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1

Role of organic matter in the Proterozoic Oklo natural fission reactors, Gabon, Africa  

International Nuclear Information System (INIS)

[en] Of the sixteen known Oklo and the Bangombe natural fission reactors (hydrothermally altered elastic sedimentary rocks that contain abundant uraninite and authigenic clay minerals), reactors 1 to 6 at Oklo contain only traces of organic matter, but the others are rich in organic substances. Reactors 7 to 9 are the subjects of this study. These organic-rich reactors may serve as time-tested analogues for anthropogenic nuclear-waste containment strategies. Organic matter helped to concentrate quantities of uranium sufficient to initiate the nuclear chain reactions. Liquid bitumen was generated from organic matter by hydrothermal reactions during nuclear criticality. The bitumen soon became a solid, consisting of polycyclic aromatic hydrocarbons and an intimate mixture of cryptocrystalline graphite, which enclosed and immobilized uraninite and the fission-generated isotopes entrapped in uraninite. This mechanism prevented major loss of uranium and fission products from the natural nuclear reactors for 1.2 b.y. 24 refs., 4 figs

1993-01-01

2

Oklo: natural fission reactor program. Progress report, July 1-September 30, 1979  

International Nuclear Information System (INIS)

Nearly 200 samples were collected at the Oklo mine in Gabon this quarter for shipment to the United States to continue studies of lead, ruthenium, and technetium migration around natural fission reactors. The first analyses of samples collected near a rich uranium ore body in Canada show the presence of radiogenic lead in pyrite and sandstone materials. Analyses of additional samples are underway to permit the interpretation of the data in terms of transport paths. A technique was developed this quarter to eliminate the interference of organic materials during the mass spectrometric analyses of ruthenium in Oklo samples with high asphaltic contents. A proposal was drafted for a study of naturally occurring radionuclide migration at rich uranium ore bodies in Australia to be performed jointly by the US Department of Energy and the Australian Atomic Energy Commission

1980-01-01

3

Uraninite recrystallization and Pb loss in the Oklo and Bangombé natural fission reactors, Gabon  

Science.gov (United States)

The Oklo and Bangombé natural fossil fission reactors formed ca. 2 Ga ago in the Franceville basin, Gabon. The response of uraninite in the natural reactors to different geological conditions has implications for the disposal of the UO 2 in spent nuclear fuel. Uraninite and galena from two reactor zones, RZ16 at Oklo and RZB at Bangombé, were studied to clarify the chronology and effect of alteration events on the reactor zones. In addition, ion microprobe U-Pb analysis of zircons from a dolerite dyke in the Oklo deposit were completed to better constrain the age of the dyke, and thereby testing the link between the dyke and an important alteration event in the reactor zones. The analyzed uraninite from RZ16 and RZB contains ca. 6 wt% PbO, indicating a substantial loss of radiogenic Pb. Transmission electron microscopy showed that microscopic uraninite grains in the reactor zones consist of mainly defect-free nanocrystalline to microcrystalline aggregates. However, the nanocrystalline regions have elevated Si contents and lower Pb contents than coarser uraninite crystallites. Single stage model ages of large, millimeter-sized galena grains at both RZ16 and RZB correlate well with the age of the Oklo dolerite dyke, 860 ± 39 Ma (2?). Thus, the first major Pb loss from uraninite occurred at both Oklo and Bangombé during regional extension and the intrusion of a dyke swarm in the Franceville basin, ˜860-890 Ma ago. Uraninite Pb isotopes from RZ16 and RZB give lower ages of ca. 500 Ma. These ages agree with the "chemical" ages of the uraninite, and show that an ancient Pb loss occurred after the intrusion of the dolerite dykes. The presence of nanocrystallites in the reactor uraninite indicates internal recrystallization, which may have occurred around 500 Ma, resulting in the 6wt% PbO uraninite. It is suggested that leaching by fluid interaction triggered by the Pan-African orogeny was important during this second Pb-loss event. Thus, there are indications that uraninite at both the Oklo and Bangombé natural reactors has experienced at least two ancient episodes of Pb loss associated with internal recrystallization. These recrystallization events have occurred without significantly depleting the 2 Ga fission products compatible with the uraninite structure.

Evins, Lena Z.; Jensen, Keld A.; Ewing, Rodney C.

2005-03-01

4

Isotopic study of natural fission reactors at Oklo and Bangombe, Gabon  

International Nuclear Information System (INIS)

[en] The Oklo and Bangombe uranium ores in the Republic of Gabon are fossils of natural fission reactors. Many elements in these natural fission reactors show isotopic anomalies derived from fission and neutron capture reactions. Isotopic analyses of uraninites and some other minerals provide useful information on the geochemical behavior of fission products and nuclear chemical characterization of the reactors. Integrated isotopic measurements by whole rock analysis with inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS) and by in-situ analysis with secondary ion mass spectrometry (SIMS) make it possible to clarify the migration processes of fissiogenic nuclides over a range of scales from micro meters to meters. (author)

1999-01-01

5

Organic free radicals and micropores in solid graphitic carbonaceous matter at the Oklo natural fission reactors, Gabon  

International Nuclear Information System (INIS)

[en] The presence, concentration, and distribution of organic free radicals as well as their association with specific surface areas and microporosities help characterize the evolution and behavior of the Oklo carbonaceous matter. Such information is necessary in order to evaluate uranium mineralization, liquid bitumen solidification, and radio nuclide containment at Oklo. In the Oklo ore deposits and natural fission reactors carbonaceous matter is often referred to as solid graphitic bitumen. The carbonaceous parts of the natural reactors may contain as much as 65.9% organic C by weight in heterogeneous distribution within the clay-rich matrix. The solid carbonaceous matter immobilized small uraninite crystals and some fission products enclosed in this uraninite and thereby facilitated radio nuclide containment in the reactors. Hence, the Oklo natural fission reactors are currently the subjects of detailed studies because they may be useful analogues to support performance assessment of radio nuclide containment at anthropogenic radioactive waste repository sites. Seven carbonaceous matter rich samples from the 1968 ± 50 Ma old natural fission reactors and the associated Oklo uranium ore deposit were studied by electron spin resonance (ESR) spectroscopy and by measurements of specific surface areas (BET method). Humic acid, fulvic acid, and fully crystalline graphite standards were also examined by ESR spectroscopy for comparison with the Oklo solid graphitic bitumens. With one exception, the ancient Oklo bitumens have higher organic free radical concentrations than the modem humic and fulvic acid samples. The presence of carbon free radicals in the graphite standard could not be determined due to the conductivity of this material. 72 refs., 7 figs., 1 tab

1997-01-01

6

Illite in the Oklo natural fission reactors in Gabon: Considerations for Cs containment  

International Nuclear Information System (INIS)

[en] The ? 2 Ga old Oklo, Okelobondo and Bangombe natural reactors in the Republic of Gabon contain solid graphitic bitumens and clay minerals, both of which have effected the containment, or partial containment, of 235U and several fission products. In laboratory experiments, sorption of 134Cs by illite, and illite coated with petroleum was measured in aqueous NaCl solutions to simulate subsurface (connate) waters in sedimentary rocks. Elevated temperatures and increasing salinity of the NaCl solutions facilitated the removal of sorbed cesium from illite

1995-01-01

7

Illite in the Oklo natural fission reactors in Gabon: Considerations for Cs containment  

Energy Technology Data Exchange (ETDEWEB)

The {approximately} 2 Ga old Oklo, Okelobondo and Bangombe natural reactors in the Republic of Gabon contain solid graphitic bitumens and clay minerals, both of which have effected the containment, or partial containment, of {sup 235}U and several fission products. In laboratory experiments, sorption of {sup 134}Cs by illite, and illite coated with petroleum was measured in aqueous NaCl solutions to simulate subsurface (connate) waters in sedimentary rocks. Elevated temperatures and increasing salinity of the NaCl solutions facilitated the removal of sorbed cesium from illite.

Szabo, G.; Guczi, J. [Frederic Joliot-Curie National Research Inst. for Radiobiology and Radiohygiene, Budapest (Hungary); Nagy, B. [Univ. of Arizona, Tucson, AZ (United States); Janeczek, J. [Uniwersytet Slaski, Sosnowiec (Poland); Ewing, R.C. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences

1995-12-31

8

Heterogeneity and alteration of uraninite from the natural fission reactor 10 at Oklo, Gabon  

International Nuclear Information System (INIS)

[en] A mineralogical study of uranium ore from reactor zone 10 revealed that uraninite in the natural reactors at Oklo, Gabon, has been altered through partial dissolution, Pb loss, and replacement by coffinite, USiO4.nH2O. The dissolution occurred during formation of the clay mantle surrounding the ore body and was probably caused by hydrothermal saline solutions under reducing conditions. The loss of lead (up to 11 wt%) from uraninite occurred approximately one billion years after the operation of the reactors. As a result, there are two generations of uraninite in the reactor zone that differ in chemical composition and unit cell parameters [a1 = 0.5495(2) and a2 = 0.5455(2) nm]. Minor coffinitization of uraninite has also occurred. Thus, the Oklo deposit has been altered since the event of nuclear criticality. This provides several distinct geochemical environments in which one may analyze the corrosion of uraninite and the subsequent retention or migration of fission products. (author). 20 refs., 3 figs., 1 tab

1993-01-01

9

Petrography and paragenesis of organic matter associated with the natural fission reactors at Oklo, Republic of Gabon: a preliminary report  

Energy Technology Data Exchange (ETDEWEB)

Sixteen known uranium-rich pockets in the sediment-hosted uranium ore deposits in the Oklo area became nuclear fission reactors 1968{+-}50 Ma ago and operated as such for up to 1 Ma. Nuclear criticality was caused by unique and fortuitous geological environments and events. These included the localized high concentrations of uranium in small pockets in the ore bodies, the fact that the relative abundance of the fissile {sup 235}U isotope was five times greater in uranium {approximately}2 Ga ago than present, the presence of water which acted as a moderator in the natural reactors and the absence of neutron poisons, which are elements that can prevent nuclear chain reactions. Organic matter has been studied in natural reactors 7 to 9 and at locations at various distances from these reactors. Bitumen in the Oklo reactors is the predominant organic phase. It is now solid bitumen. Its immediate precursor was liquid bitumen, generated from syngenetic kerogen in organic-rich sedimentary rocks in the Francevillian Basin of Gabon and in the natural reactors themselves by hydrous reaction mechanisms prior to, during, and after nuclear criticality. A preliminary paragenesis of organic matter at Oklo is defined. 36 refs., 3 figs., 1 tab.

Mossman, D.J.; Nagy, B.; Rigali, M.J.; Gauthier-Lafaye, F.; Holliger, P. [Mount Allison University, Sackville, NB (Canada). Dept. of Physics

1993-12-01

10

Natural nuclear reactor in Oklo; Naturalny reaktor jadrowy w Oklo  

Energy Technology Data Exchange (ETDEWEB)

Natural nuclear reactor in uranium ore deposits Oklo, Gabon, has been presented. The historical aspects of Oklo phenomenon have been analysed on the base of isotope ratio measurements of elements being found in uranium spurs of Oklo deposit. 4 refs, 3 figs.

Celinski, Z. [Politechnika Warszawska, Warsaw (Poland)

1997-12-01

11

The Oklo natural reactor, Gabon  

International Nuclear Information System (INIS)

[en] This paper reports how the Oklo natural reactor, Gabon, remains the best natural analog for assessing the behavior of fission products, actinides, and actinide daughters in rocks. The rocks at Oklo are porous and permeable, as well as being fractured and containing abundant water, yet many of the fission products and actinides have remained in place or close to their formation sites. The actinides Th, U, Np, Pu, and Am are similar in their crystal chemical characteristics, and all were retained in the host pitchblende. Elements incompatible in the pitchblende structure were lost by diffusion into the rocks surrounding the high grade reactor ore. Alkali and Alkaline earth elements Rb, Sr, Cs, and Ba were fixed in and very close to the reactor ores in clay minerals and in some secondary carbonates and sulfates. Local oxidizing conditions in the reactor zones caused some loss of Tc, Mo, Cd, and Ru, but the Tc, Mo, and Ru were fixed in sulfides formed close by under chemically reducing conditions. Local migration for Ag and Sn has been documented for some samples

1989-01-01

12

Oklo natural reactors: geological and geochemical conditions  

International Nuclear Information System (INIS)

Published as well as unpublished material on the Oklo natural reactors in Gabon was evaluated with regard to the long-term aspects of nuclear waste disposal. Even though the vast data base available at present can provide only a site specific description of the phenomenon, already this material gives relevant information on plutonium retention, metamictization, fission product release, hydrogeochemical stability and migration of fission products. Generalized conclusions applicable to other nuclear waste repository would require the quantitative reconstruction of t s coupled thermo-hydrologic-chemical processes. This could be achieved by studying the deviations in the 2H/1H and 18O/16O ratios of minerals at Oklo. A further generalization of the findings from Oklo could be realized by examining the newly-discovered reactor zone 10, which was active under very different thermal conditions than the other reactors. 205 refs

1986-01-01

13

X-ray photoelectron spectroscopic study of a sample from a natural fission reactor at Oklo, Gabon  

International Nuclear Information System (INIS)

[en] X-ray photoelectron spectroscopy (XPS) was used to study a sample from a natural fission reactor, reaction zone number 13, at Oklo (Gabon). Peaks due to uranium, oxygen, carbon, lead, silicon, calcium, aluminum, sulfur thorium and bismuth were seen in the XPS spectra. High-resolution spectra were recorded for the U, Pb, O, and C bands to determine the chemical state of these elements. The oxidation state of uranium in the sample is predominantly U4+, with a U6+/U4+ ratio of about 0.11. Lead was in the +2 oxidation state. The carbon signal indicated the presence of organic carbon, while the oxygen bands indicated the presence of water. The significance of the results for nuclear fuel waste management is discussed. (author). 27 refs., 7 figs., 2 tabs

1993-01-01

14

The Oklo natural nuclear reactors: neutron parameters, age and duration of the reactions, uranium and fission products migrations  

International Nuclear Information System (INIS)

Mass spectrometry and isotopic dilution technique are used in order to carry out, on various samples from the fossil nuclear reactors at Oklo, Gabon, isotopic and chemical analyses of some particular elements involved in the nuclear reactions: uranium, lead, bismuth, thorium, rare gases (krypton, xenon), rare earths (neodymium, samarium, europium, gadolinium, dysprosium), ruthenium and palladium. Interpretations of these analyses lead to the determination of many neutron parameters such as the neutron fluence received by the samples, the spectrum index, the conversion coefficient, and also the percentages of fissions due to uranium-238 and plutonium-239 and the total number of fissions relative to uranium. All these results make it possible to determine the age of the nuclear reactions by measuring the amounts of fission rare earths formed, i.e. 1.97 billion years. This study brings some informations to the general problem of radioactive wastes storage in deep geological formations, the storage of uranium, plutonium and many fission products having been carried out naturally, and for about two billion years

1979-01-01

15

The effects of water radiolysis on local redox conditions in the Oklo, Gabon, natural fission reactors 10 and 16  

International Nuclear Information System (INIS)

[en] In an underground nuclear waste repository, the chemical behavior of some stored fission products and actinides depends on the redox conditions during their long-term evolution. In this respect, radiolysis is an important phenomenon which can significantly modify the local redox conditions. The Oklo natural fission zones are good examples where the effect of radiolysis can be deduced from a mineralogical and geochemical study. Zones 10 and 16 were studied because they are located at depth of 270 m in an area devoid of any recent water circulation and not subject to the effect of the lateritic alteration occurring elsewhere in this area. In zone 10, there is a marked evolution of the U-Pb-Fe-S mineralogy from the center to the periphery of the reactor zone. In the center, uraninite shows silicification and coffinitisation with the formation of galena and native lead; the PbO content of uraninite can be as much as 20 wt%. In the periphery of the reactor zone, some radiogenic lead is present as minimum (Pb3O4) and in Pb-bearing calcite. In the surrounding sandstones, hematite is widespread. In zone 16, the mineral paragenesis is generally comparable with that of zone 10 but with some differences. Galena is the only Pb-bearing mineral associated with uraninite crystals. The PbO content of uraninite is always 2O-H2 ± CH4 inclusions were observed in healed microcracks in the detrital quartz grains. Based on microthermometric measurements, the salinity of the aqueous solution ranges from 0.2 to 18 wt% eq. NaCl. Raman analysis of the gas phase indicates that the hydrogen to oxygen ratio differs from an inclusion to the other. 41 refs., 15 figs., 3 tabs

1997-01-01

16

3D modelling of thermal and fluid transfers around a natural fission reactor (Oklo, Gabon)  

International Nuclear Information System (INIS)

[en] Numerical modelling is used to quantify heat and mass transfers around the Oklo site. A 3D model of a reactor, at decametric scale, built with the GOCAD software shows that the functioning of the reactor acts as a powerful but local thermal perturbation. This perturbation increases the temperature within a range of 50 to 250 deg C, according to assumed heat production, with a spatial extent less than 50 m. The steady state regime is reached very rapidly, in less that 100 years. The heat dissipation is essentially conductive, the reactor inducing only weak fluid movements. A forced convection model has been also investigated, where fluids come from basin scale circulations. It shows that, in the range of the studied filtration velocities, temperatures are not significantly affected by these circulations. Nevertheless, they induce an asymmetry between upstream and downstream parts of the flow. Assuming low permeability, the high temperature increase could have caused local fluid overpressures, which could lead to the development of a radial hydraulic fracturing near the reactor, as has been observed around the reactor 10. (authors)

1998-01-01

17

Oklo natural fission reactor program. Progress report, April 1-August 31, 1980  

International Nuclear Information System (INIS)

An interim report has been published on the redistribution of uranium, thorium, and lead in samples representing several million cubic meters of sandstone and metamorphosed sediments in the Athabasca Basin which is located in the northwest corner of the Canadian province of Saskatchewan. The region of study includes zones of uranium mineralization at Key Lake. Mineralization occurs at the unconformity between the Athabasca sandstone and the underlying metasediments and in fault zones within the metasediments. Lead isotopes record a radiometric age of 1300 +- 150 m.y. in samples from above and below the unconformity. This age probably reflects the time of deposition of the sandstones and an associated redistribution of uranium and/or lead in the underlying rocks. Many of the samples have been fractionated with respect to radiogenic lead and the actinide parent elements since that time. Sandstones and altered rocks from the region above the unconformity have been a transport path and are a repository for lead. In contrast, mineralized rocks are deficient in radiogenic lead and must be an important source of lead in the local geologic environment. Samples from Oklo reactor zone 9 and nearby host rocks have been prepared for isotopic analyses of ruthenium, molybdenum, uranium and lead

1980-01-01

18

Fission product retention in newly discovered organic-rich natural fission reactors at Oklo and Bangombe, Gabon  

International Nuclear Information System (INIS)

[en] The discovery of naturally occurring fission reactors in the rock strata of the Paleoproterozoic Francevillian Basin in the Republic of Gabon in equatorial West Africa led to several programs to define migration and/or retention of uranium and fissiogenic isotopes from/in the natural reactor zones. Although much understanding has been gained, new insight is needed regarding the chemical and physical parameters that control movement and retention of fission products over almost two billion years from/in the natural reactors. Seventeen known natural fission reactors sustained criticality for 0.1 to 1 million years in hydrothermally altered sedimentary rocks 1968 +/- 50 million years ago. These natural nuclear reactors attained criticality because of high concentrations of uranium in small pockets in uranium ores, the lack of neutron poisons, and because at the time they reached criticality, the abundance of 235U was five times greater than it is today. Water acted as a moderator, and temperature in the natural reactors was between 160 and 360 degrees C. Both the uranium-rich pockets and the uranium ore bodies in which these pockets are located were formed when aqueous solutions moving through highly fractured zones in the Francevillian sedimentary rocks met organic-rich sediments. This resulted in the reduction of U(VI) in the dissolved uranyl ions to U(IV), causing the precipitation of pitchblende and uraninite. It has been proposed that between 2.2 and 1.9 billion years ago, the earth's atmosphere experienced a remarkable temporary rise in O2 content; this event may account for the uranium-bearing, oxidizing aqueous solutions in the Francevillian rocks

1993-01-01

19

Fission product retention in newly discovered organic-rich natural fission reactors at Oklo and Bangombe, Gabon  

Energy Technology Data Exchange (ETDEWEB)

The discovery of naturally occurring fission reactors in the rock strata of the Paleoproterozoic Francevillian Basin in the Republic of Gabon in equatorial West Africa led to several programs to define migration and/or retention of uranium and fissiogenic isotopes from/in the natural reactor zones. Although much understanding has been gained, new insight is needed regarding the chemical and physical parameters that control movement and retention of fission products over almost two billion years from/in the natural reactors. Seventeen known natural fission reactors sustained criticality for 0.1 to 1 million years in hydrothermally altered sedimentary rocks 1968 +/- 50 million years ago. These natural nuclear reactors attained criticality because of high concentrations of uranium in small pockets in uranium ores, the lack of neutron poisons, and because at the time they reached criticality, the abundance of [sup 235]U was five times greater than it is today. Water acted as a moderator, and temperature in the natural reactors was between 160 and 360[degrees]C. Both the uranium-rich pockets and the uranium ore bodies in which these pockets are located were formed when aqueous solutions moving through highly fractured zones in the Francevillian sedimentary rocks met organic-rich sediments. This resulted in the reduction of U(VI) in the dissolved uranyl ions to U(IV), causing the precipitation of pitchblende and uraninite. It has been proposed that between 2.2 and 1.9 billion years ago, the earth's atmosphere experienced a remarkable temporary rise in O[sub 2] content; this event may account for the uranium-bearing, oxidizing aqueous solutions in the Francevillian rocks.

Nagy, B.; Rigali, M.J. (Univ. of Arizona, Tucson (United States))

1993-01-01

20

Recent outputs of the Oklo (Gabon) natural analogue study to nuclear waste disposal  

International Nuclear Information System (INIS)

[en] In the past twenty five years, the natural nuclear reactors of Oklo have been the subject of numerous detailed studies. First investigated for the physical and neutron aspects of the nuclear reaction, they were then reconsidered because they provide a unique opportunity in the world to study the containment of actinides and fission products in a geological formation over a broad timescale (two billion years). Although the sites investigated do not represent a complete analogue of a repository system, many of the processes studied (mass transfer to the surface, transport, migration / retention), the spatial extent of these processes, and the timescales involved, are compatible with processes liable to occur during the lifespan of a repository for the deep geological disposal of spent nuclear fuel. A fresh program was therefore initiated as a European Commission project in 1990, entitled''Oklo as a natural analog for transfer processes in a radioactive waste repository'- phase 7, and then extended by a phase 2 entitled Oklo, Natural Analogue - Behavior of Nuclear Reaction Products in a Natural Environment''. Researches conducted in phase I served to determine the physical conditions of the operation of the natural reactor, reconstruct the geological history of the reactor environment, and decode the behavior of actinides as well as fission products in the surrounding geological formations. Phase N, which ended in June 1999, had three main objectives: i) to assess radionuclide migration and retention processes from the reactor zones to the geological environment, ii) to define the confinement properties and long-term behavior of geological materials; iii) to test models of processes related to radionuclide migration and retention, and eventually to provide suitable data and scenarios for performance assessment of nuclear waste disposal. This paper proposes a synthesis of the main outputs of the Oklo project to the performance assessment of nuclear waste disposal, the study of the long-term evolution of spent fuel and the long-term behavior of geological materials with respect to the containment of actinides and fission products. The Oklo natural analogue displays a number of specific features that make it unique in the world. The Oklo basin is characterized by the occurrence of meter scale uraninite lenses, that were affected by nuclear fission 2 billion years ago. These ''reactor zones'' exist in three sites: Oklo, Okelobondo and Bagombe. By analogy with a repository system, they are considered as representative of the 'Source' term. Numerous isotopic and geochemical tracers are thus available in order to restrict the migration or retention processes of actinides and fission products present in these zones. The near environment of the reactor zones, called ''Near field'' by analogy, is mainly composed of clayey materials (i.e. chlorite, illite, kaolinite). Reactor zones are found at present from the surface (Bagombe under oxidizing and acid conditions, with supergene weathering) to deep (Okelobondo under reducing conditions, with a low groundwater dynamics) conditions. Some reactor zones, e.g. R.Z. 13 in Oklo mine, have been subjected to strong hydrothermal disturbances (with temperatures above 350 deg C), linked to the geological history of the Franceville basin. On the other hand, the old age of the Oklo reactors (2 Ga) implies that pressure, temperature and chemical conditions have evolved during a long geological history, with associated basin scale movements of fluids. The Oklo-natural analogue Phase II project compiled useful information and tools for persons involved in Performance Assessment of waste disposal, wasteform conception or long term behavior [10] in four main areas corresponding to major investigation fields: 1/ ''Source'' term evolution, 2/ Long term containment properties of geological materials, 3/ Migration and retention of actinides and fission or end products, and 4/Geochemical and transport modeling. The main outputs of the European Oklo project to the nuclear waste repository issue are

1999-06-00

 
 
 
 
21

Natural analogue studies in the Oklo uranium ore deposit, Republic of Gabon  

International Nuclear Information System (INIS)

[en] The Oklo uranium ore in the Republic of Gabon is one of the adequate natural analogue for radioactive waste disposal in geological formation, because it has preserved abundant fissiogenic nuclides for 2 Ga. Isotopic studies of the Oklo fission reactor zones have been carried out to estimate the geochemical behavior of fissiogenic nuclides and to evaluate some nuclear parameters for the reactor characterization. Cooperative SEM studies, isotopic measurements by whole rock analysis with TIMS and ICP-MS and by the observation with SIMS make possible to clarify the retention and/or migration process of nuclides over wide range from ?m to m. In this paper we describe the latest results obtained in the CEC Oklo project on the migration process of fissiogenic nuclides, uranium and plutonium, and discuss the application of these results to the safety assessment of geological disposal. (author)

1996-01-01

22

Oklo reactors: natural analogs to nuclear waste repositories  

International Nuclear Information System (INIS)

The 2-billion-year-old fossil reactors at Oklo are ancient natural nuclear waste sites. Isotope dilution mass spectrometric analyses of the fission products in the reactor core uraninite and the peripheral pelitic sandstone provide data for calculating the reactor operating parameters, the quantities of fissiogenic isotopes produced, the fraction of these isotopes retained in the cores, and the location in the peripheral rocks of the fissiogenic fraction lost from the cores. For a duration of criticality of 3 x 105 yrs, the thermal plus resonance neutron fluence ranged between 1020 and 1021 neutrons/cm2. The fraction of technetium (60 to 85%), ruthenium (75 to 90%), and neodymium (85 to 100%) retained is negatively correlated with fluence. The lost fission products are contained within a few tens of meters of their source, the reactor cores. The systematics of the decay of 99Tc (t/sub 1/2/ = 2.13 x 105 yr) to 99Ru limits the period of fissiogenic element migration to approximately 1 million yr at a time 2 billion yr ago. Thermodynamic calculations of the temperature-dependent solubilities indicate that the loss of fissiogenic elements is diffusion controlled, whereas retention in the surrounding rocks is a result of temperature-dependent deposition from an aqueous solution. These results concerning the geochemistry of technetium, ruthenium, and neodymium at a natural waste site support the concept of geologic burial of man-made radioactive wastes

1981-01-01

23

The role of mass spectrometry to study the Oklo-Bangombe natural reactors.  

UK PubMed Central (United Kingdom)

The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the (235)U/(238)U ratio of certain U ore samples indicated a depletion in (235)U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2 x 10(9) years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo-Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years.

De Laeter JR; Hidaka H

2007-09-01

24

The role of mass spectrometry to study the Oklo-Bangombé natural reactors.  

Science.gov (United States)

The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the (235)U/(238)U ratio of certain U ore samples indicated a depletion in (235)U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2 x 10(9) years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo-Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years. PMID:17583569

De Laeter, J R; Hidaka, H

25

Natural chain reaction in the Oklo mine in Gabon  

International Nuclear Information System (INIS)

[en] An isotopic analysis of a sample of uranium ore from the Oklo mine in Gabon showed a significantly reduced content of 235U (down to 0.296% 235U). The isotopic composition of neodymium (shown), lead, rubidium, ruthenium, strontium, krypton, and xenon proved that a chain reaction took place in the ore deposit approximately 1,800 million years ago. The reaction proceeded for about 10 to 70 thousand years. About 200 kg of 235U has undergone fission and the burn-up amounted to 25,000 MWd/t. (B.S.)

1976-01-01

26

Oklo, natural analogue of the radionuclides migration through the geological barrier; Oklo, analogue naturel de la migration de radionucleides dans l`environnement  

Energy Technology Data Exchange (ETDEWEB)

One of the main part of he CEC project `Oklo-Natural Analogue` is devoted to present time migration studies. This part comprises hydrogeology, groundwater chemistry, isotope geochemistry and modelling. Two sites are being investigated: the less perturbed reactor zone of the Oklo mine (OK84 in the southern mine extension of Okelobondo) at around 400 meters depth and the Bangombe reactor zone, sited in a shallow environment 30 km south of Oklo. The present contribution aims to define regional hydrogeology and hydro-chemistry boundary conditions for the modelling exercise, to assess the present day water-rock interaction in the vicinity of reactor zones, to gather information on the geochemical conditions which allowed the preservation of reactor zones for two billions years, to estimate the uranium migration from the reactor zone in using a natural marker (the depleted {sup 235}U/{sup 238}U ratio resulting from the fission) and to compare these data with predictive modelling. Based on the hydrogeological conceptual modelling, we have sampled waters in recharge areas, discharge areas above and below reactors, and in major local aquifers. We have been able to reconstruct the evolution of the groundwaters, in a way which is consistent with the hydrogeology, using major elements and environmental isotopes. (author) 24 refs.

Louvat, D. [CEA Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. d`Entreposage et de Stockage des Dechets

1998-12-31

27

Computational analysis of the transient behavior of the Oklo natural reactors  

Energy Technology Data Exchange (ETDEWEB)

Since their discovery, the natural geologic reactors, have provided intriguing information for the design of high-level nuclear waste repositories. Studies have shown that isotopes of plutonium, uranium, and fission products migrated only short distances from the reactor sites over the two billion years since they ceased operation. These results have been used to demonstrate that a geologic repository for the long-term storage of spent reactor fuel can be used to provide waste isolation for at least 10,000 years. The conditions that led to criticality also have implications for a geologic repository. The Oklo reactors remained critical until the enrichment decreased to below 1.5%, similar to the enrichment of spent fuel destined for Yucca Mountain. The conditions that led to criticality in the Oklo deposits can be analyzed to preclude similar situations from occurring in an engineered repository. To provide a computational verification of this transient behavior, the equations for conservation of mass, Darcy flow, neutron generation and diffusion, and the energy equation were combined in a program to predict the of the Oklo reactors. The results of this work and its implications for the design of geologic repositories are presented. (author)

Culbreth, W.G.; Viggato, J. [Nevada Univ., Las Vegas, NV (United States)

2001-07-01

28

Recent outputs of the Oklo (Gabon) natural analogue study to nuclear waste disposal; Apports recents de l'etude de l'analogue naturel Oklo (Gabon) dans le domaine du stockage des dechets nucleaires  

Energy Technology Data Exchange (ETDEWEB)

In the past twenty five years, the natural nuclear reactors of Oklo have been the subject of numerous detailed studies. First investigated for the physical and neutron aspects of the nuclear reaction, they were then reconsidered because they provide a unique opportunity in the world to study the containment of actinides and fission products in a geological formation over a broad timescale (two billion years). Although the sites investigated do not represent a complete analogue of a repository system, many of the processes studied (mass transfer to the surface, transport, migration / retention), the spatial extent of these processes, and the timescales involved, are compatible with processes liable to occur during the lifespan of a repository for the deep geological disposal of spent nuclear fuel. A fresh program was therefore initiated as a European Commission project in 1990, entitled''Oklo as a natural analog for transfer processes in a radioactive waste repository'- phase 7, and then extended by a phase 2 entitled Oklo, Natural Analogue - Behavior of Nuclear Reaction Products in a Natural Environment''. Researches conducted in phase I served to determine the physical conditions of the operation of the natural reactor, reconstruct the geological history of the reactor environment, and decode the behavior of actinides as well as fission products in the surrounding geological formations. Phase N, which ended in June 1999, had three main objectives: i) to assess radionuclide migration and retention processes from the reactor zones to the geological environment, ii) to define the confinement properties and long-term behavior of geological materials; iii) to test models of processes related to radionuclide migration and retention, and eventually to provide suitable data and scenarios for performance assessment of nuclear waste disposal. This paper proposes a synthesis of the main outputs of the Oklo project to the performance assessment of nuclear waste disposal, the study of the long-term evolution of spent fuel and the long-term behavior of geological materials with respect to the containment of actinides and fission products. The Oklo natural analogue displays a number of specific features that make it unique in the world. The Oklo basin is characterized by the occurrence of meter scale uraninite lenses, that were affected by nuclear fission 2 billion years ago. These ''reactor zones'' exist in three sites: Oklo, Okelobondo and Bagombe. By analogy with a repository system, they are considered as representative of the 'Source' term. Numerous isotopic and geochemical tracers are thus available in order to restrict the migration or retention processes of actinides and fission products present in these zones. The near environment of the reactor zones, called ''Near field'' by analogy, is mainly composed of clayey materials (i.e. chlorite, illite, kaolinite). Reactor zones are found at present from the surface (Bagombe under oxidizing and acid conditions, with supergene weathering) to deep (Okelobondo under reducing conditions, with a low groundwater dynamics) conditions. Some reactor zones, e.g. R.Z. 13 in Oklo mine, have been subjected to strong hydrothermal disturbances (with temperatures above 350 deg C), linked to the geological history of the Franceville basin. On the other hand, the old age of the Oklo reactors (2 Ga) implies that pressure, temperature and chemical conditions have evolved during a long geological history, with associated basin scale movements of fluids. The Oklo-natural analogue Phase II project compiled useful information and tools for persons involved in Performance Assessment of waste disposal, wasteform conception or long term behavior [10] in four main areas corresponding to major investigation fields: 1/ ''Source'' term evolution, 2/ Long term containment properties of geological materials, 3/ Migration and retention of actinides and fission or end products, and 4/Geochemical and transport modeling. The

Michaud, V.; Trotignon, L. [CEA Cadarache, Dept. d' Entreposage et de Stockage des Dechets (DCC/DESD/SESD), 13 - Saint-Paul-lez-Durance (France); Louvat, D. [CEA Cadarache, (IPSN/DPRE/SERNAT/LERCM), 13 - Saint-Paul-lez-Durance (France)

2000-07-01

29

Oklo natural reactor. Study of uranium and rare earths migration on a core drilled through a reaction zone. Application to determination of the date of the nuclear reaction by measurement of fission products  

International Nuclear Information System (INIS)

Isotopic and chemical analysis of uranium and five rare earths: neodymium, samarium, europium, gadolinium and dysprosium were effected on fourteen samples taken in the same core drilled through a reaction zone of the Oklo uranium deposit. This study points out the general stability of uranium and fission rare earths; spatial distributions of these elements are quite analogous. Migrations have affected about 5% only of fission neodymium in the core of the reaction zone; corresponding values for samarium and gadolinium are slightly higher. These migration phenomena have carried rare earths to no more than 80 cm out of the core. By study of the europium it is shown that nuclear reactions have stayed in the ground since the time of reactions. On the other hand it is shown by analysis of the dysprosium that rare earths have not undergone an important movement. This study allow also the datation of nuclear reactions from the measurement of the quantity of fission neodymium produced. A value of 1.98x109 years is obtained slightly higher than the value obtained by geochronology.

1977-12-21

30

Record of cycling operation of the natural nuclear reactor in the Oklo/Okelobondo area in Gabon  

International Nuclear Information System (INIS)

[en] Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to 0.03 cm3 STP/g) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5 h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction

2004-10-29

31

Record of Cycling Operation of the Natural Nuclear Reactor in the Oklo/Okelobondo Area in Gabon  

Science.gov (United States)

Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to 0.03 cm3 STP/g) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction.

Meshik, A. P.; Hohenberg, C. M.; Pravdivtseva, O. V.

2004-10-01

32

The Oklo Natural Reactor and the Time Variability of the Fundamental Constants of Nature  

Energy Technology Data Exchange (ETDEWEB)

Natural nuclear reactors? Changes in the speed of light? If either of these concepts seem implausible to you now they certainly won't once Dr. Steve Lamoreaux (LANL) delivers his SLAC Colloquium lecture in the Panofsky Auditorium on November 7th at 4:15 pm entitled The Oklo Natural Reactor and the Time Variability of the Fundamental Constants of Nature. This lecture is a rare opportunity to learn not only about Oklo's incredible natural nuclear reactors but also to gain understanding about how the present-day study of these sites may alter our understanding of fundamental constants such as the speed of light. This event is a must-see for the curious!

Lamoreaux, Steve (LANL)

2005-11-07

33

Natural fission reactors from Gabon. Contribution to the study of the conditions of stability of a natural radioactive wastes storage site (2 Ga)  

International Nuclear Information System (INIS)

[en] The natural fission reactors of Oklo consists of a core of uraninite (60%) with fission products, embedded in a pure clay matrix. Thus, the aim of geological, mineral, and geochemical studies of the Oklo Reactors is to assess the behaviour of fission products in an artificial waste depository. Previous studies have shown that Reactor Zone 10, located in the Oklo mine, represents an example for an exceptional confinement of fission products since 2 Ga. In reactor Zone 9, located in Oklo open pit, migrations are more important. Reactor ZOne 13 was influenced by a thermal event due to a doleritic intrusion, located some twenty meters far away, one Ga years after fission reaction operations. In this study,we characterized temperature and redox conditions of fluids by using stable isotopes of uraninites and clays. Moreover mineralogical and chemical characteristics were defined. (author)

1997-01-01

34

Fate of the Epsilon Phase in the Oklo Natural Reactors  

Energy Technology Data Exchange (ETDEWEB)

In spent nuclear fuel (SNF), the micron- to submicron-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of {sup 99}Tc which has a long half life (2.13 x 10{sup 5} years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In addition, Tc is predominantly present as TcO{sub 4}{sup -} under oxidizing conditions at wide range of pH, weakly adsorbed onto mineral surfaces, and unlikely to be incorporated into alteration uranyl minerals. In the Oklo natural reactor (2.0 Ga), essentially all of the {sup 99}Tc has decayed to {sup 99}Ru. Thus, this study focuses on Ru and the other metals of the epsilon phase in order to investigate the occurrence and the fate of the epsilon phase during the corrosion of this natural SNF. Samples from reactor zone (RZ)-10 (836, 819, 687); from RZ-13 (864, 910); were investigated using TEM (transmission electron microscopy). Within the UO{sub 2} matrix, a Bi-Pd particle (40-60 nm), fioodite, PdBi{sub 2}, was observed with trace amounts of As, Fe, and Te surrounded by an amorphous Pb-rich area. (Pd,Rh){sub 2}As, palladodymite or rhodarsenide, was observed (400-500 nm in size). Ruthenarsinite, (Ru,Ni)As, was identified in most samples: with a representative composition of As, 59.9: Co, 2.5: Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic percent. The particles diameters are a few hundred nanometers and, in most cases, surrounded by a Pb-rich phase (400-500 nm). Typically, the ruthenarsenite does not occur as single particle but an aggregate of {approx}200 nm-sized particles. Some Ru-particles revealed a complex phase separation within the grain such as a Ru-particle (600-700 nm) with Pb at the core of the particle and enrichment of Ni, Co, and As at the rim. Some ruthenarsenite crystals were embedded in chlorite immediately adjacent to uraninite. A few particles were still coated by Pb. These results suggest a history for the epsilon phases: (1) The original epsilon phase was transformed to, in most cases, ruthenarsenite. (2) All Mo and most of the Tc were released from the epsilon phase. Some portion of the other metals was also leached and provided a space for a precipitation of PbS between the ruthenarsenite and uraninite. (3) Once the uraninite matrix dissolved, the epsilon particles were released and sometimes captured within adjacent alteration minerals.

S. Utsunomiya; R.C. Ewing

2005-03-31

35

Characterization and modeling of groundwater flow and transport around the nuclear natural reactors at Oklo, Gabon  

International Nuclear Information System (INIS)

[en] The purpose of the study of the Oklo Natural Analogue - Transport in the Reactor for field to identify and model current groundwater flow which may mobilize elements produced in the fossil fission reaction zones. The first important step is to understand the circulation patter, of the water involved in transporting the elements and then to describe the geochemical system by which it is governed. Hydrogeologic studies were carried out at two sites: a deep site at Okelobondo which offers an opportunity to study potential radionuclide migration from the reaction zone, over a distance of 400 m. Through very heterogeneous layers and a superficial site at Bangombe with a more homogeneous layering but situated in a area of meteoric alteration. The rationale and scope of performed field studies are presented together with results of hydrogeological characterization, conceptualizations (at different scales) and results of modelling of groundwater flow and transport. After an overview of the geology and hydrogeology which inspired our treatment of the flow in the near far fields of the reaction zones, the different mathematical models used are described. The Okelobondo site is discussed first. For this site we used a hydrodynamic model together with a model of the migration of natural environmental tracers. The results lead us to propose a flow pattern associated with transfer times between the reaction zone and the surface discharge zone. Then a similar approach is used for Bangombe. For this site, we added a geochemistry model describing the migration of uranium in the vicinity of the reaction zone using the METIS, CHIMERE and STELE software, developed in the MIRAGE programme. The isotopic ratio 235U/238U was used as a natural, original, tracer of the reactor zone. (author)

1995-01-01

36

Knowledge gained from the study of natural fossil reactors at Oklo for radioactive waste disposal  

International Nuclear Information System (INIS)

[en] The natural reactors of Oklo operated about two thousand million years ago and since then the uranium has remained in place almost in its entirety; this remarkable state of preservation has made it possible to make some interesting observations regarding the containment or, conversely, the dispersion of fission-produced or radiogenic elements in the ground. The geological environment of the reactors is described briefly; the most important fact is that the thermal convection currents associated with the heat release from nuclear reactions have completely desilicated the sandstones which contained uranium, thereby forming argillaceous lenses. The behaviour of the elements studied is described, these being classified into three categories according to their geochemical stability: (1) Elements that have been almost entirely preserved apart from occasional small redistributions. These are mainly the rare earths, zirconium, the elements of platinum ore (Ru, Rh and Pd) and radiogenic thorium. It is moreover fairly certain that the plutonium remained intact in the uranium before decaying; (2) Elements that have migrated but still exist in considerable quantities, notably radiogenic lead and bismuth and molybdenum; and (3) Elements that have been practically eliminated apart from small traces. These are the rare gases (Kr and Xe), iodine, cadmium, the alkali metals (Rb and Cs) and the alkaline-earth metals (Sr and Br). It seems, however, that in certain cases the migration of these elements from uranium may not have been very rapid. The main conclusion to be drawn from these observations is that uraninite was largely responsible for the preservation; it has exhibited a very remarkable retentive capacity, especially for weakly volatile elements having ionic radii compatible with its crystal lattice. On the other hand, the retentive capacities of argillaceous gangue and of the environment seem to have been rather poor

1979-07-06

37

Preliminary investigations of samples of uranium ore from the Oklo natural reactor in Gabon  

International Nuclear Information System (INIS)

[en] The authors present the preliminary results of an investigation of samples from the Oklo deposits which were kindly supplied to the USSR by the French authorities. The theory of the existence of a natural nuclear reactor in the Oklo ore, put forward by French scientists and supported by analysis of the isotopic composition of the uranium and the large number of elements in the middle part of the periodic system, is assumed to be adequately proven. The present study aimed at finding additional confirmation for this theory. To this end the possibility of (n, ?), (n, 2n) and other reactions occurring in the uranium isotopes and certain of their long-lived decay products was analysed and isotopic and radiochemical investigations were performed in an effort to find traces of these reactions. The authors also carried out mineragraphic, X-ray-diffraction and electron-microscopic investigations on samples from the reactor zone and made an ontogenetic analysis of individual constituents and aggregates. Mineralogically the following were established together with uraninite: coffinite, pitchblende, galenite, chalcopyrite, pyrite, hematite, chlorite and hydromicas. The results of preliminary isotopic, radiochemical, mineragraphic and structural studies on Oklo samples do not contradict the theory of the existence long ago of a mineral reactor, but nevertheless it remains important to carry out more complete and systematic investigations of all aspects of the problem

1975-06-23

38

The Oklo phenomenon as an analogue of radioactive waste disposal. A review  

International Nuclear Information System (INIS)

This work demonstrates the utility of the Oklo uranium ore deposit and natural fission reactors as a long time scale analogue for man-made radioactive waste repositories. Oklo has opened a new horizon representing an unrivalled opportunity to apply isotopic geochemistry to the study of migrations of fission products after an extremely long cooling and storage time and to define the processes involved in the transport of these elements through geological materials. This is the topic of the first section of this report. In the second section the information available on retention or migration at Oklo of the most interesting fission products is presented trying to illustrate how relevant the Oklo experience is in formulating predictions on the destiny of high activity waste disposed of in stable geological formations

1990-01-01

39

Oklo. A review and critical evaluation of literature  

Energy Technology Data Exchange (ETDEWEB)

The Oklo natural fossil fission reactors in Gabon, Equatorial Africa, have been studied as a natural analogue for spent nuclear fuel in a geological environment. For these studies, it is important to know what has happened to these reactors since they formed. This review is focussed on existing geological and geochronological information concerning the Oklo reactors and the surrounding ore. A sequence of geological and geochemical events in the Oklo area, as described in the literature, is given. The data and the studies behind this established geochronology are discussed and evaluated. Of the regional geology, special attention is given to the dating of the Francevillian sediments, and the intrusion of a dolerite dyke swarm. The processes that led to the mineralisation at Oklo, the subsequent formation of the nuclear reactors and later migration of fission products are described. Further discussion concerns the studies of the dolerite dyke swarm, since this appears to be one of the most important events related to fission product migration. A close look at the data related to this event shows that further study of the age of the dolerite dykes, and their effect on the uraninite in the Oklo reactors, is needed.

Zetterstroem, Lena [Swedish Museum of Natural History, Stockholm (Sweden). Lab. for Isotope Geology

2000-10-01

40

Oklo. A review and critical evaluation of literature  

International Nuclear Information System (INIS)

[en] The Oklo natural fossil fission reactors in Gabon, Equatorial Africa, have been studied as a natural analogue for spent nuclear fuel in a geological environment. For these studies, it is important to know what has happened to these reactors since they formed. This review is focussed on existing geological and geochronological information concerning the Oklo reactors and the surrounding ore. A sequence of geological and geochemical events in the Oklo area, as described in the literature, is given. The data and the studies behind this established geochronology are discussed and evaluated. Of the regional geology, special attention is given to the dating of the Francevillian sediments, and the intrusion of a dolerite dyke swarm. The processes that led to the mineralisation at Oklo, the subsequent formation of the nuclear reactors and later migration of fission products are described. Further discussion concerns the studies of the dolerite dyke swarm, since this appears to be one of the most important events related to fission product migration. A close look at the data related to this event shows that further study of the age of the dolerite dykes, and their effect on the uraninite in the Oklo reactors, is needed

2000-01-01

 
 
 
 
41

The last natural nuclear fission reactor  

Energy Technology Data Exchange (ETDEWEB)

A group of scientists argue the case for not mining the last known nuclear fission reactor located in Oklo, Gabon. Studies of its nuclear fission reactions, which occurred 2 billion years ago, are essential to our understanding of how fission products and actinides could migrate in nuclear waste repositories. Such a resource is almost irreplacable and its commercially viable uranium contents low, adding strength to the argument for conservation. (UK).

Gauthier-Lafaye, F. [Centre National de la Recherche Scientifique, 67 - Strasbourg (France). Centre de Geochimie de la Surface

1997-05-22

42

Isotope anomalies in natural nuclear reactor - Oklo uranium deposit (Gabon Republic, Africa)  

International Nuclear Information System (INIS)

[en] Samples from two ore zones of the Oklo uranium deposit are studied. The survey chemical analysis is conducted using the mass-spectrometer with a spart source. Large and various isotopic shifts of many elements explained by the chain fission reaction proceeding under conditions of intensive neutron ore irradiation are established. Isotopic composition of xenon and krypton is studied in detail. Isotopic anomalies of xenon and krypton observed earlier in samples of other holes have been discovered in samples from SC-36 and SC-52 holes. Thus, it is confirmed that these anomalies are probably typical for the whole deposit. Excess of the neutrondeficit 130Xe isotope explained by secondary reactions on neutrons has been found out for the first time

1985-01-01

43

Neutron Moderation in the Oklo Natural Reactor and the Time Variation of alpha  

CERN Multimedia

In the analysis of the Oklo (gabon) natural reactor to test for a possible time variation of the fine structure constant alpha, a Maxwell-Boltzmann low energy neutron spectrum was assumed. We present here an analysis where a more realistic spectrum is employed and show that the most recent isotopic analysis of samples implies a non-zero change in alpha, over the last two billion years since the reactor was operating, of \\Delta\\alpha/\\alpha\\geq 2.2\\times 10^{-7} (6\\sigma confidence). Issues regarding the interpretation of the shifts of the low energy neutron resonances are discussed.

Lamoreaux, S K

2003-01-01

44

Formation and geochemical significance of micrometallic aggregates including fissiogenic platinum group elements in the Oklo natural reactor, Gabon  

Science.gov (United States)

Metallic aggregates with a size of a few tens ?m and consisting mainly of Ru, Rh, Pd, Te, Pb, As, Sb, S and Bi were found in the acid residue of SD37-S2/CD uraninite taken from Oklo natural reactor zone (RZ) 13. Quantitative analyses of major elements using an electron probe microanalyzer and in situ isotopic analyses of Zr, Mo, Ru, Pb and U using a sensitive high-resolution ion microprobe were performed on the metallic aggregates to determine the geochemical behaviors of fission products and actinides and to ascertain the processes of formation of the aggregates in the RZs. The chemical compositions of the aggregates investigated in this study are significantly different from those reported previously, showing lower Pb content and no correlation between the contents of Pb and S in the individual grains. The 235U/ 238U ratios in metallic aggregates vary significantly from 0.00478 to 0.01466, indicating chemical fractionation between U and Pu during the formation of the aggregates. The Pb isotopic data indicate that most of the Pb in the aggregates decayed from 2.05 Ga-old uraninite that existed in the RZ originally and that there was chemical fractionation between U and Pb in some aggregates. The Zr and Mo isotopic ratios, 90Zr/ 91Zr and 95Mo/ 97Mo, for most of the aggregates had small variations, which can be simply explained by constant separate mixing of fissiogenic and nonfissiogenic components. On the other hand, a large variation in the 99Ru/ 101Ru ratio (0.324-1.73) cannot be explained only by a two component mixing theory; thus, chemical fractionation between Tc and Ru during the reactor criticality is suggested. The large variations in the 235U/ 238U and 99Ru/ 101Ru isotopic ratios suggest that the aggregates formed under various redox conditions owing to the radiolysis of water.

Kikuchi, Makiko; Hidaka, Hiroshi; Gauthier-Lafaye, François

2010-08-01

45

Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronic of Fresh Core  

CERN Multimedia

Using a modern methods of reactor physics we have performed the full-scale calculations of the natural reactor Oklo. For reliability we have used the recent version of two Monte Carlo codes: the Russian code MCU REA and world wide known code MCNP (USA). Both codes produce close results. We constructed computer model of zone RZ2 of reactor Oklo which takes into account all details of design and composition. The calculations were performed for the three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a great difference between reactor spectra and Maxwell's one, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary...

Petrov, Yu V; Onegin, M S; Petrov, V Yu; Sakhnovskii, E G; Petrov, Yu.V.

2006-01-01

46

Oklo 2 Billion Years Before Fermi  

International Nuclear Information System (INIS)

The author aims to present the little-known story of the Oklo natural reactors. He recalls the historical aspects of the Oklo reactors discovery by the CEA in 1972, he explains the scientific phenomenon and the interest, notably as a ''natural analogue'' for the geological disposal of high level radioactive wastes. (A.L.B.)

2005-01-01

47

Gas, benefits and question marks. The Oklo reactors: 100 % natural. The Kyoto protocol: use it or lose it?. Small hydro power: a great leap forward. The energy mix of South Korea  

International Nuclear Information System (INIS)

This issue of Alternatives newsletter contains a main press-kit about natural gas economics worldwide and 4 articles dealing with the Oklo natural reactor, the Kyoto protocol, the small hydro-power in China, and the energy mix of South Korea: 1 - 'Gas benefits and question marks': The world's most widely distributed fossil fuel, natural gas is also the fastest-growing energy source of the past thirty years. Its position as the fuel of choice in the global energy mix is due in large part to its many domestic and industrial applications. 2 - 'The Oklo reactors: 100% natural': Another look at this extraordinary 2 billion year-old phenomenon in words and pictures: the nuclear fission reaction that created the natural reactors of Gabon. 3 - 'The Kyoto Protocol: use it or lose it?': Nearly eight years after its signature, the Kyoto Protocol is still hotly debated. Two experts give us their views: Spencer Abraham, former U.S. Secretary for Energy, and Jean-Charles Hourcade of CIRED, the international center for research on the environment and development. 4 - 'Small hydro power: a great leap forward': The Chinese government has responded to the need for rural electrification with an aid program for the country's poorest cantons. Enter the small hydro plant in northern Guangxi province. 5 - 'The energy mix of South Korea': Faced with continuing strong economic growth and energy demand, South Korea has multiplied its projects, from hydropower to tidal power to nuclear and even hydrogen in the longer term

2005-01-01

48

The Oklo phenomenon  

International Nuclear Information System (INIS)

[en] During 1972, research workers of the French Commissariat a I'Energie Atomique made an astonishing discovery: fission chain reactions had been triggered spontaneously in the very remote past within a uranium deposit in Gabon and parts of the deposit had behaved like a modern nuclear reactor for hundreds of thousands of years. Subsequent investigations showed that the reaction sites had remained in a remarkable state of preservation, so that detailed study was possible. he IAEA felt that the Oklo phenomenon would be an excellent subject for international co-operation in fundamental research and agreed to the suggestion of the Gabon Government and the French Commissariat a I'Energie Atomique that a jointly organized symposium be held. The symposium will take place at Franceville, Gabon, from 23 to 27 June 1975. (author)

1975-06-27

49

Investigations of the natural fission reactor program. Progress report, October 1977--September 1978  

International Nuclear Information System (INIS)

The U.S. study of the Oklo natural reactor began in 1973 with the principal objectives of understanding the processes that produced the reactor and that led to the retention of many of its products. Major facets of the program have been the chemical separation and mass spectrometric analysis of the reactor components and products, the petrological and mineralogical examination of samples taken from the reactor zones, and an interdisciplinary modeling of possible processes consistent with reactor physics, geophysics, and geochemistry. Most of the past work has been on samples taken within the reactor zones. Presently, these studies give greater emphasis to the measurement of mobile products in additional suites of samples collected peripherally and ''downstream'' from the reactor zones. This report summarizes the current status of research and the views of U.S. investigators, with particular reference to the extensive work of the French scientists, concerning the main features of the Oklo natural fission reactor. Also mentioned briefly is the U.S. search for natural fission reactors at other locations

1978-01-01

50

Fluid phases contemporary with sandstone diagenesis tectonic movements and the activity of the natural nuclear reactors in the Oklo deposit, Republic of Gabon  

International Nuclear Information System (INIS)

A research contract was agreed between the IAEA and the Centre de Recherches Petrographiques et Geochimiques of Nancy (France) to analyze some aspects of the fluid phases present during diagenesis of the Precambrian Francevillean sandstones of Gabon, which include the Oklo uranium deposit in which because of the geometry of the ore body, the high ore grade, etc., a natural uranium reactor was formed. The investigation was orientated to define some special characteristics of the fluid inclusions and two main methods were applied for this purpose: The Raman spectroscopy (MOLE microsonde) and microthermometric analysis. The main conclusions of the research are the following: 1. The Francevillean sandstones were buried up to a depth of 4-5 km where the corresponding geothermal temperature was of around 2400C but during the Oklo nuclear reaction, the fluid temperatures were higher than 4500C and in at least one case (Zone II) up to 6000C. 2. The tectonic fracturing has favoured the fluid circulation, which was possibly the responsible of the mineral re-concentration after the Oklo nuclear reaction. 3. The diagenetic fluids were essentially aqueous solutions and no sulphur components were identified. 4. The hydrogen presence in a quartz veinlet is surprising and possibly due to water decomposition by strong irradiation

1979-01-01

51

The Oklo bound on the time variation of the fine-structure constant revisited  

CERN Document Server

It has been pointed out by Shlyakhter that data from the natural fission reactors which operated about two billion years ago at Oklo (Gabon) had the potential of providing an extremely tight bound on the variability of the fine-structure constant alpha. We revisit the derivation of such a bound by: (i) reanalyzing a large selection of published rare-earth data from Oklo, (ii) critically taking into account the very large uncertainty of the temperature at which the reactors operated, and (iii) connecting in a new way (using isotope shift measurements) the Oklo-derived constraint on a possible shift of thermal neutron-capture resonances with a bound on the time variation of alpha. Our final (95% C.L.) results are: -0.9 \\times 10^{-7} <(alpha^{Oklo} - alpha^{now})/alpha <1.2\\times 10^{-7} and -6.7 \\times 10^{-17} {yr}^{-1} < {\\dot alpha}^{averaged}/alpha <5.0\\times10^{-17} {yr}^{-1}.

Damour, Thibault Marie Alban Guillaume; Damour, Thibault; Dyson, Freeman

1996-01-01

52

The Tokai-Mura accident: the fossil nuclear reactor of Oklo; L'accident de Tokay-Mura: le reacteur nucleaire fossile d'Oklo  

Energy Technology Data Exchange (ETDEWEB)

After the three first development of the criticality accident of Tokai-Mura is developed in this issue the Oklo phenomenon: The discovery and the explanations of this phenomenon. The study of the fission products migration in the soils of Oklo gave ideas for the deep geological storage of radioactive wastes. (N.C.)

Andurand, R

2000-10-01

53

Gamma-ray spectrometer measurement of 238U/235U in uranium ore from a natural reactor at Oklo, Gabon  

International Nuclear Information System (INIS)

[en] A sample from the Oklo deposit containing about 0.51 atom percent 235U (by mass spectrometer) was analyzed by a gamma-ray spectrometer system, using a high-purity planar germanium detector. The 238U was determined from its daughter's (234Th) 63.3 keV photopeak; the 235U was determined from its 143.8 and 163.4 keV photopeaks. The ratios of these photopeaks were compared with that from a standard having normal uranium isotopic content; the resulting calculations give a 235U abundance of 0.54 atom percent in the Oklo sample. The gamma-ray spectrum also contains lines from five other isotopes in the uranium series, which indicate the Oklo sample to be at or near secular equilibrium, as the time elapsed since the nuclear reaction ended was sufficient to permit the daughters to achieve equilibrium

1976-01-01

54

Two billion year old natural analogs for nuclear waste disposal: the natural nuclear fission reactors in Gabon (Africa)  

International Nuclear Information System (INIS)

[en] Two billion years ago, the increase of oxygen in atmosphere and the high 235U/238U uranium ratio (> 3%) made possible the occurrence of natural nuclear reactors on Earth. These reactors are considered to be a good natural analogue for nuclear waste disposal. Their preservation during such a long period of time is mainly due to the geological stability of the site, the occurrence of clays surrounding the reactors and acting as an impermeable shield, and the occurrence of organic matter that maintained the environment in reducing conditions, favourable for the stability of uraninite. Hydrogeochemical studies and modelling have shown the complexity of the geochemical system at Oklo and Bangombe (Gabon) and the lack of precise data about uranium and fission products retention and migration mechanisms in geological environments. (author)

2002-01-01

55

Far field hydrogeochemistry in the Oklo reactor area (Gabon)  

International Nuclear Information System (INIS)

[en] In the frame of a general study of the Oklo natural reactor, which takes into account the natural analogue aspect, a complete hydrogeological and hydrogeochemical study is undertaken. The partners of this study are the following: - Section de geochimie, CEA (France): P. Toulhoat, J.P. Gallien, P. L'Henoret, V. Moulin (groundwater chemistry and colloids). - Ecole des Mines de Paris (CIG, Fontainebleau) E. Ledoux, I. Gurban (hydrogeology and modelling) - SKB and Conterra AB (Sweden) J.A.T. Smellie, A. Winberg (hydrogeology, isotope geochemistry). The aim of this study is to try to understand and to characterize the possible mobilization of elements or isotopes when groundwaters come in contact with nuclear reaction zones. The first step of the study is presented here, which comprises a general geochemical and hydrodynamical characterization of the site. In this presentation, the site of Bagombe is also mentioned as it has been confirmed as sector in which nuclear fission reactions occurred as in Oklo. (author). 10 refs., 6 figs., 6 tabs

1993-01-01

56

Mineralogical, chemical and oxygen isotopic data on uraninites from natural fission reactors (Gabon): effects of weathering conditions  

International Nuclear Information System (INIS)

[en] Nuclear fission reactions occurred 2000 Ma ago in the uraninites of the Oklo-Okelobondo and Bangombe uranium deposits (Gabon). These uraninites contain actinides and fission products and therefore are considered as natural analogues for artificial nuclear spent fuel of PWR type nuclear plant. Mineralogical, chemical and oxygen isotopic analyses have been performed in order to determine the stability of the uraninites in weathering conditions. Results show that the alteration of uraninites by meteoric waters affects the cell parameters and the chemistry of the uraninites but not the oxygen isotopic composition. Radiolysis of water is invoked as a possible mechanism for the very low values of ?18O (-22.0 0/00 SMOW) measured in the uraninites. (authors)

1998-01-01

57

Uranium redistribution under oxidizing conditions in Oklo natural reactor zone 2, Gabon  

International Nuclear Information System (INIS)

[en] This mineralogical study was completed to elucidate the relationships between uranium distribution and alteration products of the host rock of natural reactor zone clays just below the reactor core. Uraninite is preserved without any alteration in the reactor core. Uranium minerals are found to be present in the fractures in the reactor zone clays associated with iron-mineral veins, galena and Ti-bearing minerals. Uranium, for which the phases could not be identified, occurs in iron-mineral veins and the iron-mineral rim of pyrite grains in the reactor zone clays. Uranium is not associated with granular iron minerals occurring in the illite matrix of the reactor zone clays. The degree of crystallinity and uranium content of the three iron-bearing alteration products suggest that they formed under different conditions; the granular iron minerals, under alteration conditions where uranium was not mobilized while the iron-mineral veins and the iron-mineral rim of pyrite, under conditions in which uranium is mobilized after the formation of the granular iron minerals

1995-01-01

58

Oklo 2 Billion Years Before Fermi; Les reacteurs naturels d'Oklo (Gabon): 2 milliards d'annees avant Fermi  

Energy Technology Data Exchange (ETDEWEB)

The author aims to present the little-known story of the Oklo natural reactors. He recalls the historical aspects of the Oklo reactors discovery by the CEA in 1972, he explains the scientific phenomenon and the interest, notably as a 'natural analogue' for the geological disposal of high level radioactive wastes. (A.L.B.)

Barre, B

2005-02-15

59

The Oklo phenomenon  

International Nuclear Information System (INIS)

[en] A scientific conference about the Oklo phenomenon took place in Gabon in West Africa on 23-27 June this year. The conference was arranged jointly by the International Atomic Energy Agency, the Gabonese Authorities and the French Atomic Energy Commission, CEA. The Oklo phenomenon, which is named after a uranium mine in Gabon, is of considerable interest to geologists, isotope geochemists and reactor physicists, as it has been discovered that nuclear reactions took place within the rich uranium ore body over a period of at least 100000 years, some 1800 million years ago. (author)

1975-01-01

60

Oklo Constraint on the Time-Variability of the Fine-Structure Constant  

CERN Multimedia

The Oklo phenomenon, natural fission reactors which had taken place in Gabon about 2 billion years ago, porvides one of the most stringent constraints on the possible time-variability of the fine-structure constant $\\alpha$. We first review briefly what it is and how reliable it is in constraining $\\alpha$. We then compare the result with a more recent result on the nonzero change of $\\alpha$ obtained from the observation of the QSO absoorption lines. We suggest a possible way to make these results consistent with each other in terms of the behavior of a scalar field which is expected to be responsible for the accelaration of the universe.

Fujii, Y

2003-01-01

 
 
 
 
61

Eh-pH diagrams for elements from Z = 40 to Z = 52: application to the Oklo natural reactor, Gabon  

International Nuclear Information System (INIS)

[en] Eh-pH diagrams for elements from Z = 40 (Zr) to Z = 52 (Te) have been constructed in order to comment on migration/retention of these elements at Oklo. Although data for fissiogenic amounts of some of these elements are lacking, where such data are available to agreement between predicted migration/retention based on the Eh-pH diagrams and actual measurement is excellent. Based on Eh-pH diagrams, migration (to what degree is uncertain) of Mo and Cd is predicted whereas retention of Y, Zr, Tc, Ru, Rh, Pd, Ag and Te is also predicted. An earlier report of Frejacques et al. of Tc migration is in disagreement with Eh-pH prediction, and recent (unpublished) data argue for Tc retention. In view of the agreement between prediction and observation, the possible migration of Sb and retention of In and Sn is proposed. These data again demonstrate the usefulness of Eh-pH diagrams for the Oklo fossil nuclear reactor but, more important, allow constraints to be placed on repositories for nuclear waste now under consideration. (Auth.)

1978-01-01

62

Mobilization and mechanisms of retardation in the Oklo natural reactor zone 2 (Gabon)--inferences from U, REE, Zr, Mo and Se isotopes  

International Nuclear Information System (INIS)

[en] Mineralogical and isotopic studies were carried out on the natural nuclear reaction zone 2 from the Oklo deposit to evaluate the mobility of several nuclear reaction products in response to the alteration of the reaction zone and to identify the mechanisms which could retard the transport of released radionuclides. To address these issues, in situ isotopic analyses by SHRIMP and a selective extraction procedure were performed to constrain the structural location of nuclear reaction products (exchangeable and non exchangeable) and their association with mineral phases. The distribution patterns of U, REE, Zr and Mo isotopes reveal that substantial amounts were released from the core and migrated through the hydrothermal alteration halo over metric distances, owing to uraninite dissolution and advective transport by hydrothermal solutions during and soon after criticality. The results emphasize the mobility of Zr at Oklo, this element being often considered as 'immobile' during water-rock interactions. The main output is the demonstration of the net effects of sorption and coprecipitation processes. Chlorite and to a lesser extent illite were found to have adsorbed significant amounts of U, REE, Zr (and probably Th) and less sorbing elements such as Mo. Coprecipitation of secondary UO2 and P-rich coffinite within the alteration halo is also an important means of retardation. The concentration of radionuclides released from the reactor were probably high and they display solubility limited transport behaviour. No retention effect was found for Se in the immediate vicinity of the reactor and this element may have moved farther from its source of production. These results have interesting implications for the evaluation of long-term containment of radionuclides. They provide a simple illustration of the performance of a clay barrier in the uptake of radionuclides by sorption onto clays and reincorporation in secondary U-minerals. This study also demonstrates the robustness of these retention processes over extremely long periods of time

2003-01-01

63

Retention of transuranic and actinide elements and bismuth at the Oklo natural reactor, Gabon: application of Eh-pH diagrams  

International Nuclear Information System (INIS)

[en] Several tons of 239Pu and lesser amounts of 240Pu and 241Pu were produced during the 0.5 Ma lifetime of the Oklo natural reactor, Gabon, some 1.8 Ga ago. Production of Pu isotopes is evidenced by slight excesses of 235U in otherwise 235U-depleted U-rich zones as well as by even slighter excesses of 232Th and 209Bi in the same zones. The low-grade ore, unaffected by nuclear reactions, contains very little Bi and Th, and U possesses a normal isotopic composition. The 241Pu-produced Bi-excess demands that 241Am, 237Np and other members of the 241Pu decay chain must not have migrated, since loss of any member from the 241Pu decay chain would prevent the Bi excesses from accumulating in the high-grade ore zones. Eh-pH diagrams for all species of importance indicate the following: Po is retained as the native metal in the Eh-pH range of interest, whereas Pu and Np are retained as PuO2 and NpO2, respectively. Am is probably retained as Am(OH)3 or as an (Eu,Am)2(CO3)3 species. The field of Bi2S3 is wide enough to prevent migration even under slightly oxidizing conditions. Collectively, these data argue for the retention of Pu, Am, Np, U, Po and Bi at Oklo and suggest that geologic sites elsewhere should be suitable for waste isolation. (Auth.)

1978-01-01

64

Oklo - A nuclear reactor 1800 million years ago  

International Nuclear Information System (INIS)

[en] A scientific conference about the so-called OKLO-phenomenon will take place in Gabon in West Africa from 23?27 June this year. The conference is arranged jointly by the International Atomic Energy Agency, the Gabonese authorities and the French Atomic Energy Commission (CEA). As the OKLO phenomenon, named after a uranium mine in Gabon, does not seem to be known outside specialist circles, it may be of interest to report on a few details about this discovery and the interesting conclusions that have been drawn about what happened during a short period of 100?500 000 years, in the earth's development 1 800 million years ago. Natural uranium contains 0.7202% of uranium-235, the fissionable isotope contained in nuclear fuel. Until June 1972 this concentration had been found to be the same for all uranium that had been discovered until that time, regardless of the place of discovery, and the same concentration was encountered in the uranium of which traces have been found on the moon. In the French gaseous diffusion plant for enrichment of the isotope-235 at Pierrelatte, regular measurements are carried out on the concentration of uranium-235 in the uranium with which the plant is supplied. This is done primarily to ensure that the contained uranium really is of natural origin and does not come from a plant where some fraction of the uranium-235 has already been used. In the course of one such isotopic analysis it was found that the uranium-235 concentration was slightly less than what one would expect from natural uranium, namely 0.7171% instead of the value just mentioned. If the scientists at Pierrelatte had not made a point of being so careful they might have overlooked this result. However, they carried out a series of checks and discovered that it was not a question of measurement error, but that they were dealing with uranium which had a composition differing from that of 'normal' uranium, with additional variations between different samples. It was soon established that the uranium had come from Gabon ? or more precisely from a mine, OKLO, in the vicinity of Franceville in south-east Gabon

1975-01-01

65

Mineralogical, chemical and oxygen isotopic data on uraninites from natural fission reactors (Gabon): effects of weathering conditions; Mineralogie, chimie et composition isotopique de l`oxygene des uraninites des reacteurs de fission naturels (Gabon): effets de l`alteration supergene  

Energy Technology Data Exchange (ETDEWEB)

Nuclear fission reactions occurred 2000 Ma ago in the uraninites of the Oklo-Okelobondo and Bangombe uranium deposits (Gabon). These uraninites contain actinides and fission products and therefore are considered as natural analogues for artificial nuclear spent fuel of PWR type nuclear plant. Mineralogical, chemical and oxygen isotopic analyses have been performed in order to determine the stability of the uraninites in weathering conditions. Results show that the alteration of uraninites by meteoric waters affects the cell parameters and the chemistry of the uraninites but not the oxygen isotopic composition. Radiolysis of water is invoked as a possible mechanism for the very low values of {delta}{sup 18}O (-22.0 0/00 SMOW) measured in the uraninites. (authors) 25 refs.

Pourcelot, L.; Gauthier-Lafaye, F. [Universite Louis Pasteur, 67 - Strasbourg (France)

1998-04-01

66

Natural fission reactors in the Franceville basin, Gabon: A review of the conditions and results of a open-quotes critical eventclose quotes in a geologic system  

International Nuclear Information System (INIS)

[en] Natural nuclear fission reactors are only known in two uranium deposits in the world, the Oklo and Bangombe deposits of the Franceville basin: Gabon. Since 1982, five new reactor zones have been discovered in these deposits and studied since 1989 in a cooperative European program. New geological, mineralogical, and geochemical studies have been carried out in order to understand the behavior of the actinides and fission products which have been stored in a geological environment for more than 2.0 Ga years. The Franceville basin and the uranium deposits remained geologically stable over a long period of time. Therefore, the sites of Oklo and Bangombe are well preserved. For the reactors, two main periods of actinide and radionuclides migration have been observed: during the criticality, under P-T conditions of 300 bars and 400-500 degrees C, respectively, and during a distention event which affected the Franceville basin 800 to 900 Ma ago and which was responsible for the intrusion of dolerite dikes close to the reactors. New isotopic analyses on uranium dioxides, clays, and phosphates allow us to determine their respective importance for the retention of fission products. The UO2 matrix appears to be efficient at retaining most actinides and fission products such as REEs, Y, and Zr but not the volatile fission products (Cd, Cs, Xe, and Kr) nor Rb, Sr, and Ba. Some fissiogenic elements such as Mo, Tc, Ru, Rh, Pd, and Te could have formed metallic and oxide inclusion in the UO2 matrix which are similar to those observed in artificial spent fuel. Clays and phosphate minerals also appear to have played a role in the retention of fissiogenic REEs and also of Pu. 82 refs., 21 figs., 12 tabs

1996-01-01

67

Search for other natural fission reactors  

International Nuclear Information System (INIS)

Precambrian uranium ores have been surveyed for evidence of other natural fission reactors. The requirements for formation of a natural reactor direct investigations to uranium deposits with large, high-grade ore zones. Massive zones with volumes approximately >1m3 and concentrations approximately >20% uranium are likely places for a fossil reactor if they are approximately >0.6x109 years old and if they contained sufficient water but lacked neutron-absorbing impurities. While uranium deposits of northern Canada and northern Australia have received most attention, ore samples have been obtained from the following world-wide locations: the Shinkolobwe and Katanga regions of Zaire; southwest Africa; Rio Grande do Norte, Brazil; the Jabiluka, Nabarlek, Koongarra, Ranger, and El Sharana ore bodies of the Northern Territory, Australia; the Beaverlodge, Maurice Bay, Key Lake, Cluff Lake, and Rabbit Lake ore bodies and the Great Bear Lake region, Canada. The ore samples were tested for isotopic variations in uranium, neodymium, samarium, and ruthenium which would indicate natural fission. Isotopic anomalies were not detected. Criticality was not achieved in these deposits because they did not have sufficient 235U content (a function of age and total uranium content) and/or because they had significant impurities and insufficient moderation. A uranium mill monitoring technique has been considered where the ''yellowcake'' output from appropriate mills would be monitored for isotopic alterations indicative of the exhumation and processing of a natural reactor. (author)

1977-12-21

68

Characterization of near- to far-field ancient migrations around Oklo reaction zones (Gabon) using minerals as geochemical tracers  

International Nuclear Information System (INIS)

We developed a method allowing the identification of ancient fluid circulations through trace-element patterns in hydrothermal minerals. Application of this technique to Oklo nuclear reactors as natural analogues involves apatite and lanthanides for early circulations, and sulfides and chalcophile elements for late events. At least four different fluid generations have been found, and are tentatively assigned to episodes of Oklo site history. (1) Zr- and U-rich fluids predate criticality near reaction zone 10. (2) Isotopic anomalies of lanthanides provide evidence for mobility of fission products during criticality. Up to now, anomalies are restricted to the near field (desilicified zone around reaction zones). (3) A first pyrite stage is focused around reaction zones, up to a few tens of meters. (4) The latest event is most probably of regional extent. Besides direct evidence of fission-product migration, the present study is expected to provide the geological background and geochemical constraints for modelling ancient fluid circulation and consequent element migration near reaction zones. (orig.).

1996-01-01

69

Two billion year old natural analogs for nuclear waste disposal: the natural nuclear fission reactors in Gabon (Africa); Des analogues naturels de sites de stockage de dechets nucleaires vieux de 2 milliards d'annees: les reacteurs de fission nucleaire naturels du Gabon (Afrique)  

Energy Technology Data Exchange (ETDEWEB)

Two billion years ago, the increase of oxygen in atmosphere and the high {sup 235}U/{sup 238}U uranium ratio (> 3%) made possible the occurrence of natural nuclear reactors on Earth. These reactors are considered to be a good natural analogue for nuclear waste disposal. Their preservation during such a long period of time is mainly due to the geological stability of the site, the occurrence of clays surrounding the reactors and acting as an impermeable shield, and the occurrence of organic matter that maintained the environment in reducing conditions, favourable for the stability of uraninite. Hydrogeochemical studies and modelling have shown the complexity of the geochemical system at Oklo and Bangombe (Gabon) and the lack of precise data about uranium and fission products retention and migration mechanisms in geological environments. (author)

Gauthier-Lafaye, F. [Centre de Geochimie de la Surface, UMR 7517 CNRS ULP, 67 - Strasbourg (France)

2002-10-01

70

Geochemistry of neo-formed minerals at Oklo (Gabon), geologic history of the Oklo basin: a contribution for the studies of geologic disposals of radioactive wastes; Geochimie des mineraux neoformes a Oklo (Gabon), histoire geologique du bassin d'Oklo: une contribution pour les etudes de stockages geologiques de dechets radioactifs  

Energy Technology Data Exchange (ETDEWEB)

Oklo uranium ore deposit (Francevillian basin,Gabon) is the unique place in the world where 2000 Ma old fossil nuclear reactors were described. The geological and thermal history of this basin, since 2000 Ma was retraced. Tholeiitic intrusion was 755 {+-} 83 Ma with Sm-Nd isochron on whole rock and plagioclase and 746 {+-} 16 Ma old with U-Pb dating on zircons. This event was linked to a pre-Pan-African rifting stage. A green schist facies metamorphism was detected on the granitic rocks of the substratum and seemed to affect the tholeiitic intrusion. Apatite fission tracks dating performed on granitic basement revealed a thermal event between Permian and middle-Jurassic time, linked to the Atlantic ocean opening. Fission track ages distribution suggest a brittle tectonics (T < 60 deg. C) occurred after middle Jurassic times. Geochemical and isotopic studies on apatites and zircons which crystallized on natural nuclear reactors let compare the confinement of these two crystalline structures. These minerals were affected by self-irradiation due to actinide incorporation. U, Pu and fission products (REE, Rb, Sr) were trapped by apatites. Zircons contain fissiogenic REE and radiogenic Ba. Apatites crystallized during the nuclear reactions, zircons at the end of this phenomenon. Isotopic study of tholeiitic intrusion minerals point out fissiogenic Nd and Sm incorporation in clinopyroxenes. This result implies a fissiogenic products remobilization during the tholeiitic intrusion event. (author)

Sere, V

1996-12-01

71

Monte-Carlo based numerical modeling and simulation of criticality conditions occurrence in natural Reactor Zone 9 in Oklo deposit (Gabon)  

International Nuclear Information System (INIS)

[en] The occurrence of the criticality with analogue modelled configurations of the fossil reactor zone n deg 9 (RZ9) from Oklo uranium deposit in Gabon is studied. The RZ9 and the other reaction zones 7 and 8, of the same deposit sector are characterized by a low thickness compared to other zones 1 to 6 and an important presence of organic matter with a lower U content. This makes the simulations performed in the past unable to explain the occurrence of that phenomenon in such zones. In the present work an extrapolation to 2 billion years ago as an initial state of the reactor is done using the MCNP Monte-Carlo based code. To make it more close to the geological reality experimental conditions and geometry, possible porosity, moderators and minimal Uranium content are considered. The minimal critical configuration is obtained by variation of a set of geometrical and physical parameters around the estimated composition of the reactor area. A set of simulations computing the corresponding effective multiplication factor keff, and reactivity are presented. The effect of organic matter as well as the influence on the criticality is discussed. (author)

2010-01-01

72

Time-variability of alpha from realistic models of Oklo reactors  

CERN Multimedia

We reanalyze Oklo $^{149}$Sm data using realistic models of the natural nuclear reactors. Disagreements among recent Oklo determinations of the time evolution of $\\alpha$, the electromagnetic fine structure constant, are shown to be due to different reactor models, which led to different neutron spectra used in the calculations. We use known Oklo reactor epithermal spectral indices as criteria for selecting realistic reactor models. Two Oklo reactors, RZ2 and RZ10, were modeled with MCNP. The resulting neutron spectra were used to calculate the change in the $^{149}$Sm effective neutron capture cross section as a function of a possible shift in the energy of the 97.3-meV resonance. We independently deduce ancient $^{149}$Sm effective cross sections, and use these values to set limits on the time-variation of $\\alpha$. Our study resolves a contradictory situation with previous Oklo $\\alpha$-results. Our suggested $2 \\sigma$ bound on a possible time variation of $\\alpha$ over two billion years is stringent: $ -...

Gould, C R; Lamoreaux, S K

2006-01-01

73

The Oklo reactors: five years of exploration of the site  

International Nuclear Information System (INIS)

The main phases of the exploration of the Oklo site since the discovery of the ''reactor'' phenomenon are outlined briefly. Over 180 sampling holes were drilled during the interruption of the mining activities in the sector concerned. Several new zones have been found. Mining was resumed in the second half of 1975, providing an opportunity for highly fruitful geological follow-up work: more precise knowledge was gained of the morphology of the reactors, and very many additional samples were taken. Plant treatment of the ore and the systematic analysis of batches have made it possible to establish a balance of missing uranium-235. A small portion containing sites of intense reaction has been preserved by being anchored to the quarry wall. Mining in this sector has now finished, but new indications of fission have been found, especially in the Okelobondo sector. (author)

1977-12-21

74

Analysis of colloids from Oklo/Okelobondo and Bangombe waters  

International Nuclear Information System (INIS)

[en] In the framework of the hydrogeological and hydrogeochemical studies carried out on the Oklo/Okelobondo and Bangombe sites, the nature and physico-chemical characteristics of the colloids present in the waters sampled in these sites have been investigated. Different techniques have been used for this purpose, namely scanning electron microscopy, X-ray microanalysis and photon correlation spectroscopy. Informations on their size, composition and content have thus been obtained. Discussion on the possible origin and formation mechanisms of these colloids is performed. (author). 7 refs., 2 figs., 2 tabs

1993-01-01

75

Geochemistry of apatites, pyrites and galenas in near- and far-field veins and sandstones around the Oklo fossil reactors (Gabon): identification of ancient hydrothermal circulations  

International Nuclear Information System (INIS)

[en] The identification and the modelling of fission-product transfer from reactor cores to near-and far-field surrounding rocks, are a prerequisite to the use of the Oklo fossil reactors as a natural analogue of radioactive waste disposal. It is thus necessary to characterize the different hydrothermal circulation stages which occurred in the deposit, for their ability to carry away radionuclides to be assessed. The problems to be solved are as follows:(1) to identify each stage, (2) to constrain the chemical composition of these fluids as precisely as possible, (3) to determine fluid pathways, and if possible, (4) to assign the source(s) of matter carried by each fluid, and the source of energy needed for fluid convection. This paper presents the geochemistry of apatites, pyrites and galenas. (author). 3 refs., 4 figs., 2 tabs

1993-01-01

76

The Oklo fossil reactor. Determinations of neutron capture cross sections of isotopes occurring in the Oklo phenomenon by irradiation in the reactor Triton  

International Nuclear Information System (INIS)

An experimental irradiation of isotopes was carried out in a pool type reactor (Triton reactor) to better the knowledge of capture cross sections of uranium fission products arising in the Oklo phenomenon. Irradiation conditions analysis techniques of samples and methods of calculation to interpret results are described. Capture cross sections of 143Nd, 145Nd, 147Sm, 99Tc, 82Kr, 83Kr, 129Xe, 131Xe were determined will precision and were estimated for dysprosium isotopes and europium isotopes. Found values confirm known data for neodymium and xenon isotopes, but are smaller for 147Sm, 82Kr and 99Tc. These results bring interesting informations in the Oklo phenomenon interpretation. In particular neutron fluence values are confirmed, dating nuclear reactions with the fission neodymium. They give more accurately the ratios water/uranium at the time of nuclear reactions by measurement of spectrum indexes. They explain also the variation, found out before, between reaction duration calculated from plutonium taking part in fissions and the one deduced from the pair 99Tc-99Ru.

1977-12-21

77

Thermal history and redox conditions in the Oklo reactor zones (Gabon); Histoire thermique et conditions redox des zones de reactions d`Oklo, Gabon  

Energy Technology Data Exchange (ETDEWEB)

In the uranium ore deposit of Oklo-Okelobondo (Gabon), the mineralization contains U-enriched zones, that have fissioned spontaneously 1.97 Ga ago. In the Okelobondo, the salinity of the diagenetic fluid is below 3 wt % NaCl for a minimal temperature ranging from 120 deg to 200 deg C. At Lastoursville, presence of a H{sub 2}O-NaCl-CH{sub 4} + CO{sub 2} immiscibility case indicate a temperature of 160-190 deg and a pressure of 1.0 + 0.2 kbar. In zone 10 core, sulphides (galena, pyrite,...), native Pb and organic matter (OM) indicate a reduced environment. At the border, minium and hematite indicate very oxidized conditions. H{sub 2}O-H{sub 2}-O{sub 2} fluid inclusions are related to water radiolysis. The conclusion is that, OM trap O{sub 2} produced by radiolysis leading to a very reduced environment. In the absence of OM, the environment becomes very oxidized. These specific conditions have lead to a stability of uraninite and fission products in the reactors but local heterogeneities are to be considered. Fluid inclusions reveal that temperatures have reached 400 deg C at the reactor border, but decreased sharply along a few meters. Fluid salinity increased drastically (< 5 % in quartz; apatite: 13-24 %; calcite: > 23 %), whereas temperature was decreasing. Salt enrichment is attributed to interactions between fluids and decays. The dolerite impact in the Oklo carrier has also been investigated. (author).

Savary, V.

1995-10-27

78

Geochemistry of neo-formed minerals at Oklo (Gabon), geologic history of the Oklo basin: a contribution for the studies of geologic disposals of radioactive wastes  

International Nuclear Information System (INIS)

[en] Oklo uranium ore deposit (Francevillian basin, Gabon) is the unique place in the world where 2000 Ma old fossil nuclear reactors were described. The geological and thermal history of this basin, since 2000 Ma was retraced. Tholeiitic intrusion was 755 ± 83 Ma with Sm-Nd isochron on whole rock and plagioclase and 746 ± 16 Ma old with U-Pb dating on zircons. This event was linked to a pre-Pan-African rifting stage. A green schist facies metamorphism was detected on the granitic rocks of the substratum and seemed to affect the tholeiitic intrusion. Apatite fission tracks dating performed on granitic basement revealed a thermal event between Permian and middle-Jurassic time, linked to the Atlantic ocean opening. Fission track ages distribution suggest a brittle tectonics (T

79

Hydrogeology of the Oklo-Okelobondo site  

International Nuclear Information System (INIS)

[en] This study gives an account of all the hydrogeological data from the Oklo-Okelobondo site obtained so far. This hydrogeological overview has led to the proposal of a hydrodynamic flow pattern for the system and the choice of a study area as a basis for a preliminary modelling of groundwater flow and solute transport in the far field. (author). 5 refs., 4 figs

1993-01-01

80

Fluid phases contemporaneous with sandstone diagenesis, tectonic movements and functioning of the Oklo nuclear reactors (Gabon)  

International Nuclear Information System (INIS)

[en] A joint study of the fluid inclusions and petrography of the sandstones in the FA at Oklo enables us to estimate the temperature and pressure conditions for the various diageneses. It also enables us to fix the time of the formation and functioning of the natural reactors, in relation to the geological events. The conditions for the siliceous diagenesis, just as for the formation of the Oklo tectonic structure at the beginning, are estimated at approximately 2400C and 1000 bar. The carbonate diagenesis, which comes after the functioning of the natural reactors, would appear to have occurred at about 1800C and 800 bar. The density of the fluids and pressure stresses (between 1000 and 800 bar) suggests that, during the nuclear reaction, the aqueous solutions may have reached temperatures between 450 and at least 6000C. (author)

1977-12-21

 
 
 
 
81

Dating by fission track method: study of neutron dosimetry with natural uranium thin films  

International Nuclear Information System (INIS)

[en] Fission track dating is described, focalizing the problem of the decay constant for spontaneous fission of 238 U and the use of neutron dosimetry in fission track analysis. Experimental procedures using thin films of natural uranium as neutron dosimeters and its results are presented. The author shows a intercomparison between different thin films and between the dosimetry with thin film and other dosimetries. (M.V.M.). 52 refs, 12 figs, 9 tabs

1990-01-01

82

Uranium deposits of Gabon and Oklo reactors. Metallogenic model for rich deposits of the lower proterozoic  

International Nuclear Information System (INIS)

The geology of the Franceville basin (Gabon) is examined: stratigraphy, tectonics and geodynamics. The mobile zone of the Ogooue is specially studied: lithology, metamorphism and tectonics, isotopic geochronologic data are given. The different uranium deposits are described. A whole chapter is devoted to the study of Oklo natural nuclear reactor. A metallogenic model is proposed evidencing conditions required for deposit genesis. Tectonics, microstructures sedimentology, organic matter, diagenesis and uraniferous mineralizations are examined

1986-01-01

83

Thermal history and redox conditions in the Oklo reactor zones (Gabon)  

International Nuclear Information System (INIS)

[en] In the uranium ore deposit of Oklo-Okelobondo (Gabon), the mineralization contains U-enriched zones, that have fissioned spontaneously 1.97 Ga ago. In the Okelobondo, the salinity of the diagenetic fluid is below 3 wt % NaCl for a minimal temperature ranging from 120 deg to 200 deg C. At Lastoursville, presence of a H2O-NaCl-CH4 + CO2 immiscibility case indicate a temperature of 160-190 deg and a pressure of 1.0 + 0.2 kbar. In zone 10 core, sulphides (galena, pyrite,...), native Pb and organic matter (OM) indicate a reduced environment. At the border, minium and hematite indicate very oxidized conditions. H2O-H2-O2 fluid inclusions are related to water radiolysis. The conclusion is that, OM trap O2 produced by radiolysis leading to a very reduced environment. In the absence of OM, the environment becomes very oxidized. These specific conditions have lead to a stability of uraninite and fission products in the reactors but local heterogeneities are to be considered. Fluid inclusions reveal that temperatures have reached 400 deg C at the reactor border, but decreased sharply along a few meters. Fluid salinity increased drastically ( 23 %), whereas temperature was decreasing. Salt enrichment is attributed to interactions between fluids and decays. The dolerite impact in the Oklo carrier has also been investigated. (author)

1995-01-01

84

Fission product studies in the symmetric mass region  

Energy Technology Data Exchange (ETDEWEB)

Fission yields can be determined by radiochemical or mass spectrometric techniques. Mass spectrometry can provide more accurate data, particularly in the symmetric mass region where the probability of fission is low and uncertainties in isometric ratios occur. Fine structure in the mass distribution can usually only be determined by mass spectrometry. Many of the elements in the valley of symmetry have high ionization potentials and are therefore difficult to measure by solid source mass spectrometry. Analytical techniques have been developed to provide the sensitivity required to measure the small sample sizes available in fission product studies. Cumulative fission yields for ruthenium, palladium, cadmium, tin, and tellurium have been measured by mass spectrometry for the thermal and epicadmium fission of {sup 233}U and for thermal and epicadmium fission of {sup 239}Pu. These fission yields, which span the mass range 101 {le} A {le} 130, can be combined to give a mass yield curve for {sup 235}U in the valley region, which is symmetrical about A = 116.8 and exhibits fine structure in the mass 113 to 114 region. Fine structure in {sup 233}U is also present at mass 111. Mass spectrometric determinations of the fission yields of uranium ore at the Oklo mine site in Gabon enable the nuclear parameters of this natural reactor to be evaluated. This in turn enables the amounts of fission products produced in the reactor zone and the surrounding rocks enables an assessment to be made of the efficiency of this geological repository for containing radioactive waste. The elemental abundances can be determined by isotope dilution mass spectrometry. Unfortunately, the paucity of good fission yield data available for {sup 238}U by fast neutrons is a severe constraint in this evaluation.

De Laeter, J.R.; Rosman, K.J.R.; Loss, R.D. [Curtin Univ. of Technology, Perth (AU)

1993-05-01

85

Oklo/obsidian/ancient glasses: applications to nuclear waste public information programs  

International Nuclear Information System (INIS)

[en] Natural analogs such as the Oklo natural nuclear reactor and archaeological data from ancient, man-made glasses can be helpful in making a more interesting presentation on nuclear waste disposal. The extent to which natural analogs and archaeological data can also be used as benchmarks for our current understanding of processes over long periods of time is sometimes overlooked. The potential pitfalls of using natural analogs and archaeological evidence in a presentation in nuclear waste disposal, as well as the benefits, must be carefully considered

1983-03-03

86

A study of radon retention and fission track annealing with temperature in natural apatite  

International Nuclear Information System (INIS)

[en] The release and the retention of radon-222, from sedimentary phosphate in which it is formed, are carried out. The heat treatment may be regarded as having two effects: an immediate effect (radon release) and a long term effect (retention of radon). In order to understand this behavior of radon to elevated temperatures, some analysis is carried out. One of them is the analysis of radiation damage (fission tracks) in natural apatite grains (Apatite Fission Track Analysis). Those tracks are produced continuously through geological time, as a result of spontaneous fission of 238U atoms and can be annealed at a rate that depends on temperature. In this work, we have examined this effect. The result is that in a single sample, the fission track density in individual apatite grains decreases with the increasing of the temperature. We study the hypothesis of the control of radon emanation by the fission track annealing process.

2001-01-01

87

Production of fission molybdenum by using irradiated natural uranium targets  

International Nuclear Information System (INIS)

In this paper a procedure is described for the production of fission molybdenum. The production method is particularly suitable for those, which do not dispose on highly enriched uranium. The aim was to realize a simple technology. Starting from irradiated uranium oxide the following steps are included: dissolution of the target in 6 M nitric acid, separation of 99Mo from uranium and the bulk of other fission products by adsorption/desorption on alumina and purification of the molybdenum fraction by thermochromatography. The waste treatment is described too. The final product 99Mo is well suited for manufacturing high quality 99Mo/99mTc generators. (author)

1988-01-01

88

Nuclide analyses of rare earth elements of the Oklo uranium ore samples: A new method to estimate the neutron fluence  

International Nuclear Information System (INIS)

[en] Isotopic ratios and abundances of all REE in two Oklo ore samples have been measured. We have succeeded in developing a new method to estimate the neutron fluence, the conversion factor of uranium and the average neutron energy (or temperature) based on Gd and U isotopic ratios. This new calculation is found to be useful in evaluating those parameters for the natural nuclear reactors at Oklo. Comparison is made between the neutron fluence values evaluated by our new method employing Gd isotopes and a previous one employing Sm and Nd isotopes. The relative agreement becomes better with the increase of fluence. A relationship between the abundances of fissiongenic nuclides of La, Ce, Nd, Sm, and Gd and their mass numbers is also presented. (orig.)

1988-01-01

89

Excitation function of 4He-ion-induced fission of Dy (natural)  

International Nuclear Information System (INIS)

As part of a long-range programme of work on the measurement of fission excitation functions of low Z (Z 4He-ions in the energy range 35-50 MeV were measured using the sensitive ''fission track'' technique using lexan polycarbonate plastic as detectors. Targets of (spec. pure grade) high purity Dy2O3, further purified by a series of anion exchange technique, deposited on high purity (99.9999%) silver foils were irradiated with 4He-ions of different energies from the Variable Energy Cyclotron at Calcutta. The heavy elements contents of both the dysprosium oxide and the silver foils were estimated to be not more than 1-3 ppb. The experimental 4He-ion-induced fission cross sections of natural Dysprosium (162.5Dy) are presented. 7 refs, 1 tab.

1995-01-01

90

Dependence of fragment angular momentum on nature of fissioning nuclei (Preprint No. NR-5)  

International Nuclear Information System (INIS)

In order to investigate the effects of fragment nuclear structure and the nature of fissioning nuclei on scission configuration, independent isomeric yield ratios of 132I have been determined radiochemically in 235U (nsub(th),f) and 252Cf (S.F.). The fragment angular momenta (B) for 132I have been deduced from independent isomeric yield ratios using spin dependent statistical model analysis. It is observed that B-value for 132I is higher than 134I (determined earlier from this laboratory) in both the fissioning nuclei. This is due to the proximity of the spherical 82n shell in the fragment for the fission product 134I. B-value for both 132I and 134I are seen to be higher in 252Cf (S.F.) than in 235U (nsub(th),f). This may be d ue to different nature of fissioning nuclei from the point of view of excitation energy and/or dynamics (i.e. descent from saddle to scission) because of which fragment deformation (at scission) and thus angular momentum are different. (author). 6 refs

1988-01-01

91

The discovery of the Oklo reactors; La decouverte des reacteurs d'Oklo  

Energy Technology Data Exchange (ETDEWEB)

Among the most important knowledge brought by the recent studies on Oklo phenomenon, we can give: models and data that could be used to quantify the interactions between uranium and lanthanides with an clayey material; information on the confinement of radioactive elements in the compounds such manganese and iron oxides, the clays, the phosphates; understanding of oxido-reduction phenomena in a clayey environment for very different burying conditions ( from the surface to 400 meters deep). These knowledge could be used for future storage sites if vitrified waste would be buried at several hundred meters deep and surrounded by clayey barriers in the aim to delay the water brought to waste contact and to confine the elements that could get out glasses including radioactive waste. (N.C.)

Dozol, J.F. [CEA Cadarache, 13 - Saint Paul lez Durance (France)

2005-07-01

92

Migration paths for Oklo reactor products and applications to the problem of geological storage of nuclear wastes  

International Nuclear Information System (INIS)

Escape of the products from the Oklo reactor proceeds, first, by escape from the uraninite (UO2) grains and, second, by transport out of the gangue. Escape from the grain by fission recoil accounts for prompt deposition in the gangue of 5-10% of the products. Escape by volume diffusion is very slow. The rate of loss by diffusion was highest during the operating period of the reactor and may have been of the order of 10-6 fraction/a for the most volatile elements. The least volatile elements have been retained in the grains. Their diffusion rates are less than 5x10-10/a. If similar loss rates can be achieved in synthetic uraninite (or thorianite), the overall rate of transport of most reactor products would be sufficiently limited by diffusion to ensure that essentially all the radioactive species would decay in situ. The principal geochemical requirements for a suitable storage site are those that ensure the survival of the UO2 matrix, particularly that the pH and Eh are similar to the values at Oklo. (author)

1977-12-21

93

Migration of U-series radionuclides around the Bangombe natural fission reactor (Gabon)  

International Nuclear Information System (INIS)

The Bangombe natural fission reactors has undergone extensive weathering phenomena and continues to be affected by the penetration of meteoric waters. Hence this system provides a model for studying the stability of spent fuel uraninite and the influence of various rock matrices on the mobilization/retardation of various actinides and fission products. The Bangombe uranium deposit has been investigated by drilling on a grid. Radiochemical analysis by alpha- and gamma-spectroscopy of the obtained rocks show significant disequilibria of the 234U/238U, 230Th/234U, and 226Ra/230Th parent-daughter pairs. In this paper, a conceptual model for spatio/temporal evolution of the Bangombe system is proposed. (J.P.N.)

1999-01-01

94

Time-variability of the coupling constants of fundamental particles and Oklo phenomena  

Energy Technology Data Exchange (ETDEWEB)

About 60 years ago, Dirac, P.A.M. presented that gravitational constant was not a constant but varied with a time in universe. As it has not obtained any determining proof experimentally, a fundamental concept on physical constants was disturbed since then, which has been succeeded to trials on the present integral theory. In special, some interesting researches on what is called coupling constants of fundamental particles, such as if fundamental charge of an electron changes actually, are continued. As proof on this change was not established, the observing and experimental upper values contain some important suggestions. The most serious result as its upper limit was obtained as well by an investigation on a surprising fact (a natural reactor) that uranium naturally reached a criticality at a place (Oklo) on the earth two billion years ago. Here were introduced on some their recent researches. (G.K.)

Fujii, Yasunori [Nihon Fukushi Univ., Handa, Aichi (Japan); Iwamoto, Akira; Hidaka, Hiroshi

2000-09-01

95

Synthesis of the mineralogic and petrographic studies of the ore minerals from Oklo, their gangues and the surrounding rocks  

International Nuclear Information System (INIS)

Observations on the spot and mineralogical studies (reflection and transmission microscopy, x-ray examination, thermal analyses) have shown that the ore in the reaction zones differs from ''normal'' Oklo ore as regards both the nature of the mineralization and the gangue and the country rock. The relationship between the two ore types on one and between them and the country rock on the other is studied. Theories concerning the creation of the uraniferous deposit and the effects of subsequent changes due to diagenesis and recent weathering are discussed

1975-06-27

96

Very-long-term storage of fission products  

International Nuclear Information System (INIS)

[en] The large majority of the fission products, with 99.9 percent of the radioactivity content, do not pose actual problems in storage in a geological formation for which we can guarantee total confinement. Safety of storage in a geological formation for the radionuclides of long half-life is based in particular on the absorption capacity of the geological formations and the example of the Oklo fossil reactor and the retention of Pu which is produced is a striking example. But the problems are not the same, and the properties that we look for in the terrain are not the same. We could thus be led to storage in different geological formations for the fission products and the long-half-life emitters. Their separation is interesting from this point of view, but the date at which the separation is made will not be necessarily that of reprocessing. But there is a question of one or the other, and these storages will offer a very high level of insurance and will present only the potential hazards that are very comparable with those presented by natural conditions

97

Immobilization of fission iodine by reaction with insoluble natural organic matter  

International Nuclear Information System (INIS)

Iodine-129 is a fission product and highly mobile in the environment. Along with other stable isotopes of iodine, 129I is released during reprocessing of nuclear fuel and must be trapped to prevent the release of radioactivity to the environment. Past studies have provided evidence that iodine can become associated with natural organic matter (NOM). This research explores the use of NOM (sphagnum peat and humic acid) to sequester iodine from the vapor and aqueous phases. NOM-associated iodine may be stable for geological storage. NOM-sequestered iodine can be recovered by pyrolysis to prepare target materials for transmutation. The nature of the NOM-iodine association has been explored. (author)

2008-01-01

98

Mechanisms of lead release from uraninite in the natural fission reactors in Gabon  

Energy Technology Data Exchange (ETDEWEB)

Twenty-four samples of uranium ore from the natural fission reactors in Gabon were studied by detailed electron microprobe analysis and backscattered electron imaging in order to determine the behavior of radiogenic Pb and fissiongenic nuclides. Lead content in uraninite varies from 19 wt% PbO in relicts of pristine uraninite, which were found only in reactor zone 10, to less than 5 wt% in altered uraninites. Different mechanisms of Pb loss from uraninite prevailed in different reactor zones and included leaching, grain boundary diffusion, exsolution via continuous precipitation, and volume diffusion. As a result of these processes, Pb content in uraninites from all the reactor zones, except for reactor zone 10, are similar and vary around a mean value of 5.2 wt% PbO. All of these processes were thermally activated and episodic. The predominance of any single mechanism in a particular reactor zone was controlled by the accessibility of solutions to the uranium ore. The thermal event which caused Pb mobilization in the deposits resulted from regional igneous activity in the Franceville Basin more than 1100 Ma after the reactors sustained spontaneous fission reactions. Reducing conditions prevented the long distance migration of Pb, as well as of fissiongenic Mo and Ru.

Janeczek, J. [Silesian Univ., Sosnowiec (Poland); Ewing, R.C. [Univ. of New Mexico, Albuquerque, NM (United States)

1995-05-01

99

3.4. About origin of fission splinters tracks in natural and lead glass  

International Nuclear Information System (INIS)

Glass track detectors like crystals have ability to register and keep during many years tracks splinters of spontaneous nucleus fission of 238U. This circumstance let carry out the measuring of track's age of various glasses, tektites by measuring of tracks density from splinters of spontaneous fission of 238U and from fission of 235U by thermal neutrons

2007-01-01

100

Anomalies of isotopic composition of Xe and Kr from Oklo deposit, Gabon, Africa  

International Nuclear Information System (INIS)

[en] Isotopic content of Xe and Kr from mineral fractions of the sample N1348, taken from the SC20 Hole (ore zone N2) of Oklo deposit, was investigated using the method of thermal annealing. A method of sample separation into mineral components is described. The tables of Xe and Kr isotopic content, the diagrams of Xe isotopic correlations, and also Xe and Kr isotopic variations at stepped annealing of fraction mineral components are presented. It was found that Xe isotopic content in the fractions, rich with uraninite is close to Xe isotopic content, formed under artificial conditions at irradiation of 235U by thermal neutrons. The Xe isotopic content in the uranium free fractions is sharply anomalous. 134Xe/136Xe, 132Xe/136Xe, 131Xe/136Xe, 129Xe/136Xe ratios amount to 1.59; 3.46; 1.20, 0.358 respectively. Linear correlations between isotopic ratios are interpreted as a result of mixing up 2 main mineral phases: the one containing normal Xe from 235U fission and the second one containing anomalous Xe with isotopic ratio 136:134:132:131:129=1.00:1.65:3.50:1.48:0.41 Anomalous Xe is also present in uraninite. It was found that sharp maximum of the extraction rate from minerals at 800 deg C, recurring in all fractions, but uraninite, is characteristic of thXe extraction kinetics. The Xe carrier is a mineral with the density of 3-4 g/cm/3. The maximum 136Xesub(a) content equals 1.9x10-6 cm3/g, its quantity being in some fractions several times higher than that of the normal fission Xe

1977-01-01

 
 
 
 
101

Problems posed by the development of the Oklo phenomenon: tentative global interpretation  

International Nuclear Information System (INIS)

This paper discusses the basic problems posed by the development of the Oklo phenomenon: the conditions in which the reactions are triggered and propagated and how they have been controlled. The reactions were maintained by the destruction of neutron poisons in the ore and were controlled by temperature. Oklo is made up of a large number of contiguous reactors. Geological problems of the origin of the clays, desilification, and uranium concentration are discussed. Oklo is shown to be a very complex phenomenon which developed in space and time. Besides the thermal, neutron, and geochemical coupling, there is also a tectonic coupling.

1977-12-21

102

A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium  

International Nuclear Information System (INIS)

This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more proliferation-resistant than that bred by conventional fast reactors. Furthermore, it can maintain constant total hybrid power output as burnup proceeds by varying the neutron source strength.

2012-06-19

103

A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium  

Science.gov (United States)

This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more proliferation-resistant than that bred by conventional fast reactors. Furthermore, it can maintain constant total hybrid power output as burnup proceeds by varying the neutron source strength.

Reed, Mark; Parker, Ronald R.; Forget, Benoit

2012-06-01

104

Naturally etched tracks in apatites and the correction of fission track dating  

CERN Document Server

Naturally etched tracks have been found in apatites from the rapid cooled, high-level Kunon pluton in the Zhangzhou Igneous Complex, SE China. This is manifested by the fact that the apatite fission track (FT) age derived from conventional counting of spontaneous and induced tracks yields a result of 140.6+-6.5 Ma, which is much older than the ages determined using other methods on different minerals from the same rock. When tracks are observed after etching the polished inner sections of the apatite grains, the naturally etched tracks characterized by having hazy boundaries can be distinguished from the normal tracks with sharp boundaries. The age obtained by omitting these fading-resistant hazy tracks, 76.5+-4.0 Ma, indicates the time of the Kunon pluton cooling down to approx 100 deg. C. The corrected peak age (73.8 Ma) is consistent with the other apatite FT peak ages (79.2 to 70.2 Ma) of the nearly contemporaneous plutons in the same igneous complex.

Tien, J L

1999-01-01

105

Naturally etched tracks in apatites and the correction of fission track dating  

International Nuclear Information System (INIS)

[en] Naturally etched tracks have been found in apatites from the rapid cooled, high-level Kunon pluton in the Zhangzhou Igneous Complex, SE China. This is manifested by the fact that the apatite fission track (FT) age derived from conventional counting of spontaneous and induced tracks yields a result of 140.6±6.5 Ma, which is much older than the ages determined using other methods on different minerals from the same rock. When tracks are observed after etching the polished inner sections of the apatite grains, the naturally etched tracks characterized by having hazy boundaries can be distinguished from the normal tracks with sharp boundaries. The age obtained by omitting these fading-resistant hazy tracks, 76.5±4.0 Ma, indicates the time of the Kunon pluton cooling down to ?100 deg. C. The corrected peak age (73.8 Ma) is consistent with the other apatite FT peak ages (79.2 to 70.2 Ma) of the nearly contemporaneous plutons in the same igneous complex

1999-01-01

106

Immobilisation of fission iodine by reaction with insoluble natural organic matter  

International Nuclear Information System (INIS)

Commercial nuclear power plants produce Iodine-129 (129I) as a fission by-product. Iodine-129, along with other stable isotopes of iodine, is released during the reprocessing of nuclear fuel. Silver-impregnated activated carbon, activated carbon, cinnabar and chalcocite have been used in the past to remove iodide and iodine from waste streams. There is environmental and geological evidence that iodine can become associated with natural organic matter (NOM). For example, a number of previous studies have shown that iodine (including 129I) can be strongly retained in organic-rich surface soils and humic material. This research explores the use of NOM (sphagnum peat) to sequester iodine from acid vapour and aqueous solution. NOM may be stable for geological storage or the sequestered iodine can be recovered to prepare target materials for transmutation. The nature of the sphagnum iodine association has been explored as well as method that can be used to concentrate and recover sequestered iodine from the peat moss. (authors)

2005-01-01

107

On the oxidation of uraninite from natural reactor cores  

Energy Technology Data Exchange (ETDEWEB)

Natural nuclear reactors provide unique evidence in helping to understand the processes that might occur over long timescales in radioactive waste disposal sites. In the presented work, the extent and kinetics of oxidation of core material from the Oklo-Bangombe natural reactors are investigated. The X-ray powder diffraction analysis shows that the uraninites core samples from the Bangombe Reactor and Oklo Reactor 2, and Oklo Reactor 13 have the same unit-cell parameters as synthetic UO{sub 2.25}. A significant amount of fourmarierite, Pb(UO{sub 2}){sub 4}O{sub 3}(OH){sub 4}.4H{sub 2}O, was identified in the core samples from two shallow reactors Bangombe and Oklo 2, but not in the deeper reactor Oklo 13. The results of U(IV)/U(IV) measurements indicate that the extent of oxidative weathering of shallow reactors (Bangombe and Oklo 2) is greater than for the deeper reactor Oklo 13. Evaporable organic compounds found in the uraninite inclusion containing bitumen at the edge of Okelobondo Reactor (400 C) and in the black shale immediately above the Bangombe Reactor (260 C) may work as a reducing buffer or/and a hydrophobic water shield to depress the oxidative dissolution of the uraninite cores.

Cui, D.; Eriksen, T.; Eklund, U.B.

1999-07-01

108

High-energy Neutron-induced Fission Cross Sections of Natural Lead and Bismuth-209  

CERN Document Server

The CERN Neutron Time-Of-Flight (n\\_TOF) facility is well suited to measure small neutron-induced fission cross sections, as those of subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors. The fragment coincidence method allows to unambiguously identify the fission events. The present experiment provides the first results for neutron-induced fission up to 1 GeV for (nat)Pb and (209)Bi. A good agreement with previous experimental data below 200 MeV is shown. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross section is close to 1 GeV.

Tarrio, D; Carrapico, C; Eleftheriadis, C; Leeb, H; Calvino, F; Herrera-Martinez, A; Savvidis, I; Vlachoudis, V; Haas, B; Koehler, P; Vannini, G; Oshima, M; Le Naour, C; Gramegna, F; Wiescher, M; Pigni, M T; Audouin, L; Mengoni, A; Quesada, J; Becvar, F; Plag, R; Cennini, P; Mosconi, M; Rauscher, T; Couture, A; Capote, R; Sarchiapone, L; Vlastou, R; Domingo-Pardo, C; Dillmann, I; Pavlopoulos, P; Karamanis, D; Krticka, M; Jericha, E; Ferrari, A; Martinez, T; Trubert, D; Oberhummer, H; Karadimos, D; Plompen, A; Isaev, S; Terlizzi, R; Cortes, G; Cox, J; Cano-Ott, D; Pretel, C; Colonna, N; Berthoumieux, E; Vaz, P; Heil, M; Lopes, I; Lampoudis, C; Walter, S; Calviani, M; Gonzalez-Romero, E; Embid-Segura, M; Stephan, C; Igashira, M; Papachristodoulou, C; Aerts, G; Tavora, L; Berthier, B; Rudolf, G; Andrzejewski, J; Villamarin, D; Ferreira-Marques, R; Tain, J L; O'Brien, S; Reifarth, R; Kadi, Y; Neves, F; Poch, A; Kerveno, M; Rubbia, C; Lazano, M; Dahlfors, M; Wisshak, K; Salgado, J; Dridi, W; Ventura, A; Andriamonje, S; Assimakopoulos, P; Santos, C; Voss, F; Ferrant, L; Patronis, N; Chiaveri, E; Guerrero, C; Perrot, L; Vicente, M C; Lindote, A; Praena, J; Baumann, P; Kappeler, F; Rullhusen, P; Furman, W; David, S; Marrone, S; Tassan-Got, L; Gunsig, F; Alvarez-Velarde, F; Massimi, C; Mastinu, P; Pancin, J; Papadopoulos, C; Tagliente, G; Haight, R; Chepel, V; Kossionides, E; Badurek, G; Marganiec, J; Lukic, S; Pavlik, A; Goncalves, I; Duran, I; Alvarez, H; Abbondanno, U; Fujii, K; Milazzo, P M; Moreau, C

2011-01-01

109

Secondary gamma ray production in iron and natural thorium from californium fission spectrum neutrons  

International Nuclear Information System (INIS)

[en] Measurement of the secondary gamma ray spectra from the interaction of a 252Cf fission neutron spectrum with Fe samples of different thicknesses and a 232Th sample have been performed at the Tower Shielding Facility at ORNL. A 5-in. by 5-in.-diam NaI (Tl) scintillation spectrometer was used. The measured or .846 MeV gamma ray from neutron inelastic scattering in Fe was compared with calculations using the differential values of cross sections as a function of incident neutron energy. This is an integral check for those differential cross sections. Thorium, as far as we know, had not been investigated before for this fast neutron energy range. Even though a peak at .184 MeV was found it was felt that the resulting large cross section value obtained made it highly improbable that the gamma ray came from a fast neutron interaction. Search for other possible neutron induced gamma rays was very difficult due to the high intensity of naturally radioactive gamma rays from thorium itself

1977-01-01

110

Dating by fission track method: study of neutron dosimetry with natural uranium thin films; Datacao com o metodo dos tracos de fissao: estudo da dosimetria de neutrons com filmes finos de uranio natural  

Energy Technology Data Exchange (ETDEWEB)

Fission track dating is described, focalizing the problem of the decay constant for spontaneous fission of {sup 238} U and the use of neutron dosimetry in fission track analysis. Experimental procedures using thin films of natural uranium as neutron dosimeters and its results are presented. The author shows a intercomparison between different thin films and between the dosimetry with thin film and other dosimetries. (M.V.M.). 52 refs, 12 figs, 9 tabs.

Iunes, P.J.

1990-06-01

111

Enhanced effect of quark mass variation in 229Th and limits from Oklo data  

CERN Multimedia

The effects of the variation of the dimensionless strong interaction parameter Xq=mq/Lambda{QCD} (mq is the quark mass, Lambda{QCD} is the QCD scale) are enhanced about 1.5 x 10**5 times in the 7.6 eV "nuclear clock" transition between the ground and first excited states in the 229Th nucleus and about 1 x 10**8 times in the relative shift of the 0.1 eV compound resonance in 150Sm.The best terrestrial limit on the temporal variation of the fundamental constants, |delta(Xq)/Xq| < 4 x 10**-9 at 1.8 billion years ago (|d(Xq/Xq)/dt| < 2.2 x 10**-18 y**-1), is obtained from the shift of this Sm resonance derived from the Oklo natural nuclear reactor data. The results for 229Th and 150Sm are obtained by extrapolation from light nuclei where the many-body calculations can be performed more accurately. The errors produced by such extrapolation may be smaller than the errors of direct calculations in heavy nuclei. The extrapolation results are compared with the "direct" estimates obtained using the Walecka model....

Flambaum, V V

2008-01-01

112

Reactor AQUILON. The hardening of neutron spectrum in natural uranium rods, with a computation of epithermal fissions (1961)  

International Nuclear Information System (INIS)

[en] - Microscopic flux measurements in reactor Aquilon have allowed to investigate the thermal and epithermal flux distribution in natural uranium rods, then to obtain the neutron spectrum variations in uranium, Wescott '?' term of the average spectrum in the rod, and the ratio of epithermal to therma fissions. A new definition for the infinite multiplication factor is proposed in annex, which takes into account epithermal parameters. (authors)[fr] - Un certain nombre de mesures effectuees dans la pile Aquilon ont permis d'etablir la distribution fine des flux thermique et epithermique dans les barreaux d'uranium, et d'en deduire les variations du spectre des neutrons dans l'uranium, le terme ? du spectre de Wescott moyen dans le barreau et le nombre de fissions epithermiques. En annexe, il est propose une definition nouvelle du coefficient de multiplication infini, qui fait intervenir les parametres epithermiques. (auteurs)

1961-01-01

113

Calculation and measurement the fission products and their distribution in natural ceramic UO2 nuclear fuel  

International Nuclear Information System (INIS)

In order to improve the fuel fabrication processes and develop them further, the determination of the fission products both qualitatively and quantitatively, as well as their distribution over the entire length of the fuel pin swelling especially at the regions where some gaseous fission products are accumulated. This study is concentrating at the post-irradiation evaluation of the ceramic UO2 nuclear fuel, by utilizing the existing facilities and equipment at the hot laboratories. Cs-137 was chosen as a precursor for the burn-up level of the irradiated fuel because of the case with which its gamma radiation is measured and due to its relatively long half-life. 19 figs.; 13 tabs.; 42 refs.; 9 apps

1990-01-01

114

Enhanced effect of quark mass variation in 229Th and limits from Oklo data  

International Nuclear Information System (INIS)

The effects of the variation of the dimensionless strong interaction parameter Xq=mq/?QCD (mq is the quark mass, ?QCD is the QCD scale) are enhanced about 1.5x105 times in the 7.6 eV ''nuclear clock'' transition between the ground and first excited states in the 229Th nucleus and about 1x108 times in the relative shift of the 0.1 eV compound resonance in 150Sm. The best terrestrial limit on the temporal variation of the fundamental constants, |?Xq/Xq|-9 at 1.8 billion years ago (|X?q/Xq|-18y-1), is obtained from the shift of this Sm resonance derived from the Oklo natural nuclear reactor data. The results for 229Th and 150Sm are obtained by extrapolation from light nuclei where the many-body calculations can be performed more accurately. The errors produced by such extrapolation may be smaller than the errors of direct calculations in heavy nuclei. The extrapolation results are compared with the ''direct'' estimates obtained using the Walecka model. A number of numerical relations needed for the calculations of the variation effects in nuclear physics and atomic spectroscopy have been obtained: for the nuclear binding energy ?E/E?-1.45 ?mq/mq, for the spin-orbit intervals ?Eso/Eso?-0.22 ?mq/mq, for the nuclear radius ?r/r?0.3 ?mq/mq (in units of ?QCD); for the shifts of nuclear resonances and weakly bound energy levels ?Er?10 ?Xq/Xq MeV.

2009-01-01

115

Split-Doa10: a naturally split polytopic eukaryotic membrane protein generated by fission of a nuclear gene.  

Science.gov (United States)

Large polytopic membrane proteins often derive from duplication and fusion of genes for smaller proteins. The reverse process, splitting of a membrane protein by gene fission, is rare and has been studied mainly with artificially split proteins. Fragments of a split membrane protein may associate and reconstitute the function of the larger protein. Most examples of naturally split membrane proteins are from bacteria or eukaryotic organelles, and their exact history is usually poorly understood. Here, we describe a nuclear-encoded split membrane protein, split-Doa10, in the yeast Kluyveromyces lactis. In most species, Doa10 is encoded as a single polypeptide with 12-16 transmembrane helices (TMs), but split-KlDoa10 is encoded as two fragments, with the split occurring between TM2 and TM3. The two fragments assemble into an active ubiquitin-protein ligase. The K. lactis DOA10 locus has two ORFs separated by a 508-bp intervening sequence (IVS). A promoter within the IVS drives expression of the C-terminal KlDoa10 fragment. At least four additional Kluyveromyces species contain an IVS in the DOA10 locus, in contrast to even closely related genera, allowing dating of the fission event to the base of the genus. The upstream Kluyveromyces Doa10 fragment with its N-terminal RING-CH and two TMs resembles many metazoan MARCH (Membrane-Associated RING-CH) and related viral RING-CH proteins, suggesting that gene splitting may have contributed to MARCH enzyme diversification. Split-Doa10 is the first unequivocal case of a split membrane protein where fission occurred in a nuclear-encoded gene. Such a split may allow divergent functions for the individual protein segments. PMID:23071509

Stuerner, Elisabeth; Kuraku, Shigehiro; Hochstrasser, Mark; Kreft, Stefan G

2012-10-04

116

Split-Doa10: a naturally split polytopic eukaryotic membrane protein generated by fission of a nuclear gene.  

UK PubMed Central (United Kingdom)

Large polytopic membrane proteins often derive from duplication and fusion of genes for smaller proteins. The reverse process, splitting of a membrane protein by gene fission, is rare and has been studied mainly with artificially split proteins. Fragments of a split membrane protein may associate and reconstitute the function of the larger protein. Most examples of naturally split membrane proteins are from bacteria or eukaryotic organelles, and their exact history is usually poorly understood. Here, we describe a nuclear-encoded split membrane protein, split-Doa10, in the yeast Kluyveromyces lactis. In most species, Doa10 is encoded as a single polypeptide with 12-16 transmembrane helices (TMs), but split-KlDoa10 is encoded as two fragments, with the split occurring between TM2 and TM3. The two fragments assemble into an active ubiquitin-protein ligase. The K. lactis DOA10 locus has two ORFs separated by a 508-bp intervening sequence (IVS). A promoter within the IVS drives expression of the C-terminal KlDoa10 fragment. At least four additional Kluyveromyces species contain an IVS in the DOA10 locus, in contrast to even closely related genera, allowing dating of the fission event to the base of the genus. The upstream Kluyveromyces Doa10 fragment with its N-terminal RING-CH and two TMs resembles many metazoan MARCH (Membrane-Associated RING-CH) and related viral RING-CH proteins, suggesting that gene splitting may have contributed to MARCH enzyme diversification. Split-Doa10 is the first unequivocal case of a split membrane protein where fission occurred in a nuclear-encoded gene. Such a split may allow divergent functions for the individual protein segments.

Stuerner E; Kuraku S; Hochstrasser M; Kreft SG

2012-01-01

117

Uraninite: A 2 Ga spent nuclear fuel from the natural fission reactor at Bangombe in Gabon, West Africa  

International Nuclear Information System (INIS)

[en] Uraninites from the Bangombe natural fission reactor (RZB) and normal uranium-ore occur as fine veins in the sandstone host-rock as well as altered, broken, and slightly displaced grains in an illitic matrix, and in nodules and veins of solid bitumen. Inclusions of galena, (Y,Gd)-rich phosphates, a Pb-oxide and a Ti-oxide? were observed. Uraninites just below RZB were partially altered to a uranyl-sulfate. Three generations of uraninite were identified based on their PbO-contents of 8--11.06 wt%, 6 wt% (the largest population), and a younger generation with 3 wt%. Diffusional loss of Pb is indicated by the presence of a Pb-oxide at the interface to the uraninites. The behavior of the metallic fission products, incompatible with the uraninite structure, may mimic the behavior of Pb in these uraninites. The averaged impurity-content ranges from 4.29 to 6.89 wt%, and consists mainly of SiO2, TiO2, ZrO2, FeO, CaO, Al2O3 and P2O5. The averaged content of Y2O3 and the Ln''s is less than 0.78 wt% and there is a scattered positive correlation with P2O5. The content of Y + Ln''s is generally highest in the uraninites from RZB. Uraninite hydration and the formation of uranopelite/zippeite have caused complete loss of Y and the Ln''s. The analytical results indicate that Y and the Ln''s, which are high yield fission products, may be released from uraninite during alteration in the presence of P

1997-01-01

118

Delayed fission  

Energy Technology Data Exchange (ETDEWEB)

Delayed fission is a nuclear decay process that couples {beta} decay and fission. In the delayed fission process, a parent nucleus undergoes {beta} decay and thereby populates excited states in the daughter. If these states are of energies comparable to or greater than the fission barrier of the daughter, then fission may compete with other decay modes of the excited states in the daughter. In this paper, mechanism and some experiments of the delayed fission will be discussed. (author)

Hatsukawa, Yuichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1997-07-01

119

Natural repository analogue program. Progress report, October 1-December 31, 1981  

Energy Technology Data Exchange (ETDEWEB)

The final draft of a paper entitled The Oklo Reactors: Natural Analogs to Nuclear Waste Repositories has been submitted for publication. This paper discusses the chemical stability of the fossil reactors with respect to uranium, neodymium, ruthenium, and technetium, the transport of elements in the geologic environment at Oklo; and the geochemical conditions that may have influenced these processes. Measurements of barium isotopic ratios limit the abundance of fissiogenic barium to <10/sup -7/ g/g and <2 x 10/sup -6/ g/g in two samples peripheral of Oklo reactor zone 9. Samples from the Oklo mines have been sent to Australia for cooperative studies on the geochemistry of palladium, silver, cadmium, tin, and tellurium. Four samples representing a traverse to the east of reactor zone 9 are being analyzed to determine the isotopic composition of molybdenum and ruthenium.

Curtis, D.B. (comp.)

1982-03-01

120

Fast fission phenomena  

International Nuclear Information System (INIS)

Experimental studies of fast fission phenomena are presented. The paper is divided into three parts. In the first part, problems associated with fast fission processes are examined in terms of interaction potentials and a dynamic model is presented in which highly elastic collisions, the formation of compound nuclei and fast fission appear naturally. In the second part, a description is given of the experimental methods employed, the observations made and the preliminary interpretation of measurements suggesting the occurence of fast fission processes. In the third part, our dynamic model is incorporated in a general theory of the dissipative processes studied. This theory enables fluctuations associated with collective variables to be calculated. It is applied to highly inelastic collisions, to fast fission and to the fission dynamics of compound nuclei (for which a schematic representation is given). It is with these calculations that the main results of the second part can be interpreted

1982-01-01

 
 
 
 
121

Petrographic analysis of samples from the uranium deposit at Oklo, Republic of Gabon  

International Nuclear Information System (INIS)

[en] This study is preliminary to detailed X-ray diffraction analysis and additional electron microprobe analyses. Twenty samples were examined; seven from reactor zone 9 (RZ-9), ten from RZ-10, two from RZ-13 and one from RZ-16. This suite of samples includes examples from reactor cores and their associated hydrothermal alteration haloes. The most striking characteristic of the Oklo samples is their heterogeneity. In particular, the samples vary with respect to texture, mineralogy, uranium mineral content, and evidence for deformation. Deformation features provide evidence for both shear and extensional stresses and include brecciation and a variety of mineralized fractures. Opaque phases include orgainc matter, uraninite, coffinite, and sulfides. In many cases, the opaque assemblage is concentrated along fractures. Considerable textural evidence, viz., embayed grain margins and fractures with nonparallel margins, suggests partial dissolution of uraninite in the Oklo ores. Uraninite with embayed margins is commonly accompanied by organic matter. Oklo uraninites are, in many cases, altered to produce coffinite (USiO4.nH2O) and are associated with varying quantities of galena at grain boundaries, within fractures, and within individual grains at intracrystalline locations. Textural evidence suggests multiple periods of uraninite formation. Electron microprobe data are presented for uraninites from RZ-13. Analytical data are discussed for Oklo reactor zones 2, 9, 10, 13, and 16 and for the reactor at Bangombe. Uraninites are compositionally similar with respect to Pb for RZ-2, RZ-9, RZ-13, RZ-16 and for the Bangombe reactor (average content of PbO is 5.92 weight %). Lead contents for uraninites from RZ-10 are generally higher and more variable than for the other reactor zones (e.g., PbO content for RZ-10 uraninites ranges from approximately 12 to 18 weight %). (orig.)

1994-01-01

122

Fission-track dating of South American natural glasses: an overview  

Energy Technology Data Exchange (ETDEWEB)

Although many glass-bearing horizons can be found in South American volcanic complexes or sedimentary series, only a relatively few tephra and obsidian-bearing volcanic fields have been studied using the fission-track (FT) dating method. Among them, the volcanics located in the Sierra de Guamani (east of Quito, Ecuador) were studied by several authors. Based upon their ages, obsidians group into three clusters: (1) very young obsidians, {approx}0.2Ma old (2) intermediate-age obsidians, {approx}0.4-{approx}0.8Ma old, and (3) older obsidians, {approx}1.4-{approx}1.6Ma old. The FT method is also an efficient alternative technique for identification of the sources of prehistoric obsidian artefacts. Provenance studies carried out in South America have shown that the Sierra de Guamani obsidian occurrences were important sources of raw material for tool making during pre-Columbian times. Glasses originated from these sources were identified in sites distributed over relatively wide areas of Ecuador and Colombia. Only a few systematic studies on obsidians in other sectors were carried out. Nevertheless, very singular glasses have been recognised in South America, such as Macusanite (Peru) and obsidian Quiron (Argentina), which are being proposed as additional reference materials for FT dating. Analyses of tephra beds interstratified with sedimentary deposits revealed the performance of FT dating in tephrochronological studies. A remarkable example is the famous deposit outcropping at Farola Monte Hermoso, near Bahia Blanca (Buenos Aires Province), described for the first time by the middle of the 19th century by Charles Darwin. Considering the large number of volcanic glasses that were recognised in volcanic complexes and in sedimentary series, South America is a very promising region for the application of FT dating. The examples given above show that this technique may yield important results in different disciplinary fields.

Bigazzi, G. [Istituto di Geoscienze e Georisorse, C.N.R., Via G. Moruzzi, 1, 56124 Pisa (Italy)]. E-mail: g.bigazzi@igg.cnr.it; Hadler Neto, J.C. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, 13083-970 Campinas SP (Brazil); Iunes, P.J. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, 13083-970 Campinas SP (Brazil); Osorio Araya, A.M. [Departamento de Fisica, Quimica e Biologia, Universidade do Estado de Sao Paulo, UNESP, 19060-900 Presidente Prudente SP (Brazil)

2005-12-01

123

Chemistry and migration behaviour of the actinides and fission products in natural aquatic systems  

International Nuclear Information System (INIS)

The 66th PTB seminar was held on April 24th and 25th, 1986, at the Munich Technical University (TUM) in Garching in cooperation with the Institute for Radiochemistry of the Munich Technical University, the 'Nuclear Chemistry' special group of the Society of German Chemists, and UB/SN responsible for the BMFT project. The seminar was organized by the TUM's Institute for Radiochemistry. The seminar dealt with the following main topics: primary geochemical reactions and colloid formation; sorption mechamisms and migration behaviour in Konrad/Gorleben aquifer systems; sampling and experimental investigations; evaluation and interpretation of the data obtained by experiments. The seminar was to achieve the following objectives: information and exchange of experience with regard to the work carried out up to the present; if necessary, formulation of new issues to be discussed; improvement of the interdisciplinary cooperation (chemistry, geosciences, modelling). The following topics and individual aspects were of particular interest and were given special attention: complementary basic research in order to interpret, support and model the results obtained by experiments (sorption mechanisms and thermodynamic data for natural systems); comparability of batch, column and diffusion tests; transferability of laboratory data to natural systems (e.g. Gorleben, Konrad); redox transitions for Np, Tc at Eh values of the natural systems; dependence of the sorption/desorption data on different influencing factors, importance of the influencing factors and selection of data for model calculations. Subject analyses of the individual contributions have been made for the Energy data base. (orig./RB).

1986-01-01

124

Coulomb fission  

International Nuclear Information System (INIS)

A semiquantal theory of Coulomb fission is presented. It is shown that Coulomb fission is a two-step process, involving multiple Coulomb excitation of an actinide target nuclear by a heavy projectile :Zp >approx. 50) followed by radioactive decay. The historical background; dynamical formalism of the theory; phenomenological models of the theory; Coulomb fission experiments; comparison of theory and experiment; and prompt Coulomb fission theory; are all discussed. (U.K.).

1985-01-01

125

Coulomb fission  

Energy Technology Data Exchange (ETDEWEB)

A semiquantal theory of Coulomb fission is presented. It is shown that Coulomb fission is a two-step process, involving multiple Coulomb excitation of an actinide target nuclear by a heavy projectile :Zp > approx. 50) followed by radioactive decay. The historical background; dynamical formalism of the theory; phenomenological models of the theory; Coulomb fission experiments; comparison of theory and experiment; and prompt Coulomb fission theory; are all discussed.

Oberacker, V.E.; Pinkston, W.T. (Vanderbilt Univ., Nashville, TN (USA). Dept. of Physics and Astronomy); Kruse, H.G.W. (Michigan State Univ., East Lansing (USA). Dept. of Physics)

1985-03-01

126

Ternary fission  

International Nuclear Information System (INIS)

This is a report on experimental results obtained with the double torus ionization chamber 'DIOGENES', which has been developed for the investigation of particle associated fission. The role of ternary fission for the understandig of the fission will be discussed. (orig.)

1988-01-01

127

Sorption of 239Np and 235U fission products by zeolite Y, Mexican natural erionite, and bentonite  

International Nuclear Information System (INIS)

[en] Zeolite Y, erionite, and bentonite have been used in this work to remove 239Np and 235U fission products from aqueous solutions at various pH values. It was found that the sorption of fission products by aluminosilicates takes place by different mechanisms, mainly ion exchange, precipitation, and electrostatic surface interaction. The radionuclides content was determined by ?-spectrometry, and X-ray diffraction was used to learn whether the solids maintained their crystallinity at different pH values

1996-01-01

128

Manifestations of a spatial variation of fundamental constants on atomic clocks, Oklo, meteorites, and cosmological phenomena  

CERN Multimedia

The remarkable detection of a spatial variation in the fine-structure constant, alpha, from quasar absorption systems must be independently confirmed by complementary searches. In this letter, we discuss how terrestrial measurements of time-variation of the fundamental constants in the laboratory, meteorite data, and analysis of the Oklo nuclear reactor can be used to corroborate the spatial variation seen by astronomers. Furthermore, we show that spatial variation of the fundamental constants may be observable as spatial anisotropy in the cosmic microwave background, the accelerated expansion (dark energy), and large-scale structure of the Universe.

Berengut, J C

2010-01-01

129

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon  

Science.gov (United States)

To study geochemical processes for migration and fixation of fissiogenic rare earth elements (REE) in association with uranium dissolution, in situ isotopic analyses using an ion microprobe were performed on U- and REE-bearing secondary minerals, such as coffinite, françoisite, uraniferous goethite, and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at Bangombé, Gabon. Phosphate minerals such as phosphatian coffinite and françoisite with depleted 235U ( 235U/ 238U = 0.00609 to 0.00638) contained large amount of fissiogenic light REE, while micro-sized uraninite grains in a solid bitumen aggregate have normal U isotopic values ( 235U/ 238U = 0.00725) and small amount of fissiogenic REE components. The proportions of fissiogenic and non-fissiogenic REE components in four samples from the core of BAX03 vary in depth ranging from 30 cm to 130 cm beneath the reactor, which suggests mixing between fissiogenic isotopes from the reactor and non-fissiogenic isotopes from original minerals in the sandstone. Significant chemical fractionation was observed between Ce and the other REE in the secondary minerals, which shows evidence of an oxidizing atmosphere during their formation. Pb-isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of U-Pb decay system due to recent geologic alteration. However, systematic Pb-isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes, Pb and U from the reactor in association with dolerite dyke intrusion ˜0.798 Ga ago and the formation of the secondary minerals by mixing event between 2.05 Ga-old original minerals and reactor materials due to recent alteration.

Hidaka, Hiroshi; Janeczek, Janusz; Skomurski, Frances N.; Ewing, Rodney C.; Gauthier-Lafaye, François

2005-02-01

130

Polar emission in fission  

International Nuclear Information System (INIS)

[en] Experimental information concerning polar emission is surveyed. The available data relate to the intensity, the angular distribution of polar particles, the energy spectra of polar particles and fission fragments, and to the mass distributions of fission fragments recorded in coincidence with polar particles. - The following hypothesis regarding the nature of this phenomenon are discussed: pre-scission emission from the fragment polar tips, snapping of the nuclear surface, bending of the trajectory by the nuclear force, diffraction and transmission through fission fragments, reactions induced by scission neutrons, the rotating remnants of the necks, delayed tripartition and evaporation from fission fragments. So far, no one of these hypotheses was able to describe all the existing data, although some of them seem to be promising. (author)

1979-05-18

131

Fission of highly excited nuclei  

Energy Technology Data Exchange (ETDEWEB)

Experimental data on the fission of nuclei by protons of intermediate and high energies are reviewed. The methods of investigating fission of nuclei by high-energy particles are described. The data on the fission cross sections, on the angular distributions and angular correlations of the fragments, and on the mass and energy distributions are analyzed for a wide range of nuclei. All the results indicate that the nature of the fission of highly excited nuclei changes in the region of the rare-earth elements.

Andronenko, L.N.; Vai-breveshnene, L.A.; Kotov, A.A.; Nesterov, M.M.; Tarasov, N.A.; Neubert, V.

1987-07-01

132

The topography of the nuclear fission barrier  

International Nuclear Information System (INIS)

Fission theory first developed within the framework of the liquid drop model. Shell model concepts were introduced into fission theory much later than they were in nuclear structure theory but then with spectacular success in explaining striking experimental results then emerging in actinide fission. In the last two decades the complex topography of the fission barrier that is the result of shell model theory has been a major theme in the expanding knowledge of fission, most experimental data finding a natural explanation within this theme. The development of the concept of shell model structure in the fission barrier is outlined in this review. (author). 140 refs., 35 figs.

1989-01-01

133

Underground mining by horizontal top slicing under concrete in the uranium mine of Oklo Fond in Gabon  

International Nuclear Information System (INIS)

[en] This article presents the mining method adopted in the uranium mine of Oklo Fond which belongs to Comut in Gabon, i.e. a method by horizontal top slicing under concreted backfilling. It discusses in particular: - the mechanical characteristics of the different types of concreted backfilling corresponding to their composition and their admixture of cement; - methods of placing this backfilling and their progressive improvement; - the bearing of this method on the problems of selectivity

1986-01-01

134

Underground mining by horizontal top slicing under concrete in the uranium mine of Oklo Fond in Gabon  

Energy Technology Data Exchange (ETDEWEB)

This article presents the mining method adopted in the uranium mine of Oklo Fond which belongs to Comut in Gabon, i.e. a method by horizontal top slicing under concreted backfilling. It discusses in particular: - the mechanical characteristics of the different types of concreted backfilling corresponding to their composition and their admixture of cement; - methods of placing this backfilling and their progressive improvement; - the bearing of this method on the problems of selectivity.

Ndjambe, A.J.

1986-11-01

135

Influence of experimental factors on dating natural and man-made glasses by the fission track method  

International Nuclear Information System (INIS)

[en] In age determination work by counting fission tracks the precision, besides the statistical counting error of spontaneous and induced tracks, largely depends on exact determination of the neutron dose and close maintenance of etching conditions. Slight variations in temperature and concentrations of etch batches may lead to considerable deviations. By dating several 'Early Victorian' U-stained glasses the authors discovered the fact that the spontaneous fission decay constant ?sp. f. is still not known with sufficient accuracy. Since an age of ? 150 yr can be inferred from the style of these glasses, the most probable value of ?sp. f. should lie closely to 8 x 10-17 yr-1. In establishing the coincidence of two geological events the uncertainty of ?sp. f. may be less important. The authors were able to confirm the agreement in the age of moldavites (14.9 ± 1.6) x 106 yr and the Ries Crater glass (14.9 ± 1.5) x 106 yr. (author)

1967-01-01

136

Current topics in nuclear fission research  

Energy Technology Data Exchange (ETDEWEB)

This year is the 50th anniversary of the discovery of nuclear fission by Otto Hahn and Fritz Strassmann. From the point of view of the fundamental physics research, nuclear fission was one of the oldest motivation of the nuclear physics. In this 50 years, many aspects of nuclear fission phenomena have been investigated. Owing to the nature that the nuclear fission involves a dynamical treatment of finite-many-body systems, there have been always some challenging new topics in nuclear fission research in these 50 years. By solving these problems one by one, we have come closer to the understanding of the nuclear fission dynamics. As examples of current topics in nuclear fission research, I will choose and discuss the following three: (1) Cold fission phenomena. (2) Heavy-particle radioactivity phenomena. (3) Transient effect phenomena. (author).

Iwamoto, Akira (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment)

1990-02-01

137

Ternary fission and cluster radioactivities  

CERN Document Server

Ternary fission yield for different kinds of light particle accompanied fission processes is compared to the Q-values for the corresponding cold phenomena, showing a striking correlation. The experimental evidence for the existence of a quasimolecular state in sup 1 sup 0 Be accompanied fission of sup 2 sup 5 sup 2 Cf may be explained using a three-center phenomenological model which generates a third minimum in the deformation energy at a separation distance very close to the touching point. This model is a natural extension of the unified approach to three groups of binary decay modes (cold fission, cluster radioactivities and alpha decay), illustrated by sup 2 sup 3 sup 4 U decay modes, and the alpha valley on the potential energy surfaces of sup 1 sup 0 sup 6 Te. New measurements of cluster decay modes, confirming earlier predictions within analytical superasymmetric fission model, are included in a comprehensive half-life systematics. (authors)

Poenaru, D N; Greiner, W; Gherghescu, R A; Hamilton, J H; Ramayya, A V

2002-01-01

138

Spontaneous fission  

International Nuclear Information System (INIS)

The spontaneous fission (SF) of the heaviest actinides and the transactinides is of particular interest because of the dramatic changes in properties observed in the region of the heavy fermion isotopes and for still heavier elements. The existing experimental information on SF properties including half-life systematics, fragment kinetic-energy and mass-yield distributions, prompt neutron emission, and gamma emission will be reviewed. Possibility for extending studies of SF properties to other regions are considered and the potential for obtaining additional information about low-energy fission properties is discussed

1993-01-01

139

Dissolution studies of natural analogues spent fuel and U(VI)-Silicon phases of and oxidative alteration process  

International Nuclear Information System (INIS)

In order to understand the long-term behavior of the nuclear spent fuel in geological repository conditions, we have performed dissolution studies with natural analogues to UO2 as well as with solid phases representatives of the oxidative alteration pathway of uranium dioxide, as observed in both natural environment and laboratory studies. In all cases, we have studied the influence of the bicarbonate concentration in the dissolution process, as a first approximation to the groundwater composition of a granitic environment, where carbonate is one of the most important complexing agents. As a natural analogue to the nuclear spent fuel some uraninite samples from the Oklo are deposit in Gabon, where chain fission reactions took place 2000 millions years ago, as well as a pitchblende sample from the mine Fe ore deposit, in Salamanca (spain) have been studied. The studies have been performed at 25 and 60 deg C and 60 deg C, and they have focussed on the determination of both the thermodynamic and the kinetic properties of the different samples studied, using batch and continuous experimental methodologies, respectively. (Author)

2000-01-01

140

Nuclear fission studies with dielectric track detector  

International Nuclear Information System (INIS)

Charged particle detectors based on dielectric materials have been used in nuclear fission studies since their advent in the late fifties. These detectors played a significant role in the understanding of fission systematics because of their use in the measurement of spontaneous fission half-lives, life-times of compound nuclei fission cross section and fission-barrier heights, The availability of heavy ion beams of high energy gave further impetus to the study of fission phenomena in a larger range of nuclear species. New reaction modes such s deep inelastic scattering and fast fission were discovered in heavy ion induced nuclear reactions. The track detectors were successfully used in the study of these processes both internationally and at PINSTECT. The sequential binary nature of apparently ternary fission events for different projectile-target combinations has been established by our group. Often, the paths of high energy heavy projectiles are seen to bifurcate inside the detector materials. We have analysed the tracks of these events to understand the reaction mechanism as the fusion of projectile ions with the detector's atoms leading to the fission of intermediate complex. The kinematical analysis of this reaction is reported briefly. The high degree of nuclear excitation produced by the absorption of a pion in the nucleus also leads to binary and ternary fission, our measurements of fission cross sections and fission probabilities are reported for the incident negatively charged pions of high energies. (author).

1995-01-01

 
 
 
 
141

Cell length growth in fission yeast: an analysis of its bilinear character and the nature of its rate change transition.  

UK PubMed Central (United Kingdom)

During their mitotic cycle, cylindrical fission yeast cells grow exclusively at their tips. Length growth starts at birth and halts at mitotic onset when the cells begin to prepare for division. While the growth pattern was initially considered to be exponential, during the last three decades an increasing amount of evidence indicated that it is rather a bilinear function (two linear segments separated by a rate change point (RCP)). The main focus of this work was to clarify this and to elucidate the further question of whether the rate change occurs abruptly at the RCP or more smoothly during a transition period around it. We have analyzed the individual growth patterns obtained by time-lapse microscopy of 60 wild type cells separately as well as that of the 'average' cell generated from their superposition. Linear, exponential, and bilinear functions were fitted to the data, and their suitability was compared using objective model selection criteria. This analysis found the overwhelming majority of the cells (70%) to have a bilinear growth pattern with close to half of them showing a smooth and not an abrupt transition. The growth pattern of the average cell was also found to be bilinear with a smooth transition. This article is protected by copyright. All rights reserved.

Horváth A; Rácz-Mónus A; Buchwald P; Sveiczer A

2013-07-01

142

Calculations of fission rates for r-process nucleosynthesis  

CERN Document Server

Fission plays an important role in the r-process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling. We present calculations of beta-delayed and neutron-induced fission rates, taking into account different fission barriers predictions and mass formulae. It is shown that an increase of fission barriers results naturally in a reduction of fission rates, but that nevertheless fission leads to the termination of the r-process. Furthermore, it is discussed that the probability of triple fission could be high for $A>260$ and have an effect on the formation of the abundances of heavy nuclei. Fission after beta-delayed neutron emission is discussed as well as different aspects of the influence of fission upon r-process calculations.

Panov, I V; Pfeiffer, B; Rauscher, T; Kratz, K L; Thielemann, F K

2005-01-01

143

Calculations of fission rates for r-process nucleosynthesis  

International Nuclear Information System (INIS)

Fission plays an important role in the r-process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling. We present calculations of beta-delayed and neutron-induced fission rates, taking into account different fission barriers predictions and mass formulae. It is shown that an increase of fission barriers results naturally in a reduction of fission rates, but that nevertheless fission leads to the termination of the r-process. Furthermore, it is discussed that the probability of triple fission could be high for A>260 and have an effect on the formation of the abundances of heavy nuclei. Fission after beta-delayed neutron emission is discussed as well as different aspects of the influence of fission upon r-process calculations

2005-01-24

144

Fission isomers  

Energy Technology Data Exchange (ETDEWEB)

The single particle (shell) effects giving rise to spontaneously fissioning shape isomeric states are outlined. Empirical data on static properties such as excitation energies and barrier heights are reviewed and compared with potential energy surface calculations. Half-life and branching ratio information are related to barrier penetration. Spectroscopic information on moments of inertia, quadrupole moments, spins and g-factors are reviewed. Recent developments on shape isomerism in other regions of the Chart of the Nuclides are presented. 22 refs., 5 figs.

Vandenbosch, R.

1989-01-01

145

Bacteria, colloids and organic carbon in groundwater at the Bangombe site in the Oklo area  

Energy Technology Data Exchange (ETDEWEB)

This report describes how microorganisms, colloids and organic matter were sampled from groundwater from six boreholes at the Bangombe site in the Oklo region and subsequently analyzed. For analysis of microorganisms, DNA was extracted from groundwater, amplified and cloned and information available in the ribosomal 16S rRNA gene was used for mapping diversity and distribution of bacteria. Each borehole was dominated by species that did not dominate in any of the other boreholes, a result that probably reflects documented differences in the geochemical environment. Analyses of sampled colloids included SEM and ICP-MS analysis of colloids on membrane and single particle analysis of samples in bottles. The colloid concentration was rather low in these Na-Mg-Ca-HCO{sub 3} type waters. Trace element results show that transition metals and some heavy metals are associated with the colloid phase. Distribution coefficients of trace elements between the water and colloid phases were estimated. For example for uranium, an average of 200 pg/ml was detected in the water, and 40 pg/ml was detected in the colloid phase. A K{sub p} value of 2* 10{sup 6} ml/g was calculated, considering (colloid) = 100 ng/ml. Groundwater samples were collected for analysis of the concentration of organic carbon (TOC), humic substances and metals associated with the humic substances. TOC varied in the range 4-14 mg/l in three boreholes, one borehole had a TOC<1.5 mg/l. The metal speciation study indicated that a large fraction, 8-67% of uranium was bound to the humic matter compared to the fractions of Ca and Fe (<0.4% and 0.02-10%, resp.). 60 refs, 8 figs, 16 tabs.

Pedersen, K. [ed.

1996-02-01

146

Fission theory and actinide fission data  

International Nuclear Information System (INIS)

The understanding of the fission process has made great progress recently, as a result of the calculation of fission barriers, using the Strutinsky prescription. Double-humped shapes were obtained for nuclei in the actinide region. Such shapes could explain, in a coherent manner, many different phenomena: fission isomers, structure in near-threshold fission cross sections, intermediate structure in subthreshold fission cross sections and anisotropy in the emission of the fission fragments. A brief review of fission barrier calculations and relevant experimental data is presented. Calculations of fission cross sections, using double-humped barrier shapes and fission channel properties, as obtained from the data discussed previously, are given for some U and Pu isotopes. The fission channel theory of A. Bohr has greatly influenced the study of low-energy fission. However, recent investigation of the yields of prompt neutrons and ? rays emitted in the resonances of 235U and 239Pu, together with the spin determination for many resonances of these two nuclei cannot be explained purely in terms of the Bohr theory. Variation in the prompt neutron and ?-ray yields from resonance to resonance does not seem to be due to such fission channels, as was thought previously, but to the effect of the (n, ?, f) reaction. The number of prompt fission neutrons and the kinetic energy of the fission fragments are affected by the energy balance and damping or viscosity effects in the last stage of the fission process, from saddle point to scission. These effects are discussed for some nuclei, especially for 240Pu. 17 figures, 56 ref

1975-03-03

147

Crystal chemistry and radiation-induced amorphization of P-coffinite from the natural fission reactor at Bangombe Gabon  

International Nuclear Information System (INIS)

[en] Phosphorous-rich coffinite, U(Si,P)O4.H2O, from the natural nuclear reactor at Bangombe, Gabon (depth 12.25 m), has been examined as an important primary mineral and alteration product of uraninite under reducing conditions. Based on electron microprobe analyses (EMPA) and textural relationships, two distinct types of coffinite have been identified: (1) P-coffinite-(i) [with P2O5 and (REE+Y)2O3 as high as 9.84 and 8.66 wt%, respectively] replaces uraninite and has a chemical formula of (U0.84±0.05 Y,REE0.12±0.02Ca0.10±0.02Th0.003±0.002= )?1.07±0.06 (Si0.41±0.07P0.34±0.03S0.08±0.05)#SIGMA= #0.84±0.05O4 and; (2) coffinite-(ii), lacks uraninite inclusions [with P2O5 and (Y+REE)2O3 up to 1.45 and 1.79 wt%, respectively] and has a chemical formula of (U0.78±0.02Ca0.05±0.003Y,REE0.03±0.01Th= 0.002±0.001)?0.87±0.02(Si1.02±0.= 02P0.06±0.01)?1.08±0.01O4. The EMPA elemental maps reveal a homogeneous distribution P,Si,Nd, and U in P-coffinite-(i). Charge-balance calculations indicate that S substitution for Si in the coffinite structure results in the enhancement of the incorporation of P and REEs. High EMPA totals (95-100 wt%), suggest that water is not an essential component of the coffinite structure. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveal the decomposition of single crystals of uraninite into 50 nm grains during the alteration process to P-coffinite-(i). High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns confirm that P-coffinite-(i) has the coffinite structure. However, P-coffinite-(i) has a large amorphous fraction probably due to radiation damage caused by alpha-decay events. The calculated cumulative dose for both types of coffinite varies from 1.6-1.9 * 1018 (?-decay events/mg), which is equivalent to 134.2-161.5 displacement per atom (dpa) that have accumulated most probably during the past 800 million years. (authors)

2009-01-01

148

Nuclear fission and reactions  

International Nuclear Information System (INIS)

[en] The nuclear fission research programs are designed to elucidate basic features of the fission process. Specifically, (1) factors determining how nucleons of a fissioning nucleus are distributed between two fission fragments, (2) factors determining kinetic energy and excitation energies of fragments, and (3) factors controlling fission lifetimes. To these ends, fission studies are reported for several heavy elements and include investigations of spontaneous and neutron-induced fission, heavy ion reactions, and high energy proton reactions. The status of theoretical research is also discussed. (U.S.)

1975-01-01

149

Seminar on Fission VI  

Science.gov (United States)

Topical reviews. Angular momentum in fission / F. Gönnenwein ... [et al.]. The processes of fusion-fission and quasi-fission of heavy and super-heavy nuclei / M. G. Itkis ... [et al.] -- Fission cross sections and fragment properties. Minor-actinides fission cross sections and fission fragment mass yields via the surrogate reaction technique / B. Jurado ... [et al.]. Proton-induced fission on actinide nuclei at medium energy / S. Isaev ... [et al.]. Fission cross sections of minor actinides and application in transmutation studies / A. Letourneau ... [et al.]. Systematics on even-odd effects in fission fragments yields: comparison between symmetric and asymmetric splits / F. Rejmund, M Caamano. Measurement of kinetic energy distributions, mass and isotopic yields in the heavy fission products region at Lohengrin / A. Bail ... [et al.] -- Ternary fission. On the Ternary [symbol] spectrum in [symbol]Cf(sf) / M. Mutterer ... [et al.]. Energy degrader technique for light-charged particle spectroscopy at LOHENGRIN / A. Oberstedt, S. Oberstedt, D. Rochman. Ternary fission of Cf isotopes / S. Vermote ... [et al.]. Systematics of the triton and alpha particle emission in ternary fission / C. Wagemans, S. Vermote, O. Serot -- Neutron emission in fission. Scission neutron emission in fission / F.-J. Hambsch ... [et al.]. At and beyond the Scission point: what can we learn from Scission and prompt neutrons? / P. Talou. Fission prompt neutron and gamma multiplicity by statistical decay of fragments / S. Perez-Martin, S. Hilaire, E. Bauge -- Fission theory. Structure and fission properties of actinides with the Gogny force / H. Goutte ... [et al.]. Fission fragment properties from a microscopic approach / N. Dubray, H. Goutte, J.-P. Delaroche. Smoker and non-smoker neutron-induced fission rates / I. Korneev ... [et al.] -- Facilities and detectors. A novel 2v2E spectrometer in Manchester: new development in identification of fission fragments / I. Tsekhanovich ... [et al.]. Development of PSD and ToF + PSD techniques for fission experiments / M. Sillanpää ... [et al.]. MYRRHA, a new fast spectrum facility / H. Aït Abderrahim, P. D'hondt, D. De Bruyn. The BR1 reactor: a versatile tool for fission experiments / J. Wagemans -- "Special" fission processes. Shape isomers - a key to fission barriers / S. Oberstedt ... [et al.]. Fission in spallation reactions / J. Cugnon, Th. Aoust, A. Boudard -- Conference photo -- List of participants.

Wagemans, Cyriel; Wagemans, Jan; D'Hondt, Pierre

2008-04-01

150

Energy released in fission  

International Nuclear Information System (INIS)

[en] The effective energy released in and following the fission of U-235, Pu-239 and Pu-241 by thermal neutrons, and of U-238 by fission spectrum neutrons, is discussed. The recommended values are: U-235 ... 192.9 ± 0.5 MeV/fission; U-238 ... 193.9 ± 0.8 MeV/fission; Pu-239 ... 198.5 ± 0.8 MeV/fission; Pu-241 ... 200.3 ± 0.8 MeV/fission. These values include all contributions except from antineutrinos and very long-lived fission products. The detailed contributions are discussed, and inconsistencies in the experimental data are pointed out. In Appendix A, the contribution to the total useful energy release in a reactor from reactions other than fission are discussed briefly, and in Appendix B there is a discussion of the variations in effective energy from fission with incident neutron energy. (author)

1969-01-01

151

Dissolution studies of natural analogues spent fuel and U(VI)-Silicon phases of and oxidative alteration process; Estudios de disolucion de analogos naturales de combustible nuclear irradiado y de fases de U(VI)-Silicio representativas de un proceso de alteracion oxidativa  

Energy Technology Data Exchange (ETDEWEB)

In order to understand the long-term behavior of the nuclear spent fuel in geological repository conditions, we have performed dissolution studies with natural analogues to UO{sub 2} as well as with solid phases representatives of the oxidative alteration pathway of uranium dioxide, as observed in both natural environment and laboratory studies. In all cases, we have studied the influence of the bicarbonate concentration in the dissolution process, as a first approximation to the groundwater composition of a granitic environment, where carbonate is one of the most important complexing agents. As a natural analogue to the nuclear spent fuel some uraninite samples from the Oklo are deposit in Gabon, where chain fission reactions took place 2000 millions years ago, as well as a pitchblende sample from the mine Fe ore deposit, in Salamanca (spain) have been studied. The studies have been performed at 25 and 60 degree centigree and 60 degree centigree, and they have focussed on the determination of both the thermodynamic and the kinetic properties of the different samples studied, using batch and continuous experimental methodologies, respectively. (Author)

Perez Morales, I.

2000-07-01

152

Fission product behavior  

International Nuclear Information System (INIS)

This paper reviews fission product transport and chemistry behavior in light water reactor coolant systems (RCS) and in containments under severe-accident conditions. In the RCS, the dominant aerosol processes are Brownian and turbulent agglomeration, gravitational settling, impaction, and turbulent deposition. These processes are effective in removing particulates under high-pressure accident conditions but are not effective under low-pressure conditions that are associated with higher throughput velocities and lower residence times. In the containment, the dominant natural processes are Brownian and gravitational agglomeration, gravitational settling, and diffusiophoresis. These processes provide effective removal of aerosols from the containment gas space if containment failure is either small in size (low leakage rates) or late in time. The relationships among the natural attenuation processes, the containment failure time, and the failure size have been explored.

1991-01-01

153

Fifty years of nuclear fission: Nuclear data and measurements series  

Energy Technology Data Exchange (ETDEWEB)

This report is the written version of a colloquium first presented at Argonne National Laboratory in January 1989. The paper begins with an historical preamble about the events leading to the discovery of nuclear fission. This leads naturally to an account of early results and understanding of the fission phenomena. Some of the key concepts in the development of fission theory are then discussed. The main theme of this discussion is the topography of the fission barrier, in which the interplay of the liquid-drop model and nucleon shell effects lead to a wide range of fascinating phenomena encompassing metastable isomers, intermediate-structure effects in fission cross-sections, and large changes in fission product properties. It is shown how study of these changing effects and theoretical calculations of the potential energy of the deformed nucleus have led to broad qualitative understanding of the nature of the fission process. 54 refs., 35 figs.

Lynn, J.E.

1989-06-01

154

Fifty years of nuclear fission: Nuclear data and measurements series  

International Nuclear Information System (INIS)

[en] This report is the written version of a colloquium first presented at Argonne National Laboratory in January 1989. The paper begins with an historical preamble about the events leading to the discovery of nuclear fission. This leads naturally to an account of early results and understanding of the fission phenomena. Some of the key concepts in the development of fission theory are then discussed. The main theme of this discussion is the topography of the fission barrier, in which the interplay of the liquid-drop model and nucleon shell effects lead to a wide range of fascinating phenomena encompassing metastable isomers, intermediate-structure effects in fission cross-sections, and large changes in fission product properties. It is shown how study of these changing effects and theoretical calculations of the potential energy of the deformed nucleus have led to broad qualitative understanding of the nature of the fission process. 54 refs., 35 figs

1989-01-01

155

Excitation-energy dependence of the nuclear fission characteristics  

Energy Technology Data Exchange (ETDEWEB)

It is known that the width parameter of the fragment mass yield distribution follows a beautiful systematics with respect to the excitation energy. According to this systematics, the fission characteristics following the systematics should disappear when the excitation energy Ex goes down to 14 MeV. The present purpose is to elucidate if, where, how and why a transition takes place in the fission characteristics of the asymmetric fission of light actinide elements. Two types of experiments are performed, one is the double-energy measurement of the kinetic energies of complementary fragments in the thermal-neutron fission of {sup 235,233}U and proton-induced fission of {sup 238}U at 13.3- and 15.7-MeV excitations, and the other is the radiochemical study of proton-induced fission and photofission of {sup 238}U at various excitation energies. In conclusion, it has demonstrated that there are two distinctive fission mechanisms in the low-energy fission of light actinide elements and the transition between them takes place around 14-MeV excitation. The characteristics of proton fission and photofission in the energy range lower than the above transition point are the essentially the same as those of thermal-neutron fission and also spontaneous fission. The results of GDR fission indicates the fission in the high-energy side starts from the nuclear collective states, whereas the lower-energy fission is of non-collective nature. It is likely that thermal-neutron fission is rather of the barrier-penetrating type like spontaneous fission than the threshold fission. (S.Y.)

Baba, H.; Saito, T.; Takahashi, N. [Osaka City Univ. (Japan). Faculty of Science] [and others

1996-03-01

156

Fragment angular distributions in fission and fission like reactions  

International Nuclear Information System (INIS)

Fragment angular distributions in fission is one of the oldest and well understood aspects of fission theory. However, recent heavy ion-induced fission and fission-like reactions have added a new dimension to this problem. The present understanding of the fragment angular distribution theory in fission and fission-like reactions is reviewed. (author). 23 refs., 7 figs.

1989-01-01

157

Fission Research at IRMM  

Directory of Open Access Journals (Sweden)

Full Text Available Fission Research at JRC-IRMM has a longstanding tradition. The present paper is discussing recent investigations of fission fragment properties of 238 U(n,f), 234 U(n,f), prompt neutron emission in fission of 252 Cf(SF) as well as the prompt fission neutron spectrum of 235 U(n,f) and is presenting the most important results.

Hambsch F.-J.; Oberstedt S.; Zeynalov S.; Kornilov N.; Fabry I.; Borcea R.; Al-Adili A.

2010-01-01

158

Solvent extraction of some fission products using tetracycline as a complexing agent : dependence on the ph of the aqueous phase and on the nature of some inorganic anions  

International Nuclear Information System (INIS)

The behavior of tetracycline as a complexing agent in solvent extraction studies is presented. The extraction curves for the fission products 90Sr, 140Ba, 99Mo, sup(99m)Tc, 95Zr, 95Nb, 103Ru and also for U have been determined for the extraction system tetracycline-benzyl alcohol. The extraction dependence on the pH of the aqueous phase as well as on the kind of electrolyte present was examined. As a practical application, the possiblity of using the tetracycline-benzyl alcohol system for separation of the fission products present in a mixture of them, as well as for the separation of uranium from those elements, was tested. (Author)

1982-01-01

159

Numerical Simulations of Fission  

Science.gov (United States)

In this paper, we use the term fission to refer to the breakup of an equilibrium celestial body driven by rapid rotation. Historically, it was conjectured that fission would lead to splitting of a body directly into two or more pieces. Numerical hydrodynamic simulation techniques have now become sufficiently powerful to study the outcome of dynamic fission instabilities. We summarize recent work and present new simulations spanning a range of rotation rates and fluid compressibility. In the best resolved cases dynamic fission instability always leads to ejection of a ring or disk of debris rather thin one or a few discrete bodies. In this case, just as in most other lunar origin theories, a fission-product Moon must accrete out of a geocentric swarm of material. Intrinsic nonaxisymmetry of the remnant Earth after fission would prevent rapid recollapse of the swarm. The revised picture aleviates some of the problems associated with earlier versions of the fission theory. The two most serious remaining objections are that it is difficult to make the proto-Earth rotate fast enough to undergo fission and that the proto-Earth must be largely molten at the time it fissions. To overcome the first objection, it may be necessary to combine fission with the planetesimal impact theory. Some advantages of such a hybrid theory are discussed. The second objection cannot be fully assessed until more is known about the fission history and accretion of the proto-Earth.

Durisen, Richard H.; Gingold, Robert A.

1987-01-01

160

Fission neutron statistical emission  

International Nuclear Information System (INIS)

[en] The statistical model approach FINESSE (FIssion NEutronS' Statistical Emission) for the description of fission neutron multiplicities, energy spectra and angular distributions is described. Based on an extended Weisskopf ansatz and on a realistic temperature distribution it provides a fragment mass number dependent description of fission neutron data. Model parameters (optical potential, n/? competition) were fixed on the basis of the 252Cf(sf) (nuclear data standard). Combined with a phenomenological fission model for predicting relevant fragment data as function of asymmetry. FINESSE can be applied to any fission reaction of actinides in the Th-Cf region without further parameter adjustment. Results are presented for 252Cf(sf) and neutron induced fission of 235U, 239Pu, 232Th. Effects of multiple-chance fission are discussed for 232Th(n,xnf) reacation. (author). 46 refs, 11 figs

1990-01-01

 
 
 
 
161

Fission level densities  

International Nuclear Information System (INIS)

Fission level densities (or fissioning nucleus level densities at fission saddle deformations) are required for statistical model calculations of actinide fission cross sections. Back-shifted Fermi-Gas Model, Constant Temperature Model and Generalized Superfluid Model (GSM) are widely used for the description of level densities at stable deformations. These models provide approximately identical level density description at excitations close to the neutron binding energy. It is at low excitation energies that they are discrepant, while this energy region is crucial for fission cross section calculations. A drawback of back-shifted Fermi gas model and traditional constant temperature model approaches is that it is difficult to include in a consistent way pair correlations, collective effects and shell effects. Pair, shell and collective properties of nucleus do not reduce just to the renormalization of level density parameter a, but influence the energy dependence of level densities. These effects turn out to be important because they seem to depend upon deformation of either equilibrium or saddle-point. These effects are easily introduced within GSM approach. Fission barriers are another key ingredients involved in the fission cross section calculations. Fission level density and barrier parameters are strongly interdependent. This is the reason for including fission barrier parameters along with the fission level densities in the Starter File. The recommended file is maslov.dat - fission barrier parameters. Recent version of actinide fission barrier data obtained in Obninsk (obninsk.dat) should only be considered as a guide for selection of initial parameters. These data are included in the Starter File, together with the fission barrier parameters recommended by CNDC (beijing.dat), for completeness. (author)

1998-01-01

162

Determination of the fission products yields, lanthanide and yttrium, in the fission of 238U with neutrons of fission spectra  

International Nuclear Information System (INIS)

A radiochemical investigation is performed to measure the cumulative fission product yields of several lantanides and yttrium nuclides in the 238U by fission neutron spectra. Natural and depleted uranium are irradiated under the same experimental conditions in order to find a way to subtract the contribution of the 235U fission. 235U percentage in the natural uranium was 3.5 times higher than in the depleted uranium. Uranium oxides samples are irradiated inside the core of the Argonaut Reactor, at the Instituto de Engenharia Nuclear, and the lantanides and yttrium are chemically separated. The fission products gamma activities were detected, counted and analysed in a system constituted by a high resolution Ge(Li) detector, 4096 multichannel analyser and a PDP-11 computer. Cumulative yields for fission products with half-lives between 1 to 33 hours are measured: 93Y, 141La, 142La, 143Ce and 149Nd. The chain total yields are calculated. The cumulative fission yields measured for 93Y, 141La, 142La, 143Ce and 149Nd are 4,49%, 4,54%, 4,95%, 4,16% and 1,37% respectively and they are in good agreement with the values found in the literature. (Author)

1981-01-01

163

Is channeling of fission tracks taking place?  

International Nuclear Information System (INIS)

A single crystal of natural zircon which is sliced to have (010) basal plane and thinned by ion thinning is electron microscopically observed after slow neutron irradiation to ascertain whether channeling of the nuclear fission fragments is taking place or not. A fairly large number of the induced fission tracks are recognized at low magnification images where a considerable number of them are parallel to low-index lattice planes such as 100, 001, 101, 301, 103 though their directions changed some time up to several degrees. High resolution images of fission tracks often show a variety of zigzag passing of the tracks along low-index lattice planes in atomistic level. The rate of the tracks which are parallel to these low-index lattice planes is fairly high as about 45%, which strongly suggests that channeling of the fission tracks is taking place.

1999-01-01

164

Fissionable nuclear fuel composition  

Energy Technology Data Exchange (ETDEWEB)

This patent describes a fissionable nuclear composition for service in a nuclear reactor fuel core consisting essentially of a ceramic body of fissionable oxide fuel material selected from the group. It consists of uranium oxides, plutonium oxide and thorium oxides, and mixtures thereof, and containing dispersed throughout the ceramic body of fissionable oxide fuel material at least one boron depletable neutron absorbent selected from the group consisting boron nitride, boron oxide and boron silicide in amounts of from about 0.02 up to about 0.50 percent by weight of the fissionable oxide fuel material.

Proebstle, R.A.; Marlowe, M.O.; Reese, A.P.

1991-03-05

165

Intermediate energy nuclear fission  

International Nuclear Information System (INIS)

Nuclear fission has been investigated with the double-kinetic-energy method using silicon surface barrier detectors. Fragment energy correlation measurements have been made for U, Th and Bi with bremsstrahlung of 600 MeV maximum energy. Distributions of kinetic energy as a function of fragment mass are presented. The results are compared with earlier photofission data and in the case of bismuth, with calculations based on the liquid drop model. The binary fission process in U, Yb, Tb, Ce, La, Sb, Ag and Y induced by 600 MeV protons has been investigated yielding fission cross sections, fragment kinetic energies, angular correlations and mass distributions. Fission-spallation competition calculations are used to deduce values of macroscopic fission barrier heights and nuclear level density parameter values at deformations corresponding to the saddle point shapes. We find macroscopic fission barriers lower than those predicted by macroscopic theories. No indication is found of the Businaro Gallone limit expected to occur somewhere in the mass range A = 100 to A = 140. For Ce and La asymmetric mass distributions similar to those in the actinide region are found. A method is described for the analysis of angular correlations between complementary fission products. The description is mainly concerned with fission induced by medium-energy protons but is applicable also to other projectiles and energies. It is shown that the momentum and excitation energy distributions of cascade residuals leading to fission can be extracted. (Author).

1982-01-01

166

Muon-induced fission  

International Nuclear Information System (INIS)

A review of recent experimental results on negative-muon-induced fission, both of 238U and 232Th, is given. Some conclusions drawn by the author are concerned with muonic atoms of fission fragments and muonic atoms of the shape isomer of 238U. (author).

1979-05-18

167

Fission Spectrum Related Uncertainties  

Energy Technology Data Exchange (ETDEWEB)

The paper presents a preliminary uncertainty analysis related to potential uncertainties on the fission spectrum data. Consistent results are shown for a reference fast reactor design configuration and for experimental thermal configurations. However the results obtained indicate the need for further analysis, in particular in terms of fission spectrum uncertainty data assessment.

G. Aliberti; I. Kodeli; G. Palmiotti; M. Salvatores

2007-10-01

168

The nuclear fission  

International Nuclear Information System (INIS)

The nuclear fission process considering initially the formation of compound nucleus and finishing with radioactive decay of fission products is studied. The process is divided in three parts which consist of the events associated to the nucleus of intermediate transitional state, the scission configuration, and the phenomenum of post scission. (M.C.K.).

1983-01-01

169

Study of hypernuclei fission  

International Nuclear Information System (INIS)

This work is about PS177 experience made on LEAR machine at CERN in 1988. The annihilation reaction of anti protons on a target of Bismuth or Uranium is studied. Lambda particles are produced by this reaction, in the nucleus in 2% of cases 7.1 10-3 hypernuclei by stopped antiproton in the target are produced. The prompt hypernucleus fission probability of uranium is 75% and that of Bismuth 10%. The mass distribution of fission fragments is symmetrical ((? the excitation energy of the nucleus is very high). If the nucleus hasn't fissioned, the non-mesonic lambda decay, gives it an energy of 100 MeV, what allows to fission later. This fission is delayed because the hypernucleus lifetime is 1.3+0.25-0.21 10-10 sec for Bismuth.

1990-01-01

170

Biomodal spontaneous fission  

Energy Technology Data Exchange (ETDEWEB)

Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic- energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties. 16 refs., 10 figs.

Hulet, E.K. (Lawrence Livermore National Lab., CA (USA))

1989-09-26

171

Spontaneous fission of nuclei  

International Nuclear Information System (INIS)

[en] Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic-energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties

1992-01-01

172

Biomodal spontaneous fission  

International Nuclear Information System (INIS)

[en] Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic- energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties. 16 refs., 10 figs

1989-01-01

173

Fission 2009 4. International Workshop on Nuclear Fission and Fission Product Spectroscopy - Compilation of slides  

International Nuclear Information System (INIS)

This conference is dedicated to the last achievements in experimental and theoretical aspects of the nuclear fission process. The topics include: mass, charge and energy distribution, dynamical aspect of the fission process, nuclear data evaluation, quasi-fission and fission lifetime in super heavy elements, fission fragment spectroscopy, cross-section and fission barrier, and neutron and gamma emission. This document gathers the program of the conference and the slides of the presentations

2009-01-01

174

The nuclear fission process  

Energy Technology Data Exchange (ETDEWEB)

Fifty years after its discovery, the nuclear fission phenomenon is of recurring interest. When its fundamental physics aspects are considered, fission is viewed in a very positive way, which is reflected in the great interest generated by the meetings and large conferences organized for the 50th anniversary of its discovery. From a purely scientific and practical point of view, a new book devoted to the (low energy) nuclear fission phenomenon was highly desirable considering the tremendous amount of new results obtained since the publication of the book Nuclear Fission by Vandenbosch and Huizenga in 1973 (Academic Press). These new results could be obtained thanks to the growth of technology, which enabled the construction of powerful new neutron sources, particle and heavy ion accelerators, and very performant data-acquisition and computer systems. The re-invention of the ionization chamber, the development of large fission fragment spectrometers and sophisticated multiparameter devices, and the production of exotic isotopes also contributed significantly to an improved understanding of nuclear fission. This book is written at a level to introduce graduate students to the exciting subject of nuclear fission. The very complete list of references following each chapter also makes the book very useful for scientists, especially nuclear physicists. The book has 12 chapters covering the fission barrier and the various processes leading to fission as well as the characteristics of the various fission reaction products. In order to guarantee adequate treatment of the very specialized research fields covered, several distinguished scientists actively involved in some of these fields were invited to contribute their expertise as authors or co-authors of the different chapters.

Wagemans, C. (ed.)

1991-01-01

175

Study on fission blanket fuel cycling of a fusion-fission hybrid energy generation system  

International Nuclear Information System (INIS)

This paper presents a preliminary study on neutron physics characteristics of a light water cooled fission blanket for a new type subcritical fusion-fission hybrid reactor aiming at electric power generation with low technical limits of fission fuel. The major objective is to study the fission fuel cycling performance in the blanket, which may possess significant impacts on the feasibility of the new concept of fusion-fission hybrid reactor with a high energy gain (M) and tritium breeding ratio (TBR). The COUPLE2 code developed by the Institute of Nuclear and New Energy Technology of Tsinghua University is employed to simulate the neutronic behaviour in the blanket. COUPLE2 combines the particle transport code MCNPX with the fuel depletion code ORIGEN2. The code calculation results show that soft neutron spectrum can yield M > 20 while maintaining TBR >1.15 and the conversion ratio of fissile materials CR > 1 in a reasonably long refuelling cycle (>five years). The preliminary results also indicate that it is rather promising to design a high-performance light water cooled fission blanket of fusion-fission hybrid reactor for electric power generation by directly loading natural or depleted uranium if an ITER-scale tokamak fusion neutron source is achievable.

2011-01-01

176

Nucleon-induced fission at intermediate energies  

Energy Technology Data Exchange (ETDEWEB)

The absence of a satisfactory theoretical description to predict isotope yields as well as the need for experimental fragment mass and charge distributions at intermediate-energies form the motivation of this work. Like the objects under study, the research presented in this thesis consists two main parts. Part 1 concerns an activation experiment that has been performed at the 'Kernfysisch Versneller Instituut' (Nuclear Physics Accelerator Institute) in Groningen, Netherlands, using the AGOR cyclotron. Fission product yields have been measured resulting from 190 MeV proton-induced fission of {sup nat}W, 197Au, {sup nat}Pb, 208Pb and 232Th. In Chapter 2 the experimental set up is discussed, followed in Chapter 3 by a description of the data analysis. The results on the reconstructed mass yields and the total fission cross sections are presented in Chapter 4. Part 2 is of a theoretical nature. The objective is to compute fission product mass yields from intermediate-energy nucleon-induced reactions. In the approach presented here, two stages can be distinguished. In the first stage the fission cross section is determined for the various fissioning isotopes as a function of their excitation energy in competition with other processes like pre-equilibrium decay and particle evaporation. ALICE-91 is a nuclear reaction code that takes care of this first stage. The second stage consists of constructing the total fission-fragment mass and charge distributions from the different contributions of all the equilibrated fissioning systems. Hence, a model is needed that gives a prediction for the fission-product mass yields in a large range of mass, charge, and excitation energy of the fissioning nucleus. For this purpose, the multi-modal random neck-rupture model by Brosa is extended with temperature-dependent shell and pairing corrections and a temperature-dependent LDM. The combination of ALICE-91 and the modified Brosa approach is used for the analysis of the experiments given in the first part of this thesis as well as other available experimental results. Chapter 5 is dedicated to the extension of the Brosa model. The multi-chance fission treatment in ALICE-91 is discussed in Chapter 6. Chapter 7 contains the coupling between ALICE-91 and the revised Brosa model as well as the results obtained in this manner. Finally, a summary and outlook can be found in Chapter 8. Appendix A contains a list explaining all the abbreviations used in this manuscript. Parts of this work have already been published in journals and conference proceedings. refs.

Duijvestijn, M.C

2000-09-29

177

Nucleon-induced fission at intermediate energies  

International Nuclear Information System (INIS)

The absence of a satisfactory theoretical description to predict isotope yields as well as the need for experimental fragment mass and charge distributions at intermediate-energies form the motivation of this work. Like the objects under study, the research presented in this thesis consists two main parts. Part 1 concerns an activation experiment that has been performed at the 'Kernfysisch Versneller Instituut' (Nuclear Physics Accelerator Institute) in Groningen, Netherlands, using the AGOR cyclotron. Fission product yields have been measured resulting from 190 MeV proton-induced fission of natW, 197Au, natPb, 208Pb and 232Th. In Chapter 2 the experimental set up is discussed, followed in Chapter 3 by a description of the data analysis. The results on the reconstructed mass yields and the total fission cross sections are presented in Chapter 4. Part 2 is of a theoretical nature. The objective is to compute fission product mass yields from intermediate-energy nucleon-induced reactions. In the approach presented here, two stages can be distinguished. In the first stage the fission cross section is determined for the various fissioning isotopes as a function of their excitation energy in competition with other processes like pre-equilibrium decay and particle evaporation. ALICE-91 is a nuclear reaction code that takes care of this first stage. The second stage consists of constructing the total fission-fragment mass and charge distributions from the different contributions of all the equilibrated fissioning systems. Hence, a model is needed that gives a prediction for the fission-product mass yields in a large range of mass, charge, and excitation energy of the fissioning nucleus. For this purpose, the multi-modal random neck-rupture model by Brosa is extended with temperature-dependent shell and pairing corrections and a temperature-dependent LDM. The combination of ALICE-91 and the modified Brosa approach is used for the analysis of the experiments given in the first part of this thesis as well as other available experimental results. Chapter 5 is dedicated to the extension of the Brosa model. The multi-chance fission treatment in ALICE-91 is discussed in Chapter 6. Chapter 7 contains the coupling between ALICE-91 and the revised Brosa model as well as the results obtained in this manner. Finally, a summary and outlook can be found in Chapter 8. Appendix A contains a list explaining all the abbreviations used in this manuscript. Parts of this work have already been published in journals and conference proceedings. refs.

2000-01-01

178

Nuclear fission of Fm isotopes  

International Nuclear Information System (INIS)

[en] Multi-modal fission has been systematically investigated for the series of isotopes of Fm and Cf. The multi-dimensional Langevin-type stochastic differential equation is used for the dynamical calculation. The primary fission mode changes from mass-asymmetric fission to mass-symmetric fission with the increase of neutron numbers for both Fm and Cf cases.

2010-06-01

179

Quasi-fission  

International Nuclear Information System (INIS)

Recent experimental and theoretical investigations have led to the characterization of a new reaction mechanism called quasi-fission. This process is characterized by the emergence of fission-like fragments, which do not originate from the fission decay of a compound nucleus formed by heavy-ion fusion, but rather from the break up of a short-lived intermediate complex. The occurrence of quasi-fission processes appear to be limited to heavy reaction systems and/or large angular momenta, although the present work demonstrates that such reactions occur for somewhat lighter projectiles than previously believed. It is thus shown that measurements of fragment angular distributions provide a signature for quasifission by being sensitive to whether or not a compound nucleus was formed during the reaction. From an analysis of such data it is concluded that the possibilities for synthesizing super-heavy elements in the range Z=112-116 are reduced considerably over previous estimates

1983-01-01

180

Quasi-fission  

Energy Technology Data Exchange (ETDEWEB)

Recent experimental and theoretical investigations have led to the characterization of a new reaction mechanism called quasi-fission. This process is characterized by the emergence of fission-like fragments, which do not originate from the fission decay of a compound nucleus formed by heavy-ion fusion, but rather from the break up of a short-lived intermediate complex. The occurrence of quasi-fission processes appear to be limited to heavy reaction systems and/or large angular momenta, although the present work demonstrates that such reactions occur for somewhat lighter projectiles than previously believed. It is thus shown that measurements of fragment angular distributions provide a signature for quasifission by being sensitive to whether or not a compound nucleus was formed during the reaction. From an analysis of such data it is concluded that the possibilities for synthesizing super-heavy elements in the range Z=112-116 are reduced considerably over previous estimates.

Back, B.B.

1983-01-01

 
 
 
 
181

INTRODUCTION TO NUCLEAR FISSION  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A short review is given of the basic observations in nuclear fission and their interpretation in terms of a semi-classical phenomenological theory. A more complete theoretical treatment is indicated in the last part.

Dietrich, K.

182

Fission products experimental programme  

Energy Technology Data Exchange (ETDEWEB)

The 'Fission Products (FPs)' experimental programme was carried out from 1998 to 2004 in CEA/Valduc Apparatus B in the framework of the IRSN-AREVA NC Common Interest Program dealing with 'burnup credit' studies. It aims at compensating for the lack of critical experiments with FPs in the literature and validating a selection of 6 stable, non-volatile, fission products representing half of the irradiated fuel absorption of all fission products: {sup 103}Rh, {sup 133}Cs, {sup 143}Nd, {sup 149}Sm, {sup 152}Sm and {sup 155}Gd. This paper provides a more exhaustive approach of the k{sub eff} results, uncertainties and tendencies associated with the different steps of the 'Fission Products' programme. (authors)

Leclaire, N. [Institut de Radioprotection et de Surete Nucleaire IRSN, BP 17, 92262 Fontenay-aux-Roses Cedex (France); Anno, J. [Commissariat a l' Energie Atomique CEA, Institut de Protection et de Surete Nucleaire (CEA/IPSN) (France); Girault, E. [Commissariat a l' Energie Atomique CEA, Centre de Valduc, 21120 Is-Sur-Tille (France); Letang, E. [Institut de Radioprotection et de Surete Nucleaire IRSN, BP 17, 92262 Fontenay-aux-Roses Cedex (France)

2006-07-01

183

Fission products experimental programme  

International Nuclear Information System (INIS)

[en] The 'Fission Products (FPs)' experimental programme was carried out from 1998 to 2004 in CEA/Valduc Apparatus B in the framework of the IRSN-AREVA NC Common Interest Program dealing with 'burnup credit' studies. It aims at compensating for the lack of critical experiments with FPs in the literature and validating a selection of 6 stable, non-volatile, fission products representing half of the irradiated fuel absorption of all fission products: 103Rh, 133Cs, 143Nd, 149Sm, 152Sm and 155Gd. This paper provides a more exhaustive approach of the keff results, uncertainties and tendencies associated with the different steps of the 'Fission Products' programme. (authors)

2006-01-01

184

Microscopic Theory of Fission  

International Nuclear Information System (INIS)

In recent years, the microscopic method has been applied to the notoriously difficult problem of nuclear fission with unprecedented success. In this paper, we discuss some of the achievements and promise of the microscopic method, as embodied in the Hartree-Fock method using the Gogny finite-range effective interaction, and beyond-mean-field extensions to the theory. The nascent program to describe induced fission observables using this approach at the Lawrence Livermore National Laboratory is presented.

2008-04-17

185

Singlet Exciton Fission Photovoltaics.  

UK PubMed Central (United Kingdom)

Singlet exciton fission, a process that generates two excitons from a single photon, is perhaps the most efficient of the various multiexciton-generation processes studied to date, offering the potential to increase the efficiency of solar devices. But its unique characteristic, splitting a photogenerated singlet exciton into two dark triplet states, means that the empty absorption region between the singlet and triplet excitons must be filled by adding another material that captures low-energy photons. This has required the development of specialized device architectures. In this Account, we review work to develop devices that harness the theoretical benefits of singlet exciton fission. First, we discuss singlet fission in the archetypal material, pentacene. Pentacene-based photovoltaic devices typically show high external and internal quantum efficiencies. They have enabled researchers to characterize fission, including yield and the impact of competing loss processes, within functional devices. We review in situ probes of singlet fission that modulate the photocurrent using a magnetic field. We also summarize studies of the dissociation of triplet excitons into charge at the pentacene-buckyball (C60) donor-acceptor interface. Multiple independent measurements confirm that pentacene triplet excitons can dissociate at the C60 interface despite their relatively low energy. Because triplet excitons produced by singlet fission each have no more than half the energy of the original photoexcitation, they limit the potential open circuit voltage within a solar cell. Thus, if singlet fission is to increase the overall efficiency of a solar cell and not just double the photocurrent at the cost of halving the voltage, it is necessary to also harvest photons in the absorption gap between the singlet and triplet energies of the singlet fission material. We review two device architectures that attempt this using long-wavelength materials: a three-layer structure that uses long- and short-wavelength donors and an acceptor and a simpler, two-layer combination of a singlet-fission donor and a long-wavelength acceptor. An example of the trilayer structure is singlet fission in tetracene with copper phthalocyanine inserted at the C60 interface. The bilayer approach includes pentacene photovoltaic cells with an acceptor of infrared-absorbing lead sulfide or lead selenide nanocrystals. Lead selenide nanocrystals appear to be the most promising acceptors, exhibiting efficient triplet exciton dissociation and high power conversion efficiency. Finally, we review architectures that use singlet fission materials to sensitize other absorbers, thereby effectively converting conventional donor materials to singlet fission dyes. In these devices, photoexcitation occurs in a particular molecule and then energy is transferred to a singlet fission dye where the fission occurs. For example, rubrene inserted between a donor and an acceptor decouples the ability to perform singlet fission from other major photovoltaic properties such as light absorption.

Lee J; Jadhav P; Reusswig PD; Yost SR; Thompson NJ; Congreve DN; Hontz E; Van Voorhis T; Baldo MA

2013-04-01

186

Natural occurring radioactive substances. Vol. 1  

International Nuclear Information System (INIS)

[en] Naturally occurring radioactive substances produced by cosmic rays of those of terrestrial origin are surveyed. The different radioactive decay series are discussed. Special emphasis is given to the element radium as regards its properties and distribution in different environmental samples. The properties of naturally occurring k-40 and its distribution in different natural media are also outlined. Induced radionuclides which are formed as a result of the interaction of cosmic rays with the constituents of the atmosphere are mentioned. In this respect the intensity of natural background radiation and the dose at different locations and levels is surveyed. Some regions of exceptionally high radioactivity which result in high exposure rates are mentioned. Monazite deposits and water springs are mentioned in some detail. The Oklo phenomenon as a natural reactor is also discussed. 8 tabs

1996-01-01

187

Nucleus-nucleus coherent Bremsstrahlung in 252Cf spontaneous fission  

International Nuclear Information System (INIS)

[en] The nature of high energy ?-ray spectra emitted in the spontaneous fission of 252Cf for energies above 10 MeV has been one of the fundamental problems of nuclear fission physics. The yield of the ?-ray in the energy range of 10 - 20 MeV is mainly associated with direct excitation of the giant dipole resonance from the daughter nuclei arising in the fission process. The calculations in different models differ by several orders of magnitude. The discrepancy in experimental and theoretical situations of coherent Bremsstrahlung from nuclear fission requires further investigation. For this reason, an extensive experiment was carried out using 252Cf source to investigate the photon emission accompanying the spontaneous fission at Variable Energy Cyclotron Centre (VECC), Kolkata

2009-01-01

188

Quantum Aspects of Low-Energy Nuclear Fission  

Science.gov (United States)

A helicity representation for fission product channels with correctly defined parity is used to describe neutron induced fission with arbitrary spin density matrix in ingoing channel. Recently obtained data for ROT effect in binary fission give evidence for high accuracy of the helicity representation just at scission. A general expression for differential cross-section of (n,f)-reaction is obtained. In the framework of multilevel, many channel R-matrix theory the reduced S-matrix for J?K effective channels rigorously derived. These channels include fission modes in natural way. Theoretical analysis of experimentally observed P-even and P-odd interference effects in low energy nuclear fission allows one to make some essential conclusions on basic mechanism of the process.

Furman, W.

2011-10-01

189

Nuclear waste criticality analysis. Final report, 1 July 1995--30 June 1996  

International Nuclear Information System (INIS)

The natural reactors that occurred in Gabon, Africa over 2 billion years ago present an interesting analog to the underground repositories proposed around the world for the long-term storage of high-level spent nuclear fuel. Many articles have been written concerning the low migration rates of actinides and fission products from the Oklo reactor sites, but Oklo also presents researchers with an opportunity to discover the conditions that led to nuclear criticality in uranium oxides with low enrichments. A computer model was developed to predict the conditions that were necessary to lead to criticality in the Oklo reactors. Critical core dimensions and infinite multiplication factors are presented as a function of time, the porosity of the host rock, and the water and uranium content of the sandstone deposits at Oklo

1995-07-01

190

Nuclear waste criticality analysis. Final report, 1 July 1995--30 June 1996  

Energy Technology Data Exchange (ETDEWEB)

The natural reactors that occurred in Gabon, Africa over 2 billion years ago present an interesting analog to the underground repositories proposed around the world for the long-term storage of high-level spent nuclear fuel. Many articles have been written concerning the low migration rates of actinides and fission products from the Oklo reactor sites, but Oklo also presents researchers with an opportunity to discover the conditions that led to nuclear criticality in uranium oxides with low enrichments. A computer model was developed to predict the conditions that were necessary to lead to criticality in the Oklo reactors. Critical core dimensions and infinite multiplication factors are presented as a function of time, the porosity of the host rock, and the water and uranium content of the sandstone deposits at Oklo.

Culbreth, W.G.

1996-07-03

191

Neutrino-driven nucleon fission reactors: Supernovae, quasars, and the big bang  

International Nuclear Information System (INIS)

[en] The purpose of this work is to establish the existence of naturally occurring celestial neutrino-driven nucleon fission chain reaction reactors as the first step in the development of controlled nucleon fission reactors on Earth. Celestial nucleon fission reactors provide functioning models that serve as starting points for reactor development. Recognizing supernovae, quasars, and the Big Bang as functioning neutrino-driven nucleon fission reactors presents the nuclear industry with a new and significant challenge. That challenge is our technological prowess to achieve a controlled nucleon fission chain reaction using the Earth's resources

1992-01-01

192

Fission product detection  

International Nuclear Information System (INIS)

[en] The response of photovoltaic cells to heavy ions and fission products have been tested on beam. Their main advantages are their extremely low price, their low sensitivity to energetic light ions with respect to fission products, and the possibility to cut and fit them together to any shape without dead zone. The time output signals of a charge sensitive preamplifier connected to these cells allows fast coincidences. A resolution of 12ns (F.W.H.M.) have been measured between two cells

1987-01-01

193

Low energy nuclear fission  

International Nuclear Information System (INIS)

In these lectures we present the liquid drop model of fission and compare some of its prediction with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. We then discuss, using the example of the oscillator model, the generality of shell effects. We show how a synthesis of the liquid drop model and of the shell model can be made using the Strutinsky shell averaging procedure. Some experimental data related to the existence of shape isomers are presented and discussed. We conclude by discussing some aspects, both experimental and theoretical, of fission dynamics

1982-02-06

194

Microscopic description of induced fission  

Science.gov (United States)

Selected aspects of the description of neutron-induced fission in 240Pu in the framework of the nuclear energy density functional theory at finite temperature are presented. In particular, we discuss aspects pertaining to the choice of thermodynamic state variables, the evolution of fission barriers as function of the incident neutron energy, and the temperatures of the fission fragments.

Schunck, Nicolas

2013-04-01

195

Fission rate sensitivities and fission fragment ranges for uranium and thorium-bearing materials irradiated with 252 Cf neutron source  

International Nuclear Information System (INIS)

The induced fission reactions of 235 U (n, f), 238 U (n,f) and 232Th (n, f) based on the activation of natural uranium and thorium in samples with 252Cf, neutron source, have been evaluated. The obtained results are the average of three samples from each test material (SRM 2710 Montana soil and Zirconia). The prepared samples have been configured in the so-called compensated - beam geometryin which both gamma spectrometry jointly with solid state nuclear track detector techniques, revealed the fission rate sensitivity of 4.64 x 107 fission per gram per second per neutron (F.h1. S1.n1), for zirconia as obtained by gamma activity arising from 134 I fission product (as a good monitor which is produced only from fissions), and the related value for SRM 2710 soil is 5.22 x 108 (F.g1 S1 .n1). while the obtained values of the mean fission fragment ranges in SRM 2710 and zirconia as estimated from the fission track densities (by CR-39) and fission rates (by gamma spectrometry) are 3.97 x 10 3 g. cm2 respectively which reveal good agreement with experiments and calculations done hitherto.

2000-01-01

196

Computer code development programs at JAERI on fission product behavior  

International Nuclear Information System (INIS)

As a part of computer code development programs on severe accident analysis, computer programs HORN and REMOVAL, are being developed for analysis of fission product release and transport in primary coolant system and containment vessel. HORN is designed to calculate fission product release and transport in primary coolant system and the code is capable of predicting chemical forms of volatile fission products in a leak path based upon equilibrium assumptions. REMOVAL is to calculate aerosol removal by natural mechanisms as well as engineered safety features in the containment vessel. The model includes steam condensation onto aerosol particles. Results of sensitivity analyses are presented along with description of the models used in each code.

1985-01-01

197

Fission product data library  

International Nuclear Information System (INIS)

[en] A library is described of data for 584 isotopes of fission products, including decay constants, branching ratios (both burn-up and decay), the type of emitted radiation, relative and absolute yields, capture cross sections for thermal neutrons, and resonance integrals. When a detailed decay scheme is not known, the mean energies of beta particles and neutrino and gamma radiations are given. In the ZVJE SKODA system the library is named BIBFP and is stored on film No 49 of the NE 803 B computer. It is used in calculating the inventory of fission products in fuel elements (and also determining absorption cross sections for burn-up calculations, gamma ray sources, heat generation) and in solving radioactivity transport problems in the primary circuit. It may also be used in the spectrometric method for burn-up determination of fuel elements. The library comprises the latest literary data available. It serves as the basis for library BIBGRFP storing group constants of fission products with independent yields of isotopes from fission. This, in turn, forms the basis for the BIBDN library collecting data on the precursors of delayed neutron emitters. (author)

1975-01-01

198

Transient fission and multiplicities  

Energy Technology Data Exchange (ETDEWEB)

The de-excitation chain of the compound nucleus is treated, including the transient character of the fission process. The equations can handle all type of emission and take into account all the nuclei of the decay chain. The results show that the particles behave differently under the transient regime. (orig.).

Hassani, S.

1989-09-01

199

Radiation Detection from Fission  

Energy Technology Data Exchange (ETDEWEB)

This report briefly describes the neutrons and gamma rays emitted in fission, briefly discusses measurement methods, briefly discusses sources and detectors relevant to detection of shielded HEU in sealand containers, and lists the measurement possibilities for the various sources. The brief descriptions are supplemented by reference.

Mihalczo, J.

2004-11-17

200

Modulation of intestinal crypt fission in the rat  

International Nuclear Information System (INIS)

Crypt fission, the longitudinal splitting of intestinal crypts, was first noted almost 100 years ago, but has received only a modest amount of attention. Although fissioning crypts have been observed by a number of investigators and referred to by different terms (splitting bifurcating, branching) the full significance of their occurrence has not been established. The aims of this investigation were to: (1) verify that crypt fission is responsible for the formation of new crypts, (2) determine if crypt fission is a local or systemic response to intestinal trauma, and (3) determine if changes in crypt cell proliferation, crypt number, crypt density, or any combination of these factors, operate to modulate crypt fission. These studies can be grouped into two general categories: (1) those based on the response to intestinal injury which include radiation injury, resection of 70% of the small bowel, and treatment with the cytotoxic drugs mechlorethamine and cyclophosphamide, (2) those based on the modification of the crypt cell proliferation rate with possible influences on the naturally high incidence of crypt fission in the juvenile rat. The results from this investigation showed that: (1) crypts of the juvenile and adult rat were formed by crypt fission, (2) crypt fission was initiated by a reduction in crypt density, (3) crypt fission was under local control, which was related to crypt density, (4) a substantial reduction in the rate of crypt cell proliferation caused no change in the percentage of crypt fission but prevented the formation of new crypts, probably by preventing the fissure from traversing the length of the crypt

1985-01-01

 
 
 
 
201

Modulation of intestinal crypt fission in the rat  

Energy Technology Data Exchange (ETDEWEB)

Crypt fission, the longitudinal splitting of intestinal crypts, was first noted almost 100 years ago, but has received only a modest amount of attention. Although fissioning crypts have been observed by a number of investigators and referred to by different terms (splitting bifurcating, branching) the full significance of their occurrence has not been established. The aims of this investigation were to: (1) verify that crypt fission is responsible for the formation of new crypts, (2) determine if crypt fission is a local or systemic response to intestinal trauma, and (3) determine if changes in crypt cell proliferation, crypt number, crypt density, or any combination of these factors, operate to modulate crypt fission. These studies can be grouped into two general categories: (1) those based on the response to intestinal injury which include radiation injury, resection of 70% of the small bowel, and treatment with the cytotoxic drugs mechlorethamine and cyclophosphamide, (2) those based on the modification of the crypt cell proliferation rate with possible influences on the naturally high incidence of crypt fission in the juvenile rat. The results from this investigation showed that: (1) crypts of the juvenile and adult rat were formed by crypt fission, (2) crypt fission was initiated by a reduction in crypt density, (3) crypt fission was under local control, which was related to crypt density, (4) a substantial reduction in the rate of crypt cell proliferation caused no change in the percentage of crypt fission but prevented the formation of new crypts, probably by preventing the fissure from traversing the length of the crypt.

St. Clair, W.H.

1985-01-01

202

Measurement of the Ratio of Fissions in U238 to Fissions in U233 Using 1.60 Mev Gamma Rays of the Fission Product La140  

International Nuclear Information System (INIS)

This paper describes a method for measuring ?28, the ratios of fissions in U238 to fissions in U235. The method was developed as a part of the D2O lattice programme at the Massachusetts Institute of Technology (MIT) ; however, it can be used for measurements in any thermal reactor of natural or slightly enriched uranium. The fast fission factor in uranium cannot be measured directly. It is, however, related to ?28 which can be measured: #Greek Lunate Epsilon Symbol# =1 + C?28 , where C is a constant involving nuclear properties of U238 and U235: Previous methods of measuring ?28 utilize a comparison of fission-product gamma or beta activity in foils of differing U235 concentration irradiated within a fuel rod in the lattice. A double fission chamber is then used to relate the U238 and U235 fission product activity to the ratio of the corresponding fission rates. Most of the experimental uncertainty associated with the measurement of ?28 a is generally attributed to the fission chamber calibration. The method developed at MIT avoids the need for a fission chamber calibration and is accomplished directly with foils irradiated within a fuel rod in the lattice. Two foils of differing U235 concentration are irradiated and allowed to cool for at least a week. The relative activity of the 1.60 MeV gamma ray of the fission product La140 is determined for the two foils. This ratio, the foil weights and atomic densities, and the ratio of fission yields ?25/?28 for La140 are then used to determine ?28. This value of ?28 is used to calibrate simpler measurements in which the relative gamma activity above 0.72 MeV is determined for sets of foils irradiated in fuel rods of the lattices of interest. The energy 0.72 MeV is a convenient discrimination level, as it is the maximum energy of Bremsstrahlung from 2.3-d Np239. This method appears to offer the advantages of direct measurement and increased accuracy (the major uncertainty being the ratio of ?25/?28 La140). In addition, the results can be improved as better fission product yield ratio data become available, and the method facilitates comparison of ?28 values obtained by different laboratories. (author). (author)

1964-01-01

203

Fission Target Design  

CERN Multimedia

The report describes the technical concepts and the main parameters adopted for the first design for the fission target of the multi-MW Target Station of EURISOL. Starting from the dimensions of liquid neutron converter as defined by Baseline Design, eight fission target containers were disposed around the converter and closely coupled to eight ion-sources. Two versions of design are presented , proposing different solutions at all levels: target geometry, heating resistance, thermal expansion compensation, supporting in the view of remote handling, type of ion source, current and high voltage powering scheme, cooling and others. At this stage of design many details are skipped, while the dimensions of different components are not yet the result of mechanical/electrical/thermal calculations.

F. Negoita, L. Serbina, L. Tecchio, E. Udup

204

SHAPED FISSIONABLE METAL BODIES  

Science.gov (United States)

A technique is presented for grooving the surface of fissionable fuel elements so that expansion can take place without damage to the interior structure of the fuel element. The fissionable body tends to develop internal stressing when it is heated internally by the operation of the nuclear reactor and at the same time is subjected to surface cooling by the circulating coolant. By producing a grooved or waffle-like surface texture, the annular lines of tension stress are disrupted at equally spaced intervals by the grooves, thereby relieving the tension stresses in the outer portions of the body while also facilitating the removal of accumulated heat from the interior portion of the fuel element.

Wigner, E.P.; Williamson, R.R.; Young, G.J.

1958-10-14

205

Fusion-fission dynamics  

International Nuclear Information System (INIS)

Classical dynamical calculations of the heavy ion induced fission process for the reactions 40Ar+141Pr, 20Ne+165Ho and 12C+175Lu leading to the iridium like nucleus have been performed. As a result prescission lifetimes were obtained and compared with the experimental values. The agreement between the calculated and experimental lifetimes indicates that the one-body dissipation picture is much more relevant in describing the fusion-fission dynamics than the two-body one. Somewhat bigger calculated times than the experimental ones in case of the C+Lu reaction at 16 MeV/nucleon may be a signal on the energy range applicability of the one-body dissipation model. (author)

1991-01-01

206

[Fission product yields of 60 fissioning reactions]. Final report  

Energy Technology Data Exchange (ETDEWEB)

In keeping with the statement of work, I have examined the fission product yields of 60 fissioning reactions. In co-authorship with the UTR (University Technical Representative) Talmadge R. England ``Evaluation and Compilation of Fission Product Yields 1993,`` LA-UR-94-3106(ENDF-349) October, (1994) was published. This is an evaluated set of fission product Yields for use in calculation of decay heat curves with improved accuracy has been prepared. These evaluated yields are based on all known experimental data through 1992. Unmeasured fission product yields are calculated from charge distribution, pairing effects, and isomeric state models developed at Los Alamos National Laboratory. The current evaluation has been distributed as the ENDF/B-VI fission product yield data set.

Rider, B.F.

1995-05-01

207

New developments in nuclear fission  

International Nuclear Information System (INIS)

[en] A few recently observed new effects in nuclear fission are reviewed from the experimental side and theoretical explanations are indicated: (i) The structures in the mass yields and in the maximum fragment kinetic energies in cold fission are due to Coulomb effects; (ii) Mass-symmetric fission of even-even nuclei does not proceed by splitting the nucleus into two equal parts and the fragments are differently deformed; (iii) The dip in the total fragment kinetic energy at symmetry is due to a different symmetric fission barrier; (iv) In analogy to the cold compact fission events with highest kinetic energy, also those events of lowest kinetic energy but highest deformation are cold at the scission point; (v) Cold fission proceeds close to the saddle point. (orig.)

1987-01-01

208

Disintegration constant of uranium-238 by spontaneous fission redetermined by glass track method  

International Nuclear Information System (INIS)

The disintegration constant of U238 by spontaneous fission using glass as fission fragment detector was redetermined. A film of natural uranium (UO3) prepared by chemical methods on the glass lamina was used in a long time experience of exposure (about 16 years). The good conditions of sample preparation and storage allow to observe, after chemical etching, fission fragment tracks. (M.C.K.).

1978-01-01

209

Fission hindrance in hot nuclei  

Energy Technology Data Exchange (ETDEWEB)

The role of dynamics in fission has attracted much interest since the discovery of this process over fifty years ago. However, the study of the dynamical aspects of fission was for many years hampered by the lack of suitable experimental observables against which theoretical calculations could be tested. For example, it was found that the total kinetic energy release in fission can be described equally well by very different dissipation mechanisms, namely the wall formula, that is based on the collisions of the nucleons with the moving wall of the system, as well as a bulk viscosity of the nuclear matter. Although early theoretical work suggested that the fission process may be described as a diffusion process over the fission barrier, this was largely forgotten because of the success of a purely statistical model which instead of enumerating the ultimate final states of the process argues that the fission rate is determined at the {open_quote}transition state{close_quote} as the system traverses the fission saddle point. It was therefore significant when Gavron showed that the transition state model was unable to describe the number of neutrons emitted prior to scission at high excitation energy in reactions of {sup 16}O+{sup 142}Nd. Subsequent experimental work using different methods to measure the fission dissipation/viscosity has confirmed these initial observations. It was therefore very surprising when Moretto in recent publications concluded that their analysis of fission excitation functions obtained with a and {alpha} and {sup 3}He induced projectiles was perfectly in accord with the transition state model and left no room for fission viscosity. In this paper we`ll show that Moretto`s analysis is flawed by assuming first chance fission only (in direct contradiction to the experimental observation of pre-scission neutron emission in heavy-ion induced fission), and reveal why the systematics presented by Moretto looked so convincing despite these flaws.

Back, B.B.; Hofman, D.J.; Nanal, V.

1997-07-01

210

Fission, fusion and the energy crisis  

Energy Technology Data Exchange (ETDEWEB)

A relatively non-technical survey of nuclear fission and nuclear fusion power sources, this book is intended for the undergraduate student. It begins with an analogy of our present level of energy consumption with the practice of living on accumulated capital reserves in which uranium and fossil fuel use represents capital depletion and renewable energy sources and fusion energy represent long-range investment planning that fails to eliminate the need for conservation. Subsequent chapter headings are: The Atom and Its Nucleus, Mass, and Energy; Fission and the Bomb; The Natural Uranium Reactor; Enriched Reactors; Control and Safety; Long-term economics; The Breeder Reactions and Nuclear Fuel Reserves; Short-term Economics; the Cost Per Kilowatt Hour; National Nuclear Power Programmes; Nuclear Power and the Environment; Renewable Energy Sources; and The Fusion Programme. 49 references, 55 figures, 7 tables. (DCK)

Hunt, S.E.

1980-01-01

211

Nature  

Science.gov (United States)

Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance, and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public. Nature publishes more articles than any other multidisciplinary journal, and retains its position as the most cited weekly science journal. The site provides free access to news stories in the latest issue; access to research articles, and to the Nature archive, is by subscription.

212

Fission: The first 50 years  

International Nuclear Information System (INIS)

The possibility of fission had been largely unanticipated prior to its discovery in 1938. This process, with its dramatically large energy release and its formation of previously unknown nuclides, immediately captured the imagination of the scientific community. Both theoretical and experimental developments occurred at a rapid pace. I will begin my discussion of fission with the far-reaching paper of Bohr and Wheeler, who in little more than half a year laid out a framework for understanding many features of the fission process. I will then turn to our current understanding of a number of aspects of fission. One of these is the pronounced tendency of many nuclear species to fission asymmetrically. In fact, the discovery of fission was based on the identification of barium isotopes produced in asymmetric fission. The dramatic changes in the preferred mass division and kinetic energy release with the addition of only a few neutrons to the spontaneously fissioning Fermium isotopes will be emphasized. The problem of the dynamics of saddle to scission will be discussed---this is one aspect of fission for which we do not have all the answers. Another dynamical effect to be discussed is the apparent failure of transition state theory at high excitation energies. The role of single particle (shell) effects in enriching the structure if the potential energy surface will be explored. Spontaneously fissioning isomers and intermediate structure resonances will be discussed. The recognition that short-lived fission isomers are superdeformed shape isomers has been followed by the recent observation of superdeformed shape isomers in the rare earth region. 18 refs., 3 figs

1989-01-01

213

Some aspects of nuclear fission  

International Nuclear Information System (INIS)

Fission is still actively studied both from the theoretical and experimental points of view in order to know better the statics and the dynamics of the process. A good knowledge of the fission barrier has been obtained by using the Strutinsky procedure. Good agreement is now reached between double-humped fission barrier heights and experiments, except for light actinides for which the calculated inner hump is too low to explain the fission data. Closer examination of the calculations together with the analysis of the best fission data for 230Th, 231Pa and 232Th neutron-induced fission lead to the conclusion that the fission barrier for 231Th is triple-humped whereas the data for 231Pa and 232Th, though consistent with a triple-humped barrier, do not provide indisputable evidence for its existence. The dynamics, in contrast to the statics, are poorly known. Detailed results have been obtained from the measurements of fragment properties for thermal-neutron induced fission of 235U. These results can be interpreted as moderate dissipation between saddle point and scission. Yet, other recent results obtained from ''cold fragmentation'' in thermal-neutron induced fission in 233U and 235U are not consistent with this hypothesis. Rather, according to recent microscopic calculations of the potential energy surface, cold fragmentation seems to stem from a new mechanism whereby the fissioning nucleus undergoes a sudden shape transition from the fission to the fusion valley. In this respect, cold fragmentation would be similar to the inverse process for heavy-ion fusion

1981-07-03

214

Baby fission chambers  

International Nuclear Information System (INIS)

The present report is intended, on the one band, as a study of the main types of fission chambers produced to date, and on the other, to deal more generally with this type of detector. Originally, it was with a view to the charting of neutron scatter in 'Proserpine' that the authors undertook the study of these chambers. During the course of the task, it was considered worth tbe trouble of developing its scope to include a more general application: neutron scatter measurement of various energy neutrons within a reduced volume with slight local disturbance. (author)

1957-01-01

215

Post-scission fission theory: Neutron emission in fission  

Energy Technology Data Exchange (ETDEWEB)

A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N (E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N (E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N (E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches.

Madland, D.G.

1997-11-01

216

Post-scission fission theory: neutron emission in fission  

International Nuclear Information System (INIS)

A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity ?-barp. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and ?-barp upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, En), where En is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. (author)

1996-05-17

217

Natural repository analogue program. Progress report, January 1-March 30, 1982  

International Nuclear Information System (INIS)

Lead and uranium isotopic abundances in rocks from the Oklo mine show large deficiencies of radiogenic lead in the mineralized regions and enormous excesses of this element outside the uraniferous zones. A fracture lined with secondary minerals and its host rock from distances as far as approx. 13 meters away contain lead that was deposited contemporaneously. The isotopic composition of lead in these samples varies systematically as a function of distance from the fracture. This regularity may reflect the nature of the processes that transported lead from the ores and deposited it in the surrounding rocks

1982-01-01

218

Natural repository analogue program. Progress report, January 1-March 30, 1982  

Energy Technology Data Exchange (ETDEWEB)

Lead and uranium isotopic abundances in rocks from the Oklo mine show large deficiencies of radiogenic lead in the mineralized regions and enormous excesses of this element outside the uraniferous zones. A fracture lined with secondary minerals and its host rock from distances as far as approx. 13 meters away contain lead that was deposited contemporaneously. The isotopic composition of lead in these samples varies systematically as a function of distance from the fracture. This regularity may reflect the nature of the processes that transported lead from the ores and deposited it in the surrounding rocks.

Curtis, D.B. (comp.)

1982-06-01

219

Recent progress in nuclear fission  

International Nuclear Information System (INIS)

[en] Important progress have been performed during the last years in nuclear fission; some results are presented to illustrate these progress[fr] Des progres importants on ete realises ces dernieres annees dans la comprehension du mecanisme de fission nucleaire; nous presentons quelques resultats pour illustrer ces progres

1981-02-06

220

Fission throughout the periodic table  

International Nuclear Information System (INIS)

[en] The dualistic view of fission and evaporation as two distinct compound nucleus processes is substituted with a unified view in which fission, complex fragment emission, and light particle evaporation are seen as different aspects of a single process. 47 refs., 22 figs

1989-01-01

 
 
 
 
221

Fission Dynamics of Compound Nuclei  

CERN Document Server

Collisions between $^{248}$Cm and $^{48}$Ca are systematically investigated by time-dependent density functional calculations with evaporation prescription. Depending on the incident energy and impact parameter, fusion, deep-inelastic and quasi-fission events are expected to appear. In this paper, possible fission dynamics of compound nuclei is presented.

Iwata, Yoritaka

2012-01-01

222

The fission-track analysis: An alternative technique for provenance studies of prehistoric obsidian artefacts  

CERN Multimedia

Comparison of fission-track parameters - age and track densities - is an alternative tool for correlating obsidian artefacts with their potential natural sources. This method was applied by different fission-track groups in various regions and results were compared with those obtained using the more popular provenance identification techniques based on chemical composition studies. Hundreds of analyses prove that fission-track dating is a complementary technique which turns out to be very useful, specially when the chemical composition does not fully discriminate different sources. Archaeologically significant results were obtained applying the fission-track analysis in various regions of earth.

Bellot-Gurlet, L; Dorighel, O; Oddone, M; Poupeau, G; Yegingil, Z

1999-01-01

223

The fission-track analysis: An alternative technique for provenance studies of prehistoric obsidian artefacts  

Energy Technology Data Exchange (ETDEWEB)

Comparison of fission-track parameters - age and track densities - is an alternative tool for correlating obsidian artefacts with their potential natural sources. This method was applied by different fission-track groups in various regions and results were compared with those obtained using the more popular provenance identification techniques based on chemical composition studies. Hundreds of analyses prove that fission-track dating is a complementary technique which turns out to be very useful, specially when the chemical composition does not fully discriminate different sources. Archaeologically significant results were obtained applying the fission-track analysis in various regions of earth.

Bellot-Gurlet, L.; Bigazzi, G.; Dorighel, O.; Oddone, M.; Poupeau, G.; Yegingil, Z

1999-06-01

224

The fission-track analysis: An alternative technique for provenance studies of prehistoric obsidian artefacts  

International Nuclear Information System (INIS)

[en] Comparison of fission-track parameters - age and track densities - is an alternative tool for correlating obsidian artefacts with their potential natural sources. This method was applied by different fission-track groups in various regions and results were compared with those obtained using the more popular provenance identification techniques based on chemical composition studies. Hundreds of analyses prove that fission-track dating is a complementary technique which turns out to be very useful, specially when the chemical composition does not fully discriminate different sources. Archaeologically significant results were obtained applying the fission-track analysis in various regions of earth

1999-01-01

225

Study on the One-Nucleon Channels of O exp 16 Nucleus Fission in Correlation Experiments.  

Science.gov (United States)

For the purpose of studying the mechanism of reactions and the nature of a fissioning nucleus continuous spectrum reactions of the one-nucleon fission of sup(16)O( pi sup(+), pi sup(+)p)sup(15)Nsup(*) nucleus and sup(16)O( pi sup(+), pi sup(+)n)sup(15)Osu...

I. V. Kirpichnikov V. A. Kuznetsov A. S. Starostin E. F. Kislyakov V. L. Korotkikh

1981-01-01

226

Nature’.  

Directory of Open Access Journals (Sweden)

Full Text Available Nature. Le monde bio-physique, pour autant qu’il concerne la société. La nature est l’ensemble des phénomènes, des connaissances, des discours et des pratiques résultant d’un processus sélectif d’incorporation des processus physiques et biologiques par la société. Bien loin d’être une instance extérieure à la société, un système autonome, la nature est une construction sociale, et elle se trouve intégrée, sous différents aspects, dans le moindre objet de société et ...

Michel Lussault

2003-01-01

227

The use of recoil for the separation of uranium fission products  

International Nuclear Information System (INIS)

The recoil distance of fission fragments in U3O8 is about 8 microns. By using highly diluted suspensions of uranium oxide particles having dimension much smaller than this figure (mean diameter 0,5 micron), we were able to study the re-adsorption of fission products on uranium oxide. Separation results have been studied as a function of the nature of the irradiation medium (solid or liquid) and the separation medium, of particle size and of concentration of particles in the dispersing medium. Decay curves can be used to discriminate between 239Np and mixed fission products. Most of the 239Np is found in the U3O8 particles. The location of fission products in solid dispersing media has been determined, fission products being found always inside the dispersing medium particles. The results obtained can be applied to the rapid separation of short-lived fission products from a uranium-free starting material. (author)

1959-01-01

228

Fifty years with nuclear fission  

International Nuclear Information System (INIS)

The news of the discovery of nuclear fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fifieth anniversary of its discovery by holding a topical meeting entitled, ''Fifty Years with Nuclear Fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent development in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicated a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two fully days of sessions (April 27 and 28) at the main site of the NIST in Gaithersburg, Maryland. The wide range of topics covered in this Volume 1 by this topical meeting included plenary invited, and contributed sessions entitled: Preclude to the First Chain Reaction -- 1932 to 1942; Early Fission Research -- Nuclear Structure and Spontaneous Fission; 50 Years of Fission, Science, and Technology; Nuclear Reactors, Secure Energy for the Future; Reactors 1; Fission Science 1; Safeguards and Space Applications; Fission Data; Nuclear Fission -- Its Various Aspects; Theory and Experiments in Support of Theory; Reactors and Safeguards; and General Research, Instrumentation, and By-Product. The individual papers have been cataloged separately.

1989-01-01

229

Fission fragment angular distribution in heavy ion induced fission  

Directory of Open Access Journals (Sweden)

Full Text Available   We have calculated the fission fragment angular anisotropy for 16O + 232Th,12C + 236U , 11B + 237 Np , 14 N + 232 Th , 11B + 235U , 12C + 232Th systems with the saddle point statistical model and compared the fission fragment angular anisotropy for these systems. This comparison was done with two methods a) without neutron correction and b) with neutron correction. Also we studied normal and anomalous behavior of the fission fragment angular anisotropy. Finally, we have predicted the average emitted neutron from compound nuclei considering the best fit for each system.

S. Soheyli; I. Ziaeian

2006-01-01

230

Pulsed fission/fusion hybrid engines  

International Nuclear Information System (INIS)

Research into high-thrust, high-specific impulse rocket engines using energy from nuclear reactions which has been conducted at this organization will be discussed. The engines are all conceptual in nature, yet are within the realization of conventional or near-term technology. The engine concepts under study at Foundation, Inc. are designed to obviate or minimize these negative effects of the ORION scheme. By using non-chemical triggers to initiate a non-breakeven fusion reaction at the core of a target composed of both fission and fusion fuel, it should be possible to employ the fusion neutrons thus produced to begin a fission reaction in U-235 or Pu-239. Since the density of the target can be increased by as much as a factor of 250 through compression of the pellet, the amount of fission material necessary to produce a critical mass can be greatly reduced. (This also means that the amount of fission products produced for a giventhrust level is also reduced from the ORION levels.) Coupling this eeffect to the large number of 14 MeV fusion neutrons produced early in the compression process and subsequently to the heating of some additional fusion fuel surrounding the critical mass leads to the very efficient burnup of the target. This insures both high yield from the target as well as low cost per MJ energy released. Finally, the use of such small pellets allows the scale of the energy released to be tailored to a level usable in rocket engines of a few tens of tons thrust level. (orig.)

1979-09-23

231

On prompt fission neutrons  

International Nuclear Information System (INIS)

[en] Results of calculations of prompt neutron emission characteristics are presented for the spontaneous fission of 252Cf. The average number ?(A) and the average center of mass kinetic energy ?(A) of the neutrons as well as the total neutron spectra are calculated in terms of the fragment mass. The available excitation energies of the fragment pairs are the input data, divided between the fragments by a thermal equilibrium assumption taking into account the equilibrium statistical fluctuations too. The total angular and energy distributions in the laboratory frame are built up of those of the individual fragments. The evaporation calculations show that the high energy behaviour of the spectra is governed rather by the temperatures than by the details of the individual cascade spectrum forms. The experimental data are reproduced by the calculated ones fairly well, so there is no need for assuming existence of additional scission neutrons. (author) 24 refs.; 4 figs

1989-01-01

232

Fifty years with nuclear fission  

International Nuclear Information System (INIS)

The news of the discovery of nucler fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fiftieth anniversary of its discovery by holding a topical meeting entitled, ''Fifty years with nuclear fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent developments in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicating a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two full days of sessions (April 27 and 28) at the main sites of the NIST in Gaithersburg, Maryland. The wide range of topics covered by Volume 2 of this topical meeting included plenary invited, and contributed sessions entitled, Nuclear fission -- a prospective; reactors II; fission science II; medical and industrial applications by by-products; reactors and safeguards; general research, instrumentation, and by-products; and fission data, astrophysics, and space applications. The individual papers have been cataloged separately.

1989-01-01

233

PhET Simulation: Nuclear Fission  

Science.gov (United States)

This webpage contains a simulation that provides qualitative pictures of alpha radiation, fission of a Uranium 235 nucleus, and controlled and uncontrolled nuclear chain reactions. Evolution of the processes over time is shown. Variables such as the number of nuclei and the containment of reactions can be altered to demonstrate the statistical nature of the reactions. Sample learning goals as well as a teacher's guide for the simulation are available. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.

2006-10-21

234

The spectroscopy of fission fragments  

International Nuclear Information System (INIS)

High-resolution measurements on ? rays from fission fragments have given a wealth of information on neutron-rich nuclei and on the mechanism of the fission process. In recent years important data have been obtained on the yrast and near-yrast structures of neutron-rich nuclei with up to ten more neutrons than the nearest stable isotope. This paper discusses the scope of measurements which can be made on prompt gamma rays from spontaneous fission fragments, the techniques used in the experiments and some results recently obtained. (author)

1997-01-01

235

Gamma Radiation from Fission Fragments  

International Nuclear Information System (INIS)

The gamma radiation from the fragments of the thermal neutron fission of 235U has been investigated, and the preliminary data are presented here with suggestions for further lines of research and some possible interpretations of the data. The data have direct bearing on the fission process and the mode of fragment de-excitation. The parameters measured are the radiation decay curve for the time interval (1 - 7) x 10-10 sec after fission, the photon yield, the total gamma ray energy yield, and the average photon energy. The last three quantities are measured as a function of the fragment mass

1969-01-01

236

Fission track studies of tektites  

International Nuclear Information System (INIS)

The fission track analysis method was used for the age determination of tektites. The tektite samples were obtained from Hainan Island and Leizhou Peninsula. The method consists in cutting and polishing two sections of a sample, irradiating one of these with a known thermal neutron flux (5.90 x 1015/cm2), etching each section identically with hydrofluoric acid, and then comparing the fission track densities in two cases with a microscope. Their fission track age is found to be around 0.7 Ma.

1991-01-01

237

The spectroscopy of fission fragments  

Energy Technology Data Exchange (ETDEWEB)

High-resolution measurements on {gamma} rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author) 24 refs., 8 figs., 1 tab.

Phillips, W.R. [Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL (United Kingdom); Collaboration: La Direction des Sciences de la Matiere du CEA (FR); Le Fonds National de la Recherche Scientifique de Belgique (BE)

1998-12-31

238

The spectroscopy of fission fragments  

International Nuclear Information System (INIS)

High-resolution measurements on ? rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author)

1998-01-01

239

Energy partition in nuclear fission  

International Nuclear Information System (INIS)

A scission point model (two spheroid model TSM) including semi-empirical temperature-dependent shell correction energies for deformed fragments at scission is presented. It has been used to describe the mass-asymmetry-dependent partition of the total energy release on both fragments from spontaneous and induced fission. Characteristic trends of experimental fragment energy and neutron multiplicity data as function of incidence energy in the Th-Cf region of fissioning nuclei are well reproduced. Based on model applications, information on the energy dissipated during the descent from second saddle of fission barrier to scission point have been deduced. (author). 39 refs, 13 figs

1990-01-01

240

Theory of nuclear fission: a review  

International Nuclear Information System (INIS)

General properties of nuclear fission are reviewed and related to our present knowledge of fission theory. For this purpose the basic reasons for the shape of the fission barriers are discussed and their consequences compared with experimental results on barrier shapes and structures. Special emphasis is put on the asymmetry of the fission barriers and mass-distributions and its relation to the shells of the nascent fragment shells. Finally the problem of calculating fission cross sections is discussed

1976-06-28

 
 
 
 
241

Charge distribution of fission products in the reaction 209Bi(12C, fission)  

International Nuclear Information System (INIS)

The yields of about twenty five fission products in the system 209Bi(12C, fission) have been measured by ?-ray analysis without chemical separation, at excitation energies of 40, 53 and 66 MeV in the 221Ac* compound nucleus. The data were used to calculate the most probable charge Zsub(p) for each mass number. On the assumption that Zsub(p) varies monotonically with A, simple functions were tested and two were found to account adequately for the data. These functions were used to calculate the mean number of emitted neutrons (bar ?) at each energy. Bar ? increases with energy at a rate of about 0.054 neutrons MeV-1. The nature of the charge distribution in the primary fragments is discussed briefly. (author).

1977-01-01

242

Background radiation from fission pulses  

International Nuclear Information System (INIS)

[en] Extensive source terms for beta, gamma, and neutrons following fission pulses are presented in various tabular and graphical forms. Neutron results from a wide range of fissioning nuclides (42) are examined and detailed information is provided for four fuels: 235U, 238U, 232Th, and 239Pu; these bracket the range of the delayed spectra. Results at several cooling (decay) times are presented. For ?- and ? spectra, only 235U and 239Pu results are given; fission-product data are currently inadequate for other fuels. The data base consists of all known measured data for individual fission products extensively supplemented with nuclear model results. The process is evolutionary, and therefore, the current base is summarized in sufficient detail for users to judge its quality. Comparisons with recent delayed neutron experiments and total ?- and ? decay energies are included. 27 refs., 47 figs., 9 tabs

1988-01-01

243

Protactinium neutron-induced fission up to 200 MeV  

Directory of Open Access Journals (Sweden)

Full Text Available The theoretical evaluation of 230-233Pa(n,F) cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutroninduced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F), 232Th(n,2n) and 238U(n,F), 238U(n,xn) data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F) reaction. Ratio surrogate data on fission probabilities of 232Th(6 Li,4 He)234Pa and 232 Th(6 Li,d)236U by Nayak et al., 2008, support the predicted 233Pa(n, F) cross section at En=11.5-16.5 MeV. The predicted trends of 230-232Pa(n, F) cross section up to En=20 MeV, are consistent with fissilities of Pa nuclides, extracted by 232Th(p,F) (Isaev et al., 2008) and 232Th(p,3n) (Morgenstern et al., 2008) data analysis. The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission for fission observables of Pa nuclei is defined by analysis of p-induced fission of 232Th at Ep=1-200 MeV. Predominantly symmetric fission in 232Th(p,F) at En( p)=200 MeV as revealed by experimental branching ratios (Dujvestijn et al., 1999) is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Pa (A?229) nuclei. A structure of the potential energy surface (a drop of f f symmetric and asymmetric fission barriers difierence (EfSYM - EfASYM) from ~3.5 MeV to ~1 MeV) of N-deficient Pa nuclides (A?226) and available phase space at outer fission saddles, are shown to be responsible for the sharp increase with En( p) of the symmetric fission component contribution for 232Th(p,F) and 230-233 Pa(n, F) reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En( p)~20(30) MeV. Predicted fission cross section of 232Pa(n,F) coincides with that of 232Th(p,F) at En(p)?80 MeV, that means that entrance channel dependence of fission cross section with increase of nucleon incident energy diminishes.

Maslov V.

2010-01-01

244

Event-by-event study of neutron observables in spontaneous and thermal fission  

Energy Technology Data Exchange (ETDEWEB)

The event-by-event fission model FREYA is extended to spontaneous fission of actinides and a variety of neutron observables are studied for spontaneous fission and fission induced by thermal neutrons with a view towards possible applications for SNM detection. We have shown that event-by-event models of fission, such as FREYA, provide a powerful tool for studying fission neutron correlations. Our results demonstrate that these correlations are significant and exhibit a dependence on the fissioning nucleus. Since our method is phenomenological in nature, good input data are especially important. Some of the measurements employed in FREYA are rather old and statistics limited. It would be useful to repeat some of these studies with modern detector techniques. In addition, most experiments made to date have not made simultaneous measurements of the fission products and the prompt observables, such as neutron and photons. Such data, while obviously more challenging to obtain, would be valuable for achieving a more complete understanding of the fission process.

Vogt, R; Randrup, J

2011-09-14

245

International handling of fissionable material  

International Nuclear Information System (INIS)

The opinion of the ministry for foreign affairs on international handling of fissionable materials is given. As an introduction a survey is given of the possibilities to produce nuclear weapons from materials used in or produced by power reactors. Principles for international control of fissionable materials are given. International agreements against proliferation of nuclear weapons are surveyed and methods to improve them are proposed. (K.K.)

1975-01-01

246

Fission track dating of quartz  

Energy Technology Data Exchange (ETDEWEB)

Fission track dating of quartz from a quartz vein containing gold has been carried out by using artificial heavy quartz grains and the chemical etching technique of quartz has been improved within 65% NaOH. Fission track ages of five quartz samples are from 100 Ma to 200 Ma. Meanwhile, uranium concentrations and microdistribution in a quartz vein containing gold have also been analyzed in this work. (Author).

Hu Ruiying; Cheng Jingping [Chinese Academy of Sciences, Guangzhou (China). Inst. of Geochemistry; Guo Shilun; Hao Xiuhong [Academia Sinica, Beijing, BJ (China). Inst. of Atomic Energy

1993-12-31

247

Transient times in nuclear fission  

International Nuclear Information System (INIS)

Heavy-ion induced fission at excitation energies of 100 MeV or more shows deviations from the statistical model in the numbers of light particles emitted prior to the fission. A quantitative theory is presented which assumes that slow relaxation times of collective nuclear degrees of freedom and the transients associated therewith are responsible for such departures. Numerical results show encouraging agreement with the data. (orig.).

1987-01-01

248

Fission product tin in sediments  

Energy Technology Data Exchange (ETDEWEB)

We describe a method for the determination of long-lived tin isotopes arising from nuclear fission. The isotopes are extracted from sediments with hydrochloric acid and separated by methylisobutylketone extraction, ion-exchange chromatography, precipitation of cesium hexachlorostannate and ferric hydroxide coprecipitation. The 100 000-year {sup 126}Sn was not detected but beta activity consistent with {sup 121m}Sn (55 year) was found in sediment samples from a location known to be contaminated with fission products. (author).

Patton, T.L. (Argonne National Lab., IL (USA)); Penrose, W.R. (Transducer Research Inc., Naperville, IL (USA))

1989-01-01

249

The Microscopic Theory of Fission  

Energy Technology Data Exchange (ETDEWEB)

Fission-fragment properties have been calculated for thermal neutron-induced fission on a {sup 239}Pu target, using constrained Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction. A quantitative criterion based on the interaction energy between the nascent fragments is introduced to define the scission configurations. The validity of this criterion is benchmarked against experimental measurements of the kinetic energies and of multiplicities of neutrons emitted by the fragments.

Younes, W; Gogny, D

2009-06-09

250

Measurement of fission gas release from irradiated nuclear fuel elements  

International Nuclear Information System (INIS)

A fission gas measurement system for the analysis of released gases from MOX and PHWR fuels has been designed, fabricated and commissioned in the hot cells of Post Irradiation Examination Division of Bhabha Atomic Research Centre, Mumbai. The system was used for the measurement of fission gases released from natural UO2 fuels and ThO2 fuels from PHWRs. The burnups of these fuels ranged from 2 GWD/TeU to 15 GWD/TeU. Some of the results from PHWR fuel elements from Kakrapar Atomic Power Station are presented in the paper, to highlight the utility of the system. (author)

2005-01-01

251

Probability of fission of radium and actinium near threshold  

International Nuclear Information System (INIS)

[en] The natures of the structures in the fission probabilities of 227Ra and 227Ac near threshold are studied. The cross sections for fission of 226Ra by neutrons have been measured with improved energy resolution and decreased background. The data obtained confirm the existence of a plateau-shaped irregularity in the 227Ra fission probability. Special attention is devoted to calculation of the spectrum of transition states on the basis of the superfluid model with use of the single-particle spectra of a deformed potential. It is shown that the irregularities in the fissility of 227Ra and 227Ac are the result of the properties of the spectra of transition states in the framework of the one-hump barrier model. Here no hypotheses are required regarding the existence of quasistationary states in the third potential minimum

1983-01-01

252

Measurements of the effective range of fission fragments in UO2 and the disintegration constant for spontaneous fission of 238U  

International Nuclear Information System (INIS)

The results of measuments of the disintegration constant for spontaneous fission in 238U are presented, with a discussion on the method used for the detection of fission tracks in muscovite mica. Samples of muscovite mica sandwiched between two natural uranium dioxide cylinders were irradiated with fragments of spontaneous fission and the etched tracks counted with projetion optical microscope. The effective thickness of the UO2 layer which contributed to the observed tracks was measured through irradiation of mica samples, in contact with the UO2 cylinder with 14,0 MeV neutrons from a (d,t) reaction. (Author).

1978-01-01

253

Reference reactor module for NASA's lunar surface fission power system  

International Nuclear Information System (INIS)

Surface fission power systems on the Moon and Mars may provide the first US application of fission reactor technology in space since 1965. The Affordable Fission Surface Power System (AFSPS) study was completed by NASA/DOE to determine the cost of a modest performance, low-technical risk surface power system. The AFSPS concept is now being further developed within the Fission Surface Power (FSP) Project, which is a near-term technology program to demonstrate system-level TRL-6 by 2013. This paper describes the reference FSP reactor module concept, which is designed to provide a net power of 40 kWe for 8 years on the lunar surface; note, the system has been designed with technologies that are fully compatible with a Martian surface application. The reactor concept uses stainless-steel based. UO2-fueled, pumped-NaK fission reactor coupled to free-piston Stirling converters. The reactor shielding approach utilizes both in-situ and launched shielding to keep the dose to astronauts much lower than the natural background radiation on the lunar surface. The ultimate goal of this work is to provide a 'workhorse' power system that NASA can utilize in near-term and future Lunar and Martian mission architectures, with the eventual capability to evolve to very high power, low mass systems, for either surface, deep space, and/or orbital missions.

2009-06-15

254

Energy production using fission fragment rockets  

Energy Technology Data Exchange (ETDEWEB)

Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: Approximately twice as efficient if one can directly convert the fission fragment energy into electricity; by reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster; and collecting the fission fragments outside the reactor could simplify the waste disposal problem. 6 refs., 4 figs., 2 tabs.

Chapline, G.; Matsuda, Y.

1991-08-01

255

Energy production using fission fragment rockets  

International Nuclear Information System (INIS)

Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: Approximately twice as efficient if one can directly convert the fission fragment energy into electricity; by reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster; and collecting the fission fragments outside the reactor could simplify the waste disposal problem. 6 refs., 4 figs., 2 tabs

1991-01-01

256

Modelling and the rate fission product release from the reactor containment  

International Nuclear Information System (INIS)

The phenomena associated with fission product release from reactor containment have been studied. One or fission products will be released from the reactor containment if a malfunction of the reactor containment occurs or if the inherent condition of the containment has been of extreme condition. naturally each containment is subjected to limits for design leakage. Once the limits are reached, the leakage occurs. This occurrence will lead to (result in) the release of fission products which depends on the fission product content in the reactor containment atmosphere, reactor containment characteristics (i.e.leakage and pressure design) and the pressure in the reactor containment. This paper is aimed to provide a picture of modelling and the rate of fission product release from the reactor containment

1999-05-05

257

Muon induced fission and fission track dating of minerals  

International Nuclear Information System (INIS)

The effects of muon induced fission on geological dating of samples by the fission track method are evaluated for the case of muscovite minerals. It is found a small but significant effect, greater for the longer ages. Since calculations are developped under the hypothesis of constant atmosphere and primary cosmic ray flux it is suggested that any discrepancy found in ages of very old material that cannot be accounted for by well known environmental influences, be taken as an indication of variation on either the atmospheric stopping power or the intensity of cosmic radiation along the ages. (author)

1988-01-01

258

Change over from compound nuclear fission to quasi-fission  

Directory of Open Access Journals (Sweden)

Full Text Available Fission fragment mass distribution has been measured in two reactions to populate compound nucleus 246Bk. Both the target nuclei were deformed. However, entrance channel mass asymmetry of the two systems was on the either side of the Businaro Gallone mass asymmetry parameter. Near the Coulomb barrier, at similar excitation energies, the width of the fission fragment mass distribution was found to be significantly different for the 14N+232Th reaction compared to the 11B+235U reaction. The entrance channel mass asymmetry was found to play a significant role in deciding the fusion process.

Ghosh T.K.; Banerjee K.; Bhattacharya C.; Bhattacharya S.; Kundu S.; Meena J.K.; Mukherjee G.; Mukhopadhyay S.; Rana T.K.; Golda K.S.; Bhattacharya P.

2010-01-01

259

Experimental approach to fission process of actinides  

Energy Technology Data Exchange (ETDEWEB)

From experimental views, it seems likely that the mechanism of nuclear fission process remains unsolved even after the Bohr and Weeler`s study in 1939. Especially, it is marked in respect of mass distribution in unsymmetric nuclear fission. The energy dependency of mass distribution can be explained with an assumption of 2-mode nuclear fission. Further, it was demonstrated that the symmetrical fission components and the unsymmetrical ones have different saddle and fission points. Thus, the presence of the 2-mode fission mechanism was confirmed. Here, transition in the nuclear fission mechanism and its cause were investigated here. As the cause of such transition, plausible four causes; a contribution of multiple-chance fission, disappearance of shell effects, beginning of fission following collective excitation due to GDR and nuclear phase transition were examined in the condition of excitation energy of 14.0 MeV. And it was suggested that the transition in the nuclear fission concerned might be related to phase transition. In addition, the mechanism of nuclear fission at a low energy and multi-mode hypothesis were examined by determination of the energy for thermal neutron fission ({sup 233,235}U and {sup 239}Pu) and spontaneous nuclear fission ({sup 252}Cf). (M.N.)

Baba, Hiroshi [Osaka Univ., Toyonaka (Japan). Faculty of Science

1997-07-01

260

Report of fission study meeting  

International Nuclear Information System (INIS)

[en] This book is the report of fission Study Meeting held from September 19 to 21, 1985 in the Research Center for Nuclear Physics, Osaka University. The objective of this study meeting was to stimulate the research on nuclear physics in Japan, which began to show new development accompanying the advance of the research on heavy ion nuclear reaction, and to make this a new starting point. More than 50 participants from physical, chemical and engineering fields, who have interest in the theory and experiment related to nuclear fission, gathered, and the meeting was a success beyond expectation. The contents covered a wide range including nuclear smashing reaction as well as nuclear fission in a narrow sense. In this book, the gists of 28 papers are collected. (Kako, I.)

1986-01-01

 
 
 
 
261

Study of conventional fission and fast fission; Etude de la fission conventionnelle et de la fission rapide  

Energy Technology Data Exchange (ETDEWEB)

For numerous systems (light or light projectiles) the critical angular momentum l{sub cr} does not exceed the value of l{sub bf=0}, the angular momentum corresponding to the nuclear fission stability line due to centrifugal effects. For heavy systems were the fission is still observed l{sub cr} may exceed l{sub bf=0} and corresponds to the so-called fast fission. In an experiment with the systems {sup 20}Ne + {sup 185}Re and {sup 40}Ar + {sup 165}Ho leading to the same compound nucleus {sup 205}At at 157 MeV excitation energy it was not possible to reveal the differences between the two processes from a comparison of the experimental results with the theoretical predictions. In order to achieve that a determination of the characteristic times of the two processes by means of a neutron clock was performed. This implied the measurement of multiplicity, energy and angular distributions of the neutrons emitted by the compound nucleus, the measurement of the analog properties of the neutrons emitted by excited fission fragments as well as the measurement of the properties of light charged particles emitted by the products of these reactions. The data of this experiments are now analysed. From the obtained results and by means of the code Gemimi it was possible to deduce the lifetime of the first compound system mentioned above as 7.2 x 10{sup -20} s while for the second system the code which can not reproduce the pre-fission multiplicity allowed to estimate from the post-fission multiplicity a characteristic time of 3.3 x 10{sup -20} s 2 refs.

Regimbart, R. [Lab. de Physique Corpusculaire, Caen Univ., 14 (France); Collaboration DEMON

1997-12-31

262

Fission properties of the heaviest elements  

International Nuclear Information System (INIS)

[en] The authors discuss fission properties of the heaviest elements. In particular they focus on stability with respect to spontaneous fission and on the prospects of extending the region of known nuclei beyond the peninsula of currently known nuclides

1994-12-02

263

Concept of fusion-fission hybrids  

Energy Technology Data Exchange (ETDEWEB)

Some aspects of fusion-fission hybrid based on Tokamak concept are briefly discussed. The necessities, requirements, and problems of hybrid concept are also identified along with the performance of fission blanket.

Hwang, W.G. (Kyung Hee Univ., Seoul (Republic of Korea))

1984-03-01

264

Absolute calibration technique for spontaneous fission sources  

International Nuclear Information System (INIS)

An absolute calibration technique for a spontaneously fissioning nuclide (which involves no arbitrary parameters) allows unique determination of the detector efficiency for that nuclide, hence of the fission source strength.

1984-01-01

265

Fission distribution measurements of Atucha's fuel pellets with solid state track detectors  

International Nuclear Information System (INIS)

[en] Distribution of fissions in a UO2 rod has been measured by means of solid state detectors. Mica muscovite and Makrofol-N detectors were used in the experiment. The merits of mica muscovite relative to the Makrofol-N for the detection of fission fragments have been verified. However both fission track detectors closely agree (0,5%) in the final fission distribution of the UO2 rod. Sensitivity of the detectors shows to be linear in the range between 50.000and 360.000 fission tracks per square centimeter. Due to the high spatial resolution this method is better than any other technique. Determination were made in UO2 pellets similar to the fuel element of the Atucha reactor. The average fission rate in the rod has been measured within 0,8% error, and provides an accurate determination for the distribution of fissions in the rod wich is needed for the determination of energy liberated per fission in the natural uranium rod.(author)

1979-01-01

266

NEACRP thermal fission product benchmark  

International Nuclear Information System (INIS)

The objective of the thermal fission product benchmark was to compare the range of fission product data in use at the present time. A simple homogeneous problem was set with 200 atoms H/1 atom U235, to be burnt up to 1000 days and then decay for 1000 days. The problem was repeated with 200 atoms H/1 atom Pu239, 20 atoms H/1 atom U235 and 20 atoms H/1 atom Pu239. There were ten participants and the submissions received are detailed in this report. (author)

1989-01-01

267

Determination of fission yields in the fast neutron induced fission of 238U, 237Np and 243Am using fission track etch-cum gamma spectrometry  

International Nuclear Information System (INIS)

The absolute fission yields of 39 fission products in pure 238U(99,9997 atom percent), 36 fission products in 237Np and 30 fission products in 243Am (99.998 atom percent) were determined in the fast neutron induced fission, employing fission track etch-cum gamma spectrometry. The fissions were induced by a well defined reactor neutron spectrum which was measured by using threshold detectors. 5 refs, 3 tabs.

1995-01-01

268

Multiple-Coincidence Interrogation of Fissionables  

International Nuclear Information System (INIS)

The multiple coincidence technique uses 14.1 MeV neutrons to produce (n, multiple-?) coincidences to detect fissile and fissionable materials. Measurements of n-?-? coincidences with targets of depleted uranium (DU), W, and Pb, show that the counting rate for the DU is substantially above that for the non-fissionables. Also, the data involving prompt neutrons and delayed gammas in the DU time spectra provide a signature for fissionables that is distinct from that of non-fissionables.

2009-01-01

269

Fission track etching and annealing of tourmaline  

International Nuclear Information System (INIS)

The annealing behaviour of fission tracks is an important parameter to make the fission track dates of any mineral to be meaningful. After the etching conditions of tourmaline were established by Fleischer and Price (Geochim. Cosmochim. Acta; 28:1705 (1964)) no fission track worker has reported about the thermal retentivity of fission tracks in tourmaline, which forms the subject matter of the present note and where etching conditions are different from those reported by Fleischer and Price (1964). (author)

1977-01-01

270

Nuclear fission in covariant density functional theory  

CERN Multimedia

The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation.

Afanasjev, A V; Ring, P

2013-01-01

271

Nuclear fission as a macroscopic quantum tunneling  

Energy Technology Data Exchange (ETDEWEB)

We discuss nuclear fission from the point of view of a macroscopic quantum tunneling, one of whose major interests is to study the effects of environments on the tunneling rate of a macroscopic variable. We show that a vibrational excitation of the fissioning nucleus significantly enhances the fission rate. We show this effect by two different methods. The one is to treat the vibrational excitation as an environmental degree of freedom, the other treats the fission as a two dimensional quantum tunneling. (author).

Takigawa, N. [Tohoku Univ., Sendai (Japan). Dept. of Physics

1995-04-01

272

Neutronics for critical fission reactors and subcritical fission in hybrids  

Energy Technology Data Exchange (ETDEWEB)

The requirements of future innovative nuclear fuel cycles will focus on safety, sustainability and radioactive waste minimization. Critical fast neutron reactors and sub-critical, external source driven systems (accelerator driven and fusion-fission hybrids) have a potential role to meet these requirements in view of their physics characteristics. This paper provides a short introduction to these features.

Salvatores, Massimo [CEA-Cadarache, DEN-Dir, Bat. 101, St-Paul-Lez-Durance 13108 (France)

2012-06-19

273

Change over from compound nuclear fission to quasi-fission  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fission fragment mass distribution has been measured in two reactions to populate compound nucleus 246Bk. Both the target nuclei were deformed. However, entrance channel mass asymmetry of the two systems was on the either side of the Businaro Gallone mass asymmetry parameter. Near the Coulomb b...

Ghosh T.K.; Banerjee K.; Bhattacharya C.; Bhattacharya S.; Kundu S.; Meena J.K.; Mukherjee G.; Mukhopadhyay S.; Rana T.K.

274

Investigation of exotic fission modes  

International Nuclear Information System (INIS)

Fission approach to the cluster radioactivities and ?-decay has been systematically developed during the last two decades. A more complex process, the ternary fission, was observed since 1946 both in neutron-induced and spontaneous fission. We obtained interesting results concerning the binary fission saddle-point reflection asymmetric nuclear shapes, and we can explain how a possible nuclear quasimolecular state is formed during the 10 Be accompanied cold fission of 252 Cf. The equilibrium nuclear shapes in fission theory are usually determined by minimizing the deformation energy for a given surface equation. We developed a method allowing to obtain a very general saddle-point shape as a solution of a differential equation without an a priori introduction of a shape parametrization. In the approach based on a liquid drop model (LDM), saddle-point shapes are always reflection symmetric: the deformation energy increases with the mass-asymmetry parameter ? = (A1 - A2)/(A1 + A2). By adding the shell corrections to the LDM deformation energy, we obtained minima at a finite mass asymmetry for parent nuclei 238 U, 232,228 Th in agreement with experiments. This correction was calculated phenomenologically. A technique based on the fragment identification by using triple ? coincidences in the large arrays of Ge-detectors, like GAMMASPHERE, was employed at Vanderbilt University to discover new characteristics of the fission process, and new decay modes. The possibility of a whole family of new decay modes, the multicluster accompanied fission, was envisaged. Besides the fission into two or three fragments, a heavy or superheavy nucleus spontaneously breaks into four, five or six nuclei of which two are asymmetric or symmetric heavy fragments and the others are light clusters, e.g. ?-particles, 10 Be, 14 C, or combinations of them. Examples were presented for the two-, three- and four cluster accompanied cold fission of 252 Cf and 262 Rf, in which the emitted clusters are: 2?, ? + 6 He, ? + 10 Be, 3?, etc. The strong shell effect corresponding to the doubly magic heavy fragment 132 Sn was emphasized. We concluded that the most favorable mechanism of such decay modes should be the cluster emission from an elongated neck formed between the two heavy fragments. A formation mechanism of the touching configuration, based on a three-center phenomenological model is suggested. It is derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment is obtained by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. During the first stage of the deformation one has a two-center evolution until the neck radius becomes equal to the radius of the emitted particle. Then the three center starts developing by decreasing with the same amount the two tip distances. In such a way a new minimum, typical for a cluster molecule, appears in the deformation energy. A single-particle three center shell model just developed by us will be used in the future. It represents an extension of the advanced two center shell model which takes into account 5 deformation coordinates. The existence of this minimum proves the quasimolecular character of the aligned configuration of three fragments in touch. It explains why the 3.368 MeV ?-ray, by which decays the first excited state of 10 Be accompanying cold fission of 252 Cf, is not Doppler-broadened as it should be if this ?-ray would be emitted in flight. (authors)

2002-01-01

275

Post-scission dynamics in fission  

Energy Technology Data Exchange (ETDEWEB)

A dynamical model for fission from the classical turning point to scission and beyond is presented. We consider the fissioning nucleus as well as the fission fragments as incompressible irrotational deformable charged liquid drops. We focus on the post-scission time evolution of the neck, stretching of the fragments, kinetic energy and excitation energy.

Samanta, B.C.; Sperber, D.; Zielinska-Pfabe, M. (Rensselaer Polytechnic Inst., Troy, NY (USA). Dept. of Physics); Samaddar, S.K. (Darjeeling Government Coll. (India). Dept. of Physics)

1982-01-14

276

Correlation measurements of fission-fragment properties  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments’ heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on ...

Oberstedt S.; Belgya T.; Billnert R.; Borcea R.; Cano-Ott D.; Göök A.; Hambsch F.-J.; Karlsson J.; Kis Z.; Martinez T.

277

Hybrid nuclear cycles for nuclear fission sustainability  

International Nuclear Information System (INIS)

Nuclear fission can play and must play an important role in paving the road to Energy Sustainability. Nuclear Fission does not produce CO2 emissions, and it is already exploited at commercial level with the current NPP (Nuclear Power Plants). Most of them are based on LWR reactors, which have a very good safety record. It must be noted, however, that all LWR (including the advanced or evolutionary ones) have some drawbacks, particularly their very poor efficiency in exploiting the natural resources of nuclear fuels. In this paper, an analysis is presented on how to maximize the energy actually generated from the potential contents of fission natural resources. The role of fertile-to-fissile breeding is highlighted, as well as the need of attaining a very high safety performance in the reactors and other installations of the fuel cycle. The proposal presented in this paper is to use advanced and evolutionary LWR as energy producing reactors, and to use subcritical fast assemblies as breeders. The main result would be to increase by two orders of magnitude the percentage of energy effectively exploited from fission natural resources, while keeping a very high level of safety standards in the full fuel cycle. Breeders would not be intended for energy production, so that safety standards could rely on very low values of the thermal magnitudes, so allowing for very large safety margins for emergency cooling. Similarly, subcriticality would offer a very large margin for not to reach prompt criticality in any event. The main drawback of this proposal is that a sizeable fraction of the energy generated in the cycle (about 1/3, maybe a little more) would not be useful for the thermodynamic cycle to produce electricity. Besides that, a fraction of the generated electricity, between 5 and 10 %, would have to be recirculated to feed the accelerator activating the neutron source. Even so, the overall result would be very positive, because more than 50 % of the natural resources could be exploited with such a cycle, using very safe reactors. This percentage is much higher than the actual value for the once-through cycle (0.5 %) and the value for multiple Pu recycling in the MOX scheme (1 %). Moreover, thorium could also be exploited through fertile conversion into U-233 in the subcritical breeders. The separation between energy production (to be done in LWR) and nuclear breeding (to be done in subcritical hybrids) presents a scenario with very appealing safety features and a high potential for an efficient utilization of all natural resources of uranium and thorium, that account for 1024 J, i.e., 25 Gtoe, which is 35,000 times as large as the annual production of Nuclear Energy nowadays, and about 2,500 times as large as the total annual energy consumption all over the globe.

2007-01-01

278

Fission track dating of zeolites  

International Nuclear Information System (INIS)

Reconnaissance studies of fission track dating of zeolites are reported. The etching conditions for some zeolites, in particular the minerals chabazite, stilbite and heulandite are described and the track recording and retention characteristics for chabazite, with particular reference to fossil hydrothermal systems in the Faeroe Islands are detailed. (U.K.).

1981-01-01

279

Spin determination of fission resonances  

International Nuclear Information System (INIS)

[en] The present status of available information on the channel quantum numbers for resonance fission and the most urgently needed additional experiments are examined. The role of spin in the 235U + n system is emphasized. The discussion relies heavily on recent alignment measurements and polarization results

1976-07-06

280

Nuclear data for fission reactors  

International Nuclear Information System (INIS)

Nuclear reactions induced by neutrons play an important role in fission reactors and relevant cross-sections need to be known with great accuracy. After a brief history and a general presentation, the nuclear data situation is discussed for Pressurized-Water and Liquid-Metal Fast Breeder Reactors

1982-09-17

 
 
 
 
281

Microscopic description of nuclear fission  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Starting from a completely microscopic description of the nucleus, we try to extract the characteristic features of the collective dynamics of the fission phenomenon in the case of the 240Pu nucleus. In particular, we give an interpretation for the mechanism of the scission process.

Berger, J.-F.; Girod, M.; Gogny, D.

282

Nuclear fission reactors as energy sources for the giant outer planets  

Energy Technology Data Exchange (ETDEWEB)

Of the giant planets, Jupiter, Saturn, and Neptune presently radiate into space approximately twice as much energy as they receive from the Sun; Uranus, however, emits little, if any, energy other than absorbed solar energy. Currently, speculative explanations for the energy sources involved propose gravitational potential energy release. The purpose of the present paper is to suggest the possibility of naturally occurring nuclear fission reactors in the giant outer planets. The discovery of a naturally occurring, terrestrial, nuclear fission, 'breeder' reactor is reviewed. Quantitative estimates are made of the planetary energy release by nuclear fission and of the duration that present planetary power output levels could be sustained by nuclear fission energy. (orig.).

Herndon, J.M. (Herndon Science und Software, Inc., San Diego, CA (United States))

1992-01-01

283

Binary and ternary fission within statistical approach  

International Nuclear Information System (INIS)

Binary fission observables are described within the scission-point model by calculating the potential energy with the dinuclear system model. For the description of ternary fission we extend the scission-point model of binary fission. The ternary system with a light nucleus between two heavy fragments is assumed to be formed from the binary configuration near to the scission point. Charge number distributions, mean total kinetic energies and neutron multiplicity distributions are treated and compared with the experimental data for binary fission of actinides and for ternary fission of 252Cf accompanied by different light charged particles. (authors)

2007-01-01

284

Weathering processes at the natural nuclear reactor of Bangombe (Gabon). Identification and geochemical modeling of the retention and migration mechanisms of uranium and rare earth elements  

International Nuclear Information System (INIS)

[en] The natural nuclear fission reactor of Bangombe (Gabon) was discovered in 1985. It is located 30 km SE of the uranium Oklo ore deposit which is well-known for its reactors discovered in 1972. In contrast to the latter ones, the reaction zone of Bangombe is situated close to the surface and therefore has been affected by supergene weathering processes. The purpose of this study was to characterize the main effects related to these alteration processes on the rocks surrounding the Bangombe reactor zone as well as to determine the major mechanisms, influencing the migration and retention of U and REE in this geological system. The different approaches considered in this study comprise mineralogical and geochemical investigations, mass balance calculations, sequential extraction experiments as well as thermodynamic simulations. It could be shown that the present rock and mineral assemblages result from a complex and multi-stage history during which the rocks were affected by diagenetic, hydrothermal, tectonic and recent alteration processes. Multiple transformations led to the setting of different horizons characterized by very specific physico-chemical conditions and mineral associations. It has been shown that in the various units of the weathering sequence, the mechanisms and mineral phases determining the U and REE migration/retention behaviour are quite different and highly dependent on the physico-chemical conditions prevailing in the ambient environment. Apart from residual and neo-formed clays, especially amorphous and crystalline Fe- and Mn oxides and oxy-hydroxides, phosphates as well as minor phases such as carbonates and heavy minerals were identified to play an important role in REE and U mobility. The acquisition of hydrodynamic data enabled to simulate water-rock interaction and mass-transfer processes which have been produced during the alteration of the Bangombe reactor zone. Thermodynamic simulations showed that elevated U-concentrations downstream the reactor zone at present-days may be simply explained by local re-equilibration of the aquifer forming pelites (containing primary and secondary U-minerals) with the ambient weathering solution. (authors)

2000-01-01

285

Symmetric/asymmetric p- and n-induced fission of Th, Pa, U and Np  

International Nuclear Information System (INIS)

[en] The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission of fission observables of Th(Pa) and U(Np) nuclei is interpreted for nucleon-induced fission cross sections of 232Th(p, F)(232Th(n, F)) and 238U(p, F) ( 238U(n, F)) reactions at En(p) = 1-200 MeV. Predominantly symmetric fission in 232Th(p, F) and roughly equal contributions of symmetric and asymmetric modes in 238U(n, F) at En(p) = 200 MeV as revealed by experimental branching ratios is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Th(Pa) (n(p)?200 MeV. A structure of the potential energy surface (a drop of symmetric and asymmetric fission barriers difference (ESYMf-EASYM'f) from ?3.5 MeV to ?1 MeV) of N-deficient Pa nuclides (n(p) of the symmetric fission component contribution for Th(p, F) and 232Th(n, F) reactions. That is a strong evidence of emissive fission nature of highly excited actinides, reliably quantified only up to En(p)?20(30) MeV. In case of U nucleon-induced fission the much lower yield of the symmetric fission mode at En(p)?200 MeV is due to much lower contribution of neutron-deficient U(Np)nuclides, which may split symmetrically. (authors)

2010-01-01

286

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the eleventh issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); Neutron reaction cross sections of fission products; Data related to the radioactive decay of fission products; Delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS

1985-01-01

287

Fission product behaviour in severe accidents  

International Nuclear Information System (INIS)

[en] The understanding of fission product (FP) behaviour in severe accidents is important for source term assessment and accident mitigation measures. For example in accident management the operator needs to know the effect of different actions on the behaviour and release of fission products. At VTT fission product behaviour have been studied in different national and international projects. In this presentation the results of projects in EU funded 4th framework programme Nuclear Fission Safety 1994-1998 are reported. The projects are: fission product vapour/aerosol chemistry in the primary circuit (FI4SCT960020), aerosol physics in containment (FI4SCT950016), revaporisation of test samples from Phebus fission products (FI4SCT960019) and assessment of models for fission product revaporisation (FI4SCT960044). Also results from the national project 'aerosol experiments in the Victoria facility' funded by IVO PE and VTT Energy are reported

1998-11-24

288

Kinetics of the accumulation of uranium fission tracts in geochronometry  

International Nuclear Information System (INIS)

Kinetics of accumulation of uranium fission tracks in volcanic glass during geochonometry according to tracks is studied. On the base of experimental investigation of track behaviour in volcanic glass and calculations of the hypothetical model it is established that utilization of track artificial annealing plottings in Arrenius coordinates for the determination of their stability under natural condutions is not tolerated. This conclusion is extended to all minerals used for dating.

1984-01-01

289

A brief history of the ''Delayed'' discovery of nuclear fission  

International Nuclear Information System (INIS)

[en] This year marks the Fiftieth Anniversary of the discovery of Nuclear Fission. In the early 1930's, the neutron was discovered, followed by the discovery of artificial radioactivity and then the use of the neutron to produce artificial radioactivity. The first experiments resulting in the fission of uranium took place in 1934. A paper which speculated on fission as an explanation was almost immediately published, yet no one took it seriously not even the author herself. Why did it take an additional five years before anyone realized what had occurred? This is an abnormally long time in a period when discoveries, particularly in nuclear physics, seemed to be almost a daily occurrence. The events which led up to the discovery are recounted, with an attempt made to put them into their historical perspective. The role played by Mendeleev's Periodic Table, the role of the natural radioactive decay chain of uranium, the discovery of protactinium, the apparent discovery of masurium (technetium) and a speculation on the reason why Irene Curie may have missed the discovery of nuclear fission will all be discussed. 43 refs

290

The influence of fission products on UO2 matrix microstructure  

International Nuclear Information System (INIS)

The presence of the fission products, regardless of their chemical or physical state, drastically affects the fuel properties. With increasing burnup, defects in the pellet microstructure appear, their mobility enhances, the rate of fission gas release enlarges, and the central hole creates, leading to the impairing of fuel quality. The study of processes occurring in the nuclear fuel at high burnups is made on the simulated fuel type SIMFUEL in order to avoid the problems which appear because of the special safety conditions imposed to the irradiated fuel work (the working in hot cell). The SIMFUEL consists in a natural UO2 matrix in which chemical compounds (fission products) were introduced, without radioactivity and having the microstructure compatible to the burnup level. The paper presents the experimental results on the sintered SIMFUEL pellets and the influence of oxidic compounds that appear as fission products on UO2 matrix. The sintered SIMFUEL pellets were characterized by density, mean grain size, porosity, and the presence of oxides' agglomerates by destructive methods and ultra-acoustic microscopy. The experimental data concerning the manufacturing of sintered simulated fuel are presented in tables, diagrams and images of their microstructural characteristics. (authors)

2002-01-01

291

Cluster fission from the standpoint of nuclear fission  

Energy Technology Data Exchange (ETDEWEB)

Atomic nucleus belongs to a quantal finite many body system. Nucleus shows great resemblance to cluster, above all metal cluster, although the strength of interaction is different. The works of Brechignac group, Saunder, Martin and P. Froeblich are explained by the critical size Nc as the central term. The differences between cluster and nucleus are investigated and a future view of cluster fission is explained. (S.Y.)

Lee, Sangmoo [Tsukuba Univ., Ibaraki (Japan). Inst. of Physics

1996-03-01

292

DSP Algorithms for Fission Fragment and Prompt Fission Neutron Spectroscopy  

International Nuclear Information System (INIS)

Digital signal processing (DSP) algorithms are in high demand for modern nuclear fission investigation due to importance of increase the accuracy of fissile nuclear data for new generation of nuclear power stations. DSP algorithms for fission fragment (FF) and prompt fission neutron (PFN) spectroscopy are described in the present work. The twin Frisch-grid ionization chamber (GTIC) is used to measure the kinetic energy-, mass- and angular distributions of the FF in the 252Cf(SF) reaction. Along with the neutron time-of-flight (TOF) measurement the correlation between neutron emission and FF mass and energy is investigated. The TOF is measured between common cathode of the GTIC and the neutron detector (ND) pulses. Waveform digitizers (WFD) having 12 bit amplitude resolution and 100 MHz sampling frequency are used for the detector pulse sampling. DSP algorithms are developed as recursive procedures to perform the signal processing, similar to those available in various nuclear electronics modules, such as constant fraction discriminator (CFD), pulse shape discriminator (PSD), peak-sensitive analogue-to-digital converter (pADC) and pulse shaping amplifier (PSA). To measure the angle between FF and the cathode plane normal to the GTIC a new algorithm is developed having advantage over the traditional analogue pulse processing schemes. Algorithms are tested by comparing the numerical simulation of the data analysis of the 252Cf(SF) reaction with data available from literature.

2009-10-29

293

Nuclear-fission studies with relativistic secondary beams: analysis of fission channels  

CERN Multimedia

Nuclear fission of several neutron-deficient actinides and pre-actinides from excitation energies around 11 MeV was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around 226Th are systematically investigated and interpreted as the superposition of three fission channels. Properties of these fission channels have been determined for 15 systems. A global view on the properties of fission channels including previous results is presented. The positions of the asymmetric fission channels are found to be constant in element number over the whole range of systems investigated.

Böckstiegel, C; Schmidt, K -H; Clerc, H -G; Grewe, A; Heinz, A; De Jong, M; Junghans, A R; Müller, J; Voss, B

2007-01-01

294

Terracentric Nuclear Fission Reactor: Background, Basis, Feasibility, Structure, Evidence, and Geophysical Implications  

CERN Multimedia

The background, basis, feasibility, structure, evidence, and geophysical implications of a naturally occurring Terracentric nuclear fission georeactor are reviewed. For a nuclear fission reactor to exist at the center of the Earth, all of the following conditions must be met: (1) There must originally have been a substantial quantity of uranium within Earth's core; (2) There must be a natural mechanism for concentrating the uranium; (3) The isotopic composition of the uranium at the onset of fission must be appropriate to sustain a nuclear fission chain reaction; (4) The reactor must be able to breed a sufficient quantity of fissile nuclides to permit operation over the lifetime of Earth to the present; (5) There must be a natural mechanism for the removal of fission products; (6) There must be a natural mechanism for removing heat from the reactor; (7) There must be a natural mechanism to regulate reactor power level, and; (8) The location of the reactor or must be such as to provide containment and prevent ...

Herndon, J Marvin

2013-01-01

295

Study of actinides fission induced by multi-nucleon transfer reactions in inverse kinematics  

International Nuclear Information System (INIS)

The study of actinide fission encounters two major issues. On one hand, measurements of the fission fragment distributions and the fission probabilities allow a better understanding of the fission process itself and the discrimination among the models of nuclear structure and dynamics. On the other hand, new measurements are required to improve nuclear data bases, which are a key component for the design of new generation reactors and radio-toxic waste incinerators. This thesis is in line with different French and American experimental projects using the surrogate method, i.e. transfer reactions leading to the same compound nuclei as in neutron irradiation, allowing the study of fission of actinides which are inaccessible by conventional techniques, whereas they are important for applications. The experiment is based on multi-nucleon transfer reactions between a 238U beam and a 12C target, using the inverse kinematics technique to measure, for each transfer channel, the complete isotopic distributions of the fission fragments with the VAMOS spectrometer. The work presented in this dissertation is focused on the identification of the transfer channels and their properties, as their angular distributions and the distributions of the associated excitation energy, using the SPIDER telescope to identify the target recoil nuclei. This work of an exploratory nature aims to generalize the surrogate method to heavy transfers and to measure, for the first time, the fission probabilities in inverse kinematics. The obtained results are compared with available direct kinematics and neutron irradiation measurements. (author)

2010-01-01

296

Evaluation of the fission track analysis for determination of trace-amounts of 239Pu  

International Nuclear Information System (INIS)

[en] The fission track technique was studied and evaluated for critical circumstances in the overall process of the analysis. Fission Track Analysis (FTA) is used for determination of 239Pu at a femto gram level in biological and environmental samples. The technique is a type of neutron activation where 239Pu is determined by the registration of fission fragments in quartz after irradiation with thermal neutrons in a nuclear reactor. Plutonium is extracted from the sample by chemical separation processes in several steps in order to retrieve a pure plutonium sample. The method for the chemical separation was selected to suppress the influence from naturally occurring uranium in the sample since the cross-section of thermal neutron fission of 235U is in the same order of magnitude as the cross-section for 239Pu. The following parts of the fission track analysis were regarded as critical and subjects of further evaluation: the quenching of fission tracks, the efficiency of the solvent extraction used in the final step of the chemical separation, the efficiency of the uranium de-contamination, the background contribution from the yield determinant 236Pu, the interference from 232Th (which fissions with fast neutrons) and the calibration process. The study was performed in order to assure the accuracy of the 239Pu determination and showed that none of the mentioned critical parts prevent a successful performance of FTA with a ?Bq detection limit

1999-03-01

297

Proliferation resistant fission energy systems  

Energy Technology Data Exchange (ETDEWEB)

Fission energy systems that significantly reduce the need for the user country to be involved in the nuclear operations and technology could simplify implementation and reduce the proliferation potential. Conceptual system designs with improved (relative to the once-through LWR fuel cycle) proliferation resistance for application in developing countries are being evaluated. The fission energy systems being studied include all activities and equipment necessary to produce energy, recycle selected materials, and dispose of the waste. The systems currently being studied are required to function with no refueling of the reactors on the user site. These requirements are being used to initiate the study, on the assumption that removal of these operations from within the developing countries will improve the proliferation resistance. Preliminary evaluations of a small fast reactor core cooled either by sodium or lead-bismuth are provided.

Brown, N. W., LLNL

1997-07-02

298

Charged particle induced nuclear fission  

International Nuclear Information System (INIS)

[en] Preliminary results of the following three experiments are reported. In the first experiment, cross-sections for the 232Th(?,xn)sup(236-x)U, 232Th(?,pxn)sup(235-x)Pa and 232Th(?,?'xn)sup(232-x)Th reactions were measured at bombarding energies of 30 to 110 MeV. In the second one, isomeric cross-section ratios were obtained for antimony isotopes produced in the fission of 232Th induced by ? particles with energies of 30 and 110 MeV. The third experiment was carried out to obtain a mass yield curve of 232Th fission induced by 110 MeV ? particles. (author)

1978-09-13

299

Sensitivity of Makrofol fission track detectors  

International Nuclear Information System (INIS)

Neutron fluence can be determined by means of fission track detectors consisting of fission foils in contact with suitable dielectrics (Makrofol E plastic was used in this case). Fission fragments emitted from the fissionable material into the plastic sheet generate permanent damage trails which can be made visible by an etching process. These tracks are then counted by means of an optical microscope or other methods and the number of tracks is proportional to the neutron fluence. The efficiency is defined as the ration of the number of tracks counted to the number of fissions in the fissionable layer. It is calculated from the mean range of the fission products in the fissionable material and in the plastic. The loss of very flat tracks with a small penetration angle caused by etching a certain bulk layer from the plastic foil is also taken into account. The formulas for the efficiency are deduced for thin fission layers and for thick fission foils. These calculations are made on the basis of the experimentally confirmed assumption that the ratio V of the track etching rate to the bulk etching rate is at least equal to 200. These high values for this ratio V are valid if an adequate period (several days) of oxygen influence to the damage trails is guaranteed. The calculated values of the efficiency are compared with experimental values and the uncertainty is discussed. (orig./HP)

1981-01-01

300

Fission properties for r-process nuclei  

CERN Document Server

We present a systematics of fission barriers and fission lifetimes for the whole landscape of super-heavy elements (SHE), i.e. nuclei with Z>100. The fission lifetimes are also compared with the alpha-decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parameterizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. The computation of fission lifetimes takes care of the crucial ingredients of the large-amplitude collective dynamics along the fission path, as self-consistent collective mass and proper quantum corrections. We discuss the different topologies of fission landscapes which occur in the realm of SHE (symmetric versus asymmetric fission, regions of triaxial fission, bi-modal fission, and the impact of asymmetric ground states). The explored region is extended deep into the regime of very neutron-rich isotopes as they are expec...

Erler, J; Loens, H P; Martínez-Pinedo, G; Reinhard, P -G

2011-01-01

 
 
 
 
301

Thomas-Fermi fission barriers  

International Nuclear Information System (INIS)

The Thomas-Fermi model of average nuclear properties described in Parts 1 and 2 is applied to the calculation of fission barriers and charge distributions. Comparison with experimental data reveals a barriers vs. size discrepancy. The suggestion is made that an extension of the Thomas-Fermi method is called for in order to describe the presence in nuclei of the ''quantal halo,'' i.e. of the classically forbidden region around the nuclear surface where matter exists at negative kinetic energy

1992-01-01

302

Fission tracks dating for obsidian  

International Nuclear Information System (INIS)

[en] Obsidian from South America are dated by fission tracks methods. Samples are irradiated in a nuclear reactor with a flux of 1015 n/cm2. Results, corrected by 'Plateau' methods, are the following: obsidian from Bolivia: 4.14 x 106 yr., Ecuador: 8.79 x 105 yr., Colombia: 3.52 x 106 yr., Peru: 6.55 x 106 yr., Chile: 1.13 x 106 yr. (MMZ). 5 refs., 3 tabs

1991-01-01

303

Fine structure in superasymmetric fission  

Energy Technology Data Exchange (ETDEWEB)

The influence of the Landau-Zener effect on the fine structure of cluster decay phenomenon is emphasized. Estimations of hindrance factors are reported for the {sup 14}C emission from {sup 223}Ra. The half-lives are computed considering the cluster decay as a superasymmetric fission process. The level scheme is evaluated with the superasymmetric two-center shell model. (orig.). 11 refs.

Mirea, M. [Institutul de Fizica Atomica, Bucharest (Romania); Clapier, F. [Institut de Physique Nucleaire, 91 - Orsay (France)

1997-12-01

304

Fission fusion hybrids- recent progress  

Science.gov (United States)

Fission-fusion hybrids enjoy unique advantages for addressing long standing societal acceptability issues of nuclear fission power, and can do this at a much lower level of technical development than a competitive fusion power plant- so it could be a nearer term application. For waste incineration, hybrids can burn intransigent transuranic residues (with the long lived biohazard) from light water reactors (LWRs) with far fewer hybrid reactors than a comparable system within the realm of fission alone. For fuel production, hybrids can produce fuel for ˜4 times as many LWRs with NO fuel reprocessing. For both waste incineration or fuel production, the most severe kind of nuclear accident- runaway criticality- can be excluded, unlike either fast reactors or typical accelerator based reactors. The proliferation risks for hybrid fuel production are, we strongly believe, far less than any other fuel production method, including today's gas centrifuges. US Thorium reserves could supply the entire US electricity supply for centuries. The centerpiece of the fuel cycle is a high power density Compact Fusion Neutron Source (major+minor radius ˜ 2.5-3.5 m), which is made feasible by the super-X divertor.

Kotschenreuther, M.; Valanju, P.; Mahajan, S.; Covele, B.

2012-03-01

305

Fission properties of the BCPM functional  

CERN Multimedia

We explore the properties of the Barcelona Catania Paris Madrid (BCPM) energy density functional concerning fission dynamics. Potential energy surfaces as well as collective inertias relevant in the fission process are computed for several nuclei where experimental data exists. Inner and outer barrier heights as well as fission isomer excitation energies are reproduced quite well in all the cases. The spontaneous fission half lives $t_{\\textrm{\\textrm{SF}}}$are also computed using the standard semiclasical approach and the results are compared with the experimental data. A reasonable agreement with experiment is found over a range of 27 orders of magnitude but the theoretical predictions suffer from large uncertainties associated to the values of the parameters entering the spontaneous fission half life formula. The impact that increasing the pairing correlations strengths has in the spontaneous fission half lives is analyzed and found to be large in all the nuclei considered. Given the satisfactory descripti...

Giuliani, Samuel A

2013-01-01

306

Collective spectra along the fission barrier  

Directory of Open Access Journals (Sweden)

Full Text Available Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states) and in the intermediate wells (superdeformed and hyperdeformed states) play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two–cluster configurations in a dynamical way, permitting exchange of upper–shell nucleons between clusters. The impact of theoretical spectra on neutron–induced fission cross sections and, in combination with an improved version of the scission–point model, on angular distribution of fission fragments is evaluated for plutonium isotopes of interest to nuclear energy applications.

Shneidman T. M.; Andreev A. V.; Pigni M. T.; Massimi C.; Vannini G.; Ventura A.

2012-01-01

307

?-ray studies of the fission of 238U induced by 12C, spectroscopy and fission dynamics  

International Nuclear Information System (INIS)

Fission studies have been known for a long time to provide neutron-rich nuclei in various states of excitation energy, spin and deformation. Although many studies have been performed concerning fission fragments from spontaneous fission and neutron induced fission, a renewed interest in fission-fragment spectroscopy has occurred with the elaboration of large Ge detector arrays such as EUROBALL. We have recently performed an experiment with EUROBALL III using SAPhIR; a fission-fragment detector made from photovoltaic cells. The compact and versatile geometry of SAPhIR allows it to be installed inside the ?-ray detector, and to obtain additional information from the fission process as well as a timing reference. Neutron-rich nuclei have been populated in the fusion-fission reaction 238U+12C leading to the compound nucleus 250Cf. First results of this experiment are presented

1998-10-26

308

What do we learn on the dynamics of fission from ?-accompanied fission data  

International Nuclear Information System (INIS)

Measurements of the angular distribution of ?-particles emitted by thermal fission of 236U are presented. Also the dependence of the angular distribution on the kinetic energy of the fission products is studied. (WL)

1978-01-21

309

?-ray studies of the fission of 238U induced by 12C, spectroscopy and fission dynamics  

Science.gov (United States)

Fission studies have been known for a long time to provide neutron-rich nuclei in various states of excitation energy, spin and deformation. Although many studies have been performed concerning fission fragments from spontaneous fission and neutron induced fission, a renewed interest in fission-fragment spectroscopy has occurred with the elaboration of large Ge detector arrays such as EUROBALL. We have recently performed an experiment with EUROBALL III using SAPhIR; a fission-fragment detector made from photovoltaic cells. The compact and versatile geometry of SAPhIR allows it to be installed inside the ?-ray detector, and to obtain additional information from the fission process as well as a timing reference. Neutron-rich nuclei have been populated in the fusion-fission reaction 238U+12C leading to the compound nucleus 250Cf. First results of this experiment are presented.

Houry, M.; Korten, W.; Le Coz, Y.; Lucas, R.; Theisen, Ch.; Barreau, G.; Doan, T. P.; Aiche, M.; Aleonard, M. M.; Chemin, J. F.; Scheurer, J. N.; Belier, G.; Meot, V.; Ethvignot, Th.; Durell, J.; Grimwood, D.; Phillips, W. R.; Roach, A.; Smith, A. G.; Varley, B. J.; Deloncle, I.; Porquet, M. G.; Astier, A.; Perries, S.; Redon, N.

1998-10-01

310

Sustainable and safe nuclear fission energy. Technology and safety of fast and thermal nuclear reactors  

Energy Technology Data Exchange (ETDEWEB)

Written by one of the world-leading specialists in reactor physics and safety Most comprehensive book on nuclear fission technology, new safety concepts and waste disposal Complete description and evaluation of nuclear fission power generation Covers the whole nuclear fuel cycle, from the extraction of natural uranium, uranium conversion and enrichment up to the fabrication of fuel elements Description of the different fuel cycle options Presents viable solutions for safe and long-term storage of nuclear waste Recently developed new safety concepts for fission reactors Unlike existing books of nuclear reactor physics, nuclear engineering and nuclear chemical engineering this book covers a complete description and evaluation of nuclear fission power generation. It covers the whole nuclear fuel cycle, from the extraction of natural uranium from ore mines, uranium conversion and enrichment up to the fabrication of fuel elements for the cores of various types of fission reactors. This is followed by the description of the different fuel cycle options and the final storage in nuclear waste repositories. In addition the release of radioactivity under normal and possible accidental conditions is given for all parts of the nuclear fuel cycle and especially for the different fission reactor types.

Kessler, Guenter

2012-07-01

311

Analysis of fission-product effects in a Fast Mixed-Spectrum Reactor concept  

International Nuclear Information System (INIS)

The Fast Mixed-Spectrum Reactor (FMSR) concept has been proposed by BNL as a means of alleviating certain nonproliferation concerns relating to civilian nuclear power. This breeder reactor concept has been tailored to operate on natural uranium feed (after initial startup), thus eliminating the need for fuel reprocessing. The fissile material required for criticality is produced, in situ, from the fertile feed material. This process requires that large burnup and fluence levels be achievable, which, in turn, necessarily implies that large fission-product inventories will exist in the reactor. It was the purpose of this study to investigate the effects of large fission-product inventories and to analyze the effect of burnup on fission-product nuclide distributions and effective cross sections. In addition, BNL requested that a representative 50-group fission-product library be generated for use in FMSR design calculations.

1980-01-01

312

Analysis of fission-product effects in a Fast Mixed-Spectrum Reactor concept  

Energy Technology Data Exchange (ETDEWEB)

The Fast Mixed-Spectrum Reactor (FMSR) concept has been proposed by BNL as a means of alleviating certain nonproliferation concerns relating to civilian nuclear power. This breeder reactor concept has been tailored to operate on natural uranium feed (after initial startup), thus eliminating the need for fuel reprocessing. The fissile material required for criticality is produced, in situ, from the fertile feed material. This process requires that large burnup and fluence levels be achievable, which, in turn, necessarily implies that large fission-product inventories will exist in the reactor. It was the purpose of this study to investigate the effects of large fission-product inventories and to analyze the effect of burnup on fission-product nuclide distributions and effective cross sections. In addition, BNL requested that a representative 50-group fission-product library be generated for use in FMSR design calculations.

White, J.R.; Burns, T.J.

1980-02-01

313

Fission-product retention in HTGR fuels  

Energy Technology Data Exchange (ETDEWEB)

Retention data for gaseous and metallic fission products are presented for both Triso-coated and Biso-coated HTGR fuel particles. Performance trends are established that relate fission product retention to operating parameters, such as temperature, burnup, and neutron exposure. It is concluded that Biso-coated particles are not adequately retentive of fission gas or metallic cesium, and Triso-coated particles which retain cesium still lose silver. Design implications related to these performance trends are identified and discussed.

Homan, F.J.; Kania, M.J.; Tiegs, T.N.

1982-01-01

314

Fission barriers and half-lives  

Energy Technology Data Exchange (ETDEWEB)

We briefly review the development of theoretical models for the calculation of fission barriers and half-lives. We focus on how results of actual calculations in a unified macroscopic-microscopic approach provide an interpretation of the mechanisms behind some of the large number of phenomena observed in fission. As instructive examples we choose studies of the rapidly varying fission properties of elements at the end of the periodic system. 31 refs., 10 figs.

Moeller, P.; Nix, J.R.; Swiatecki, W.J.

1989-01-01

315

Monte carlo sampling of fission multiplicity.  

Energy Technology Data Exchange (ETDEWEB)

Two new methods have been developed for fission multiplicity modeling in Monte Carlo calculations. The traditional method of sampling neutron multiplicity from fission is to sample the number of neutrons above or below the average. For example, if there are 2.7 neutrons per fission, three would be chosen 70% of the time and two would be chosen 30% of the time. For many applications, particularly {sup 3}He coincidence counting, a better estimate of the true number of neutrons per fission is required. Generally, this number is estimated by sampling a Gaussian distribution about the average. However, because the tail of the Gaussian distribution is negative and negative neutrons cannot be produced, a slight positive bias can be found in the average value. For criticality calculations, the result of rejecting the negative neutrons is an increase in k{sub eff} of 0.1% in some cases. For spontaneous fission, where the average number of neutrons emitted from fission is low, the error also can be unacceptably large. If the Gaussian width approaches the average number of fissions, 10% too many fission neutrons are produced by not treating the negative Gaussian tail adequately. The first method to treat the Gaussian tail is to determine a correction offset, which then is subtracted from all sampled values of the number of neutrons produced. This offset depends on the average value for any given fission at any energy and must be computed efficiently at each fission from the non-integrable error function. The second method is to determine a corrected zero point so that all neutrons sampled between zero and the corrected zero point are killed to compensate for the negative Gaussian tail bias. Again, the zero point must be computed efficiently at each fission. Both methods give excellent results with a negligible computing time penalty. It is now possible to include the full effects of fission multiplicity without the negative Gaussian tail bias.

Hendricks, J. S. (John S.)

2004-01-01

316

Determination of fission products in the KNK  

International Nuclear Information System (INIS)

No fuel element damage has occured during the KNK operation with thermal reactor core. The fission products observed in spite of this originated from a surface contamination of the fuel elements. The measured results given thus describe the behaviour of fission products under normal operational conditions of the KNK-I. The methods discussed to determine fission products, however, simultaneously outline the possibilities for quantitative analytical monitoring of the fission product inventory in the KNK-II primary system in accidents with the occurence of cladding damage. (orig./LH)

1976-06-01

317

Some Fission Problems Circa 1950 and 2008  

Science.gov (United States)

In the first part of the talk I will recall conversations with Niels Bohr and John Wheeler concerning the puzzle of the asymmetric mass division in nuclear fission. In 1950 this was the outstanding problem in fission theory, and for a brief period I foolishly believed to have found the solution by relaxing the incompressibility assumption in the liquid drop model of fission. In the second part I will describe recent progress in the formulation and streamlining of the transition-state formulae for the competition between the disintegration of an excited compound nucleus by particle emission and fission.

?wiatecki, W. J.

318

Fusion and fission of heavy nuclei  

International Nuclear Information System (INIS)

The theories used to calculate the potential energy surface and the mass parameters are reviewed. For nuclear fission the theoretical data can be quantitatively compared with experimental data, but of heavy ion interactions a quantitative theory is still missing. Damping of collective motion by the concept of nuclear viscosity is discussed and its consequences for fission and fusion described. The structure of compound nuclei at high excitation energies as they are being formed in a heavy ion reaction is discussed. The close relationship between fission and heavy ion processes is stressed by using formalisms for the description of the latter that originated in fission theory. (Auth.)

1980-01-01

319

Attachment of gaseous fission products to aerosols  

International Nuclear Information System (INIS)

The circumstances under which gaseous fission products may be attached to aerosols are examined. A simple model is assumed for the interaction between the fission product molecules and the aerosol, in which the probability of attachment of a molecule on any encounter is given by a constant ?, the sticking probability. It is concluded that when gaseous fission products are released in the presence of a population of particles, particularly small particles, there is a strong possibility that they will attach rapidly to those particles. In such circumstances gaseous fission product transport would be governed by the transport properties of the particles. (author)

1985-01-01

320

Process for the extraction of fission products  

International Nuclear Information System (INIS)

A process is described for the extraction of fission products contained in irradiated nuclear fuel elements which have been subject to a temperature of at least 12000C during their irradiation prior to dissolving the fuel by the wet process. After mechanically treating the elements in order to decan and/or cut them they are brought into contact with water in order to pass the fission products into aqueous solution. The treated elements are then separated from the thus obtained aqueous solution. At least one of the fission products is then recovered from the aqueous solution. The fission products are iodine, cesium, rubidium and tritium

1979-01-01

 
 
 
 
321

Fission-track dating of obsidians  

Energy Technology Data Exchange (ETDEWEB)

Fission-track dating is applied to 16 obsidian artifacts from an archaeological excavation at Cayonu Tepesi in southeastern Anatolia. Since obsidian samples are rich in bubbles and inclusions, only the six most compact samples were found to be usable for fission-track measurements. Size studies of etched fossil- and induced-fission tracks showed that no strong thermal effects occurred during the history of these glasses so that no fading correction has been applied to the computed ages. The fission-track ages obtained range between 8.95 Myr and 25.14 Myr. It may be stated that these obsidian samples are from two different origins.

Yegingil, Z.; Goksu, Y. (Cukurova Univ., Adana (Turkey). Dept. of Physics and Space Sciences)

1982-03-01

322

Fusion-fission in light nuclear systems  

International Nuclear Information System (INIS)

The fission process, which has been largely ignored for reactions involving light nuclear systems, will be shown to play a significant role in the 32S + 24Mg reaction at energies greater than about 1 1/2 times the Coulomb barrier energy. The magnitude of the fusion-fission cross section ant its fragment mass dependence are found to be consistent with newer estimates of the fission barriers in lighter systems. The presence of the fission mechanism has significance for understanding the limitation to fusion at higher energies and has implications for comparisons of model calculations of evaporation-residue and associated light-particle yields with experiment. 17 refs., 8 figs

1988-01-01

323

Status of fission product yield data  

International Nuclear Information System (INIS)

The topics covered in this paper are: (a) cumulative yields in thermal neutron fission and in fast fission up to 14 MeV incident neutron energy, (b) dependence of the yields on incident neutron energy and spectrum, (c) independent yields, (d) charge dispersion and distribution, and (e) yields of light particles from ternary fission. The paper reviews information on these subjects for fission of actinides from 232Th upwards with special emphasis on data published since the 1973 Bologna FPND Panel, compares data sets, and discusses the gaps still to be found in them. (author).

1977-09-09

324

Theoretical Description of the Fission Process  

Energy Technology Data Exchange (ETDEWEB)

The main goals of the project can be summarized as follows: Development of effective energy functionals that are appropriate for the description of heavy nuclei. Our goal is to improve the existing energy density (Skyrme) functionals to develop a force that will be used in calculations of fission dynamics. Systematic self-consistent calculations of binding energies and fission barriers of actinide and trans-actinide nuclei using modern density functionals. This will be followed by calculations of spontaneous fission lifetimes and mass and charge divisions using dynamic adiabatic approaches based on the WKB approximation. Investigate novel microscopic (non-adiabatic) methods to study the fission process.

Witold Nazarewicz

2003-07-01

325

Fission-energy release for 16 fissioning nuclides. Final report  

International Nuclear Information System (INIS)

Results are presented of a least-squares evaluation of the components of energy release per fission in 232Th, 233U, 235U, 238U, 239Pu, and 241Pu. For completeness, older (1978) results based on systematics are presented for these and ten other isotopes of interest. There have been recent indications that the delayed energy components may be somewhat higher than those used previously, but the LSQ results do not seem to change significantly when modest (approx. 1 MeV) increases in the total delayed energy are included in the inputs. Additional measurements of most of the energy components are still needed to resolve remaining discrepancies

1981-01-01

326

Langevin calculations of fission fragment mass distribution in fission of excited nuclei  

International Nuclear Information System (INIS)

A stochastic approach based on two-dimensional Langevin equations was applied to study the main features of fission fragment mass distributions of excited fissioning systems. The forms and the variances of fission fragment mass distributions in the fissility parameter range 20 2 / A

1998-01-01

327

Large-scale fission product containment tests  

International Nuclear Information System (INIS)

The Containment Systems Experiment (CSE) program is reviewed, with emphasis on the inherent processes that remove fission products from containment atmospheres and reduce their leakage to the environment. The CSE containment vessel was sized to represent a 1/5 linear scale model of a typical 1000 MW(e) PWR. Nineteen tests were performed in a steam-air atmosphere simulating post-LOCA conditions. In eight tests containment sprays were operated, in five tests a recirculating filter-adsorber loop was operated, and in six tests only natural, passive processes occurred. Sprays were the most effective in removing airborne iodine and particulate aerosols, followed by the filter loop. Although not as effective as the engineered safety features, natural processes of diffusion to surfaces, reaction with paint, gravity settling, and removal in leak paths are shown to be significant. Together they caused a reduction in leakage of 10-2 and 10-3 for iodine and cesium, respectively, during the initial 2-h period. These attenuation factors increased to 10-3 and 10-4, respectively, for the first 24-h period

1980-11-21

328

Least squares analysis of fission neutron standard fields  

International Nuclear Information System (INIS)

A least squares analysis of fission neutron standard fields has been performed using the latest dosimetry cross sections. Discrepant nuclear data are identified and adjusted spectra for 252Cf spontaneous fission and 235U thermal fission fields are presented.

1997-01-01

329

Gabon's natural reactors: nature shows how to contain radioactive waste  

International Nuclear Information System (INIS)

[en] When the Okla ''natural'' fission reactors were discovered in 1972, investigators were soon surprised at how little several of the fission products or U-235 had moved in the two billion years since they were active. Studies underway in several countries are seeking to determine whether these ancient reactors can serve as time-tested analogs for the modern processes needed for a nuclear waste repository. (author)

1994-01-01

330

Stochastic resonance in nuclear fission  

International Nuclear Information System (INIS)

Fission decay of highly excited periodically driven compound nuclei is considered in the framework of Langevin approach. We used residual-time distribution (RTD) as a tool for studying the dynamic features in the presence of periodic perturbation. The structure of RTD essentially depends on the relation between Kramers decay rate and the frequency ? of periodic perturbation. In particular, the intensity of the first peak in RTD has a sharp maximum at certain nuclear temperature depending on ?. This maximum should be considered as fist-hand manifestation of stochastic resonance in nuclear dynamics.

2001-11-03

331

Fission barriers of excited nuclei  

International Nuclear Information System (INIS)

The 240Pu fission barrier is calculated in the finite temperature Hartree-Fock approximation with Skyrme effective forces for temperatures ranging from 0 to 3 MeV. The disappearance of the double hump barrier structure and of the underlying liquid drop barrier, when increasing the excitation energy, is shown. The latter is quantitatively related to an increase of the fissility parameter through self-consistent semi-classical calculations. The results of our calculations are shown to be compatible with experimental (p,f) cross sections in rare-earth nuclei. (orig.)

1985-02-28

332

Fission barriers of excited nuclei  

Energy Technology Data Exchange (ETDEWEB)

The /sup 240/Pu fission barrier is calculated in the finite temperature Hartree-Fock approximation with Skyrme effective forces for temperatures ranging from 0 to 3 MeV. The disappearance of the double hump barrier structure and of the underlying liquid drop barrier, when increasing the excitation energy, is shown. The latter is quantitatively related to an increase of the fissility parameter through self-consistent semi-classical calculations. The results of our calculations are shown to be compatible with experimental (p,f) cross sections in rare-earth nuclei.

Bartel, J.; Quentin, P.

1985-02-28

333

Fission track geochronology of India  

Energy Technology Data Exchange (ETDEWEB)

The fission track ages of cogenetic/co-existing minerals namely garnet, muscovite and apatite from three mica belts i.e., Bihar, Rajasthan, Nellore of peninsular India and Himalayan region, coupled with the corresponding closing temperatures of the minerals have been used to reveal the thermal and uplift histories of these regions. The data show that the extra-peninsular part of the subcontinent during Himalayan orogenic cycle (upper cretaceous-tertiary) witnessed the highest cooling and uplift rates in comparison to the older cycles in peninsular India.

Nagpaul, K.K. (Kurukshetra Univ. (India). Dept. of Physics)

1981-12-01

334

Fission track grochronology of India  

International Nuclear Information System (INIS)

The fission track ages of cogenetic/co-existing minerals namely garnet, muscovite and apatite from three mica belts i.e., Bihar, Rajasthan, Nellore of peninsular India and Himalayan region, coupled with the corresponding closing temperatures of the minerals have been used to reveal the thermal and uplift histories of these regions. The data show that the extra-peninsular part of the subcontinent during Himalayan orogenic cycle (upper cretaceous-tertiary) witnessed the highest cooling and uplift rates in comparison to the older cycles in peninsular India. (author)

1981-01-01

335

Spallation - Neutrons Beyond Nuclear Fission  

Science.gov (United States)

The classical research neutron sources are fission reactors. They have reached their technical limits as far as neutron flux is concerned. But there is an alternative way with many advantages: spallation. The emphasis in this context is on pulsed operation, which is easily achieved with spallation as being accelerator-driven. The extension of neutron scattering to fields not covered with reactors is discussed as well as the utilization of spallation neutrons for other fields such as nuclear waste transmutation and future power reactors.

Conrad, Harald

336

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the seventh issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report are measurements, compilations and evaluations of: fission product yields (neutron induced and spontaneous fission); neutron reaction cross sections of fission products; data related to the radioactive decay of fission products; delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The sixth issue of this series has been published in June 1980 as INDC(NDS)-113/G+P. The present issue includes contributions which were received by NDS between 1 August 1980 and 25 May 1981.

1980-08-01

337

Qualitative specific features of nuclear fission dynamics  

International Nuclear Information System (INIS)

Influence of the attainment of a statistical equilibrium on compound nucleus decay by means of fission or neutron emission was investigated. Analitic expressions for the probabilities of distribution in time and for the pre-equilibrium fission fragments spectra were obtained. They were determined by character of initial state, excitation energy and shell structure of compound nucleus

1975-06-13

338

Correlation measurements of fission-fragment properties  

Directory of Open Access Journals (Sweden)

Full Text Available For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments’ heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on a good understanding of the particular mechanism of scission, the mass fragmentation and partition of excitation energy. Experimental observables are fission-fragment properties like mass- and energy-distributions, and the prompt neutron as well as ?-ray multiplicities and emission spectra. The latter quantities should preferably be known as a function of fragment mass and excitation energy. Those data are highly demanded as published by the OECD-NEA in its high priority data request list. With the construction of the double (v, E) spectrometer VERDI we aim at measuring pre- and post-neutron masses directly and simultaneously to avoid prompt neutron corrections. From the simultaneous measurement of pre- and post-neutron fission-fragment data the prompt neutron multiplicity may then be inferred fully correlated with fragment mass yield and total kinetic energy. Using an ultra-fast fission event trigger spectral prompt fission ?-ray measurements may be performed. For that purpose recently developed lanthanum-halide detectors, with excellent timing characteristics, were coupled to the VERDI spectrometer allowing for a very good discrimination of fission ?-rays and prompt neutrons due to their different time-of-flight.

Oberstedt S.; Belgya T.; Billnert R.; Borcea R.; Cano-Ott D.; Göök A.; Hambsch F.-J.; Karlsson J.; Kis Z.; Martinez T.; Oberstedt A.; Szentmiklosi L.; Takác K.

2010-01-01

339

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

[en] This is the eighth issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS. Therefore, the IAEA cannot be held responsible for the information contained nor for any consequences resulting from the use of this information. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); Neutron reaction cross sections of fission products; Data related to the radioactive decay of fission products; Delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The seventh issue of this series has been published in July 1981 as INDC(NDS)-116. The present issue includes contributions which were received by NDS between 1 August 1981 and 15 June 1982

1981-08-01

340

Get Close to a Nuclear Fission Reaction!  

Science.gov (United States)

This animation-enhanced essay from the FRONTLINE Web site details what happens inside a nuclear reactor core. Learn how engineers and technicians have designed nuclear facilities to control fission activity, regulate the tremendous heat released during fission, contain radiation, and process electricity.

2004-01-29

 
 
 
 
341

The fission track dating of obsidian  

International Nuclear Information System (INIS)

[en] Recent work has been done using fission track detection to date obsidian artefact source material. The limitations of the method and realistic errors of dates produced are discussed. The long half-life of 238U spontaneous fission and the low levels of uranium present in most artefacts of archaeological interest will always limit the technique to a minor role in archaeometry

1982-01-01

342

Nuclear shape parametrization for multicluster fission  

International Nuclear Information System (INIS)

A realistic parametrization able to characterize, at least from a qualitative point of view, the evolution of nuclear shape for a multicluster fission process was developed. It is developed using seven smoothly joined portions of quadratic surfaces of revolution and it can fairly reproduce the initial, middle and final stages for binary, ternary and beyond ternary symmetrical and asymmetrical fission processes. (author)

2000-01-01

343

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the ninth issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); Neutron reaction cross sections of fission products; Data related to the radioactive decay of fission products; Delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The eighth issue of this series has been published in July 1982 as INDC(NDS)-130. The present issue includes contributions which were received by NDS between 1 August 1982 and 25 June 1983

1982-08-01

344

Spontaneous fission properties and lifetime systematics  

Energy Technology Data Exchange (ETDEWEB)

Half-lives for spontaneous fission of nuclides with even and odd numbers of particles are compared with recent theoretical calculations. A summary of odd particle hindrance factors is given. The most recent measurements of kinetic-energy and mass distributions and neutron emission for spontaneous fission of the heaviest nuclides are summarized and discussed. 51 refs., 9 figs.

Hoffman, D.C.

1989-03-01

345

Spontaneous fission properties and lifetime systematics  

International Nuclear Information System (INIS)

Half-lives for spontaneous fission of nuclides with even and odd numbers of particles are compared with recent theoretical calculations. A summary of odd particle hindrance factors is given. The most recent measurements of kinetic-energy and mass distributions and neutron emission for spontaneous fission of the heaviest nuclides are summarized and discussed. 51 refs., 9 figs

1989-01-01

346

Experimental Fission Studies at Intermediate Energies  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A series of nuclear fission experiments have been performed in the intermediate energy range. The dynamics of the fission process have been studied by means of detection of neutrons emitted from compound nuclei formed by ion beams of protons, ?-particles, and 12C-ions, all at a beam en...

Elmgren, Klas

347

Calculation code of the fission products activity  

International Nuclear Information System (INIS)

The document describes the two codes for the calculation of the fission products activity. The ''Pepin le bref'' code gives the exact value of the beta and gamma activities of completely known fission products. The code ''Plus Pepin'' introduces the beta and gamma activities whose properties are partially known. (A.L.B.)

1967-01-01

348

Dynamics of incomplete fusion-fission reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fifty years after its first observation, nuclear fission is still a lively field of research. The contemporary interest in this well established phenomenon is mainly related to heavy-ion physics, where fission provides a valuable means for the study of reaction mechanisms. Until recently, most of th...

Crouzen, Paulus Caorlus Nicolaas,

349

SOURCE OF PRODUCTS OF NUCLEAR FISSION  

Science.gov (United States)

A source of fission product recoil energy suitable for use in radiation chemistry is reported. The source consists of thermal neutron irradiated glass wool having a diameter of 1 to 5 microns and containing an isotope fissionable by thermal neutrons, such as U/sup 235/.

Harteck, P.; Dondes, S.

1960-03-15

350

Dissipation and friction in nuclear fission  

International Nuclear Information System (INIS)

We give a short review on experimental evidence for dissipation in nuclear fission as well as on the development of theories of nuclear dissipation and friction applied to the fission process. Theories span from two-body viscosity and one-body dissipation via the time dependent Schroedinger equation to linear response theory and the Fokker-Planck equation. (orig.)

1988-01-01

351

Cumulative fission yield of Ce-148 produced by thermal-neutron fission of U-235  

International Nuclear Information System (INIS)

[en] Cumulative fission yield of 148 cesium isotopes and some other fission products produced by thermal-neutron fission of 235 uranium is determined by Germanium/Lithium spectroscopic methods. The measuremets were done at Tsing-Hua open pool reactor using 3 to 4 mg of 93.15% enriched 235 uranium samples. Gamma rays are assigned to the responsible fission products by matching gamma rays energies and half lives. Fission rate is calculated by fission track method. Cumulative fission yields of 148 cesium, 90 krypton, 130 iodine, 144 lanthanum, 89 krypton, 136 xenon, 137 xenon and 140 cesium are calculated. This values are compared with previously predicted values and showed good agreement. 21 Ref

1984-01-01

352

Theoretical Description of the Fission Process  

International Nuclear Information System (INIS)

Advanced theoretical methods and high-performance computers may finally unlock the secrets of nuclear fission, a fundamental nuclear decay that is of great relevance to society. In this work, we studied the phenomenon of spontaneous fission using the symmetry-unrestricted nuclear density functional theory (DFT). Our results show that many observed properties of fissioning nuclei can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. From the calculated collective potential and collective mass, we estimated spontaneous fission half-lives, and good agreement with experimental data was found. We also predicted a new phenomenon of trimodal spontaneous fission for some transfermium isotopes. Our calculations demonstrate that fission barriers of excited superheavy nuclei vary rapidly with particle number, pointing to the importance of shell effects even at large excitation energies. The results are consistent with recent experiments where superheavy elements were created by bombarding an actinide target with 48-calcium; yet even at high excitation energies, sizable fission barriers remained. Not only does this reveal clues about the conditions for creating new elements, it also provides a wider context for understanding other types of fission. Understanding of the fission process is crucial for many areas of science and technology. Fission governs existence of many transuranium elements, including the predicted long-lived superheavy species. In nuclear astrophysics, fission influences the formation of heavy elements on the final stages of the r-process in a very high neutron density environment. Fission applications are numerous. Improved understanding of the fission process will enable scientists to enhance the safety and reliability of the nation's nuclear stockpile and nuclear reactors. The deployment of a fleet of safe and efficient advanced reactors, which will also minimize radiotoxic waste and be proliferation-resistant, is a goal for the advanced nuclear fuel cycles program. While in the past the design, construction, and operation of reactors were supported through empirical trials, this new phase in nuclear energy production is expected to heavily rely on advanced modeling and simulation capabilities.

2009-01-01

353

Theoretical Description of the Fission Process  

Energy Technology Data Exchange (ETDEWEB)

Advanced theoretical methods and high-performance computers may finally unlock the secrets of nuclear fission, a fundamental nuclear decay that is of great relevance to society. In this work, we studied the phenomenon of spontaneous fission using the symmetry-unrestricted nuclear density functional theory (DFT). Our results show that many observed properties of fissioning nuclei can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. From the calculated collective potential and collective mass, we estimated spontaneous fission half-lives, and good agreement with experimental data was found. We also predicted a new phenomenon of trimodal spontaneous fission for some transfermium isotopes. Our calculations demonstrate that fission barriers of excited superheavy nuclei vary rapidly with particle number, pointing to the importance of shell effects even at large excitation energies. The results are consistent with recent experiments where superheavy elements were created by bombarding an actinide target with 48-calcium; yet even at high excitation energies, sizable fission barriers remained. Not only does this reveal clues about the conditions for creating new elements, it also provides a wider context for understanding other types of fission. Understanding of the fission process is crucial for many areas of science and technology. Fission governs existence of many transuranium elements, including the predicted long-lived superheavy species. In nuclear astrophysics, fission influences the formation of heavy elements on the final stages of the r-process in a very high neutron density environment. Fission applications are numerous. Improved understanding of the fission process will enable scientists to enhance the safety and reliability of the nation’s nuclear stockpile and nuclear reactors. The deployment of a fleet of safe and efficient advanced reactors, which will also minimize radiotoxic waste and be proliferation-resistant, is a goal for the advanced nuclear fuel cycles program. While in the past the design, construction, and operation of reactors were supported through empirical trials, this new phase in nuclear energy production is expected to heavily rely on advanced modeling and simulation capabilities.

Witold Nazarewicz

2009-10-25

354

Power burst facility fission product detection system  

International Nuclear Information System (INIS)

Fuel performance tests at the Idaho National Engineering Laboratory (INEL) offer a unique opportunity for detailed studies of fission product behavior during light water reactor (LWR)-type fuel failure. A fission product detection system (FPDS), which includes an advanced gamma spectrometer, was installed on the test loop of the Power Burst Facility (PBF) to provide continuous measurement of the fission product concentrations in the coolant. The detection system instrumentation is discussed in detail with emphasis placed on the advanced features. Examples are shown of gross detector response and reduced spectrometer data which indicate test fuel condition and fission product behavior. Performance of the system during initial tests has exceeded expectations, and the project is now contributing significantly to fission product behavior research

1979-07-27

355

Physics of neutron emission in fission  

International Nuclear Information System (INIS)

The document contains the proceedings of the IAEA Consultants' Meeting on the Physics of Neutron Emission in Fission, Mito City (Japan), 24-27 May 1988. Included are the conclusions and recommendations reached at the meeting and the papers presented by the meeting participants. These papers cover the following topics: Energy dependence of the number of fission neutrons ?-bar (3 papers), multiplicity distribution of fission neutrons (3 papers), competition between neutron and ?-ray emission (4 papers), the fission neutron yield in resonances (2 papers) and the energy spectrum of fission neutrons in experiment (9 papers), theory (4 papers) and evaluation (1 paper). A separate abstract was prepared for each of these papers. Refs, figs and tabs.

1989-01-01

356

Systematics of Fission-Product Yields  

Energy Technology Data Exchange (ETDEWEB)

Empirical equations representing systematics of fission-product yields have been derived from experimental data. The systematics give some insight into nuclear-structure effects on yields, and the equations allow estimation of yields from fission of any nuclide with atomic number Z{sub F} = 90 thru 98, mass number A{sub F} = 230 thru 252, and precursor excitation energy (projectile kinetic plus binding energies) PE = 0 thru {approx}200 MeV--the ranges of these quantities for the fissioning nuclei investigated. Calculations can be made with the computer program CYFP. Estimates of uncertainties in the yield estimates are given by equations, also in CYFP, and range from {approx} 15% for the highest yield values to several orders of magnitude for very small yield values. A summation method is used to calculate weighted average parameter values for fast-neutron ({approx} fission spectrum) induced fission reactions.

A.C. Wahl

2002-05-01

357

Mechanisms of mitochondrial fission and fusion.  

UK PubMed Central (United Kingdom)

Mitochondria continually change shape through the combined actions of fission, fusion, and movement along cytoskeletal tracks. The lengths of mitochondria and the degree to which they form closed networks are determined by the balance between fission and fusion rates. These rates are influenced by metabolic and pathogenic conditions inside mitochondria and by their cellular environment. Fission and fusion are important for growth, for mitochondrial redistribution, and for maintenance of a healthy mitochondrial network. In addition, mitochondrial fission and fusion play prominent roles in disease-related processes such as apoptosis and mitophagy. Three members of the Dynamin family are key components of the fission and fusion machineries. Their functions are controlled by different sets of adaptor proteins on the surface of mitochondria and by a range of regulatory processes. Here, we review what is known about these proteins and the processes that regulate their actions.

van der Bliek AM; Shen Q; Kawajiri S

2013-06-01

358

Event-by-Event Fission with FREYA  

Energy Technology Data Exchange (ETDEWEB)

The recently developed code FREYA (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. The presentation first discusses the present status of FREYA, which has now been extended up to energies where pre-equilibrium emission becomes significant and one or more neutrons may be emitted prior to fission. Concentrating on {sup 239}Pu(n,f), we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also briefly suggest novel fission observables that could be measured with modern detectors.

Randrup, J; Vogt, R

2010-11-09

359

Los Alamos National Laboratory Fission Basis  

Energy Technology Data Exchange (ETDEWEB)

This report is an overview of two main publications that provide a comprehensive review of the Los Alamos National Laboratory (LANL) Fission Basis. The first is the experimental paper, {sup F}ission Product Data Measured at Los Alamos for Fission Spectrum and Thermal Neutrons on {sup 239}Pu, {sup 235}U, {sup 238}U, [Selby, H. D., et al., Nucl. Data Sheets, Vol. 111 2010, pp. 2891-2922] and the second is the theoretical paper, Fission Product Yields from Fission Spectrum n+ {sup 239}Pu for ENDF/B-VII.1, [Chadwick, M. B., et al., Nucl. Data Sheets, Vol. 111, 2010, pp. 2923-2964]. One important note is that none of this work would have been possible without the great documentation of the experimental details and results by G.W. Knobeloch, G. Butler, C.I. Browne, B. Erdal, B. Bayhurst, R. Prestwood, V. Armijo, J. Hasty and many others. (authors)

Keksis, A.L.; Chadwick, M.B.; Selby, H.D.; Mac Innes, M.R.; Barr, D.W.; Meade, R.A.; Burns, C.J.; Wallstrom, T.C. [Los Alamos National Laboratory, NM 87545 (United States)

2011-07-01

360

Los Alamos National Laboratory Fission Basis  

International Nuclear Information System (INIS)

This report is an overview of two main publications that provide a comprehensive review of the Los Alamos National Laboratory (LANL) Fission Basis. The first is the experimental paper, Fission Product Data Measured at Los Alamos for Fission Spectrum and Thermal Neutrons on 239Pu, 235U, 238U, [Selby, H. D., et al., Nucl. Data Sheets, Vol. 111 2010, pp. 2891-2922] and the second is the theoretical paper, Fission Product Yields from Fission Spectrum n+ 239Pu for ENDF/B-VII.1, [Chadwick, M. B., et al., Nucl. Data Sheets, Vol. 111, 2010, pp. 2923-2964]. One important note is that none of this work would have been possible without the great documentation of the experimental details and results by G.W. Knobeloch, G. Butler, C.I. Browne, B. Erdal, B. Bayhurst, R. Prestwood, V. Armijo, J. Hasty and many others. (authors)

2011-01-01

 
 
 
 
361

Theory of neutron emission in fission  

International Nuclear Information System (INIS)

Following a summary of the observables in neutron emission in fission, a brief history is given of theoretical representations of the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity bar ?p. This is followed by descriptions, together with examples, of modern approaches to the calculation of these quantities including recent advancements. Emphasis will be placed upon the predictability and accuracy of the modern approaches. In particular, the dependence of N(E) and bar ?p on the fissioning nucleus and its excitation energy will be discussed, as will the effects of and competition between first-, second- and third-chance fission in circumstances of high excitation energy. Finally, properties of neutron-rich (fission-fragment) nuclei are discussed that must be better known to calculate N(E) and bar ?p with higher accuracy than is currently possible.

1989-01-01

362

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the first issue of a report series on Fission Product Nuclear Data (FPND), published every six months by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). Its purpose is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The types of activities being included in this report are measurements, compilations and evaluations of: fission product yields; neutron cross-section data of fission products; data related to ?-, ?-decay of fission products; delayed neutron data; and fission product decay-heat. The present issue includes contributions which were received by NDS before 1 November 1975.

1975-11-01

363

Theory of neutron emission in fission  

Energy Technology Data Exchange (ETDEWEB)

Neutron emission in fission is usually described in terms of two observables: the energy spectrum of emitted neutrons N(E) and the average number of neutrons emitted per fission, or average neutron multiplicity, /bar v/p. These observables are measured before the residual fission fragments decay toward the valley of ..beta.. stability and are therefore referred to as the prompt neutron spectrum N(E) and the average prompt neutron multiplicity /bar v/p. They are of fundamental importance to the design of macroscopic systems that are driven by the fission reaction, such as thermal or fast reactors. It is the purpose of this paper to describe existing theoretical models for these two observables. Other observables for neutron emission in fission will not be described here due to space limitations. 12 refs., 2 figs.

Madland, D.G.

1988-01-01

364

Theoretical study of fission dynamics with muons  

International Nuclear Information System (INIS)

Following muon capture by actinide atoms, some of the inner shell muonic transitions proceed by inverse internal conversion, i.e. the excitation energy of the muonic atom is transferred to the nucleus. In particular, the muonic E2:(3d?1s) transition energy is close to the peak of the isoscalar giant quadrupole resonance in actinide nuclei which exhibits a large fission width. Prompt fission in the presence of a bound muon allows us to study the dynamics of large-amplitude collective motion. We solve the time-dependent Dirac equation for the muonic spinor wave function in the Coulomb field of the fissioning nucleus on a 3-dimensional lattice and demonstrate that the muon attachment probability to the light fission fragment is a measure of the nuclear energy dissipation between the outer fission barrier and the scission point

1992-01-01

365

Spontaneous fission in the heavy elements  

International Nuclear Information System (INIS)

[en] Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results were surprising in that spontaneous fission half-lives turned out to be much longer than expected and mass and kinetic-energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments caused a re-evaluation of the understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties. (author) 22 refs.; 14 figs

1990-01-01

366

Fission fragment induction of bone sarcomas  

International Nuclear Information System (INIS)

[en] Fission fragments, emitted by the spontaneous fission of 252Cf, were much less effective per unit energy than were ?-particles in the induction of bone sarcomas in C57B1 mice. This agrees with a similar finding by A. L. Brooks et al. on the ineffectiveness of fission fragments from 252Cf in producing chromosome aberrations in the livers of Chinese hamsters. The reduced effectiveness of fission fragments is attributed to their extremely high LET (about 4000 keV/?m of tissue) which results in fewer cellular traversals, and probably more overkill per cell traversed than occurs with the same dose of ?-particles, for which the LET is about 135 keV/?m. The indicated RBE of fission fragments relative to ?-particles in the induction of bone sarcomas was between the 95 percent confidence limits of (--) 0.85 and (+) 0.35. Our best estimate of the RBE is about 0.03, based on theoretical considerations

1975-03-31

367

Fission product measurements in the inpile fission product loop  

International Nuclear Information System (INIS)

The behavior of fission gases in a circulating sodium system was investigated. The release rates to the covergas were strongly influenced by the sodium temperature. For the system I-135 /Xe-135 m, Xe-135 the release behavior of the xenon isotopes followed exactly the adsorption of iodine within the loop. The behavior of nuclides formed during irradiation is more complex and could not be explained completely. Two kinds of half lives for the degassing process were found. Degassing half lives in the range of 17 to 32 minutes are explained by diffusion through the sodium-covergas interface. Another kind of degassing half life, ranging from 80 to over 200 minutes must be explained by some special features of the system.

1976-05-06

368

Fission-suppressed fusion breeder on the thorium cycle and nonproliferation  

Science.gov (United States)

Fusion reactors could be designed to breed fissile material while suppressing fissioning thereby enhancing safety. The produced fuel could be used to startup and makeup fuel for fission reactors. Each fusion reaction can produce typically 0.6 fissile atoms and release about 1.6 times the 14 MeV neutron's energy in the blanket in the fission-suppressed design. This production rate is 2660 kg/1000 MW of fusion power for a year. The revenues would be doubled from such a plant by selling fuel at a price of 60/g and electricity at $0.05/kWh for Q=Pfusion/Pinput=4. Fusion reactors could be designed to destroy fission wastes by transmutation and fissioning but this is not a natural use of fusion whereas it is a designed use of fission reactors. Fusion could supply makeup fuel to fission reactors that were dedicated to fissioning wastes with some of their neutrons. The design for safety and heat removal and other items is already accomplished with fission reactors. Whereas fusion reactors have geometry that compromises safety with a complex and thin wall separating the fusion zone from the blanket zone where wastes could be destroyed. Nonproliferation can be enhanced by mixing 233U with 238U. Also nonproliferation is enhanced in typical fission-suppressed designs by generating up to 0.05 232U atoms for each 233U atom produced from thorium, about twice the IAEA standards of ``reduced protection'' or ``self protection.'' With 2.4% 232U, high explosive material is predicted to degrade owing to ionizing radiation after a little over 1/2 year and the heat rate is 77 W just after separation and climbs to over 600 W ten years later. The fissile material can be used to fuel most any fission reactor but is especially appropriate for molten salt reactors (MSR) also called liquid fluoride thorium reactors (LFTR) because of the molten fuel does not need hands on fabrication and handling.

Moir, R. W.

2012-06-01

369

Fission-suppressed fusion breeder on the thorium cycle and nonproliferation  

International Nuclear Information System (INIS)

Fusion reactors could be designed to breed fissile material while suppressing fissioning thereby enhancing safety. The produced fuel could be used to startup and makeup fuel for fission reactors. Each fusion reaction can produce typically 0.6 fissile atoms and release about 1.6 times the 14 MeV neutron's energy in the blanket in the fission-suppressed design. This production rate is 2660 kg/1000 MW of fusion power for a year. The revenues would be doubled from such a plant by selling fuel at a price of 60/g and electricity at $0.05/kWh for Q=Pfusion/Pinput=4. Fusion reactors could be designed to destroy fission wastes by transmutation and fissioning but this is not a natural use of fusion whereas it is a designed use of fission reactors. Fusion could supply makeup fuel to fission reactors that were dedicated to fissioning wastes with some of their neutrons. The design for safety and heat removal and other items is already accomplished with fission reactors. Whereas fusion reactors have geometry that compromises safety with a complex and thin wall separating the fusion zone from the blanket zone where wastes could be destroyed. Nonproliferation can be enhanced by mixing 233U with 238U. Also nonproliferation is enhanced in typical fission-suppressed designs by generating up to 0.05 232U atoms for each 233U atom produced from thorium, about twice the IAEA standards of “reduced protection” or “self protection.” With 2.4%232U, high explosive material is predicted to degrade owing to ionizing radiation after a little over 1/2 year and the heat rate is 77 W just after separation and climbs to over 600 W ten years later. The fissile material can be used to fuel most any fission reactor but is especially appropriate for molten salt reactors (MSR) also called liquid fluoride thorium reactors (LFTR) because of the molten fuel does not need hands on fabrication and handling.

2012-06-19

370

Fission-suppressed fusion breeder on the thorium cycle and nonproliferation  

Energy Technology Data Exchange (ETDEWEB)

Fusion reactors could be designed to breed fissile material while suppressing fissioning thereby enhancing safety. The produced fuel could be used to startup and makeup fuel for fission reactors. Each fusion reaction can produce typically 0.6 fissile atoms and release about 1.6 times the 14 MeV neutron's energy in the blanket in the fission-suppressed design. This production rate is 2660 kg/1000 MW of fusion power for a year. The revenues would be doubled from such a plant by selling fuel at a price of 60/g and electricity at $0.05/kWh for Q=P{sub fusion}/P{sub input}=4. Fusion reactors could be designed to destroy fission wastes by transmutation and fissioning but this is not a natural use of fusion whereas it is a designed use of fission reactors. Fusion could supply makeup fuel to fission reactors that were dedicated to fissioning wastes with some of their neutrons. The design for safety and heat removal and other items is already accomplished with fission reactors. Whereas fusion reactors have geometry that compromises safety with a complex and thin wall separating the fusion zone from the blanket zone where wastes could be destroyed. Nonproliferation can be enhanced by mixing {sup 233}U with {sup 238}U. Also nonproliferation is enhanced in typical fission-suppressed designs by generating up to 0.05 {sup 232}U atoms for each {sup 233}U atom produced from thorium, about twice the IAEA standards of 'reduced protection' or 'self protection.' With 2.4%{sup 232}U, high explosive material is predicted to degrade owing to ionizing radiation after a little over 1/2 year and the heat rate is 77 W just after separation and climbs to over 600 W ten years later. The fissile material can be used to fuel most any fission reactor but is especially appropriate for molten salt reactors (MSR) also called liquid fluoride thorium reactors (LFTR) because of the molten fuel does not need hands on fabrication and handling.

Moir, R. W. [Vallecitos Molten Salt Research, 607 E. Vallecitos Rd., Livermore, CA 94550 925-447-8804 (United States)

2012-06-19

371

Downstream behavior of fission products  

International Nuclear Information System (INIS)

[en] The downstream behavior of fission products has been investigated by injecting mixtures of CsOH, CsI, and Te into a flowing steam/hydrogen stream and determining the physical and chemical changes that took place as the gaseous mixture flowed down a reaction duct on which a temperature gradient (10000 to 2000C) had been imposed. Deposition on the wall of the duct occurred by vapor condensation in the higher temperature regions and by aerosol deposition in the remainder of the duct. Reactions in the gas stream between CsOH and CsI and between CsOH and Te had an effect on the vapor condensation. The aerosol was characterized by the use of impingement tabs placed in the gas stream

1986-01-01

372

Downstream behavior of fission products  

Energy Technology Data Exchange (ETDEWEB)

The downstream behavior of fission products has been investigated by injecting mixtures of CsOH, CsI, and Te into a flowing steam/hydrogen stream and determining the physical and chemical changes that took place as the gaseous mixture flowed down a reaction duct on which a temperature gradient (1000/sup 0/ to 200/sup 0/C) had been imposed. Deposition on the wall of the duct occurred by vapor condensation in the higher temperature regions and by aerosol deposition in the remainder of the duct. Reactions in the gas stream between CsOH and CsI and between CsOH and Te had an effect on the vapor condensation. The aerosol was characterized by the use of impingement tabs placed in the gas stream.

Johnson, I.; Farahat, M.K.; Settle, J.L.; Johnson, C.E.; Ritzman, R.

1986-01-01

373

Geology behind nuclear fission technology  

International Nuclear Information System (INIS)

Geology appears to have played an important role of a precursor to Nuclear Fission Technology (NFT), in the latter's both birth from the nucleus of an atom of and most important application as nuclear power extracted from Uranium (U), present in its minerals. NFT critically depends upon the availability of its basic raw material, viz., nuclear fuel as U and/ or Th, extracted from U-Th minerals of specific rock types in the earth's crust. Research and Development of the Nuclear Fuel Cycle (NFC) depends heavily on 'Geology'. In this paper, a brief review of the major branches of geology and their contributions during different stages of NFC, in the Indian scenario, is presented so as to demonstrate the important role played by 'Geology' behind the development of NFT, in general, and NFC, in particular. (author)

2005-01-01

374

Recent Advances in Singlet Fission  

Science.gov (United States)

A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation.

Smith, Millicent B.; Michl, Josef

2013-04-01

375

Recent advances in singlet fission.  

UK PubMed Central (United Kingdom)

A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation.

Smith MB; Michl J

2013-01-01

376

On the mechanism of fission neutron emission  

International Nuclear Information System (INIS)

This review represents the present knowledge of the mechanism of prompt fission neutron emission. Starting with a brief fission process characterization related with neutron emission, possible emission mechanisms are discussed. It is emphasized that the experimental study of special mechanisms, i.e. scission neutron emission processes, requires a sufficiently correct description of emission probabilities on the base of the main mechanism, i.e. the evaporation from fully accelerated fragments. Adequate statistical-model approaches have to account for the complexity of nuclear fission reflected by an intricate fragment distribution. The present picture of scission neutron emission is not clarified neither experimentally nor theoretically. Deduced data are contradictory and depend on the used analysis procedures often involving rough discriptions of evaporated-neutron distributions. The contribution of two secondary mechanisms of fission neutron emission, i.e. the neutron evaporation during fragment acceleration and neutron emission due to the decay of 5He after ternary fission, is estimated. We summarize the recent progress of the theoretical description of fission neutron spectra in the framework of statistical models considering the standard spectrum of 252Cf(sf) neutrons especially. The main experimental basis for the study of fission neutron emission is the accurate measurement of emission probabilities as a function of emission energy and angle (at least) as well as fragment parameters (mass number ratio and kinetic energy). The present status is evaluated. (author).

1986-01-01

377

Particular aspects of particle-accompanied fission  

International Nuclear Information System (INIS)

A brief survey is presented of particular recent experiments on particle accompanied fission. Very recently, a new experiment was performed to re-measure the ternary ?-particle energy spectrum in 252Cf spontaneous fission by time-of-flight techniques. Compared to many previous experiments, which entailed detection thresholds of 6 to 9 MeV ?-particle energy due to the ?E - E method applied and use of protection foils on detectors, the energy distribution of ternary ?-particles could, for the first time, be measured down to 1 MeV.We, furthermore, report on experimental studies on quaternary fission in spontaneous fission of 252Cf, on the one hand, and the neutron-induced fission reactions 233,235U(nth,f), on the other hand. Finally, in a third experiment, ternary fission in the reaction 235U(n,f) with cold polarised neutrons was under investigation. From peculiar but unmistakable shifts in the ?-particle angular distribution when flipping the neutron spin the fissioning nucleus was deduced to undergo rotation at scission. This startling new phenomenon was dubbed the 'ROT' effect. (authors)

2007-01-01

378

Combined effect of simultaneous exposure with fission neutron and ?-rays  

International Nuclear Information System (INIS)

[en] By using four methods of data processing, several kinds of diological endopoints (LD50/5 day; LD50/30 day; weight loss of thymus: 3H-TdR incorporation of bone marrow DNA; specific activity of bone marrow DNA; synthetic cells of bone marrow DNA and dicentric yield of bone marrow cells) have been analyzed. The preliminary results indicate that combined effect of simultaneous exposure with fission neutron and ?-rays are additive in nature for above-mentioned endpoins

1988-01-01

379

Submicroscopic observation of fission product tracks in mica  

Energy Technology Data Exchange (ETDEWEB)

The method of folding the replica of tracks has been shown to be a useful tool to analyze nuclear tracks at submicroscopic level. To date, this methodology was applied only to organic SSNTD. In the present study its applications are extended to an inorganic material. Muscovite mica was irradiated with fission products and replicas of track profiles were evaluated by TEM up to 10 A resolution. The tracks showed a central amorphous damaged region and an external bulk zone where the crystalline nature of the mica was presented. (author).

Meoli, P.; Mazzei, R.; Bernaola, O.A. [National Atomic Energy Commission, Buenos Aries (Argentina)

1993-12-31

380

Fission, fusion and the energy crisis. 2. ed.  

International Nuclear Information System (INIS)

[en] The subject is covered in chapters, entitled: living on capital (energy reserves and consumption forecasts); the atom and its nucleus, mass and energy; fission and the bomb; the natural uranium reactor; enriched reactors; control and safety; long-term economics (the breeder reactions and nuclear fuel reserves); short-term economics (cost per kilowatt hour); national nuclear power programmes; nuclear power and the environment (including reprocessing, radioactive waste management, public relations); renewable energy sources; the fusion programme; summary and comment. (U.K.)

1980-01-01

 
 
 
 
381

Uranium isotopic data in uraninite spent fuel from the Bangombe natural nuclear reactor (Gabon) and its surroundings  

International Nuclear Information System (INIS)

[en] In the framework of the 'Oklo-Natural Analogue Phase II' Project, uraninite from the Bangombe natural reactor and samples from its host rock were analyzed to determine their uranium isotopic composition by thermal ionisation mass spectrometry, inductively coupled plasma mass spectrometry and alpha spectrometry. There were several objectives for this work: (i) to validate the 235U/238U isotopic ratios obtained by these techniques; (ii) to test the use of the 235U/238U ratio of uraninite as a tracer of migration/retention processes of uranium from the source term to the far field; (iii) to evaluate the most recent migration/retention processes of uranium in the system by U-series disequilibrium

2000-07-15

382

Future challenges for nuclear data research in fission (u)  

Energy Technology Data Exchange (ETDEWEB)

I describe some high priority research areas in nuclear fission, where applications in nuclear reactor technologies and in modeling criticality in general are demanding higher accuracies in our databases. We focus on fission cross sections, fission neutron spectra, and fission product data.

Chadwick, Mark B [Los Alamos National Laboratory

2010-01-01

383

Dissociation and fission of small sodium and strontium clusters  

International Nuclear Information System (INIS)

Fission of charged small sodium and strontium clusters has been studied by the ab initio density functional theory methods. Dissociation energies and fission barriers have been calculated for all possible fission channels for the Na102+ and Sr72+ clusters. The dissociation energies and fission barriers have been analyzed as functions of the daughter fragment size. (authors)

2005-01-01

384

Pulsed neutron uranium borehole logging with prompt fission neutrons  

International Nuclear Information System (INIS)

The gross count natural gamma log normally used for uranium borehole logging is seriously affected by disequilibrium. Methods for the direct measurement of uranium, such as neutron logging, which are not affected by disequilibrium have been the object of considerable effort in recent years. This paper describes a logging system for uranium which uses a small accelerator to generate pulses of 14 MeV neutrons to detect and assay uranium by the measurement of prompt fission neutrons in the epithermal energy range. After an initial feasibility study, a prototype logging probe was built for field evaluation which began in January 1976. Physical and operational characteristics of the prototype probe, the neutron tube-transformer assembly, and the neutron tube are described. In logging operations, only the epithermal prompt fission neutrons detected between 250 microseconds to 2500 microseconds following the excitation neutron pulse are counted. Comparison of corrected neutron logs with the conventional gross count natural gamma logs and the chemical assays of cores from boreholes are shown. The results obtained with this neutron probe clearly demonstrate its advantages over the gross count natural gamma log, although at this time the accuracy of the neutron log assay is not satisfactory under some conditions. The necessary correction factors for various borehole and formation parameters are being determined and, when applied, should improve the assay accuracy.

1976-10-25

385

Origin of the Moon by rotational fission  

Energy Technology Data Exchange (ETDEWEB)

Consistent with the current understanding of the Moon's bulk composition, internal structure, seismic and tectonic characteristics, evidence is discussed which suggests that the Moon originated by fission. The concepts discussed are: (1) all stars are members of close or contact binary systems; (2) advances in dynamical studies of the fission hypothesis show that stellar bodies also undergo fission; (3) the newly formed proto moon would have lost a large fraction of its original mass via mass transfer; and (4) due to the foregoing concepts the result would be a moon of terrestrial mantle material which was depleted in both metallic iron and volatiles.

Binder, A.B.

1984-01-01

386

Nuclear fission with a Langevin equation  

International Nuclear Information System (INIS)

[en] A microscopically derived Langevin equation is applied to thermally induced nuclear fission. An important memory effect is pointed out and discussed. A strong friction coefficient, estimated from microscopic quantities, tends to decrease the stationary limit of the fission rate and to increase the transient time. The calculations are performed with a collective mass depending on the collective variable and with a constant mass. Fission rates calculated at different temperatures are shown and compared with previous available results. (author) 23 refs.; 7 figs

1992-01-01

387

Fission tracks and cooling rates of meteorites  

Energy Technology Data Exchange (ETDEWEB)

Recent work on fission track studies of meteorite samples to obtain cooling rates of meteorite parent bodies is reviewed. The cooling rates of chondrites are in excess of 1/sup 0/K/10/sup 6/ yr. Fission track studies of phosphate grains in mesosiderites do not support the extremely slow cooling rates of 0.1/sup 0/K/10/sup 6/ yr for these meteorites, inferred from metallographic studies. The accumulating evidence from fission track studies indicates a gross underestimation of the cooling rates of meteorites as determined by the metallographic techniques.

Crozaz, G. (Physical Research Lab., Ahmedabad (India))

1981-12-01

388

Mitochondrial fission facilitates mitophagy in Saccharomyces cerevisiae.  

UK PubMed Central (United Kingdom)

As a highly dynamic organelle, mitochondria undergo constitutive fusion and fission as well as biogenesis and degradation. Mitophagy, selective mitochondrial degradation through autophagy, is a conserved cellular process used for the elimination of excessive and damaged mitochondria in eukaryotes. Despite the significance of mitophagy in cellular physiology and pathophysiologies, the underlying mechanism of this process is far from clear. In this report, we studied the role of mitochondrial fission during mitophagy, and uncover a direct link between the fission complex and mitophagy machinery in Saccharomyces cerevisiae.

Mao K; Klionsky DJ

2013-09-01

389

Nuclear fission induced by high energy protons  

International Nuclear Information System (INIS)

The fission of 203Pb, 232Th, 238U, 239Pu, 209Br nuclei in the energy region T approximately equal to 0.1-2 GeV is considered on the basis of intranuclear cascade model. The competition between fission and evaporation of excited nuclei remaining after the cascade phase of the interaction is taken into account. Fong's model is used to calculate the fission process. The multiplicity of produced particles (d, t, 3He, ?), the energy spectra of neutrons, the distributions of residual nuclei are discussed. The calculated results are compared with the experiment and with the known theoretical data

1979-01-01

390

A third minimum in the fission barrier  

International Nuclear Information System (INIS)

The latest refinements of the fission barrier pinpointed the occurrence of a third minimum. This paper reviews the search for such a minimum through high energy resolution fission probability measurements. After successful experiments with neutrons, deuteron beams were used. Higher J spin members of a pair of rotational bands with opposite parities were found, in the (d,pf) experimental results, as expected. The experimental fission barrier parameters are compared to the theoretical calculations obtained from the macroscopic-microscopic model and the purely microscopic one. The properties of nuclei at the third minimum deformation are also discussed

1989-01-01

391

Fusion-fission of heavy systems  

International Nuclear Information System (INIS)

The influence of the entrance channel on fission processes was studied by forming the same composite system by two different target-projectile combinations (40Ar + 209Bi and 56Fe + 187Re, respectively). Compound nucleus fission and quasi fission were observed and the analysis was performed in the framework of the extra-extra-push model, which provides a qualitative interpretation of the results; limits for the extra-extra-push threshold are given, but problems with quantitative predictions for the extra-push are noted. (orig.).

1988-01-01

392

Detection of fission fragments by secondary emission  

International Nuclear Information System (INIS)

This fission fragment detecting apparatus is based on the principle that fragments traversing a thin foil will cause emission of secondary electrons. These electrons are then accelerated (10 kV) and directly detected by means of a plastic scintillator and associated photomultiplier. Some of the advantages of such a detector are, its rapidity, its discriminating power between alpha particles and fission fragments, its small energy loss in detecting the fragments and the relatively great amount of fissionable material which it can contain. This paper is subdivided as follows: a) theoretical considerations b) constructional details of apparatus and some experimental details and c) a study of the secondary emission effect itself. (author)

1965-01-01

393

Deep-Earth reactor: Nuclear fission, helium, and the geomagnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Geomagnetic field reversals and changes in intensity are understandable from an energy standpoint as natural consequences of intermittent and/or variable nuclear fission chain reactions deep within the Earth. Moreover, deep-Earth production of helium, having 3He/4He ratios within the range obser...

Hollenbach, D. F.; Herndon, J. M.

394

Neutron emission as a probe of fusion-fission and quasi-fission dynamics  

International Nuclear Information System (INIS)

Pre- and post scission neutron yeilds have been measured as a function of projectile mass, compound nucleus fissility, and fission mass-split and total kinetic energy (TKE) for 27 fusion-fission and quasi-fission reactions induced by beams of 16,18O, 40Ar and 64Ni. A new method of interpretation of experimental pre-scission neutron multiplicities ?-pre and mean kinetic energies ?? allows the extraction of fission time scales with much less uncertainty than previously, all fusion-fission results being consistent with a dynamical time scale of (35±15) x 10-21s for symmetric fission. All reactions show that ?-pre falls quite rapidly with increasing mass-asymmetry; evidence is presented that for fusion-fission reactions this is partly due to a reduction of the dynamical fission time scale with mass-asymmetry. For quasi-fission, the data indicate that the pre-scission multiplicity and mean neutron kinetic energy are very sensitive to the final mass-asymmetry, but that the time scale is virtually independent of mass-asymmetry. It is concluded that for fusion-fission there is no dependence of ?-pre on TKE, whilst for 64Ni-induced quasi-fission reactions, a strong increase of ?-pre with decreasing TKE is observed, probably largely caused by neutron emission during the acceleration time of the fission fragments in these fast reactions. Interpretation of post-scission multiplicities in terms of fragment excitation energies leads to deduced time scales consistent with those determined from the pre-scission data. 54 refs., 17 tabs., 25 figs

1991-01-01

395

Fusion-fission in light nuclear systems  

Energy Technology Data Exchange (ETDEWEB)

The fission process, which has been largely ignored for reactions involving light nuclear systems, will be shown to play a significant role in the /sup 32/S + /sup 24/Mg reaction at energies greater than about 1 1/2 times the Coulomb barrier energy. The magnitude of the fusion-fission cross section ant its fragment mass dependence are found to be consistent with newer estimates of the fission barriers in lighter systems. The presence of the fission mechanism has significance for understanding the limitation to fusion at higher energies and has implications for comparisons of model calculations of evaporation-residue and associated light-particle yields with experiment. 17 refs., 8 figs.

Sanders, S.J.

1988-01-01

396

Bimodality in macroscopic dynamics of nuclear fission  

International Nuclear Information System (INIS)

The elastodynamic collective model of nuclear fission is outlined whose underlying idea is that the stiff structure of nuclear shells imparts to nucleus properties typical of a small piece of an elastic solid. Emphasis is placed on the macroscopic dynamics of nuclear deformations resulting in fission by two energetically different modes. The low-energy S-mode is the fission due to disruption of elongated quadrupole spheroidal shape. The characteristic features of the high-energy T-mode of division by means of torsional shear deformations is the compact scission configuration. Analytic and numerical estimates for the macroscopic fission-barrier heights are presented, followed by discussion of fingerprints of the above dynamical bimodality in the available data

2000-01-01

397

Fast fission of {sup 238}U  

Energy Technology Data Exchange (ETDEWEB)

Independent and cumulative yields of about 150 products from fast fission of {sup 238}U, many of them with half-lives of the order of seconds, have been measured at Studsvik. Some results are reported here.

Rudstam, G.; Johansson, P.I.; Aleklett, K. [Studsvik Neutron Research Lab., Nykoeping (Sweden)

1994-12-31

398

Fission-product release during accidents  

International Nuclear Information System (INIS)

One of the aims when managing a reactor accident is to minimize the release of radioactive fission products. Release is dependent not only on the temperature, but also on the partial pressure of oxygen. Strongly oxidizing atmospheres, such as those that occurred during the Chernobyl accident, released semi-volatile elements like ruthenium, which has volatile oxides. At low temperatures, UO2 oxidization to U3O8 can result in extensive breakup of the fuel, resulting in the release of non-volatile fission products as aerosols. Under less oxidizing conditions, when hydrogen accumulates from the zirconium-water reaction, the resulting low oxygen partial pressure can significantly reduce these reactions. At TMI-2, only the noble gases and volatile fission products were released in significant quantities. A knowledge of the effect of atmosphere as well as temperature on the release of fission products from damaged reactor cores is therefore a useful, if not necessary, component of information required for accident management.

1991-01-01

399

Neutron and ?-emission from fission fragments  

International Nuclear Information System (INIS)

The statistical model of nuclear reactions is applied to describe the fission fragment neutron and gamma emission characteristics for spontaneous fission of 252Cf and fission of 235U by thermal neutrons. Averaged excitation energies of fission fragments were obtained from experimental neutron multiplicities. The observable characteristics of an emission are reproduced in a wide range of complementary fragments' total kinetic energies and fragment masses. Observed averaged spins are also reproduced. The fractional independent isomeric yield calculation method, based on the gamma-cascade model, is used to describe experimental data for the 235U(nth,f) and 238U(?,f) reactions. The influence on the calculated isomeric yields of two opposing assumptions regarding the nuclear population spin distributions - one based on the rotational degrees of freedom and one on the internal degrees of freedom of completely accelerated fragments - is investigated. (author)

2001-01-01

400

Aqueous cutting fluid for machining fissionable materials  

Energy Technology Data Exchange (ETDEWEB)

The present invention is directed to a cutting fluid for machining fissionable material. The cutting fluid is formed of glycol, water and boron compound in an adequate concentration for effective neutron attenuation so as to inhibit criticality incidents during machining.

Duerksen, Walter K. (Norris, TN); Googin, John M. (Oak Ridge, TN); Napier, Jr., Bradley (Powell, TN)

1984-01-01

 
 
 
 
401

Development of fission Mo-99 production technology  

Energy Technology Data Exchange (ETDEWEB)

Fission Mo-99 is the only parent nuclide of Tc-99m, an extremely useful tool for mdeical diagnosis, with an estimated usage of greater than 80% of nuclear medicine applicatons. HEU and LEU targets to optimize in HANARO irradiation condition suggested and designed for domestic production of fission Mo-99. The optimum process conditions are established in each unit process to meet quality requirements of fission Mo-99 products, and the results of performance test in combined process show Mo separation and purification yield of the above 97%. The concept of Tc generator production process is established, and the result of performance test show Tc production yield of 98.4% in Tc generator procuction process. The drafts is prepared for cooperation of technical cooperation and business investment with foreign country. Evaluation on economic feasibility is accompanied for fission Mo-99 and Tc-99m generator production.

Park, Jin Ho; Choung, W. M.; Lee, K. I. and others

2000-05-01

402

Feasibility study on fission moly target development  

Energy Technology Data Exchange (ETDEWEB)

A multi-purpose research reactor, HANARO has been operated on the beginning of 1995 and can be utilized for production of various radioisotopes. And a R and D program for fission Mo production was established, and the technical and economical feasibility study has been performed for fission Mo production in Korea. In this study the process for fission Mo production was recommended as follows; 1. Target : UO{sub 2} of annulus type. 2. Separation and purification : Nitric acid dissolution {yields} Alumina adsorption {yields} Benzoin oxime precipitation {yields} Alumina adsorption. And more desirable plan for steady supply of fission Mo were suggested in following viewpoints; 1. Technical collaboration with foreign company. 2. Backup supply system. 3. Marketing arrangement. (Author).

Kim, Byung Ku; Kim, Seong Nyun; Shon, Dong Seong; Choi, Chang Beom; Lee, Jae Kuk; Park, Jin Ho; Jeong, Won Myung; Jeon, Kwan Sik; You, Jae Hyung; Kang, Kyung Chul; Ahn, Jong Hwan; Ju, Po Kuk [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

1996-01-01

403

Nuclear Fission and the Transuranium Elements.  

Science.gov (United States)

Many of the transuranium elements are produced and isolated in large quantities through the use of neutrons furnished by nuclear fission reactions: plutonium (atomic number 94) in ton quantities; neptunium (93), americium (95), and curium (96) in kilogram...

G. T. Seaborg

1989-01-01

404

Optimal Control of Multigroup Neutron Fission Systems  

International Nuclear Information System (INIS)

This article considers the optimal control of nuclear fission reactors modeled by parabolic partial differential equations. The neutrons are divided into fast and thermal groups with two equations describing their interaction and fission, while a third equation describes the temperature in the reactor. The coefficient for the fission and absorption of the thermal neutron is assumed to be controlled by a function through the use of control rods in the reactor. The object is to maintain a target neutron flux shape, while a desired power level and adjustment costs are taken into consideration. A nonlinear optimality system of six equations is deduced, characterizing the optimal control. An iterative procedure is shown to contract toward the solution of the optimality system in small time intervals. The theory is extended to include the effect of other fission products, leading to coupled ordinary and partial differential equations. Numerical experiments are also included, suggesting directions for further research

1999-01-01

405

Particle emission from hot fissioning nuclei  

International Nuclear Information System (INIS)

Langevin equation has been used in one dimension for dynamical description of fission process and coupled with evaporation of light particles. Only symmetric fission has been considered where the nuclear shape parameter and its conjugate momentum are the relevant dynamical variables. The conservative force in the Langevin equation was calculated from the free energy while the diffuse surface liquid drop model with Yukawa-plus- exponential folding was used to calculate the nuclear potential

2000-01-01

406

Qualitative and quantitative description of fission  

CERN Document Server

A model is used to determine the fission products of sup 2 sup 3 sup 8 U. The deformation energy of the decaying system is obtained within the microscopic macroscopic model using a two-center nuclear shape parametrization. This model takes into account the excitation energy of the target nucleus and the evaporation of prompt neutrons. The isotopic yields of the induced fission are obtained for all mass partitions. (authors)

Mirea, M

2001-01-01

407

A revised calculational model for fission  

Energy Technology Data Exchange (ETDEWEB)

A semi-empirical parametrization has been developed to calculate the fission contribution to evaporative de-excitation of nuclei with a very wide range of charge, mass and excitation-energy and also the nuclear states of the scission products. The calculational model reproduces measured values (cross-sections, mass distributions, etc.) for a wide range of fissioning systems: Nuclei from Ta to Cf, interactions involving nucleons up to medium energy and light ions. (author)

Atchison, F.

1998-09-01

408

MCNP6 Fission Multiplicity with FMULT Card  

International Nuclear Information System (INIS)

With the merger of MCNPX and MCNP5 into MCNP6, MCNP6 now provides all the capabilities of both codes allowing the user to access all the fission multiplicity data sets. Detailed in this paper is: (1) the new FMULT card capabilities for accessing these different data sets; (2) benchmark calculations, as compared to experiment, detailing the results of selecting these separate data sets for thermal neutron induced fission on U-235.

2012-01-01

409

MCNP6 Fission Multiplicity with FMULT Card  

Energy Technology Data Exchange (ETDEWEB)

With the merger of MCNPX and MCNP5 into MCNP6, MCNP6 now provides all the capabilities of both codes allowing the user to access all the fission multiplicity data sets. Detailed in this paper is: (1) the new FMULT card capabilities for accessing these different data sets; (2) benchmark calculations, as compared to experiment, detailing the results of selecting these separate data sets for thermal neutron induced fission on U-235.

Wilcox, Trevor [Los Alamos National Laboratory; Fensin, Michael Lorne [Los Alamos National Laboratory; Hendricks, John S. [Los Alamos National Laboratory; James, Michael R. [Los Alamos National Laboratory; McKinney, Gregg W. [Los Alamos National Laboratory

2012-06-18

410

Overview of tritium fast-fission yields  

Energy Technology Data Exchange (ETDEWEB)

Tritium production rates are very important to the development of fast reactors because tritium may be produced at a greater rate in fast reactors than in light water reactors. This report focuses on tritium production and does not evaluate the transport and eventual release of the tritium in a fast reactor system. However, if an order-of-magnitude increase in fast fission yields for tritium is confirmed, fission will become the dominant production source of tritium in fast reactors.

Tanner, J.E.

1981-03-01

411

Our 50-year odyssey with fission: Summary  

Energy Technology Data Exchange (ETDEWEB)

On the occasion of this International Conference on Fifty Years Research in Nuclear Fission, we summarize our present understanding of the fission process and the challenges that lie ahead. The basic properties of fission arise from a delicate competition between disruptive Coulomb forces, cohesive nuclear forces, and fluctuating shell and pairing forces. These static forces are primarily responsible for such experimental phenomena as deformed ground-state nuclear shapes, fission into fragments of unequal size, sawtooth neutron yields, spontaneously fissioning isomers, broad resonances and narrow intermediate structure in fission cross sections, and cluster radioactivity. However, inertial and dissipative forces also play decisive roles in the dynamical evolution of a fissioning nucleus. The energy dissipated between the saddle and scission points is small for low initial excitation energy at the saddle point and increases with increasing excitation energy. At moderate excitation energies, the dissipation of collective energy into internal single-particle excitation energy proceeds largely through the interaction of nucleons with the mean field and with each other in the vicinity of the nuclear surface, as well as through the transfer of nucleons between the two portions of the evolving dumbell-like system. These unique dissipation mechanisms arise from the Pauli exclusion principle for fermions and the details of the nucleon-nucleon interaction, which make the mean free path of a nucleon near the Fermi surface at low excitation energy longer than the nuclear radius. With its inverse process of heavy-ion fusion reactions, fission continues to yield surprises in the study of large-amplitude collective nuclear motion. 87 refs., 12 figs.

Nix, J.R.

1989-01-01

412

Modeling Fission Product Sorption in Graphite Structures  

Energy Technology Data Exchange (ETDEWEB)

The goal of this project is to determine changes in adsorption and desorption of fission products to/from nuclear-grade graphite in response to a changing chemical environment. First, the project team will employ principle calculations and thermodynamic analysis to predict stability of fission products on graphite in the presence of structural defects commonly observed in very high- temperature reactor (VHTR) graphites. Desorption rates will be determined as a function of partial pressure of oxygen and iodine, relative humidity, and temperature. They will then carry out experimental characterization to determine the statistical distribution of structural features. This structural information will yield distributions of binding sites to be used as an input for a sorption model. Sorption isotherms calculated under this project will contribute to understanding of the physical bases of the source terms that are used in higher-level codes that model fission product transport and retention in graphite. The project will include the following tasks: Perform structural characterization of the VHTR graphite to determine crystallographic phases, defect structures and their distribution, volume fraction of coke, and amount of sp2 versus sp3 bonding. This information will be used as guidance for ab initio modeling and as input for sorptivity models; Perform ab initio calculations of binding energies to determine stability of fission products on the different sorption sites present in nuclear graphite microstructures. The project will use density functional theory (DFT) methods to calculate binding energies in vacuum and in oxidizing environments. The team will also calculate stability of iodine complexes with fission products on graphite sorption sites; Model graphite sorption isotherms to quantify concentration of fission products in graphite. The binding energies will be combined with a Langmuir isotherm statistical model to predict the sorbed concentration of fission products on each type of graphite site. The model will include multiple simultaneous adsorbing species, which will allow for competitive adsorption effects between different fission product species and O and OH (for modeling accident conditions).

Szlufarska, Izabela; Morgan, Dane; Allen, Todd

2013-04-08

413

Nuclear Qsub(?)-values for fission products  

International Nuclear Information System (INIS)

Experimental Qsub(?)-values for fission products are presented. The sources were produced as mass separated fission products at the OSIRIS on-line isotope separator. Recently determined Qsub(?)-values for 79,81Ga, 79,81,82Ge, 89,90Br, 116,121Ag, 119,121Cd and 139I are, together with 40 earlier measured values, compared with mass formula predictions. (orig.)

1981-07-20

414

Fission product release mechanisms: research in Canada  

International Nuclear Information System (INIS)

Research and development activities in Canada on fission product release and fuel behaviour during normal and reactor accident conditions is outlined in support of industry and regulatory requirements. An overview of key mechanisms and phenomena identified which impact the fission product release behaviour highlighting the contribution of Canadian research is reviewed. The structure of the research program, target research areas as well as the available facilities in Canada is also described. (author)

2008-01-01

415

Hyperfission - a new mode of nuclear fission  

International Nuclear Information System (INIS)

In this paper the nuclear hyperfission as a new mode of fission, possible for heavy elements with Z > 92, is investigated. The Q-systematics, hyperfissibility parameters, hyperfission barrier as well as the essential hindrance factors are presented. The hyperfission hindrance factor relative to that of fission is found to be in the interval 1.0x10-17 - 3.4x10-16 for the parent nuclei with Z = 92-108. (orig.).

1988-01-01

416

Actinide nuclei fission cross-section irregularities  

Energy Technology Data Exchange (ETDEWEB)

The energy dependence of the fission cross-sections for the nuclei with the effectively one-humped fission barrier is examined. The relation of the near-barrier peculiarities in these nuclei to the structure of the transition states is shown. The results indicate the necessity of taking into account the deformation asymmetry for the inner and the reflection asymmetry for the outer barrier.

Egorov, S.A.; Rubchenya, V.A.; Khlebnikov, S.V.

1989-03-27

417

Qualitative and quantitative description of fission  

International Nuclear Information System (INIS)

A model is used to determine the fission products of 238 U. The deformation energy of the decaying system is obtained within the microscopic macroscopic model using a two-center nuclear shape parametrization. This model takes into account the excitation energy of the target nucleus and the evaporation of prompt neutrons. The isotopic yields of the induced fission are obtained for all mass partitions. (authors)

2001-01-01

418

Adsorption of fission products on mediterranean mud  

International Nuclear Information System (INIS)

[en] Partition coefficients of some fission products have been measured in sea water on mud taken from the bottom of the Mediterranean sea. A discussion follows on the behaviour of these radioisotopes. (author)[fr] On a mesure les coefficients de partage dans l'eau de mer de quelques produits de fission a longue periode sur des echantillons de vase preleves en Mediterranee. Les valeurs trouvees sont elevees. Le comportement de ces isotopes radioactifs est discutee. (auteur)

1960-01-01

419

Transport properties of fission product vapors  

Energy Technology Data Exchange (ETDEWEB)

Kinetic theory of gases is used to calculate the transport properties of fission product vapors in a steam and hydrogen environment. Provided in tabular form is diffusivity of steam and hydrogen, viscosity and thermal conductivity of the gaseous mixture, and diffusivity of cesium iodide, cesium hydroxide, diatomic tellurium and tellurium dioxide. These transport properties are required in determining the thermal-hydraulics of and fission product transport in light water reactors.

Im, K.H.; Ahluwalia, R.K.

1983-07-01

420

FFTF [Fast Flux Test Facility] Fission Gas Monitor Computer System  

International Nuclear Information System (INIS)

The Fast Flux Test Facility (FFTF) is a liquid-metal-cooled, fast neutron test reactor located on the Hanford Site. A dual computer system has been developed to monitor the reactor cover gas to detect and characterize any fuel or test pin fission gas releases. The system acquires gamma spectra data, identifies isotopes, calculates specific isotope and overall cover gas activity, presents control room alarms and displays, and records and prints data and analysis reports. The Fission Gas Monitor System (FGMS) integrates commercially available hardware and software, providing a reliable and easily maintained system. The design provides extensive automation of previous manual operations, reducing the need for operator training and minimizing the potential for operator error. The dual nature of the system allows either system A or B to be taken out of service for periodic tests or maintenance without interrupting the overall system performance. A control room color display tracks the specific activity of selected isotopes, provides alarms when a fission gas release is detected, and characterizes the nature and source of the release. Sources in the FFTF that can be uniquely identified include fuel pins, control rod absorber pins, and N- and M-type test pins which are irradiated in the reactor Materials Open Test Assembly (MOTA). The principal method used to characterize the source of the assembly leak involves the analysis of four isotopes, namely Xe-125, Xe-133, Xe-135, and Kr-85m, and the ratios of Xe-133/Xe-135 and Xe-133/Kr-85m. The computer analysis also compensates for Xe-133 buildup which reaches a saturation value after about 20 days of full-power operation. In addition, the computer calculates the specific activity of 20 isotopes which are used to help perform a detailed analysis of leaks from fuel assemblies

1987-09-03