunneling Features in Polar III-Nitride Resonant Tunneling Diodes

Directory of Open Access Journals (Sweden)

Jimy Encomendero

2017-10-01

Full Text Available For the past two decades, repeatable resonant tunneling transport of electrons in III-nitride double barrier heterostructures has remained elusive at room temperature. In this work we theoretically and experimentally study III-nitride double-barrier resonant tunneling diodes (RTDs, the quantum transport characteristics of which exhibit new features that are unexplainable using existing semiconductor theory. The repeatable and robust resonant transport in our devices enables us to track the origin of these features to the broken inversion symmetry in the uniaxial crystal structure, which generates built-in spontaneous and piezoelectric polarization fields. Resonant tunneling transport enabled by the ground state as well as by the first excited state is demonstrated for the first time over a wide temperature window in planar III-nitride RTDs. An analytical transport model for polar resonant tunneling heterostructures is introduced for the first time, showing a good quantitative agreement with experimental data. From this model we realize that tunneling transport is an extremely sensitive measure of the built-in polarization fields. Since such electric fields play a crucial role in the design of electronic and photonic devices, but are difficult to measure, our work provides a completely new method to accurately determine their magnitude for the entire class of polar heterostructures.
Theoretical consideration of spin-polarized resonant tunneling in magnetic tunnel junctions

International Nuclear Information System (INIS)

Mu Haifeng; Zhu Zhengang; Zheng Qingrong; Jin Biao; Wang Zhengchuan; Su Gang

2004-01-01

A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations
Histological Observation of Regions around Bone Tunnels after Compression of the Bone Tunnel Wall in Ligament Reconstruction

International Nuclear Information System (INIS)

Maeda, Shintaro; Ishikawa, Hiroki; Tanigawa, Naoaki; Miyazaki, Kyosuke; Shioda, Seiji

2012-01-01

The objectives of this study were to investigate the time-course of influence of compression of bone tunnel wall in ligament reconstruction on tissue around the bone tunnel and to histologically examine the mechanism of preventing the complication of bone tunnel dilation, using rabbit tibia. A model in which the femoral origin of the extensor digitorum longus tendon was cut and inserted into a bone tunnel made proximal to the tibia was prepared in the bilateral hind legs of 20 Japanese white rabbits. In each animal, a tunnel was made using a drill only in the right leg, while an undersized bone tunnel was made by drilling and then dilated by compression using a dilator to the same tunnel size as that in the right leg. Animals were sacrificed at 0, 2, 4, 8 and 12 weeks after surgery (4 animals at each time point). Observation of bone tunnels by X-ray radiography showed osteosclerosis in the 2- and 4-week dilation groups. Osteosclerosis appeared as white lines around the bone tunnel on X-ray radiography. This suggests that dilation promotes callus formation in the bone tunnel wall and prevents the complication of bone tunnel enlargement after ligament reconstruction

From the semicircular vault to the flattened vault in masonry bridges. The influence of rise/span ratio and the resistant backfill in the breaking load

Directory of Open Access Journals (Sweden)

J. R. Urruchi-Rojo

2017-04-01

Full Text Available The shape of the vaults in masonry bridges has evolved during the history, so that we can find bibliography where, besides recommending one way of build instead of others depending on the period, is also prescribed the way to carry out the backfill of the extrados. All of this emerged initially as a result of the experiences acquired during the construction and the observation of bridges. Hence, during the 18th century new formulations started to arise, but they led to one result in some cases and to the opposite in others. This article tries to make a comparison between some of these formulations, as well as carrying out an analysis of the influence of both, the lowering rise/span ratio of the vaults and the presence of a resistant backfill in its extrados, on the variation of the breaking load.
Physical and chemical properties of bentonite as backfill and sealing material in a final repository of radioactive wastes. A literature study

International Nuclear Information System (INIS)

Schmidt, W.; Kessler, J.; Sitz, P.

1992-11-01

Results of a literature study concerning the properties and the changes in properties of bentonite backfill are presented on the basis of current concepts envisaged for final disposal of radioactive waste in Switzerland. The literature preferentially used in this study is that of NAGRA, international papers and special publications from universities in Germany, Austria and Switzerland. Mechanical, physico-mineralogical and chemical properties of bentonite and bentonite-water systems are considered as the central point, particularly taking into account the types MX-80 and Montigel which are favoured in the Swiss concept. Technological problems associated with radioactive waste disposal are only touched on or are taken as being understood. Special attention is paid to considering mutual interactions between different complexes of properties, considering certain aspects of longevity and long-term stability, the discussion is focused on potential physical and chemical impacts of the bentonite backfill. Further investigations should consider the interrelations between mechanical and physical properties, diffusion properties and the influence on bentonite of higher temperatures, of water vapor, of iron corrosion products and of the products of interactions in the water-concrete system. (author) figs., tabs., refs
Tunnel fire testing and modeling the Morgex North tunnel experiment

CERN Document Server

Borghetti, Fabio; Gandini, Paolo; Frassoldati, Alessio; Tavelli, Silvia

2017-01-01

This book aims to cast light on all aspects of tunnel fires, based on experimental activities and theoretical and computational fluid dynamics (CFD) analyses. In particular, the authors describe a transient full-scale fire test (~15 MW), explaining how they designed and performed the experimental activity inside the Morgex North tunnel in Italy. The entire organization of the experiment is described, from preliminary evaluations to the solutions found for management of operational difficulties and safety issues. This fire test allowed the collection of different measurements (temperature, air velocity, smoke composition, pollutant species) useful for validating and improving CFD codes and for testing the real behavior of the tunnel and its safety systems during a diesel oil fire with a significant heat release rate. Finally, the fire dynamics are compared with empirical correlations, CFD simulations, and literature measurements obtained in other similar tunnel fire tests. This book will be of interest to all ...
Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation

International Nuclear Information System (INIS)

Nam, C.H.; Shim, Heejae; Kim, K.S.; Cho, B.K.

2004-01-01

Oxidation of an AlO x insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 A thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer
Cost effects of Cu powder and bentonite on the disposal costs of an HLW repository in

International Nuclear Information System (INIS)

Kim, Sung Ki; Lee, Min Soo; Lee, Jong Youl; Choi, Heui Joo; Choi, Jong Won

2008-01-01

This paper provides the cost effect results of Cu powder and bentonite on the disposal cost for an HLW repository in Korea. In the cost analysis for both of these cost drivers, the price of Cu powder and the bentonite can affect the canister cost and the bentonite cost of the disposal holes as well as backfilling cost of the tunnels, respectively. Finally, we found that the unit cost of Cu and bentonite was the dominant cost drivers for the surface and underground facilities of an HLW repository. Therefore, an optimization of a canister and the layout of a disposal hole and disposal tunnels are essential to decrease the direct disposal cost of spent fuels. The disposal costs can be largely divided into two parts such as a surface facilities' cost and an underground facilities' cost. According to the KRS' cost analysis, the encapsulation material as well as the buffering and backfilling cost were the significant costs. Especially, a canister's cost was approximately estimated to be more than one fourth of the overall disposal costs. So it can be estimated that the unit cost of Cu powder is an important cost diver. Because the outer shell of the canister was made of Cu powder by a cold spray coating method. In addition, the unit cost of bentonite can also affect the buffering and the backfilling costs of the disposal holes and the disposal tunnels. But, these material costs will be highly expensive and unstable due to the modernization of the developing countries. So the studies for a material cost should be continued to identify the actual cost of an HLW repository
Mineralogy and sealing properties of various bentonites and smectite-rich clay materials

Energy Technology Data Exchange (ETDEWEB)

Karnland, Ola; Olsson, Siv; Nilsson, Ulf (Clay Technology AB (SE))

2006-12-15

The present work includes a coherent study of Wyoming bentonite with respect to the most relevant properties for use in a repository, and a parallel study of other potential buffer and tunnel backfilling materials. The reason for this is twofold; to quantify the effect of mineralogical variations on the various important sealing properties of bentonite, and to verify that there are alternative potential sources of bentonite. The latter is motivated by the fact that Sweden alone plans to deposit at least 6,000 copper canisters which include approximately 130,000 metric tones bentonite buffer material and several times more as tunnel backfill material. Different types of sealing clay materials may also be relevant to use, since the demands on the clay will be different at the various locations in a repository. Alternative sources of bentonite would consequently be valuable in order to secure quality, supply, and price. Important aspects on buffer and tunnel backfilling materials may be summarized as: Original sealing properties. Hazardous substances in any respect. Short-term effects of ground-water chemistry. Long-term stability, i.e. effects of temperature and ground-water chemistry. Availability. Costs. The focus in this study is on the first three items. The long-term stability is indirectly considered in that mineralogical composition is determined. The availability is only considered in such a way that most of the analyzed materials represent huge clay formations, which contain much more material than needed for a repository. The cost aspects have not been included, mainly because the present day price is not relevant due to the time frame of the construction of a repository
Assessment of hydration process and mechanical properties of cemented paste backfill by electrical resistivity measurement

Science.gov (United States)

Xu, Wenbin; Tian, Xichun; Cao, Peiwang

2018-04-01

Cemented paste backfill (CPB) is an emerging mine backfill technique that allows environmentally hazardous tailings to return to the underground openings or stopes, thereby maximising the safety, efficiency and productivity of operation. Uniaxial compressive strength (UCS) is one of the most commonly used parameters for evaluating the mechanical performance of CPB; the prediction of the UCS of CPB structures from early to advanced ages is of great practical importance. This study aims to investigate the predictability of the UCS of CPB during the hydration process based on electrical resistivity (ER) measurement. For this purpose, the samples prepared at different cement-to-tailing ratios and solid contents were subjected to the ER test during the whole hydration process and UCS tests at 3, 7, 28 days of curing periods. The effect of cement-to-tailing ratio and solid content on the ER and UCS of CPB samples was obtained; the UCS values were correlated with the corresponding ER data. Microstructural analysis was also performed on CPB samples to understand the effect of microstructure on the ER data. The result shows that the ER of CPB decreases first and then increases with the speed which is faster in the previous part than the latter. The ER and UCS of CPB samples increased with increasing cement-to-tailing ratio and solid content and curing periods. A logarithmic relationship is established for each mixture in order to predict the UCS of CPB based on ER. Scanning electron microscope analyses have revealed that the microstructure of the CPB changes with the age from the initial floc to honeycomb, and eventually to the compact clumps. The ER properties of CPB samples were highly associated with their respective microstructural properties. The major output of this study is that ER test is effectively capable for a preliminary prediction of the UCS of CPB.
Quantum mechanical tunneling in chemical physics

CERN Document Server

Nakamura, Hiroki

2016-01-01

Quantum mechanical tunneling plays important roles in a wide range of natural sciences, from nuclear and solid-state physics to proton transfer and chemical reactions in chemistry and biology. Responding to the need for further understanding of multidimensional tunneling, the authors have recently developed practical methods that can be applied to multidimensional systems. Quantum Mechanical Tunneling in Chemical Physics presents basic theories, as well as original ones developed by the authors. It also provides methodologies and numerical applications to real molecular systems. The book offers information so readers can understand the basic concepts and dynamics of multidimensional tunneling phenomena and use the described methods for various molecular spectroscopy and chemical dynamics problems. The text focuses on three tunneling phenomena: (1) energy splitting, or tunneling splitting, in symmetric double well potential, (2) decay of metastable state through tunneling, and (3) tunneling effects in chemical...
Tunneling into quantum wires: regularization of the tunneling Hamiltonian and consistency between free and bosonized fermions

OpenAIRE

Filippone, Michele; Brouwer, Piet

2016-01-01

Tunneling between a point contact and a one-dimensional wire is usually described with the help of a tunneling Hamiltonian that contains a delta function in position space. Whereas the leading order contribution to the tunneling current is independent of the way this delta function is regularized, higher-order corrections with respect to the tunneling amplitude are known to depend on the regularization. Instead of regularizing the delta function in the tunneling Hamiltonian, one may also obta...
A compact atomic force-scanning tunneling microscope for studying microelectronics and environmental aerosols

International Nuclear Information System (INIS)

Chen, G.

1996-06-01

This dissertation describes the characteristics and the construction of a compact atomic force/scanning tunneling microscope (AFM/STM). The basics and the method of preparing a tunneling junction between a chemically etched tunneling tip and a micro-manufactured cantilever is outlined by analyzing the forces between tunneling tip and cantilever as well as between force-sensing tip and sample surfaces. To our best knowledge this instrument is the first one using a commercial cantilever with only one piezoelectric tube carrying the whole tunneling sensor. The feedback control system has been optimized after a careful analysis of the electronic loop characteristics. The mode of operation has been determined by analyzing the dynamic characteristics of the scan heads and by investigating the time characteristics of the data acquisition system. The vibration isolation system has been calibrated by analyzing the characteristics of the damping setup and the stiffness of the scan head. The calculated results agree well with the measured ones. Also, a software package for data acquisition and real time display as well as for image processing and three-dimensional visualization has been developed. With this home-made software package, the images can be processed by means of a convolution filter, a Wiener filter and other 2-D FFT filters, and can be displayed in different ways. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) and graphite surfaces have been obtained in AFM and STM mode. New theoretical explanations have been given for the observed anomalous STM and AFM images of graphite by calculating the asymmetric distribution of quantum conductance and tip-surface forces on a graphite surface. This not only resolved the theoretical puzzles of STM and AFM of graphite, but also revealed the relation between atomic force microscopy and scanning tunneling microscopy of graphite. Applications of STM and AFM to micro-electronic devices have been investigated
Plugs for deposition tunnels in a deep geologic repository in granitic rock. Concepts and experience

International Nuclear Information System (INIS)

Dixon, D. A.; Boergesson, L.; Gunnarsson, D.; Hansen, J.

2009-11-01

Regardless of the emplacement geometry selected in a geological repository for spent nuclear fuel, there will be a requirement for the access tunnels to remain open while repository operations are ongoing. The period of repository operation will stretch for many years (decades to more than a century depending on disposal concept and number of canisters to be installed). Requirements for extended monitoring of the repository before final closure may further extend the period over which the tunnels must remain open. The intersection of the emplacement rooms/drifts and the access tunnels needs to be physically closed in order to ensure that the canisters remain undisturbed and that no undesirable hydraulic conditions are allowed to develop within the backfilled volume. As a result of these requirements, generic guidelines and design concepts have been developed for 'Plugs' that are intended to provide mechanical restraint, physical security and hydraulic control functions over the short-term (repository operational and pre-closure monitoring periods). This report focuses on the role and requirements of plugs to be installed at emplacement room/ tunnel/drift entrances or in other locations within the repository that may require installation of temporary mechanical or hydraulic control structures. These plugs are not necessarily a permanent feature of the repository and may, if required, be removed for later installation of a permanent seal. Room/Drift plugs are also by their defined function, physically accessible during repository operation so their performance can be monitored and remedial actions taken if necessary (e.g. increased seepage past the plug). A considerable number of sealing demonstrations have been undertaken at several research laboratories that are focussed on development of technologies and materials for use in isolation of spent nuclear fuel and these are briefly reviewed in this report. Additionally, technologies developed for non
Plugs for deposition tunnels in a deep geologic repository in granitic rock. Concepts and experience

Energy Technology Data Exchange (ETDEWEB)

Dixon, D.A. (AECL, Chalk River (Canada)); Boergesson, L. (Clay Technology, Lund (Sweden)); Gunnarsson, D. (Swedish Nuclear Fuel and Waste Management Co, Stockholm (Sweden)); Hansen, J. (Posiva Oy, Eurajoki (Finland))

2009-11-15

Regardless of the emplacement geometry selected in a geological repository for spent nuclear fuel, there will be a requirement for the access tunnels to remain open while repository operations are ongoing. The period of repository operation will stretch for many years (decades to more than a century depending on disposal concept and number of canisters to be installed). Requirements for extended monitoring of the repository before final closure may further extend the period over which the tunnels must remain open. The intersection of the emplacement rooms/drifts and the access tunnels needs to be physically closed in order to ensure that the canisters remain undisturbed and that no undesirable hydraulic conditions are allowed to develop within the backfilled volume. As a result of these requirements, generic guidelines and design concepts have been developed for 'Plugs' that are intended to provide mechanical restraint, physical security and hydraulic control functions over the short-term (repository operational and pre-closure monitoring periods). This report focuses on the role and requirements of plugs to be installed at emplacement room/ tunnel/drift entrances or in other locations within the repository that may require installation of temporary mechanical or hydraulic control structures. These plugs are not necessarily a permanent feature of the repository and may, if required, be removed for later installation of a permanent seal. Room/Drift plugs are also by their defined function, physically accessible during repository operation so their performance can be monitored and remedial actions taken if necessary (e.g. increased seepage past the plug). A considerable number of sealing demonstrations have been undertaken at several research laboratories that are focussed on development of technologies and materials for use in isolation of spent nuclear fuel and these are briefly reviewed in this report. Additionally, technologies developed for non
Tunnelling of a molecule

International Nuclear Information System (INIS)

Jarvis, P.D.; Bulte, D.P.

1998-01-01

A quantum-mechanical description of tunnelling is presented for a one-dimensional system with internal oscillator degrees of freedom. The 'charged diatomic molecule' is frustrated on encountering a barrier potential by its centre of charge not being coincident with its centre of mass, resulting in transitions amongst internal states. In an adiabatic limit, the tunnelling of semiclassical coherent-like oscillator states is shown to exhibit the Hartman and Bueuttiker-Landauer times t H and t BL , with the time dependence of the coherent state parameter for the tunnelled state given by α(t) = α e -iω(t+Δt) , Δt = t H - it BL . A perturbation formalism is developed, whereby the exact transfer matrix can be expanded to any desired accuracy in a suitable limit. An 'intrinsic' time, based on the oscillator transition rate during tunnelling, transmission or reflection, is introduced. In simple situations the resulting intrinsic tunnelling time is shown to vanish to lowest order. In the general case a particular (nonzero) parametrisation is inferred, and its properties discussed in comparison with the literature on tunnelling times for both wavepackets and internal clocks. Copyright (1998) CSIRO Australia
Influence of quasiparticle multi-tunneling on the energy flow through the superconducting tunnel junction

International Nuclear Information System (INIS)

Samedov, V. V.; Tulinov, B. M.

2011-01-01

Superconducting tunnel junction (STJ) detector consists of two layers of superconducting material separated by thin insulating barrier. An incident particle produces in superconductor excess nonequilibrium quasiparticles. Each quasiparticle in superconductor should be considered as quantum superposition of electron-like and hole-like excitations. This duality nature of quasiparticle leads to the effect of multi-tunneling. Quasiparticle starts to tunnel back and forth through the insulating barrier. After tunneling from biased electrode quasiparticle loses its energy via phonon emission. Eventually, the energy that equals to the difference in quasiparticle energy between two electrodes is deposited in the signal electrode. Because of the process of multi-tunneling, one quasiparticle can deposit energy more than once. In this work, the theory of branching cascade processes was applied to the process of energy deposition caused by the quasiparticle multi-tunneling. The formulae for the mean value and variance of the energy transferred by one quasiparticle into heat were derived. (authors)
Enhanced MRI in carpal tunnel syndrome

International Nuclear Information System (INIS)

Hayakawa, Katsuhiko; Nakane, Takashi; Kobayashi, Shigeru; Asai, Takahiro; Wada, Kunio; Yoshizawa, Hidezo

1998-01-01

In this study, we performed contrast-enhanced MRI in patients with idiopathic carpal tunnel syndrome and examined the morphologic change in the carpal tunnel. In the transverse section of the opening of carpal tunnel where scaphoid and pisiform bones are figured out, we measured and examined 4 items, viz. the soft carpal tunnel volume, flat rate of median nerve, position of median nerve and thickness of palmer ligaments composing the base of carpal tunnel, with an image analyzer attached to the MRI apparatus. Whereas the average carpal tunnel volume in 12 hands of normal controls was 166.8 mm 2 , that in 74 hands of carpal tunnel syndrome was 207.2 mm 2 , a significant increase compared with the normal controls. The flat rate of median nerve was 46% in the controls, but that was 37.5% in the carpal tunnel syndrome, a significant flattening was noted. We connected the peaks of the scaphoid node and pisiform bone with a line and named it standard line. When we observed the position of median nerve in the carpal tunnel, the nerve in 9 of 12 hands, 75%, lay below the standard line in the controls, but the nerve in 65 of 74 hands, 87.8%, lay above the standard line in the carpal tunnel syndrome, clearly showing that the median nerve had shifted to the palmar side. Regarding these morphologic changes of the carpal tunnel, the internal pressure of the carpal tunnel is considered to be raised with swelling of the soft tissues mainly composing the inside of carpal tunnel, thus the area of cross section of carpal tunnel to be increased, the median nerve to be shifted to the palmar side and the median nerve to be compressed by the transverse carpal ligament at that time. Although we can observe these morphological changes readily in MRI images, these images show only the results of carpal tunnel syndrome after all, and do not specify the direct causes. However, we believe that these facts are important factors in the manifestation of idiopathic carpal tunnel syndrome. (author)
Josephson tunneling and nanosystems

OpenAIRE

Ovchinnikov, Yurii; Kresin, Vladimir

2010-01-01

Josephson tunneling between nanoclusters is analyzed. The discrete nature of the electronic energy spectra, including their shell ordering, is explicitly taken into account. The treatment considers the two distinct cases of resonant and non-resonant tunneling. It is demonstrated that the current density greatly exceeds the value discussed in the conventional theory. Nanoparticles are shown to be promising building blocks for nanomaterials-based tunneling networks.
Probing spin-polarized tunneling at high bias and temperature with a magnetic tunnel transistor

NARCIS (Netherlands)

Park, B.G.; Banerjee, T.; Min, B.C.; Sanderink, Johannes G.M.; Lodder, J.C.; Jansen, R.

2005-01-01

The magnetic tunnel transistor (MTT) is a three terminal hybrid device that consists of a tunnel emitter, a ferromagnetic (FM) base, and a semiconductor collector. In the MTT with a FM emitter and a single FM base, spin-polarized hot electrons are injected into the base by tunneling. After
Control of tunneling in heterostructures

International Nuclear Information System (INIS)

Volokhov, V M; Tovstun, C A; Ivlev, B

2007-01-01

A tunneling current between two rectangular potential wells can be effectively controlled by applying an external ac field. A variation of the ac frequency by 10% may lead to the suppression of the tunneling current by two orders of magnitude, which is a result of quantum interference under the action of the ac field. This effect of destruction of tunneling can be used as a sensitive control of tunneling current across nanosize heterostructures
Preferences in Sleep Position Correlate With Nighttime Paresthesias in Healthy People Without Carpal Tunnel Syndrome.

Science.gov (United States)

Roth Bettlach, Carrie L; Hasak, Jessica M; Krauss, Emily M; Yu, Jenny L; Skolnick, Gary B; Bodway, Greta N; Kahn, Lorna C; Mackinnon, Susan E

2017-10-01

Carpal tunnel syndrome has been associated with sleep position preferences. The aim of this study is to assess self-reported nocturnal paresthesias and sleeping position in participants with and without carpal tunnel syndrome diagnosis to further clinical knowledge for preventive and therapeutic interventions. A cross-sectional survey study of 396 participants was performed in young adults, healthy volunteers, and a patient population. Participants were surveyed on risk factors for carpal tunnel syndrome, nocturnal paresthesias, and sleep preferences. Binary logistic regression analysis was performed comparing participants with rare and frequent nocturnal paresthesias. Subanalyses for participants without carpal tunnel syndrome under and over 21 years of age were performed on all factors significantly associated with subclinical compression neuropathy in the overall population. Thirty-three percent of the study population experienced nocturnal paresthesias at least weekly. Increased body mass index ( P < .001) and sleeping with the wrist flexed ( P = .030) were associated with a higher frequency of nocturnal paresthesias. Side sleeping was associated with less frequent nocturnal symptoms ( P = .003). In participants without carpal tunnel syndrome, subgroup analysis illustrated a relationship between nocturnal paresthesias and wrist position. In participants with carpal tunnel syndrome, sleeping on the side had a significantly reduced frequency of nocturnal paresthesias. This study illustrates nocturnal paresthesias in people without history of carpal tunnel syndrome including people younger than previously reported. In healthy patients with upper extremity subclinical compression neuropathy, sleep position modification may be a useful intervention to reduce the frequency of nocturnal symptoms prior to developing carpal tunnel syndrome.
Implementation of the full-scale emplacement (FE) experiment at the Mont Terri rock laboratory

Energy Technology Data Exchange (ETDEWEB)

Müller, H.R.; Garitte, B.; Vogt, T.; and others

2017-04-15

Opalinus Clay is currently being assessed as the host rock for a deep geological repository for high-level and low- and intermediate-level radioactive wastes in Switzerland. Within this framework, the 'Full-Scale Emplacement' (FE) experiment was initiated at the Mont Terri rock laboratory close to the small town of St-Ursanne in Switzerland. The FE experiment simulates, as realistically as possible, the construction, waste emplacement, backfilling and early post-closure evolution of a spent fuel/vitrified high-level waste disposal tunnel according to the Swiss repository concept. The main aim of this multiple heater test is the investigation of repository-induced thermo-hydro-mechanical (THM) coupled effects on the host rock at this scale and the validation of existing coupled THM models. For this, several hundred sensors were installed in the rock, the tunnel lining, the bentonite buffer, the heaters and the plug. This paper is structured according to the implementation timeline of the FE experiment. It documents relevant details about the instrumentation, the tunnel construction, the production of the bentonite blocks and the highly compacted 'granulated bentonite mixture' (GBM), the development and construction of the prototype 'backfilling machine' (BFM) and its testing for horizontal GBM emplacement. Finally, the plug construction and the start of all 3 heaters (with a thermal output of 1350 Watt each) in February 2015 are briefly described. In this paper, measurement results representative of the different experimental steps are also presented. Tunnel construction aspects are discussed on the basis of tunnel wall displacements, permeability testing and relative humidity measurements around the tunnel. GBM densities achieved with the BFM in the different off-site mock-up tests and, finally, in the FE tunnel are presented. Finally, in situ thermal conductivity and temperature measurements recorded during the first heating months

Initial field testing definition of subsurface sealing and backfilling tests in unsaturated tuff; Yucca Mountain Site Characterization Project

Energy Technology Data Exchange (ETDEWEB)

Fernandez, J.A. [Sandia National Labs., Albuquerque, NM (United States); Case, J.B.; Tyburski, J.R. [I. T. Corp., Albuquerque, NM (United States)

1993-05-01

This report contains an initial definition of the field tests proposed for the Yucca Mountain Project repository sealing program. The tests are intended to resolve various performance and emplacement concerns. Examples of concerns to be addressed include achieving selected hydrologic and structural requirements for seals, removing portions of the shaft liner, excavating keyways, emplacing cementitious and earthen seals, reducing the impact of fines on the hydraulic conductivity of fractures, efficient grouting of fracture zones, sealing of exploratory boreholes, and controlling the flow of water by using engineered designs. Ten discrete tests are proposed to address these and other concerns. These tests are divided into two groups: Seal component tests and performance confirmation tests. The seal component tests are thorough small-scale in situ tests, the intermediate-scale borehole seal tests, the fracture grouting tests, the surface backfill tests, and the grouted rock mass tests. The seal system tests are the seepage control tests, the backfill tests, the bulkhead test in the Calico Hills unit, the large-scale shaft seal and shaft fill tests, and the remote borehole sealing tests. The tests are proposed to be performed in six discrete areas, including welded and non-welded environments, primarily located outside the potential repository area. The final selection of sealing tests will depend on the nature of the geologic and hydrologic conditions encountered during the development of the Exploratory Studies Facility and detailed numerical analyses. Tests are likely to be performed both before and after License Application.
Tunnelling in Soft Soil : Tunnel Boring Machine Operation and Soil Response

NARCIS (Netherlands)

Festa, D.; Broere, W.; Bosch, J.W.

2013-01-01

Constructing tunnels in soft soil with the use of Tunnel Boring Machines may induce settlements including soil movements ahead of the face, soil relaxation into the tail void, possible heave due to grouting, long lasting consolidation processes, and potentially several other mechanisms. A
Seismic prediction ahead of tunnel constructions

Science.gov (United States)

Jetschny, S.; Bohlen, T.; Nil, D. D.; Giese, R.

2007-12-01

To increase safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel can become a valuable tool. Within the \\it OnSite project founded by the BMBF (German Ministry of Education and Research) within \\it GeoTechnologien a new forward looking seismic imaging technique is developed to e.g. determine weak and water bearing zones ahead of the constructions. Our approach is based on the excitation and registration of \\it tunnel surface waves. These waves are excited at the tunnel face behind the cutter head of a tunnel boring machine and travel into drilling direction. Arriving at the front face they generate body waves (mainly S-waves) propagating further ahead. Reflected S-waves are back- converted into tunnel surface waves. For a theoretical description of the conversion process and for finding optimal acquisition geometries it is of importance to study the propagation characteristics of tunnel surface waves. 3D seismic finite difference modeling and analytic solutions of the wave equation in cylindric coordinates revealed that at higher frequencies, i.e. if the tunnel diameter is significantly larger than the wavelength of S-waves, these surface waves can be regarded as Rayleigh-waves circulating the tunnel. For smaller frequencies, i.e. when the S-wavelength approaches the tunnel diameter, the propagation characteristics of these surface waves are then similar to S- waves. Field measurements performed by the GeoForschungsZentrum Potsdam, Germany at the Gotthard Base Tunnel (Switzerland) show both effects, i.e. the propagation of Rayleigh- and body-wave like waves along the tunnel. To enhance our understanding of the excitation and propagation characteristics of tunnel surface waves the transition of Rayleigh to tube-waves waves is investigated both analytically and by numerical simulations.
Gap anisotropy and tunneling currents. [MPS3

DEFF Research Database (Denmark)

Lazarides, N.; Sørensen, Mads Peter

1996-01-01

The tunneling Hamiltonian formalism is applied to calculate the tunnelingcurrents through a small superconducting tunnel junction. The formalism isextended to nonconstant tunneling matrix elements. The electrodes of thejunction are assumed to......The tunneling Hamiltonian formalism is applied to calculate the tunnelingcurrents through a small superconducting tunnel junction. The formalism isextended to nonconstant tunneling matrix elements. The electrodes of thejunction are assumed to...
Magnetic Fluxtube Tunneling

Science.gov (United States)

Dahlburg, Russell B.; Antiochos,, Spiro K.; Norton, D.

1996-01-01

We present numerical simulations of the collision and subsequent interaction of two initially orthogonal, twisted, force free field magnetic fluxtubes. The simulations were carried out using a new three dimensional explicit parallelized Fourier collocation algorithm for solving the viscoresistive equations of compressible magnetohydrodynamics. It is found that, under a wide range of conditions, the fluxtubes can 'tunnel' through each other. Two key conditions must be satisfied for tunneling to occur: the magnetic field must be highly twisted with a field line pitch much greater than 1, and the magnetic Lundquist number must be somewhat large, greater than or equal to 2880. This tunneling behavior has not been seen previously in studies of either vortex tube or magnetic fluxtube interactions. An examination of magnetic field lines shows that tunneling is due to a double reconnection mechanism. Initially orthogonal field lines reconnect at two specific locations, exchange interacting sections and 'pass' through each other. The implications of these results for solar and space plasmas are discussed.
Scanning tunneling microscopy I general principles and applications to clean and adsorbate-covered surfaces

CERN Document Server

Wiesendanger, Roland

1992-01-01

Scanning Tunneling Microscopy I provides a unique introduction to a novel and fascinating technique that produces beautiful images of nature on an atomic scale. It is the first of three volumes that together offer a comprehensive treatment of scanning tunneling microscopy, its diverse applications, and its theoretical treatment. In this volume the reader will find a detailed description of the technique itself and of its applications to metals, semiconductors, layered materials, adsorbed molecules and superconductors. In addition to the many representative results reviewed, extensive references to original work will help to make accessible the vast body of knowledge already accumulated in this field.
Atomistic modeling trap-assisted tunneling in hole tunnel field effect transistors

Science.gov (United States)

Long, Pengyu; Huang, Jun Z.; Povolotskyi, Michael; Sarangapani, Prasad; Valencia-Zapata, Gustavo A.; Kubis, Tillmann; Rodwell, Mark J. W.; Klimeck, Gerhard

2018-05-01

Tunnel Field Effect Transistors (FETs) have the potential to achieve steep Subthreshold Swing (S.S.) below 60 mV/dec, but their S.S. could be limited by trap-assisted tunneling (TAT) due to interface traps. In this paper, the effect of trap energy and location on OFF-current (IOFF) of tunnel FETs is evaluated systematically using an atomistic trap level representation in a full quantum transport simulation. Trap energy levels close to band edges cause the highest leakage. Wave function penetration into the surrounding oxide increases the TAT current. To estimate the effects of multiple traps, we assume that the traps themselves do not interact with each other and as a whole do not modify the electrostatic potential dramatically. Within that model limitation, this numerical metrology study points to the critical importance of TAT in the IOFF in tunnel FETs. The model shows that for Dit higher than 1012/(cm2 eV) IO F F is critically increased with a degraded IO N/IO F F ratio of the tunnel FET. In order to have an IO N/IO F F ratio higher than 104, the acceptable Dit near Ev should be controlled to no larger than 1012/(cm2 eV) .
Using prior risk-related knowledge to support risk management decisions: lessons learnt from a tunneling project

NARCIS (Netherlands)

Chivatá Cárdenas, Ibsen; Al-Jibouri, Saad H.S.; Halman, Johannes I.M.; van de Linde, W.; Kaalberg, F.

2014-01-01

The authors of this article have developed six probabilistic causal models for critical risks in tunnel works. The details of the models' development and evaluation were reported in two earlier publications of this journal. Accordingly, as a remaining step, this article is focused on the
Lowest order in inelastic tunneling approximation : efficient scheme for simulation of inelastic electron tunneling data

NARCIS (Netherlands)

Rossen, E.T.R.; Flipse, C.F.J.; Cerda, J.I.

2013-01-01

We have developed an efficient and accurate formalism which allows the simulation at the ab initio level of inelastic electron tunneling spectroscopy data under a scanning tunneling microscope setup. It exploits fully the tunneling regime by carrying out the structural optimization and vibrational
Scanning tunneling microscopic images and scanning tunneling spectra for coupled rectangular quantum corrals

International Nuclear Information System (INIS)

Mitsuoka, Shigenori; Tamura, Akira

2011-01-01

Assuming that an electron confined by double δ-function barriers lies in a quasi-stationary state, we derived eigenstates and eigenenergies of the electron. Such an electron has a complex eigenenergy, and the imaginary part naturally leads to the lifetime of the electron associated with tunneling through barriers. We applied this point of view to the electron confined in a rectangular quantum corral (QC) on a noble metal surface, and obtained scanning tunneling microscopic images and a scanning tunneling spectrum consistent with experimental ones. We investigated the electron states confined in coupled QCs and obtained the coupled states constructed with bonding and anti-bonding states. Using those energy levels and wavefunctions we specified scanning tunneling microscope (STM) images and scanning tunneling spectra (STS) for the doubly and triply coupled QCs. In addition we pointed out the feature of resonant electron states associated with the same QCs at both ends of the triply coupled QCs.
Ivar Giaever, Tunneling, and Superconductors

Science.gov (United States)

dropdown arrow Site Map A-Z Index Menu Synopsis Ivar Giaever, Tunneling, and Superconductors Resources with in Superconductors Measured by Electron Tunneling; Physical Review Letters, Vol. 5 Issue 4: 147 - 148 ; August 15, 1960 Electron Tunneling Between Two Superconductors; Physical Review Letters, Vol. 5 Issue 10
Physics of optimal resonant tunneling

NARCIS (Netherlands)

Racec, P.N.; Stoica, T.; Popescu, C.; Lepsa, M.I.; Roer, van de T.G.

1997-01-01

The optimal resonant tunneling, or the complete tunneling transparence of a biased double-barrier resonant-tunneling (DBRT) structure, is discussed. It is shown that its physics does not rest on the departure from the constant potential within the barriers and well, due to the applied electric
Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

NARCIS (Netherlands)

Prins, M.W.J.; Jansen, R.; Kempen, van H.

1996-01-01

We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate
Submucosal tunneling techniques: current perspectives.

Science.gov (United States)

Kobara, Hideki; Mori, Hirohito; Rafiq, Kazi; Fujihara, Shintaro; Nishiyama, Noriko; Ayaki, Maki; Yachida, Tatsuo; Matsunaga, Tae; Tani, Johji; Miyoshi, Hisaaki; Yoneyama, Hirohito; Morishita, Asahiro; Oryu, Makoto; Iwama, Hisakazu; Masaki, Tsutomu

2014-01-01

Advances in endoscopic submucosal dissection include a submucosal tunneling technique, involving the introduction of tunnels into the submucosa. These tunnels permit safer offset entry into the peritoneal cavity for natural orifice transluminal endoscopic surgery. Technical advantages include the visual identification of the layers of the gut, blood vessels, and subepithelial tumors. The creation of a mucosal flap that minimizes air and fluid leakage into the extraluminal cavity can enhance the safety and efficacy of surgery. This submucosal tunneling technique was adapted for esophageal myotomy, culminating in its application to patients with achalasia. This method, known as per oral endoscopic myotomy, has opened up the new discipline of submucosal endoscopic surgery. Other clinical applications of the submucosal tunneling technique include its use in the removal of gastrointestinal subepithelial tumors and endomicroscopy for the diagnosis of functional and motility disorders. This review suggests that the submucosal tunneling technique, involving a mucosal safety flap, can have potential values for future endoscopic developments.
Ultrafast scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

1995-09-01

I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.
The comparison between limited open carpal tunnel release using direct vision and tunneling technique and standard open carpal tunnel release: a randomized controlled trial study.

Science.gov (United States)

Suppaphol, Sorasak; Worathanarat, Patarawan; Kawinwongkovit, Viroj; Pittayawutwinit, Preecha

2012-04-01

To compare the operative outcome of carpal tunnel release between limited open carpal tunnel release using direct vision and tunneling technique (group A) with standard open carpal tunnel release (group B). Twenty-eight patients were enrolled in the present study. A single blind randomized control trial study was conducted to compare the postoperative results between group A and B. The study parameters were Levine's symptom severity and functional score, grip and pinch strength, and average two-point discrimination. The postoperative results between two groups were comparable with no statistical significance. Only grip strength at three months follow up was significantly greater in group A than in group B. The limited open carpal tunnel release in the present study is effective comparable to the standard open carpal tunnel release. The others advantage of this technique are better cosmesis and improvement in grip strength at the three months postoperative period.
13th Australian tunnelling conference. Proceedings

Energy Technology Data Exchange (ETDEWEB)

NONE

2008-07-01

The theme of the conference was 'Engineering in a changing environment'. Topics covered include Australian tunnelling projects, design and development of ground support, tunnelling, international projects, fire and life safety, mining projects, risk management in tunnelling, and tunnel boring machine tunnelling. Papers of particular interest to the coal industry are: improving roadway development in underground coal mine (G. Lewis and G. Gibson), and polymer-based alternative to steel mesh for coal mine strata reinforcement (C. Lukey and others).
Does flexible tunnel drilling affect the femoral tunnel angle measurement after anterior cruciate ligament reconstruction?

Science.gov (United States)

Muller, Bart; Hofbauer, Marcus; Atte, Akere; van Dijk, C Niek; Fu, Freddie H

2015-12-01

To quantify the mean difference in femoral tunnel angle (FTA) as measured on knee radiographs between rigid and flexible tunnel drilling after anatomic anterior cruciate ligament (ACL) reconstruction. Fifty consecutive patients that underwent primary anatomic ACL reconstruction with a single femoral tunnel drilled with a flexible reamer were included in this study. The control group was comprised of 50 patients all of who underwent primary anatomic ACL reconstruction with a single femoral tunnel drilled with a rigid reamer. All femoral tunnels were drilled through a medial portal to ensure anatomic tunnel placement. The FTA was determined from post-operative anterior-to-posterior (AP) radiographs by two independent observers. A 5° difference between the two mean FTA was considered clinically significant. The average FTA, when drilled with a rigid reamer, was 42.0° ± 7.2°. Drilling with a flexible reamer resulted in a mean FTA of 44.7° ± 7.0°. The mean difference of 2.7° was not statistically significant. The intraclass correlation coefficient for inter-tester reliability was 0.895. The FTA can be reliably determined from post-operative AP radiographs and provides a useful and reproducible metric for characterizing femoral tunnel position after both rigid and flexible femoral tunnel drilling. This has implications for post-operative evaluation and preoperative treatment planning for ACL revision surgery. IV.
Large-Scale Experimental and Numerical Study of Blast Acceleration Created by Close-In Buried Explosion on Underground Tunnel Lining

Directory of Open Access Journals (Sweden)

Mohamad Reza Soheyli

2016-01-01

Full Text Available Despite growing demands for structures in water transportation tunnels, underground installations, subsurface dams, and subterranean channels, there is limited field knowledge about the dynamic behavior of these structures in the face of near-fault earthquakes or impulse excitations. This study conducted a large-scale test on underground tunnel excited by two close-in subsurface explosions. The horizontal and vertical acceleration were recorded on the vertical wall of the tunnel and the free field data including the acceleration on the ground surface at 11-meter distance from the tunnel. The frequency domain analysis of recorded results determined the frequency 961 Hz and 968 Hz for 1.69 kg and 2.76 kg equivalent T.N.T., respectively. Then, finite element analysis results were compared with the test data. The comparisons demonstrated a good correlation and satisfied the field data. Finally, based on numerical modeling, a parametric study was applied to determine the effects of shear wave velocity distance of the crater with respect to the tunnel on impulse response of the tunnel.
Derivation of the tunnelling exchange time for the model of trap-assisted tunnelling

International Nuclear Information System (INIS)

Racko, J.; Ballo, P.; Benko, P.; Harmatha, L.; Grmanova, A.; Breza, J.

2014-01-01

We present derivation of the tunnelling exchange times that play the key role in the model of trap assisted tunnelling (TAT) considering the electron and hole exchange processes between the trapping centre lying in the forbidden band of the semiconductor and the conduction band, valence band or a metal. All exchange processes are quantitatively described by respective exchange times. The reciprocal values of these exchange times represent the frequency with which the exchange processes contribute to the probability of occupation of the trap by free charge carriers. The crucial problem in any model of TAT is the calculation of the occupation probability. In our approach this probability is expressed in terms of only thermal and tunnelling exchange times. The concept of tunnelling exchange times presents a dominant contribution to our model of TAT. The new approach allows to simply calculate the probability of occupation of the trapping centre by a free charge carrier and subsequently to get the thermal and tunnelling generation-recombination rates occurring in the continuity equations. This is why the TAT model based on thermal and tunnelling exchange times is suitable for simulating the electrical properties of semiconductor nanostructures in which quantum mechanical phenomena play a key role. (authors)

Electronic noise of superconducting tunnel junction detectors

International Nuclear Information System (INIS)

Jochum, J.; Kraus, H.; Gutsche, M.; Kemmather, B.; Feilitzsch, F. v.; Moessbauer, R.L.

1994-01-01

The optimal signal to noise ratio for detectors based on superconducting tunnel junctions is calculated and compared for the cases of a detector consisting of one single tunnel junction, as well as of series and of parallel connections of such tunnel junctions. The influence of 1 / f noise and its dependence on the dynamical resistance of tunnel junctions is discussed quantitatively. A single tunnel junction yields the minimum equivalent noise charge. Such a tunnel junction exhibits the best signal to noise ratio if the signal charge is independent of detector size. In case, signal charge increases with detector size, a parallel or a series connection of tunnel junctions would provide the optimum signal to noise ratio. The equivalent noise charge and the respective signal to noise ratio are deduced as functions of tunnel junction parameters such as tunneling time, quasiparticle lifetime, etc. (orig.)
Tunneling of Atoms, Nuclei and Molecules

International Nuclear Information System (INIS)

Bertulani, C.A.

2015-01-01

This is a brief review of few relevant topics on tunneling of composite particles and how the coupling to intrinsic and external degrees of freedom affects tunneling probabilities. I discuss the phenomena of resonant tunneling, different barriers seen by subsystems, damping of resonant tunneling by level bunching and continuum effects due to particle dissociation. (author)
Chaos regularization of quantum tunneling rates

International Nuclear Information System (INIS)

Pecora, Louis M.; Wu Dongho; Lee, Hoshik; Antonsen, Thomas; Lee, Ming-Jer; Ott, Edward

2011-01-01

Quantum tunneling rates through a barrier separating two-dimensional, symmetric, double-well potentials are shown to depend on the classical dynamics of the billiard trajectories in each well and, hence, on the shape of the wells. For shapes that lead to regular (integrable) classical dynamics the tunneling rates fluctuate greatly with eigenenergies of the states sometimes by over two orders of magnitude. Contrarily, shapes that lead to completely chaotic trajectories lead to tunneling rates whose fluctuations are greatly reduced, a phenomenon we call regularization of tunneling rates. We show that a random-plane-wave theory of tunneling accounts for the mean tunneling rates and the small fluctuation variances for the chaotic systems.
Excavation of the Surikamigawa dam diversion tunnel. Surikamigawa dam karihaisui tunnel kantsu

Energy Technology Data Exchange (ETDEWEB)

Ikeda, T.; Konno, T. (Ministry of Construction, Tokyo (Japan))

1994-04-01

A bypass tunnel construction has been completed at the Surikamigawa dam (Japan). This paper describes the summary of the construction. The full-swing dam construction work is scheduled to begin in 1995. The soils distributed near the dam site consist of lapillus tuff containing andesite-based light stones and tuff-based conglomerates containing large gravels. Excavation of the dam diversion tunnel has used a blasting method, and the tunnel construction has adopted an automatic tunnel cross section marking system and a non-electric explosion method. This marking system is a system to irradiate a laser beam onto the facing to depict excavation lines that realizes labor saving and high-accuracy excavation. The error at the tunnel completion was found 20 mm. The non-electric explosion method ignites a coated explosive layer with an impact wave, which is electrostatically safe, and reduces blasting vibration. Electric detonators have also been used because of using ANFO explosives. The result obtained from measurements of inner space displacement necessary for the blasting process has indicated that the area near the dam site consists of stable mountains. 6 figs., 4 tabs.
Charge Islands Through Tunneling

Science.gov (United States)

Robinson, Daryl C.

2002-01-01

It has been recently reported that the electrical charge in a semiconductive carbon nanotube is not evenly distributed, but rather it is divided into charge "islands." This paper links the aforementioned phenomenon to tunneling and provides further insight into the higher rate of tunneling processes, which makes tunneling devices attractive. This paper also provides a basis for calculating the charge profile over the length of the tube so that nanoscale devices' conductive properties may be fully exploited.
Tunneling progress on the Yucca Mountain Project

International Nuclear Information System (INIS)

Hansmire, W.H.; Munzer, R.J.

1996-01-01

The current status of tunneling progress on the Yucca Mountain Project (YMP) is presented in this paper. The Exploratory Studies Facility (ESF), a key part of the YMP, has been long in development and construction is ongoing. This is a progress report on the tunneling aspects of the ESF as of January 1, 1996. For purposes of discussion in this summary, the tunneling has progressed in four general phases. The paper describes: tunneling in jointed rock under low stress; tunneling through the Bow Ridge Fault and soft rock; tunneling through the Imbricate Fault Zone; and Tunneling into the candidate repository formation
Peak stresses shift from femoral tunnel aperture to tibial tunnel aperture in lateral tibial tunnel ACL reconstructions: a 3D graft-bending angle measurement and finite-element analysis.

Science.gov (United States)

Van Der Bracht, Hans; Tampere, Thomas; Beekman, Pieter; Schepens, Alexander; Devriendt, Wouter; Verdonk, Peter; Victor, Jan

2018-02-01

To investigate the effect of tibial tunnel orientation on graft-bending angle and stress distribution in the ACL graft. Eight cadaveric knees were scanned in extension, 45°, 90°, and full flexion. 3D reconstructions with anatomically placed anterior cruciate ligament (ACL) grafts were constructed with Mimics 14.12 ® . 3D graft-bending angles were measured for classic medial tibial tunnels (MTT) and lateral tibial tunnels (LTT) with different drill-guide angles (DGA) (45°, 55°, 65°, and 75°). A pivot shift was performed on 1 knee in a finite-element analysis. The peak stresses in the graft were calculated for eight different tibial tunnel orientations. In a classic anatomical ACL repair, the largest graft-bending angle and peak stresses are seen at the femoral tunnel aperture. The use of a different DGA at the tibial side does not change the graft-bending angle at the femoral side or magnitude of peak stresses significantly. When using LTT, the largest graft-bending angles and peak stresses are seen at the tibial tunnel aperture. In a classic anatomical ACL repair, peak stresses in the ACL graft are found at the femoral tunnel aperture. When an LTT is used, peak stresses are similar compared to classic ACL repairs, but the location of the peak stress will shift from the femoral tunnel aperture towards the tibial tunnel aperture. the risk of graft rupture is similar for both MTTs and LTTs, but the location of graft rupture changes from the femoral tunnel aperture towards the tibial tunnel aperture, respectively. I.
Hypersonic Tunnel Facility (HTF)

Data.gov (United States)

Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...
Klein tunneling phenomenon with pair creation process

Science.gov (United States)

Wu, G. Z.; Zhou, C. T.; Fu, L. B.

2018-01-01

In this paper, we study the Klein tunneling phenomenon with electron-positron pair creation process. Pairs can be created from the vacuum by a supercritical single-well potential (for electrons). In the time region, the time-dependent growth pattern of the created pairs can be characterized by four distinct regimes which can be considered as four different statuses of the single well. We find that if positrons penetrate the single well by Klein tunneling in different statuses, the total number of the tunneling positrons will be different. If Klein tunneling begins at the initial stage of the first status i.e. when the sing well is empty, the tunneling process and the total number of tunneling positrons are similar to the traditional Klein tunneling case without considering the pair creation process. As the tunneling begins later, the total tunneling positron number increases. The number will finally settle to an asymptotic value when the tunneling begins later than the settling-down time t s of the single well which has been defined in this paper.
Tunneling time, what is its meaning?

International Nuclear Information System (INIS)

McDonald, C R; Orlando, G; Vampa, G; Brabec, T

2015-01-01

The tunnel time ionization dynamics for bound systems in laser fields are investigated. Numerical analysis for a step function switch-on of the field allows for the tunnel time to be defined as the time it takes the ground state to develop the under-barrier wavefunction components necessary to achieve the static field ionization rate. A relation between the tunnel time and the Keldysh time is established. The definition of the tunnel time is extended to time varying fields and experimental possibilities for measuring the tunnel time are discussed
Transonic Dynamics Tunnel (TDT)

Data.gov (United States)

Federal Laboratory Consortium — The Transonic Dynamics Tunnel (TDT) is a continuous flow wind-tunnel facility capable of speeds up to Mach 1.2 at stagnation pressures up to one atmosphere. The TDT...
Effects of neglecting carrier tunneling on electrostatic potential in calculating direct tunneling gate current in deep submicron MOSFETs

OpenAIRE

Hakim, MMA; Haque, A

2002-01-01

We investigate the validity of the assumption of neglecting carrier tunneling effects on self-consistent electrostatic potential in calculating direct tunneling gate current in deep submicron MOSFETs. Comparison between simulated and experimental results shows that for accurate modeling of direct tunneling current, tunneling effects on potential profile need to be considered. The relative error in gate current due to neglecting carrier tunneling is higher at higher gate voltages and increases...
Road and Railroad Tunnels

Data.gov (United States)

Department of Homeland Security — Tunnels in the United States According to the HSIP Tiger Team Report, a tunnel is defined as a linear underground passageway open at both ends. This dataset is based...
PUREX Storage Tunnels dangerous waste permit application

International Nuclear Information System (INIS)

1991-12-01

The PUREX Storage Tunnels are a mixed waste storage unit consisting of two underground railroad tunnels: Tunnel Number 1 designated 218-E-14 and Tunnel Number 2 designated 218-E-15. The two tunnels are connected by rail to the PUREX Plant and combine to provide storage space for 48 railroad cars (railcars). The PUREX Storage Tunnels provide a long-term storage location for equipment removed from the PUREX Plant. Transfers into the PUREX Storage Tunnels are made on an as-needed basis. Radioactively contaminated equipment is loaded on railcars and remotely transferred by rail into the PUREX Storage Tunnels. Railcars act as both a transport means and a storage platform for equipment placed into the tunnels. This report consists of part A and part B. Part A reports on amounts and locations of the mixed water. Part B permit application consists of the following: Facility Description and General Provisions; Waste Characteristics; Process Information; Groundwater Monitoring; Procedures to Prevent Hazards; Contingency Plan; Personnel Training; Exposure Information Report
Settlement mechanism of the backfilled ground around nuclear power plant buildings. Part 2. A series of centrifuge tests and a numerical simulation by using FEM about a typical test result

International Nuclear Information System (INIS)

Kawai, Tadashi; Ishimaru, Makoto

2009-01-01

During the Niigataken Chuetsu-oki earthquake, rather large settlements of the backfill ground around the rigid and stable buildings were observed. In this study, five cases of centrifuge tests with shaking events were conducted to reproduce the similar type of the settlements in order to examine the mechanism of the settlements. The results from those tests showed that the ground was settled by the negative dilatancy of sandy soils anywhere in the model ground and the additional settlements were suddenly caused when the backfill ground was apart from the rigid wall modeling the rigid and stable buildings, namely a sliding failure in an active state was occurred in the backfill ground near the structure. It was confirmed that these settlements were able to be estimated by a simple method proposed in this report, in which only the differences between the self-weight of the sliding block and the soil strength calculated at the initial stress conditions were considered as the driving forces of the sliding failure, and then the accelerations calculated from the forces being divided by the mass of the sliding block were simply integrated two times with respected to the time when the ground was apart from the structure. Further, a numerical simulation by using FEM about a typical test result was conducted, and these settlements were well simulated. (author)
Electrically tunable tunneling rectification magnetoresistance in magnetic tunneling junctions with asymmetric barriers.

Science.gov (United States)

Wang, Jing; Huang, Qikun; Shi, Peng; Zhang, Kun; Tian, Yufeng; Yan, Shishen; Chen, Yanxue; Liu, Guolei; Kang, Shishou; Mei, Liangmo

2017-10-26

The development of multifunctional spintronic devices requires simultaneous control of multiple degrees of freedom of electrons, such as charge, spin and orbit, and especially a new physical functionality can be realized by combining two or more different physical mechanisms in one specific device. Here, we report the realization of novel tunneling rectification magnetoresistance (TRMR), where the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated in Co/CoO-ZnO/Co magnetic tunneling junctions with asymmetric tunneling barriers. Moreover, by simultaneously applying direct current and alternating current to the devices, the TRMR has been remarkably tuned in the range from -300% to 2200% at low temperature. This proof-of-concept investigation provides an unexplored avenue towards electrical and magnetic control of charge and spin, which may apply to other heterojunctions to give rise to more fascinating emergent functionalities for future spintronics applications.
Scanning tunneling microscopy

International Nuclear Information System (INIS)

Binnig, G.; Rohrer, H.

1983-01-01

Based on vacuum tunneling, a novel type of microscope, the scanning tunneling microscope (STM) was developed. It has an unprecedented resolution in real space on an atomic scale. The authors review the important technical features, illustrate the power of the STM for surface topographies and discuss its potential in other areas of science and technology. (Auth.)
Scanning tunneling microscope nanoetching method

Science.gov (United States)

Li, Yun-Zhong; Reifenberger, Ronald G.; Andres, Ronald P.

1990-01-01

A method is described for forming uniform nanometer sized depressions on the surface of a conducting substrate. A tunneling tip is used to apply tunneling current density sufficient to vaporize a localized area of the substrate surface. The resulting depressions or craters in the substrate surface can be formed in information encoding patterns readable with a scanning tunneling microscope.
Superconducting tunneling with the tunneling Hamiltonian. II. Subgap harmonic structure

International Nuclear Information System (INIS)

Arnold, G.B.

1987-01-01

The theory of superconducting tunneling without the tunneling Hamiltonian is extended to treat superconductor/insulator/superconductor junctions in which the transmission coefficient of the insulating barrier approaches unity. The solution for the current in such junctions is obtained by solving the problem of a particle hopping in a one-dimensional lattice of sites, with forward and reverse transfer integrals that depend on the site. The results are applied to the problem of subgap harmonic structure in superconducting tunneling. The time-dependent current at finite voltage through a junction exhibiting subgap structure is found to have terms that oscillate at all integer multiples of the Josephson frequency, n(2eV/h). The amplitudes of these new, and as yet unmeasured, ac current contributions as a function of voltage are predicted
Dirac particle tunneling from black rings

International Nuclear Information System (INIS)

Jiang Qingquan

2008-01-01

Recent research shows that Hawking radiation can be treated as a quantum tunneling process, and Hawking temperatures of Dirac particles across the horizon of a black hole can be correctly recovered via the fermion tunneling method. In this paper, motivated by the fermion tunneling method, we attempt to apply the analysis to derive Hawking radiation of Dirac particles via tunneling from black ring solutions of 5-dimensional Einstein-Maxwell-dilaton gravity theory. Finally, it is interesting to find that, as in the black hole case, fermion tunneling can also result in correct Hawking temperatures for the rotating neutral, dipole, and charged black rings.

Engineers win award for Swiss tunnel

CERN Multimedia

2003-01-01

A Derby engineering consultancy has won the Tunnelling Industry Award 2003 for Excellence in Tunnel Design, offered by the British Tunnelling Society, for its work on the LHC in Geneva, Switzerland (1/2 page).
Semiclassical description of resonant tunneling

International Nuclear Information System (INIS)

Bogomolny, E.B.; Rouben, D.C.

1996-01-01

A semiclassical formula is calculated for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The tunneling current is measured at the second interface of this well and the calculations idealized an experimental situation where a strong magnetic field tilted with respect to an electric field was used. It is shown that the contribution to the tunneling current, due to trajectories which begin at the first interface and end on the second, is dominant for periodic orbits which hit both walls of the quantum well. (author)
A Top Pilot Tunnel Preconditioning Method for the Prevention of Extremely Intense Rockbursts in Deep Tunnels Excavated by TBMs

Science.gov (United States)

Zhang, Chuanqing; Feng, Xiating; Zhou, Hui; Qiu, Shili; Wu, Wenping

2012-05-01

The headrace tunnels at the Jinping II Hydropower Station cross the Jinping Mountain with a maximum overburden depth of 2,525 m, where 80% of the strata along the tunnels consist of marble. A number of extremely intense rockbursts occurred during the excavation of the auxiliary tunnels and the drainage tunnel. In particular, a tunnel boring machine (TBM) was destroyed by an extremely intense rockburst in a 7.2-m-diameter drainage tunnel. Two of the four subsequent 12.4-m-diameter headrace tunnels will be excavated with larger size TBMs, where a high risk of extremely intense rockbursts exists. Herein, a top pilot tunnel preconditioning method is proposed to minimize this risk, in which a drilling and blasting method is first recommended for the top pilot tunnel excavation and support, and then the TBM excavation of the main tunnel is conducted. In order to evaluate the mechanical effectiveness of this method, numerical simulation analyses using the failure approaching index, energy release rate, and excess shear stress indices are carried out. Its construction feasibility is discussed as well. Moreover, a microseismic monitoring technique is used in the experimental tunnel section for the real-time monitoring of the microseismic activities of the rock mass in TBM excavation and for assessing the effect of the top pilot tunnel excavation in reducing the risk of rockbursts. This method is applied to two tunnel sections prone to extremely intense rockbursts and leads to a reduction in the risk of rockbursts in TBM excavation.
Buffer mass test - Rock drilling and civil engineering

International Nuclear Information System (INIS)

Pusch, R.

1982-09-01

The buffer mass test (BMT) is being run in the former 'ventilation drift' in which a number of rock investigations were previously conducted. A number of vertical pilot holes were drilled from the tunnel floor to get information of the water inflow in possible heater hole position. The final decision of the location of the heater holes was then made, the main principle being that much water should be available in each hole with the possible exception of one of the holes. Thereafter, the diameter 0.76 m heater holes were drilled to a depth of 3-3.3 m. Additional holes were then drilled for rock anchoring of the lids of the four outer heater holes, for the rock mechanical investigation, as well as for a number of water pressure gauges. The inner, about 12 m long part of the tunnel, was separated from the outer by bulwark. The purpose of this construction was to confine a backfill, the requirements of the bulwark being to withstand the swelling pressure as well as the water pressure. Outside the bulwark an approximately 1.5-1.7 m thick concrete slab was cast on the tunnel floor, extending about 24.7 m from the bulwark. Boxing-outs with the same height as the slab and with the horizontal dimensions 1.8 x 1.8 m, were made and rock-anchored concrete lids were cast on top of them after backfilling. The slab which thus represents 'rock', also forms a basal support of the bulwark. The lids permits access to the backfill as well as to the underlying, highly compacted bentonite for rapid direct determination of the water distributin at the intended successive test stops. The construction of the slab and lids will be described in this report. (Author)
Tunneling Ionization of Diatomic Molecules

DEFF Research Database (Denmark)

Svensmark, Jens Søren Sieg

2016-01-01

When a molecule is subject to a strong laser field, there is a probability that an electron can escape, even though the electrons are bound by a large potential barrier. This is possible because electrons are quantum mechanical in nature, and they are therefore able to tunnel through potential...... barriers, an ability classical particles do not possess. Tunnelling is a fundamental quantum mechanical process, a process that is distinctly non-classical, so solving this tunnelling problem is not only relevant for molecular physics, but also for quantum theory in general. In this dissertation the theory...... of tunneling ionizaion of molecules is presented and the results of numerical calculations are shown. One perhaps surprising result is, that the frequently used Born-Oppenheimer approximation breaks down for weak fields when describing tunneling ionization. An analytic theory applicable in the weak-field limit...
Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

KAUST Repository

Useinov, Arthur

2012-06-01

In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.
Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

KAUST Repository

Useinov, Arthur; Gooneratne, Chinthaka Pasan; Kosel, Jü rgen

2012-01-01

In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.
Tunneling magnetoresistance and electroresistance in Fe/PbTiO3/Fe multiferroic tunnel junctions

International Nuclear Information System (INIS)

Dai, Jian-Qing

2016-01-01

We perform first-principles electronic structure and spin-dependent transport calculations for a Fe/PbTiO 3 /Fe multiferroic tunnel junction with asymmetric TiO 2 - and PbO-terminated interfaces. We demonstrate that the interfacial electronic reconstruction driven by the in situ screening of ferroelectric polarization, in conjunction with the intricate complex band structure of barrier, play a decisive role in controlling the spin-dependent tunneling. Reversal of ferroelectric polarization results in a transition from insulating to half-metal-like conducting state for the interfacial Pb 6p z orbitals, which acts as an atomic-scale spin-valve by releasing the tunneling current in antiparallel magnetization configuration as the ferroelectric polarization pointing to the PbO-terminated interface. This effect produces large change in tunneling conductance. Our results open an attractive avenue in designing multiferroic tunnel junctions with excellent performance by exploiting the interfacial electronic reconstruction originated from the in situ screening of ferroelectric polarization.
Atomistic nature in band-to-band tunneling in two-dimensional silicon pn tunnel diodes

International Nuclear Information System (INIS)

Tabe, Michiharu; Tan, Hoang Nhat; Mizuno, Takeshi; Muruganathan, Manoharan; Anh, Le The; Mizuta, Hiroshi; Nuryadi, Ratno; Moraru, Daniel

2016-01-01

We study low-temperature transport properties of two-dimensional (2D) Si tunnel diodes, or Si Esaki diodes, with a lateral layout. In ordinary Si Esaki diodes, interband tunneling current is severely limited because of the law of momentum conservation, while nanoscale Esaki diodes may behave differently due to the dopants in the narrow depletion region, by atomistic effects which release such current limitation. In thin-Si lateral highly doped pn diodes, we find clear signatures of interband tunneling between 2D-subbands involving phonon assistance. More importantly, the tunneling current is sharply enhanced in a narrow voltage range by resonance via a pair of a donor- and an acceptor-atom in the pn junction region. Such atomistic behavior is recognized as a general feature showing up only in nanoscale tunnel diodes. In particular, a donor-acceptor pair with deeper ground-state energies is likely to be responsible for such a sharply enhanced current peak, tunable by external biases.
Hydro-mechanical evolution of the EDZ as transport path for radionuclides and gas: insights from the Mont Terri rock laboratory (Switzerland)

Energy Technology Data Exchange (ETDEWEB)

Paul Marschall, P.; Giger, S. [National Cooperative for the Disposal of Radioactive Waste (NAGRA), Wettingen (Switzerland); La Vassière De, R. [Agence Nationale pour la Gestion des Déchets Radioactifs ANDRA, Meuse Haute-Marne, Center RD 960, Bure (France); and others

2017-04-15

The excavation damaged zone (EDZ) around the backfilled underground structures of a geological repository represents a release path for radionuclides, which needs to be addressed in the assessment of long-term safety. Additionally, the EDZ may form a highly efficient escape route for corrosion and degradation gases, thus limiting the gas overpressures in the backfilled repository structures. The efficiency of this release path depends not only on the shape and extent of the EDZ, but also on the self-sealing capacity of the host rock formation and the prevailing state conditions, such as in situ stresses and pore pressure. The hydro-mechanical and chemico-osmotic phenomena associated with the formation and temporal evolution of the EDZ are complex, thus precluding a detailed representation of the EDZ in conventional modelling tools for safety assessment. Therefore, simplified EDZ models, able to mimic the safety-relevant functional features of the EDZ in a traceable manner are required. In the framework of the Mont Terri Project, a versatile modelling approach has been developed for the simulation of flow and transport processes along the EDZ with the goal of capturing the evolution of hydraulic significance of the EDZ after closure of the backfilled underground structures. The approach draws on both empirical evidence and experimental data, collected in the niches and tunnels of the Mont Terri rock laboratory. The model was benchmarked with a data set from an in situ self-sealing experiment at the Mont Terri rock laboratory. This paper summarises the outcomes of the benchmark exercise that comprises relevant empirical evidence, experimental data bases and the conceptual framework for modelling the evolution of the hydraulic significance of the EDZ around a backfilled tunnel section during the entire re-saturation phase. (authors)
Hydro-mechanical evolution of the EDZ as transport path for radionuclides and gas: insights from the Mont Terri rock laboratory (Switzerland)

International Nuclear Information System (INIS)

Paul Marschall, P.; Giger, S.; La Vassière De, R.

2017-01-01

The excavation damaged zone (EDZ) around the backfilled underground structures of a geological repository represents a release path for radionuclides, which needs to be addressed in the assessment of long-term safety. Additionally, the EDZ may form a highly efficient escape route for corrosion and degradation gases, thus limiting the gas overpressures in the backfilled repository structures. The efficiency of this release path depends not only on the shape and extent of the EDZ, but also on the self-sealing capacity of the host rock formation and the prevailing state conditions, such as in situ stresses and pore pressure. The hydro-mechanical and chemico-osmotic phenomena associated with the formation and temporal evolution of the EDZ are complex, thus precluding a detailed representation of the EDZ in conventional modelling tools for safety assessment. Therefore, simplified EDZ models, able to mimic the safety-relevant functional features of the EDZ in a traceable manner are required. In the framework of the Mont Terri Project, a versatile modelling approach has been developed for the simulation of flow and transport processes along the EDZ with the goal of capturing the evolution of hydraulic significance of the EDZ after closure of the backfilled underground structures. The approach draws on both empirical evidence and experimental data, collected in the niches and tunnels of the Mont Terri rock laboratory. The model was benchmarked with a data set from an in situ self-sealing experiment at the Mont Terri rock laboratory. This paper summarises the outcomes of the benchmark exercise that comprises relevant empirical evidence, experimental data bases and the conceptual framework for modelling the evolution of the hydraulic significance of the EDZ around a backfilled tunnel section during the entire re-saturation phase. (authors)
Quantum tunneling with friction

Science.gov (United States)

Tokieda, M.; Hagino, K.

2017-05-01

Using the phenomenological quantum friction models introduced by P. Caldirola [Nuovo Cimento 18, 393 (1941), 10.1007/BF02960144] and E. Kanai [Prog. Theor. Phys. 3, 440 (1948), 10.1143/ptp/3.4.440], M. D. Kostin [J. Chem. Phys. 57, 3589 (1972), 10.1063/1.1678812], and K. Albrecht [Phys. Lett. B 56, 127 (1975), 10.1016/0370-2693(75)90283-X], we study quantum tunneling of a one-dimensional potential in the presence of energy dissipation. To this end, we calculate the tunneling probability using a time-dependent wave-packet method. The friction reduces the tunneling probability. We show that the three models provide similar penetrabilities to each other, among which the Caldirola-Kanai model requires the least numerical effort. We also discuss the effect of energy dissipation on quantum tunneling in terms of barrier distributions.
INCAS TRISONIC WIND TUNNEL

Directory of Open Access Journals (Sweden)

Florin MUNTEANU

2009-09-01

Full Text Available The 1.2 m x 1.2 m Trisonic Blowdown Wind Tunnel is the largest of the experimental facilities at the National Institute for Aerospace Research - I.N.C.A.S. "Elie Carafoli", Bucharest, Romania. The tunnel has been designed by the Canadian company DSMA (now AIOLOS and since its commissioning in 1978 has performed high speed aerodynamic tests for more than 120 projects of aircraft, missiles and other objects among which the twin jet fighter IAR-93, the jet trainer IAR-99, the MIG-21 Lancer, the Polish jet fighter YRYDA and others. In the last years the wind tunnel has been used mostly for experimental research in European projects such as UFAST. The high flow quality parameters and the wide range of testing capabilities ensure the competitivity of the tunnel at an international level.
In-mine (tunnel-to-tunnel) electrical resistance tomography in South African platinum mines

CSIR Research Space (South Africa)

Van Schoor, Abraham M

2009-12-01

Full Text Available The applicability of tunnel-to-tunnel electrical resistance tomography (ERT) for imaging disruptive geological structures ahead of mining, in an igneous platinum mining environment is assessed. The geophysical targets of interest are slump...
Wind tunnel and CFD modelling of wind pressures on solar energy systems on flat roofs

NARCIS (Netherlands)

Bronkhorst, A.J.; Franke, J.; Geurts, C.P.W.; Bentum, van C.A.; Grepinet, F.

2010-01-01

Design of solar energy mounting systems requires more knowledge on the wind patterns around these systems. To obtain more insight in the flow patterns, which cause the pressure distributions on the solar energy systems, a wind tunnel test and Computational Fluid Dynamics analysis have been
Destructive quantum interference in spin tunneling problems

OpenAIRE

von Delft, Jan; Henley, Christopher L.

1992-01-01

In some spin tunneling problems, there are several different but symmetry-related tunneling paths that connect the same initial and final configurations. The topological phase factors of the corresponding tunneling amplitudes can lead to destructive interference between the different paths, so that the total tunneling amplitude is zero. In the study of tunneling between different ground state configurations of the Kagom\\'{e}-lattice quantum Heisenberg antiferromagnet, this occurs when the spi...
TrigDB back-filling method in EEW for the regional earthquake for reducing false location of the deep focus earthquake event by considering neighborhood triggers and forced association.

Science.gov (United States)

Park, J. H.; Chi, H. C.; Lim, I. S.; Seong, Y. J.; Pak, J.

2017-12-01

During the first phase of EEW(Earthquake Early Warning) service to the public by KMA (Korea Meteorological Administration) from 2015 in Korea, KIGAM(Korea Institute of Geoscience and Mineral Resources) has adopted ElarmS2 of UC Berkeley BSL and modified local magnitude relation, travel time curves and association procedures so called TrigDB back-filling method. The TrigDB back-filling method uses a database of sorted lists of stations based on epicentral distances of the pre-defined events located on the grids for 1,401 × 1,601 = 2,243,001 events around the Korean Peninsula at a grid spacing of 0.05 degrees. When the version of an event is updated, the TrigDB back-filling method is invoked. First, the grid closest to the epicenter of an event is chosen from the database and candidate stations, which are stations corresponding to the chosen grid and also adjacent to the already-associated stations, are selected. Second, the directions from the chosen grid to the associated stations are averaged to represent the direction of wave propagation, which is used as a reference for computing apparent travel times. The apparent travel times for the associated stations are computed using a P wave velocity of 5.5 km/s from the grid to the projected points in the reference direction. The travel times for the triggered candidate stations are also computed and used to obtain the difference between the apparent travel times of the associated stations and the triggered candidates. Finally, if the difference in the apparent travel times is less than that of the arrival times, the method forces the triggered candidate station to be associated with the event and updates the event location. This method is useful to reduce false locations of events which could be generated from the deep (> 500 km) and regional distance earthquakes happening on the subduction pacific plate boundaries. In comparison of the case study between TrigDB back-filling applied system and the others, we could get
Snow and ice blocking of tunnels

Energy Technology Data Exchange (ETDEWEB)

Lia, Leif

1998-12-31

Hydroelectric power development in cold regions causes much concern about operational reliability and dam safety. This thesis studies the temperature distribution in tunnels by means of air temperature measurements in six tunnel spillways and five diversion tunnels. The measurements lasted for two consecutive winters. The air through flow tunnel is used as it causes cooling of both rock and water. In open spillway tunnels, frost reaches the entire tunnel. In spillway tunnels with walls, the frost zones reach about 100 m from the downstream end. In mildly-inclined diversion tunnels, a frost free zone is located in the middle of the tunnel and snow and ice problems were only observed in the inlet and outlet. Severe aufeis is accumulation is observed in the frost zones. The heat transfer from rock to air, water and ice is calculated and used in a prediction model for the calculation of aufeis build-up together with local field observation data. The water penetration of snow plugs is also calculated, based on the heat balance. It takes 20 to 50 days for water to enter the blocked tunnel. The empirical values are 30 to 60 days, but only 1 day if the temperature of the snow pack is 0{sup o}C. Sensitivity analyses are carried out for temperature variations in rock, snow, water and ice. Systematic field observation shows that it is important for hydropower companies to know about the effects of snow and ice blocking in an area. A risk analysis of dam safety is presented for a real case. Finally, the thesis proposes solutions which can reduce the snow and ice problems. 79 refs., 63 figs., 11 tabs.
Investigation of Corner Effect and Identification of Tunneling Regimes in L-Shaped Tunnel Field-Effect-Transistor.

Science.gov (United States)

Najam, Faraz; Yu, Yun Seop

2018-09-01

Corner-effect existing in L-shaped tunnel field-effect-transistor (LTFET) was investigated using numerical simulations and band diagram analysis. It was found that the corner-effect is caused by the convergence of electric field in the sharp source corner present in an LTFET, thereby increasing the electric field in the sharp source corner region. It was found that in the corner-effect region tunneling starts early, as a function of applied bias, as compared to the rest of the channel not affected by corner-effect. Further, different tunneling regimes as a function of applied bias were identified in the LTFET including source to channel and channel to channel tunneling regimes. Presence of different tunneling regimes in LTFET was analytically justified with a set of equations developed to model source to channel, and channel to channel tunneling currents. Drain-current-gate-voltage (Ids-Vgs) characteristics obtained from the equations is in reasonable qualitative agreement with numerical simulation.
Scanning Tunneling Optical Resonance Microscopy

Science.gov (United States)

Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

2003-01-01

Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically tunneling current

Fiber coupled ultrafast scanning tunneling microscope

DEFF Research Database (Denmark)

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

1997-01-01

We report on a scanning tunneling microscope with a photoconductive gate in the tunneling current circuit. The tunneling tip is attached to a coplanar transmission line with an integrated photoconductive switch. The switch is illuminated through a fiber which is rigidly attached to the switch...... waveguide. The measurements show that the probe works as a transient voltage detector in contact and a capacitively coupled transient field detector in tunneling mode. We do not measure the transient voltage change in the ohmic tunneling current. In this sense, the spatial resolution for propagating...... substrate. By using a firmly attached fiber we achieve an excellent reproducibility and unconstrained positioning of the tip. We observe a transient signal with 2.9 ps pulse width in tunneling mode and 5 ps in contact mode. The instrument is applied to investigating the mode structure on a coplanar...
Experimental Evidence for Quantum Tunneling Time

Science.gov (United States)

Camus, Nicolas; Yakaboylu, Enderalp; Fechner, Lutz; Klaiber, Michael; Laux, Martin; Mi, Yonghao; Hatsagortsyan, Karen Z.; Pfeifer, Thomas; Keitel, Christoph H.; Moshammer, Robert

2017-07-01

The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the "tunnel exit."
Tunneling from the past horizon

Science.gov (United States)

Kang, Subeom; Yeom, Dong-han

2018-04-01

We investigate a tunneling and emission process of a thin-shell from a Schwarzschild black hole, where the shell was initially located beyond the Einstein-Rosen bridge and finally appears at the right side of the Penrose diagram. In order to obtain such a solution, we should assume that the areal radius of the black hole horizon increases after the tunneling. Hence, there is a parameter range such that the tunneling rate is exponentially enhanced, rather than suppressed. We may have two interpretations regarding this. First, such a tunneling process from the past horizon is improbable by physical reasons; second, such a tunneling is possible in principle, but in order to obtain a stable Einstein-Rosen bridge, one needs to restrict the parameter spaces. If such a process is allowed, this can be a nonperturbative contribution to Einstein-Rosen bridges as well as eternal black holes.
Molecular series-tunneling junctions.

Science.gov (United States)

Liao, Kung-Ching; Hsu, Liang-Yan; Bowers, Carleen M; Rabitz, Herschel; Whitesides, George M

2015-05-13

Charge transport through junctions consisting of insulating molecular units is a quantum phenomenon that cannot be described adequately by classical circuit laws. This paper explores tunneling current densities in self-assembled monolayer (SAM)-based junctions with the structure Ag(TS)/O2C-R1-R2-H//Ga2O3/EGaIn, where Ag(TS) is template-stripped silver and EGaIn is the eutectic alloy of gallium and indium; R1 and R2 refer to two classes of insulating molecular units-(CH2)n and (C6H4)m-that are connected in series and have different tunneling decay constants in the Simmons equation. These junctions can be analyzed as a form of series-tunneling junctions based on the observation that permuting the order of R1 and R2 in the junction does not alter the overall rate of charge transport. By using the Ag/O2C interface, this system decouples the highest occupied molecular orbital (HOMO, which is localized on the carboxylate group) from strong interactions with the R1 and R2 units. The differences in rates of tunneling are thus determined by the electronic structure of the groups R1 and R2; these differences are not influenced by the order of R1 and R2 in the SAM. In an electrical potential model that rationalizes this observation, R1 and R2 contribute independently to the height of the barrier. This model explicitly assumes that contributions to rates of tunneling from the Ag(TS)/O2C and H//Ga2O3 interfaces are constant across the series examined. The current density of these series-tunneling junctions can be described by J(V) = J0(V) exp(-β1d1 - β2d2), where J(V) is the current density (A/cm(2)) at applied voltage V and βi and di are the parameters describing the attenuation of the tunneling current through a rectangular tunneling barrier, with width d and a height related to the attenuation factor β.
Automated Boundary Conditions for Wind Tunnel Simulations

Science.gov (United States)

Carlson, Jan-Renee

2018-01-01

Computational fluid dynamic (CFD) simulations of models tested in wind tunnels require a high level of fidelity and accuracy particularly for the purposes of CFD validation efforts. Considerable effort is required to ensure the proper characterization of both the physical geometry of the wind tunnel and recreating the correct flow conditions inside the wind tunnel. The typical trial-and-error effort used for determining the boundary condition values for a particular tunnel configuration are time and computer resource intensive. This paper describes a method for calculating and updating the back pressure boundary condition in wind tunnel simulations by using a proportional-integral-derivative controller. The controller methodology and equations are discussed, and simulations using the controller to set a tunnel Mach number in the NASA Langley 14- by 22-Foot Subsonic Tunnel are demonstrated.
FUNDAMENTAL TUNNELING PROCESSES IN MOSa SOLAR CELLS

OpenAIRE

Balberg , I.; Hanak , J.; Weakliem , H.; Gal , E.

1981-01-01

In previous studies of tunneling through a MOSa tunnel junction, where Sa was a-Si : H, it was shown that their characteristics resemble those of MOSc devices where Sc was crystalline silicon. In the present work we would like to report a demonstration of fundamental tunneling processes in such tunnel junctions. In particular, the transition from semiconductor controlled regime to tunneling controlled regime can be clearly distinguished. The present results represent one of the rare cases whe...
Distribution of tunnelling times for quantum electron transport

International Nuclear Information System (INIS)

Rudge, Samuel L.; Kosov, Daniel S.

2016-01-01

In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.
Een systeem voor classificatie van korte tunnels.

NARCIS (Netherlands)

Schreuder, D.A.

1985-01-01

The most difficult problems in the lighting of tunnels occur in daylight and in particular in the entrance of the tunnel, while drivers approaching the tunnel must be able to look into the tunnel from the outside to detect the road course and eventual obstacles. A classification should The made on
Effects of the finite duration of quantum tunneling in laser-assisted scanning tunneling microscopy

International Nuclear Information System (INIS)

Hagmann, M.J.

1994-01-01

Previous measurements of tunnel conductance in heterostructures and experiments with Josephson junctions suggest quantum tunneling has a definite duration. The authors use semiclassical methods to determine the effects of this delay on the tunneling current in a laser-assisted STM. A planar-planar STM model is used with the exact multiple image potential, and the energy distribution for a free-electron metal. It is necessary to average over the phase at barrier entry, and iteration with back propagated solutions is required to obtain the transmission coefficients for evenly spaced phases and specified energies at barrier entry. The simulations suggest that the dependence of the tunneling current on the wavelength of illumination can serve as a basis for determining the duration of barrier traversal. A power flux density of 10 11 W/m 2 would be required at several wavelengths from 1 to 10 μm. It is possible that thermal effects could be separated from the modeled phenomena by determining the time dependence of the tunneling current with a pulsed laser
Dependences of the Tunnel Magnetoresistance and Spin Transfer Torque on the Sizes and Concentration of Nanoparticles in Magnetic Tunnel Junctions

Science.gov (United States)

Esmaeili, A. M.; Useinov, A. N.; Useinov, N. Kh.

2018-01-01

Dependences of the tunnel magnetoresistance and in-plane component of the spin transfer torque on the applied voltage in a magnetic tunnel junction have been calculated in the approximation of ballistic transport of conduction electrons through an insulating layer with embedded magnetic or nonmagnetic nanoparticles. A single-barrier magnetic tunnel junction with a nanoparticle embedded in an insulator forms a double-barrier magnetic tunnel junction. It has been shown that the in-plane component of the spin transfer torque in the double-barrier magnetic tunnel junction can be higher than that in the single-barrier one at the same thickness of the insulating layer. The calculations show that nanoparticles embedded in the tunnel junction increase the probability of tunneling of electrons, create resonance conditions, and ensure the quantization of the conductance in contrast to the tunnel junction without nanoparticles. The calculated dependences of the tunnel magnetoresistance correspond to experimental data demonstrating peak anomalies and suppression of the maximum magnetoresistances at low voltages.
Proceedings of the meeting on tunneling reaction and low temperature chemistry, 98 August. Tunneling reaction and its theory

Energy Technology Data Exchange (ETDEWEB)

Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru [eds.

1998-10-01

Present report is the proceedings of the 4th Meeting on Tunneling Reaction and Low Temperature Chemistry held in August 3 and 4, 1998. The main subject of the meeting is `Tunneling Reaction and Its Theory`. In the present meeting the theoretical aspects of tunneling phenomena in the chemical reaction were discussed intensively as the main topics. Ten reports were presented on the quantum diffusion of muon and proton in the metal and H{sub 2}{sup -} anion in the solid para-hydrogen, the theory of tunnel effect in the nuclear reaction and the tunneling reaction in the organic compounds. One special lecture was presented by Prof. J. Kondo on `Proton Tunneling in Solids`. The 11 of the presented papers are indexed individually. (J.P.N.)
Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions.

Science.gov (United States)

Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S; Saeys, Mark; Yang, Hyunsoo

2014-09-30

While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical strain, achieving an enhancement factor of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further correlate this strain-enhanced TMR with coherent spin tunneling through the MgO barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium Green's function (NEGF) quantum transport calculations. Our results help elucidate the TMR mechanism at the atomic level and can provide a new way to enhance, as well as tune, the quantum properties in nanoscale materials and devices.
Trap assisted tunneling and its effect on subthreshold swing of tunnel field effect transistors

OpenAIRE

Sajjad, Redwan N.; Chern, Winston; Hoyt, Judy L.; Antoniadis, Dimitri A.

2016-01-01

We provide a detailed study of the interface Trap Assisted Tunneling (TAT) mechanism in tunnel field effect transistors to show how it contributes a major leakage current path before the Band To Band Tunneling (BTBT) is initiated. With a modified Shockley-Read-Hall formalism, we show that at room temperature, the phonon assisted TAT current always dominates and obscures the steep turn ON of the BTBT current for common densities of traps. Our results are applicable to top gate, double gate and...
78 FR 46117 - National Tunnel Inspection Standards

Science.gov (United States)

2013-07-30

... busiest vehicular tunnel in the world. The Fort McHenry Tunnel handles a daily traffic volume of more than... vehicular, transit, and rail tunnels in the New York City metropolitan area. Although it is still too early... congestion along alternative routes, and save users both dollars and fuel. If these tunnels were closed due...
Tunneling magnetoresistance and electroresistance in Fe/PbTiO{sub 3}/Fe multiferroic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Dai, Jian-Qing, E-mail: djqkust@sina.com [School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

2016-08-21

We perform first-principles electronic structure and spin-dependent transport calculations for a Fe/PbTiO{sub 3}/Fe multiferroic tunnel junction with asymmetric TiO{sub 2}- and PbO-terminated interfaces. We demonstrate that the interfacial electronic reconstruction driven by the in situ screening of ferroelectric polarization, in conjunction with the intricate complex band structure of barrier, play a decisive role in controlling the spin-dependent tunneling. Reversal of ferroelectric polarization results in a transition from insulating to half-metal-like conducting state for the interfacial Pb 6p{sub z} orbitals, which acts as an atomic-scale spin-valve by releasing the tunneling current in antiparallel magnetization configuration as the ferroelectric polarization pointing to the PbO-terminated interface. This effect produces large change in tunneling conductance. Our results open an attractive avenue in designing multiferroic tunnel junctions with excellent performance by exploiting the interfacial electronic reconstruction originated from the in situ screening of ferroelectric polarization.
Tunnel nitrogen spill experiment

International Nuclear Information System (INIS)

Ageyev, A.I.; Alferov, V.N.; Mulholland, G.T.

1983-01-01

The Energy Saver Safety Analysis Report (SAR) found the tunnel oxygen deficiency considerations emphasized helium spills. These reports concluded the helium quickly warms and because of its low denisty, rises to the apex of the tunnel. The oxygen content below the apex and in all but the immediate vicinity of the helium spill is essentially unchanged and guarantees an undisturbed source of oxygen especially important to fallen personnel. In contrast nitrogen spills warm slower than helium due to the ratio of the enthalpy changes per unit volume spilled spread more uniformly across the tunnel cross-section when warmed because of the much smaller density difference with air, and generally provides a greater hazard than helium spills as a result. In particular there was concern that personnel that might fall to the floor for oxygen deficiency or other reasons might find less, and not more, oxygen with dire consequences. The SAR concluded tunnel nitrogen spills were under-investigated and led to this work
Effect of desliming of sulphide-rich mill tailings on the long-term strength of cemented paste backfill.

Science.gov (United States)

Ercikdi, Bayram; Baki, Hakan; İzki, Muhammet

2013-01-30

This paper presents the effect of desliming on the short- and long-term strength, stability and rheological properties of cemented paste backfill (CPB) produced from two different mill tailings. A 28-day unconfined compressive strength (UCS) of ≥1.0 MPa and the maintenance of stability over 224 days of curing were selected as the design criteria for the evaluation of paste backfill performance. Desliming induced some changes in the physical, chemical, mineralogical and rheological properties of the tailings. CPB mixture of the deslimed tailings achieved the required consistency at a lower water to cement ratio. The short-term UCSs of CPB samples of the deslimed tailings were found to be 30-100% higher than those samples of the reference tailings at all the binder dosages and curing times. CPB samples of the deslimed tailings achieved the long-term stability at relatively low binder dosages (e.g. 5 wt% c.f. ≥6.1% for the reference tailings). It was also estimated that desliming could allow a 13.4-23.1% reduction in the binder consumption depending apparently on the inherent characteristics of the tailings. Over the curing period, generation of sulphate and acid by the oxidation of pyrite present in the tailings was also monitored to correlate with the strength losses observed in the long term. Scanning electron microscope (SEM) and Mercury Intrusion Porosimetry (MIP) analyses provided an insight into the microstructure of CPB and the formation of secondary mineral phases (i.e. gypsum) confirming the beneficial effect of desliming. These findings suggest that desliming can be suitably exploited for CPB of sulphide-rich mill tailings to improve the strength and stability particularly in the long term and to reduce binder consumption. Copyright © 2012 Elsevier Ltd. All rights reserved.
New generation of free-piston shock tunnels

Science.gov (United States)

Morrison, W. R. B.; Stalker, R. J.; Duffin, J.

1990-01-01

Consideration is given to three free-piston driven hypersonic tunnels under construction that will greatly enhance existing test capabilities. The tunnel being built at Caltech will feature energy capabilities about 40 percent higher than those of the world's largest operational free-piston tunnel to date. The second tunnel under construction will allow full-size engine hardware at near-orbital speeds. The third facility is a high-performance expansion tube that will be capable of generating high enthalpy flows at speeds of up to 9 km/sec. It will provide flows with dissociation levels much lower than are attainable with a reflected shock tunnel, approaching actual flight conditions. A table shows the tunnels' characteristics.
Geological Prediction Ahead of Tunnel Face in the Limestone Formation Tunnel using Multi-Modal Geophysical Surveys

Science.gov (United States)

Zaki, N. F. M.; Ismail, M. A. M.; Hazreek Zainal Abidin, Mohd; Madun, Aziman

2018-04-01

Tunnel construction in typical karst topography face the risk which unknown geological condition such as abundant rainwater, ground water and cavities. Construction of tunnel in karst limestone frequently lead to potentially over-break of rock formation and cause failure to affected area. Physical character of limestone which consists large cavity prone to sudden failure and become worsen due to misinterpretation of rock quality by engineer and geologists during analysis stage and improper method adopted in construction stage. Consideration for execution of laboratory and field testing in rock limestone should be well planned and arranged in tunnel construction project. Several tests including Ground Penetration Radar (GPR) and geological face mapping were studied in this research to investigate the performances of limestone rock in tunnel construction, measured in term of rock mass quality that used for risk assessment. The objective of this study is to focus on the prediction of geological condition ahead of tunnel face using short range method (GPR) and verified by geological face mapping method to determine the consistency of actual geological condition on site. Q-Value as the main indicator for rock mass classification was obtained from geological face mapping method. The scope of this study is covering for tunnelling construction along 756 meters in karst limestone area which located at Timah Tasoh Tunnel, Bukit Tebing Tinggi, Perlis. For this case study, 15% of GPR results was identified as inaccurate for rock mass classification in which certain chainage along this tunnel with 34 out of 224 data from GPR was identified as incompatible with actual face mapping.
Backfill barriers: the use of engineered barriers based on geologic materials to assure isolation of radioactive wastes in a repository. [Nickel-iron alloys

Energy Technology Data Exchange (ETDEWEB)

Apps, J.A.; Cook, N.G.W.

1981-06-01

A preliminary assessment is made to show that canisters fabricated of nickel-iron alloys, and surrounded by a suitable backfill, may produce an engineered barrier where the canister material is thermodynamically stable with respect to its environment. As similar conditions exist in nature, the performance of such systems as barriers to isolate radionuclides can be predicted over very long periods, of the order of 10/sup 6/ years.

129I- and 99TcO4-scavengers for low level radioactive waste backfills

International Nuclear Information System (INIS)

Balsley, S.D.; Brady, P.V.; Krumhansl, J.L.; Anderson, H.L.

1997-03-01

Minimization of 129 I - and 99 TcO 4 - transport to the biosphere is critical to the success of low level radioactive waste (LLRW) storage facilities. Here we experimentally identify and classify optimal sorbent materials for inclusion in LLRW backfills. For low pH conditions (pH 4-5), Cu-sulfides and possibly imogolite-rich soils provide K d 's (surface-solution partition coefficients) of roughly 10 3 ml g -1 for iodide, and 10 2 ml g -1 for technetium. At near neutral pH, hydrotalcites, Cu-oxides, Cu-sulfides and lignite coal possess K d 's on the order of 10 2 ml g -1 for both iodine and technetium. At high pH (pH > 10), such as might occur in a cementitious LLRW facility, calcium monosulfate aluminate K d 's are calculated to be roughly 10 2 ml g -1 for both iodine and technetium
D Modelling of Tunnel Excavation Using Pressurized Tunnel Boring Machine in Overconsolidated Soils

Science.gov (United States)

Demagh, Rafik; Emeriault, Fabrice

2013-06-01

The construction of shallow tunnels in urban areas requires a prior assessment of their effects on the existing structures. In the case of shield tunnel boring machines (TBM), the various construction stages carried out constitute a highly three-dimensional problem of soil/structure interaction and are not easy to represent in a complete numerical simulation. Consequently, the tunnelling- induced soil movements are quite difficult to evaluate. A 3D simulation procedure, using a finite differences code, namely FLAC3D, taking into account, in an explicit manner, the main sources of movements in the soil mass is proposed in this paper. It is illustrated by the particular case of Toulouse Subway Line B for which experimental data are available and where the soil is saturated and highly overconsolidated. A comparison made between the numerical simulation results and the insitu measurements shows that the 3D procedure of simulation proposed is relevant, in particular regarding the adopted representation of the different operations performed by the tunnel boring machine (excavation, confining pressure, shield advancement, installation of the tunnel lining, grouting of the annular void, etc). Furthermore, a parametric study enabled a better understanding of the singular behaviour origin observed on the ground surface and within the solid soil mass, till now not mentioned in the literature.
Tunneling Flight Time, Chemistry, and Special Relativity.

Science.gov (United States)

Petersen, Jakob; Pollak, Eli

2017-09-07

Attosecond ionization experiments have not resolved the question "What is the tunneling time?". Different definitions of tunneling time lead to different results. Second, a zero tunneling time for a material particle suggests that the nonrelativistic theory includes speeds greater than the speed of light. Chemical reactions, occurring via tunneling, should then not be considered in terms of a nonrelativistic quantum theory calling into question quantum dynamics computations on tunneling reactions. To answer these questions, we define a new experimentally measurable paradigm, the tunneling flight time, and show that it vanishes for scattering through an Eckart or a square barrier, irrespective of barrier length or height, generalizing the Hartman effect. We explain why this result does not lead to experimental measurement of speeds greater than the speed of light. We show that this tunneling is an incoherent process by comparing a classical Wigner theory with exact quantum mechanical computations.
Tunnel Face Stability & New CPT Applications

NARCIS (Netherlands)

Broere, W.

2001-01-01

Nearly all tunnels bored in soft soils have encountered problems with the stability of the tunnel face. In several cases these problems led to an extended stand-still of the boring process. A better understanding of the face stability, and of the soil conditions around the tunnel boring machine, can
Behavior of cement paste as backfill in waste disposal boreholes

International Nuclear Information System (INIS)

Ferreira, Eduardo G.A.; Isiki, Vera L.K.; Miyamoto, Hissae; Marumo, Julio T.; Vicente, Roberto

2011-01-01

The Radioactive Waste Management Laboratory (GRR) at the Nuclear and Energy Research Institute (IPEN) in Sao Paulo, Brazil, is developing the concept a repository for disposition of disused sealed radioactive sources in a deep borehole, aiming at providing a feasible and inexpensive alternative for final disposal. A relevant fraction of the Brazilian inventory of sources has long half-life which prevents them to be disposed of in shallow ground disposal facilities. In the concept of repository under study, Portland cement paste is intended to be used as a backfill between the steel casing and the geological formation around the borehole. Cement paste will function as structural, an additional barrier against the migration of radionuclides outside the repository, and as a blockage against the transport of water between the different strata of the geological setting. The durability of cementitious materials under the conditions prevailing at the depth of disposal is as yet unknown. The objective of this research is to investigate the behavior of the cement paste and to estimate its service life. In this paper we present the results of mechanical strength measurements and chemical and mineralogical analysis of samples to detect the changes caused by radiation, temperature and aggressive chemicals present in ground water. Techniques of analysis included Inductively Coupled Plasma Atomic Emission Spectroscopy, Ion Chromatography, X-Ray Diffraction, and Thermo-Gravimetric Analysis. (author)
Shaft and tunnel sealing considerations

International Nuclear Information System (INIS)

Kelsall, P.C.; Shukla, D.K.

1980-01-01

Much of the emphasis of previous repository sealing research has been placed on plugging small diameter boreholes. It is increasingly evident that equal emphasis should now be given to shafts and tunnels which constitute more significant pathways between a repository and the biosphere. The paper discusses differences in requirements for sealing shafts and tunnels as compared with boreholes and the implications for seal design. Consideration is given to a design approach for shaft and tunnel seals based on a multiple component design concept, taking into account the requirements for retrievability of the waste. A work plan is developed for the future studies required to advance shaft and tunnel sealing technology to a level comparable with the existing technology for borehole sealing
Computational Multiqubit Tunnelling in Programmable Quantum Annealers

Science.gov (United States)

2016-08-25

ARTICLE Received 3 Jun 2015 | Accepted 26 Nov 2015 | Published 7 Jan 2016 Computational multiqubit tunnelling in programmable quantum annealers...state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational ...qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational
Evaluation of the Influence Caused by Tunnel Construction on Groundwater Environment: A Case Study of Tongluoshan Tunnel, China

Directory of Open Access Journals (Sweden)

Jian Liu

2015-01-01

Full Text Available Problems related to water inflow during tunnel construction are challenging to designers, workers, and management departments, as they can threaten tunneling project from safety, time, and economic aspects. Identifying the impacts on groundwater environment resulting from tunnel drainage and making a correct assessment before tunnel construction is essential to better understand troubles that would be encountered during tunnel excavation and helpful to adopt appropriate countermeasures to minimize the influences. This study presents an indicator system and quantifies each indicator of Tongluoshan tunnel, which is located in southwest China with a length of 5.2 km and mainly passes through carbonate rocks and sandstones, based on field investigation and related technological reports. Then, an evaluation is made using fuzzy comprehensive assessment method, with a result showing that it had influenced the local groundwater environment at a moderate degree. Information fed back from environmental investigation and hydrologic monitoring carried out during the main construction period proves the evaluation, as the flow of some springs and streams located beside the tunnel route was found experiencing an apparent decline.
Investigation into scanning tunnelling luminescence microscopy

International Nuclear Information System (INIS)

Manson-Smith, S.K.

2001-01-01

This work reports on the development of a scanning tunnelling luminescence (STL) microscope and its application to the study of Ill-nitride semiconductor materials used in the production of light emitting devices. STL microscopy is a technique which uses the high resolution topographic imaging capabilities of the scanning tunnelling microscope (STM) to generate high resolution luminescence images. The STM tunnelling current acts as a highly localised source of electrons (or holes) which generates luminescence in certain materials. Light generated at the STM tunnelling junction is collected concurrently with the height variation of the tunnelling probe as it is scanned across a sample surface, producing simultaneous topographic and luminescence images. Due to the very localised excitation source, high resolution luminescence images can be obtained. Spectroscopic resolution can be obtained by using filters. Additionally, the variation of luminescence intensity with tunnel current and with bias voltage can provide information on recombination processes and material properties. The design and construction of a scanning tunnelling luminescence microscope is described in detail. Operating under ambient conditions, the microscope has several novel features, including a new type of miniature inertial slider-based approach motor, large solid-angle light collection optical arrangement and a tip-height regulation system which requires the minimum of operator input. (author)
Proceedings of the meeting on tunneling reaction and low temperature chemistry, 97 October. Tunneling reaction and quantum medium

Energy Technology Data Exchange (ETDEWEB)

Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru [eds.

1998-02-01

Present report is the proceedings of the 3rd Meeting on Tunneling Reaction and Low Temperature Chemistry held in Oct. 13 and 14, 1997. The main subject of the meeting is `Tunneling Reaction and Quantum Medium`. In the meeting, the physical and chemical phenomena in the liquid helium such as quantum nucleation, spectroscopy of atoms and molecules, and tunneling abstraction reaction of tritium atom were discussed as the main topics as well as the tunneling reactions in the solid hydrogen and organic compounds. Through the meetings held in 1995, 1996, and 1997, the tunneling phenomena proceeding at various temperatures (room temperature to mK) in the wide fields of chemistry, biology, and physics were discussed intensively and the importance of the tunneling phenomena in the science has been getting clear. The 12 of the presented papers are indexed individually. (J.P.N.)
Proceedings of the meeting on tunneling reaction and low temperature chemistry, 97 October. Tunneling reaction and quantum medium

International Nuclear Information System (INIS)

Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru

1998-02-01

Present report is the proceedings of the 3rd Meeting on Tunneling Reaction and Low Temperature Chemistry held in Oct. 13 and 14, 1997. The main subject of the meeting is 'Tunneling Reaction and Quantum Medium'. In the meeting, the physical and chemical phenomena in the liquid helium such as quantum nucleation, spectroscopy of atoms and molecules, and tunneling abstraction reaction of tritium atom were discussed as the main topics as well as the tunneling reactions in the solid hydrogen and organic compounds. Through the meetings held in 1995, 1996, and 1997, the tunneling phenomena proceeding at various temperatures (room temperature to mK) in the wide fields of chemistry, biology, and physics were discussed intensively and the importance of the tunneling phenomena in the science has been getting clear. The 12 of the presented papers are indexed individually. (J.P.N.)
Tunneling anisotropic magnetoresistance in Co/AIOx/Al tunnel junctions with fcc Co (111) electrodes

NARCIS (Netherlands)

Wang, Kai; Tran, T. Lan Ahn; Brinks, Peter; Brinks, P.; Sanderink, Johannes G.M.; Bolhuis, Thijs; van der Wiel, Wilfred Gerard; de Jong, Machiel Pieter

2013-01-01

Tunneling anisotropic magnetoresistance (TAMR) has been characterized in junctions comprised of face-centered cubic (fcc) Co (111) ferromagnetic electrodes grown epitaxially on sapphire substrates, amorphous AlOx tunnel barriers, and nonmagnetic Al counterelectrodes. Large TAMR ratios have been
Mechanical stability of repository tunnels and factors to be considered for determining tunnel spacing

International Nuclear Information System (INIS)

Takeuchi, Kunifumi

1994-01-01

Kristallin-1 organized by Nagra is currently advanced as a synthetic project regarding a high level radioactive waste (HLW) repository in Switzerland. Its host rock is granitic rocks, and the potential siting area is located in northern Switzerland. The objective of this project is to demonstrate the long term safety of a HLW repository under more site-specific conditions than before. As the detailed geological data were investigated, the average size of undisturbed crystalline rock blocks is limited horizontally to about several hundred meter, therefore, the HLW repository area must be divided into several panels to avoid fracture zones. It is necessary to make tunnel spacing as small as possible for the purpose of reasonably designing the entire layout of repository tunnels. The main factors to be considered for determining repository tunnel spacing are listed. Rock mass modeling, rock mass material properties, the analysis model and parameters, the numerical analysis of repository tunnel stability and its main conclusion are reported. The numerical analysis of the temperature distribution in near field was carried out. Tunnel spacing should be set more than 20 m in view of the maximum temperature. (K.I.)
Resonance tunneling electron-vibrational spectroscopy of polyoxometalates.

Science.gov (United States)

Dalidchik, F I; Kovalevskii, S A; Balashov, E M

2017-05-21

The tunneling spectra of the ordered monolayer films of decamolybdodicobaltate (DMDC) compounds deposited from aqueous solutions on HOPG were measured by scanning tunnel microscopy in air. The DMDC spectra, as well as the tunneling spectra of other polyoxometalates (POMs), exhibit well-defined negative differential resistances (NDRs). The mechanism of formation of these spectral features was established from the collection of revealed NDR dependences on the external varying parameters and found to be common to all systems exhibiting Wannier-Stark localization. A model of biresonance tunneling was developed to provide an explanation for the totality of experimental data, both the literature and original, on the tunneling POM probing. A variant of the tunneling electron-vibrational POM spectroscopy was proposed allowing the determination of the three basic energy parameters-energy gaps between the occupied and unoccupied states, frequencies of the vibrational transitions accompanying biresonance electron-tunneling processes, and electron-vibrational interaction constants on the monomolecular level.
Current noise in tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Frey, Moritz; Grabert, Hermann [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104, Freiburg (Germany)

2017-06-15

We study current fluctuations in tunnel junctions driven by a voltage source. The voltage is applied to the tunneling element via an impedance providing an electromagnetic environment of the junction. We use circuit theory to relate the fluctuations of the current flowing in the leads of the junction with the voltage fluctuations generated by the environmental impedance and the fluctuations of the tunneling current. The spectrum of current fluctuations is found to consist of three parts: a term arising from the environmental Johnson-Nyquist noise, a term due to the shot noise of the tunneling current and a third term describing the cross-correlation between these two noise sources. Our phenomenological theory reproduces previous results based on the Hamiltonian model for the dynamical Coulomb blockade and provides a simple understanding of the current fluctuation spectrum in terms of circuit theory and properties of the average current. Specific results are given for a tunnel junction driven through a resonator. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Anomalous Tunnel Magnetoresistance and Spin Transfer Torque in Magnetic Tunnel Junctions with Embedded Nanoparticles

Science.gov (United States)

Useinov, Arthur; Ye, Lin-Xiu; Useinov, Niazbeck; Wu, Te-Ho; Lai, Chih-Huang

2015-01-01

The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature. PMID:26681336
A 2D analytical cylindrical gate tunnel FET (CG-TFET) model: impact of shortest tunneling distance

Science.gov (United States)

Dash, S.; Mishra, G. P.

2015-09-01

A 2D analytical tunnel field-effect transistor (FET) potential model with cylindrical gate (CG-TFET) based on the solution of Laplace’s equation is proposed. The band-to-band tunneling (BTBT) current is derived by the help of lateral electric field and the shortest tunneling distance. However, the analysis is extended to obtain the subthreshold swing (SS) and transfer characteristics of the device. The dependency of drain current, SS and transconductance on gate voltage and shortest tunneling distance is discussed. Also, the effect of scaling the gate oxide thickness and the cylindrical body diameter on the electrical parameters of the device is analyzed.
A 2D analytical cylindrical gate tunnel FET (CG-TFET) model: impact of shortest tunneling distance

International Nuclear Information System (INIS)

Dash, S; Mishra, G P

2015-01-01

A 2D analytical tunnel field-effect transistor (FET) potential model with cylindrical gate (CG-TFET) based on the solution of Laplace’s equation is proposed. The band-to-band tunneling (BTBT) current is derived by the help of lateral electric field and the shortest tunneling distance. However, the analysis is extended to obtain the subthreshold swing (SS) and transfer characteristics of the device. The dependency of drain current, SS and transconductance on gate voltage and shortest tunneling distance is discussed. Also, the effect of scaling the gate oxide thickness and the cylindrical body diameter on the electrical parameters of the device is analyzed. (paper)
Instabilities in thin tunnel junctions

International Nuclear Information System (INIS)

Konkin, M.K.; Adler, J.G.

1978-01-01

Tunnel junctions prepared for inelastic electron tunneling spectroscopy are often plagued by instabilities in the 0-500-meV range. This paper relates the bias at which the instability occurs to the barrier thickness
Characterization of a backfill candidate material, IBECO-RWC-BF Baclo Project - Phase 3 Laboratory tests

International Nuclear Information System (INIS)

Johannesson, Lars-Erik; Sanden, Torbjoern; Dueck, Ann; Ohlsson, Lars

2010-01-01

A backfill candidate material, IBECO-RWC-BF, which origin from Milos, Greece, has been investigated. The material was delivered both as granules and as pellets. The investigation described in this report aimed to characterize the material and evaluate if it can be used in a future repository. The following investigations have been done and are presented in this report: 1. Standard laboratory tests. Water content, liquid limit and swelling potential are examples on standard tests that have been performed. 2. Block manufacturing. The block compaction properties of the material have been determined. A first test was performed in laboratory but also tests in large scale have been performed. After finishing the test phase, 60 tons of blocks were manufactured at Hoeganaes Bjuf AB. The blocks will be used in large scale laboratory tests at Aespoe HRL. 3. Mechanical parameters. The compressibility of the material was investigated with oedometer tests (four tests) where the load was applied in steps after saturation. The evaluated oedometer modulus varied between 34.50 MPa. Tests were made to evaluate the elastic parameters of the material (E, ν). Altogether three tests were made on specimens with dry densities of about 1,710 kg/m 3 . The evaluated E-modulus and Poisson's ratio varied between 231-263 MPa and 0.16-0.19 respectively. The strength of the material, both the compressive strength and the tensile strength were measured on specimens compacted to different dry densities. The test results yielded a relation between density and the two types of strength. Furthermore, tests have been made in order to determine the compressibility of the unsaturated filling of pellets. Two tests were made where the pellets were loosely filled in a Proctor cylinder and then compressed at a constant rate of strain during continuously measurement of the applied load. 4. Swelling pressure and hydraulic conductivity. There is, as expected, a very clear influence of the dry density on the

Tunneling time in fluctuating symmetric double wells: Suppression and enhancement of tunneling by spatial symmetry-preserving perturbations

International Nuclear Information System (INIS)

Kar, Susmita; Bhattacharyya, S.P.

2011-01-01

Graphical abstract: Spatial symmetry-preserving sinusoidal fluctuations of symmetric double-well parameters cause enhancement of tunneling at ω ∼ ω 0 while rectified sinusoidal fluctuations suppress it at ω∼(ω 0 )/2 . Research highlights: → Spatial symmetry-preserving sinusoidal and rectified sinusoidal fluctuations of symmetrical double-well parameters have contrasting effects on tunneling. → Sinusoidal fluctuations at frequency ω ∼ ω 0 causes resonance enhancement of tunneling, ω 0 being the 0 + ↔ 1 + transition frequency. → Under rectified sinusoidal fluctuations at a frequency ω∼1/2 ω 0 suppression or coherent destruction of tunneling is observed due to barrier localization. → The observations are explained by energy-gain analysis and analysis of the time-dependent overlap amplitudes. - Abstract: We investigate how tunneling-time gets affected by spatial symmetry preserving fluctuations in the parameters determining the width, barrier height and well-depth of a symmetric double-well potential. Sinusoidal and rectified sinusoidal fluctuations of the well-parameters are shown to have contrasting effects. Significant enhancement of tunneling is noticed when the well-parameters fluctuate sinusoidally with frequency ω ∼ ω 0 while under rectified sinusoidal perturbation, quenching of tunneling takes place at a fluctuation frequency ω∼1/2 ω 0 ,ω 0 , being the frequency of the lowest transition allowed by the fluctuation induced spatial perturbation of even parity. Time-dependent Hellmann-Feynman theorem is invoked to analyze the energy changes induced by fluctuations. It turns out that the enhancement of tunneling in the sinusoidally fluctuating double well at frequency ω ∼ ω 0 is caused by transition to 1 ± levels under the barrier while in the rectified sinusoidal field at ω∼1/2 ω 0 , a two-photon like process suppresses the tunneling by inducing barrier localization.
Tunnelling in Dante's Inferno

Energy Technology Data Exchange (ETDEWEB)

Furuuchi, Kazuyuki [Manipal Centre for Natural Sciences, Manipal University, Dr.T.M.A. Pai Planetarium Building, Madhav Nagar, Manipal, Karnataka 576104 (India); Sperling, Marcus, E-mail: kazuyuki.furuuchi@manipal.edu, E-mail: marcus.sperling@univie.ac.at [Fakultät für Physik, Universität Wien, Boltzmanngasse 5, A-1090 Wien (Austria)

2017-05-01

We study quantum tunnelling in Dante's Inferno model of large field inflation. Such a tunnelling process, which will terminate inflation, becomes problematic if the tunnelling rate is rapid compared to the Hubble time scale at the time of inflation. Consequently, we constrain the parameter space of Dante's Inferno model by demanding a suppressed tunnelling rate during inflation. The constraints are derived and explicit numerical bounds are provided for representative examples. Our considerations are at the level of an effective field theory; hence, the presented constraints have to hold regardless of any UV completion.
Fire safety assessment of tunnel structures

DEFF Research Database (Denmark)

Gkoumas, Konstantinos; Giuliani, Luisa; Petrini, Francesco

2011-01-01

.g. structural and non structural, organizational, human behavior). This is even more truth for the fire safety design of such structures. Fire safety in tunnels is challenging because of the particular environment, bearing in mind also that a fire can occur in different phases of the tunnel’s lifecycle. Plans...... for upgrading fire safety provisions and tunnel management are also important for existing tunnels. In this study, following a brief introduction of issues regarding the above mentioned aspects, the structural performance of a steel rib for a tunnel infrastructure subject to fire is assessed by means...
Tunnelling in Dante's Inferno

International Nuclear Information System (INIS)

Furuuchi, Kazuyuki; Sperling, Marcus

2017-01-01

We study quantum tunnelling in Dante's Inferno model of large field inflation. Such a tunnelling process, which will terminate inflation, becomes problematic if the tunnelling rate is rapid compared to the Hubble time scale at the time of inflation. Consequently, we constrain the parameter space of Dante's Inferno model by demanding a suppressed tunnelling rate during inflation. The constraints are derived and explicit numerical bounds are provided for representative examples. Our considerations are at the level of an effective field theory; hence, the presented constraints have to hold regardless of any UV completion.
Tunneling path toward spintronics

International Nuclear Information System (INIS)

Miao Guoxing; Moodera, Jagadeesh S; Muenzenberg, Markus

2011-01-01

The phenomenon of quantum tunneling, which was discovered almost a century ago, has led to many subsequent discoveries. One such discovery, spin polarized tunneling, was made 40 years ago by Robert Meservey and Paul Tedrow (Tedrow and Meservey 1971 Phys. Rev. Lett. 26 192), and it has resulted in many fundamental observations and opened up an entirely new field of study. Until the mid-1990s, this field developed at a steady, low rate, after which a huge increase in activity suddenly occurred as a result of the unraveling of successful spin tunneling between two ferromagnets. In the past 15 years, several thousands of papers related to spin polarized tunneling and transport have been published, making this topic one of the hottest areas in condensed matter physics from both fundamental science and applications viewpoints. Many review papers and book chapters have been written in the past decade on this subject. This paper is not exhaustive by any means; rather, the emphases are on recent progress, technological developments and informing the reader about the current direction in which this topic is moving.
Utilization of geothermal energy in tunnels driven by tunnel drilling machines; Nutzung von Geothermie in TBM vorgetriebenen Tunneln

Energy Technology Data Exchange (ETDEWEB)

Pralle, Norbert; Franzius, Jan-Niklas [Ed. Zueblin AG, Stuttgart (Germany). Zentrale Technik; Liebel, Volker [Rehau AG und Co, Erlangen (Germany)

2009-07-01

Tunnels are nowadays more and more often constructed by means of tunnel boring machines rather than by conventional tunnel excavation. This is because tunnel boring provides a greater degree of safety for neighbouring structures, especially when it takes place in near-surface unconsolidated rock. However, bored tunnels offer less favourable framework conditions for the exploitation of geothermal energy because they are usually lined with concrete tubbings. Depending on the tunnel's diameter this normally involves rings of 1 to 2 metres width made up of several concrete elements. Adapting this type of design for geothermal energy production requires the use of an absorber piping system which permits coupling between the individual concrete elements while at the same time meeting the strict geometric tolerances required for its installation. A system of this type has been developed in a cooperation between the Rehau AG +Co. and Ed. Zueblin AG (Central Technology Services). These energy tubbings have already been installed in two tunnel structures and have also been examined in laboratory tests. An extensive measurement programme is under preparation which is aimed at gaining insights for the further optimisation of energy tubbings.
Tunneling anisotropic magnetoresistance driven by magnetic phase transition.

Science.gov (United States)

Chen, X Z; Feng, J F; Wang, Z C; Zhang, J; Zhong, X Y; Song, C; Jin, L; Zhang, B; Li, F; Jiang, M; Tan, Y Z; Zhou, X J; Shi, G Y; Zhou, X F; Han, X D; Mao, S C; Chen, Y H; Han, X F; Pan, F

2017-09-06

The independent control of two magnetic electrodes and spin-coherent transport in magnetic tunnel junctions are strictly required for tunneling magnetoresistance, while junctions with only one ferromagnetic electrode exhibit tunneling anisotropic magnetoresistance dependent on the anisotropic density of states with no room temperature performance so far. Here, we report an alternative approach to obtaining tunneling anisotropic magnetoresistance in α'-FeRh-based junctions driven by the magnetic phase transition of α'-FeRh and resultantly large variation of the density of states in the vicinity of MgO tunneling barrier, referred to as phase transition tunneling anisotropic magnetoresistance. The junctions with only one α'-FeRh magnetic electrode show a magnetoresistance ratio up to 20% at room temperature. Both the polarity and magnitude of the phase transition tunneling anisotropic magnetoresistance can be modulated by interfacial engineering at the α'-FeRh/MgO interface. Besides the fundamental significance, our finding might add a different dimension to magnetic random access memory and antiferromagnet spintronics.Tunneling anisotropic magnetoresistance is promising for next generation memory devices but limited by the low efficiency and functioning temperature. Here the authors achieved 20% tunneling anisotropic magnetoresistance at room temperature in magnetic tunnel junctions with one α'-FeRh magnetic electrode.
Electron tunneling in chemistry

International Nuclear Information System (INIS)

Zamaraev, K.I.; Khajrutdinov, R.F.; Zhdanov, V.P.; Molin, Yu.N.

1985-01-01

Results of experimental and theoretical investigations are outlined systematically on electron tunnelling in chemical reactions. Mechanism of electron transport to great distances is shown to be characteristic to chemical compounds of a wide range. The function of tunnel reactions is discussed for various fields of chemistry, including radiation chemistry, electrochemistry, chemistry of solids, chemistry of surface and catalysis
Signatures of unstable semiclassical trajectories in tunneling

International Nuclear Information System (INIS)

Levkov, D G; Panin, A G; Sibiryakov, S M

2009-01-01

It was found recently that processes of multidimensional tunneling are generally described at high energies by unstable semiclassical trajectories. We study two observational signatures related to the instability of trajectories. First, we find an additional power-law dependence of the tunneling probability on the semiclassical parameter as compared to the standard case of potential tunneling. The second signature is a substantial widening of the probability distribution over final-state quantum numbers. These effects are studied using a modified semiclassical technique which incorporates stabilization of the tunneling trajectories. The technique is derived from first principles. We obtain expressions for the inclusive and exclusive tunneling probabilities in the case of unstable semiclassical trajectories. We also investigate the 'phase transition' between the cases of stable and unstable trajectories across certain 'critical' values of energy. Finally, we derive the relation between the semiclassical probabilities of tunneling from the low-lying and highly excited initial states. This puts on firm ground a conjecture made previously in the semiclassical description of collision-induced tunneling in field theory
Disc Bit Abrasion Parameters in TBM Tunnelling regarded exemplarily for the Gotthard Base Tunnel

Directory of Open Access Journals (Sweden)

Edmund a Wax

2005-11-01

Full Text Available In this article the author presents Amund Bruland’s empirical approach to determine the disc bit abrasion of TBMs (Tunnel Boring Machines, transforms the respective empirical dependencies into approximated mathematical relations and verifies them exemplarily for the currently constructed Gotthard Base Tunnel.
Magnetic reconstruction induced magnetoelectric coupling and spin-dependent tunneling in Ni/KNbO_3/Ni multiferroic tunnel junctions

International Nuclear Information System (INIS)

Zhang, Hu; Dai, Jian-Qing; Song, Yu-Min

2016-01-01

We investigate the magnetoelectric coupling and spin-polarized tunneling in Ni/KNbO_3/Ni multiferroic tunnel junctions with asymmetric interfaces based on density functional theory. The junctions have two stable polarization states. We predict a peculiar magnetoelectric effect in such junctions originating from the magnetic reconstruction of Ni near the KO-terminated interface. This reconstruction is induced by the reversal of the ferroelectric polarization of KNbO_3. Furthermore, the change in the magnetic ordering filters the spin-dependent current. This effect leads to a change in conductance by about two orders of magnitude. As a result we obtain a giant tunneling electroresistance effect. In addition, there exist sizable tunneling magnetoresistance effects for two polarization states. - Highlights: • We study the ME coupling and electron tunneling in Ni/KNbO_3/Ni junctions. • There is magnetic reconstruction of Ni atoms near the KO-terminated interface. • A peculiar magnetoelectric coupling effect is obtained. • Predicted giant tunneling electroresistance effects.
Unified time analysis of photon and particle tunnelling

International Nuclear Information System (INIS)

Olkhovsky, V.S.; Recami, Erasmo; Jakiel, Jacek

2004-01-01

A unified time analysis of photon and nonrelativistic particle tunnellings is presented, in which time is regarded as a quantum observable, canonically conjugated to energy. Within this approach, one can introduce self-consistent definitions of the tunnelling times, on the basis of conventional quantum mechanics (or one-dimensional quantum electrodynamics) only. The validity of the Hartman effect [which states the tunnelling duration to be independent of the (opaque) barrier width, with superluminal group velocities of the tunnelling packet as a consequence] is verified for all the known expressions of the mean tunnelling time. However, some noticeable generalizations of (and deviations from) the Hartman effect are, as well, briefly investigated. Moreover, the analogy between particle and photon tunnelling is suitably exploited; on the basis of such an analogy, an explanation of some recent interesting microwave and optical experimental results on tunnelling times is proposed. Attention is devoted, at last, to some aspects of the causality problem for particle and photon tunnelling
The anisotropic tunneling behavior of spin transport in graphene-based magnetic tunneling junction

Science.gov (United States)

Pan, Mengchun; Li, Peisen; Qiu, Weicheng; Zhao, Jianqiang; Peng, Junping; Hu, Jiafei; Hu, Jinghua; Tian, Wugang; Hu, Yueguo; Chen, Dixiang; Wu, Xuezhong; Xu, Zhongjie; Yuan, Xuefeng

2018-05-01

Due to the theoretical prediction of large tunneling magnetoresistance (TMR), graphene-based magnetic tunneling junction (MTJ) has become an important branch of high-performance spintronics device. In this paper, the non-collinear spin filtering and transport properties of MTJ with the Ni/tri-layer graphene/Ni structure were studied in detail by utilizing the non-equilibrium Green's formalism combined with spin polarized density functional theory. The band structure of Ni-C bonding interface shows that Ni-C atomic hybridization facilitates the electronic structure consistency of graphene and nickel, which results in a perfect spin filtering effect for tri-layer graphene-based MTJ. Furthermore, our theoretical results show that the value of tunneling resistance changes with the relative magnetization angle of two ferromagnetic layers, displaying the anisotropic tunneling behavior of graphene-based MTJ. This originates from the resonant conduction states which are strongly adjusted by the relative magnetization angles. In addition, the perfect spin filtering effect is demonstrated by fitting the anisotropic conductance with the Julliere's model. Our work may serve as guidance for researches and applications of graphene-based spintronics device.
Improved multidimensional semiclassical tunneling theory.

Science.gov (United States)

Wagner, Albert F

2013-12-12

We show that the analytic multidimensional semiclassical tunneling formula of Miller et al. [Miller, W. H.; Hernandez, R.; Handy, N. C.; Jayatilaka, D.; Willets, A. Chem. Phys. Lett. 1990, 172, 62] is qualitatively incorrect for deep tunneling at energies well below the top of the barrier. The origin of this deficiency is that the formula uses an effective barrier weakly related to the true energetics but correctly adjusted to reproduce the harmonic description and anharmonic corrections of the reaction path at the saddle point as determined by second order vibrational perturbation theory. We present an analytic improved semiclassical formula that correctly includes energetic information and allows a qualitatively correct representation of deep tunneling. This is done by constructing a three segment composite Eckart potential that is continuous everywhere in both value and derivative. This composite potential has an analytic barrier penetration integral from which the semiclassical action can be derived and then used to define the semiclassical tunneling probability. The middle segment of the composite potential by itself is superior to the original formula of Miller et al. because it incorporates the asymmetry of the reaction barrier produced by the known reaction exoergicity. Comparison of the semiclassical and exact quantum tunneling probability for the pure Eckart potential suggests a simple threshold multiplicative factor to the improved formula to account for quantum effects very near threshold not represented by semiclassical theory. The deep tunneling limitations of the original formula are echoed in semiclassical high-energy descriptions of bound vibrational states perpendicular to the reaction path at the saddle point. However, typically ab initio energetic information is not available to correct it. The Supporting Information contains a Fortran code, test input, and test output that implements the improved semiclassical tunneling formula.
Superconducting tunnel-junction refrigerator

International Nuclear Information System (INIS)

Melton, R.G.; Paterson, J.L.; Kaplan, S.B.

1980-01-01

The dc current through an S 1 -S 2 tunnel junction, with Δ 2 greater than Δ 1 , when biased with eV 1 +Δ 2 , will lower the energy in S 1 . This energy reduction will be shared by the phonons and electrons. This device is shown to be analogous to a thermoelectric refrigerator with an effective Peltier coefficient π* approx. Δ 1 /e. Tunneling calculations yield the cooling power P/sub c/, the electrical power P/sub e/ supplied by the bias supply, and the cooling efficiency eta=P/sub c//P/sub e/. The maximum cooling power is obtained for eV= +- (Δ 2 -Δ 1 ) and t 1 =T 1 /T/sub c/1 approx. 0.9. Estimates are made of the temperature difference T 2 -T 1 achievable in Al-Pb and Sn-Pb junctions with an Al 2 O 3 tunneling barrier. The performance of this device is shown to yield a maximum cooling efficiency eta approx. = Δ 1 /(Δ 2 -Δ 1 ) which can be compared with that available in an ideal Carnot refrigerator of eta=T 1 /(T 2 -T 1 ). The development of a useful tunnel-junction refrigerator requires a tunneling barrier with an effective thermal conductance per unit area several orders of magnitude less than that provided by the A1 2 O 3 barrier in the Al-Pb and Sn-Pb systems
TunnelVision: LHC Tunnel Photogrammetry System for Structural Monitoring

CERN Document Server

Fallas, William

2014-01-01

In this document an algorithm to detect deformations in the LHC Tunnel of CERN is presented. It is based on two images, one represents the ideal state of the tunnel and the other one the actual state. To find the differences between both, the algorithm is divided in three steps. First, an image enhancement is applied to make easier the detection. Second, two different approaches to reduce noise are applied to one or both images. And third, it is defined a group of characteristics about the type of deformation desired to detect. Finally, the conclusions show the effectiveness of the algorithm in the experimental results.
Electric and VLF-MT survey of Tegatayama tunnel; Tegatayama tunnel no denki tansa oyobi VLF tansa

Energy Technology Data Exchange (ETDEWEB)

Nishitani, T [Akita University, Akita (Japan). Mining College

1997-05-27

To survey the structure at the depth between 20 and 30 m, field tests were conducted by means of vertical electric and VFL-MT (magnetotelluric) survey. Tegatayama tunnel has a total length of 276 m, width of 7.5 m, and height of 4.7 m, and the depth from the surface is about 28 m near the top of mountain. Near the tunnel, the thickness of surface soil is about 60 cm, which consists of clay soil including soft mudstone gravel. It was found that terrace deposit is distributed up to the depth of 8 m, and that mudstone is distributed below the depth of 8 m. Weighted four-electrode method was adopted for the vertical electrical survey. Measurements were conducted at the immediately above the tunnel, 10 m apart from the center of tunnel in the right and left, and 20 m apart from the center in the east. For the VLF-MT method, component of frequency 22.2 kHz was used. As a result of the tests, it was difficult to illustrate the existence of tunnel from the vertical electrical survey only at one point. Feature of the tunnel could be well illustrated by means of the VLF-MT method. 3 refs., 9 figs.
Characterization of the influence of building a road on the stability of the tunnel lining in a Banska Bystrica railway tunnel

Directory of Open Access Journals (Sweden)

Vavrek Pavol

2001-06-01

Full Text Available This paper deals with solving the problem of tunnel lining stability in a railway tunnel. The road cut was made into the overburden of the tunnel. I investigated the effect of the road cut on the stability of tunnel lining. The FLAC3D mathematical modelling technique was used for this purpose. The solution consist of: - - - - - - - - - - - -modelling the initial situation before building the intervention,Determing the internal characteristics of the tunnel lining in its original state,modelling the situation after making the road cut,Determing the internal characteristics of the tunnel lining after the building intervention,Comparison of the internal characteristics of the tunnel lining before and after the building intervention.In the model, I used these general geotechnical properties of the rock environment and the tunnel lining:Material Youngus modulus [MPa] Poissons RatioClay 8 0,42Weakly wheathered calcite 3 000 0,25Hard wheathered calcite 600 0,30Fill 300 0,25Lining 20 000 0,20The arbitration of the tunnel lining stability was executed on the basis of the Mohr Coulomb limit of the state. Building the road cut does not lead to loss of stability in the tunnel a at Station 1.225 00 or at Station 1.300 00.
Electron tunneling in proteins program.

Science.gov (United States)

Hagras, Muhammad A; Stuchebrukhov, Alexei A

2016-06-05

We developed a unique integrated software package (called Electron Tunneling in Proteins Program or ETP) which provides an environment with different capabilities such as tunneling current calculation, semi-empirical quantum mechanical calculation, and molecular modeling simulation for calculation and analysis of electron transfer reactions in proteins. ETP program is developed as a cross-platform client-server program in which all the different calculations are conducted at the server side while only the client terminal displays the resulting calculation outputs in the different supported representations. ETP program is integrated with a set of well-known computational software packages including Gaussian, BALLVIEW, Dowser, pKip, and APBS. In addition, ETP program supports various visualization methods for the tunneling calculation results that assist in a more comprehensive understanding of the tunneling process. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.
Tunneling Anomalous and Spin Hall Effects.

Science.gov (United States)

Matos-Abiague, A; Fabian, J

2015-07-31

We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

Some links on this page may take you to non-federal websites. Their policies may differ from this site.