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1

Isotopic studies relative to the Oklo natural fission reactors  

International Nuclear Information System (INIS)

It has been clearly demonstrated that natural fission reactors operated about 2 10"9 years ago, in rich uranium one deposits of the Oklo mine in the Republique of Gabon. Six reactions zones have been identified in which approximately six tons of "2"3"5U were consumed and the same amount of fission products deposited in the ground. These fission products, their filiation isotopes and nuclei formed from neutron captures are precious tracers, which now can be analysed on well localized samples, to obtain informations on the stability in soil of such elements and data on the nuclear parameters and characteristics of the nuclear reactors. The studies which have been developed at Saclay concern several aspects of this phenomenon: the migrations of fission products, the age of the nuclear reaction, the date of the uranium deposit and the temperature of the reaction zones during the operation of the reactors

1978-08-25

2

Fission yields of molybdenum in the Oklo natural reactor  

International Nuclear Information System (INIS)

The isotopic compositions of molybdenum in six uranium-rich samples from the Oklo Zone 9 natural reactor were accurately measured by thermal ionization mass spectrometry. The samples were subjected to an ion exchange separation process that removed the isobaric elements zirconium and ruthenium, with high efficiency and a low blank. Molybdenum possesses seven isotopes of which 92,94,96Mo are unaffected by the fission process, enabling the raw data to be corrected for isotope fractionation by normalising to 92Mo/96Mo, and to use 94Mo to correct for the primordial component in each of the fission-produced isotopes. This enables the relative fission yields of Mo to be calculated from the isotopic composition measurements, to give cumulative fission yields of 1:0.941:0.936:1.025 for 95,97,98,100Mo, respectively. These data demonstrate that the most important nuclear process involved in reactor Zone 9 was the thermal neutron fission of 235U. The consistency of the relative cumulative fission yields of all six samples from different locations in the reactor, implies that Mo is a mobile element in the uraninite comprising Zone 9, and that a significant fraction of molybdenum was mobilized within the reactor zone and probably escaped from Zone 9, a conclusion in agreement with earlier published work. (author)

2012-09-01

3

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

Science.gov (United States)

Of the sixteen known Oklo and the Bangombé natural fission reactors (hydro-thermally altered clastic 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.

Nagy, Bartholomew; Gauthier-Lafaye, François; Holliger, Philippe; Mossman, David J.; Leventhal, Joel S.; Rigali, Mark J.

1993-07-01

4

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

International Nuclear Information System (INIS)

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

1993-07-01

5

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

6

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

Energy Technology Data Exchange (ETDEWEB)

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.

Norris, A.E.

1980-01-01

7

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

8

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

International Nuclear Information System (INIS)

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

9

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

Science.gov (United States)

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 radionuclide 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 radionuclide 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 radionuclide 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 modern 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. Oklo solid bitumen samples were subjected to various pressures of O 2, a paramagnetic gas. O 2-organic free radical interactions, as revealed by ESR spectral line broadening, indicate that the organic free radicals of the Oklo solid bitumens are, with one exception, accessible to O 2. This indicates that the organic free radicals are located at or very near the surfaces of these organic solids, including the internal surfaces of pores. The presence of pores was deduced from the BET analyses. The presence of porosity and related permeability has important implications for fluid flow through the uraniferous graphitic bitumen affecting radionuclide containment at Oklo. However, the very small average pore sizes (18.5-38.1Å) together with the non-wettability by aqueous solutions of the uraniferous graphitic bitumen indicate that the pores did not serve as effective conduits for the transport of radionuclides by aqueous solutions through and out of the solid bitumen matrix. The ESR data obtained from the O 2 experiments is comparable to the BET N 2 adsorption data, indicating that the ESR O 2 experiment reflects physical adsorption, and not chemisorption, of O 2 on the Oklo bitumen surfaces.

Rigali, Mark J.; Nagy, Bartholomew

1997-01-01

10

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1997-01-01

11

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

International Nuclear Information System (INIS)

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

12

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

13

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

International Nuclear Information System (INIS)

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

1994-10-23

14

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

International Nuclear Information System (INIS)

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

1992-04-06

15

The Oklo Fossil Fission Reactors  

Science.gov (United States)

This web page gives an overview of the Oklo Fossil Fission Reactors, including the history of the area where the reactor is located, the science behind the nuclear reactions, and reasons for studying this nuclear reactor. This page also includes graphics describing the Physics behind the reactors, maps, and pictures of the reactor.

Loss, Robert

2012-06-15

16

"9"9Tc, Pb and Ru migration around the Oklo natural fission reactors  

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. It has been shown that the ores and nearby rocks were open to the loss and gain of "9"9Tc, ruthenium, and lead relative to uranium. Identified regions of element deficiencies and those which are correspondingly enriched are separated by less than 10 meters. However, more extensive sampling is required to define the overall extent of the element migration. Element fractionation took place on at least two vastly different time scales; "9"9Tc was fractionated from ruthenium within one million years of the end of reactor criticality. Lead-uranium fractionation has been ongoing for most of the two billion years since the ores were formed. Diffusion loss of lead from host uraninite appears to be an important process in the fractionation of lead from uranium

1979-11-29

17

Geochemical and Neutronic Characteristics of the Natural Fossil Fission Reactors at Oklo and Bangombé, Gabon  

Science.gov (United States)

Isotopic studies have been completed on samples from the natural fission reactors at Oklo and Bangombé in order to determine the conditions under which they functioned when critical and to evaluate the retention and migration of fissiogenic radionuclides. The abundances and isotopic compositions of the elements Rb, Sr, Zr, Ru, Pd, Ag, Te, Ba, rare earth elements (REEs), and U have been measured by thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). Isotopic analyses and in situ ion imaging have also been performed by using an ion microprobe. Seven samples were taken from the SF84 borehole (zone 10), one from the S2 borehole in gallery SD37 (zone 13), both being zones in the Oklo deposit, and one from the BA145 borehole in the Bangombé deposit. The isotopic data allow for a detailed description of the functional conditions of these reactors, and based on these results, we have calculated the retention rates of the fissiogenic nuclides and nucleogenic Bi and Th. The nuclear parameters of the natural fission reactors are characterized by the isotopic abundances of Ru, Nd, Sm, Gd, Er, Yb, Lu, and U: neutron fluence (n/cm 2), fission proportions of 235U, 238U, and 239Pu, the restitution factor of 235U resulting from 239Pu decay, average temperature (°C) in the reactor, and duration of functioning (yr). In the 70 cm thick reactor core encountered by borehole SF84, the neutron fluence is in the range from 5.3x10 20 to 8.0x10 20 (n/cm 2). The variation in 235U depletion shows a strong positive correlation with the restitution factor and an inverse correlation with neutron fluence, which demonstrates the stability of the reaction zone since the period of criticality. Large depletions of 149Sm, 155Gd, and 157Gd have been detected in a sample of sandstone from 60 cm below this reactor core which also had a normal uranium isotopic ratio ( 235U/ 238U = 0.007254); this resulted from neutron capture reactions. The neutron fluence calculated from these isotopic anomalies is relatively high (6.2x10 18 n/cm 2) and probably shows that nuclear reactions began, but that criticality could never be sustained due to an excess of neutron poisons (e.g., Sm and Gd). The results obtained from SD37 reveal that reactor zone 13 is not similar to the other reactor zones. The proportion of 238U fission as calculated from the isotopic composition of Ru is extremely high (18% of the total), while that of SF84 (zone 10) is at most 5.0% of total fission. This result implies that the duration of criticality in reactor zone 13 was much shorter than in other reactor zones. In the Bangombé reactor zone BA145, the chemical and nuclear characteristics are close to those of SF84. The retentivities of many fission products as compared with fissiogenic Nd have been assessed for the reactor core samples. From the measured and calculated relative retentions, more than 90% of fissiogenic Ru, Rh, Pd, Te, and REEs have been retained in SF84 and SD37. In these same zones, however, the relative retentions of fissiogenic alkaline and alkaline earth elements are less than 20%. The retentions of long-lived radioisotopes, such as 90Sr, 99Tc, 137Cs, 236U, and 237Np have been calculated by reference to their radiogenic daughters 90Zr, 99Ru, 137Ba, 232Th, and 209Bi, respectively. The excess or depletion of isotopic abundances measured in the daughter nuclides has allowed the prediction of the rate of chemical fractionation between the parent and daughter nuclides in the reactor during criticality. These results greatly improve the understanding of the Oklo phenomenon and provide important data for the evaluation of the concept of long-term storage of radioactive wastes in geological formations.

Hidaka, Hiroshi; Holliger, Philippe

1998-01-01

18

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

19

The Oklo natural reactor, Gabon  

International Nuclear Information System (INIS)

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

1989-10-23

20

The Oklo reactors: natural analogues to nuclear waste repositories  

International Nuclear Information System (INIS)

Natural reactors at Oklo offer a unique opportunity to study the geochemical stability of fission products. Despite high temperatures, large radiation doses and circulating fluids the Oklo minesite successfully contained large quantities of radioactive waste material for some two billion years. Despite the fact that some radioactive species migrated, the actinides remained in-situ. The relevance of the Oklo evidence to high-level waste disposal is stressed

1983-11-30

 
 
 
 
21

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

22

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

International Nuclear Information System (INIS)

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

1992-04-06

23

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

24

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

International Nuclear Information System (INIS)

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

1997-11-01

25

Coupled processes at the Oklo Natural reactor  

International Nuclear Information System (INIS)

This paper discusses how the Oklo Natural Reactor, Gabon, is an excellent site in which to study, asses, and evaluate coupled processes of interest to radionuclide migration in natural media. The uranium accumulations in which the fission reactions occured are dated at about two Gy (billions of years), and the nuclear reactions lasted for some 500,000 y (plus). Temperatures in the reactor zones were on the order of 300-450C, although local, higher temperatures may have been reached. This thermal regime aided in the diffusion of some fission products, and possibly actinides, from host pitch-blende. Post-reactor diagenesis events have masked some of the radionuclide mThis paper discusses how the Oklo Natural Reactor, Gabon, is an excellent site in which to study, asses, and evaluate coupled processes of interest to radionuclide migration in natural media. The uranium accumulations in which the fission reactions occurred are dated at about two Gy (billions of years), and the nuclear reactions lasted for some 500,000 y (±). Temperatures in the reactor zones were on the order of 300-450 degrees C, although local, higher temperatures may have been reached. This thermal regime aided in the diffusion of some fission products, and possibly actinides, from host pitch-blende. Post-reactor diagenesis events have masked some of the radionuclide migration paths, but most can still be studied.igration paths, but most can still be studied

1987-01-01

26

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

International Nuclear Information System (INIS)

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)

1995-11-06

27

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

28

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

International Nuclear Information System (INIS)

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

1993-06-20

29

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

30

The deposit of Oklo and its natural nuclear reactors  

International Nuclear Information System (INIS)

In the uranium deposit of Oklo (Republic of Gabon), seven zones have been discovered since 1972, in which natural fission reactions took place. Since 1974, a thorough geological study of these zones has been undertaken. It includes field studies, observations of drilled samples and laboratory studies. These studies permit the authors to define the geological environment of the reactors and to point out the influence of nuclear reactions on the surrounding formations. All this work was completed by a geological and metallogenic study of the deposit of Oklo and of the uraniferous basin of Franceville. The deposit of Oklo is situated in a detrital, sandstone-like and pelitic series belonging to the Francevillian. The Francevillian and the mineralization are dated as Middle Precambrian (1800-2000 M.A.). The ore of Oklo is the result of two concentration stages. In the first, uranium seems to have been fixed by hydrocarbons that were concentrated in oil traps. After a tectonic event, circulations of oxidizing solutions generated reconcentrations that are associated with hematite and have contents of UO2 between 1 and 20%. The fission reactions developed in the high-graded ores which had formed during the last phase of UO2 concentration. A thorough tectonic analysis of the ore deposit shows that high-graded ores and fission reactors are controlled by fractures. The working of nuclear reactors results in a local increase of temperature which gave a rise to circulation of warm water. The results of this hydrothermal circulation and of the neutron bombardment are seen in a succession of facies surrounding the reactors. At the centre of the reactor all sedimentary structures have been destroyed; within the reaction zone the following clays mineral zones are founded: (1) 1 Md illite and ferrous chlorite corresponding to the common Francevillian sediment; (2) 2 Md illite, (3) magnesium chlorite and (4) 1 Md illite and chlorite-vermiculite in the very rich uraninite ore. These dydrothermal circulations also caused removal of silica toward the outer zones which reacted affecting the geometry of the reactors by fracturing

31

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

International Nuclear Information System (INIS)

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 shown. The

1999-06-00

32

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

International Nuclear Information System (INIS)

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)

1996-02-01

33

Identification of the conditions required for the starting of the natural reactors of Oklo and Bagombe  

International Nuclear Information System (INIS)

The Oklo phenomenon discovered in 1972 stays exceptional and unique. From 1972 to 1988 about fifteen zones in which nuclear fission occurred, were discovered in 2 uranium deposits in Gabon aged about 2 billion years. This study gives an explanation to the evolution that led to the starting of this natural reactor through quantifying 2 adverse phenomena: the local concentration of uranium and the progressive disappearance of U235. With the help of Monte-Carlo simulations it has been possible to define a domain of realistic solutions able to justify the criticality, and to explain the expansion, the operating and the end of the Oklo natural reactors. This study has shown the impact of geologic processes like for instance rock faulting on the starting of natural reactors, the progressive formation of clay around these natural cores has been essential to reduce the thermalization of neutrons that led to the stopping of the chain reactions. It is important to note that the build-up of clay around the natural cores has allowed fission products to stay confined almost totally in the area. The Oklo natural reactors could be considered as a natural analogue of radioactive waste disposal sites. (A.C)

2013-11-01

34

Gamma-ray fluxes in Oklo natural reactors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Uncertainty in the operating temperatures of Oklo reactor zones impacts the precision of bounds derived for time variation of the fine structure constant $\\alpha$. Improved $^{176}$Lu/$^{175}$Lu thermometry has been discussed but its usefulness may be complicated by photo excitation of the isomeric state $^{176m}$Lu by $^{176}$Lu($\\gamma,\\gamma^\\prime $) fluorescence. We calculate prompt, delayed and equilibrium $\\gamma$-ray fluxes due to fission of $^{235}$U in pulsed mode ...

Gould, C. R.; Sharapov, E. I.; Sonzogni, A. A.

2012-01-01

35

Natural chain reaction in the Oklo mine in Gabon  

International Nuclear Information System (INIS)

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

36

Oklo, natural analogue of the radionuclides migration through the geological barrier  

International Nuclear Information System (INIS)

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 235U/238U 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)

1995-06-01

37

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

38

Gamma-ray fluxes in Oklo natural reactors  

CERN Document Server

Uncertainty in the operating temperatures of Oklo reactor zones impacts the precision of bounds derived for time variation of the fine structure constant $\\alpha$. Improved $^{176}$Lu/$^{175}$Lu thermometry has been discussed but its usefulness may be complicated by photo excitation of the isomeric state $^{176m}$Lu by $^{176}$Lu($\\gamma,\\gamma^\\prime $) fluorescence. We calculate prompt, delayed and equilibrium $\\gamma$-ray fluxes due to fission of $^{235}$U in pulsed mode operation of Oklo zone RZ10. We use Monte Carlo modeling to calculate the prompt flux. We use improved data libraries to estimate delayed and equilibrium spectra and fluxes. We find $\\gamma$-ray fluxes as a function of energy and derive values for the coefficients $\\lambda_{\\gamma,\\gamma^\\prime}$ that describe burn-up of $^{176}$Lu through the isomeric $^{176m}$Lu state. The contribution of the ($\\gamma,\\gamma^\\prime $) channel to the $^{176}$Lu/$^{175}$Lu isotopic ratio is negligible in comparison to the neutron burn-up channels. Lutetium...

Gould, C R; Sonzogni, A A; 10.1103/PhysRevC.86.054602

2012-01-01

39

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 1.98x10"9 years is obtained slightly higher than the value obtained by geochronology

1977-12-21

40

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

International Nuclear Information System (INIS)

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

 
 
 
 
41

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

42

What we learn from the nuclear data in Oklo natural reactor  

International Nuclear Information System (INIS)

We reexamined the constraint for the time variation of the coupling constant of the fundamental interaction by studying the isotropic abundance of Sm observed at Oklo natural reactor. Using the most modern and reliable data, together with the study of the isotropic abundance of Gd, we found that the original finding of Shlyakhter is essentially correct, that is, the Oklo data provides us the most stringent limit for the time variation compared with any other methods. (author)

2001-03-01

43

Investigations of the Natural Fission Reactor Program. Progress report, October 1976--September 1977  

Energy Technology Data Exchange (ETDEWEB)

During Fiscal Year 1977, efforts of the Natural Fission Reactor Program have been directed toward (1) further measurements and predictions of reactor product migration at Oklo, (2) uraninite solubility studies, (3) radiogenic equilibria studies of natural Pu, Ra, and Th in U ores, (4) search for evidence of other natural fission reactors, and (5) supportive analytical measurements and procedures development.

Apt, K.E. (ed.)

1977-11-01

44

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

45

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)

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

46

Fate of the epsilon phase in the Oklo natural reactors  

International Nuclear Information System (INIS)

Full text of publication follows: In spent nuclear fuel (SNF), the micron- to submicron-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of 99Tc which has a long half life (2.13 x 105 years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In addition, Tc is predominantly present as TcO4 - 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 99Tc has decayed to 99Ru. 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 UO2 matrix, a Bi-Pd particle (40-60 nm), froodite, PdBi2, was observed with trace amounts of As, Fe, and Te surrounded by an amorphous Pb-rich area. (Pd,Rh)2As, 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 ?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: (i) The original epsilon phase was transformed to, in most cases, ruthenarsenite. (ii) 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. (iii) Once the uraninite matrix dissolved, the epsilon particles were released and sometimes captured within adjacent alteration minerals. (authors)

2005-09-18

47

The neutron balance of the natural reactors at Oklo  

International Nuclear Information System (INIS)

The authors discuss the main parameters determining criticality: the concentration of fissionable nuclei in the uranium; concentration of neutron-capturing nuclei in the gangue; concentration of uranium in the ore and rearrangement of the uranium to form ''critical masses''; amount of water present. Moderation was caused partly by the water of constitution of the clays in the gangue. Examination of the available data indicates that criticality could quite well have been achieved. A computer code (BINOCLE) was written for handling the neutron physics problems raised by the natural reactors. This very simple code, which can nevertheless handle the important points in sufficient detail, is well suited for describing the ores, providing a clear breakdown of the neutron balance and the quantities necessary for interpreting the analyses. It is designed to serve as a subprogram to a series of other codes: one-dimensional criticality; point evolution; spatial evolution; consideration of thermal transfers. Results showing the role of the main parameters are presented. The physical quantities measured by fission-product analysis are also found: proportions of fast fissions; conversion coefficient; spectral indices

1975-06-23

48

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

International Nuclear Information System (INIS)

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

49

Preliminary studies of groundwater flow and migration of uranium isotopes around the Oklo natural reactors (Gabon)  

Science.gov (United States)

In specific zones of the Oklo uranium deposit, critically was naturally reached 2 Ga ago. This site thus provides a unique opportunity to show whether the stable nuclear reaction end-products have remained or not in the vicinity of the reactor zones after the termination of nuclear reactions. In addition, the evaluation of the stability of the uraninite matrix over very long periods of time provides information on the possible long-term stability of waste forms such as spent fuel. The Commission of the European Communities initiated in 1991 the Oklo Natural Analogue Programme, a part of which is devoted to present-day migration studies. The Swedish Nuclear Fuel and Waste Management Company (SKB) supports this programme, with special interest in the Bangombe reactor, a shallow reaction zone possibly affected by surficial alteration processes. The Oklo study comprises hydrogeology, groundwater chemistry, isotopic analyses (environmental isotopes, U series, 235U/ 238U), and modelling. Two sites are being thoroughly investigated: the less perturbed OK84 reactor zone in Okelobondo (200 m south from Oklo) and the Bangombe reactor zone, 30 km south of Oklo. We focus our study on uranium migration from these reactor zones, using tracers such as the 235U/ 238U isotope ratio. After preliminary field campaigns, a conceptual model was constructed, both for Okelobondo and Bangombe. For this purpose, groundwaters have been characterised for three years in different areas around Oklo: Okelobondo groundwaters in mines and boreholes and surface waters, and Bangombe, both in boreholes and surface waters. Detailed investigations were then conducted in order to validate our conceptual models, and finally to enabling us to model U migration from the reaction zones, and to evaluate the performance assessment of deep geological disposal of radioactive wastes. After the presentation of regional and local geology and hydrogeology, we give a complete description and interpretation of groundwater chemical evolution both in Okelobondo and Bangombe. It concerns major-element behaviour, redox control and uranium behaviour. Preliminary conclusions for the conceptual model drawn from hydrogeological studies and from groundwater chemistry agree closely. In addition, we have successfully tested the use of 235U/ 238U isotope ratios in groundwaters to evaluate the migration of uranium from reactor zones.

Toulhoat, Pierre; Gallien, Jean Paul; Louvat, Didier; Moulin, Valérie; l'Henoret, Pascal; Guérin, Roland; Ledoux, Emmanuel; Gurban, Ioana; Smellie, John A. T.; Winberg, Anders

1996-02-01

50

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

International Nuclear Information System (INIS)

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

51

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

International Nuclear Information System (INIS)

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

52

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

53

The Oklo reactors  

International Nuclear Information System (INIS)

The Oklo reactors comprise up to nine 235-U depleted zones in an uranium ore in the Republic of Gabon in West Africa. The depletion in fissile U-235 has been proved to have caused by nuclear chain reactions. The study of the Oklo phenomenon indicates that very efficient retardation mechanisms may operate in nature - at least under special conditions. A closer study of these processes ought to be made to establish the limitations to their occurrence. The Oklo sandstone formation today would probably be considered unacceptable as a host rock for a repository. (EG)

1982-09-01

54

Reactive transport modelling of uranium around a natural nuclear reactor at Bangombe (Oklo, Gabon)  

International Nuclear Information System (INIS)

On the Bangombe site (Oklo, Gabon), a natural nuclear reactor 1.95 Gyr old, and 12 m deep is submitted to weathering. The geochemical behaviour of uranium and trace elements around the reaction zone has been carried out using a reactive transport code HYTEC-2D. The buffer redox capacity of the organic matter associated with FeII/FeIII minerals around the reactor can explain the uraninite stability into the reaction zone and its weak migration during the geological time. (authors)

2000-11-01

55

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

CERN Document Server

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

56

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

International Nuclear Information System (INIS)

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 "1"3"0Xe isotope explained by secondary reactions on neutrons has been found out for the first time

1985-01-01

57

Oklo working group meeting  

International Nuclear Information System (INIS)

Natural analogue studies have been carried out for several years in the framework of the European Community's R and D programme on radioactive waste; and within its recent fourth five-year programme on 'Management and storage of radioactive waste (1990-94)' the Community is participating in the Oklo study, natural analogue for transfer processes in a geological repository. The Oklo project is coordinated by CEA-IPSN (F) and involves laboratories from several CEA directorates (IPSN, DTA and DCC) which collaborate with other institutions from France: CREGU, Nancy; CNRS, Strasbourg and ENSMD, Fontainebleau. Moreover, institutes from non-EC member States are also taking part in the Oklo study. The second joint CEC-CEA progress meeting of the Oklo Working Group was held in April 1992 in Brussels and gave the possibility of reviewing and discussing progress made since its first meeting in February 1991 at CEA in Fontenay-aux-Roses. About 40 participants from 15 laboratories and organizations coming from France, Canada, Gabon, Japan, Sweden and the USA underline the great interest in the ongoing research activities. The meeting focused on the different tasks within the CEC-CEA Oklo project concerning (i) field survey and sampling, (ii) characterization of the source term, (iii) studies of the petrographical and geochemical system, and (iv) studies of the hydrogeological system and hydrodynamic modelling. (author) 17 papers are presented

1992-04-06

58

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

59

Geochemical characteristics of an ancient nuclear reactor 'Oklo'  

International Nuclear Information System (INIS)

The Oklo uranium deposit at the Republic of Gabon, central Africa, had partly functioned as natural fission reactors. Many elements of the Oklo reactor zones and the related samples show the variations in the isotopic composition caused by a combination of nuclear fission, neutron capture, and radioactive decay. Isotopic studies provide useful information to estimate reactor conditions and to understand behavior of radionuclides in geological media. In my recent work, in-situ REE, Pb, and U isotopic analyses of individual tiny minerals in and around reactor zones have been performed using a Sensitive High Resolution Ion Micro-Probe (SHRIMP). The data suggest the adsorption property of apatite in trapping fissiogenic LREE and Pu migrated from the reactor zone, and distribution of fissiogenic REE under oxidizing atmosphere. (author)

2007-10-01

60

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

 
 
 
 
61

Search for traces of natural fission chain reaction  

International Nuclear Information System (INIS)

To search signs of fission chain reactions in uranium ores samples from certain deposits of the world have been studied. The deposits must necessarily have conditions for the start of chain reaction: high uranium concentration, amount of water in the deposit of approximately 20%, mineralization age above 1.5 milliard years. Three isotopic methods have been used: xenon-uranium and neodymium. The analysis technique is described. According to the isotopic composition of xenon, neodymium and the 235U/238U ratio, which in the limits of determination errors do not differ from the normal ones, conclusion is made on the absence of chain reaction traces in the samples analyzed, that is also reaffirmed by evaluation results of the effective neutron flux in ore manifestations. The samples were compared with several samples from ''natural nuclear reactor'' of the OKLo deposit

1980-01-01

62

THE FATE OF THE EPSILON PHASE IN UO2 OF THE OKLO NATURAL FISSON REACTORS  

International Nuclear Information System (INIS)

In spent nuclear fuel (SNF), the micron- to nano-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of 99Tc which has a long half life (2.13 x 105 years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In order to examine the occurrence and the fate of the epsilon phase during the corrosion of SNF over long time periods, samples of uraninite from the Oklo natural reactors (?2.0 Ga) have been investigated using transmission electron microscopy (TEM). Because essentially all of the 99Tc has decayed to 99Ru, this study focuses on 4d-elements of the epsilon phase. Samples were obtained from the research collection at University of Michigan representing reactor zone (RZ) 10 (836, 819,687) and from RZ 13 (864,910). Several phases with 4d-metals have been identified within UO2 matrix at the scale of 50-700 nm; fioodite, PdBi2, with trace amounts of As, Fe, and Te, and palladodymite or rhodarsenide, (Pd,Rh)2As. The most abundant 4d-metal phase is ruthenarsinite, (Ru,Ni)As, which has a representative composition: As, 59.9; Coy 2.5; Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic%. Ruthenarsenite nanoparticles are typically surrounded by Pb-rich domains, galena in most cases; whereas, some particles reveal a complexly zoned composition within the grain, such as a Pb-rich domain at the core and enrichment of Ni, Co, and As at the rim. Some ruthenarsenites and Rh-Bi-particles are embedded in surrounding alteration products, e.g., chlorite, adjacent to uraninite (no further than ?5 (micro)m). A few of those particles are still coated by a Pb-rich layer. Based on these results, the history that epsilon phases have experienced can be described as follows: (1) The original epsilon phase was changed to, in most cases, ruthenarsenite, by As-rich fluids with other trace metals. Dissolution and a simultaneous precipitation may be responsible for the phase change. (2) All Mo and most of the Tc were released from the epsilon phase. Galena precipitated surrounding the 4d-metal phases. (3) Once the uraninite matrix has dissolved, the epsilon nanoparticles were released and ''captured'' within alteration phases that are immediately adjacent to the uraninite

2005-01-01

63

THE FATE OF THE EPSILON PHASE IN UO2 OF THE OKLO NATURAL FISSON REACTORS  

Energy Technology Data Exchange (ETDEWEB)

In spent nuclear fuel (SNF), the micron- to nano-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 order to examine the occurrence and the fate of the epsilon phase during the corrosion of SNF over long time periods, samples of uraninite from the Oklo natural reactors ({approx}2.0 Ga) have been investigated using transmission electron microscopy (TEM). Because essentially all of the {sup 99}Tc has decayed to {sup 99}Ru, this study focuses on 4d-elements of the epsilon phase. Samples were obtained from the research collection at University of Michigan representing reactor zone (RZ) 10 (836, 819,687) and from RZ 13 (864,910). Several phases with 4d-metals have been identified within UO{sub 2} matrix at the scale of 50-700 nm; fioodite, PdBi{sub 2}, with trace amounts of As, Fe, and Te, and palladodymite or rhodarsenide, (Pd,Rh){sub 2}As. The most abundant 4d-metal phase is ruthenarsinite, (Ru,Ni)As, which has a representative composition: As, 59.9; Coy 2.5; Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic%. Ruthenarsenite nanoparticles are typically surrounded by Pb-rich domains, galena in most cases; whereas, some particles reveal a complexly zoned composition within the grain, such as a Pb-rich domain at the core and enrichment of Ni, Co, and As at the rim. Some ruthenarsenites and Rh-Bi-particles are embedded in surrounding alteration products, e.g., chlorite, adjacent to uraninite (no further than {approx}5 {micro}m). A few of those particles are still coated by a Pb-rich layer. Based on these results, the history that epsilon phases have experienced can be described as follows: (1) The original epsilon phase was changed to, in most cases, ruthenarsenite, by As-rich fluids with other trace metals. Dissolution and a simultaneous precipitation may be responsible for the phase change. (2) All Mo and most of the Tc were released from the epsilon phase. Galena precipitated surrounding the 4d-metal phases. (3) Once the uraninite matrix has dissolved, the epsilon nanoparticles were released and ''captured'' within alteration phases that are immediately adjacent to the uraninite.

S. Utsunomiya; R.C. Ewing

2005-09-08

64

Reactive transport modelling of uranium around a natural nuclear reactor at Bangombe (Oklo, Gabon); Modelisation du transport reactif de l'uranium autour du reacteur nucleaire naturel de Bangombe (Oklo, Gabon)  

Energy Technology Data Exchange (ETDEWEB)

On the Bangombe site (Oklo, Gabon), a natural nuclear reactor 1.95 Gyr old, and 12 m deep is submitted to weathering. The geochemical behaviour of uranium and trace elements around the reaction zone has been carried out using a reactive transport code HYTEC-2D. The buffer redox capacity of the organic matter associated with Fe{sup II}/Fe{sup III} minerals around the reactor can explain the uraninite stability into the reaction zone and its weak migration during the geological time. (authors)

Made, B.; Ledoux, E.; Le Boursicaud, B. [Ecole des Mines de Paris, Centre d' Informatique Geologique, UMR-CNRS 7619 Sisyphe, 77 - Fontainebleau (France); Salignac, A.L. [Gaz de France (GDF), Dir. de la Recherche, 93 - La Plaine-Saint-Denis (France); Gurban, I. [Duke Engineering and Service, Ottawa ON (Canada)

2000-11-01

65

Radioactive wastes in Oklo  

International Nuclear Information System (INIS)

The acceptance of the Nuclear Energy as electric power supply implies to give answer to the population on the two main challenges to conquer in the public opinion: the nuclear accidents and the radioactive wastes. Several of the questions that are made on the radioactive wastes, its are the mobility migration of them, the geologic stability of the place where its are deposited and the possible migration toward the aquifer mantels. Since the half lives of the radioactive waste of a Nuclear Reactor are of several hundred of thousands of years, the technical explanations to the previous questions little convince to the public in general. In this work summary the results of the radioactive waste generated in a natural reactor, denominated Oklo effect that took place in Gabon, Africa, it makes several thousands of millions of years, a lot before the man appeared in the Earth. The identification of at least 17 reactors in Oklo it was carried out thanks to the difference in the concentrations of Uranium 235 and 238 prospective, and to the analysis of the non-mobility of the radioactive waste in the site. It was able by this way to determine that the reactors with sizes of hardly some decimeter and powers of around 100 kilowatts were operating in intermittent and spontaneous form for space of 150,000 years, with operation cycles of around 30 minutes. Recent studies have contributed information valuable on the natural confinement of the radioactive waste of the Oklo reactors in matrixes of minerals of aluminum phosphate that caught and immobilized them for thousands of millions of years. This extracted information from the nature contributes guides and it allows 'to verify' the validity of the current proposals on the immobilization of radioactive wastes of a nuclear reactor. This work presents in clear and accessible form to the public in general on the secure 'design', operation, 'decommissioning' and 'storage' of the radioactive waste of the reactors that the nature put into operation in Oklo before the man appeared in the Earth. (Author)

2006-09-03

66

The discovery and study of the nuclear reactor in Oklo  

International Nuclear Information System (INIS)

The work leading to the discovery of naturally sustained chain-reactions at Oklo (Gabon), is described. Conditions for this occurence are discussed. Information derived from analytical studies is detailed, particularly age of the deposit, duration of the chain sustained reactions, total power evolved - Typical values are respectively 2x109 years 106 years - 20000MWh per reactor. Migration of fission products and transuranium elements can be studied. Rare earths stay mostly with uranium. No indication of plutonium migration is found. Finally other, but rare similar sites could still be found, according to the data discussed

1976-09-13

67

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

68

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

International Nuclear Information System (INIS)

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

69

Behavior of radionuclides around Oklo reactor  

International Nuclear Information System (INIS)

Re-examination of a vast amount of data on the Oklo reactors which have been accumulated in the past reveals that radionuclides which have been retained and preserved at the site of nuclear reactions during the past 1.7 billion years have high melting and boiling points. Gaseous elements and elements with melting points lower than that of tellurium (452degC) appear to have mostly migrated out of the reactor. About one percent of fissiogenic xenon isotopes have been retained, however, and the isotopic compositions of small amounts of xenon released from the natural reactors were found to be abnormal in that the relative abundances of "1"3"1Xe and "1"3"2Xe are markedly enhanced. It seems that the origin of this anomalous xenon can be attributed to the nonlinear oscillatory mode of operation of the reactors at temperatures of about 400degC, periodically being turned on and off in a manner similar to the present-day geysers or intermittent hot springs. The time period during which the reactor was turned off was calculated to be about 3 hours from the observed ratios of "1"3"2Xe, "1"3"4Xe and "1"3"6Xe in the anomalous xenon. The knowledge gained from the study of the Oklo phenomenon has recently played a key role in solving some of the most difficult problems in the field of geochemistry and cosmochemistry: for example, the so-called 'puzzle of the xenon isotopes', which have remained unsolved for a period of a quarter-century since the 1960's. Results of latest calculations indicate that the carbonaceous chondrites and lunar fines contain amounts of "2"4"4Pu fission xenon which are much greater than hitherto believed and they appear to have started to retain their xenon 4800 to 4900 million years ago. (author)

1991-03-13

70

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

International Nuclear Information System (INIS)

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

71

Far field hydrogeochemistry in the Oklo reactor area (Gabon)  

International Nuclear Information System (INIS)

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

1992-04-06

72

Oklo reactors and implications for nuclear science  

CERN Document Server

We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temperatures than earlier assumed. Nuclear cross sections are input to all Oklo modeling and we discuss a parameter, the $^{175}$Lu ground state cross section for thermal neutron capture leading to the isomer $^{176\\mathrm{m}}$ Lu, that warrants further investigation. Studies of the time dependence of dimensionless fundamental constants have been a driver for much of the recent work on Oklo. We critically review neutron resonance energy shifts and their dependence on the fine structure constant $\\alpha$ and the ratio $X_q=m_q/\\Lambda$ (where $m_...

Davis, E D; Sharapov, E I

2014-01-01

73

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

International Nuclear Information System (INIS)

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)

1998-04-01

74

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

International Nuclear Information System (INIS)

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

1994-10-23

75

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

CERN Document Server

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

76

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

International Nuclear Information System (INIS)

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

77

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

International Nuclear Information System (INIS)

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

78

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)

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

2003-12-01

79

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

80

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)

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

1996-12-01

 
 
 
 
81

Oklo reactors and implications for nuclear science  

Science.gov (United States)

We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temperatures than earlier assumed. Nuclear cross-sections are input to all Oklo modeling and we discuss a parameter, the 175Lu ground state cross-section for thermal neutron capture leading to the isomer 176mLu, that warrants further investigation. Studies of the time dependence of dimensionless fundamental constants have been a driver for much of the recent work on Oklo. We critically review neutron resonance energy shifts and their dependence on the fine structure constant ? and the ratio Xq = mq/? (where mq is the average of the u and d current quark masses and ? is the mass scale of quantum chromodynamics (QCD)). We suggest a formula for the combined sensitivity to ? and Xq that exhibits the dependence on proton number Z and mass number A, potentially allowing quantum electrodynamic (QED) and QCD effects to be disentangled if a broader range of isotopic abundance data becomes available.

Davis, E. D.; Gould, C. R.; Sharapov, E. I.

2014-04-01

82

Reactive transport modelling of uranium at Bangombe (Oklo, Gabon)  

International Nuclear Information System (INIS)

The Oklo uranium deposit in the Francevillian sedimentary series, SE Gabon, has retained abundant fission fragments produced from 2.2 Ga ago. Sixteen natural fission reactors have been recognised at Bangombe uranium ores. The geochemical behaviour of uranium and trace elements around the reaction zone has been carried out using an approach based on the reactive transport modelling HYTEC-2D. The buffer redox capacity of the organic matter associated with FeII/FeIII minerals around the reactor can be explain the uraninite stability into the reaction zone and its weak migration. Nevertheless, the oxidising groundwater dissolves the redox buffer zone and this one cannot protect the reactor of oxidation. Thus, a plume of depleted uranium (235U/238U ratio) coming to the dissolution of the uraninite from the reactor can be simulated by the coupled reactive transport codes. The aqueous uranium concentration predicted is in good agreement with the groundwater analysis in boreholes. The redox buffer controlled by the organic matter could explain the preservation of reactor along the geological time. Thus, the organic matter (graphite type) seems a very interesting mineral for the stabilisation of hydro-geochemical parameters into the nuclear waste storage. (authors)

2000-10-02

83

Search for other natural fission reactors  

Energy Technology Data Exchange (ETDEWEB)

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 greater than 1 m/sup 3/ and concentrations approximately greater than 20 percent uranium are likely places for a fossil reactor if they are approximately greater than 0.6 b.a. 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 worldwide 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 /sup 235/U 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.

Apt, K.E.; Balagna, J.P.; Bryant, E.A.; Cowan, G.A.; Daniels, W.R.; Vidale, R.J.

1977-01-01

84

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

85

Uranium mill monitoring for natural fission reactors  

International Nuclear Information System (INIS)

Isotopic monitoring of the product stream from operating uranium mills is proposed for discovering other possible natural fission reactors; aspects of their occurrence and discovery are considered. Uranium mill operating characteristics are formulated in terms of the total uranium capacity, the uranium throughput, and the dilution half-time of the mill. The requirements for detection of milled reactor-zone uranium are expressed in terms of the dilution half-time and the sampling frequency. Detection of different amounts of reactor ore with varying degrees of "2"3"5U depletion is considered

1977-01-01

86

Uranium mill monitoring for natural fission reactors  

Energy Technology Data Exchange (ETDEWEB)

Isotopic monitoring of the product stream from operating uranium mills is proposed for discovering other possible natural fission reactors; aspects of their occurrence and discovery are considered. Uranium mill operating characteristics are formulated in terms of the total uranium capacity, the uranium throughput, and the dilution half-time of the mill. The requirements for detection of milled reactor-zone uranium are expressed in terms of the dilution half-time and the sampling frequency. Detection of different amounts of reactor ore with varying degrees of /sup 235/U depletion is considered.

Apt, K.E.

1977-12-01

87

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

88

Determinations by irradiation in the Triton reactor of neutron capture cross-sections for isotopes involved in the Oklo phenomenon  

International Nuclear Information System (INIS)

Experimental irradiations of separate elements and isotopes were carried out in a swimming-pool reactor (Triton) in order to obtain better information on the capture cross-sections of uranium fission products involved in the Oklo phenomenon. The irradiation conditions, sample analysis techniques, and calculation methods used to interpret the results are described. The elements irradiated were the following: uranium 93% and 20% enriched in 235U, 240Pu, sup(143+145)Nd, 147Sm, 99Tc, natural dysprosium, mixture of natural europium + natural gadolinium, natural krypton and natural xenon. The uranium and plutonium were used to determine the fluence and spectrum received by the other samples. The irradiations were carried out in two different locations of the Triton reactor to permit work with different spectra; the spectral indices, r, were 0.03 and 0.15. In this way accurate determinations were made of the effective capture cross-sections of a large number of isotopes as a function of the spectrum. In some cases the results differ considerably from those published in the literature. These findings contribute information which is of interest in interpreting the Oklo phenomenon. More particularly, they confirm the values for neutron fluence, and hence the age of the nuclear reaction determined from the fission neodymium balances. They afford a more accurate knowledge of the water/uranium ratios at the time of the nuclear reactions (through measurement of the spectral indices). They also explain the discrepancy observed earlier between the value for the duration of the reaction calculated on the basis of the participation of plutonium in the fissions and that deduced from the pair 99Tc-99Ru. (author)

1977-12-21

89

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)

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)

90

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

91

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

92

Galena crystallization and the origin of sulfur in the Oklo and Bangombe natural reactors: the effects of ca. 900 Ma thermal event  

International Nuclear Information System (INIS)

Galena in the ca. 1950 Ma old natural fossil fission reactors in Gabon crystallized sometime between 980 Ma and 750 Ma during a period of regional extension and the intrusion of a dolerite dyke swarm. The S isotopic composition of galena, containing radiogenic Pb from uraninite, gives information about the origin of the S. Results from ion microprobe analyses of galena from the reactor zones indicate that S mainly originates from the surrounding sediment. Galena in a thin, altered dolerite dyke also contains non-magmatic S. The presented data gives no positive evidence for the involvement of magmatic S during the ca. 900 Ma galena crystallisation, however, the possibility cannot be ruled out. Copyright (2001) Material Research Society

2000-08-27

93

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)

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)

2010-10-17

94

Time-variability of alpha from realistic models of Oklo reactors  

CERN Document Server

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

95

Occurrence of Pu and fissiogenic REE in hydrothermal apatites om the fossil nuclear reactor 16 at Oklo (Gabon)  

International Nuclear Information System (INIS)

Neutron-fission induced nuclear reactions took place 2 Ga ago in the Oklo uranium deposit which is located in the Franceville sedimentary basin (Gabon). The heat released during the running time of the natural reactors led to extensive alteration and desilicification of the sandstones enclosing the reactors and subsequent new formation of clays and apatites, among other phases. The purpose of this study is to determine the capacity of hydrothermally formed apatite to retain actinides and fission products. Combined optical microscopy, scanning electron microscopy and electron microprobe observations revealed the occurrence of fluoroapatite in reaction zone 16. Isotopic and elemental analysis of U, Sm-Nd, Rb-Sr, Bi and Th were performed by ICP-MS and MS-thermoionization on separated apatite grains of various sizes devoid of uraninite inclusions. Most fractions show a slight depletion in 235U. However, one sample shows a significant 235U enrichment (235U/238U = 0.00804 instead of 0.007254 for the natural U) together with high contributions of fissiogenic Nd and Sm. This result shows that 239Pu which is produced by 238U epithermal neutron capture was trapped by the apatite structure during the nuclear reactions or soon after the end of the reactions. It is suggested that combined in situ epithermal neutron irradiation and chemical Pu/U fractionation during the high temperature leaching had contributed to the occurrence of the high 235U/238U ratio in the sample. (orig.)

1996-01-01

96

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)

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

1992-04-06

97

Geochemistry of actinides and fission products in natural aquifer systems  

International Nuclear Information System (INIS)

The progress in the research area of the community project MIRAGE: 'Geochemistry of actinides and fission products in natural aquatic systems' has been reviewed. This programme belongs to a specific research and technical development programme for the European Atomic Energy Community in the field of management and storage of radioactive waste. The review summarizes research progresses in subject areas: complexation with organics, colloid generation in groundwater and basic retention mechanisms in the framework of the migration of radionuclides in the geosphere. The subject areas are being investigated by 23 laboratories under interlaboratory collaborations or independent studies. (orig.)

1989-01-01

98

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

99

Nature of fission-product deposits inside LWR fuel rods  

International Nuclear Information System (INIS)

The deposits of fission products observed on the inner clad surfaces of the high fission gas release population of Maine Yankee Core 1 rods and of a low gas release rod from the H.B. Robinson reactor are discussed. Available thermodynamic data are used to provide the basis for a phenomenological model for the formation of the various observed fission product deposits. The relationship between the deposits and the inferred fuel rod chemistry is discussed. 22 refs

1981-05-11

100

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

International Nuclear Information System (INIS)

Fission track dating is described, focalizing the problem of the decay constant for spontaneous fission of "2"3"8 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

 
 
 
 
101

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

International Nuclear Information System (INIS)

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

102

The origin of the chemical elements and the Oklo phenomenon  

International Nuclear Information System (INIS)

Major developments in the field of nuclear geochemistry and cosmochemistry are reviewed in this monograph. Following a brief introduction, an historical account of the early ideas concerning the cosmic abundance of the elements and the searches made for the ''missing'' elements 43 (Tc) and 61 (Pm) in nature are given. The sequence of events which culminated in the discovery of the Oklo Phenomenon (Pre-Fermi reactor), and the topics related to the synthesis of the elements in stars are then discussed as are the ideas concerning the extinct radioactivities and the discoveries of the extinct nuclides 129I and 244Pu. In the final chapter on isotopic anomalies in the early solar system, the author presents an unbiased review of an area that - although dating back to the days of ancient Greek philosophers and regarded by many as the most fundamental in the entire compass of our modern science - is far from settled and is perhaps not quite ready for incorporation into textbooks. (orig.)

1982-01-01

103

Origin of the chemical elements and the Oklo phenomenon  

Energy Technology Data Exchange (ETDEWEB)

Major developments in the field of nuclear geochemistry and cosmochemistry are reviewed in this monograph. Following a brief introduction, an historical account of the early ideas concerning the cosmic abundance of the elements and the searches made for the ''missing'' elements 43 (Tc) and 61 (Pm) in nature are given. The sequence of events which culminated in the discovery of the Oklo Phenomenon (Pre-Fermi reactor), and the topics related to the synthesis of the elements in stars are then discussed as are the ideas concerning the extinct radioactivities and the discoveries of the extinct nuclides /sup 129/I and /sup 244/Pu. In the final chapter on isotopic anomalies in the early solar system, the author presents an unbiased review of an area that - although dating back to the days of ancient Greek philosophers and regarded by many as the most fundamental in the entire compass of our modern science - is far from settled and is perhaps not quite ready for incorporation into textbooks.

Kuroda, P.K.

1982-01-01

104

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

Science.gov (United States)

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 dosim...

P. J. Iunes

1990-01-01

105

Bagombe - a unique natural site for studying the migration of fission products under surface weathering conditions  

International Nuclear Information System (INIS)

The uranium deposits in the basin of Franceville (Gabon) host the only natural fission reactors known in the world. Unique geologic conditions favored a natural fission reaction 2 Ga ago. This was detected by anomalous isotopic compositions of rare earth elements (fission products) and uranium. In total 16 reactor zones were found. Most of the them are mined out. A current research project of the European Commission concentrates on the reactor zone of Bagombe, which is only 10-11 m below the surface. This reactor zone has been influenced by surface weathering processes. Six drill cores have been sampled at the site of the reactor zone of Bagombe during the course of the project. Only one drill core (BAX 08) hit the core of the reactor which is approximately 10 cm thick, 2-3 m wide and 4-6 m long. The migration of fission products can be traced by the anomalous isotope ratios of REE due to the fisson process. The normal and constant ratio of 149Sm/147Sm is 0.92. The isotope ratio of 149Sm/147Sm close to the reactor zone is as low as 0.28 due to the intense neutron capture of 149Sm and subsequent decay. Similar changes in isotopic patterns are detectable on other rare earth elements (REE). The isotope ratios of Sm and other REE of whole rock and fracture samples surrounding the reactor indicate that fission products migrated only a few centimeters above and mainly below the reactor zone. Organic matter (bitumen, kerogen) seems to act as a trap for fission products. REE-patterns show a less intense weathering with depth in the log profile. (orig.)

1998-09-15

106

Double sequential fission events produced in the interaction of 1539 MeV 208Pb ions with natural lead  

International Nuclear Information System (INIS)

The 2?-geometry arrangement of mica track detectors has been employed for the study of multiprong fission events produced in the interaction of 1539 MeV 208Pb ions with natural lead. Particular attention was given to the analysis of four-pronged events. There is an indication of double sequential fission in the interactions. (orig.)

1980-06-01

107

Nuclear fission as a global energy resource  

International Nuclear Information System (INIS)

This chapter describes the role and the extent of nuclear fission as a global energy resource. The chapter begins with a history of nuclear fission, starting with the Oklo Reactor of about 2 billion years ago and continues through man-made reactors and their current ramifications and problems. Energy resources are described under the topics of impact, fossil resources, fission-water reactors, and fusion-fission-coal. Nuclear applications for oil replacement, propulsion, electric utilities, cogeneration, desalting, and enhanced oil recovery are discussed. Other topics covered in this chapter are: energy requirements and energy availability of uranium enrichment; plant construction of breeder reactors along with antiproliferation and the energy available from breeder reactors in comparison with water reactors; and the energy available from enrichment tailings. The author concludes that nuclear fission is indeed the largest world energy resource available today and hopes the US and the world use it wisely

1980-11-14

108

Investigation of the fundamental constants stability based on the reactor Oklo burn-up analysis  

CERN Document Server

The burn-up for SC56-1472 sample of the natural Oklo reactor zone 3 was calculated using the modern Monte Carlo codes. We reconstructed the neutron spectrum in the core by means of the isotope ratios: $^{147}$Sm/$^{148}$Sm and $^{176}$Lu/$^{175}$Lu. These ratios unambiguously determine the spectrum index and core temperature. The effective neutron absorption cross section of $^{149}$Sm calculated using this spectrum was compared with experimental one. The disagreement between these two values allows to limit a possible shift of the low laying resonance of $^{149}$Sm even more . Then, these limits were converted to the limits for the change of the fine structure constant $\\alpha$. We found that for the rate of $\\alpha$ change the inequality $|\\delta \\dot{\\alpha}/\\alpha| \\le 5\\cdot 10^{-18}$ is fulfilled, which is of the next higher order than our previous limit.

Onegin, M S

2010-01-01

109

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

International Nuclear Information System (INIS)

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

1977-12-01

110

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

111

News on the natural nuclear reactor  

International Nuclear Information System (INIS)

Data characterizing conditions of occurrence and the status of a natural nuclear reactor the remnants of which are discovered in the ore open pit of the Oklo deposit (Gabon) are presented. Transport of alkali earth elements (Rb, Sr, Cs and Ba) as well as Pd, Ag, Cd and Te isotopes near the reactor was investigated. Reactor criticality arose, probably, during or soon after U deposition. The reactor has ceased after 500000 years of operation; the energy of about 15 GW x year was generated. Approximately 80 t of uranium (12 tons of sup(235)U) were utilized during reactor operation. Approximately 10 tons of fission products and 4 tons of sup(239)Pu were formed. Reactor operation was periodical, multiply repeated. Water migrating over sandstone pores was not only a moderator but a self-regulator as well

1986-01-01

112

Natural radioactivity measurements in some Siwalik vertebrates using fission track technique  

International Nuclear Information System (INIS)

Uranium, thorium and their daughter products are significant sources of natural radioactivity in the environment. They may constitute health hazard effects if their concentrations are considerably high enough. Uranium and thorium concentrations in the geological samples are helpful for study of environmental pollution, geochemical exploration and for establishing a correlation between uranium and elemental composition of vertebrates. The results of uranium content of some fossil bone samples collected from Siwalik Himalayas are reported in this paper. Uranium concentration of Siwalik vertebrates are estimated by the fission track technique, using solid state nuclear track detectors (SSNTDs). The uranium concentration in these samples has been found to be varying from 20-55 ppm, which is quite low as compared to uranium contents observed in the fossil bones from the uranium mineralised zones. (author)

2000-01-01

113

Neutron Dose Estimation Using a Natural Uranium Fission Fragment Track Personnel Dosimeter  

International Nuclear Information System (INIS)

The idea of using a natural uranium fission fragment track dosimeter, in the neutron field of thermal, intermediate and fast neutrons in air, has recently been introduced. The system can be used for thermal neutron dose estimation as well as intermediate plus fast neutron dose estimation if the spectrum and the percentage contribution of each neutron group is known. This paper investigates feasibility of the use of such dosimeters when they are worn by radiation workers. Detailed study of the system shows the possibility of differentiating between doses received from fast, intermediate and thermal neutrons if one takes into account reflection from the body of thermal, intermediate and fast neutrons as consisting only of thermal neutrons. (author)

1971-06-01

114

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

115

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

116

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)

2004-11-09

117

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

118

Implications of the Oklo phenomenon in a chiral approach to nuclear matter  

CERN Document Server

It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant $\\alpha$ over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both $\\alpha$ and the average $m_q$ of the $u$ and $d$ current quark masses, and which makes explicit the dependence on mass number $A$ and atomic number $Z$. (Recent model independent results on hadronic $\\sigma$-terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics (QCD) and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivi...

Davis, Edward D

2014-01-01

119

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

120

La138/139 Isotopic Data and Neutron Fluences for Oklo RZ10 Reactor  

CERN Multimedia

Recent years have seen a renewed interest in the Oklo phenomenon, particularly in relation to the study of time variation of the fine structure constant. The neutron fluence is one of the crucial parameters for Oklo reactors. Several approaches to its determination were elaborated in the past. We consider whether it possible to use the present isotopic La138/139 data for RZ10 as an additional indicator of neutron fluences in the active cores of the reactors. We calculate the dependence of the Oklo La138 abundance on neutron fluence and elemental lanthanum concentration. The neutron fluence in RZ10 can be deduced from lanthanum isotopic data, but requires reliable data on the primordial elemental abundance. Conversely, if the fluence is known, the isotope ratio provides information on the primordial lanthanum abundance that is not otherwise easily determined.

Gould, C R; 10.1103/PhysRevC.86.027601

2012-01-01

 
 
 
 
121

Fission, total and neutron capture cross section measurements at ORELA for {sup 233}U, {sup 27}Al and natural chlorine  

Energy Technology Data Exchange (ETDEWEB)

The authors have made use of the Oak Ridge Electron Linear Accelerator (ORELA) to measure the fission cross section of {sup 233}U in the neutron energy range of 0.36 eV to {approximately} 700 keV. This paper reports integral data and average cross sections. In addition they measured the total neutron cross section of {sup 27}Al and natural chlorine, as well as the capture cross section of Al over an energy range from 100 eV up to about 400 keV.

Guber, K.H.; Spencer, R.R.; Leal, L.C.; Larson, D.C.; Santos, G. Dos; Harvey, J.A.; Hill, N.W.

1998-08-01

122

Fission, total and neutron capture cross section measurements at ORELA for 233U, 27Al and natural chlorine  

International Nuclear Information System (INIS)

The authors have made use of the Oak Ridge Electron Linear Accelerator (ORELA) to measure the fission cross section of 233U in the neutron energy range of 0.36 eV to ? 700 keV. This paper reports integral data and average cross sections. In addition they measured the total neutron cross section of 27Al and natural chlorine, as well as the capture cross section of Al over an energy range from 100 eV up to about 400 keV

1998-10-05

123

Quantum nature of ROT and TRI asymmetries in the ternary fission of nuclei  

International Nuclear Information System (INIS)

Effects of T-odd asymmetry in ternary-nuclear-fission reactions induced by polarized cold neutrons are considered within quantum theory. It is shown that the asymmetry coefficient can be expressed in terms of experimental angular distributions of third particles in reactions induced by unpolarized neutrons. The explicit form of this coefficient makes it possible to explain the difference in the magnitudes and signs of the TRI and ROT effects observed experimentally for different targets.

2010-08-01

124

Natural uranium impurities in fission track detectors and associated geocronological parameters  

International Nuclear Information System (INIS)

A technique, based in counting neutron induced fission tracks, has been developed for the measurement of uranium impurities in mica. Uranium concentrations of 10-10 and 10-9 (U atom/mica atom) have been measured. As a part of the development of this technique, the mica geological age was also measured, by fossil and induced track detection. The agreement obtained by this method, T = (472+-52) x 106 years with that of (450+-15) x 106 years obtained by the Ar-K technique is satisfactory and is an indirect test of the fission track technique used. A careful analysis of the neutron field parameters and nuclear data used in the age determination was made. This analysis is useful for applications in geocronology. According to this analysis a value of lambdasub(f)=(7.1+-0.1) x 10-17 years-1 is recommended for the spontaneous fission of U238. However, in order to compare the results, the quoted age, T=(472+-52) x 106 years, was obtained with the generally accepted value of lambdasub(f)=(6.85-0.20) x 10-17 years-1 (Fleischer and Price 1964). (author)

1981-01-01

125

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

International Nuclear Information System (INIS)

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"-"7 g/g and <2 x 10"-"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

1982-01-01

126

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

Energy Technology Data Exchange (ETDEWEB)

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 SiO{sub 2}, TiO{sub 2}, ZrO{sub 2}, FeO, CaO, Al{sub 2}O{sub 3} and P{sub 2}O{sub 5}. The averaged content of Y{sub 2}O{sub 3} and the Ln`s is less than 0.78 wt% and there is a scattered positive correlation with P{sub 2}O{sub 5}. 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.

Jensen, K.A. [Aarhus Univ. (Denmark). Dept. of Earth Sciences; Ewing, R.C. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences; Gauthier-Lafaye, F. [Centre National de la Recherche Scientifique, Strasbourg (France). Centre de Geochemie de la Surface

1997-12-31

127

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

International Nuclear Information System (INIS)

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

1996-12-02

128

Uranium transport around the reactor zone at Okelobondo (Oklo). Data evaluation with M3 and HYTEC  

Energy Technology Data Exchange (ETDEWEB)

The Swedish Nuclear Fuel and Waste Management Company (SKB) is conducting and participating in Natural Analogue activities as part of various studies regarding the final disposal of high level nuclear waste (HLW). The aim of this study is to use the hydrogeological and hydrochemical data from Okelobondo (Oklo Natural Analogue) to compare the outcome of two independent modelling approaches (HYTEC and M3). The modelling helps to evaluate the processes associated with nuclear natural reactors such as redox, adsorption/desorption and dissolution/precipitation of the uranium and to develop more realistic codes which can be used for site investigations and data evaluation. HYTEC (1D and 2D) represents a deterministic, transport and multi-solutes reactive coupled code developed at Ecole des Mines de Paris. M3 (Multivariate Mixing and Mass balance calculations) is a mathematical-statistical concept code developed for SKB. M3 can relatively easily be used to calculate mixing portions and to identify sinks or sources of element concentrations that may exist in a geochemical system. M3 helped to address the reactions in the coupled code HYTEC. Thus, the major flow-paths and reaction paths were identified and used for transport evaluation. The reactive transport results (one-dimensional and two-dimensional simulations) are in good agreement with the statistical approach using the M3 model. M3 and HYTEC show a dissolution of the uranium layer in contact with upwardly oxidising waters. M3 and HYTEC show a gain of manganese rich minerals downstream the reactor. A comparison of the U and Mn plots for M3 deviation and HYTEC results showed an almost mirror behaviour. The U transport stops when the Mn gain increases. Thus, HYTEC and M3 modelling predict that a possible reason for not having U transport up to the surface in Okelobondo is due to an inorganic trap which may hinder the uranium transport. The two independent modelling approaches can be used to complement each other and to better understand the processes that can take place in nature. This provides the opportunity to assess the necessary tools for site investigations, data evaluation and helps to trace the reactions and to identify the hydro-geo-chemical system. Thus, we can build reliable tools which can be used to assess the performance of possible waste repository sites.

Gurban, I.; Laaksoharju, M. [INTERA KB, Sollentuna (Sweden); Made, B.; Ledoux, E. [Ecole des Mines, Paris (France)

1999-12-01

129

Uranium transport around the reactor zone at Okelobondo (Oklo). Data evaluation with M3 and HYTEC  

International Nuclear Information System (INIS)

The Swedish Nuclear Fuel and Waste Management Company (SKB) is conducting and participating in Natural Analogue activities as part of various studies regarding the final disposal of high level nuclear waste (HLW). The aim of this study is to use the hydrogeological and hydrochemical data from Okelobondo (Oklo Natural Analogue) to compare the outcome of two independent modelling approaches (HYTEC and M3). The modelling helps to evaluate the processes associated with nuclear natural reactors such as redox, adsorption/desorption and dissolution/precipitation of the uranium and to develop more realistic codes which can be used for site investigations and data evaluation. HYTEC (1D and 2D) represents a deterministic, transport and multi-solutes reactive coupled code developed at Ecole des Mines de Paris. M3 (Multivariate Mixing and Mass balance calculations) is a mathematical-statistical concept code developed for SKB. M3 can relatively easily be used to calculate mixing portions and to identify sinks or sources of element concentrations that may exist in a geochemical system. M3 helped to address the reactions in the coupled code HYTEC. Thus, the major flow-paths and reaction paths were identified and used for transport evaluation. The reactive transport results (one-dimensional and two-dimensional simulations) are in good agreement with the statistical approach using the M3 model. M3 and HYTEC show a dissolution of the uranium layer in contact with upwardly oxidising waters. M3 and HYTEC show a gain of manganese rich minerals downstream the reactor. A comparison of the U and Mn plots for M3 deviation and HYTEC results showed an almost mirror behaviour. The U transport stops when the Mn gain increases. Thus, HYTEC and M3 modelling predict that a possible reason for not having U transport up to the surface in Okelobondo is due to an inorganic trap which may hinder the uranium transport. The two independent modelling approaches can be used to complement each other and to better understand the processes that can take place in nature. This provides the opportunity to assess the necessary tools for site investigations, data evaluation and helps to trace the reactions and to identify the hydro-geo-chemical system. Thus, we can build reliable tools which can be used to assess the performance of possible waste repository sites

1999-01-01

130

Indications of uranium transport around the reactor zone at Bagombe (Oklo)  

International Nuclear Information System (INIS)

The aim of this study is to use the hydrogeological and hydrochemical data from Oklo Natural Analogue to compare the outcome of two independent modelling approaches (HYTEC-2D and M3) which can be used to model natural conditions surrounding the reactor. HYTEC-2D represents a 2D, deterministic, transport and multi-solutes reactive coupled code developed at Ecole des Mines de Paris. M3 (named Multivariate Mixing and Mass balance) is a mathematical-statistical concept code developed for SKB. The M3 results are visualised using the Voxel Analyst code and the outcome of the uranium transport predictions are made from a performance assessment point of view. This exercise was in the beginning intended to represent a validation for M3, by comparing this statistic approach with the standard hydrodynamic - geochemical coupled code HYTEC-2D. It was realized that the codes complete each other and a better understanding of the geochemical studied system is obtained. Thus, M3 can relatively easily be used to calculate mixing portions and to identify sinks or sources of element concentrations that may exist in a geochemical system. This can help to address the reactions in the coupled code such as HYTEC-2D, to identify the hydrodynamic and hydrochemical system and to reduce the computation time. M3 shows the existence of the buffer around the reactor. No transport of uranium was indicated downstream the reactor. HYTEC-2D gives the same result in the case when we consider the existence of the redox buffer in the model. M3 shows an increase of the alkalinity in the reactor zone. The increase of the alkalinity was indicated by the M3 modelling to be associated with microbial decomposition of organic material which added reducing capacity to the system. The modelling result was supported by new results from the last field campaign, which included in-situ Eh measurements and microbial sampling and identification. The effects from the same process was indicated also by the HYTEC-2D predictions which show an increase of the pH in the reactor zone, due to the existence of the buffer. The two modelling approaches can be used to complete each other and to better understand the processes that can take place in nature. Thus, we can build confident tools which can be used to support performance assessment

1998-01-01

131

Uranium transport around the reactor zone at Bangombé and Okélobondo (Oklo): examples of hydrogeological and geochemical model integration and data evaluation  

Science.gov (United States)

The sites at Bangombé and Okélobondo (Oklo) in Gabon provide a unique opportunity to study the behaviour of products from natural nuclear reactions in the vicinity of reactor zones which were active around two billion years ago. The Commission of the European Communities initiated the Oklo Natural Analogue Programme. One of the principal aims was to study indications of present time migration of elements from the reactor zones under ambient conditions. The hydrogeological and hydrochemical data from the Oklo sites were modelled in order to better understand the geochemical behaviour of radionuclides in the natural system, by using independent models and by comparing the modelling outcome. Two modelling approaches were used: M3 code (hydrochemical mixing and mass balance model), developed by the Swedish Nuclear Fuel and Waste Management Company (SKB) and HYTEC (reactive transport model) developed by Ecole des Mines de Paris. Two different reactor zones were studied: Bangombé, a shallow site, the reactor being at 11 m depth, and OK84 at Okélobondo, situated at about 450 m depth, more comparable with a real repository location. This allowed the validation of modelling tools in two different sedimentary environments: one shallow, with a more homogeneous layering situated in an area of meteoric alteration, and the other offering the opportunity to study radionuclide migration from the reaction zone over a distance of 450 m through very heterogeneous sedimentary layers. The modeling results indicate that the chemical reactions retarding radionuclide transport are very different at the two sites. At Bangombé, the decomposition of organic material consumes oxygen and at Okélobondo the oxygen is consumed by inorganic reactions resulting, in both cases, in uranium retardation. Both modelling approaches (statistic with M3 code and deterministic with HYTEC code) could describe this situation. The goal of this exercise is to test codes which can help to describe and understand the processes taking place at the sites, validate the models with in situ data, and thus build confidence in the tools used for future site characterization. Ultimately, this allows identifying and selecting processes and parameters that can be used as input into repository performance assessment calculations and modelling exercises.

Gurban, I.; Laaksoharju, M.; Madé, B.; Ledoux, E.

2003-03-01

132

Imprints left by natural radioactivity in geological materials: uranium fission tracks and thermoluminescence applications in earth sciences  

International Nuclear Information System (INIS)

In a rock, all minerals which contain uranium are host to a number of spontaneous fission phenomena forming a single damaged area called a ''latent track'', observations of which may lead to dating, uranium mapping and finding paleo-geo-thermometers (thermal history, used in oil exploration). The radioactive elements during the decay process release energy which is trapped as electrons into the physical or chemical defects of the crystalline lattice; this energy can be later released by heating the mineral (thermic stimulated luminescence); the thermoluminescence is characterized by a glow which spectrum constitutes a typical feature of the mineral, its crystallization conditions and the subsequent evolution of the material. Natural and induced glow curve may be produced. 6 figs., 52 refs

1994-01-01

133

Anomalous Xenon in the Precambrian Nuclear Reactor in Okelobondo (Gabon): A Possible Connection to the Fission Component in the Terrestrial Atmosphere  

Science.gov (United States)

Some CFF-Xe (Chemically Fractionated Fission Xenon), whose isotopic composition is established by simultaneous decay and migration of radioactive fission products, is probably present in the Earth's lithosphere, a conclusion based on available Xe data from various crustal and mantle rocks . Our recent isotopic analysis of Xe in alumophosphate from zone 13 of Okelobondo (southern extension of Oklo), along with the independent estimation of the isotopic composition of atmospheric fission Xe , supports the hypothesis that CFF-Xe was produced on a planetary scale. Additional information is contained in the original extended abstract.

Meshik, A. P.; Kehm, K.; Hohenberg, C. M.

1999-01-01

134

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

International Nuclear Information System (INIS)

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 (USiO_4.nH_2O) 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

135

2.05 x 10"9 age of the Oklo uranium deposit  

International Nuclear Information System (INIS)

U and Pb isotopic data on samples (10 to 100 gram) 2 to 10 m away from the borders of the Oklo reactor zones indicate a primary age of 2.05 x 10"9 years for the Oklo deposit and a secondary age of 0.375 x 10"9 years. All samples show effects of Pb loss; the average loss is 50 percent. Both the U--Pb and Pb isotopic data are consistent with a model of a primary 2.05 x 10"9 year age of the deposit, continuous volume diffusion of Pb from uraninite, and either continuous or recent loss of this Pb. In this case the 0.375 x 10"9 year age is an artifact without time significance. Using an average value of D/a"2 3.5 x 10"-"1"1 a"-"1 (Cowan, this conference) this model explains the apparent 1.8 x 10"9 year Pb age observed by other workers. From the "2"0"8Pb/"2"0"6Pb data the average U/Th value calculated for the Oklo deposit is approximately 100

1977-12-21

136

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

International Nuclear Information System (INIS)

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, ?0.2Ma old (2) intermediate-age obsidians, ?0.4-?0.8Ma old, and (3) older obsidians, ?1.4-?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

2005-12-01

137

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)

1986-04-24

138

Fission gas release  

International Nuclear Information System (INIS)

The fission event in oxide fuels gives rise to at least two fission products. The peaks of the fission product yield curves occur in the vicinity of the xenon and krypton isotopes and approximately thirty of these atoms - fission gases - are created per hundred fissions. This amounts to approximately 30 ml of fission gas at STP for every MWd of burn-up and poses a number of problems in the operation of reactors, particularly at higher burn-ups. The fission gases aggregate into two types of porosity. Within the grains, intra-granular pores are created and these can grow rapidly during transients to produce large swellings, which may cause strong pellet-clad interactions (PCI) and fuel failure. Inter-granular porosity occurs on the grain faces and the coalescence and subsequent venting to the grain edges leads to the development of continuous release pathways. This report describes the development of the different types of porosity and how this affects the subsequent release of fission gas. The fission gas release threshold is shown to be a natural consequence of the storage capacity of the grain boundaries and the effects of different models for irradiation induced re-solution are highlighted. The release of short-lived fission products, in particular, the iodine isotopes, is controlled by the microstructure created during the release of stable gases. It is shown that a model based on the fractal nature of the surface of UO2 can be used to reconcile the conflicting results obtained for the diffusion coefficients of short-lived and long-lived fission gas atoms. (author). 65 refs., 37 figs., 3 tabs

2000-01-01

139

Ternary Fission  

International Nuclear Information System (INIS)

The fission process in which heavy nuclei fragment into three large charged panicles, in place of the usual two, has been studied in the case of thermal-neutron-induced fission of U235 and the spontaneous fission of Cf252. Solid-state detectors, a fast triple coincidence system and a three-coincident-parameter analyser were used to measure the three fission fragment energies parallel with the detection of each ternary fission event. Experimental evidence is presented supporting the existence of ternary fission by specifically excluding recoil phenomena and accidental events as contributing to the observed three-fold coincidence events. Mass-energy-angular correlations of ternary fission have been determined and are summarized as follows: The total kinetic energy release in ternary fission appears to be slightly higher (by approximately 10 MeV) than that for binary fission. In the case of the spontaneous ternary fission of Cf252, the frequency of occurrence is observed to be greater than 2.2 x 10-6 ternary fission events per binary fission event. Tripartition of Cf252 results preferentially in division into two medium mass particle (one of which has a mass number near 56) and one larger mass. In the case of thermal-neutron-induced fission of U235, the frequency of occurrence is observed to be greater than 1.2 x 10-6 ternary fission events per binary fission event. Ternary fission of U236: results in the formation of one light fragment (near mass 36) and two large fragments or, as in the case of Cf252, two medium fragments and one large one. These results indicate that axially asymmetric distortion modes are possible in the pre-scission configurations of the fissioning nucleus. A description is given of experiments designed to radiochemically detect the light fragment resulting from ternary fission. (author)

1965-07-01

140

Geochemical behavior of radionuclides in highly altered zircon above the Bangombé natural fission reactor, Gabon  

Science.gov (United States)

The isotopic compositions of rare earth elements (REE), Pb and U of highly altered zircons from the clay and black shale layers above the Bangombé natural reactor, Gabon, were determined by a sensitive high resolution ion microprobe (SHRIMP) to discuss the redistribution processes of elements into zircons under the supergene weathering. The clay layer trapped most of the fissiogenic Nd, Sm and Eu derived from the reactor and prevented them migrating into the black shale layer. On the other hand, only the Ce isotopic ratios of the clay and black shale layers have about 2 times larger variations than the other REE. This result suggests that a large chemical fractionation between Ce and other REE above the reactor occurred under the oxidizing condition. The U-Pb data of zircons suggest that the U-Pb system was largely disturbed by migration of chemically fractionated Pb and U from the 2.0 Ga-old uraninite in association with recent weathering.

Kikuchi, Makiko; Hidaka, Hiroshi; Horie, Kenji

 
 
 
 
141

Nuclear fission  

International Nuclear Information System (INIS)

The nuclear fission process is pedagogically reviewed from a macroscopic-microscopic point of view. The Droplet model is considered. The fission dynamics is discussed utilizing path integrals and semiclassical methods. (L.C.)

1981-01-01

142

Syngenetic model for some early Proterozoic uranium deposits. Evidence from Oklo  

International Nuclear Information System (INIS)

Massive, vein-like accumulations of uranium in Early Proterozoic metamorphic rocks have conventionally been explained by hydrothermal processes, metamorphism of original syngenetic or early epigenetic sedimentary deposits, mechanical accumulations, supergene processes, or some combination of these processes. Many of these deposits are located at unconformities and may be controlled by basement fault systems, but the unconformities are not necessarily the primary control for ore formation. Exploration of Proterozoic sedimentary basins is, for economic factors, usually restricted to the basin edges where distance to the unconformities is minimal. The 2.0+-0.1 billion year old Oklo uranium deposit, Republic of Gabon, is unique in that very high grade ore has apparently been derived from low grade ore in unmetamorphosed sedimentary rocks. The low grade ore is similar to Phanerozoic syngenetic or early epigenetic sandstone type deposits; the assemblage pitchblende-illite (1 Md polytype)-chlorite-organic carbon-dolomite is common. Uranium was mobilized from the low grade ore zones and concentrated as high grade ore in fractures. Pitchblende-illite (2M1 polytype)-chlorite-hematite-pyrite in the virtual absence of quartz and carbon is common in the high grade ore. Crystallization temperatures near 2000C at P=0.5-2 kb and Eh conditions favouring formation of either pyrite or hematite, in the pH range of 6-8 were likely. The reductant for the mobilized uranium was apparently carbon which was oxidized as fractures opened, thus also accounting for the absence of quartz. The high grade ore, concentrated in shale-rich material down-filled into broken sandstone layers, was then severely folded and fractured. In cross sections, then, much of the Oklo ore resembles cross sections of high grade uranium ore in metamorphic rocks. It is proposed that Oklo may either be a hybrid type of deposit or a precursor to typical deposits in metamorphic rocks noted in Canada and elsewhere. It is considered significant that the Oklo deposit is located within the sedimentary sequence and not at the unconformity between this sequence and the basement granitic massif

1979-06-08

143

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

144

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

145

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

146

Nuclear fission  

Energy Technology Data Exchange (ETDEWEB)

V.M. STRUTINSKY's semi-classical method is the most precise to determine the energy of the different states along the fission way. The double-humped fission barrier explains fission isomerism. V.M. STRUTINSKY's barrier explains the ''intermediate structure'' observed in the cross section under the threshold; it provides also the observed effect of ''vibrational resonances'' with an interpretation. Taking an asymmetry parameter in consideration, a triple-humped fission barrier seems to be essential now for the light actinides. There is still a microscopic fission barrier to be explained.

Michaudon, A.

1982-09-01

147

Measurements of Nucleon-Induced Fission Cross-Sections of Separated Tungsten Isotopes and Natural Tungsten in the 50-200 MeV Energy Region  

CERN Document Server

Neutron- and proton-induced fission cross-sections of separated isotopes of tungsten (182W, 183W, 184W, and 186W) and natural tungsten relative to 209Bi have been measured in the incident nucleon energy region 50-200 MeV using fission chambers based on thin-film breakdown counters (TFBC) at quasi-monoenergetic neutrons from the 7Li(p,n) reaction and at the proton beams of The Svedberg Laboratory (TSL), Uppsala University (Uppsala, Sweden). The preliminary experimental data are presented in comparison with the recent data for nuclei in the lead-bismuth region, as well as with predictions by the CEM03.01 event generator.

Eismont, V P; Smirnov, A N; Soloviev, S M; Blomgren, J; Conde, H; Prokofiev, A V; Mashnik, S G

2005-01-01

148

On the use of thin natural uranium film dosimetry in mineral dating by the fission track method  

International Nuclear Information System (INIS)

Three obsidian samples were irradiated in a neutron facility and their age was measured by the fission track method; using a thin uranium film dosemeter. The results were compared to others made previously on the same type of rock using conventional neutron dosimetry. The use of thin uranium film for age determination is discussed. (F.E.). 20 refs, 4 tabs

1993-11-07

149

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

International Nuclear Information System (INIS)

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

150

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

151

Absolute fission ratio measurements with semi-conductor fission chambers  

International Nuclear Information System (INIS)

For the purpose of measuring absolute fission ratios in fast critical assemblies, fission chambers using semi-conductor detectors were prepared. By electrical deposition, thin homogeneous foils of U-233, U-235, natural uranium and neptunium-237 were obtained. The effective number of fissile atoms was determined both by alpha particle countings and by fission event recordings in standard thermal neutron column. Except for natural uranium chambers the determined effective number of atoms agreed within experimental errors. The detectors were used to measure equilibrium spectrum in the natural uranium blocks and the fast reactor spectrum in a fast critical core (FCA VI-2). The results were compared with those of other laboratories and those of calculation. It was found that the fission chambers of this type would be of practical use in fast reactor critical experiment. (auth.)

1976-01-01

152

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

153

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

154

Bimodal fission  

International Nuclear Information System (INIS)

In recent years, the author has measured the mass and kinetic-energy distributions from the spontaneous fission of 258Fm, 259Md, 260Md, 258No, 262No, and 260[104]. All are observed to fission with a symmetrical division of mass, whereas the total-kinetic-energy (TKE) distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the TKE distributions are resolved into two Gaussians, the constituent peaks lie near 200 and near 233 MeV. He concludes two modes or bimodal fission is occurring in five of the six nuclides studied. Both modes are possible in the same nuclide, but one generally predominates. He also concludes the low-energy but mass-symmetrical model is likely to extend to far heavier nuclei; while the high-energy mode will be restricted to a smaller region, a region of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in 132Sn

1989-04-25

155

Bimodal fission  

Energy Technology Data Exchange (ETDEWEB)

In recent years, we have measured the mass and kinetic-energy distributions from the spontaneous fission of /sup 258/Fm, /sup 259/Md, /sup 260/Md, /sup 258/No, /sup 262/No, and /sup 260/(104). All are observed to fission with a symmetrical division of mass, whereas the total-kinetic-energy (TKE) distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the TKE distributions are resolved into two Gaussians the constituent peaks lie near 200 and near 233 MeV. We conclude two modes or bimodal fission is occurring in five of the six nuclides studied. Both modes are possible in the same nuclides, but one generally predominates. We also conclude the low-energy but mass-symmetrical mode is likely to extend to far heavier nuclei; while the high-energy mode will be restricted to a smaller region, a region of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in /sup 132/Sn. 16 refs., 7 figs., 1 tab.

Hulet, E.K.

1989-04-19

156

From transmutation to fission  

International Nuclear Information System (INIS)

The article explains the historical background of the discovery of nuclear fission, observed by O. Hahn and F. Strassmann. Becquerel's discovery of the natural radioactivity, in 1986, had made physicists waver in their belief in their fundamental concept which then was based on classical mechanics, Maxwell's electrodynamics, and Gibbs' theory of thermodynamics. The novel research activities then started have led to the discoveries and findings by E. Rutherford, Pierre and Marie Curie, F. Soddy, E. Fermi, and many other scientists. The article traces back the events which span the first observed transmutations as a result of studies on the nature of emanations, the first application of alpha particles for exploring the atomic structure, the development of particle accelerators, the discovery of artificial radioactivity, and the application of neutrons for inducing nuclear fission processes. (RB)

1988-01-01

157

An evaluation of the dissolution process of natural uranium ore as an analogue of nuclear fuel  

International Nuclear Information System (INIS)

The assumption of congruent dissolution of uraninite as a mechanism for the dissolution behaviour of spent fuel was critically examined with regard to the fate of toxic radionuclides. The fission and daughter products of uranium are typically present in spent unreprocessed fuel rods in trace abundances. The principles of trace element geochemistry were applied in assessing the behaviour of these radionuclides during fluid/solid interactions. It is shown that the behaviour of radionuclides in trace abundances that reside in the crystal structure can be better predicted from the ionic properties of these nuclides rather than from assuming that they are controlled by the dissolution of uraninite. Geochemical evidence from natural uranium ore deposits (Athabasca Basin, Northern Territories of Australia, Oklo) suggests that in most cases the toxic radionuclides are released from uraninite in amounts that are independent of the solution behaviour of uranium oxide. Only those elements that have ionic and thus chemical properties similar to U4+, such as plutonium, americium, cadmium, neptunium and thorium can be satisfactorily modelled by the solution properties of uranium dioxide and then only if the environment is reducing. (84 refs., 7 tabs.)

1991-01-01

158

Fission meter  

Science.gov (United States)

A neutron detector system for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly into information that a first responder can use to discriminate materials. The system comprises counting neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source.

Rowland, Mark S. (Alamo, CA); Snyderman, Neal J. (Berkeley, CA)

2012-04-10

159

Antiproton induced fission  

International Nuclear Information System (INIS)

Antiproton induced fission has been investigated with a novel double-arm fission fragment spectrometer and with a special arrangement to determine absolute fission yields in various targets. The spectrometer measures five parameters per fission event: Two masses, two energies and the folding angle. Asymmetric, symmeric and pre-equilibrium fission was observed. The number of nucleons emitted before and after scission was deduced indicating fast fission of hot nuclei. (orig.)

1993-06-07

160

Fission energy  

International Nuclear Information System (INIS)

Fission energy research and development in the Division during this report period has spanned two primary programs. In one of these programs, some unique and important dissolution and solvent extraction work with fast reactor spent fuels was completed. Most of this work was done for the Consolidated Fuel Reprocessing Program (CFRP); a smaller project was completed under contract for Rockwell International Corp., Hanford, Washington. Specific studies on solvent cleanup were conducted under contract for Westinghouse Idaho Nuclear Company, Inc. Other work done by Chem Tech for CFRP included completing the preparation of 12 kg of uranium-plutonium mixed-oxide microspheres for fuel fabrication and irradiation tests. Detailed results from these studies are not included here, because of regulations governing the distribution of applied technology information. Results of this work are published in CFRP topical quarterly progress reports. The second area of Chem Tech's fission energy development has been in support work for the High-Temperature Gas-Cooled Reactor (HTGR) program. The applied technology information is not reported here in compliance with DOE regulations. Most of this work has been reported in internal documents and annual progress reports

1985-10-01

 
 
 
 
161

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

International Nuclear Information System (INIS)

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

162

Fission Research at IRMM  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

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

2010-01-01

163

Induction of nuclear fission by high-voltage application  

CERN Multimedia

In nuclear power generation, fissile materials are mainly used. For example, $U^{235}$ is fissile and therefore quite essential for use of nuclear energy. However, the material $U^{235}$ has very small natural abundance less than 1 %. We should seek possibility of utilizing fissionable materials such as $U^{238}$ because natural abundance of such fissionable materials is generally much larger than fissile ones. In this paper, we show that thermal neutrons with vanishing kinetic energy can induce nuclear fission when high voltage is applied to fissionable materials. To obtain this result, we use the liquid-drop model for nuclei. Finally, we propose how fissionable materials can be utilized.

Maruyama, Hirokazu

2007-01-01

164

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

165

Recent Results from Investigation of Prompt Fission Neutron Emission in Spontaneous Fission of 252CF  

International Nuclear Information System (INIS)

The main motivation of the present work was investigation of the nature of anomalous (from the point of view of modern theory) dependence of the average prompt fission neutron number on the total kinetic energy of the fission fragments using modern digital signal processing approach. A twin Frisch-grid ionization chamber was used for fission fragment mass and kinetic energy spectroscopy. A fast neutron detector with NE213 (or analog) scintillation liquid was used for prompt fission neutron time of flight measurement. About 107 fission events, coinciding with prompt fission neutron detection was acquired in the experiment. Correlated fission fragment kinetic energies, their masses, an angle between fission axis and the prompt fission neutron, the prompt fission neutron velocity were measured with help of eight channel set-up of synchronized waveform digitizers, having 100 MHz sampling frequency and 12-bit pulse height resolution. Analysis of the acquired data revealed effects causing distortion of measured angular distribution of prompt fission neutron and the dependence of their average number on total kinetic energy of the fission fragment. Special modification of the experiment and respective modifications in the data analysis procedure brought to reasonable agreement between experimental results and theoretical calculations. In the first time the linear dependence of the average number of prompt fission neutron on total kinetic energy in the range of (140 - 220) MeV was demonstrated. The long time existing contradiction between experiment and theory was resolved and, a new measurement procedure allowing avoidance of above mentioned systematic errors in experiments with actinide targets like 235U, 239Pu, etc. was proposed. (author)

2013-06-01

166

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

167

Fifty years of nuclear fission: Nuclear data and measurements series  

International Nuclear Information System (INIS)

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

168

Comparisons of theoretical and experimental neutron spectra, "1"1"5In(n,n') and fission rates, in the centre of three spherical natural uranium and iron shell configurations, located at BR1  

International Nuclear Information System (INIS)

Three spherical configurations of iron and uranium shells have been studied. The configurations were a 1-cm thick natural uranium shell, a 1-cm thick natural uranium shell with an inner 7-cm thick iron shell and a 1-cm thick natural uranium shell with an inner iron shell of 14-cm thickness. For the measurements, the shells were located at the centre of a hollow cavity, 100-cm in diameter, in the vertical graphite thermal column of the BR1 reactor. The central neutron spectra were calculated by means of the DTF-IV code, using the 208-group KEDAK-3 library, and by means of the ANISN code, using the 171-group VITAMIN-C library. Central neutron spectra, measured by the proton-recoil and "6Li(n,?)t spectrometry techniques, are compared to the theory between ? 100 keV and 5 MeV. Mean fission cross-sections of "2"4"0Pu, "2"3"7Np, "2"3"4U, "2"3"5U, "2"3"6U and "2"3"8U were deduced from the calculations. Their ratios with respect to "2"3"8U are compared to measurements made with NBS dual fission chambers. (Auth.)

1984-09-24

169

ChemTeacher: Fission  

Science.gov (United States)

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Fission page includes resources for teaching students about the discovery and applications of fission.

2011-01-01

170

Fission Mass Yield Studies  

International Nuclear Information System (INIS)

Mass yields from fission induced by a span of neutron energies up to 18 MeV have been measured for Th232, U235 and U238 target nuclei. Particular attention has been given to the dependence of symmetric fission yields on energy. To study the effect of angular momentum, fission yields from the U236 compound nucleus formed by alpha-particle irradiations of Th232 were also studied over the same span of excitation energies. A standard set of Pd109, Ag111, Pd112 and Ag113 symmetric fission yields was generally measured for all irradiations. In addition, yields of Eu156, Cs136 and 2.3-d Cd115 were measured for some selected combinations of projectile, energy and target nucleus. Assays for Zr97 and sometimes also Ba139 served as fission monitors. Altogether 150 fission yields were measured for these combinations of target nucleus, projectile and incident energy. About one-third of these were checked by replicated irradiations. At highest energies for the U236 compound nucleus the symmetric fission yield from alpha-particle-induced fission is about 13% higher than for neutron-induced fission. Dips in symmetric fission yield were observed at the energy onset of third-chance fission for each target and projectile. Some indication of a small central peak in the mass distribution was observed in the yields from U236 compound nucleus fission, but not from the Th233 compound nucleus fission. Detailed mathematical methods have been developed to separate the effects of fissions preceding and following neutron emission. These methods were used to remove the effects of second- and third-chance fissions from the measured symmetric fission yields. These calculated yields for first-chance fission show no dips with energy. The calculations also show that perhaps half the difference between symmetric yields for alpha- particle-induced fission of Th232 and neutron-induced fission of U235 is attributable to angular momentum effects. Both calculated first-chance yields and measured yields (resulting from first-, second- and third-chance fissions) for the U236 compound nucleus are compared with the two-mode-of-fission hypothesis. Similar analyses are made for yields from neutron-induced fission of Th232 and U238. (author)

1965-07-01

171

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.

Al-Adili A.

2010-03-01

172

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

173

The Fission Vision  

Science.gov (United States)

Leo Szilard, a Hungarian physicist, imagined the two steps needed to free the energy in an atom's nucleus: one, a nuclear chain reaction, and two, a critical mass of the right element to set off and sustain it. Does he envision the process we now call "fission," the splitting of nuclei? Yes, he seems to, but Szilard's ideas are not yet clearly expressed. And he doesn't know which element will provide nuclei that can be easily split. This chapter describes his quest and that of his contemporaries, to identify this missing element--which ultimately unleashed nuclear energy into the world. In addition, this compelling chapter clearly illustrates the nature of science and science as a human endeavor as recommended in the National Science Education Standards.

Hakim, Joy

2007-08-17

174

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)

1998-08-01

175

Determination of natural uranium in soil, grass and water samples around the rare earth research and development center by neutron activation and fission track methods  

International Nuclear Information System (INIS)

The purpose of this study was the determination of the background level of uranium in the environment around the Rare-Earth Research and Development Center. The information obtained will be used for the future environmental impact database. Soil, grass and water around this center were chosen as representative environmental samples. In this work two techniques were exploited to determine uranium content. One was neutron activation analysis and the another was fission track method. Soil and grass samples were analysed by Instrumental Neutron Activation Analysis (INAA) while the water samples were analysed by Radiochemical Neutron Activation Analysis (RNAA) For fission track method, mica was used as detector. It was found that the uranium content determined by the two techniques were comparable. In surface water sample contain uranium in the range of 0.87-2.00 ppb in summer and 0.71-0.93 ppb in rainy and cold seasons. Groundwater was found to have a higher level of Uranium, i.e. 6.60-7.25 ppb in summer, 3.74-4.92 ppb in rainy and cold seasons. Uranium level in grass (ash) was 0.43-1.32 ppm in summer, 0.17-0.48 ppm in rainy and cold seasons. Uranium level in soil and sediment showed no seasonal variation and the concentration was between 3.03-9.72 ppm

1991-01-01

176

Is channeling of fission tracks taking place?  

CERN Multimedia

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.

Yada, K

1999-01-01

177

Fission fragment angular distributions  

International Nuclear Information System (INIS)

A statistical scission model (SSM) is developed and applied to fragment angular distributions from alpha- and heavy-ion-induced fission. Although the formal equations for fragment angular distributions in the statistical scission and transition state models are of the same structure, the variances in the distribution of angular momentum projections on the fission direction are established at very different stages of the fission process in the two models. The SSM predicts angular distributions in reasonable agreement with those measured for heavy-ion-induced fission of some reaction systems where the fission barrier was vanished or is very small relative to the nuclear temperature. For a number of these systems, the transition state model (TSM) is inapplicable. The SSM, however, predicts the variance to have too weak an energy dependence, possibly indicating dynamical effects. Inclusion of pre- and post-scission particle emission and asymmetric fission does not remove this discrepancy. The TSM gives a better representation of fragment angular distributions from alpha-particle-induced fission of several targets (low-spin systems) as a function of fissility parameter. The very large experimental variances, observed for systems with large spin and no fission barrier, are inconsistent with the concepts of fast or preequilibrium fission, occurring on a time scale too short for relaxation of the tilting mode. Fragment spins from ?-ray multiplicities are compared with predictions of the two above models

1986-08-01

178

Fission fragment angular distributions  

International Nuclear Information System (INIS)

A statistical scission model is developed and applied to fragment angular distributions from alpha- and heavy-ion-induced fission. Although the formal equations for fragment angular distributions in the statistical scission and transition-state models are of the same structure, the variances in the distribution of angular momentum projections on the fission direction are established at very different stages of the fission process in the two models. The statistical scission model predicts angular distributions in reasonable agreement with those measured for heavy-ion-induced fission of some reaction systems where the fission barrier has vanished or is very small relative to the nuclear temperature. For a number of these systems, the transition state model is inapplicable. The statistical scission model, however, predicts the variance to have too weak an energy dependence, possibly indicating dynamical effects. Inclusion of pre- and post-scission particle emission and asymmetric fission does not completely remove this discrepancy. The transition state model gives a better representation of fragment angular distributions from alpha-particle-induced fission of several targets (low-spin systems) as a function of fissility parameter. The large effective variances, deduced for systems with large spin and no fission barrier, are inconsistent with the concepts of ''fast'' or ''pre-equilibrium'' fission, occurring on a time scale too short for relaxation of the tilting mode. Some of the present discrepancies between the effective variances deduced from fragment angular distributions and those calculated with the statistical scission model may be due to small contributions of incomplete fusion followed by fission or due to sequential fission

1986-01-01

179

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

180

Fission Xenon on Mars  

Science.gov (United States)

Fission Xe components due to Pu-244 decay in the early history of Mars have been identified in nakhlites; as in the case of ALH84001 and Chassigny the fission gas was assimilated into indigenous solar-type Xe. Additional information is contained in the original extended abstract.

Mathew, K. J.; Marti, K.; Marty, B.

2002-01-01

 
 
 
 
181

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

182

Uranium content of petroleum by fission track technique  

International Nuclear Information System (INIS)

The feasibility of the fission track registration technique to investigate the natural uranium concentration in petroleum is examined. The application of this technique to petroleum is briefly described and discussed critically. The results obtained so far indicate uranium concentrations in samples of Brazilian petroleum which are over the detect ion limit of fission track technique. (Author)

1981-01-01

183

Uranium content of petroleum by Fission track technique  

International Nuclear Information System (INIS)

This paper examines the feasibility of the fission track registration technique to investigate the natural uranium concentration in petroleum. The application is briefly described and the results obtained indicate the presence of uranium concentrations in samples of Brazilian petroleum which are over the detection limit of the fission track technique. The irradiations were performed by using fluxes with predominance of thermal neutrons, which have a fission cross-section for U 235 equal to 579 barns. Since the neutron fluxes were not comp sed exclusively of thermal neutrons, fissions from fast neutrons would also be taken into account for U 238 and Th 232

1982-01-01

184

Nuclear fission sustainability with hybrid nuclear cycles  

International Nuclear Information System (INIS)

An analysis is presented on the main requirements to develop nuclear fission in the context of social, economic and environmental sustainability. This analysis is mainly focused on maximizing the energy actually generated from the potential contents of fissionable 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 light water reactors (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 fissionable natural resources while keeping a very high level of safety standards in the full fuel cycle

2007-05-01

185

Isomers in Fission Fragments  

Science.gov (United States)

The structure of neutron-rich nuclei produced as secondary fission fragments was investigated using the EUROGAM and GAMMASPHERE ACS arrays, the LOHENGRIN fission-fragment mass separator and the FIFI fission-fragment identifier. Fission products were populated in spontaneous fission of 248Cm and 252Cf and in thermal neutron-induced fission of 233U, 235U and 241Pu at ILL Grenoble. Particularly useful in such studies are isomeric states, well populated in fission due to their yrast character, easy to detect due to their long half lives and easy to interpret because of their relatively simple composition. We discuss their role in studies of neutron-rich nuclei, giving examples of isomers found in our recent experiments. A special type of K-isomers, resulting from `crossing' of extruder and intruder orbitals plays a role in the mechanism of a sudden onset of deformation in the A = 100 and A = 150 regions. We present evidence for these isomers in both regions. Possible further studies in this field are proposed.

Urban, W.; Faust, H.; Jentschel, M.; Köster, U.; Krempel, J.; Materna, Th.; Mutti, P.; Soldner, T.; Genevey, J.; Pinston, J. A.; Simpson, G.; RzaCa-Urban, T.; Z?omaniec, A.; ?ukasiewicz, M.; Sieja, K.; Nowacki, F.; Dorvaux, O.; Gall, B. J. P.; Roux, B.; Dare, J. A.; Durell, J. L.; Smith, A. G.; Varley, B. J.; Tsekhanovich, I.; Jolie, J.; Linnemann, A.; Scherillo, A.; Orlandi, R.; Smith, J. F.; Ahmad, I.

2009-01-01

186

Natural occurring radioactive substances. Vol. 1  

International Nuclear Information System (INIS)

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

1996-03-01

187

Fiftieth anniversary of nuclear fission  

International Nuclear Information System (INIS)

Few discoveries have influenced mankind and few discoveries have had such an intricate history as that of nuclear fission. Thus it is natural that it is remembered and commemorated in many places on its fiftieth anniversary. The author participated in the early phases in Rome and later in the USA and he knew well most of the principals, except Fritz Strassmann. He gives a short outline; a detailed history would require many hours and would be laborious to follow in detail. He begins the story with the first neutron bombardment of uranium

1989-04-25

188

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

1983-04-14

189

Fission foil characteristics  

International Nuclear Information System (INIS)

From the users' point of view the most important characteristics of fission samples are considered taking into account their influence on the final results of nuclear data measurements. (author). Abstract only

1988-10-01

190

Fission Systems for Mars Exploration  

Science.gov (United States)

Fission systems are used extensively on earth, and 34 such systems have flown in space. The energy density of fission is over 10 million times that of chemical reactions, giving fission the potential to eliminate energy density constraints for many space missions. Potential safety and operational concerns with fission systems are well understood, and strategies exist for affordably developing such systems. By enabling a power-rich environment and highly efficient propulsion, fission systems could enable affordable, sustainable exploration of Mars.

Houts, Michael G.; Kim, T.; Dorney, D. J.; Swint, Marion Shayne

2012-01-01

191

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

192

Singlet exciton fission photovoltaics.  

Science.gov (United States)

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. PMID:23611026

Lee, Jiye; Jadhav, Priya; Reusswig, Philip D; Yost, Shane R; Thompson, Nicholas J; Congreve, Daniel N; Hontz, Eric; Van Voorhis, Troy; Baldo, Marc A

2013-06-18

193

Prompt Neutrons from Fission  

International Nuclear Information System (INIS)

A survey is given of the present state of knowledge of the spectrum, angular distribution and number of prompt fission neutrons, as functions of incident neutron energy and individual fragment mass, for low-energy fission. The energy spectrum of prompt neutrons has been found to be of the same form (nearly Maxwellian) for many different types of fission. It has been shown that this type of spectrum is to be expected on the basis of evaporation from moving fragments, and theoretical predictions of the spectrum agree very accurately with experimental data. Some data are now available on the variation of the neutron spectrum with fragment mass and angle of emission. Only recently has it become possible to take accurate data on the angular distribution of the neutrons. It appears that the neutrons have the angular distribution to be expected if emitted almost isotropically from the moving fragments, with a possibility that some small fraction are not emitted in this way, but directly from the fissioning nuclide. Much work has been done on the variation of fission neutron number v with incident neutron energy for neutron-induced fission. The neutron number increases roughly linearly with energy, with a slope of about 0.15 n/MeV. There is now evidence that this slope changes somewhat with energy. This change must be associated with other changes in the-fission process. The most interesting recent discovery concerning fission neutrons is the strong dependence of neutron number on individual fragment mass. The data are being rapidly improved by means of the newer techniques of determining fragment mass yields from velocity and pulse-height data, and of determining neutron yields from cumulative mass yields. There is evidence of similar dependence of neutron yield on fragment mass in a number of cases. It has been suggested that this property is directly connected with the deformability of the fragments, and in particular with the near-spherical shapes of magic-number fragments. On the basis of a simple fragment-deformation theory, the deformation parameter is calculated directly from experimental data, and is seen to have a very similar dependence on mass for four types of fission. These ideas seem likely to lead to a more basic understanding of the fission process, including the mass yields and energies of the fragments. (author)

1965-07-01

194

Fission-to-spallation ratio and fission dynamics manifestation  

International Nuclear Information System (INIS)

Fission of highly excited nuclei is affected by the viscous character of the system motion in deformation coordinates for very heavy nuclei with Z ? 90. The long-time scale fission was proved for such systems formed in heavy-ion induced reactions. The overdamped diabatic motion may influence also fission of the spallation-residue products in reactions with protons at intermediate energy. The experimental results on fission-to-spallation ratio are analyzed and the evidences for the long-time scale fission are found in the fission excitation functions for medium-mass targets with Z=70-75

2008-01-01

195

Fission Track Membrane Filters  

International Nuclear Information System (INIS)

Latent tracks on thin polycarbonate (PC) film were created by fission fragments from nuclear fission reaction between thermal neutron from the Thai Research Reactor and U-235 in uranium screen. The track etching in 6N NaOH solution at 60?C could produce 2-8 ?m diameter through holes proportional to 30-120 minutes etching time. The polyethylene gratings of 1-6 mm thickness were placed between uranium screen and the PC film during exposure. The grating allowed only the fission fragments incident to the film at or close to right angle to pass through. Varying the thickness of the grating plate from 0 mm to 6 mm resulted in the production of the track densities in the range of 12,000 to 2,000 tracks per square millimeter respectively

2003-12-01

196

Current position on fission product behavior  

International Nuclear Information System (INIS)

The following phenomena are treated and modeled: fission product release from fuel, both in-vessel and ex-vessel; fission product deposition in the primary system, fission product deposition in the containment, and fission product revolatization

1988-05-16

197

Low energy nuclear fission  

International Nuclear Information System (INIS)

In these lectures the liquid drop model of fission is presented and some of its predictions compared with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. It is shown 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

1980-08-23

198

Fission gas measuring technology  

Energy Technology Data Exchange (ETDEWEB)

Safety and economy of nuclear plant are greatly affected by the integrity of nuclear fuels during irradiation reactor core. A series of post-irradiation examination (PIE) including non-destructive and destructive test is to be conducted to evaluate and characterize the nuclear performance. In this report, a principle of the examination equipment to measure and analyse fission gases existing nuclear fuels were described and features of the component and device consisting the fission gas measuring equipment are investigated. (author). 4 refs., 2 tabs., 6 figs.

Lee, Hyung Kwon; Kim, Eun Ka; Hwang, Yong Hwa; Lee, Eun Pyo; Chun, Yong Bum; Seo, Ki Seog; Park, Dea Gyu; Chu, Yong Sun; Ahn, Sang Bok

1998-02-01

199

Mirror fusion--fission hybrids  

International Nuclear Information System (INIS)

The fusion-fission concept and the mirror fusion-fission hybrid program are outlined. Magnetic mirror fusion drivers and blankets for hybrid reactors are discussed. Results of system analyses are presented and a reference design is described

1978-03-31

200

''In situ'' investigations of the radioactive fissionable element infiltration and retention in different soils  

International Nuclear Information System (INIS)

''In situ'' investigations of the natural and forced infiltration and retention of the fissionable elements from a liquid residue in several natural compacted soils and compacted clays are presented. The velocities and flow rates for different stages of the residue infiltration are determined. The retention of the fissionable elements by variation of the fissionable element concentration with the distance from the place of the residue depot is investigated. (author)

1980-01-01

 
 
 
 
201

Process for treating fission waste  

Energy Technology Data Exchange (ETDEWEB)

A method is described for the treatment of fission waste. A glass forming agent, a metal oxide, and a reducing agent are mixed with the fission waste and the mixture is heated. After melting, the mixture separates into a glass phase and a metal phase. The glass phase may be used to safely store the fission waste, while the metal phase contains noble metals recovered from the fission waste.

Rohrmann, Charles A. (Kennewick, WA); Wick, Oswald J. (Richland, WA)

1983-01-01

202

Low-energy ternary fission  

Energy Technology Data Exchange (ETDEWEB)

The actual situation of the research on ternary fission, mainly {alpha}-particle accompanied fission, is reviewed, with the accentuation on recent experimental and theoretical investigations. The results of multiparameter experiments are discussed in more detail, and the role of fragment deformation for a correct description of the ternary fission process is outlined. (orig.).

Theobald, J.P.; Heeg, P.; Mutterer, M. (Technische Hochschule Darmstadt (Germany, F.R.). Inst. fuer Kernphysik)

1989-10-09

203

Status of fission yield measurements  

International Nuclear Information System (INIS)

Fission yield measurement and yield compilation activities in the major laboratories of the world are reviewed. In addition to a general review of the effort of each laboratory, a brief summary of yield measurement activities by fissioning nuclide is presented. A new fast reactor fission yield measurement program being conducted in the US is described

1979-10-05

204

Microscopic Description of Induced Fission  

CERN Multimedia

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, N

2013-01-01

205

Pulsed Fission Propulsion Concept  

Science.gov (United States)

In the 1960's U.S. Government laboratories, under Project Orion, investigated a pulsed nuclear fission propulsion system. Small nuclear pulse units would be sequentially discharged from the aft end of the vehicle. A blast shield and shock absorber system would protect the crew and convert the shock loads into a continuous propulsive force.

1999-01-01

206

Fusion-Fission Analogy.  

Science.gov (United States)

The analogy of plasma ignition of fusion devices to criticality in fission systems is shown. The four-factor formula is presented and special emphasis is given to the energy utilization factor, which now dominates fusion research. Instead of keeping books...

J. R. McNally

1977-01-01

207

Fission yield evaluation  

International Nuclear Information System (INIS)

The report presents the topics discussed at the Specialists' Meeting on Fission Yield Evaluation organized by the IAEA at Studsvik, Sweden, between 11 and 15 September 1987, the conclusions and the recommendations drafted in order to establish a closer cooperation between evaluators, improve the communication with measurers and to define further experimental and evaluation work needed

1987-09-11

208

Fission product data library  

International Nuclear Information System (INIS)

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

209

Fission before K equilibration  

International Nuclear Information System (INIS)

Preequilibrium fission can give rise to a large anisotropy at sub-barrier energy. It was postulated that the emission of fission fragments not only came from the compound nucleus but also may take place after equilibration of all degrees of freedom except the K degree of freedom. Immediately following fusion the system has the K-state distribution of the entrance channel and this initial distribution is broadened with time due to a coupling between the intrinsic and collective rotational degrees of freedom. Our theory was tested and confirmed by Lestone et al.. It is shown that the K-equilibration fission can explain decrease of mass resolved fission fragment anisotropy at larger mass asymmetries. Two competing mechanisms contribute to the anisotropy. The effective moment of inertia and Ko2 decreases with the increase of the mass asymmetry and contribute to the increase of anisotropy. On the other hand for larger asymmetries barriers are higher and lifetimes are longer. Such systems are more K-equilibrated and will have smaller anisotropy. (authors)

1998-09-25

210

Transient fission and multiplicities  

International Nuclear Information System (INIS)

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.)

1989-01-01

211

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

212

Antiproton-induced nuclear fission  

International Nuclear Information System (INIS)

A dynamical model, which takes into account all stages of fission induced by stopped antiprotons (atomic cascade, intranuclear cascade, evaporation cascade, fission of a compound nucleus, and evaporation from fission fragments), has been formulated. In particular, the dynamics of the descent of fissioning nuclei from the saddle point to the scission point has been described by the diffusion model. The data on bar p-induced fission have been analyzed in the framework of this model and a good agreement between the experiment and theory has been observed. 17 refs., 8 figs

1994-07-01

213

Statistical theory of nuclear fission  

International Nuclear Information System (INIS)

The development of the statistical theory of nuclear fission and its applications to the mass distribution of fission products (asymmetric fission), charge distribution, kinetic energy distribution, prompt neutron distribution, spin distribution, energy dependence of the distributions, spontaneous fission distributions, ternary fission, long-range ? particle distributions and so on are reviewed. Results are compared with experimental data. Early discrepancies are resolved. Several simple applications, such as charge and spin distributions are clear cut; their verification justifies the general validity of the statistical concepts. The more involved asymmetric fission problem can be unravelled by a large body of theoretical and experimental studies which establish that the asymmetric fission modes are indeed energetically favored and the shell effect on level density will not compromise the energy advantage. The successful derivation of the mass distribution curve concludes the study

1986-04-20

214

Nature  

Digital Repository Infrastructure Vision for European Research (DRIVER)

From the ancient times to the present debates on nature and environment, the idea of Nature has been one of the main concepts which interested Geographers. This paper deals with the representations of this idea in the works of thinkers who played a major role in shaping modern Geography, with a special focus on the Mediterranean world. It aims to clarify how Nature was important in defining heuristic strategies of the geographical sciences and their explications of reality. In the first part ...

Ferretti, Federico; Schmidt Di Friedberg, Marcella

2012-01-01

215

Fission Target Design  

CERN Document Server

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

216

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: ? =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)

1964-02-01

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

Charge particle induced fission and fission like reactions  

International Nuclear Information System (INIS)

Some selected aspects of charged particle induced fission studies are discussed to explore the scope of further studies at cyclotron energies. The primary topics of discussion include fission barriers, fragment angular distributions, fission excitation functions and fragment kinetic energies. The recently discovered phenonenon of strongly damped collisions in heavy ion induced reactions is also touched upon to point out the experimental evidences of energy dissipation and nucleon diffusions on a fast time scale. Relevance of a similar theoretical description for the last stages of the fission process is also pointed out. (author)

1977-09-14

219

Coulomb fission and transfer fission at heavy ion collisions  

International Nuclear Information System (INIS)

In the present thesis the first direct evidence of nuclear fission after inelastic scattering of heavy ions (sup(183,184)W, "1"5"2Sm ? "2"3"8U; "1"8"4W ? "2"3"2Th; "1"8"4W, "2"3"2Th ? "2"4"8Cm) is reported. Experiments which were performed at the UNILAC of the Gesellschaft fuer Schwerionenforschung in Darmstadt show the observed heavy ion induced fission possesses significant properties of the Coulomb fission. The observed dependence of the fission probability for inelastic scattering on the projectile charge proves that the nuclear fission is mediated by the electromagnetic interaction between heavy ions. This result suggests moreover a multiple Coulomb-excitation preceding the fission. Model calculations give a first indication, that the Coulomb fission proceeds mainly from the higher ? phonons. In the irradiation with "1"8"4W the fission probability of "2"3"2Th is for all incident energies about 40% smaller that at "2"3"8U. The target dependence of the Coulomb fission however doesn't allow, to give quantitative statements about the position and B(E2)-values of higher lying ? phonons. (orig./HSI)

1981-01-01

220

Isoscaling behavior in fission dynamics  

International Nuclear Information System (INIS)

The fission processes of 112Sn+112Sn and 116Sn+116Sn are simulated with the combination of the Langevin equation and the statistical decay model. The masses of two fission fragments are given by assuming the process of symmetric fission or asymmetric fission by Monte Carlo sampling with the Gaussian probability distribution. From the analysis of the isotopic/isotonic ratios of the fission fragments from both reactions, the isoscaling behavior has been observed and investigated in detail. Isoscaling parameters ? and ? are extracted as a function of the charge number and neutron number, respectively, in different widths of the sampling Gaussian probability distribution. It seems that ? is sensitive to the width of fission probability distribution of the mass asymmetrical parameter, but ? is not. Both ? and ? drop with increasing beam energy and reduced friction parameter

2005-12-01

 
 
 
 
221

Low-energy ternary fission  

International Nuclear Information System (INIS)

With the detector system DIOGENES thermal neutron induced and spontaneous ? particle associated fission and spontaneous nuclear tripartition into three fragments of similar masses has been investigated. DIOGENES is a concentric arrangement of toroidal angular position sensitive ionization chambers and proportional counters to measure the kinetic energies and relative angular distributions of the three reaction products of ternary fission. For ?-particle accompanied fission some of the many possible ? particle fission-fragment parameter correlations will be discussed. For nearly symmetric low-energy nuclear tripartition new upper limits are presented. Former experimental results which pretended evidence for so called true ternary fission could be explained by charged-particle associated fission with a light particle in the mass range of 13 < A < 23

1989-04-25

222

Ternary fission within statistical approach  

International Nuclear Information System (INIS)

The ternary system with a light nucleus between two heavy fragments is assumed to appear from the binary configuration near scission. The formation of a third light nucleus in the binary system is considered. The calculated charge distributions in spontaneous ternary fission of 252Cf and in induced ternary fission of 56Ni are compared with the available experimental data. The neutron multiplicity from the fission fragments is described. The fine structures of the TKE-mass distribution are predicted. (orig.)

2006-12-01

223

Neutron emission prior to fission  

International Nuclear Information System (INIS)

Neutron emission in coincidence with fission fragments has been measured in the reaction 16O+142Nd?158Er at 207 MeV. The neutron multiplicity preceding fission is interpreted by including the effects of transients and saddle-to-scission time on neutron emission prior to fission, and determines the limit ??5x1021 s-1 for the reduced nuclear dissipation coefficient ?. (orig.)

1986-08-28

224

On the Fission Spectrum Uncertainty  

International Nuclear Information System (INIS)

The fission spectrum can be analytically represented in several different forms, such as a simple Maxwellian, the Watt fission spectrum, or the more modern and physically sound Madland-Nix representation. A quantitative estimate of the uncertainty matrix associated with the fission spectrum is needed in many nuclear data applications. Criticality safety, neutron cross section adjustment and reactor pressure vessel surveillance dosimetry are just a few examples

2004-02-17

225

Calculation of the fast fission factor from basic nuclear data  

International Nuclear Information System (INIS)

Using a two group model the ratio of U238 fissions to U235 fissions, and hence the fast fission factor, ?, is calculated from basic nuclear data in near natural uranium fuelled lattices. Proper account is taken of reflection of fast neutrons from the moderator and of interaction between rods in separate channels. Both these effects are shown to he significant. The calculated fission ratios are compared with the results of a number of experiments in graphite lattices. Agreement is excellent with some 20 metal rod experiments carried out at Harwell and at Brookhaven, the calculated values being within the experimental error for all except the largest rods. Although agreement is not uniformly good with four oxide cluster experiments carried out at Winfrith, the greatest discrepancy amounts to less than 0.3% in ?. (author)

1963-01-01

226

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

International Nuclear Information System (INIS)

The disintegration constant of U"2"3"8 by spontaneous fission using glass as fission fragment detector was redetermined. A film of natural uranium (UO_3) 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

227

Fusion-fission type collisions  

International Nuclear Information System (INIS)

Three examples of fusion-fission type collisions on medium-mass nuclei are investigated whether the fragment properties are consistent with fission from equilibrated compound nuclei. Only in a very narrow band of angular momenta the data fulfill the necessary criteria for this process. Continuous evolutions of this mechanism into fusion fission and into a deep-inelastic process and particle emission prior to fusion have been observed. Based on the widths of the fragment-mass distributions of a great variety of data, a further criterion for the compound-nucleus-fission process is tentatively proposed

1979-10-25

228

Fission in Rapidly Rotating Nuclei  

Directory of Open Access Journals (Sweden)

Full Text Available We study the effect of rotation in fission of the atomic nucleus 256Fm using an independent-particle shell model with the mean field represented by a deformed Woods-Saxon potential and the shapes defined through the Cassinian oval parametrization. The variations of barrier height with increasing angular momentum, appearance of double hump in fission path are analysed. Our calculations explain the appearance of double hump in fission path of 256Fm nucleus. The second minimum vanishes with increase in angular momentum which hints that the fission barrier disappears at large spin.

A. K. Rhine Kumar

2014-02-01

229

Hidden systematics of fission channels  

Directory of Open Access Journals (Sweden)

Full Text Available It is a common procedure to describe the fission-fragment mass distributions of fissioning systems in the actinide region by a sum of at least 5 Gaussian curves, one for the symmetric component and a few additional ones, together with their complementary parts, for the asymmetric components. These components have been attributed to the influence of fragment shells, e.g. in the statistical scission-point model of Wilkins, Steinberg and Chasman. They have also been associated with valleys in the potential-energy landscape between the outer saddle and the scission configuration in the multi-channel fission model of Brosa. When the relative yields, the widths and the mean mass-asymmetry values of these components are fitted to experimental data, the mass distributions can be very well reproduced. Moreover, these fission channels are characterised by specific values of charge polarisation, total kinetic energy and prompt-neutron yields. The present contribution investigates the systematic variation of the characteristic fission-channel properties as a function of the composition and the excitation energy of the fissioning system. The mean position of the asymmetric fission channels in the heavy fragment is almost constant in atomic number. The deformation of the nascent fragments at scission, which is the main source of excitation energy of the separated fission fragments ending up in prompt-neutron emission, is found to be a unique function of Z for the light and the heavy fragment of the asymmetric fission channels. A variation of the initial excitation energy of the fissioning system above the fission saddle is only seen in the neutron yield of the heavy fragment. The charge polarisation in the two most important asymmetric fission channels is found to be constant and to appreciably exceed the macroscopic value. The variation of the relative yields and of the positions of the fission channels as a function of the composition and excitation energy of the fissioning system obey a hidden systematics that can be explained by the number of states in the vicinity of the outer fission barrier as a function of mass asymmetry, if the potential is constructed as the sum of the macroscopic contribution of the compound nucleus and empirically determined fragment shells. This hidden systematics also explains the transition from asymmetric to symmetric fission around 226Th and around 258Fm.

Schmidt Karl-Heinz

2013-12-01

230

Fusion-fission type collisions  

International Nuclear Information System (INIS)

Three examples of fusion-fission type collisions on medium-mass nuclei are investigated whether the fragment properties are consistent with fission from equilibrated compound nuclei. Only in a very narrow band of angular momenta the data fulfill the necessary criteria for this process. Continuous evolutions of this mechnism into fusion fission and into a deep-inelastic process and particle emission prior to fusion have been observed. Based on the widths of the fragment-mass distributions of a great variety of data, a further criterion for the compound-nucleus-fission process is tentatively proposed. (orig.)

1979-10-25

231

Ternary fission of 252Cf  

International Nuclear Information System (INIS)

Tripartition in the spontaneous fission of 252Cf was studied by measuring both the energy and angular distribution of ternary fragments with a toroidal position sensitive ionization chamber. Most registered ternary events are identified as light charged particle emission from the neck region of the fissioning system. Upper limits deduced for real ternary fission processes that would lead either to an 'asymmetric' or 'symmetric' mass distribution are much lower than concluded from previous counting experiments. Observations on charged particle accompanied fission are presented. (orig.)

1987-05-04

232

Spatial distribution of thorium fission rate in a fast spallation and fission neutron field: An experimental and Monte Carlo study  

Science.gov (United States)

The Energy plus Transmutation (EpT) set-up of the Joint Institute for Nuclear Research (JINR), Dubna, Russia is composed of a lead spallation target surrounded by a blanket of natural uranium. The resultant neutron spectrum is a combination of spallation and fission spectra, modified by a reflective external layer of polyethylene and an internal absorbing layer of cadmium. The EpT set-up was irradiated with a beam of 4 GeV deuterons from the Nuclotron Accelerator at JINR. The spatial distribution of thorium fission rate within the assembly was determined experimentally, using a fission track detector technique, and compared with Monte Carlo predictions of the MCNPX code. Contributions of neutrons, protons, deuterons, photons and pions to total fission were taken into account. Close agreement between the experimental and calculated results was found.

Borger, J. J.; Hashemi-Nezhad, S. R.; Alexiev, D.; Brandt, R.; Westmeier, W.; Thomauske, B.; Adam, J.; Kadykov, M.; Tiutiunnikov, S.

2012-02-01

233

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

234

Fission and Fusion Game  

Science.gov (United States)

In this activity, students play a board game where they learn the characteristics of and differences between fission and fusion, as well as the real world applications of these energy-releasing reactions. Reproducible game cards and and game board are included in the resource. The investigation supports material presented in chapter 3, "What Heats the Earth's Interior?" in the textbook, Energy flow, part of the Global System Science, an interdisciplinary course for high school students that emphasizes how scientists from a wide variety of fields work together to understand significant problems of global impact.

235

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

1989-01-03

236

Observation of cold fission in 242Pu spontaneous fission  

International Nuclear Information System (INIS)

Coincidence ?-ray data from the spontaneous fission of 242Pu were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of 242Pu and the yields from thermal-neutron-induced fission of 241Pu are also presented. copyright 1996 The American Physical Society

1996-07-01

237

Nuclear dissipation, fission probability and neutron multiplicity prior to fission  

International Nuclear Information System (INIS)

We discuss the effects of nuclear dissipation of fission probabilities that are characteristic of a diffusion model of the fission process. Reproducing the experimental fission probabilities at low excitation energies fixes the ratio asub(f)/asub(n) of the level density parameters for a given strength of the reduced dissipation coefficient ?. These low energy constraints on asub(f)/asub(n) and ? balance the effects of transients on neutron multiplicities prior to fission at higher excitation energies. For the competitive decay of "1"5"8Er formed in the reaction "1"6O+"1"4"2Nd at 207 MeV we show that due to transients only the multiplicity of pre-fission neutrons is enhanced with respect to the prediction of the statistical model in a manner consistent with our earlier general analysis. (orig.)

1986-01-01

238

Biological danger of fission products  

International Nuclear Information System (INIS)

Basic aspects of biological danger of fission products formed during nuclear weapons tests and by nuclear enterprise releases are considered. Impact of internal and external irradiation on animals and man, toxicity of nuclear products fission depending on their age, preventive measures and urgent treatment in case of radiational injuries are discussed. 3 tabs

1995-05-01

239

Fission fragment driven neutron source  

International Nuclear Information System (INIS)

Fissionable uranium formed into a foil is bombarded with thermal neutrons in the presence of deuterium-tritium gas. The resulting fission fragments impart energy to accelerate deuterium and tritium particles which in turn provide approximately 14 MeV neutrons by the reactions t(d,n)"4He and d(t,n)"4He

1976-01-01

240

Modern Pulsed Fission Propulsion Concept  

Science.gov (United States)

In the 1960's U.S. Government laboratories, under Project Orion, investigated a pulsed nuclear fission propulsion system. Based on Project Orion, an interplanetary vehicle using pulsed fission propulsion would incorporate modern technologies for momentum transfer, thermal management, and habitation design.

1999-01-01

 
 
 
 
241

Tritium production from ternary fission  

Energy Technology Data Exchange (ETDEWEB)

The tritium gas emission in the thermal neutron induced ternary fission of {sup 249}Cf has been determined for the first time in a measurement at the intense neutron beam PF1B of the Laue-Langevin Institute in Grenoble (France). A {sup 249}Cf sample was mounted in the centre of a vacuum chamber, at a short distance of a {delta}E-E telescope which permitted the identification of the ternary particles. The binary fission fragments were detected in a separate run, using only the E detector. From these measurements, the energy distributions and the emission probabilities of the ternary {sup 3}H particles emitted in the thermal neutron induced ternary fission of {sup 249}Cf could be determined. Based on this result and on measurements published by us recently, we could enlarge the database related to {sup 3}H emission probabilities (denoted t/B) and their energy distributions in particular for the Cm and Cf isotopes. The impact of the excitation energy of the fissioning nucleus on the ternary particle emission probability is discussed, comparing for a given compound nucleus, the t/B data obtained from thermal neutron induced fission (excitation energy of the fissioning nucleus equals the neutron binding energy) and from spontaneous fission (excitation energy equals zero). In addition, semi-empirical relations between t/B data and characteristics of the binary fission process are proposed. (authors)

Serot, O. [CEA Cadarache (DEN/DER/SPRC/LEPh), 13 - Saint Paul lez Durance (France). Dept. d' Etudes des Reacteurs; Wagemans, C.; Vermote, S. [Gent Univ., Dept. of Subatomic and Radiation Physics (Belgium); Heyse, J. [EC-JRC, Institute for Reference Materials and Measurements, Geel (Belgium); Soldner, T.; Geltenbort, P. [Institut Laue-Langevin, 38 - Grenoble (France); AlMahamid, I. [Wadsworth Center, New York State Dept. of Health, Albany, NY (United States); AlMahamid, I.; Floyd, J.; Lukens, W.W. [Lawrence Berkeley National Laboratory, Berkeley, CA (United States)

2008-07-01

242

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the tenth issue of a report series on Fission Product Data, which informs us about all the activities in this field, which are planned, ongoing, or have recently been completed. The types of activities included 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, lumped fission product data (decay heat, absorption, etc.). There is also a section with recent references relative to fission product nuclear data

1984-01-01

243

Status of fission yield data  

International Nuclear Information System (INIS)

In this paper first we summarize the current status of the US evaluation for 34 fissioning nuclides at one or more neutron incident energies and for spontaneous fission. Currently there are 50 yields sets, and for each we have independent and cumulative yields and uncertainties for approximatively 1100 fission products. When finalized the recommended data will become part of the next version of the US ENDF/B VI. In a second part we review the different models developed to derive independent yields sets. The Zp and empirical models have been extensively studied for 6 fissioning nuclides. Comparison of model estimates with experimental data will be presented. The parameters for other fissioning systems will be derived by the use of systematic trends. A comparison of model estimates with some recent experimental data, obtained from Lohengrin (249 Cf T) will be given

1988-06-03

244

Monte Carlo Based Toy Model for Fission Process  

CERN Document Server

Fission yield has been calculated notoriously by two calculations approach, macroscopic approach and microscopic approach. This work will proposes another calculation approach which the nucleus is treated as a toy model. The toy model of fission yield is a preliminary method that use random number as a backbone of the calculation. Because of nucleus as a toy model hence the fission process does not represent real fission process in nature completely. Fission event is modeled by one random number. The number is assumed as width of distribution probability of nucleon position in compound nuclei when fission process is started. The toy model is formed by Gaussian distribution of random number that randomizes distance like between particle and central point. The scission process is started by smashing compound nucleus central point into two parts that are left central and right central points. These three points have different Gaussian distribution parameters such as mean ({\\mu}CN, {\\mu}L, {\\mu}R), and standard d...

Kurniadi, R; Viridi, S

2014-01-01

245

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

2006-06-01

246

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

247

On prompt fission neutrons  

International Nuclear Information System (INIS)

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

248

Thirty years of nuclear fission in Yugoslavia  

International Nuclear Information System (INIS)

Experimental nuclear reactor 'RB' in Boris Kidric Institute in Vinca is the first nuclear facility built in Yugoslavia in which the first Yugoslav controlled nuclear fission was achieved thirty years ago on April 26, 1958. Designed by Yugoslav scientist as a bare, natural uranium-heavy water critical assembly, the 'RB' reactor has survived a series of modifications trying to follow directions of contemporary nuclear research. The actual 'RB' reactor technical characteristics and experimental possibilities are described. The modifications are underlined, the experience gained and plans for future are presented. A brief review of reactor operation and experiments performed is shown. (author)

1989-04-25

249

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

1990-03-01

250

Intrinsic energy partition in fission  

Directory of Open Access Journals (Sweden)

Full Text Available The intrinsic energy partition between two complementary fission fragments is investigated microscopically. The intrinsic excitation energy of fission fragments is dynamically evaluated in terms of the time-dependent pairing equations. These equations are corroborated with two conditions. One of them fixes the number of particles and the other separates the pairing active spaces associated to the two fragments in the vicinity of the scission configuration. The excitation energy in a wide distribution of fission fragments is calculated for the 234U parent nucleus.

Mirea M.

2013-03-01

251

Gas heating by fission fragments  

International Nuclear Information System (INIS)

The authors describe the use of fission fragments for the direct heating and ionization of gases. The maximum of the ratio of the amount of energy transferred to the gas by fragments to the nonuniformity coefficient of energy release in the gas is used here as the optimization criterion. Parameters are given of heat release nonuniformity and gas heating efficiency in a flat channel. Specific values of the mean free path of fission fragments in different gases are presented. It is found that the optimum conditions of gas heating by fission fragments are not heavily dependent on the law of fragment moderation or on the differences between their initial energies and ranges

1987-01-01

252

Gas heating by fission fragments  

Energy Technology Data Exchange (ETDEWEB)

The authors describe the use of fission fragments for the direct heating and ionization of gases. The maximum of the ratio of the amount of energy transferred to the gas by fragments to the nonuniformity coefficient of energy release in the gas is used here as the optimization criterion. Parameters are given of heat release nonuniformity and gas heating efficiency in a flat channel. Specific values of the mean free path of fission fragments in different gases are presented. It is found that the optimum conditions of gas heating by fission fragments are not heavily dependent on the law of fragment moderation or on the differences between their initial energies and ranges.

Karelin, A.V.; Sereda, O.V.; Kharitonov, V.V.; Chikin, K.R.; Naumkin, F.Yu.

1987-01-01

253

Performance simulation of fusion-fission hybrid blanket concepts in existing fission test facilities  

International Nuclear Information System (INIS)

This paper examines the usefulness of testing hybrid fusion-fission blanket components in fission reactors, and reports the results of calculations indicating that blanket heating profiles, tritium breeding rates, fertile breeding rates, and fast-fission rates can be accurately duplicated in a fission reactor test. These results indicate that fission testing can play a major part in the hybrid blanket development program

1982-04-15

254

The spontaneous fission decay constant of 238U using SSNTD  

International Nuclear Information System (INIS)

Results of 5 measurements of the 238U decay constant for spontaneous fission, ?f, carried out using solid state nuclear track detectors (SSNTD), resulting in a mean value of ?f = (8.35 ± 0.24) x 10-17 y-1 is reported. The neutron fluence of the irradiations needed for these measurements were monitored with thin films of natural uranium. (author)

2000-08-01

255

Quantum Relaxation in Singlet Fission  

Science.gov (United States)

Singlet fission is a multielectron process in organic chromophores, where an initially excited singlet state decays into two independent triplets. First observed in organic semiconductors almost 40 years ago, the phenomenon may be a promising route for increasing yields in next-generation photovoltaics. Early theories that ignored quantum coherence between excited states were capable of explaining the fission process on nanosecond timescales, but recent observations of fission on sub picosecond timescales call several tenants of those theories into question. We present a theory of optical dephasing and decoherence in singlet fission, drawing on ideas from quantum information theory to establish conditions for decoherence and disentanglement between the relevant quantum states on the picosecond timescale.

Teichen, Paul; Eaves, Joel

2013-03-01

256

Background radiation from fission pulses  

Energy Technology Data Exchange (ETDEWEB)

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: /sup 235/U, /sup 238/U, /sup 232/Th, and /sup 239/Pu; these bracket the range of the delayed spectra. Results at several cooling (decay) times are presented. For ..beta../sup -/ and ..gamma.. spectra, only /sup 235/U and /sup 239/Pu 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 ..beta../sup -/ and ..gamma.. decay energies are included. 27 refs., 47 figs., 9 tabs.

England, T.R.; Arthur, E.D.; Brady, M.C.; LaBauve, R.J.

1988-05-01

257

Chemical Production using Fission Fragments  

International Nuclear Information System (INIS)

Some reactor design considerations of the use of fission recoil fragment energy for the production of chemicals of industrial importance have been discussed previously in a paper given at the Second United Nations International Conference on the Peaceful Uses of Atomic Energy [A/Conf. 15/P.76]. The present paper summarizes more recent progress made on this topic at AERE, Harwell. The range-energy relationship for fission fragments is discussed in the context of the choice of fuel system for a chemical production reactor, and the experimental observation of a variation of chemical effect along the length of a fission fragment track is described for the irradiation of nitrogen-oxygen mixtures. Recent results are given on the effect of fission fragments on carbon monoxide-hydrogen gas mixtures and on water vapour. No system investigated to date shows any outstanding promise for large-scale chemical production. (author)

1960-07-01

258

Background radiation from fission pulses  

International Nuclear Information System (INIS)

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

259

Measurement of fission cross sections  

International Nuclear Information System (INIS)

A review is presented on the recent progress in the experiment of fission cross section measurement, including recent activity in Japan being carried out under the project of nuclear data measurement. (author)

2005-03-01

260

Binary fission origin of the moon  

International Nuclear Information System (INIS)

The major arguments for and against the binary fission model of lunar origin are reviewed. Unresolved problems include: (1) how the protoearth acquired sufficient angular velocity to fission, and (2) how the earth-moon system lost its excess angular momentum after fission. Despite these uncertainties, the compositional similarities between the earth's mantle and the bulk moon suggest that the fission model is worth considering. The proposed sequence of events in the formation of the moon by binary fission is given. 54 references

1986-01-01

 
 
 
 
261

Advanced Space Fission Propulsion Systems  

Science.gov (United States)

Fission has been considered for in-space propulsion since the 1940s. Nuclear Thermal Propulsion (NTP) systems underwent extensive development from 1955-1973, completing 20 full power ground tests and achieving specific impulses nearly twice that of the best chemical propulsion systems. Space fission power systems (which may eventually enable Nuclear Electric Propulsion) have been flown in space by both the United States and the Former Soviet Union. Fission is the most developed and understood of the nuclear propulsion options (e.g. fission, fusion, antimatter, etc.), and fission has enjoyed tremendous terrestrial success for nearly 7 decades. Current space nuclear research and technology efforts are focused on devising and developing first generation systems that are safe, reliable and affordable. For propulsion, the focus is on nuclear thermal rockets that build on technologies and systems developed and tested under the Rover/NERVA and related programs from the Apollo era. NTP Affordability is achieved through use of previously developed fuels and materials, modern analytical techniques and test strategies, and development of a small engine for ground and flight technology demonstration. Initial NTP systems will be capable of achieving an Isp of 900 s at a relatively high thrust-to-weight ratio. The development and use of first generation space fission power and propulsion systems will provide new, game changing capabilities for NASA. In addition, development and use of these systems will provide the foundation for developing extremely advanced power and propulsion systems capable of routinely and affordably accessing any point in the solar system. The energy density of fissile fuel (8 x 10(exp 13) Joules/kg) is more than adequate for enabling extensive exploration and utilization of the solar system. For space fission propulsion systems, the key is converting the virtually unlimited energy of fission into thrust at the desired specific impulse and thrust-to-weight ratio. This presentation will discuss potential space fission propulsion options ranging from first generation systems to highly advanced systems. Ongoing research that shows promise for enabling second generation NTP systems with Isp greater than 1000 s will be discussed, as will the potential for liquid, gas, or plasma core systems. Space fission propulsion systems could also be used in conjunction with simple (water-based) propellant depots to enable routine, affordable missions to various destinations (e.g. moon, Mars, asteroids) once in-space infrastructure is sufficiently developed. As fuel and material technologies advance, very high performance Nuclear Electric Propulsion (NEP) systems may also become viable. These systems could enable sophisticated science missions, highly efficient cargo delivery, and human missions to numerous destinations. Commonalities between NTP, fission power systems, and NEP will be discussed.

Houts, Michael G.; Borowski, Stanley K.

2010-01-01

262

Dissipation effects in cluster fission.  

Science.gov (United States)

The fission of Sr(2+)(n) is studied from time-of-flight (TOF) measurements. The TOF acts both as a mass spectrometer and as a velocity dispersion analyzer. Evidence of the postfission ejection of a fast neutral atom is shown. It is explained assuming a strong deformation of the fissioning system at the transition state. The relaxation of the deformation energy into vibrations promotes the evaporation of the large fragment. PMID:14995772

Bréchignac, C; Cahuzac, Ph; Concina, B; Leygnier, J

2004-02-27

263

Fission barrier of 153Tb  

International Nuclear Information System (INIS)

The fission barrier of 153Tb was found to be 28.5 +- 1.7 MeV, which is about 83% of the predicted liquid-drop value. This result is consistent with calculations of nuclear masses and with barriers obtained from 4He-induced fission. Barrier estimates of (51--65)% of liquid-drop values deduced for nonrotating nuclei from results of others appear to be in error

1980-08-04

264

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

265

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

266

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

267

Alpha Particle Emission in Fission  

International Nuclear Information System (INIS)

Soon after it was discovered that alpha particles are occasionally emitted in fission, it was concluded, on the basis of the energy and angular distributions of these particles, that they are emitted from the space between the fragments at times close to that of the snapping of the neck that connects them. It is shown that, independent of any (still unknown) dynamic features of the alpha-particle ejection process, the energy required to emit alpha particles from between the fragments at the indicated time is barely available. Presumably the rareness of alpha particles in fission, and the apparent absence of still heavier ''third'' particles, is associated with the marginal energy supply at the time of actual fragment division. The fact that the total kinetic energy release in so-called ternary fission is roughly equal to that in normal binary fission instead of being about 20 MeV larger is shown to imply that the mean fragment separation at the division time is larger in ternary fission. This is interpreted to indicate that alpha particles are emitted with greatest probability n those fissions where ample energy happens to be provided through the stretching of an abnormally long neck between the fragments before they actually divide. It is suggested that the release of the alpha particles is a sudden rather than adiabatic process. (author)

1965-07-01

268

Protactinium neutron-induced fission up to 200 MeV  

International Nuclear Information System (INIS)

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 neutron-induced 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(6Li,4He)234Pa and 232Th(6Li,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 fissile properties 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 symmetric and asymmetric fission barriers difference (Ef(SYM) - Ef(ASYM)) from about 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 230-233Pa(n,F) reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En(p) about 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. (authors)

2009-10-05

269

Protactinium neutron-induced fission up to 200 MeV  

Science.gov (United States)

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.

2010-03-01

270

An analytical procedure for calculating the fast fission factor  

International Nuclear Information System (INIS)

Processes occurring in fast reactors or in thermal reactors due to fast neutrons are treated by multigroup method. This is needed because of the complexity of operator representing the inelastic scattering on heavy nuclei. This paper shows and analytical procedure for solving the slowing-down equation in the fuel. This procedure is applied to calculate the fast fission spectrum and number of reactions in the natural uranium fuel element. The method for calculating the fast fission factor in the isolated fuel element is shown as well

1968-01-01

271

Status of fission power  

International Nuclear Information System (INIS)

Fission energy is reviewed from the viewpoints of technology, economics, politics, manufacturers, consumers, and foreign countries. Technically, the reactor program is operating and the light water reactor industry shows signs of maturing, although recent business has been disappointing. Marketing of gas-cooled reactors depends, not on technical, but economic and political issues. Liquid metal fast breeder reactors have been demonstrated worldwide, while the gas-cooled fast breeder remains an undemonstrated option. Nuclear plants, currently costing the same as coal plants with scrubbers, are the cheapest option for utilities because most of the cost is imbedded. The defeat of nuclear initiatives in seven states indicates that public feeling is not as anti-nuclear as opponents to nuclear power claim. The harshness of last winter demonstrated the advantages of a power source that is not so sensitive to the weather for reliable operation and transport, as well as low cost energy. Other nations are proceeding to build a nuclear capability, which the U.S. may jeopardize because of concerns about the fuel cycle, nuclear waste disposal, uranium reserves, and nuclear proliferation

1977-03-14

272

New perspectives of the statistical theory of fission  

International Nuclear Information System (INIS)

Recent studies on spin distribution, excitation energy and its variance shed new light on the statistical theory of fission. They establish the conceptual validity of the statistical approach and correctly predict new experimental results. Together with earlier studies it can now be concluded that the statistical theory has generally explained all the phenomena it is designed to explain, i.e. those pertaining to the late stage of fission, and any theory capable of explaining these facts must be statistical in nature. Recent dynamical study based on the one-body dissipation mechanism leads to results in excellent agreement with those of the statistical theory and therefore may be regarded as the dynamical interpretation of the statistical theory. The long controversy between these two approaches concerning the perennial question of asymmetric fission is now resolved. (author)

1979-05-18

273

Probability of fission of radium and actinium near threshold  

International Nuclear Information System (INIS)

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

1983-04-01

274

Probability of fission of radium and actinium near threshold  

Energy Technology Data Exchange (ETDEWEB)

The natures of the structures in the fission probabilities of /sup 227/Ra and /sup 227/Ac near threshold are studied. The cross sections for fission of /sup 226/Ra 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 /sup 227/Ra 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 /sup 227/Ra and /sup 227/Ac 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.

Nemilov, Y.A.; Rubchenya, V.A.; Selitskii, Y.A.; Funshtein, V.B.; Khlebnikov, S.V.; Yakovlev, V.A.

1983-04-01

275

Neutron Emission in Fission And Quasi-Fission of Hs  

International Nuclear Information System (INIS)

Mass and energy distributions of fission-like fragments obtained in the reactions 26Mg+248Cm, 36S+238U and 58Fe+208Pb leading to the formation of 266,274Hs are reported. From the analysis of TKE distributions for symmetric fragment it was found that at energies below the Coulomb barrier the bimodal fission of 274Hs, formed in the reaction 26Mg+248Cm, is observed, while in the reaction 36S+238U at these energies the main part of the symmetric fragments arises from the quasi-fission process. At energies above the Coulomb barrier the fusion-fission is a main process leading to the formation of symmetric fragment for the both reactions. In the case of 58Fe+208Pb reaction the quasi-fission process is the main reaction mechanism at all measured energies. The pre- and post-scission neutron multiplicities as a function of the fragment mass have been obtained for all studied reactions.

2010-04-30

276

Measurements of the effective range of fission fragments in UO_2 and the disintegration constant for spontaneous fission of "2"3"8U  

International Nuclear Information System (INIS)

The results of measuments of the disintegration constant for spontaneous fission in "2"3"8U 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 UO_2 layer which contributed to the observed tracks was measured through irradiation of mica samples, in contact with the UO_2 cylinder with 14,0 MeV neutrons from a (d,t) reaction. (Author)

1978-01-01

277

Fission product solvent extraction  

International Nuclear Information System (INIS)

Two main objectives concerning removal of fission products from high-level tank wastes will be accomplished in this project. The first objective entails the development of an acid-side Cs solvent-extraction (SX) process applicable to remediation of the sodium-bearing waste (SBW) and dissolved calcine waste (DCW) at INEEL. The second objective is to develop alkaline-side SX processes for the combined removal of Tc, Cs, and possibly Sr and for individual separation of Tc (alone or together with Sr) and Cs. These alkaline-side processes apply to tank wastes stored at Hanford, Savannah River, and Oak Ridge. This work exploits the useful properties of crown ethers and calixarenes and has shown that such compounds may be economically adapted to practical processing conditions. Potential benefits for both acid- and alkaline-side processing include order-of-magnitude concentration factors, high rejection of bulk sodium and potassium salts, and stripping with dilute (typically 10 mM) nitric acid. These benefits minimize the subsequent burden on the very expensive vitrification and storage of the high-activity waste. In the case of the SRTALK process for Tc extraction as pertechnetate anion from alkaline waste, such benefits have now been proven at the scale of a 12-stage flowsheet tested in 2-cm centrifugal contactors with a Hanford supernatant waste simulant. SRTALK employs a crown ether in a TBP-modified aliphatic kerosene diluent, is economically competitive with other applicable separation processes being considered, and has been successfully tested in batch extraction of actual Hanford double-shell slurry feed (DSSF)

1998-03-17

278

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

279

Compact fission counter for DANCE  

International Nuclear Information System (INIS)

The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF2 crystals with equal solid-angle coverage. DANCE is a 4? ?-ray calorimeter and designed to study the neutron-capture reactions on small quantities of radioactive and rare stable nuclei. These reactions are important for the radiochemistry applications and modeling the element production in stars. The recognition of capture event is made by the summed ?-ray energy which is equivalent of the reaction Q-value and unique for a given capture reaction. For a selective group of actinides, where the neutron-induced fission reaction competes favorably with the neutron capture reaction, additional signature is needed to distinguish between fission and capture ? rays for the DANCE measurement. This can be accomplished by introducing a detector system to tag fission fragments and thus establish a unique signature for the fission event. Once this system is implemented, one has the opportunity to study not only the capture but also fission reactions. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to ? particles, which is important for experiments with ?-emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. A PPAC with an ingenious design was fabricated in 2006 by integrating amplifiers into the target assembly. However, this counter was proved to be unsuitable for this application because of issues related to the stability of amplifiers and the ability to separate fission fragments from ?'s. Therefore, a new design is needed. A LLNL proposal to develop a new PPAC for DANCE was funded by NA22 in FY09. The design goal is to minimize the mass for the proposed counter and still be able to maintain a stable operation under extreme radioactivity and the ability to separate fission fragments from ?'s. In the following sections, the description is given for the design and performance of this new compact PPAC, for studying the neutron-induced reactions on actinides using DANCE at LANL.

2010-01-01

280

Early results utilizing high-energy fission product gamma rays to detect fissionable material in cargo  

International Nuclear Information System (INIS)

Full text: A concept for detecting the presence of special nuclear material (235U or 239Pu) concealed in inter modal cargo containers is described. It is based on interrogation with a pulsed beam of 6-8 MeV neutrons and fission events are identified between beam pulses by their ?-delayed neutron emission or ? -delayed high-energy ?-radiation. The high-energy ?-ray signature is being employed for the first time. Fission product ?-rays above 3 MeV are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. High-energy ?-radiation is nearly 10X more abundant than the delayed neutrons and penetrates even thick cargo's readily. The concept employs two large (8x20 ft) arrays of liquid scintillation detectors that have high efficiency for the detection of both delayed neutrons and delayed ?-radiation. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified. This information, together with predicted signature strength, has been applied to the estimation of detection probability for the nuclear material and estimation of false alarm rates. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48

2004-10-01

 
 
 
 
281

Neutron emission prior to fission  

International Nuclear Information System (INIS)

In recent years, many groups have measured neutrons and light charged particles in coincidence with fission fragments in heavy ion reactions. In most cases, particles emitted with an energy spectrum and angular distribution characteristic of that of compound nucleus evaporation have been measured in excess of statistical model predictions. They have chosen to investigate this effect in detail by studying neutron emission in the "1"5"8Er composite system. The advantage of this system is that it can be produced by a variety of projectile target combinations. They have chosen four combinations which form "1"5"8Er with similar critical angular momenta but varying excitation energy. The rationale is to form the same system with different neutron emission times; if the enhanced neutrons are being emitted during the fission process, the different emission time scales might possibly be used to time the fission process. In addition, they impose an additional constraint - that they have a significant fission barrier for most of the partial waves involved in the fission process. The reactions they have selected are "1"6O + "1"4"2Nd (207 MeV beam energy), "2"4Mg + "1"3"4Ba (180 MeV), "3"2S + "1"2"6Te (180 MeV), "5"0Ti + "1"0"8Pd (216 MeV)

1986-04-01

282

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.

Bhattacharya P.

2010-03-01

283

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

284

Singlet exciton fission in solution  

Science.gov (United States)

Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley-Queisser limit in single-junction solar cells. Although the process through which singlet fission occurs is not well characterized, some local order is thought to be necessary for intermolecular coupling. Here, we report a triplet yield of 200% and triplet formation rates approaching the diffusion limit in solutions of bis(triisopropylsilylethynyl (TIPS)) pentacene. We observe a transient bound excimer intermediate, formed by the collision of one photoexcited and one ground-state TIPS-pentacene molecule. The intermediate breaks up when the two triplets separate to each TIPS-pentacene molecule. This efficient system is a model for future singlet-fission materials and for disordered device components that produce cascades of excited states from sunlight.

Walker, Brian J.; Musser, Andrew J.; Beljonne, David; Friend, Richard H.

2013-12-01

285

Report of fission study meeting  

International Nuclear Information System (INIS)

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.)

1985-09-19

286

Sampling ENDL Watt Fission Spectra  

Energy Technology Data Exchange (ETDEWEB)

All of the fission spectra in the Evaluated Nuclear Data Library, ENDL [1], are defined by a simple analytical function: a Watt spectrum [2], W(a,b,E') = C*Exp[-a*E']*Sinh[(b*E'){sup 1/2}]. Where the normalization, C, is given by, C = [{pi}b/4a]{sup 1/2} Exp[b/4a]/a. The coefficients a and b vary from one isotope to another and also vary weakly with the incident neutron energy. Here E' is the secondary energy, i.e., the energy at which the fission neutrons are emitted. In ENDL energy units of MeV for incident neutron energies between 0 and 20 MeV, in all cases b is very close to 1.0, and a varies over a rather small range near 1.0. Currently there are 38 fissionable isotopes in ENDL. For each of these isotopes I have parameterized a as a simple function of the incident neutron energy, and I treat b as always equal to unity. The values of these parameters are available to TART users as part of the TART CD package [3]. This parameterization coupled with the general Watt sampling method described below results in a very fast and accurate method of sampling all of the fission spectra in ENDL. In all cases I select the fissioning isotope, define a based on isotope and incident neutron energy, and then use the below described method to sample the energy E' of a neutron emitted due to fission.

Cullen, D E

2004-04-01

287

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

288

Effects of pre-fission neutron emission on the fission fragment angular distributions in heavy-ion induced fission  

International Nuclear Information System (INIS)

In view of the recent observation of significant pre-fission neutron multiplicities in heavy-ion induced fusion-fission reactions, we have carried out calculation of fragment anisotropies taking into account the effect of pre-fission neutron emission to make a better comparison of the standard saddle point statistical model (SSPSM) with the experimental results. (author). 10 refs., 2 figs

1993-01-01

289

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)

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

290

Ceramic Hosts for Fission Products Immobilization  

International Nuclear Information System (INIS)

Natural spinel, perovskite and zirconolite rank among the most leach resistant of mineral forms. They also have a strong affinity for a large number of other elements and including actinides. Specimens of natural perovskite and zirconolite were radioisotope dated and found to have survived at least 2 billion years of natural process while still remain their loading of uranium and thorium . Developers of the Synroc waste form recognized and exploited the capability of these minerals to securely immobilize TRU elements in high-level waste . However, the Synroc process requires a relatively uniform input and hot pressing equipment to produce the waste form. It is desirable to develop alternative approaches to fabricate these durable waste forms to immobilize the radioactive elements. One approach is using a high temperature process to synthesize these mineral host phases to incorporate the fission products in their crystalline structures. These mineral assemblages with immobilized fission products are then isolated in a durable high temperature glass for periods measured on a geologic time scale. This is a long term research concept and will begin with the laboratory synthesis of the pure spinel (MgAl2O4), perovskite (CaTiO3) and zirconolite (CaZrTi2O7) from their constituent oxides. High temperature furnace and/or thermal plasma will be used for the synthesis of these ceramic host phases. Nonradioactive strontium oxide will be doped into these ceramic phases to investigate the development of substitutional phases such as Mg1-xSrxAl2O4, Ca1-xSrxTiO3 and Ca1-xSrxZrTi2O7. X-ray diffraction will be used to establish the crystalline structures of the pure ceramic hosts and the substitution phases. Scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) will be performed for product morphology and fission product surrogates distribution in the crystalline hosts. The range of strontium doping is planned to reach the full substitution of the divalent metal ions, Mg and Ca, in the ceramic host phases. The immobilization of rear earth (lanthanide series) fission products in these ceramic host phases will also be studied this year. Cerium oxide is chosen to represent the rear earth fission product for substitution studies in spinel, perovskite and zirconolite ceramic hosts. Cerium has +3 and +4 oxidation states and it can replace some of the trivalent or tetravalent host ions to produce the substitution ceramics such as MgAl2-xCexO4, CaTi1-xCexO3, CaZr1-xCexTi2O7 and CaZrTi2-xCexO7. X-ray diffraction analysis will be used to compare the crystalline structures of the pure ceramic hosts and the substitution phases. SEM-EDX analysis will be used to study the Ce distribution in the ceramic host phases. The range of cerium doping is planned to reach the full substitution of the trivalent or tetravalent ions, Al, Ti and Zr, in the ceramic host phases.

2010-01-01

291

Search for Singlet Fission Chromophores  

Energy Technology Data Exchange (ETDEWEB)

Singlet fission, in which a singlet excited chromophore shares its energy with a ground-state neighbor and both end up in their triplet states, is of potential interest for solar cells. Only a handful of compounds, mostly alternant hydrocarbons, are known to perform efficiently. In view of the large number of conditions that a successful candidate for a practical cell has to meet, it appears desirable to extend the present list of high performers to additional classes of compounds. We have (i) identified design rules for new singlet fission chromophores and for their coupling to covalent dimers, (ii) synthesized them, and (iii) evaluated their performance as neat solids or covalent dimers.

Havlas, Z.; Akdag, A.; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, J.

2012-01-01

292

Fission gases in nuclear fuels  

International Nuclear Information System (INIS)

The mechanisms of the basic release processes (diffusion, trapping, bubble formation, re-solution, grain boundary bubble formation and venting) of the fission rare gases Kr and Xe in nuclear reactor fuels are described. The fuels treated are oxides (UO2,(U,Pu)O2) and advanced fuels (U,Pu)C and (U,Pu)N. The behavior of other volatile fission products (Te, I, Rb, Cs) is also discussed, as well as effects of irradiation and burn-up of the fuel. 16 figs, 37 refs

1989-01-01

293

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

294

Antiproton induced fission and fragmentation  

International Nuclear Information System (INIS)

This is a report on the results of experiment PS203 at LEAR/CERN. Antiprotons were stopped in targets of 238U, 232Th and 209Bi. Energy, mass and opening angle of conincident fission fragments have been measured with a double-arm spectromneter. Mass spectra can be shown as a function of the excitation energy and the momentum distribution of the nucleus before scission is obtained. The ration of particles emitted before and after scission suggests that fission takes place the earlier the higher the excitation energy is. Events which could come from multifragmentation were observed

1992-01-01

295

Photo fission of actinide targets  

International Nuclear Information System (INIS)

The photofission cross-section of 232Th, 238U and 237Np was measured using Bremsstrahlung radiation in the energy range 7.4 to 9.2 MeV from microtron at Mangalore University. In the present work SSNTD lexan polycarbonate films were used to detect the fission tracks. The experimental photofission cross-section measurements were compared with the results obtained from the theoretical predictions of EMPIRE-II code for various potential barrier parameters and analytical fission barrier formula. (author)

2009-01-07

296

Fission properties of the heaviest elements  

International Nuclear Information System (INIS)

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

297

Fission Matrix Capability for MCNP Monte Carlo  

Science.gov (United States)

We describe recent experience and results from implementing a fission matrix capability into the MCNP Monte Carlo code. The fission matrix can be used to provide estimates of the fundamental mode fission distribution, the dominance ratio, the eigenvalue spectrum, and higher mode forward and adjoint eigenfunctions of the fission neutron source distribution. It can also be used to accelerate the convergence of the power method iterations and to provide basis functions for higher-order perturbation theory. The higher-mode fission sources can be used in MCNP to determine higher-mode forward fluxes and tallies, and work is underway to provide higher-mode adjoint-weighted fluxes and tallies. Past difficulties and limitations of the fission matrix approach are overcome with a new sparse representation of the matrix, permitting much larger and more accurate fission matrix representations. The new fission matrix capabilities provide a significant advance in the state-of-the-art for Monte Carlo criticality calculations.

Brown, Forrest; Carney, Sean; Kiedrowski, Brian; Martin, William

2014-06-01

298

Fission properties of the heaviest elements  

International Nuclear Information System (INIS)

We discuss fission properties of the heaviest elements. In particular we 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. (author)

1995-06-01

299

Absolute calibration technique for spontaneous fission sources  

Energy Technology Data Exchange (ETDEWEB)

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.

Zucker, M.S.; Karpf, E.

1984-01-01

300

Absolute Calibration Technique for Spontaneous Fission Sources.  

Science.gov (United States)

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. (ERA citation 09:032764)

M. S. Zucker E. Karpf

1984-01-01

 
 
 
 
301

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

1984-05-14

302

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the 12th issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the 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 type of activities included 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 first part of the report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The second part contains recent references relative to fission product nuclear data, which were not covered by the contributions submitted, and selected papers from conferences

1988-01-01

303

Isotonic yields and neutron evaporation in fission  

International Nuclear Information System (INIS)

A Monte-Carlo simulation has been set up to treat the neutron evaporation from fission fragments. The influence of the neutron evaporation on different distribution and fission parameters has been studied. (orig.)

1992-01-01

304

Characterization of Samples with Spontaneously Fissioning Isotopes  

International Science & Technology Center (ISTC)

Development of the Method for Characterization of the Samples, Containing Spontaneously Fissioning Radionuclides, by Measuring Fission Products Gamma-Radiation (for the System of NM Control and Accountability of the Federal State Unitarian Enterprise "PA"Mayak")

305

Reexamination of fission fragment angular distributions and the fission process: Analysis of data  

International Nuclear Information System (INIS)

A reanalysis of selected fission fragment angular distributions is made using formulae derived in the previous paper. In contrast to previous results it is concluded that the recent heavy-ion-induced fission data is consistent with standard assumptions of fission, although it is suggested that incomplete fusion plays a major role in high energy heavy ion collisions leading to fission

1985-01-01

306

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

International Nuclear Information System (INIS)

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

307

Cold (neutronless) ? ternary fission of 252Cf  

International Nuclear Information System (INIS)

The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of 252Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of 36Kr-60Nd, 38Sr-58Ce, 40Zr-56Ba, 42Mo-54Xe, 44Ru-52Te, and 46Pd-50Sn were observed to be associated with ? ternary fission of 252Cf. Yields of cold ? ternary fission were extracted. copyright 1998 The American Physical Society

1998-05-01

308

Nuclear fission in covariant density functional theory  

Directory of Open Access Journals (Sweden)

Full Text Available 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.

2013-12-01

309

Multiple-Coincidence Interrogation of Fissionables  

Energy Technology Data Exchange (ETDEWEB)

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.

J.P. Hurley, R.P. Keegan, J.R. Tinsley, R. Trainham

2009-05-01

310

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 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 ene...

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

2010-01-01

311

Multiple-coincidence interrogation of fissionables  

Science.gov (United States)

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.

Hurley, J. P.; Keegan, R. P.; Tinsley, J. R.; Trainham, R.

2009-05-01

312

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

313

Experimental study of three-component structure of mass-energy distribution of fission fragments in the vicinity of Pb  

International Nuclear Information System (INIS)

Measurements and regression analysis of mass-energy distributions of fragments from 213At, 210Po, and 205Bi fission have been made. The results have proved three-component structure of fragment kinetic energy spectra. The nature of the phenomenon and its similarity to recently observed bimodal spontaneous fission of nuclei in the vicinity of Fm are discussed

1988-01-01

314

Influence of fission dynamics on formation of fragment charge distribution  

International Nuclear Information System (INIS)

The results of calculations of the isobaric charge distribution of fission fragments are reviewed. The calculations were made in the framework of dynamical approaches based on the Fokker-Planck equation for the distribution function of the collective variables and a Schroedinger equation with friction for a harmonic oscillator with time-dependent coefficients. Three collective coordinates were taken into account: the main fission coordinate, i.e., the distance between the centers of mass of the nascent fragments (or elongation parameter), the neck parameter, and a collective coordinate that determines the charges of the future fragments (charge coordinate). The use of the dynamical model of the formation of the charge distribution shows that statistical equilibrium with respect to the charge mode can be established at each time during almost the entire descent from the saddle point to scission, except for the very final stage directly preceding the breaking of the neck. This explains the successful use of the statistical model for calculations of the fission-fragment charge distribution. The deviation of the variance of the charge distribution from its equilibrium value in the final stage of the process before fission is due to the sharp growth of the inertia and friction coefficients of the charge mode. This growth open-quotes freezesclose quotes the variance of the charge distribution. The study of the variances of the fragment charge distribution as a function of the excitation energy indicates that the fluctuations of the charge mode in fission are mainly of a quantum nature. The possibility of estimating the magnitude and mechanism of nuclear viscosity in fission from the observed even-odd effect in the yields of the fragment charges is discussed. 107 refs., 16 figs., 2 tabs

1992-01-01

315

A wavepacket description of ternary fission  

International Nuclear Information System (INIS)

Ternary fission is approximated by the time-dependent evolution of the alpha-particle wavepacket in the potential generated by two moving fission fragments from ternary fission of 235U + n. The time-dependent Schroedinger equation is solved numerically by a finite elements method on an axially symmetric spatial mesh. (author)

1981-01-01

316

Absolute fission rates in the FFTF  

International Nuclear Information System (INIS)

The part of the FFTF Reactor Characterization Program reported in this paper is a measurement of absolute fission rates of eight major fuel isotopes at two different positions within the reactor. The instruments employed in these tests were fission ionization chambers for which the absolute efficiency and fissionable deposit mass assay have been rigorously established

1981-12-04

317

Competition between the symmetric and asymmetric fission; Competition entre la fission symetrique et la fission asymetrique  

Energy Technology Data Exchange (ETDEWEB)

The mass asymmetry dependence of the fission process in the fission-like deformation valley is studied within the framework of the generalized rotating liquid drop model taking into account the proximity and temperature effects. The experimental Businaro-Gallone point is well reproduced in this deformation valley. The rotation as well as the thermal excitation favour the symmetric splitting. Independently of the asymmetry, the saddle-point corresponds always to two separated fragments maintained in an unstable equilibrium through the balance between the repulsive Coulomb forces and the attractive proximity nuclear forces 2 refs.

Haddad, F.; Royer, G. [Laboratoire de Physique Subatomique et des Technologies Associees - SUBATECH, Centre National de la Recherche Scientifique, 44 - Nantes (France)

1997-10-01

318

Multimodal fission and neutron evaporation  

Energy Technology Data Exchange (ETDEWEB)

The average multiplicities nu-bar(A) of prompt neutrons emitted in the spontaneous fission of /sup 252/Cf and /sup 258/Fm are derived. Two new features are predicted: A simple sawtooth for /sup 258/Fm and a triple one for /sup 252/Cf. Experiments to check these predictions should be feasible now.

Brosa, U.

1988-10-01

319

Chemical effects of fission recoils  

International Nuclear Information System (INIS)

The temperature in the track of a 235U fission recoil is probed by utilizing the difference in the heats of formation of the isopropyl and normal propyl radicals (3.6 kcal/mol). End products of the reactions of the isomeric propyl radicals are analyzed in the radiolysis of gaseous propane and a mixture of methane, ammonia and propane with #betta# rays or fission recoils at the same density. The product distribution is independent of density in the #betta# radiolysis while it varies in the fission recoil radiolysis in a manner suggesting an increase in temperature with density. Kinetic analysis leads to an 'effective' temperature, which is a time average of a localized temperature from the time of particle passage until end product formation. The 'effective temperature' varies approximately linearly with density from ambient at 5 g/L to 40 deg C above ambient at 100 g/L. This is much lower than the rise calculated by assuming that the track region is heated adiabatically by the entire energy lost by the fission recoil. This is ascribed to diffusive migration of the initially produced species during the physico-chemical stage for a finite relaxation interval. This model suggests a relaxation interval of 2 x 10-10 sec. (author)

1983-01-01

320

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.)

1981-11-26

 
 
 
 
321

Space Fission System Test Effectiveness  

International Nuclear Information System (INIS)

Space fission technology has the potential to enable rapid access to any point in the solar system. If fission propulsion systems are to be developed to their full potential, however, near-term customers need to be identified and initial fission systems successfully developed, launched, and utilized. One key to successful utilization is to develop reactor designs that are highly testable. Testable reactor designs have a much higher probability of being successfully converted from paper concepts to working space hardware than do designs which are difficult or impossible to realistically test. ''Test Effectiveness'' is one measure of the ability to realistically test a space reactor system. The objective of this paper is to discuss test effectiveness as applied to the design, development, flight qualification, and acceptance testing of space fission systems. The ability to perform highly effective testing would be particularly important to the success of any near-term mission, such as NASA's Jupiter Icy Moons Orbiter, the first mission under study within NASA's Project Prometheus, the Nuclear Systems Program

2004-02-04

322

Slowing down of fission neutrons  

International Nuclear Information System (INIS)

Interactions of 252Cf fission neutrons at different locations within a buckled-up paraffin wax structure were studied. Some interesting physical parameters could be derived. These comprise the buildup factor, the age flux, and the migration area. The diffusion lengths of neutrons in thermal and epithermal regions were also investigated. (author)

1988-01-01

323

Power generation by nuclear fission  

International Nuclear Information System (INIS)

The principles of power production by chemical combustion of fossil fuels and by nuclear fission are compared. It is pointed out that fossil fuels ought not be combusted but used as chemical raw materials. The second part of the paper discusses isotope separation in general and uranium isotope separation in particular. (GG)

1980-01-01

324

Energetics of the fission process  

Energy Technology Data Exchange (ETDEWEB)

The mass asymmetry of fragments from nuclear fission of heavy nuclei is reviewed. While mass asymmetry is a common and well-known phenomenon for low-energy fission of the lighter actinides, more recent experiments have demonstrated that, for the heaviest actinides, the mass distribution switches to a symmetric one. On the other hand, it has been discovered that, though for fissioning nuclei with mass numbers A< or [approx]225 the mass distribution is basically symmetric, an asymmetric component is clearly to be identified for nuclei down to the Pb-region. In the absence of a generally accepted dynamical theory of fission, the above experimental findings are discussed in terms of static energy considerations. Triggered from the outset by the structure of the potential energy surface at the saddlepoint, the energy balance at the scission point between the available energy (Q-value) of the reaction and the Coulomb and deformation energy of the nascent fragments is shown to steer the characteristics of the fragment mass distributions. (orig.)

Goennenwein, F. (Physikalisches Inst., Univ. Tuebingen (Germany))

1994-09-01

325

Geochemical study of the insoluble organic material (kerogen) in the Oklo uranium ore and the associated Francevillian schists  

International Nuclear Information System (INIS)

The purpose of this study was to describe the organic material associated with uranium ore and ore transformations undergone by it, in terms of the following problems: (1) In the natural reactor zones, evolution of the organic material in the core and as a function of the distance away from it; (2) Comparison of organic materials from a rich and a poor ore; (3) Intercomparison of organic materials in the dispersed and concentrated state; (4) Comparison of organic materials in the uranium ore zones and in the adjacent non-mineralized Francevillian. The organic material from the reactor core could not be isolated by the normal techniques of treatment with acid. It is found in other cases that the organic material is oxidized in the uranium-bearing sediments and that the nearer to the reaction zone, the greater the oxidation, irrespective of the state of dispersion of the organic material in the rock. The uranium content does not affect this phenomenon, which is attributed to the action of the water raised to a high temperature in the vicinity of the reaction zones. On the basis of the present distribution of organic material and uranium the authors suggest a pattern for the formation of the deposit that would take into account localization of the ore in the sandstones and the part played by organic material in the accumulation process. (author)

1977-12-21

326

Fission track dating of zircon crystal  

International Nuclear Information System (INIS)

The track etching and fission track (f.t) age studies are carried out on various natural planes of zircon crystal collected from Khammam District of Andhra Pradesh. The etching studies are carried out using two different sets of etchants viz. (a)1:1 mixture of H2SO4:HF and (b)4:15:6 mixture of NaOH:KOH:LiOH.H2O. It is observed that the track etching anisotropy is more in the basic medium (b)than that in acidic medium (a). This leads to the different values of track etching efficiency on various planes of zircon. Because of this anisotropic etching behaviour of the crystal, the fossil track density is found to vary, from plane to plane. However, the concordant f.t. ages are obtained on various planes of zircon, by applying the appropriate corrections for anisotropic etching. (author). 4 tabs., 9 refs

1990-09-01

327

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

The purpose of this series is to inform scientists working on Fission Product Nuclear Data, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. This report consists of reproductions of essentially unaltered original contributions which the authors have sent to IAEA/NDS. 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

1976-01-01

328

Comparative study of pulsed laser and fission fragment induced desorption with nucleotic compounds  

International Nuclear Information System (INIS)

Mass spectra obtained under pulsed laser induced and fission fragment induced desorption of nucleosides and their nucleobases are reported and compared. No striking differences are observed. The nature of the excitation process for both methods is discussed. Fission fragment induced desorption is known to be due mainly to a sudden non-resonant electric perturbation, which in conjunction with thermal activation also plays a major role in laser induced desorption. (author)

1980-01-01

329

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

330

Actinide nuclei fission at medium excitation energies  

International Nuclear Information System (INIS)

An analysis of results on energy dependence of fission cross section, mass distribution to the ratio of symmetric to asymmetric fission yields are presented for wide energy range of 3 He, 4 He ion interacted with some actinide nuclei. The particular attention was directed to study contribution of pre-fission processes. Energy dependence of shell effects are discussed. A simple method of description of fission fragment mass distributions dependence on total angular moment of a fissioning nucleus was proposed. The analysis of large number of experimental data for fission of some actinide nuclei formed in reactions with neutrons, deuterons, ?-particles and ?-rays with the same excitation energy but different total angular moment testifies that consideration of influence of total angular moment for description of fission fragment mass distributions is necessary

1994-09-07

331

Fission product behaviour in severe accidents  

International Nuclear Information System (INIS)

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

332

Space Fission Propulsion System Development Status  

Science.gov (United States)

The world's first man-made self-sustaining fission reaction was achieved in 1942. Since then fission has been used to propel submarines, generate tremendous amounts of electricity, produce medical isotopes, and provide numerous other benefits to society. Fission systems operate independently of solar proximity or orientation, and are thus well suited for deep space or planetary surface missions. In addition, the fuel for fission systems (enriched uranium) is virtually non-radioactive. The primary safety issue with fission systems is avoiding inadvertent system start. Addressing this issue through proper system design is straight-forward. Despite the relative simplicity and tremendous potential of space fission systems, the development and utilization of these systems has proven elusive. The first use of fission technology in space occurred 3 April 1965 with the US launch of the SNAP-10A reactor. There have been no additional US uses of space fission systems. While space fission systems were used extensively by the former Soviet Union, their application was limited to earth-orbital missions. Early space fission systems must be safely and affordably utilized if we are to reap the benefits of advanced space fission systems. NASA's Marshall Space Flight Center, working with Los Alamos National Laboratory (LANL), Sandia National Laboratories, and others, has conducted preliminary research related to a Safe Affordable Fission Engine (SAFE). An unfueled core has been fabricated by LANL, and resistance heaters used to verify predicted core thermal performance by closely mimicking heat from fission. The core is designed to use only established nuclear technology and be highly testable. In FY01 an energy conversion system and thruster will be coupled to the core, resulting in an 'end-to-end' nuclear electric propulsion demonstrator being tested using resistance heaters to closely mimic heat from fission. Results of the SAFE test program will be presented. The applicability of a SAFE-powered electric propulsion system to outer planet science missions will also be discussed.

Houts, M.; Van Dyke, M. K.; Godfroy, T. J.; Pedersen, K. W.; Martin, J. J.; Dickens, R.; Williams, E.; Harper, R.; Salvail, P.; Hrbud, I.

2001-01-01

333

Fission product behaviour during faults in light water reactors  

International Nuclear Information System (INIS)

The most important chemical reactions of the fission iode from serious faults in light water reactors have been taken into account in the latest transfer models (in the Federal Republic of Germany in the code IMPAIR), which describes behaviour and release in the case of core melt-down. The result of this study is that even when there are serious faults, the fission iode emitted from the fuel as a result of reactions determined by the law of nature is kept predominantly within the reactor plant and only a very small proportion reaches the surrounding neighbourhood. As proof that these model analyses are also valid in real practice, the behaviour of the fission iode can be valid for the accident at TMI 2. In such a serious incident only very small parts (an order of magnitude of 10"-"4%) of the fission iode released from the fuel escaped into the surrounding environment as a result of the chemical reactions of that kind. (orig.)

1986-01-01

334

Unifying fission, quasi-fission and the extra push  

Directory of Open Access Journals (Sweden)

Full Text Available Using the above-barrier fusion probabilities of Berriman and the appropriate extra-push energies, we re-investigate the quasi-fission dynamics of reactions leading to the compound nucleus 220Th. A consistent description is obtained in terms of the entrance-channel barriers that are known to determine the initial capture process. The different dynamical deformations that give rise to these barriers significantly influence the potential-energy landscapes onto which the captured system is injected.

Rowley Neil

2013-12-01

335

Fission of heavy nuclei induced by stopped antiprotons. II. Correlations between fission fragments  

International Nuclear Information System (INIS)

Antiproton-induced fission has been investigated with a novel double-arm fission fragment spectrometer. The correlations in mass, energy, and velocity between two fragments were measured. The dependence of total kinetic energy, velocity, momentum of the fissioning nucleus, and momentum of the fission fragments on the mass loss was deduced and analyzed in the framework of the dynamical statistical model. This model takes into account all stages before, during and after bar p-induced fission (atomic cascade, intranuclear cascade, evaporation cascade, fission of the compound nucleus, evaporation from the fission fragments). The mass loss was used as a measure of the excitation energy to classify the fission events according to the corresponding excitation energies. Some discrepancies between the model calculation and the experiment show the important role of dissipative effects in the bar p-induced fission process. copyright 1996 The American Physical Society

1996-11-01

336

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

337

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

CERN Document Server

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

338

Sexual differentiation in fission yeast  

DEFF Research Database (Denmark)

The regulation of sexual reproduction in yeast constitutes the highest level of differentiation observed in these unicellular organisms. The various ramifications of this system involve DNA rearrangement, transcriptional control, post-translational modification (such as protein phosphorylation) and receptor/signal processing. A few basic similarities are common to both fission and budding yeasts. The wiring of the regulatory circuitry, however, varies considerably between these divergent yeast groups.

Egel, R; Nielsen, O

1990-01-01

339

The VERDI fission fragment spectrometer  

International Nuclear Information System (INIS)

The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD) diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD) show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution. (authors)

2013-05-28

340

Nuclear Masses and Fission Barriers  

Science.gov (United States)

We review the Hartree-Fock-Bogolyubov mass models of the Brussels-Montreal group, and compare their suitability for astrophysical purposes with the FRDM of Möller et al. and the Duflo-Zuker 1995 model. In addition to considering the quality of their fits to the 2003 data compilation, we also compare their extrapolations out towards the neutron drip line. The implications for fission barriers and the role of the equation of state of neutron matter are both discussed.

Pearson, J. M.

2004-09-01

 
 
 
 
341

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

1992-01-18

342

Fission tracks dating for obsidian  

International Nuclear Information System (INIS)

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

343

FY04&05 LDRD Final Report Fission Fragment Sputtering  

Energy Technology Data Exchange (ETDEWEB)

Fission fragments born within the first 7 {micro}m of the surface of U metal can eject a thousand or more atoms per fission event. Existing data in the literature show that the sputtering yield ranges from 10 to 10,000 atoms per fission event near the surface, but nothing definitive is known about the energy of the sputtered clusters. Experimental packages were constructed allowing the neutron irradiation of natural uranium foils to investigate the amount of material removed per fission event and the kinetic energy distribution of the sputtered atoms. Samples were irradiated but were never analyzed after irradiation. Similar experiments were attempted in a non-radioactive environment using accelerator driven ions in place of fission induced fragments. These experiments showed that tracks produced parallel to the surface (and not perpendicular to the surface) are the primary source of the resulting particulate ejecta. Modeling studies were conducted in parallel with the experimental work. Because the reactor irradiation experiments were not analyzed, data on the energy of the resulting particulate ejecta was not obtained. However, some data was found in the literature on self sputtering of {sup 252}Cf that was used to estimate the velocity and hence the energy of the ejected particulates. Modeling of the data in the literature showed that the energy of the ejecta was much lower than had been anticipated. A mechanism to understand the nature of the ejecta was pursued. Initially it was proposed that the fission fragment imparts its momenta on the electrons which then impart their momenta on the nuclei. Once the nuclei are in motion, the particulate ejecta would result. This initial model was wrong. The error was in the assumption that the secondary electrons impart their momenta directly on the nuclei. Modeling and theoretical considerations showed that the secondary electrons scatter many times before imparting all their momenta. As a result, their energy transfer is more isotropic than directional. It was therefore concluded that the nuclei are set in motion not by direct collisions with the secondary electrons, but by repulsive forces cased by the temporary net positive local charge of the nuclei. This is cased by ejected electrons and by the reduced bonding nature of the nuclei cased by many of the local electrons being in excited and in nonbonding states.

Ebbinghaus, B; Trelenberg, T; Meier, T; Felter, T; Sturgeon, J; Kuboda, A; Wolfer, B

2006-02-22

344

Status of fission yield evaluations  

International Nuclear Information System (INIS)

Very few yield compilations are also evaluations, and very few contain an extensive global library of measured data and extensive models for unmeasured data. The earlier U.K. evaluations and US evaluations were comparable up to the retirements of the primary evaluators. Only the effort in the US has been continued and expanded. The previous U.K. evaluations have been published. In this paper we summarize the current status of the US evaluation, philosophy, and various integral yield tests for 34 fissioning nuclides at one or more neutron incident energies and/or for spontaneous fission. Currently there are 50 yield sets and for each we have independent and cumulative yields and uncertainties for approximately 1100 fission products. When finalized, the recommended data will become part of the next version of the US Evaluated Nuclear Data File (ENDF/B-VI). The complete set of data, including the basic input of measured yields, will be issued as a sequel to the General Electric evaluation reports (better known by the authors' names: Rider - or earlier - Meek and Rider). 16 references

1983-10-24

345

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

346

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

347

Fission-track dating using object-based image analysis  

International Nuclear Information System (INIS)

Full text: Geological dating with the help of fission track analysis is based on a time-consuming counting of the spontaneous and induced tracks in the minerals. Fission tracks are damage trails in minerals caused by fast charged particles, released in nuclear fission. In this study the 950;-method is used for fission-track dating. In order to determine the age, spontaneous tracks in the apatite and induced tracks in the muscovite external detector have to be counted. The automatic extraction and identification would not only improve the speed of track counting and eliminate the personal factor. Pixel values alone are not enough to distinguish between tracks and background. Traditional pixel based approaches are therefore inefficient for fission track counting. Image analysis based on objects, which include shape, texture and contextual information is a more promising method. A procedure for automatic object - based classification is used to extract the track objects. Resolving the individual tracks in a multi-track object is based on morphological operations. The individual track objects are skeletonized and the number of individual tracks in the object is counted by processing the skeletons. To give the right fission track age, there has to be a calibration of every single user manually counting the tracks. We calibrate the automatic approach for counting in the same way. Durango apatite standard samples are used to determine the 950;- and Z-calibration factor. The automatic approach is useful for counting tracks in apatite standards and induced tracks in muscovite external detectors where the quality and quantities of the etched tracks is high. Muscovite detectors irradiated against glasses can also be used to determine the thermal neutron fluence, which is necessary to determine an absolute age. These images are of high quality and free of disturbing background irregularities. Here the automatic approach is a practical alternative. However for natural samples of small grain size, low track-numbers and background irregularities, the implementation is questionable. The algorithm for the automatic extraction and counting of fission tracks in standard samples of Durango Apatite and muscovite external detectors is shown to be self-consistent. (author)

2007-04-15

348

Fission properties of the BCPM functional  

CERN Document Server

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

349

Investigation of sequential fission of heavy nuclei  

International Nuclear Information System (INIS)

Sequential fission was investigated in the reaction 238U + 248Cm at 8.43 MeV/u. From the absence of Coulomb final state interactions a time limit of 1-1.5 x 10-20 s is deduced for the lifetime of intermediate fissioning systems with Z up to 120. The angular distributions of sequential fission in the reaction of 208Pb + 90Zr were studied vs. energy loss. In-plane anisotropies of proportional 1:2 are found at moderate energy losses which decrease and even change sign towards larger energy losses. In the system U + U at 7.5 MeV, sequential fission events associated with low excitations were investigated. The fission probability, measured down to 10-3 for scattering angles forward of grazing, behaves as expected for compound fission induced by Coulomb excitation. (orig.)

1983-01-01

350

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.

Pigni M. T.

2012-12-01

351

International conference on fifty years research in nuclear fission  

International Nuclear Information System (INIS)

These proceedings contain extended abstracts of the papers presented at the named conference. They deal with static properties of fission, instrumentation for fission studies, fission in compound-nucleus reactions, fission dynamics, fission-like heavy ion reactions, and fusion reactions. See hints under the relevant topics. (HSI)

1989-04-03

352

Comparative evaluation of solar, fission, fusion, and fossil energy resources. Part 2: Power from nuclear fission  

Science.gov (United States)

Different types of nuclear fission reactors and fissionable materials are compared. Special emphasis is placed upon the environmental impact of such reactors. Graphs and charts comparing reactor facilities in the U. S. are presented.

Clement, J. D.

1973-01-01

353

Fission of heavy nuclei induced by stopped antiprotons. I. Inclusive characteristics of fission fragments  

International Nuclear Information System (INIS)

Antiproton-induced fission has been investigated with a novel double-arm fission fragment spectrometer. Inclusive distributions of total mass, individual mass, and total kinetic energy of the fragments, and of the momentum of the fissioning nucleus, were measured. A dynamical model which takes into account all stages of bar p-induced fission (atomic cascade, intranuclear cascade, evaporation cascade, fission of compound nucleus, evaporation from fission fragments) was formulated for the first time. In particular, the dynamics of the descent of fissioning nuclei from saddle point to scission point are described by the diffusion model. The data on bar p-induced fission were analyzed in the framework of this model and good agreement between experiment and theory was obtained

1994-05-01

354

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

355

Measurements of Fission Cross Sections of Actinides  

CERN Multimedia

A measurement of the neutron induced fission cross sections of $^{237}$Np, $^{241},{243}$Am and of $^{245}$Cm is proposed for the n_TOF neutron beam. Two sets of fission detectors will be used: one based on PPAC counters and another based on a fast ionization chamber (FIC). A total of 5x10$^{18}$ protons are requested for the entire fission measurement campaign.

Wiescher, M; Cox, J; Dahlfors, M

2002-01-01

356

The discovery and contribution of nuclear fission  

International Nuclear Information System (INIS)

This report is a panel discussion by representatives from France, Australia, Italy, and the USA about the history of nuclear fission. Two initial discoveries led to the discovery of nuclear fission: the neutron in 1932, and artificial radioactivity in 1934. Very few scientists were involved, and they were all in Europe. A process was developed to extract plutonium and separate it from uranium and fission products

1988-11-04

357

Pion-induced fission of actinide targets  

International Nuclear Information System (INIS)

Fission cross sections have been measured using Makrofol track detector techniques for targets of 209Bi, 231Pa, 233U, 234U, 235U, 237Np, 241Pu, and 242Pu using a ?+ beam of 138 MeV, and ?- beams of 131 and 138 MeV. Fission probabilities are about 80% for the heaviest targets, for both pion signs. Smaller and sign-dependent fission probabilities are found for bismuth. (orig.)

1992-06-22

358

Membrane Fission: Model for Intermediate Structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Membrane budding-fission is a fundamental process generating intracellular carriers of proteins. Earlier works were focused only on formation of coated buds connected to the initial membrane by narrow membrane necks. We present the theoretical analysis of the whole pathway of budding-fission, including the crucial stage where the membrane neck undergoes fission and the carrier separates from the donor membrane. We consider two successive intermediates of the reaction: 1), a constricted membra...

Kozlovsky, Yonathan; Kozlov, Michael M.

2003-01-01

359

Prompt neutrons from the low-energy fission of atomic nuclei  

Energy Technology Data Exchange (ETDEWEB)

The characteristics of prompt fission neutrons (PFN)--spectra and average number of neutrons--are important for nuclear reactor calculations. This paper takes into account the special features associated with the characteristics of the fission fragments. The Hauser-Feshbach statistical theory is used to calculate the characteristics of PFN with the following differences: a more accurate account of the cascade nature of neutron emission is presented, a different method of determining the average excitation energy of the fragments is used, and an expression for the level density which takes account of the shell structure of nuclei is given. Results are presented of a calculation of the spectra and multiplicity distribution of PFN for the most important cases, namely the spontaneous fission of Cf 252 and the thermal-neutron fission of U 235.

Gerasimenko, B.F.; Rubchenya, V.A.

1986-05-01

360

Prompt neutrons from the low-energy fission of atomic nuclei  

International Nuclear Information System (INIS)

The characteristics of prompt fission neutrons (PFN)--spectra and average number of neutrons--are important for nuclear reactor calculations. This paper takes into account the special features associated with the characteristics of the fission fragments. The Hauser-Feshbach statistical theory is used to calculate the characteristics of PFN with the following differences: a more accurate account of the cascade nature of neutron emission is presented, a different method of determining the average excitation energy of the fragments is used, and an expression for the level density which takes account of the shell structure of nuclei is given. Results are presented of a calculation of the spectra and multiplicity distribution of PFN for the most important cases, namely the spontaneous fission of Cf 252 and the thermal-neutron fission of U 235

1986-05-01

 
 
 
 
361

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

International Nuclear Information System (INIS)

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)

1994-02-01

362

Theoretical Description of the Fission Process  

Science.gov (United States)

Spontaneous fission is one the oldest decay modes known, but is still not fully understood. On the one hand, various nuclear structure models have been applied to fission barriers, lifetimes, and mass/charge distributions, and they provide a good overall description of the phenomenon and, in many cases, detailed predictions. On the other hand, the full-fledged, non-adiabatic description of fission, based on effective nucleon-nucleon interactions, still does not exist. The aim of our project on ``Theoretical Description of the Fission Process,'' supported by NNSA (www.phys.utk.edu/witek/fission/fission.html), is to attack the problem of spontaneous fission using modern theoretical methods and state-of-the-art computational tools. During the first stage of the project, we have studied static fission barriers of the even-even actinide and transactinide nuclei within the self-consistent Density Functional Theory. The computations are carried out applying a code that makes it possible to break all self-consistent symmetries of the nuclear mean field, including axial symmetry and reflection symmetry. Particular attention has been paid to symmetry-breaking effects along the fission path.

Nazarewicz, Witold

2006-10-01

363

Fission of relativistic intermediate-mass nuclei  

International Nuclear Information System (INIS)

We have studied the fission of nuclei with 36< or =Z< or =79 produced in interactions of 1A GeV Au nuclei in CR-39 plastic track detectors. The energy released is typical of fission at lower energies, and the transverse momentum transferred to fissioning species is consistent with a peripheral interaction. The distributions of heavy-to-light fragment mass ratios are very broad, as in fission of nuclei with 28< or =Z< or =83 by 600 MeV and 1 GeV protons

1984-01-01

364

Theoretical Description of the Fission Process  

International Nuclear Information System (INIS)

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

2003-01-01

365

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.

366

Fission investigations and evaluation activities at IRMM  

International Nuclear Information System (INIS)

The IRMM has a longstanding tradition in the field of neutron induced fission physics studies. It is especially well equipped with world-class facilities as the high resolution neutron time-of-flight spectrometer GELINA and the 7 MV Van de Graaff accelerator for the quasi-monoenergetic neutron production. During the past decade several neutron induced fission reactions have been studied in the energy range from eV up to 6 MeV and spontaneous fission. The isotopes under investigation were 235,238 U(n,f), 239 Pu(n,f), 237 Np(n,f), 252 Cf(SF) and 233 Pa(n,f). For all isotopes but 233 Pa, the fission fragment mass-yield and total kinetic energy distributions were measured. 233 Pa was only investigated for the fission cross-section. The results have been described within the multi-modal fission model. The three most dominant fission modes, the two asymmetric standard I (S1) and standard II (S2) as well as the the symmetric superlong mode were used for all the isotopes but 252 Cf. For this isotope at least one other fission mode had to be taken into account, the so--called standard III (S3) mode. Since the theoretical interpretation of experimental results was rather successful also an attempt was made to improve the evaluation of the respective fission cross-section as well as their neutron multiplicities and spectra. Here, the statistical model for fission cross-section evaluation was extended by including the multi-modality concept for fission. Based on the underlying model, separate outer fission barriers have been considered for each mode, while the inner barriers and isomeric wells are assumed to be the same. The self-consistent calculations of the fission cross-section as well as total, capture, elastic and inelastic cross-sections were in good agreement with the experimental data and evaluated nuclear data libraries. As a side product, also fission fragment mass yield distributions have been deduced at incident neutron energies hitherto unaccessible. Very surprising results will be presented. Concerning the neutron multiplicities and spectra, here the commonly used Los Alamos model was modified to take into account again the multi-modal fission. Additionally, it has been extended to a larger base of fission-fragment masses and takes into account the linear prompt gamma-ray energy dependence on prompt neutron multiplicity. These aspects let to an improved agreement with experimental data. Also here new results will be presented. (authors)

2003-09-07

367

Fission - track age of the Marjalahti Pallasite  

International Nuclear Information System (INIS)

Full text: Investigation of fossil charged-particle tracks in various mineral phases of extraterrestrial samples is a powerful method for research the early stages of the solar system. Over geological time, meteorites crystals have accumulated a record of tracks produced by heavily charged energetic particles from both internal (spontaneous fission of 238U and some other extinct isotopes) and external sources (galactic cosmic rays with Z>20). The fortunate fact that meteorite grains can accumulate latent and very long-lived tracks since soon after the end of nucleosynthesis in the solar nebula enables one to decode their radiation history and to detect any thermal events in the meteorite cosmic history by revealing these tracks through suitable etching procedures. Only a few minerals in meteorites (mainly phosphates) contain small amount of uranium; the fact that 238U undergoes fission with fission-decay constant ?f?8.2x10-17 yr-1 allows one to use this isotope as a chronometer. By measuring the U concentration in the crystals (by reactor irradiation) and the density of the spontaneous-fission tracks it is relatively easy to calculate the 'fission-track age' if 238U is the main source of fission tracks. However the fission-track dating of extraterrestrial samples compared with the terrestrial ones has some peculiar features due to presence of a number of other potential track sources except the spontaneous fission of 238U, such as the spontaneous fission of presently extinct 244Pu, heavy nuclei of cosmic rays and induced fission by cosmic ray primaries. Only tracks from the spontaneous fission of U and Pu are suitable for fission-track dating. The competing effects of these fissioning elements, whose half-lives differ by a factor of ?50, form a basis for a fission-track chronology for samples older than ? 4.0 Gyr. Over small intervals in time (? few x108 yr ) the track density from spontaneous fission of 238U is nearly constant. However, the contribution from 244Pu doubles every 82 Myr providing a very sensitive measure of the age of a studied sample. The results of the determination of the fission-track age of the Marjalahti pallasite (stony-iron meteorite) are presented. Thorough examination of fossil tracks in the phosphate (whitlockite) crystals coupled with U content determination in whitlockites allowed us to estimate the contributions of all possible track sources to the total track density and to calculate a value of the model fission-track age. It was found out that whitlockite crystals of the Marjalahti pallasite contain fossil tracks due to galactic cosmic rays (VH, VVH nuclei); induced fission of U and Th by cosmic rays; spontaneous fission of 238U; spontaneous fission of extinct short-lived 244Pu nuclei presented in significant quantities in the early solar system. The initial ratio (244Pu/238U)0 at the time of the pallasite parent body formation (taken as 4.6x109 yr) was estimated as 0.015. A great track density attributed to the extinct 244Pu testified to the high value of the fission-track age. The model fission-track ages of (4.37± 0.02)x109 yr for the Marjalahti pallasite was calculated. The comparison of the represented data with petrographic analyses allowed us to interpret a value of the fission-track age as the time of the last intensive shock/thermal event in the cosmic history of the pallasite. (author)

2006-09-01

368

Channel Effects in the Kinetic Energy of Fragments of Fission Induced by Low-Energy Resonance Neutrons  

International Nuclear Information System (INIS)

Recently, Blyumkina et al. have noted tfte existence ot fission channel ettects in the total kinetic energy of fragments of fission induced by s- and p-wave neutrons. Effects of this nature can also be expected in the variation of the fragment kinetic energies from resonance to resonance in low-energy (s-wave) neutron-induced fission. A fission-fragment detector whose efficiency is dependent on the kinetic energy of the fragments was used in the study of the slow-neutron-induced fission of U235. Comparing the counting-rate of this detector with a conventional fission detector, whose efficiency is independent of the fragment kinetic energy, shows that there exists a variation in the kinetic energy of certain fragments with neutron energy in the neutron energy region from 0.025 to 1 eV. In order to determine the response of the kinetic-energy-sensitive detector, it was necessary to measure the rangè-energy relations of fission fragments in various media, including noble gases and metallic foils. It was estimated from these data that the variation in the fragment kinetic energy release is ?500 keV, for those fission events that give the lightest and most energetic of the heavy fragments. The variation in fragment kinetic energy is strongly asymmetric about the 0.28-eV resonance in U235, and suggests that the fragment kinetic energy sensitively reflects the presence of interference effects among resonances in fission. A multi-level multi-channel analysis of the data has been made, based on the parameters of Vogt and under the assumption that different fission channels lead to different configurations at scission, such that the kinetic energy release is also different. Previously a major objection to multi-level multi-channel analysis in fission has been that the parameters obtained are not unique. However, the possibility of observing partial fission cross-sections (fission occurring by way of one channel only) removes one of the ambiguities inherent in the multi-level approach. Studies of this type can not only be expected to give information on the nature of the constraints that exist during the transition from the saddle point to the scission point in the fission process, but may also be of interest in inferring the existence of small variations from resonance to resonance in v, the average number of neutrons emitted per fission. (author)

1965-07-01

369

Beta and gamma spectra of short-lived fission products  

International Nuclear Information System (INIS)

Continuous spectra of beta particles and gamma rays emitted in the decay of short-lived fission products have been measured. These spectra, which cover the complete energy range available, can be used for checking results of detailed spectroscopic work on the decay of the nuclides studied. Another application of basic nature is the use of the beta spectra to evaluate the antineutrino spectrum in the vicinity of a nuclear reactor. There are also many applications of these spectra in nuclear technology, for instance the evaluation of the shape of the gamma-ray spectrum in a nuclear rector and in nuclear waste. Accurate average beta and gamma energies, obtained from the spectra, are essential input data for summation calculations of the heat developed in nuclear fuel elements by the decaying fission products

1990-01-01

370

Yields of fission products produced by thermal-neutron fission of /sup 243/Cm  

International Nuclear Information System (INIS)

On the basis of measured yields for 72 gamma rays and known nuclear data, cumulative fission-product yields were deduced for 69 fission products having half-lives between 36 seconds and 65 days representing 41 mass chains created during thermal-neutron fission of /sup 243/Cm

1986-01-01

371

The phebus fission product project  

Science.gov (United States)

A new facility is being built at the Phebus test reactor in Cadarache, France, for investigations into phenomena of fuel damage and fission product (FP) release under severe power reactor accident conditions, as part of a large international research program. Phebus FP simulates core, cooling system and containment of an accidented reactor by appropriate scaled-down experimental components. The test fuel, with 25 to 30 GWd/t burnup, is re-irradiated in situ and then overheated up to UO 2 melting. Fission products and other aerosols are swept through the primary pipework into the containment vessel, by hot steam and hydrogen. Experimental instrumentation and posttest analyses will enable the following main phenomena to be studied: structural material and fuel dislocation, final fuel state; release, chemical form and transport/depletion of fission products in the facility, particularly aerosol physics, including nonfission product material and iodine chemistry in terms of volatile species formation through radiolysis, reactions with organic material, aerosol-vapor reactions, etc. Design and development of equipment and experimental procedures are supported by modeling and code calculations with the scope of predicting the experimental sequence, on one hand, and to prepare code validation through the results, on the other hand. More than 25 organisation from Europe and overseas, collaborate in the scientific and technological development of the Phebus FP program. The first in-pile test is planned for spring 1993, and five subsequent experiments are scheduled to follow in yearly intervals. This paper describes facility and support activities, and highlights a number of nuclear materials aspects involved.

von der Hardt, P.; Tattegrain, A.

1992-06-01

372

Neutron emission prior to fission  

Energy Technology Data Exchange (ETDEWEB)

Neutron emission in the /sup 158/Er composite system is studied in order to investigate particle emission with energy spectrum and angular distribution in excess of statistical model predictions. Data are analyzed using a modified statistical model which incorporates effects due to nuclear dissipation, and also calculates neutron emission during the descent from the saddle to the scission point. Calculations consider the Kramers effect and the Transient effect. It is concluded that a detailed interpretation of enhanced neutron emission preceding fission in compound nucleus reactions is possible, and that an upper limit may be set on the reduced nuclear dissipation coefficient. 5 refs., 2 figs. (LEW)

Gavron, A.; Gayer, A.; Boissevain, J.; Britt, H.C.; Nix, J.R.; Sierk, A.J.; Grange, P.; Hassani, S.; Weidenmueller, H.A.; Beene, J.R.

1986-01-01

373

Fission fragment angular distribution measurements for {sup 16}O + {sup 194}Pt reaction at energies near the Coulomb barrier  

Energy Technology Data Exchange (ETDEWEB)

Fission fragment angular distributions have been measured for {sup 16}O + {sup 194}Pt reaction forming the compound system {sup 210}Rn, in the laboratory energy range from 79 to 90 MeV. The measured fission fragment anisotropies as a function of E{sub c.m.}/V{sub B} are compared with the predictions of standard saddle point statistical model (SSPM). Anisotropies calculated using the average excitation energy and angular momentum values could not reasonably fit the experimental data. Statistical model calculations were performed using the PACE with modified fission barrier and level density parameters. Fission probability, evaporation residue cross section and neutron multiplicity were simultaneously used to fix the statistical parameters. Model calculations incorporating the chance nature of fission decay and scaled values of the rotating finite range model (RFRM) moment of inertia could reasonably fit the fragment angular anisotropies.

Prasad, E., E-mail: prasad.e.nair@gmail.com [Department of Physics, School of Mathematical and Physical Sciences, Central University of Kerala, Nileshwar, 671328 (India); Department of Physics, University of Calicut, Calicut, 673635 (India); Varier, K.M. [Department of Physics, University of Calicut, Calicut, 673635 (India); Thomas, R.G. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085 (India); Vinodkumar, A.M. [Department of Physics, University of Calicut, Calicut, 673635 (India); Mahata, K. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085 (India); Appannababu, S. [Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara, 390002 (India); Sugathan, P.; Golda, K.S. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, Post Box 10502, New Delhi, 110067 (India); Babu, B.R.S. [Department of Physics, University of Calicut, Calicut, 673635 (India); Department of Physics, Sultan Qaboos University, Muscat (Oman); Saxena, A.; John, B.V.; Kailas, S. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085 (India)

2012-05-15

374

Fission fragment angular distribution measurements for 16O + 194Pt reaction at energies near the Coulomb barrier  

International Nuclear Information System (INIS)

Fission fragment angular distributions have been measured for 16O + 194Pt reaction forming the compound system 210Rn, in the laboratory energy range from 79 to 90 MeV. The measured fission fragment anisotropies as a function of Ec.m./VB are compared with the predictions of standard saddle point statistical model (SSPM). Anisotropies calculated using the average excitation energy and angular momentum values could not reasonably fit the experimental data. Statistical model calculations were performed using the PACE with modified fission barrier and level density parameters. Fission probability, evaporation residue cross section and neutron multiplicity were simultaneously used to fix the statistical parameters. Model calculations incorporating the chance nature of fission decay and scaled values of the rotating finite range model (RFRM) moment of inertia could reasonably fit the fragment angular anisotropies.

2012-05-15

375

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

International Nuclear Information System (INIS)

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

376

Ignored priorities: first fission fragment (1925) and first mention of fission (1934)  

International Nuclear Information System (INIS)

This year is being hailed as the 50th anniversary of the discovery of fission. But what has been ignored is that the first fission fragment was found in 1925 and the process of fission first postulated in 1934. During her scientific career the German chemist Ida Noddack-Tacke twice touched upon aspects of fission: in 1925 together with Walter Noddack and Otto Berg she first observed a fission product and in 1934 she suggested that neutron-irradiated uranium could break up into lighter elements. 18 refs., 1 tab

1988-01-01

377

Factors influencing audiovisual fission and fusion illusions  

DEFF Research Database (Denmark)

Information processing in auditory and visual modalities interacts in many circumstances. Spatially and temporally coincident acoustic and visual information are often bound together to form multisensory percepts [B.E. Stein, M.A. Meredith, The Merging of the Senses, A Bradford Book, Cambridge, MA, (1993), 211 pp.; Psychol. Bull. 88 (1980) 638]. Shams et al. recently reported a multisensory fission illusion where a single flash is perceived as two flashes when two rapid tone beeps are presented concurrently [Nature 408 (2000) 788; Cogn. Brain Res. 14 (2002) 147]. The absence of a fusion illusion, where two flashes would fuse to one when accompanied by one beep, indicated a perceptual rather than cognitive nature of the illusion. Here we report both fusion and fission illusions using stimuli very similar to those used by Shams et al. By instructing subjects to count beeps rather than flashes and decreasing the sound intensity to near threshold, we also created a corresponding visually induced auditory illusion. We discuss our results in light of four hypotheses of multisensory integration, each advocating a condition for modality dominance. According to the discontinuity hypothesis [Cogn. Brain Res. 14 (2002) 147], the modality in which stimulation is discontinuous dominates. The modality appropriateness hypothesis [Psychol. Bull. 88 (1980) 638] states that the modality more appropriate for the task at hand dominates. The information reliability hypothesis [J.-L. Schwartz, J. Robert-Ribes, P. Escudier, Ten years after Summerfield: a taxonomy of models for audio-visual fusion in speech perception. In: R. Campbell (Ed.), Hearing by Eye: The Psychology of Lipreading, Lawrence Earlbaum Associates, Hove, UK, (1998), pp. 3â??51] claims that the modality providing more reliable information dominates. In strong forms, none of these three hypotheses applies to our data. We re-state the hypotheses in weak forms so that discontinuity, modality appropriateness and information reliability are factors which increase a modality's tendency to dominate. All these factors are important in explaining our data. Finally, we interpret the effect of instructions in light of the directed attention hypothesis which states that the attended modality is dominant [Psychol. Bull. 88 (1980) 638]. Keyword: Modality appropriateness,Illusory flashes Sensory systems,Directed attention,Multisensory,Discontinuity hypothesis,illusions,Information reliability

Andersen, Tobias; Tiippana, Kaisa

2004-01-01

378

Adsorption and excess fission xenon  

Science.gov (United States)

The adsorption of Xe and Kr on lunar soil 10084 was measured by a method that employs only very low fractions of monolayer coverage. Results are presented as parameters for calculation of the Henry constant for adsorption as a function of temperature. The adsorption potentials are about 3 kcal/mole for Kr and 5 kcal/mole for Xe; heating the sample in vacuum increased the Xe potential to nearly 7 kcal/mole. Henry constants at the characteristic lunar temperature are about 0.3 cu cm STP/g-atm. These data were applied to consider whether adsorption is important in producing the excess fission Xe effect characteristic of highland breccias. Sorption equilibrium with a transient lunar atmosphere vented fission Xe produces concentrations seven orders of magnitude lower than observed concentrations. Higher concentrations result because of the resistance of the regolith to upward diffusion of Xe. A diffusion coefficient of 0.26 sq cm/sec is estimated for this process.

Podosek, F. A.; Bernatowicz, T. J.; Kramer, F. E.

379

Spectroscopy of selected fission fragments  

Energy Technology Data Exchange (ETDEWEB)

The spectroscopy of nuclei produced as fragments in the fission process has been undertaken using the EUROGAM II {gamma}-ray multidetector array. The first experiment involved a spontaneously fissioning {sup 248}Cm source and produced neutron-rich nuclei. The data analysis concentrated on the odd-A Ce isotopes and the present contribution details the structure of {sup 151}Ce which results from the strong coupling of the odd neutron to the core. The results of a preliminary analysis of the yrast structure of {sup 138}Te will also be given. In a second experiment performed at the VIVITRON accelerator in Strasbourg, nuclei on the neutron-rich side of the valley of stability were produced via the {sup 28}Si + {sup 176}Yb reaction at 145 MeV bombarding energy. The level schemes of {sup 99}Mo, {sup 101}Tc and {sup 103}Ru have been extended to high spins ({approximately} 20h). Two new high lying structures in {sup 101}Tc are explained with the help of cranked shell model calculations.

Hoellinger, F.; Schulz, N.; Gall, B. J. P.; Bentaleb, M.; Courtin, S.; Lubkiewicz, E.; Durell, J. L.; Jones, M. A.; Leddy, M.; Phillips, W. R.; Smith, A. G.; Urban, W.; Varley, B. J.; Deloncle, I.; Porquet, M.-G.; Wilson, A.; Ahmad, I.; Morss, L. R.; Kutsarova, T.; Minkova, A.; Duprat, J.; Sergolle, H.; Gautherin, C.; Lucas, R.

1999-10-22

380

Downstream behavior of fission products  

International Nuclear Information System (INIS)

The downstream behavior of fission products (Cs, I, and Te) has been studied by injection into a stream of super-heated steam and analyzing the deposits formed on the wall of a reaction duct on which a temperature gradient (1,000-200 degree C) had been imposed. Deposits were formed by vapor and aerosol deposition. Studies of mixtures of CsI and CsOH indicated that the formation of a complex, CsI · CsOH, in the gas phase influenced the vapor deposition. Studies of mixtures of CsOH, CsI, Te, and TeO2 indicated the existence of gas phase reactions between Te, TeO2, and CsOH which effected the deposition. The revaporization of fission product deposits, as would occur due to radioactive decay heating, has been studied by the rapid heating of a section of the reaction duct, on which a deposit had been formed, in a stream of steam

1986-09-08

 
 
 
 
381

Methods for determination of fission gases  

International Nuclear Information System (INIS)

This paper describes procedures for determination of fission gases by measuring the quantity of released and remaining gases in the fuel after irradiation. Experiments are described for determining the quantity of fission gases release from fuel during irradiation in the reactor as well as the pressure of gases in fuel cladding. Principles of gamma scintillation spectroscopy, mass spectrometry and gas chromatography are included

1966-11-01

382

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 A.

2010-10-01

383

Options for Affordable Fission Surface Power Systems  

Science.gov (United States)

Fission surface power systems could provide abundant power anywhere on free surface of the moon or Mars. Locations could include permanently shaded regions on the moon and high latitudes on Mars. To be fully utilized; however, fission surface power systems must be safe, have adequate performance, and be affordable. This paper discusses options for the design and development of such systems.

Houts, Mike; Gaddis, Steve; Porter, Ron; VanDyke, Melissa; Martin Jim; Godfroy, Tom; Bragg-Sitton, Shannon; Garber, Anne; Pearson, Boise

2006-01-01

384

Neutronics of Laser Fission-Fusion Systems  

International Nuclear Information System (INIS)

Neutronics of Fission-Fusion microsystems inertially confined by Lasers are analysed by transport calculation, both stationary (DTF, TIHOC) and time dependent (TDA, TIHEX), discussing the results obtained for the basic parameters of the fission process (multiplication factor, neutron generation time and Rossi-?). (Author) 14 refs

1976-01-01

385

Fission decay of reaction products with A  

International Nuclear Information System (INIS)

Fissionlike decay was observed for fragments resulting from reactions of 58Ni+ 58Ni at 15.3-MeV/u incident energy. The measured probabilities for fission decay, as well as previous measurements, are consistent with equilibrium fission calculations

1985-09-02

386

Nuclear Power from Fission Reactors. An Introduction.  

Science.gov (United States)

The purpose of this booklet is to provide a basic understanding of nuclear fission energy and different fission reaction concepts. Topics discussed are: energy use and production, current uses of fuels, oil and gas consumption, alternative energy sources, fossil fuel plants, nuclear plants, boiling water and pressurized water reactors, the light…

Department of Energy, Washington, DC. Technical Information Center.

387

Volatile fission products: a thermochemical approach  

International Nuclear Information System (INIS)

Since the TMI accident the investigation of the chemical properties of volatile fission products is strongly intensified. Thermochemical considerations can give an important contribution to this since they allow, in a relatively simple way, for calculations of complicated equilibrium situations in the fission materials and the outcome of an accident. (Auth.)

1986-11-01

388

Collective and relative motion of fission fragments  

International Nuclear Information System (INIS)

A classical dynamical calculation has been performed to study the time evolution of deformation, kinetic energy, and internal excitation in post-scission motion of the fission fragments. The model has been applied to the spontaneous fission of "2"5"2Cf and results compare favourably with experiment. (author)

1981-12-28

389

Induced-Fission Imaging of Nuclear Material  

Energy Technology Data Exchange (ETDEWEB)

This paper presents initial results from development of the induced-fission imaging technique, which can be used for the purpose of measuring or verifying the distribution of fissionable material in an unopened container. The technique is based on stimulating fissions in nuclear material with 14 MeV neutrons from an associated-particle deuterium-tritium (D-T) generator and counting the subsequent induced fast fission neutrons with an array of fast organic scintillation detectors. For each source neutron incident on the container, the neutron creation time and initial trajectory are known from detection of the associated alpha particle of the d + t {yields} {alpha} + n reaction. Many induced fissions will lie along (or near) the interrogating neutron path, allowing an image of the spatial distribution of prompt induced fissions, and thereby fissionable material, to be constructed. A variety of induced-fission imaging measurements have been performed at Oak Ridge National Laboratory with a portable, low-dose D-T generator, including single-view radiographic measurements and three-dimensional tomographic measurements. Results from these measurements will be presented along with the neutron transmission images that have been performed simultaneously. This new capability may have applications to a number of areas in which there may be a need to confirm the presence or configuration of nuclear materials, such as nuclear material control and accountability, quality assurance, treaty confirmation, or homeland security applications.

Hausladen, Paul [ORNL; Blackston, Matthew A [ORNL; Mullens, James Allen [ORNL; McConchie, Seth M [ORNL; Mihalczo, John T [ORNL; Bingham, Philip R [ORNL; Ericson, Milton Nance [ORNL; Fabris, Lorenzo [ORNL

2010-01-01

390

Fission gas behavior in safety experiments  

International Nuclear Information System (INIS)

This book examines fission product release from power reactors during reactor safety experiments. Topics considered include modes and mechanisms of gas precipitation and migration, results and analysis of recent transient in pile experiments, modelling of fission gas behavior, and a review of knowledge and future work

1985-01-01

391

A Computer Code For Calculation Of Fission Product Concentrations For Time Following Fission Burst  

International Nuclear Information System (INIS)

Precise information of the variation of fission product concentration for time after a fission burst is necessary for safety designs and operations of nuclear power reactors, fuel storage, transport flasks, and for spent fuel management and processing. In this study, a computer code has been developed for exact analysis of the buildup and decay of fission products for time following a fission burst. In which, a new numerical measure to solve the linear and nonlinear decay chains was introduced. The analytical data of fission product concentration, obtained by using the present code, was applied to calculate aggregate fission product decay heat from neutron fission of 235U, 238U, 233U, 239Pu, 241Pu and 232Th. (author)

2008-01-01

392

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

International Nuclear Information System (INIS)

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

393

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

394

Fission Surface Power Technology Development Status  

Science.gov (United States)

Power is a critical consideration in planning exploration of the surfaces of the Moon, Mars, and beyond. Nuclear power is an important option, especially for locations in the solar system where sunlight is limited in availability or intensity. NASA is maintaining the option for fission surface power for the Moon and Mars by developing and demonstrating technology for an affordable fission surface power system. Because affordability drove the determination of the system concept that this technology will make possible, low development and recurring costs result, while required safety standards are maintained. However, an affordable approach to fission surface power also provides the benefits of simplicity, robustness, and conservatism in design. This paper will illuminate the multiplicity of benefits to an affordable approach to fission surface power, and will describe how the foundation for these benefits is being developed and demonstrated in the Exploration Technology Development Program s Fission Surface Power Project.

Palac, Donald T.; Mason, Lee S.; Houts, Michael G.; Harlow, Scott

2010-01-01

395

Nuclear Fission as a Markov Process  

International Nuclear Information System (INIS)

Starting from the assumption of a random transfer of nucleons between the two sides of a; fissioning nucleus, during the time from saddle point to scission, it is shown that the mass distribution data in low, intermediate and high energy fission can be given a reasonable -explanation based on the ground state properties of nuclei. The theory is extended to explain the shape of the deformation energy mass curves. These relations follow as a direct consequence of the equilibrium conditions that determine the mass distributions while the gap in the ''zig-zag'' curves is essentially due to the proton transfers. The time of fission is shown to be about 500 nucleonic times in thermal fission and this results from the properties of the transition matrix. The theory is also able to explain the small range of the threshold energies of fission, and the formation of a symmetry axis early in the process. (author)

1965-07-01

396

Theory of neutron emission in fission  

Energy Technology Data Exchange (ETDEWEB)

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 /nu///sub 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 /nu///sub 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 /nu///sub p/ with higher accuracy than is currently possible. 17 refs., 11 figs.

Madland, D.G.

1989-01-01

397

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

398

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

399

Radiation Specifications for Fission Power Conversion Component Materials  

Science.gov (United States)

NASA has been supporting design studies and technology development that could provide power to an outpost on the moon, Mars, or an asteroid. One power-generation system that is independent of sunlight or power-storage limitations is a fission-based power plant. There is a wealth of terrestrial system heritage that can be transferred to the design and fabrication of a fission power system for space missions, but there are certain design aspects that require qualification. The radiation tolerance of the power conversion system requires scrutiny because the compact nature of a space power plant restricts the dose reduction methodologies compared to those used in terrestrial systems. An integrated research program has been conducted to establish the radiation tolerance of power conversion system-component materials. The radiation limit specifications proposed for a Fission Power System power convertor is 10 Mrad ionizing dose and 5 x 10(exp 14) neutron per square centimeter fluence for a convertor operating at 150 C. Specific component materials and their radiation tolerances are discussed. This assessment is for the power convertor hardware; electronic components are not covered here.

Bowman, Cheryl L.; Shin, E. Eugene; Mireles, Omar R.; Radel, Ross F.; Qualls, A. Louis

2011-01-01

400

Fissioned triangular schemes via sharply 3-transitive groups  

CERN Document Server

n [D. de Caen, E.R. van Dam. Fissioned triangular schemes via the cross-ratio, {Europ. J. Combin.}, 22 (2001) 297-301], de Caen and van Dam constructed a fission scheme $\\FT(q+1)$ of the triangular scheme on $\\PG(1,q)$. This fission scheme comes from the naturally induced action of $\\PGL(2,q)$ on the 2-element subsets of $\\PG(1,q)$. The group $\\PGL(2,q)$ is one of two infinite families of finite sharply 3-transitive groups. The other such family $\\Mq(q)$ is a "twisted" version of $\\PGL(2,q)$, where $q$ is an even power of an odd prime. The group $\\PSL(2,q)$ is the intersection of $\\PGL(2,q)$ and $\\Mq(q)$. In this paper, we investigate the association schemes coming from the actions of $\\PSL(2,q)$, $\\Mq(q)$ and $\\PML(2,q)$, respectively. Through the conic model introduced in [H.D.L. Hollmann, Q. Xiang. Association schemes from the actions of $\\PGL(2, q) $ fixing a nonsingular conic, {J. Algebraic Combin.}, 24 (2006) 157-193], we introduce an embedding of $\\PML(2,q)$ into $\\PML(3,q)$. For each of the three grou...

Ma, Jianmin

2011-01-01

 
 
 
 
401

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

402

Laser driven fusion fission hybrids  

International Nuclear Information System (INIS)

The role of the fusion-fission hybrid reactor (FFHR) as a fissile fuel and/or power producer is discussed. As long range options to supply the world energy needs, hybrid-fueled thermal-burner reactors are compared to liquid metal fast breeder reactors (LMFBR). A discussion of different fuel cycles (thorium, depleted uranium, and spent fuel) is presented in order to compare the energy multiplication, the production of fissile fuel, the laser efficiency and pellet gain requirements of the hybrid reactor. Lawrence Livermore Laboratory (LLL) has collaborated with Bechtel Corporation and with Westinghouse in two engineering design studies of laser fusion driven hybrid power plants. The hybrid designs which have resulted from these two studies are briefly described and analyzed by considering operational parameters, such as energy multiplication, power density, burn-up and plutonium production as a function time

1977-11-17

403

Nuclear fission industry in Japan  

International Nuclear Information System (INIS)

The status of the nuclear fission industry in Japan is described. Japanese nuclear policy, vision, goals, and supporting organizational structures are reviewed. The facilities of the Japanese Atomic Energy Research Institute (JAERI), Power Reactor and Nuclear Fuel development Corporation (PNC), and the Japan Atomic Power Company (JAPCO) are illustrated and described. Nuclear power statistics and power generation costs by power source are shown for Japan. Photographic details and technical descriptions are presented for Japan's: nuclear fuel cycle (NFC), light water reactor (LWR), advanced thermal reactor (ATR), fast breeder reactor (FBR), gas centrifuge uranium enrichment, LWR spent fuel reprocessing, ATR and FBR spent fuel uranium/plutonium mixed oxide fuel (MOX) co-conversion process, high level nuclear waste management (NWM) policy, reactor operation safety, newly developed decommissioning and dismantling policy for obsolete nuclear facilities, and new future technology

1990-08-12

404

Laser driven fusion fission hybrids  

International Nuclear Information System (INIS)

The role of the fusion-fission hybrid reactor (FFHR) as a fissile fuel and/or power producer is discussed. As long range options to supply the world energy needs, hybrid-fueled thermal-burner reactors are compared to liquid metal fast breeder reactors (LMFBR). A discussion of different fuel cycles (thorium, depleted uranium, and spent fuel) is presented in order to compare the energy multiplication, the production of fissile fuel, the laser efficiency and pellet gain requirements of the hybrid reactor. LLL has collaborated with Bechtel Corporation and with Westinghouse on the conceptual design of laser fusion power plants. The neutronic studies of these two designs are discussed. The operational parameters, such as energy multiplication, power density, burn-up and plutonium production as a function of time, are also presented

1977-11-17

405

Downstream behavior of fission products  

International Nuclear Information System (INIS)

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"0 to 200"0C) 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

1986-09-07

406

Aerosols and fission product transport  

International Nuclear Information System (INIS)

A survey is presented of current knowledge of the possible role of aerosols in the consequences of in- and out-of-core LOCAs and of end fitting failures in CANDU reactors. An extensive literature search has been made of research on the behaviour of aerosols in possible accidents in water moderated and cooled reactors and the results of various studies compared. It is recommended that further work should be undertaken on the formation of aerosols during these possible accidents and to study their subsequent behaviour. It is also recommended that the fission products behaviour computer code FISSCON II should be re-examined to determine whether it reflects the advances incorporated in other codes developed for light water reactors which have been extensively compared. 47 refs

1987-01-01

407

Fluidized bed nuclear fission reactor  

International Nuclear Information System (INIS)

For the further development of nuclear fission reactors, the feasibility of a new concept is evaluated. It concerns a fluidized bed reactor in which carbon particles with a uranium core are fluidized and cooled by a high velocity pressurized helium flow. Nuclear reaction takes place if the bed is in fluidized conditions at a void fraction above 80% and it stops as soon as the bed is unfluidized, i.e. when no coolant flow is available. The feasibility has been evaluated by design calculations of the nuclear reactor physics and heat transfer, and by an experimental study of an appropriate large particle high velocity fluidized bed. During the experimental study, pressure measurements and ?-ray transmission measurements have been performed along the height of a Geldart D powder fluidized bed in a 38 cm diameter column. From these measurements, axial void fraction profiles have been calculated, the regimes have been analysed and the frequencies of the major bed fluctuations have been determined. (Author)

1996-01-01

408

Fission barriers of transfermium elements  

International Nuclear Information System (INIS)

The fission barriers of transfermium elements are calculated using the single-particle spectra of the realistic Woode-Saxon potential with axial asymmetry of nuclear shape taken into account. The deformination energy is minimized as a function of hexadecapole deformation. The magnitude and structure of the barriers are determined. A prominent feature of the results is a splitting of the conventional first barrier into two barriers separated by a well of depth 2-3 MeV, leading to the possible existence of nuclear-shape isomers in the considered region. This feature may also influence the formation of nuclei in this Z-range in heavy-ion induced reactions. (orig.)

1983-11-28

409

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

410

Fission time measurement by crystal blocking method  

International Nuclear Information System (INIS)

The nucleus evolution to the scission point is slowed down by nuclear dissipation in highly excited nuclei. This phenomena leads to longer fission times than expected by the Bohr and Wheeler's statistical model. A dynamical description of the nucleus has to be taken into account. Measuring fission times is then a real 'probe' of nuclear dissipation effects. We made a reverse kinematic experiment at GANIL in the 4 ? neutron detector ORION, using a lead beam accelerated at 29 MeV/u on a single crystal silicon target mounted on a goniometer. We measured fission times of the projectile-like nuclei with the crystal blocking method, as a function of initial excitation energy. This method, which consists in measuring directly the recoil distance to a row of atoms where the fission occurs in the crystal, gives access to long fission times (> 10-19 s) in the fission times distribution. Blocking dips of the axis and (001) and (110) planes has been analysed with Monte-Carlo simulation code. For the first time in such simulation the particle evaporation of the fission fragments has been calculated in a precise way. (author)

411

Progress in fission product nuclear data  

International Nuclear Information System (INIS)

This is the fifth 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 fourth issue of this series has been published in July 1978 as INDC(NDS)-95/G+P. The present issue includes contributions which were received by NDS between 1 August 1978 and 15 May 1979. The next issue of this report series is envisaged to be published in June 1980

1978-08-01

412

Sub-threshold fission in the actinides  

International Nuclear Information System (INIS)

Two experiments, which have been performed on the Harwell Synchrocyclotron using fast neutrons, are described and the results discussed. In one experiment the neutron-induced fission cross-section of the isotope "2"3"1Pa was measured by detection of the fission fragments in a gas scintillation detector. In the other, sub-threshold fission of the isotope "2"3"2Th was investigated by the detection of the neutrons emitted during the fission process. The results are interpreted in the light of the double-humped fission barriers, which are a consequence of the Strutinsky model which combines the effects of the liquid drop and shell models of the nucleus. A new method is presented for calculating the penetrability of such barriers, and comparison is made with the measured fission cross-sections of two isotopes, "2"3"0Th and "2"3"2Th. The low energy fission cross-section of "2"3"1Pa is found to be consistent with the concept of a series of rotational bands based upon vibrational levels. (U.K.)

1978-01-01

413

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

414

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

415