WorldWideScience

Sample records for oklo natural fission

  1. Plutonium Fission in the Oklo Natural Reactor

    International Nuclear Information System (INIS)

    The Oklo natural reactor was discovered in 1972. Experimental evidence has indicated that the fuel source was primarily 235U with a small contribution of 7 to 9 percent from the fission of 239Pu. This article's reevaluation of data indicates that 239Pu was an important source of fuel in some areas of the reactor. A small portion of xenon and krypton released from Oklo sample 1348 appears to have originated from a source enriched in 239Pu. That fuel source may have been the core of a natural breeder reactor

  2. Retention of reactor products in the Oklo natural fission reactor

    International Nuclear Information System (INIS)

    Analysis of the fission product distribution in the Oklo reactor and its environs support the conclusions that a mineral such as uraninite can retain its integrity and composition to a remarkable degree while immersed in natural ground water. The transport of uranium out of the principal reactor zones averaged no more than 20 percent in the most affected regions with a fractional loss of uranium of 10-10 per year

  3. Geochemical controls on the retention of fission products at the Oklo natural fission reactors

    International Nuclear Information System (INIS)

    A unique example of the utility of isotope geochemistry may be found in studies of the isotopic abundances of elements in samples from the Oklo uranium mine in the African Republic of Gabon. These studies demonstrate that two billion years ago, in a span of a few hundred thousand years, nuclear fission and associated processes profoundly changed the isotopic and chemical composition of discrete lenses of highly uraniferrous rock within the mine. These changes can be quantified by characterizing operating parameters of the natural nuclear fission reactors and interpreting them in the context of the systematics of the nuclear reactions. Comparisons between the present, measured composition of the natural reactor remnants and their calculated nuclear-reaction induced composition provides a quantitative characterization of compositional changes in the rocks during the last two billion years. We have measured the abundances and isotopic compositions of uranium and eight fission product elements in samples from well-defined locations in an area containing the cross-section of a fossil reactor. The data have been used to examine the retention of fission products in the reactor zone and to explain this retention by analogy to properties of irradiated anthropogenic UO2 reactor fuel. (author)

  4. 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

  5. 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

  6. Coupled processes at the Oklo Natural Reactor

    International Nuclear Information System (INIS)

    The Oklo Natural Reactor, Gabon, is an excellent site in which to study, assess 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 -4500C, although local, higher temperatures may have been reached. This thermal regime aided in the diffusion of some fission products, and possibly actinides, from host pitchblende. Post-reactor diagenesis events have masked some of the radionuclide migration paths, but most can still be studied. The combined thermal and geochemical aspects of Oklo allow estimates of degree of radionuclide migration to be estimated, and aspects of both near-field and far-field behavior can be evaluated from combined theoretical and experimental studies. After some twelve years research, it appears that most of the Oklo fission products and actinides did not migrate any appreciable distance from the host pitchblende, and that the rocks at the Oklo site are adequate to fix migrating radionuclides in them

  7. 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

  8. Cumulative fission yields of cadmium in Oklo samples

    International Nuclear Information System (INIS)

    The relative fission yields of the five stable isotopes of cadmium, 111Cd, 112Cd, 113Cd, 114Cd and 116Cd, produced in three uranium ore samples from the Oklo mine site (Republic of Gabon) have been measured by solid source mass spectrometry. The fission yields for 111Cd and 112Cd measured with respect to 116Cd indicate that thermal neutron fission of 235U was the most significant contributor to the fission yields, but that the thermal fission of 239Pu was also important. The relative amounts of 235U to 239Pu thermal fission correlates with the measured 235U abundance in the three samples. 113Cd is severely depleted in all three ore samples whilst 114Cd is correspondingly enhanced. The results suggest that there was very little natural cadmium in the uranium ore at the time the Oklo natural reactor was operative, but that the majority of the cadmium produced by fission during the irradiation period has been removed from the uranium samples by chemical redistribution processes. The stable isotope dilution technique has been used to measure the present-day abundance of cadmium in the three samples. The results show that samples 433/3, 1498 and 1470 have 125, 74 and 64 ppb respectively. Approximately 10% of this is fission-product cadmium. The isotopes 110Cd and 108Cd, which are shielded and 108Cd, which are shielded from fission by the isobars 110Pd and 108Pd, also show small but significant enrichments with respect to terrestrial cadmium. The enrichment in 108Cd and 110Cd is due to neutron capture on 107Ag and 109Ag, respectively, all the 107Ag being terrestrial silver contamination, but the 109Ag being a mixture of fission-product silver and terrestrial silver contamination. This implies an upper limit to the duration of the irradiation process. (author)

  9. Thermoluminescence and electron-spin resonance studies of the Oklo natural-fission reactor materials

    International Nuclear Information System (INIS)

    In a previous paper, the authors had concluded that the remarkable thermoluminescence (TL) properties of samples obtained from within the 'reaction zone 2', namely the total absence of natural TL in them and their inability to exhibit artificially induced TL, could be attributed to a high degree of radiation damage suffered by them in the reactor core. By contrast, samples from outside the reaction zone exhibited normal TL properties. In the present investigation, a 'second set' of samples (six in number) are examined, which had been collected from outside the reaction zone. Preliminary geological examination during their selection had indicated that one subset of three samples had a clay matrix very similar to that of the ore of the core, and the second subset of three samples consisted of rich ore but with a very low reaction rate. X-ray fluorescence (XRF), TL, and electron-spin resonance (ESR) studies of the 'second set' have been carried out with a view to ascertaining whether the differences in the TL properties of the in-core and off-core samples in the 'first set' could be attributed to compositional differences rather than to radiation damage. It is found that considerable compositional inhomogeneity exists within the 'second-set' samples. However, on comparing samples in the first and second sets that have broad compositional likeness, it is concluded that the original radiation-damage hypothesis is still tenable. The hypothesis is lent further support by an hypothesis is lent further support by an experiment in which material from two in-core samples of the 'first set' was heated at 10000C for three days and it was observed that the resulting recrystallization enabled these samples to exhibit normal TL. Also, a certain degree of correlation has been found between the ESR and TL properties of each set. (author)

  10. Migration and retention of elements at the Oklo natural reactor

    International Nuclear Information System (INIS)

    The Oklo natural reactor, Gabon, permits study of fission-produced elemental behavior in a natural geologic environment. The uranium ore that sustained fission reactions formed about 2 billion years before present (BYBP), and the reactor was operative for about 5 x 105 yrs between about 1.95 to 2 BYBP. The many tons of fission products can, for the most part, be studied for their abundance and distribution today. Since reactor shutdown, many fissiogenic elements have not migrated from host pitchblende, and several others have migrated only a few tens of meters from the reactor ore. Only Xe and Kr have apparently been largely removed from the reactor zones. An element by element assessment of the Oklo rocks' ability to retain the fission products, and actinides and radiogenic Pb and Bi as well, leads to the conclusion that no widespread migration of the elements occurred. This suggests that rocks with more favorable geologic characteristics are indeed well suited for consideration for the storage of radioactive waste

  11. Sorption-desorption of cesium on-from illite and illite coated with petroleum with reference to Oklo natural fission reactors

    International Nuclear Information System (INIS)

    Full text of publication follows: For 0.1 to 1.0 Myr there were natural nuclear reactors 1950 Myr ago in Gabon, Africa. They are small pockets of highly uraniferous, hydrothermally altered sedimentary rocks in Oklo, Okelobondo and Bangombe uranium ore deposits. The natural reactors contain illite, Fe, Mg chlorite, uraninite and some quartz. Several of them also contain abundant carbonaceous matter (up to 66% by weight) Corg. in heterogeneous distribution with clay and quartz. To elucidate the containment and migration of some of the radionuclides in the natural reactors, the sorption-desorption processes on-from illite of Cs was determined by simulated laboratory experiments. 134Cs was sorbed and desorbed on-from illite from aqueous solutions before and after the illite was coated with petroleum. Simulated connate water contained 0.001-1.0 M NaCl was used in the experiment. The effects on desorption of cesium by 0.1-1.0 M KCl solutions was also evaluated. The radiolabelled and coated illite samples were heated at 250 deg. C in different air conditions using normal air (containing O2) or N2 atmosphere. After the heating the effect on the stability of coating and the leachability of Cs was determined The desorption of Cs from illite increases with increasing temperature and increasing concentration of Na+ and K+, the latter is more effective in removing Cs. Petroleum coatings on illite hinders the desorpteum coatings on illite hinders the desorption of Cs, most effectively when the coatings occurred after Cs sorption, as thought to have occurred at Oklo. Heating in nitrogen atmosphere significantly decreased Cs leachability from the petroleum coated illite comparing with the illite heated in air containing oxygen. Radionuclide desorption from clays is of interest to current radioactive waste containment. (authors)

  12. Thermoluminescence and fission-track studies of the Oklo fossil reactor materials

    International Nuclear Information System (INIS)

    Thermoluminescence (TL), both natural and that induced by artificial irradiation, has been studied in Oklo fines as a function of distance from the edge of a reaction zone. No natural TL was found in samples within reaction zone 2, nor was it possible to induce TL in them, in complete contrast to samples from outside the zone. This is attributed to the high degree of radiation damage suffered by the core material, rather than to mineralogical differences. The hypothesis is supported by observing the TL behaviour of quartz samples from Brazil as well as of Oklo samples outside the reaction zone as a result of massive doses (approximately 1011 rad) of 10-MeV protons. The age of the formation (or the last severe heating) of six quartz crystals from two locations outside reaction zone 2 has been calculated by the fission-track analysis method. After applying various corrections, particularly that for the thermal fading of tracks over geological time periods, a self-consistent set of ages, with a mean value of 1.73x109 yr, has been obtained. This age, which ignores any contribution from natural induced fission, agrees well with determinations based on other independent methods. (author)

  13. Oklo reactors: natural analogs to nuclear waste repositories

    International Nuclear Information System (INIS)

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

  14. Inception and evolution of Oklo natural nuclear reactors; Genese et evolution des reacteurs nucleaires fossiles d'Oklo

    Energy Technology Data Exchange (ETDEWEB)

    Bentridi, Salah-Eddine [UMR 7517, laboratoire d' hydrologie et de geochimie de Strasbourg, CNRS/universite de Strasbourg, 1, rue Blessig, 67084 Strasbourg (France); Laboratoire de l' energie et des systemes intelligents, CUKM, route de Theniet, El-Hed 44225 (Algeria); Gall, Benoit [UMR 7178, institut pluridisciplinaire Hubert-Curien, CNRS-IN2P3/universite de Strasbourg, 23, rue du Loess, 67037 Strasbourg (France); Gauthier-Lafaye, Francois [UMR 7517, laboratoire d' hydrologie et de geochimie de Strasbourg, CNRS/universite de Strasbourg, 1, rue Blessig, 67084 Strasbourg (France); Seghour, Abdeslam [Centre de recherches nucleaires d' Alger - CRNA, 2, boulevard Frantz-Fanon, 16000 Alger (Algeria); Medjadi, Djamel-Eddine [Ecole normale superieure, Vieux-Kouba, 16050 Alger (Algeria)

    2011-11-15

    The occurrence of more than 15 natural nuclear Reactor Zones (RZ) in a geological environment remains a mystery even 40 years after their discovery. The present work gives for the first time an explanation of the chemical and physical processes that caused the start-up of the fission reactions with two opposite processes, uranium enrichments and progressive impoverishment in {sup 235}U. Based on Monte-Carlo neutronics simulations, a solution space was defined taking into account realistic combinations of relevant parameters acting on geological conditions and neutron transport physics. This study explains criticality occurrence, operation, expansion and end of life conditions of Oklo natural nuclear reactors, from the smallest to the biggest ones. (authors)

  15. The fate of the epsilon phase (Mo-Ru-Pd-Tc-Rh) in the UO2 of the Oklo natural fission reactors

    International Nuclear Information System (INIS)

    In spent nuclear fuel (SNF), the micrometer- to nanometer-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; froodite, PdBi2, with trace amounts of As, Fe, and Te, and palladodymite or rhodarsenide, (Pd, Rh)2As. The most abundant 4d-metal phase is ruthenarsenite, (Ru, Ni)As, which has a representative composition: As, 59.9; Co, 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 atcore 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 ?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: (i) 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. (ii) All Mo and most of the Tc were released from the epsilon phase. Galena precipitated surrounding the 4d-metal phases. (iii) Once the uraninite matrix has dissolved, the epsilon nanoparticles were released and ''captured'' within alteration phases that are immediately adjacent to the uraninite. (orig.)

  16. Organic matter and containment of uranium and fissiogenic isotopes at the Oklo natural reactors

    International Nuclear Information System (INIS)

    Some of the Precambrian natural fission reactors at Oklo in Gabon contain abundant organic matter, part of which was liquefied at the time of criticality and subsequently converted to a graphitic solid. The liquid organic matter helps to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite. It is known that in the prevailing reactor environments, precipitated uraninite grains incorporated fission products. We report here observations which show that these uraninite crystals were held immobile within the re-solidified, graphitic bituminous organics at Oklo thus enhanced radionuclide containment. Uraninite encased in solid graphitic matter in the organic-rich reactor zones lost virtually no fissiogenic lanthanide isotopes. The first major episode of uranium and lead migration was caused by the intrusion of a swarm of adjacent dolerite dykes about 1,100 Myr after the reactors went critical. Our results from Oklo imply that the use of organic, hydrophobic solids such as graphitic bitumen as a means of immobilizing radionuclides in pre-treated nuclear waste warrants further investigation. (author)

  17. Radiolysis in nature: Evidence from the Oklo natural reactors

    International Nuclear Information System (INIS)

    An examination of the mineralogy of the reactor zones at Oklo shows that they have been significantly altered. The rocks immediately adjacent to these zones are also mineralogically modified with respect to normal uranium bearing rocks. The mineralogic changes appear to be the consequence of radiation damage, changes in the bulk chemistry of the system and increased temperatures. Chemical changes were the consequence of convectively circulating fluids that transported elements in and out of the rocks. There were also changes in the electrochemical conditions in the rocks. These changes can most reasonably be attributed to oxidizing and reducing species produced by the radiolysis of water. We have calculated radiation doses and examined the production of radiolysis products in the fluid phase which lead to the following conclusions: 1) There was a net reduction of iron, probably associated with a net increase in total iron in the rocks of the reactor zones. The reduction of iron was most likely the result of hydrogen produced by the radiolysis of water. 2) Commensurate with the iron reduction, there was an oxidation of uranium and multivalent fission products, resulting in their transport out of the reactor zone. 3) Approximately 10 percent of the uranium and various proportions of these fission products were removed and redeposited in rocks within a few meters of the reactor zones. 4) The calculated radiation doses from alpha radiation and the inferred hydrogen production suggest an effective radiation yield of 0.06 molecules of hydrogen per 100 eV of energy imparted to the fluid phase. Considering radiation from both alpha and beta sources, the G value for hydrogen production is reduced to 0.01 to 0.002 molecules H2/100 eV. (author)

  18. Gamma-ray fluxes in Oklo natural reactors

    CERN Document Server

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

    2012-01-01

    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...

  19. 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

  20. Oklo Natural Reactor and the Time Variability of the Fundamental Constants of Nature

    International Nuclear Information System (INIS)

    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

  1. Fate of the Epsilon Phase in the Oklo Natural Reactors

    International Nuclear Information System (INIS)

    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), fioodite, 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: (1) The original epsilon phase was transformed to, in most cases, ruthenarsenite. (2) All Mo and most of the Tc were released from the epsilon phase. Some portion of the other metals was also leached and provided a space for a precipitation of PbS between the ruthenarsenite and uraninite. (3) Once the uraninite matrix dissolved, the epsilon particles were released and sometimes captured within adjacent alteration minerals

  2. 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, sw 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)

  3. 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

  4. Oklo. A review and critical evaluation of literature

    Energy Technology Data Exchange (ETDEWEB)

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

    2000-10-01

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

  5. Oklo. A review and critical evaluation of literature

    International Nuclear Information System (INIS)

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

  6. Natural fission reactor

    Energy Technology Data Exchange (ETDEWEB)

    Cowan, G.A.

    1976-07-01

    The evidence supporting the establishment of the zones of a natural fission reactor that occurred about 2 billion years ago is presented. The reactor evidence was found in an open-pit uranium mine in the southeastern part of the Gabon Republic, near the Equator on the coast of West Africa. The history of the probable sequence of events leading to the reaction is recounted. Reasons for the ceasing of the fission reaction are set forth. The spectrum of fission products in the area is thought to be so distinctive that it serves as an unmistakable sign that a chain reaction has taken place. Geological features of the area are related to conditions before and after the fission took place. (BLM)

  7. 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

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

    CERN Document Server

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

    2006-01-01

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

  9. 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.)

  10. 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

  11. Natural nuclear reactor at Oklo and variation of fundamental constants: Computation of neutronics of a fresh core

    Science.gov (United States)

    Petrov, Yu. V.; Nazarov, A. I.; Onegin, M. S.; Petrov, V. Yu.; Sakhnovsky, E. G.

    2006-12-01

    Using modern methods of reactor physics, we performed full-scale calculations of the Oklo natural reactor. For reliability, we used recent versions of two Monte Carlo codes: the Russian code MCU-REA and the well-known international code MCNP. Both codes produced similar results. We constructed a computer model of the Oklo reactor zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities, and neutron fluxes were calculated. We also estimated the temperature and void effects for the fresh core. As would be expected, we found for the fresh core a significant difference between reactor and Maxwell spectra, which had been used before for averaging cross sections in the Oklo reactor. The averaged cross section of 62149Sm and its dependence on the shift of a resonance position Er (due to variation of fundamental constants) are significantly different from previous results. Contrary to the results of previous papers, we found no evidence of a change of the samarium cross section: a possible shift of the resonance energy is given by the limits -73??Er?62 meV. Following tradition, we have used formulas of Damour and Dyson to estimate the rate of change of the fine structure constant ?. We obtain new, more accurate limits of -4×10-17??·/??3×10-17yr-1. Further improvement of the accuracy of the limits can be achieved by taking account of the core burn-up. These calculations are in progress.

  12. Natural nuclear reactor at Oklo and variation of fundamental constants: Computation of neutronics of a fresh core

    International Nuclear Information System (INIS)

    Using modern methods of reactor physics, we performed full-scale calculations of the Oklo natural reactor. For reliability, we used recent versions of two Monte Carlo codes: the Russian code MCU-REA and the well-known international code MCNP. Both codes produced similar results. We constructed a computer model of the Oklo reactor zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities, and neutron fluxes were calculated. We also estimated the temperature and void effects for the fresh core. As would be expected, we found for the fresh core a significant difference between reactor and Maxwell spectra, which had been used before for averaging cross sections in the Oklo reactor. The averaged cross section of 62149Sm and its dependence on the shift of a resonance position Er (due to variation of fundamental constants) are significantly different from previous results. Contrary to the results of previous papers, we found no evidence of a change of the samarium cross section: a possible shift of the resonance energy is given by the limits -73??Er?62 meV. Following tradition, we have used formulas of Damour and Dyson to estimate the rate of change of the fine structure constant ?. We obtain new, more accurate limits of -4x10-17??·/??3x10-17 yr-1. F>-17 yr-1. Further improvement of the accuracy of the limits can be achieved by taking account of the core burn-up. These calculations are in progress

  13. Nuclear fission

    International Nuclear Information System (INIS)

    It is pointed out that although a comparison of nuclear fission and coal as sources of energy shows that the former has more advantages, yet there is still much opposition to its further development. The contribution that can be made by research in the next 25 years to the removal of this opposition is examined. In particular LWR, LOFT, HTGR, the fast reactor, and the OKLO natural fossil reactors are considered. (D.J.B.)

  14. 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

  15. The Oklo phenomenon

    International Nuclear Information System (INIS)

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

  16. 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)

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  19. OKLO: fossil reactors

    International Nuclear Information System (INIS)

    Events leading up to the discovery during the summer of 1972 of the Oklo fossil reactor in Gabon and its subsequent exploration are reviewed. Results of studies are summarized; future investigations are outlined

  20. 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

  1. Radioactive wastes in Oklo; Desechos radiactivos en Oklo

    Energy Technology Data Exchange (ETDEWEB)

    Balcazar, M.; Flores R, J.H.; Pena, P.; Lopez, A. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

    2006-07-01

    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)

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

    Energy Technology Data Exchange (ETDEWEB)

    Barre, B

    2005-02-15

    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.)

  3. The Oklo phenomenon

    International Nuclear Information System (INIS)

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

  4. 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 t 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

  5. 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.) waste isolation. (Auth.)

  6. Oklo - A nuclear reactor 1800 million years ago

    International Nuclear Information System (INIS)

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

  7. Etching of fission tracks in silicate glasses by means of deionized water

    International Nuclear Information System (INIS)

    Fission tracks have been revealed in silicate glasses with deionized water. Their sharp conical shape implies a marked enhancement of the dissolution rate along their core and consequently a cone angle and an etching efficiency (close to 100%) much higher than previously reported for glasses. We show that etching of fission tracks in natural environments has generally very limited geochemical implications except in specific cases such as that found in the Oklo uranium ores

  8. Detection of natural fission products in groundwater

    International Nuclear Information System (INIS)

    The proposed disposal of high-level radioactive waste in geologic formations has spurred research on nuclear techniques for age-dating old groundwater and on field studies of radionuclide behavior in geochemical analogs to waste repositories. Lithospheric production and solute transport of natural fission product 129I is of interest for both applications. Using tandem accelerator mass spectrometry, natural levels of this isotope were recently measured in groundwater in two field studies: Stripa granite in Sweden and uranium ore deposits in Northern Territory, Australia. Results and preliminary interpretation are presented here

  9. Time variability of ? from realistic models of Oklo reactors

    International Nuclear Information System (INIS)

    We reanalyze Oklo 149Sm data using realistic models of the natural nuclear reactors. Disagreements among recent Oklo determinations of the time evolution of ?, 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 149Sm 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 149Sm effective cross sections and use these values to set limits on the time variation of ?. Our study resolves a contradictory situation with previous Oklo ? results. Our suggested 2? bound on a possible time variation of ? over 2 billion years is stringent: -0.11???/??0.24, in units of 10-7, but model dependent in that it assumes only ? has varied over time

  10. Time variability of ? from realistic models of Oklo reactors

    Science.gov (United States)

    Gould, C. R.; Sharapov, E. I.; Lamoreaux, S. K.

    2006-08-01

    We reanalyze Oklo Sm149 data using realistic models of the natural nuclear reactors. Disagreements among recent Oklo determinations of the time evolution of ?, 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 Sm149 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 Sm149 effective cross sections and use these values to set limits on the time variation of ?. Our study resolves a contradictory situation with previous Oklo ? results. Our suggested 2? bound on a possible time variation of ? over 2 billion years is stringent: -0.11???/??0.24, in units of 10-7, but model dependent in that it assumes only ? has varied over time.

  11. 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 appropriat the ''yellowcake'' output from appropriate mills would be monitored for isotopic alterations indicative of the exhumation and processing of a natural reactor. (author)

  12. Origin of the chemical elements and the Oklo phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Kuroda, P.K.

    1982-01-01

    Present knowledge on the formation of the elements is surveyed. The subjects addressed include: the abundance of the elements, elements 43 and 61 in nature, the Oklo phenomenon, synthesis of the elements in stars, plutonium-244 in the early solar system, and isotopic anomalies in the early solar system. 164 references.

  13. 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.)

  14. 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 tios 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)

  15. 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 intrusibilization during the tholeiitic intrusion event. (author)

  16. Uranium solubilities in the Oklo reactor zones

    International Nuclear Information System (INIS)

    It was hypothesized that uraninite grains in the reactor zones at Oklo (Gabon) might show zonation with respect to the isotopic composition of the uranium. A more nearly natural composition might be expected in the rims of such grains since solutions moving into the reactor zones from the undepleted ore zone would carry natural uranium. Several uraninite grains were examined by means of an ion microprobe capable of resolving a rim of 10 microns width. Within the approximately 5% precision of the instrument no zoning was detected. The absence of detectable zoning in the isotopic compositions of the uraninite grains might be caused by low solubility of uraninite in the Oklo ore body resulting in insignificant uranium transport. That this is a reasonable assumption is borne out by solubility calculations for uraninite in equilibrium with uranium ions and uranium oxide, hydroxide, and carbonate ions in aqueous solution. These calculations indicate that if 02 and CO2 are in equilibrium with the solid assemblage magnetite, hematite, and graphite total uranium molalities in the pH range from 5 to 6.8 are less than 10-9. Under these conditions, and assuming no other important aqueous uranium species, uranium transport would be insufficient to produce observable zoning in the reactor zone uraninite

  17. Time-variability of alpha from realistic models of Oklo reactors

    CERN Document Server

    Gould, C R; Lamoreaux, S K

    2006-01-01

    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: $ -...

  18. Time-variability of alpha from realistic models of Oklo reactors

    Science.gov (United States)

    Gould, Chris; Sharapov, Eduard; Lamoreaux, Steve

    2006-10-01

    We reanalyze Oklo ^149Sm data using realistic models of the natural nuclear reactors. Disagreements among recent Oklo determinations of the time evolution of ?, 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 ^149Sm 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 ^149Sm effective cross sections, and use these values to set limits on the time-variation of ?. Our study resolves a contradictory situation with previous Oklo ?-results. Our suggested 2 ? bound on a possible time variation of ? over two billion years is stringent: -0.11 <=??? <=0.24, in units of 10-7, but model dependent in that it assumes only ? has varied over time.

  19. The Oklo reactors: five years of exploration of the site

    International Nuclear Information System (INIS)

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

  20. Analysis of colloids from Oklo/Okelobondo and Bangombe waters

    International Nuclear Information System (INIS)

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

  1. Relevance of nuclide migration at Oklo to the problem of geologic storage of radioactive waste

    International Nuclear Information System (INIS)

    Analyses of Oklo samples published by French scientists and the data presented by U. S. scientists at this symposium indicate that escape of radioactive products from the Oklo reactor zones was quite limited. Apparently, the major radioactive products that might have been measured in the surrounding environment at the time of the reaction would have been due to 85Kr and, possibly, 137Cs and 90Sr. Other fission product elements which have been significantly displaced over the intervening epochs include Xe, Rb, Ba, Mo, and I. The heavy elements have remained relatively fixed. These conclusions must remain tentative until additional analyses are completed on samples taken near the interfaces between reactor and non-reactor zones. Relevance of these tentative conclusions to other geologic formations must await further study of comparative geochemistry and geology. (U.S.)

  2. Hydrogeology of the Oklo-Okelobondo site

    International Nuclear Information System (INIS)

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

  3. Technical Application of Nuclear Fission

    Science.gov (United States)

    Denschlag, J. O.

    The chapter is devoted to the practical application of the fission process, mainly in nuclear reactors. After a historical discussion covering the natural reactors at Oklo and the first attempts to build artificial reactors, the fundamental principles of chain reactions are discussed. In this context chain reactions with fast and thermal neutrons are covered as well as the process of neutron moderation. Criticality concepts (fission factor ?, criticality factor k) are discussed as well as reactor kinetics and the role of delayed neutrons. Examples of specific nuclear reactor types are presented briefly: research reactors (TRIGA and ILL High Flux Reactor), and some reactor types used to drive nuclear power stations (pressurized water reactor [PWR], boiling water reactor [BWR], Reaktor Bolshoi Moshchnosti Kanalny [RBMK], fast breeder reactor [FBR]). The new concept of the accelerator-driven systems (ADS) is presented. The principle of fission weapons is outlined. Finally, the nuclear fuel cycle is briefly covered from mining, chemical isolation of the fuel and preparation of the fuel elements to reprocessing the spent fuel and conditioning for deposit in a final repository.

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

    International Nuclear Information System (INIS)

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

  5. 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 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

  6. Contribution of radiation damage studies to the understanding of the Oklo phenomenon

    International Nuclear Information System (INIS)

    Radiation damage features were investigated in minerals extracted from various zones of the Oklo fossil nuclear reactors. The main results of these investigations are: (1) No high concentration of radiation damage was observed in clay minerals extracted from the reaction zones. Results from laboratory simulation experiments then give a plausible explanation for this observation, in strongly suggesting that the track registering minerals initially present in the reactor cores suffered a drastic in-situ regeneration, which was triggered by the deep groundwater etching of the nuclear particle tracks registered in the grains; (2) the highly heterogeneous uranium distribution found in the quartz grains sampled outside the reaction zones prevents the application of the classical fission-track dating technique. A new method was thus developed with a view to using the microscopic fission-fragment ''stars'' originating from tiny uranium-rich inclusions imbedded in the quartz grains for determining a track ''model'' age for the grains. In the normal zones far from the reactor borders the ages of the quartz grains cluster at a value of about 2.5+-0.5x109 a, which is quite compatible with the formation age of the Chaillu Massif; (3) uraninite grains extracted from the Oklo reactor zones are very different from those found in other uranium ore deposits. Indeed they contain a very high density of tiny crystallites, observable with a high-voltage electron microscope, and h a high-voltage electron microscope, and which disappear at a high temperature (18000C). These crystallites, which likely represent radiation damage remnants acquired at the time of the chain reactions, should also help in understanding the functioning of the Oklo reactor

  7. 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)ted. (author)

  8. Time variation of the fine structure constant ? from realistic models of Oklo reactors.

    Science.gov (United States)

    Gould, C. R.; Sharapov, E. I.; Lamoreaux, S. K.

    2006-11-01

    The topic of whether the fundamental constants of nature vary with time has been a subject of great interest since Dirac originally proposed the possibility that GN˜1/tuniverse. Recent observations of absorption spectra lines from distant quasars appeared to indicate a possible increase in the fine structure constant ? over ten billion years. Contrarily, analyses of the time evolution of ? from Oklo natural nuclear reactor data have yielded inconsistent results, some indicating a decrease over two billion years while others indicated no change. We have used known Oklo reactor epithermal spectral indices as criteria for selecting realistic reactor models. Reactors RZ2 and RZ10 were modeled with MCNP and the resulting neutron spectra were used to calculate the change in the ^149Sm capture cross section as a function of a possible shift in the energy of the 97.3-meV resonance. Our study resolves the contradictory situation with previous Oklo ?-results. Our suggested 2 ? bound on a possible time variation of ? over two billion years is stringent: -0.11 <=??? <=0.24, in units of 10-7, but model dependent in that it assumes only ? has varied over time.

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

    CERN Document Server

    Onegin, M S

    2014-01-01

    New severe constraints on the variation of the fine structure constant have been obtained from reactor Oklo analysis in our previous work. We investigate here how these constraints confine the parameter of BSBM model of varying $\\alpha$. Integrating the coupled system of equations from the Big Bang up to the present time and taking into account the Oklo limits we have obtained the following margin on the combination of the parameters of BSBM model: $$ |\\zeta_m (\\frac{l}{l_{pl}})^2|<6\\cdot 10^{-7}, $$ where $l_{pl}=(\\frac{G\\hbar}{c^3})^{\\frac{1}{2}} \\approx 1.6 \\cdot 10^{-33}$ cm is a Plank length and $l$ is the characteristic length of the BSBM model. The natural value of the parameter $\\zeta_m$ - the fraction of electromagnetic energy in matter - is about $10^{-4}$. As a result it is followed from our analysis that the characteristic length $l$ of BSBM theory should be considerably smaller than the Plank length to fulfill the Oklo constraints on $\\alpha$ variation.

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

    International Nuclear Information System (INIS)

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

  11. Decontamination of radioactive waste fission products by treated natural clays

    International Nuclear Information System (INIS)

    The removal of carrier free long living fission products such as iodine-131, strontium-90 and cesium-137 by treated local clays is successfully achieved with large capacity. Iodine-131 which is difficultly adsorbed has been removed completely by silver treated phosphate clay. Strontium-90 and cesium-137 have been almost removed by adequate heat treating of the clays. The results of column experiments agree well with the authors' batch experiments. (author)

  12. Limits on cosmological variation of strong interaction and quark masses from big bang nucleosynthesis, cosmic, laboratory and Oklo data

    International Nuclear Information System (INIS)

    Recent data on the cosmological variation of the electromagnetic fine structure constant from distant quasar (QSO) absorption spectra have inspired a more general discussion of the possible variation of other constants. We discuss the variation of strong scale and quark masses. We derive limits on their relative change from (i) primordial big bang nucleosynthesis, (ii) the Oklo natural nuclear reactor, (iii) quasar absorption spectra, and (iv) laboratory measurements of hyperfine intervals

  13. Thermal stability of fission tracks in natural and synthetic glasses: An assessment of compositional effects

    CERN Document Server

    Singh-Sandhu, A; Preece, S J

    1999-01-01

    A series of laboratory annealing experiments are designed to evaluate the thermal annealing characteristics of fission tracks for a large number of glasses of varying chemical compositions. A comparative study of thermal stability has been made by comparing the calculated value of activation energy (Ea) for each glass. The present investigations suggest that fission tracks in glass samples with a high silica content are more resistant to annealing than those with a low silica content. In addition, the influence of chemical composition on etching characteristics for both synthetic and natural glasses has also been investigated.

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

    International Nuclear Information System (INIS)

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

  15. 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, kerreactor 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.)

  16. Delayed neutron measurements with a natural uranium fission product source in Fast Breeder Test Reactor

    International Nuclear Information System (INIS)

    Highlights: • Delayed neutron measurements performed with a Fission Product Source (FPS) FBTR. • FPS provided by natural U–Ni pins with perforated clad. • Measurements have helped in quantification of sensitivity of DND system in FBTR. - Abstract: An assessment of the sensitivity and localization capabilities of clad failure detection by Delayed Neutron Detection (DND) system in Fast Breeder Test Reactor at Kalpakkam has been done, by a series of delayed neutron measurements. Experimental simulation of failed fuel pin is done by considering a natural uranium fission product source in the form of special subassembly containing natural uranium pins, each having a large exposed area in the form of small holes. The measurements and analysis of delayed neutron signals with special subassembly in several selected locations are presented

  17. Exploration of the Oklo reaction sites

    International Nuclear Information System (INIS)

    After the discovery of the Oklo phenomenon, the search for the reaction sites began. In the course of efforts to reconstruct the history of the exploration activities from the existing documents, the conclusion was reached that there must have been at least two reaction sites, that not too much of the sites had been removed and that the sites probably extended into the still unexploited part of the deposit. The prolongations were sought first through investigation of the outcrops and then by means of borehole drilling downstream. It was found that each of the reaction sites consisted of a compact accumulation of very rich uranium ore, virtually in a single block, flattened in the direction of the stratum. An effort was made to delimit the sites with a relatively high degree of precision: the length is 10-20 m and the thickness is about one metre. The concentrations in the reactor ore accumulations are generally over 50 times higher than in the surrounding ore. Four other reaction zones, not yet reached in the course of exploitation, were later identified; the total weight of uranium participating in the reaction appears to have been about 800 tons. Considerable sampling was carried out. Fairly serious difficulties were encountered at first because the ore tended to crumble; later, however, core extraction and sample preparation were improved. Beside some 750 samples taken at the surface, core samples were obtained through about a hundred boreholes which completely trat a hundred boreholes which completely traversed the uraniferous stratum. A fairly large number of core samples have been studied in detail (gamma spectrometry; analyses of 1-10 cm lengths after halving and quartering the core samples). As regards the future of the sites, it is hoped that part of the reaction zone can be preserved when exploitation resumes

  18. 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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  1. Des analogues naturels de sites de stockage de déchets nucléaires vieux de 2 milliards d'années : les réacteurs de fission nucléaire naturels du Gabon (Afrique)

    Science.gov (United States)

    Gauthier-Lafaye, François

    2002-10-01

    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 Bangombé (Gabon) and the lack of precise data about uranium and fission products retention and migration mechanisms in geological environments. To cite this article: F. Gauthier-Lafaye, C. R. Physique 3 (2002) 839-849.

  2. Analysis of waters from the Oklo reactor area: preliminary results on the content of organic substances and colloids

    International Nuclear Information System (INIS)

    The migration of radionuclides, in a nuclear waste disposal in geological formation, depends in part on the physico-chemical forms of the radioelements present in the natural aquifer. In particular, the presence of colloids (entities defined as dispersed particles with size of 1 nm-1 ?m) may alter the speciation of radioelements and hence, change their behaviour. Their mobility may be enhanced or decreased by sorption or complexation reactions. These colloids may be inorganic particles (silicates, silico-aluminates, metallic hydroxides, etc) or organic particles (such as humic substances constituted by humic and fulvic acids). Moreover, these colloids may exist in different natural systems (e.g. surface, marine and groundwaters) often associated with humic substances. The evaluation of the importance of colloids in the dissemination of radioactivity necessitates, in particular, the determination of their concentration in the waters sampled on the site, and their characterization (composition, size). In the framework of a general study of the Oklo natural reactor, a complete hydrogeochemical and hydrogeological study is undertaken. Preliminary studies on the colloid content of different water samples from the Oklo reactor area have been performed to complete the study of the groundwater chemistry presented by Toulhoat et al. (1991, 1992). These complementary studies have, as objectives, to evaluate: - the occurrence of colloids by scanning electron microscopy (after u by scanning electron microscopy (after ultrafiltration) and by photon correlation spectroscopy, -the occurrence of organic materials by the analysis of the total organic carbon content. (author). 4 refs., 8 figs

  3. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

    Reed, Mark; Parker, Ronald R.; Forget, Benoit [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)

    2012-06-19

    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.

  5. On the oxidation of uraninite from natural reactor cores

    International Nuclear Information System (INIS)

    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 UO2.25. A significant amount of fourmarierite, Pb(UO2)4O3(OH)4.4H2O, 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

  6. 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)

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

    CERN Document Server

    Tien, J L

    1999-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

    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 natPb and 209Bi relative to 235U and 238U 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 natPb and 209Bi. 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.

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

    CERN Document Server

    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

    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.

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

    CERN Document Server

    Gould, C R; 10.1103/PhysRevC.86.027601

    2012-01-01

    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.

  12. Comparison of the Economic Aspects of the Treatment and Storage of Fission Products from Installations Processing Irradiated Natural Uranium

    International Nuclear Information System (INIS)

    The paper summarizes the main policies adopted for the management of fission product effluents and briefly describes the essential technical features of the stainless steel storage installations (in acid medium) used in France, giving a breakdown of the costs involved. The dependence of these costs on the activity of the solutions stored and on their heat release is shown. The second part of the paper discusses the cost of storage in terms of feasible tank size. The optimum size for such tanks and the rate at which they are placed in service are determined in relation to the characteristics of the fission products to be stored and to the respective capacities of the installations for processing irradiated natural uranium. It is shown that although storage costs depend on the assumptions made regarding the useful life of installations, rates of interest and operating costs, optimum policy decisions (as to size and rate of entry into service) are independent of these assumptions, being determined solely by the variation in the cost of tanks, according to size. These are the factors which enter into the optimized cost of storing these effluents indefinitely. In the third part, this method of indefinite storage is compared with other possibilities of fission product management, e.g. vitrification and separation of Cs and Sr. The paper discusses the economics of the various methods and summarizes some possible long-term solutions. (author)(author)

  13. Statistical nature of neutron activity in the fission of heavy nuclei

    International Nuclear Information System (INIS)

    It is shown that some characteristics of the neutron emission can be explained in the framework of statistical theory, which studies the stability of the ensemble of nuclear fragments and fission neutrons. The theory able to reproduce the known experimental sawtooth-curve of the neutron multiplicity n(A) and allows one to set the total neutron multiplicity as a function of (A, Z) and the excitation energy of the initial nucleus

  14. 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)

  15. Oklo: The fossil nuclear reactors. Physics study - Translation of chapters 6, 13 and conclusions

    International Nuclear Information System (INIS)

    Three parts of the 1991 book 'Oklo: reacteurs nucleaires fossiles. Etude physique' have been translated in this report. The chapters bear the titles 'Study of criticality'(45 p.), 'Some problems with the overall functioning of the reactor zones'(45 p.) and 'Conclusions' (15 p.), respectively

  16. Oklo: The fossil nuclear reactors. Physics study - Translation of chapters 6, 13 and conclusions

    Energy Technology Data Exchange (ETDEWEB)

    Naudet, R. [CEA, Paris (France)

    1996-09-01

    Three parts of the 1991 book `Oklo: reacteurs nucleaires fossiles. Etude physique` have been translated in this report. The chapters bear the titles `Study of criticality`(45 p.), `Some problems with the overall functioning of the reactor zones`(45 p.) and `Conclusions` (15 p.), respectively.

  17. 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 (USiO4.nH2O) and are associated with varying quantities of galena at grain boundaries, within fractures, and within individual grains at intracrystalline locations. Textural evidence suggests multiple periods of uraninite formation. Electron microprobe data are presented for uraninites from RZ-13. Analytical data are discussed for Oklo reactor zical 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.)

  18. Fast fission phenomena

    International Nuclear Information System (INIS)

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

  19. 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)

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

    1999-01-01

    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.

  20. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-12-01

    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.

  2. Speciation of actinides and fission products at smectite rich natural clay-water interface

    International Nuclear Information System (INIS)

    Speciation of actinides (Am(lll), Pu(lV), Np(V)) and long lived fission products, (Cs(l), Sr(II), Tc(VII)) at the interface between smectite rich clay and water has been studied by batch sorption experiments under different experimental conditions of pH, ionic strength and metal ion concentration. Modeling of the sorption data have been used to delineate the mechanism of the sorption of the metal ions on the clay. The study revealed different mechanisms (surface complexation, ion exchange) operating under different pH conditions and for different metal ions. Studies have been extended to diffusion of these radionuclides in the compacted clay to obtain the diffusion coefficient in saturated clay

  3. 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

  4. 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 resn 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

  5. On The Geometric Nature of ``Singlet Fission'' in Certain Crystalline Conjugated Polymers

    Science.gov (United States)

    Rahman, Noah

    2013-03-01

    In recent years, the coherent fission of low-lying singlet electronic excitations in conjugated polymers has attracted interest as a possible way to exceed the Shockley-Queisser limit in organic photovoltaics. Femtosecond spectroscopic and fluorescence measurements of such singlets and the resulting triplets in crystalline anthracene, tetracene and naphthalene reveal curious phenomena associated with certain vibrational modes, such as ultrafast propagation on a timescale inconsistent with conventional intersystem crossing, long-lived electronic coherence, and triplet magnetic anisotropy whose structure is consistent across all three materials. This conflicts with NRG and quantum chemical simulations, which posit isotropic triplets. I explain this by a dynamical Rashba spin-orbit interaction that decays as R-6. This arises from a geometric SU(2) gauge potential generated by a nuclear-motion-induced parametric near-degeneracy of the molecular electronic states. The anisotropy is shown to follow from the work of Affleck and Oshikawa on spin one-half Heisenberg chains. Possible directions for future work are discussed, especially with regard to adiabatic pumping and topological insulators.

  6. 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)

  7. Coulomb fission

    International Nuclear Information System (INIS)

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

  8. Coulomb fission

    Energy Technology Data Exchange (ETDEWEB)

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

    1985-03-01

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

  9. 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)

  10. Natural genetic variation impacts expression levels of coding, non-coding, and antisense transcripts in fission yeast.

    Science.gov (United States)

    Clément-Ziza, Mathieu; Marsellach, Francesc X; Codlin, Sandra; Papadakis, Manos A; Reinhardt, Susanne; Rodríguez-López, María; Martin, Stuart; Marguerat, Samuel; Schmidt, Alexander; Lee, Eunhye; Workman, Christopher T; Bähler, Jürg; Beyer, Andreas

    2014-01-01

    Our current understanding of how natural genetic variation affects gene expression beyond well-annotated coding genes is still limited. The use of deep sequencing technologies for the study of expression quantitative trait loci (eQTLs) has the potential to close this gap. Here, we generated the first recombinant strain library for fission yeast and conducted an RNA-seq-based QTL study of the coding, non-coding, and antisense transcriptomes. We show that the frequency of distal effects (trans-eQTLs) greatly exceeds the number of local effects (cis-eQTLs) and that non-coding RNAs are as likely to be affected by eQTLs as protein-coding RNAs. We identified a genetic variation of swc5 that modifies the levels of 871 RNAs, with effects on both sense and antisense transcription, and show that this effect most likely goes through a compromised deposition of the histone variant H2A.Z. The strains, methods, and datasets generated here provide a rich resource for future studies. PMID:25432776

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

    International Nuclear Information System (INIS)

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

  12. A small flat fission chamber

    International Nuclear Information System (INIS)

    With fission materials of depleted uranium, natural uranium, enriched uranium, 239Pu, and 237Np, the authors have designed and made a series of small flat fission chamber. The authors narrated the construction of the fission chamber and its technological process of manufacture, and furthermore, the authors have measured and discussed the follow correct factor, self-absorption, boundary effect, threshold loss factor, bottom scatter and or so

  13. Sorption of {sup 239}Np and {sup 235}U fission products by zeolite Y, Mexican natural erionite, and bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Olguin, M.T.; Solache, M.; Iturbe, J.L. [Instituto Nacional de Investigaciones Nucleares, C.P. (Mexico)]|[Universidad Autonoma Metropolitana, C.P. (Mexico)] [and others

    1996-09-01

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

  14. The topography of the nuclear fission barrier

    International Nuclear Information System (INIS)

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

  15. 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

  16. Measurements of the spallation and fission product production for depleted uranium and natural lead targets bombarded by 1100 MeV protons

    International Nuclear Information System (INIS)

    In order to simulate the spallation source target, 3 cm diameter by 1 mm thick disks of natural lead and depleted uranium were irradiated at 1100 MeV proton energy. The targets were inbedded between 5 cm thick bricks of the respective material. Gamma-ray spectrometric methods of gamma-peak and halflife analysis were developed to deduce mass yield distributions of the radionuclides produced. Both for lead and uranium fission products have been observed. The mass yield distributions and axial distributions of some isotopes are given. For lead the total production rates of some isotopes with a 100 x 50 x 450 mm target block are given

  17. Fission isomers

    International Nuclear Information System (INIS)

    After a short historical account of superdeformed nuclei which are able to de-excite by spontaneous fission (hence their name of fission isomers) the principles of different experimental set-ups are described. These set-ups were used to study various properties: half-life, excitation energy, spin, gyromagnetic factor, moment of inertia and quadrupole moment. The most significant values are given. Finally, the question of the various types of excited states of fission isomers is tackled. (author) 20 refs.; 17 figs

  18. Contribution of lead and thorium to the history of the Oklo reactors

    International Nuclear Information System (INIS)

    The authors report the results of measuring lead and thorium in a series of representative samples of the superconcentrations of uranium found in the Oklo mineralization. Interpretation of the data reveals the complexity of the history of lead in the deposit, but makes it possible to derive a number of important facts, namely early disturbance and recent, massive remobilization of lead. One is led to conclude that the date of the uranium emplacement may be greater than 1900 million years. The absence of high thorium contents in the ''normal'' rich ore confirms the importance of dating the nuclear reaction on the basis of the Th/U balance. This determination, which draws on the same set of data as for the Nd/U balance, gives a mean value close to 1930 million years. (author)

  19. Lead and thorium contribution to the history of the Oklo fossil reactor

    International Nuclear Information System (INIS)

    Results of lead and thorium measurement on a line of samples representative of uraniferous overconcentrations found in Oklo mineralization are presented. Interpretation of these data shows the complexity of lead history in the deposit but some important facts like an ancient perturbation, a new and massive lead remobilization are coming out. These results lead to the conclusion that age of uranium could be over 1900 million years. Absence of important thorium content in the 'normal' high-grade ore confirm the interest of date determination of nuclear reaction from the balance Th/U. This determination using the same data that for the balance Nd/U gives about the same mean value 1,93 million years

  20. New fission modes

    International Nuclear Information System (INIS)

    Fission approach to the cluster radioactivities and ?-decay has been systematically developed during the last two decades. One has to stress the quantum nature of these decay modes and of the fission process as well. The three groups of binary phenomena are taking place by tunneling through a potential barrier. A more complex phenomenon, the ternary fission, was observed since 1946 both in neutron-induced and spontaneous fission. Several such processes, in which the charged particle is a proton, deuteron, triton, 3-6,8 He, 6-11 Li, 7-14 Be, 10-17 B, 13-18 C, 15-20 N, 15-22 O, have been detected. A very powerful technique, based on the fragment identification by using triple ? coincidences in the large arrays of Ge-detectors, like GAMMASPHERE, was employed to discover new characteristics of the fission process, and new decay modes (emission of an alpha particle and of 10 Be, accompanying the cold fission of 252 Cf, the double fine structure, and the triple fine structure in binary and ternary fission, respectively). The possibility of a whole family of new decay modes, the multi-cluster accompanied fission, was recently envisaged. Besides fissioning into two or three fragments, a heavy or superheavy nucleus spontaneously breaks into four, five or six nuclei of which two are asymmetric or symmetric heavy fragments and the others are light clusters, e.g. ?-particles, 10 Be, 14 C, 20 O, or combinations of them. Examples were presented for the two-, three- and four cluster accompanied cold fission of 252 Cf and 262 Rf, in which the emitted clusters are: 2?, ? + 6 He, ? + 10 Be, ? + 14 C, 3?, ? + 6 He + 10 Be, 2? + 6 He, 2? + 8 Be, 2? + 14 C, and 4?. The strong shell effect corresponding to the doubly magic heavy fragment 132 Sn was emphasized. From the analysis of different configurations of fragments in touch, we concluded that the most favorable mechanism of such a decay mode should be the cluster emission from an elongated neck formed between the two heavy fragments. The fact that the potential barrier height is lower, suggests that in a competition between aligned and compact configurations, the former should prevail. This idea is further exploited by suggesting a formation mechanism of the touching configuration, based on a three-center phenomenological model. able to explain the difference in the observed yield of a particle-accompanied fission and that of binary fission. It is derived from the Myers-Swiatecki's liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment is obtained by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. During the first stage of the deformation one has a two-center evolution until the neck radius becomes equal to the radius of the emitted particle. Then the three center starts developing by decreasing with the same amount the two tip distances. In such a way a second minimum, typical for a cluster molecule, appears in the deformation energy. An example is presented for 252 Cf parent nucleus emitting 10 Be and a heavy fragment 132 Sn. The corresponding deformation energy for the binary cold fission of the same nucleus is also shown. We would like to stress two striking features. Besides the first ground state minimum, there is a second minimum, proving the nuclear molecular character of the aligned configuration of three fragments in touch. On the second hand, by comparing the surface areas under the deformation energy curves of the binary and ternary processes, one can see the difference, which can qualitatively explain the difference in yield of the binary and ternary cold fission. (authors)

  1. Ternary fission and cluster radioactivities

    CERN Document Server

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

    2002-01-01

    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)

  2. Benchmarking Nuclear Fission Theory

    CERN Document Server

    Bertsch, G F; Nazarewicz, W; Talou, P

    2015-01-01

    We suggest a small set of fission observables to be used as test cases for validation of theoretical calculations. The purpose is to provide common data to facilitate the comparison of different fission theories and models. The proposed observables are chosen from fission barriers, spontaneous fission lifetimes, fission yield characteristics, and fission isomer excitation energies.

  3. Monte Carlo Based Toy Model for Fission Process

    OpenAIRE

    Kurniadi, R.; Waris, A.; Viridi, S.

    2014-01-01

    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...

  4. Fission dynamics within time-dependent Hartree-Fock: deformation-induced fission

    CERN Document Server

    Goddard, P M; Rios, A

    2015-01-01

    Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide $^{240}$Pu as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate non-adiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the ...

  5. Calculations of fission rates for r-process nucleosynthesis

    CERN Document Server

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

    2005-01-01

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

  6. Fission meter

    Science.gov (United States)

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

    2012-04-10

    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.

  7. Fission isomers

    International Nuclear Information System (INIS)

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

  8. 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.)

  9. g-factor measurements of fission isomers

    International Nuclear Information System (INIS)

    The current status of g-factor measurements of fission isomers is reviewed. In particular, the authors concentrate on magnetic and electric extranuclear perturbations affecting the fission isomers in solid environments. Recent results for isomers in 237Pu and 239Am are summarized and the single particle nature of these states is discussed. (Auth.)

  10. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Pedersen, K. [ed.

    1996-02-01

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

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

    International Nuclear Information System (INIS)

    This report describes how microorganisms, colloids and organic matter were sampled from groundwater from six boreholes at the Bangombe site in the Oklo region and subsequently analyzed. For analysis of microorganisms, DNA was extracted from groundwater, amplified and cloned and information available in the ribosomal 16S rRNA gene was used for mapping diversity and distribution of bacteria. Each borehole was dominated by species that did not dominate in any of the other boreholes, a result that probably reflects documented differences in the geochemical environment. Analyses of sampled colloids included SEM and ICP-MS analysis of colloids on membrane and single particle analysis of samples in bottles. The colloid concentration was rather low in these Na-Mg-Ca-HCO3 type waters. Trace element results show that transition metals and some heavy metals are associated with the colloid phase. Distribution coefficients of trace elements between the water and colloid phases were estimated. For example for uranium, an average of 200 pg/ml was detected in the water, and 40 pg/ml was detected in the colloid phase. A Kp value of 2* 106 ml/g was calculated, considering (colloid) = 100 ng/ml. Groundwater samples were collected for analysis of the concentration of organic carbon (TOC), humic substances and metals associated with the humic substances. TOC varied in the range 4-14 mg/l in three boreholes, one borehole had a TOC<1.5 mg/l. The metal speciation study indicated that a large fraction, 8-67% of uranium was bound to the humic matter compared to the fractions of Ca and Fe (<0.4% and 0.02-10%, resp.). 60 refs, 8 figs, 16 tabs

  13. Fission theory and actinide fission data

    Energy Technology Data Exchange (ETDEWEB)

    Michaudon, A.

    1975-06-01

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

  14. Fission theory and actinide fission data

    International Nuclear Information System (INIS)

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

  15. Radiochemical studies on fission

    Energy Technology Data Exchange (ETDEWEB)

    None

    1973-07-01

    Research progress is reported on nuclear chemistry; topics considered include: recoil range and kinetic energy distribution in the thermal neutron ftssion of /sup 245/Cm; mass distribution and recoil range measurements in the reactor neutron-induced fission of /sup 232/U; fission yields in the thermal neutron fission of /sup 241/PU highly asymmetric binary fission of uranium induced by reactor neutrons; and nuclear charge distribution in low energy fission. ( DHM)

  16. g-factor measurements of fission isomers

    International Nuclear Information System (INIS)

    The current status of g-factor measurements of fission isomers is reviewed. Recent results for isomers in 237Pu and 239Am are summarized and the single particle nature of these states is discussed. (author)

  17. Seminar on Fission VI

    Science.gov (United States)

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

    2008-04-01

    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.

  18. Thorium-uranium fission radiography

    Science.gov (United States)

    Haines, E. L.; Weiss, J. R.; Burnett, D. S.; Woolum, D. S.

    1976-01-01

    Results are described for studies designed to develop routine methods for in-situ measurement of the abundance of Th and U on a microscale in heterogeneous samples, especially rocks, using the secondary high-energy neutron flux developed when the 650 MeV proton beam of an accelerator is stopped in a 42 x 42 cm diam Cu cylinder. Irradiations were performed at three different locations in a rabbit tube in the beam stop area, and thick metal foils of Bi, Th, and natural U as well as polished silicate glasses of known U and Th contents were used as targets and were placed in contact with mica which served as a fission track detector. In many cases both bare and Cd-covered detectors were exposed. The exposed mica samples were etched in 48% HF and the fission tracks counted by conventional transmitted light microscopy. Relative fission cross sections are examined, along with absolute Th track production rates, interaction tracks, and a comparison of measured and calculated fission rates. The practicality of fast neutron radiography revealed by experiments to data is discussed primarily for Th/U measurements, and mixtures of other fissionable nuclei are briefly considered.

  19. Energy released in fission

    International Nuclear Information System (INIS)

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

  20. Synthesis report on the relevant diffusion coefficients of fission products and helium in spent nuclear fuels

    International Nuclear Information System (INIS)

    This document corresponds to the deliverable D2 of the Work Package 1 of the 'Spent Fuel Stability under repository conditions' (SFS) European project. It constitutes a synthesis report on relevant diffusion coefficients of fission products and helium in spent nuclear fuels at high and low temperatures. Coefficients corresponding to thermally activated diffusion were reviewed from literature data for O, U (self-diffusion coefficients), fission gases and other fission products. Data showed that thermal diffusion was irrelevant at temperatures expected in repository conditions. The occurrence of diffusion enhanced by alpha self-irradiation was studied through different theoretical approaches. A 'best estimate' value of the alpha self-irradiation diffusion coefficient, D (m2.s-1), is proposed. It is extrapolated from enhanced diffusion under irradiation observed in reactor and would be proportional to the volume alpha activity in the spent nuclear fuel, Av (Bq.m-3) as: D/Av ? 2.10-41 (m5)The migration of stable Pb in Oklo's uraninites was studied in order to validate the proposed diffusion coefficient. The obtained value is one order of magnitude higher than the theoretical proposed value. As for He behaviour in spent nuclear fuel, a few data are today available in open literature. The document will be completed as soon as new experimental results are available. (authors)

  1. 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

  2. Fifty years of nuclear fission: Nuclear data and measurements series

    Energy Technology Data Exchange (ETDEWEB)

    Lynn, J.E.

    1989-06-01

    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.

  3. Excitation-energy dependence of the nuclear fission characteristics

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-03-01

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

  4. Fragment angular distributions in fission and fission like reactions

    International Nuclear Information System (INIS)

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

  5. ChemTeacher: Fission

    Science.gov (United States)

    2011-01-01

    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.

  6. Geometry of membrane fission.

    Science.gov (United States)

    Frolov, Vadim A; Escalada, Artur; Akimov, Sergey A; Shnyrova, Anna V

    2015-01-01

    Cellular membranes define the functional geometry of intracellular space. Formation of new membrane compartments and maintenance of complex organelles require division and disconnection of cellular membranes, a process termed membrane fission. Peripheral membrane proteins generally control membrane remodeling during fission. Local membrane stresses, reflecting molecular geometry of membrane-interacting parts of these proteins, sum up to produce the key membrane geometries of fission: the saddle-shaped neck and hour-glass hemifission intermediate. Here, we review the fundamental principles behind the translation of molecular geometry into membrane shape and topology during fission. We emphasize the central role the membrane insertion of specialized protein domains plays in orchestrating fission in vitro and in cells. We further compare individual to synergistic action of the membrane insertion during fission mediated by individual protein species, proteins complexes or membrane domains. Finally, we describe how local geometry of fission intermediates defines the functional design of the protein complexes catalyzing fission of cellular membranes. PMID:25062896

  7. Physics and chemistry of fission

    International Nuclear Information System (INIS)

    Full text: In the pleasant and hospitable atmosphere of the Kernforschungsanlage Juelich in the Federal Republic of Germany, the IAEA symposium on the Physics and Chemistry of Fission took place. Almost 200 scientists attended, 154 abstracts were submitted, and 57 papers presented, but more important than the numbers was the quality of the contributions and the progress reported at the symposium. The neutron was discovered almost 50 years ago; 40 years ago the idea of nuclear fission was born. Since then, a number of laboratories have worked hard to explain the phenomenon of fission One would expect that by now scientists would know exactly what happens in a nucleus before and during the process of fission, particularly as there are hundreds of power and research reactors in operation, and fission of uranium isotopes is the basis of their functioning. At first glance, fission seems a simple process: a neutron hits and penetrates the uranium nucleus which becomes excited, i.e. has a surplus of energy. One way to get rid of this energy is for the nucleus to split into two parts; additional products of this process are energy and more neutrons. Nature, however, seems to dislike such straightforward explanations. In the case of fission, scientists have observed a number of phenomena which disagree with a simple model. Sometimes, a nucleus will split into two parts without being 'attacked' by a neutron; this spontaneous fission opens up a new line of fission research and sns up a new line of fission research and several contributions at the symposium reported on sophisticated experiments designed to unravel some of its specific details. Sometimes, a fissioning nucleus will emit another particle: ternary fission has become a powerful tool for studying the properties of nuclei during the fission process. For the scientist, it is fascinating to observe how the nucleus behaves during fission. They invent models which are supposed to reproduce the most probable course of events leading to fission. In one of these models, the nucleus is imagined to be a very small drop of liquid; the theorist then devises many schemes that lead to its splitting into two smaller drops. It is surprising how many detailed features theorists can predict, based on such simple models, and how well these predictions have been confirmed by experiments. The symposium summarized the progress in this field, and indicated how many intricate details can be introduced into a simple liquid drop model to give better agreement with experimental results. Step by step, a picture is emerging and being continuously improved, coming closer and closer to the truth. However, the liquid drop model has several competitors of which the most prominent is the shell model. This model assumes that the constituents of the nucleus are sorted into well defined energy levels, or shells; the distribution of protons and neutrons in these shells, and their movements from one shell to another, can provide an explanation for many experimentally observed facts New theoretical results drawn from these models were reported at the symposium, together with some efforts to combine different theoretical concepts, thereby trying to create a unified picture of nuclear fission. The nucleus is too small for the scientist to be able to observe directly what is happening inside it. There is really only one way for an experimenter to study a process in a nucleus, he must measure the energies of the particles coming out of it. In the case of fission, these 'messengers' can be the fission fragments, i.e. nuclei of elements that are being created from the splitting atom, but they can also be the neutrons or gamma rays which emerge during and after the fission process. Several sessions in the symposium were devoted to reports of such studies. With the help of sophisticated electronics systems, or complicated radiochemical methods, experimenters have measured the energies of fission fragments, neutrons, gamma and X-rays, and other particles emerging from fissioning nuclei, with great accuracy. By putting t

  8. Activation Energy for Fission

    Energy Technology Data Exchange (ETDEWEB)

    Seaborg, Glenn T.

    1952-08-29

    The experimentally determined exponential dependence of spontaneous fission rate on Z{sup 2}/A has been used to derive an expression for the dependence of the fission activation energy on Z{sup 2}/A. This expression has been used to calculate the activation energy for slow neutron induced fission and photofission. The correlation with the experimental data on these types of fission seems to be quite good.

  9. Fission Research at IRMM

    Directory of Open Access Journals (Sweden)

    Al-Adili A.

    2010-03-01

    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.

  10. Dynamics of Coulomb fission

    OpenAIRE

    Kruse, Hans; Pinkston, W. T.; Greiner, Walter; Oberacker, Volker

    2006-01-01

    A general formalism is described for the treatment of Coulomb fission, within the framework of the semiquantal theory. We develop a model for the fission probabilities of levels excited in Coulomb excitation. This model contains penetration of the double-humped fission barrier, competition from gamma and neutron emission, and the spreading of the collective states into noncollective compound states. For 74184W + 92238U, the fission probability at ?c.m.=180° is increased by a factor of 3...

  11. Optical studies of fission tracks in apatite

    International Nuclear Information System (INIS)

    Fossil fission track damage in natural fluorapatite has been studied by absorption spectroscopy. It was found that for samples cut perpendicular to the c-axis, the dominant annealing process for the absorbing defects (identified as H(II)centers) is, in the early stage of annealing, diffusion to the sample surface with a measured diffusion coefficient of D = (1.2 +- 0.4) x 10-9 cm2 s-1 (at T = 673 K). In addition, we have also studied the properties of freshly induced fission tracks with the aim of using optical absorption detection to develop an alternative fission track dating method. (author)

  12. Binary fission in damped rotating polytropes

    International Nuclear Information System (INIS)

    The fission sequences of Gingold and Monaghan are recomputed using a significantly larger number (800) of particles in the smoothed-particle-hydrodynamic treatment. The results confirm the general mode of fission found earlier for polytropes with n = 0.5. An interesting three-pointed 'star fish' structure is now apparent before fission and a low-mass third object is formed. The nature of the disruption of n = 1.5 polytropes is clarified and discussed in relation to the problem of binary star formation. (author)

  13. Boron shield effect on neutron fission chambers

    International Nuclear Information System (INIS)

    The contribution to signal of fission chamber with natural uranium stemming from 238U and 235U according to the thickness of boron screen is analyzed. Estimations of the 239Pu accumulation and 238U burnup are performed using group cross sections of the 238U capture, cross sections of the 238U and 239Pu fission, as well as obtained group values Ta(E)?E/E. It is shown that in lack of boron screen under the fluence of thermal neutrons 1017 cm-2 because of the 239Pu formation the increase of sensitivity of the fission chamber with natural uranium takes place. Application of the boron screen (? = 1 g/cm2) allows to save stability of sensitivity of the fission chamber up to fluence of thermal neutrons 5 x 1022 cm-2

  14. The Fission Vision

    Science.gov (United States)

    Joy Hakim

    2007-08-17

    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.

  15. Numerical Simulations of Fission

    Science.gov (United States)

    Durisen, Richard H.; Gingold, Robert A.

    1987-01-01

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

  16. Fission neutron statistical emission

    International Nuclear Information System (INIS)

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

  17. Modernizing the Fission Basis

    Science.gov (United States)

    Bhatia, C.; Fallin, B.; Howell, C.; Tornow, W.; Gooden, M.; Kelley, J.; Arnold, C.; Bond, E.; Bredeweg, T.; Fowler, M.; Moody, W.; Rundberg, R.; Rusev, G.; Vieira, D.; Wilhemy, J.; Becker, J.; Macri, R.; Ryan, C.; Sheets, S.; Stoyer, M.; Tonchev, A.

    2012-10-01

    A recent Fission Product Review Panel study has identified important issues associated with the possible neutron energy dependence of the fission product isotope ^147Nd. As a result, we initiated a program at TUNL to obtain high-precision and self-consistent data for the energy dependence of fission product yields in the 1 to 15 MeV energy range. Three dual fission ionization chambers dedicated to ^235U, ^238U, and ^239Pu thick target foils and thin monitor foils, respectively, were exposed to neutron beams produced via the reactions ^2H(d,n)^3He and ^3H(d,n)^4He. After irradiation, the characteristic ? rays from specific fission products were recorded over a period of many weeks using HPGe detectors in a low-background environment. Results for the yield of seven fission isotopes obtained at 4.6, 9.0 and 14.8 MeV are reported.

  18. Is channeling of fission tracks taking place?

    CERN Document Server

    Yada, K

    1999-01-01

    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.

  19. Synthesis report on the relevant diffusion coefficients of fission products and helium in spent nuclear fuels; Rapport de synthese sur les coefficients de diffusion des produits de fission et de l'helium dans le combustible irradie

    Energy Technology Data Exchange (ETDEWEB)

    Lovera, P.; Ferry, C.; Poinssot, Ch. [CEA Saclay, Dept. de Physico-Chimie (DPC), 91 - Gif sur Yvette (France); Johnson, L. [Nagra, Baden (Switzerland)

    2003-07-01

    This document corresponds to the deliverable D2 of the Work Package 1 of the 'Spent Fuel Stability under repository conditions' (SFS) European project. It constitutes a synthesis report on relevant diffusion coefficients of fission products and helium in spent nuclear fuels at high and low temperatures. Coefficients corresponding to thermally activated diffusion were reviewed from literature data for O, U (self-diffusion coefficients), fission gases and other fission products. Data showed that thermal diffusion was irrelevant at temperatures expected in repository conditions. The occurrence of diffusion enhanced by alpha self-irradiation was studied through different theoretical approaches. A 'best estimate' value of the alpha self-irradiation diffusion coefficient, D (m{sup 2}.s{sup -1}), is proposed. It is extrapolated from enhanced diffusion under irradiation observed in reactor and would be proportional to the volume alpha activity in the spent nuclear fuel, A{sub v} (Bq.m{sup -3}) as: D/A{sub v} {approx_equal} 2.10{sup -41} (m{sup 5})The migration of stable Pb in Oklo's uraninites was studied in order to validate the proposed diffusion coefficient. The obtained value is one order of magnitude higher than the theoretical proposed value. As for He behaviour in spent nuclear fuel, a few data are today available in open literature. The document will be completed as soon as new experimental results are available. (authors)

  20. Status of geological studies undertaken in France on the Oklo deposit since the Libreville Symposium

    International Nuclear Information System (INIS)

    The questions posed since the Libreville symposium can be grouped under four headings: origin of the deposits and the over-concentrations; degree of burial reached by the series; temperatures attained during the reactions, and effects of the reactions; perturbations subsequent to the reactions. These questions have been the subject of multidisciplinary investigations, including conventional petrographic and mineralogical investigations (Cogema, Fontenay-aux-Roses and the Centre for Sedimentology and Geochemistry of the Surface, Strasbourg), a study of fluid inclusions (Centre for Petrographic and Geochemical Research, Nancy), studies of organic material (French Institute of Petroleum, Rueil, and Cerchar, Verneuil-en-Halatte) and a study of fission traces (Rene Barnas Laboratory, Orsay). (author)

  1. Xenon and krypton isotopic anomalies in a natural nuclear reactor and at the epicenter of a nuclear explosion

    International Nuclear Information System (INIS)

    The purpose of this work was to investigate the possibility of the appearance of Xe and Kr isotopic anomalies in a natural reactor owing to migration processes. Four objects of study were used. The first was a soil sample from the crater formed by the first atomic bomb in Alamagordo, New Mexico, in 1945. The second sample consisted of standard uranium resin circa 130 million years old. The third object consisted of samples of uranium black and the fourth object consisted of samples of uranium resins Nos. 1470 and 1348 from the natural reactor in large ore lenses of the Oklo uranium deposit. Isotope ratios from stepwise and thermal annealing, unirradiated as well as irradiated with neutrons, and subjected to strong heating or melting in rock, were determined. The migratory mechanism was found to operate in the natural nuclear reactor in the Oklo uranium deposit

  2. Intermediate energy nuclear fission

    International Nuclear Information System (INIS)

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

  3. Fission product yields

    International Nuclear Information System (INIS)

    Data are summed up necessary for determining the yields of individual fission products from different fissionable nuclides. Fractional independent yields, cumulative and isobaric yields are presented here for the thermal fission of 235U, 239Pu, 241Pu and for fast fission (approximately 1 MeV) of 235U, 238U, 239Pu, 241Pu; these values are included into the 5th version of the YIELDS library, supplementing the BIBFP library. A comparison is made of experimental data and possible improvements of calculational methods are suggested. (author)

  4. Preliminary results utilizing high-energy fission product ?-rays to detect fissionable material in cargo

    International Nuclear Information System (INIS)

    A concept for detecting the presence of special nuclear material (235U or 239Pu) concealed in intermodal cargo containers is described. It is based on interrogation with a pulsed beam of 7 MeV neutrons that produce fission events and their ?-delayed neutron emission or ?-delayed high-energy ? radiation between beam pulses provide the detection signature. Fission product ?-delayed ?-rays above 3 MeV are nearly 10 times more abundant than ?-delayed neutrons and are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified

  5. Muon-induced fission

    International Nuclear Information System (INIS)

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

  6. 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)

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Zhou, Z.; Yang, Y.; Xu, H.

    2011-10-01

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

  9. Isomers in Fission Fragments

    Science.gov (United States)

    Urban, W.; Faust, H.; Jentschel, M.; Köster, U.; Krempel, J.; Materna, Th.; Mutti, P.; Soldner, T.; Genevey, J.; Pinston, J. A.; Simpson, G.; Rz?ca-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

    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.

  10. Isomers in Fission Fragments

    International Nuclear Information System (INIS)

    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.

  11. 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

  12. Fission Systems for Mars Exploration

    Science.gov (United States)

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

    2012-01-01

    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.

  13. 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

  14. Evaluation of fission yields

    International Nuclear Information System (INIS)

    Taking 135Xe produced by neutron induced fission of 235U as an example, the evaluation method for fission yield was introduced using the all experimental data available. The evaluation procedure includes the experimental data collection, correction, evaluation, error assessment and data analysis. The study of the uncertainty covariance, application of semi-empirical theoretical calculation and the yield energy-dependence of 135Xe in the incident energy range 0?20 MeV were emphasized in this work. (authors)

  15. Review of Fission Theory

    International Nuclear Information System (INIS)

    A survey of the present state of fission theory is attempted. The basic requirements of a theory of a physical process are outlined and against this background the state of fission theory is summarized, with special emphasis on developments in the past few years. An attempt is made to bring out the most important outstanding problems to be settled by future experiments and theory. (author)

  16. Characteristics of Coulomb fission

    OpenAIRE

    Oberacker, Volker; Greiner, Walter; Kruse, Hans; Pinkston, William T.

    2006-01-01

    Within an extended semiquantal theory we perform large-sized coupled-channel calculations involving 260 collective levels for Coulomb fission of 238U. Differential Coulomb fission cross sections are studied as a function of bombarding energy and impact parameter for several projectiles. In the Xe + U case, total cross sections are also given. We find a strong dependence on projectile charge number, PCF(180°)?(Zp)6 in the region 50?Zp?92 for a fixed ratio E/ECoul, which migh...

  17. Induction of nuclear fission by high-voltage application

    OpenAIRE

    Maruyama, Hirokazu

    2007-01-01

    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 kine...

  18. Singlet exciton fission photovoltaics.

    Science.gov (United States)

    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

    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

  19. 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)

  20. Potentials of fissioning plasmas

    International Nuclear Information System (INIS)

    Successful experiments with the nuclear pumping of lasers have demonstrated that in gaseous medium the kinetic energy of fission fragments can be converted directly into non-equilibrium optical radiation. This confirms the concept that the fissioning medium in a gas-phase nuclear reactor shows an internal structure such as a plasma in nearly thermal equilibrium varying up to a state of extreme-non-equilibrium. The accompanying variations of temperatures, pressure and radiative spectrum suggest wide ranges of applications. For example, in the gas-phase fission reactor concept enriched uranium hexafluoride or an uranium plasma replaces conventional fuel elements and permits operation above the melting point of solid materials. This potential has been motivation for the US National Aeronautics and Space Administration (NASA) to conduct relevant research for high specific impulse propulsion in space. The need to separate the high temperature gaseous fuel from the surfaces of a containing vessel and to protect them against thermal radiation has led to the concept of an externally moderated reactor in which the fissioning gaseous material is suspended by fluid dynamic means and the flow of opaque buffer gas removes the power. The gaseous nuclear fuel can slowly be circulated through the reactor for continuous on-site reprocessing including the annihilation of transuranium actinides at fission when being fed back into the reactor. An equilibrium of the generation and destruc equilibrium of the generation and destruction of such actinides at fission when being fed back into the reactor. An equilibrium of the generation and destruction of such actinides can thus be achieved. These characteristics and the unique radiative properties led to the expectation that the gas-phase fission reactor could feature improved safety, safeguarding and economy, in addition to new technologies such as processing, photochemistry and the transmission of power over large distances in space

  1. 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

  2. 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

  3. Potentials of fissioning plasmas

    Science.gov (United States)

    Thom, K.

    1979-01-01

    Successful experiments with the nuclear pumping of lasers have demonstrated that in a gaseous medium the kinetic energy of fission fragments can be converted directly into nonequilibrium optical radiation. This confirms the concept that the fissioning medium in a gas-phase nuclear reactor shows an internal structure such as a plasma in near thermal equilibrium varying up to a state of extreme nonequilibrium. During 20 years of research under NASA support major elements of the fissioning plasma reactor were demonstrated in theory and experiment, culminating in a proof-of-principle reactor test conducted at the Los Alamos Scientific Laboratory. It is concluded that the construction of a gaseous fuel reactor power plant is within the reach of present technology.

  4. Fission in sea anemones: integrative studies of life cycle evolution.

    Science.gov (United States)

    Geller, Jonathan B; Fitzgerald, Laurie J; King, Chad E

    2005-08-01

    Sea anemones (Phylum Cnidaria; Class Anthozoa, Order Actiniaria) exhibit a diversity of developmental patterns that include cloning by fission. Because natural histories of clonal and aclonal sea anemones are quite different, the gain and loss of fission is an important feature of actiniarian lineages. We have used mitochondrial DNA and nuclear intron DNA phylogenies to investigate the evolution of longitudinal fission in sixteen species in the genus Anthopleura, and reconstructed an aclonal ancestor that has given rise at least four times to clonal descendents. For A. elegantissima from the northeastern Pacific Ocean, a transition to clonality by fission was associated with an up-shore habitat shift, supporting prior hypotheses that clonal growth is an adaptation to the upper shore. Fission in Actiniaria likely precedes its advent in Anthopleura, and its repeated loss and gain is perplexing. Field studies of the acontiate sea anemone Aiptasia californica provided insight to the mechanisms that regulate fission: subtidal Aiptasia responded to experimentally destabilized substrata by increasing rates of pedal laceration. We put forth a general hypothesis for actiniarian fission in which sustained tissue stretch (a consequence of substratum instability or intrinsic behavior) induces tissue degradation, which in turn induces regeneration. The gain and loss of fission in Anthopleura lineages may only require the gain and loss of some form of stretching behavior. In this view, tissue stretch initiates a cascade of developmental events without requiring complex gene regulatory linkages. PMID:21676808

  5. Mirror fusion--fission hybrids

    Energy Technology Data Exchange (ETDEWEB)

    Lee, J.D.

    1978-05-01

    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.

  6. Fission gas measuring technology

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  7. Fission gas measuring technology

    International Nuclear Information System (INIS)

    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

  8. Fission fragment angular distributions

    International Nuclear Information System (INIS)

    Many recent papers have found that calculations with the standard angular distribution formula for fission fragments from compound nuclei do not reproduce the strong anisotropies observed in the decay of high spin systems. They conclude that a noncompound nuclear process must exist for some partial waves and postulate an ad-hoc angular distribution for this process in order to reproduce the strong anisotropies. It is the purpose of this contribtion to demonstrate that much of the data are, in fact, consistent with compound nucleus formation and to emphasize that the standard model is not a generally valid way to calculate fission fragment angular distributions from a compound nucleus

  9. Uncertainties in nuclear fission data

    Science.gov (United States)

    Talou, Patrick; Kawano, Toshihiko; Chadwick, Mark B.; Neudecker, Denise; Rising, Michael E.

    2015-03-01

    We review the current status of our knowledge of nuclear fission data, and quantify uncertainties related to each fission observable whenever possible. We also discuss the roles that theory and experiment play in reducing those uncertainties, contributing to the improvement of our fundamental understanding of the nuclear fission process as well as of evaluated nuclear data libraries used in nuclear applications.

  10. 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 each laboratories efforts, a brief summary of yield measurement activities by fissioning nuclide is presented. A new fast reactor fission yield measurement program being conducted in the U.S. is described

  11. Microscopic Description of Induced Fission

    OpenAIRE

    Schunck, N.

    2013-01-01

    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.

  12. Fission fragment transport effects on heat transfer in fissioning gases

    International Nuclear Information System (INIS)

    This paper discusses direct energy transfer by fission fragments near the wall of a cavity containing fissioning gas studied in plane and cylindrical geometries. Analytical formulas are derived for the fission fragment energy flux. Heat transfer equations are solved for optically thick fissioning gases by taking into account the fission fragment energy transport effect. The results are applied to a heat transfer analysis of the fuel assemblies of a heterogeneous gas core reactor. The energy transfer mechanism in the fissioning gas is essentially nonlinear. Thus, the cooling effect due to direct fission fragment energy loss to the container walls does not become significant until the stopping range considerably exceeds the characteristic dimensions of the container

  13. 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

  14. 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.)

  15. 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)

  16. Nuclear fission and multifragmentation

    International Nuclear Information System (INIS)

    The many-body nuclear decay known as multifragmentation is considered as a process competing with nuclear fission. It is shown that, in the particular case of disintegration of 238U by relativistic protons, the two processes occur simultaneously in the same nuclear reaction. 5 refs., 5 figs

  17. A threshold for dissipative fission

    International Nuclear Information System (INIS)

    The empirical domain of validity of statistical theory is examined as applied to fission data on pre-fission data on pre-fission neutron, charged particle, and ?-ray multiplicities. Systematics are found of the threshold excitation energy for the appearance of nonstatistical fission. From the data on systems with not too high fissility, the relevant phenomenological parameter is the ratio of the threshold temperature Tthresh to the (temperature-dependent) fission barrier height EBar(T). The statistical model reproduces the data for Tthresh/EBar(T) thresh/EBar(T) independent of mass and fissility of the systems

  18. Modulation of intestinal crypt fission in the rat

    International Nuclear Information System (INIS)

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

  19. Propagation of a constant velocity fission wave

    Science.gov (United States)

    Deinert, Mark

    2011-10-01

    The ideal nuclear fuel cycle would require no enrichment, minimize the need fresh uranium, and produce few, if any, transuranic elements. Importantly, the latter goal would be met without the reprocessing. For purely physical reasons, no reactor system or fuel cycle can meet all of these objectives. However, a traveling-wave reactor, if feasible, could come remarkably close. The concept is simple: a large cylinder of natural (or depleted) uranium is subjected to a fast neutron source at one end, the neutrons would transmute the uranium downstream and produce plutonium. If the conditions were right, a self-sustaining fission wave would form, producing yet more neutrons which would breed more plutonium and leave behind little more than short-lived fission products. Numerical studies have shown that fission waves of this type are also possible. We have derived an exact solution for the propagation velocity of a fission wave through fertile material. The results show that these waves fall into a class of traveling wave phenomena that have been encountered in other systems. The solution places a strict conditions on the shapes of the flux, diffusive, and reactive profiles that would be required for such a phenomenon to persist. The results are confirmed numerically.

  20. 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 La140140 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)

  1. Condensed fission products

    International Nuclear Information System (INIS)

    It is presented a method to calculate cross sections of condensed fission product. The group constants are generated by NJOY code, from ENDF/B-V and JENDL-1 data. Cross section of 28 nuclides were grouped with the RRB fast reactor characteristics. To verify the time, number of PF and influence of fuel composition, the one energy group calculation for a fast reactor of 1000/MWE were done. (M.C.K.)

  2. Ternary fission of neutron induced uranium fissioning isomers

    Energy Technology Data Exchange (ETDEWEB)

    Makarenko, V.E.; Molchanov, Yu.D.; Otroshenko, G.A.; Yankov, G.B. (Gosudarstvennyj Komitet po Ispol' zovaniyu Atomnoj Ehnergii SSSR, Moscow. Inst. Atomnoj Ehnergii)

    1989-10-09

    Spontaneously fissioning isomers (SFI) of uranium were produced in {sup 236,238}U(n, n') reactions at 4.5 MeV mean neutron energy. A pulsed beam electrostatic accelerator was used and a time analysis of fission events was applied. Fission fragments were detected by a scintillation method, and long-range fission particles were detected by an ionization technique. Relative fission probabilities through the SFI state for both the nuclei were determined as (1.30+-.01).10{sup -4} in {sup 236}U and (1.48+-.02).10{sup -4} in {sup 238}U case. The SFI half-lives were determined as 121+-2 ns and 267+-13 ns respectively. As a result of uranium SFI ternary fission study it was observed that one ternary per 163+-44 binary fissions of {sup 236mf}U and one ternary per 49+-14 binary fissions of {sup 238mf}U took place. These figures seem to be rather high as compared with nonisomeric ternary fission probability data, and tentative effect of a particular nucleon configuration in the uranium SFI is supposed. (orig.).

  3. Nuclear fission yesterday and today

    International Nuclear Information System (INIS)

    After an outline of the experiments which led to the discovery of nuclear fission by O. Hahn and F. Strassmann in December 1938, the present state of knowlege of the fission process is reviewed. Important aspects of this process such as the double-humped shape of the fission barrier have been recognized only during the last decade. Other aspects such as the behavior of the fissioning nucleus between saddle point and scission point and the asymmetry of the mass division are not yet fully understood. In addition to further experimental and theoretical studies of the fission process itself, work on nuclear reactions between heavy nuclei may lead to better insights since these reactions, like the fission process, reveal the dynamical behaviour of nuclear matter. (orig.)

  4. Fission of radioactive ion beams

    International Nuclear Information System (INIS)

    In the present article, we describe the production and the identification procedure of the secondary beams. The production cross sections and the cross sections of the complementary fission events are used to extract the influence of the nuclear dissipation on the fission probability at high excitation energies. The detailed results on 234U and a few other secondary beams for which the fission after electromagnetic excitations could be distinguished from fission after nuclear collisions is discussed. They give access to the low-energy fission probabilities for short-lived radioactive nuclei, especially in the vicinity of the 126 neutron shell. Finally, the fission-fragment nuclear-charge distribution of 234U after electromagnetic excitations is presented and discussed. (orig.)

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

    International Nuclear Information System (INIS)

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

  6. 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.)

  7. Magnetic influence on fission chambers

    International Nuclear Information System (INIS)

    On large tokamak devices neutron measurements are performed by means of fission chambers can be affected because of the presence of high magnetic fields (E * B drift). A study has been carried out of the magnetic field influence on the fission chamber performances. By means of code, the drift properties of the electrons have been evaluated at different values of crossed E and B fields. The application of incore fission chambers on large tokamak devices results feasible

  8. Hidden systematics of fission channels

    Directory of Open Access Journals (Sweden)

    Schmidt Karl-Heinz

    2013-12-01

    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.

  9. Transmission measurements of 235U fission fragments in Mg, Al, Fe, Ni, Ag

    International Nuclear Information System (INIS)

    Transmission measurements of the fission fragments arising in 235U thermal-neutron-induced fission were performed by irradiating a back-to-back fission chamber in the thermal column of the RB-2 reactor of Montecuccolino (Bologna) Italy. The back-to-back fission chamber is a gas-flow counter utilizing argon containing 2 per cent nitrogen. The electrode spacing was 10 mm and the gas pressure was adjusted slightly above ambient pressure. The operating voltage was 100 V positive applied to each anode. The source of fission fragments consists of a thin layer of natural uranium (?0.2mg/cm2) evaporated under vacuum on a Pt disc. This uranium deposit is located in one of the two fission chambers of the counter. Irradiations were made in a neutron flux of ? 109 cm-2 s-1. During irradiation the fission fragments, which a r e able to penetrate a thin sheet of variable thickness (1-10 mg/cm2 ) of the element investigated, are directly counted. By repeating the measurements with different thickness of the sheets, one obtains a transmission curve of the 235U fission fragments for each element investigated. Another natural uranium deposit located in the second fission chamber acts as a monitor for the neutron flux for the different sorts of irradiation. From the transmission curves it is possible to derive the relative effective stopping power of the different targets, and the ranges of the fission fragts, and the ranges of the fission fragments in the different elements investigated. Actually the ranges a r e obtained by coupling the measured relative stopping powers with the absolute value of the range of 235U fission fragment in Al, measured by Segre and Wiegand, by an independent experiment using the activation technique. The results obtained a r e compared with theoretical calculations concerning the loss of energy of fission fragments in material. (author)

  10. Measurement of Fission Product Yields from Fast-Neutron Fission

    Science.gov (United States)

    Arnold, C. W.; Bond, E. M.; Bredeweg, T. A.; Fowler, M. M.; Moody, W. A.; Rusev, G.; Vieira, D. J.; Wilhelmy, J. B.; Becker, J. A.; Henderson, R.; Kenneally, J.; Macri, R.; McNabb, D.; Ryan, C.; Sheets, S.; Stoyer, M. A.; Tonchev, A. P.; Bhatia, C.; Bhike, M.; Fallin, B.; Gooden, M. E.; Howell, C. R.; Kelley, J. H.; Tornow, W.

    2014-09-01

    One of the aims of the Stockpile Stewardship Program is a reduction of the uncertainties on fission data used for analyzing nuclear test data [1,2]. Fission products such as 147Nd are convenient for determining fission yields because of their relatively high yield per fission (about 2%) and long half-life (10.98 days). A scientific program for measuring fission product yields from 235U,238U and 239Pu targets as a function of bombarding neutron energy (0.1 to 15 MeV) is currently underway using monoenergetic neutron beams produced at the 10 MV Tandem Accelerator at TUNL. Dual-fission chambers are used to determine the rate of fission in targets during activation. Activated targets are counted in highly shielded HPGe detectors over a period of several weeks to identify decaying fission products. To date, data have been collected at neutron bombarding energies 4.6, 9.0, 14.5 and 14.8 MeV. Experimental methods and data reduction techniques are discussed, and some preliminary results are presented.

  11. Thorium-uranium fission radiography

    International Nuclear Information System (INIS)

    The high energy secondary neutron flux, produced by stopping the 650 MeV proton beam of the Los Alamos Meson Physics Facility (LAMPF), has been tested for use in measurements of the microscale distribution of Th in heterogeneous samples, particularly rocks. Polished samples are covered with mica which serves as a detector for neutron-induced fission tracks. The sample is also irradiated in a nuclear reactor in order to measure the U distribution and to determine the correction required for U fission in the high energy exposure. The relative Th/U fission rates range from 0.14 to 0.31, depending on the amount of internal neutron moderation within the samples. The relative 232Th/238U fission rate, as calculated from the theoretical beam stop spectrum is somewhat higher (0.5), probably reflecting a contribution from low energy 235U fission in the observed ratio. The measured relative 209Bi/232Th fission rates are higher by a factor of 2-7 than those calculated from the theoretical neutron spectrum indicating that the flux of high energy (200 MeV) neutrons has been underestimated in the theoretical spectrum. Th fission track production rates of (0.5-2)x104/cm2. mA.h.ppm Th were measured, with the low values being more in accord with those calculated from the theoretical spectrum. The technique is limited by background from recoil tracks in the mica. The relative rate of fission to recoil is approxlative rate of fission to recoil is approximately 3 x 10-6 fission/recoil .ppm Th. However, by differential annealing of the recoil track, we are able to count fission tracks in the presence of a large background of recoil tracks. (Auth.)

  12. Fifty years with nuclear fission

    International Nuclear Information System (INIS)

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

  13. Some aspects of nuclear fission

    International Nuclear Information System (INIS)

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

  14. 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)

  15. Post-scission fission theory: Neutron emission in fission

    International Nuclear Information System (INIS)

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

  16. Post-scission fission theory: neutron emission in fission

    International Nuclear Information System (INIS)

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

  17. Post-scission fission theory: Neutron emission in fission

    Energy Technology Data Exchange (ETDEWEB)

    Madland, D.G.

    1997-11-01

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

  18. 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

  19. Fission fragment damage in zircon

    International Nuclear Information System (INIS)

    X-ray diffraction, electron microscope and optical studies have been made on zircons damaged by fission fragments derived from the action of neutrons on uranium impurities in the zircon lattice. A dosage of about 1014 fission events .cm-3 was required to produce diffuse x-ray scattering, observable by conventional photographic methods, and a dosage of about 1016 fission events .cm-3 appears to be required to render a zircon amorphous. An optical absorption band, generated apparently by ?-rays, was observed near 270 nm in undoped zircon. The valence state of the uranium impurities was unchanged by irradiation with 1014 fission events .cm-3, 2 x 1018 nvt of fast neutrons, or approximately 1010 R of ?-rays. A fission event in zircon was deduced to produce approximately 104 times more displacement damage than an ?-recoil atom. Individual fission tracks were observed directly by electron microscopy after dosage of 1010 to 1013 fission events .cm-3 the tracks being similar in appearance to those found by other workers in other materials. With increasing dosage, fission fragment irradiation appears to produce a progessive disordering of the lattice, as was previously deduced for the case of ?-recoil irradiation, rather than the formation of new crystallographic phases. (author)

  20. Fission at high angular momenta

    International Nuclear Information System (INIS)

    By studies on the system 40Ar+165Ho by means of selected measuring methods which made a differential selection of certain angular momentum ranges and by this a discrimination between ''fast fission'' and compound-nucleus fission possible the validity of fundamental predictions of the model of the ''fast fission'' hitherto experimentally no yet confirmed was studied: 1) At the turning point of the trajectory for ''fast fission'' calculated by Gregoire the corresponding shape of which must be responsible for the angular distribution the centers of the two fragments must be separated by about 11 fm. 2) The widths of the mass distributions after ''fast fission'' and compound-nucleus fission must be different by a factor 2. The measurements of the angular dependence showed that both prediction cannot be simultaneously brought into accordance with the experimental results. The results of coincidence measurements between fission fragments and alpha particles confirmed the assumption mentioned under topic 2. The analysis of the angular dependence then yielded for the shape of the nuclear complex leading to ''fast fission'' a more compact shape than that indicated by Gregoire, namely with a distance of the fragments of about 7 fm. (orig.)

  1. Optical spectroscopy of fission isomers

    International Nuclear Information System (INIS)

    An experiment is prepared at the EN-Tandem accelerator to measure spins, hyperfine constants and the isomer shifts of the odd-odd fission isomers sup(242,244m)Am and the odd-even isomer sup(243m)Am. The signal will be the fission fragment anisotropy after laser induced nuclear orientation (optical pumping with polarized light). (orig.)

  2. Fission throughout the periodic table

    Energy Technology Data Exchange (ETDEWEB)

    Moretto, L.G.; Wozniak, G.J.

    1989-04-01

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

  3. Tritium production from ternary fission

    International Nuclear Information System (INIS)

    The tritium gas emission in the thermal neutron induced ternary fission of 249Cf 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 249Cf sample was mounted in the centre of a vacuum chamber, at a short distance of a ?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 3H particles emitted in the thermal neutron induced ternary fission of 249Cf could be determined. Based on this result and on measurements published by us recently, we could enlarge the database related to 3H 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)

  4. The fundamental role of fission during r-process nucleosynthesis in neutron star mergers

    Science.gov (United States)

    Goriely, S.

    2015-02-01

    The rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A > 60 stable nuclei observed in nature. Despite important efforts, the astrophysical site of the r-process remains unidentified. Here we study r-process nucleosynthesis in a material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars. r-process nucleosynthesis during the decompression is known to be largely insensitive to the detailed astrophysical conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140. Due to the important role played by fission in such a scenario, the impact of fission is carefully analyzed. We consider different state-of-the-art global models for the determination of the fission paths, nuclear level densities at the fission saddle points and fission fragment distributions. Based on such models, the sensitivity of the calculated r-process abundance distribution is studied. The fission path is found to strongly affect the region of heavy nuclei responsible for the fission recycling, while the fission fragment distribution of nuclei along the A ? 278 isobars defines the abundance pattern of nuclei produced in the 110 ? A ? 170 region. The late capture of prompt fission neutrons is also shown to affect the abundance distribution, and in particular the shape of the third r-process peak around A ? 195.

  5. Chemical dependence of uranium fission

    International Nuclear Information System (INIS)

    A difference on the order of 4% in the delayed neutron yield from /sup 235/U after fission induced by thermal neutrons has been previously reported for samples of U/sub 3/O/sub 8/ and UO/sub 2/. Both theoretical calculations and experimental checks have been made in an attempt to verify the effect. The calculation of the effect of phonon distribution on fission cross section using an Einstein model of the lattice phonon distribution shows no significant dependence on the chemical state. Experimental measurements of the fission fragment yield from thermal-induced fission of /sup 235/U in UO/sub 2/ and U/sub 3/O/sub 8/ were made. The relative fission fragment yield was: UO/sub 2//U/sub 3/O/sub 8/..9972/plus or minus/.0003 where the error is from the counting statistics only. 6 refs

  6. Decay modes in spontaneous fission

    CERN Document Server

    Gönnenwein, F

    1999-01-01

    Spontaneous fission (SF) is considered to be the choice reaction for studying the influence of shell and pairing effects in fission in general, and in particular their impact on the mass and energy distributions of fission fragments. For the time being some 35 SF reactions have been analysed in detail for elements ranging from Pu up to Rf. Going from the lighter to the heavier actinides both, the distributions of fragment mass (or charge) and of total kinetic energy undergo dramatic changes. It is observed in experiment, however, that these distributions may be well described as a superposition of a few fission modes, each with its own characteristic mass an energy pattern. The experimental modes are traced in theory to fine structures in the potential energy surface of a fissioning nucleus, provided shell and pairing corrections to the basic liquid drop model are accounted for.

  7. Spontaneous fission of heavy nuclei

    International Nuclear Information System (INIS)

    The fundamental investigations of heavy nucleus spontaneous fission are placed into a historical perspective since as early as 1939. The investigations have been conducted in two basic directions. The first one is connected with spontaneous fission mechanism. The second relates to clarifying the role of spontaneous fission in the problem of heavy nicleus stability. It is concluded from the data available on heavy nucleus half-lives that the droplet model reflects but the rude average picture, and that the nuclear structure plays a significant part. The fundamentals of the isomeric nucleus fission theory are considered which provides a tool to calculate nucleus energy under large deformations conditions and, therefore, the shape and height of fission barriers. The experimental results of searching for superheavy nuclei in meteorites and by an artificial synthesis are discussed. It is noted that a qualitative break-through in synthesizing artificially transuranium elements can be attained only by heavy ion nuclear reactions

  8. Fission of heavy and superheavy nuclei at low excitation energies

    CERN Document Server

    Itkis, M G; Hanappe, F; Itkis, Y M; Kelic, A; Kondratev, N A; Kozulin, E M; Oganessian, Yu T; Pokrovsky, I V; Prokhorova, E V; Rudolf, G; Rusanov, A Ya; Stuttgé, L

    1999-01-01

    The talk presents the results of an investigation of the main characteristics (mass and energy distributions of fission fragments and multiplicity of neutrons) of the fission of the nuclei of sup 2 sup 2 sup 0 Ra, sup 2 sup 2 sup 6 Th, sup 2 sup 5 sup 6 No, sup 2 sup 7 sup 0 Sg, sup 2 sup 8 sup 6 112 produced in reactions with ions of sup 1 sup 8 O, sup 2 sup 2 Ne and sup 4 sup 8 Ca at energies close to and essentially below the Coulomb barrier. The data obtained show that the form of the mass and energy distributions of the fission fragments of sup 2 sup 2 sup 6 Th and sup 2 sup 7 sup 0 Sg is accounted for by the multimodal nature of the fission. In addition, for sup 2 sup 2 sup 6 Th, a new phenomenon was established: there is a significant difference between the numbers of prescission neutrons for symmetric and asymmetric fission modes. It was found that, for the low-energy fission of the nucleus of sup 2 sup 8 sup 6 112, the mass distribution of the fragments is of a clear-cut asymmetric form, contrary to ...

  9. 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

  10. Fission product yields in 238Np thermal fission

    International Nuclear Information System (INIS)

    Relative cumulative yields for 23 products in the range A=131-155 thermal fission of short-lived odd-odd 238Np nuclide are determined, using mass spectrometric method. The curve of mass yield in the region of heavy product peak is plotted, the absolute yields of the above-mentioned masses and the main parameters of the heavy product peak are evaluated. Irregularities in the curve of fission product mass distribution, observed in the ranges of mass yields A=134-136, A=137-140, A=144 and A=151-152, are explained in the framework of the Wilkins-Steinberg-Chasman statistical model of fission

  11. 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.)

  12. Brownian shape motion: Fission fragment mass distributions

    International Nuclear Information System (INIS)

    Although nuclear fission can be understood qualitatively as an evolution of the nuclear shape, a quantitative description has proven to be very elusive. In particular, until now, there exists no model with demonstrated predictive power for the fission fragment mass yields. Exploiting the expected strongly damped character of nuclear dynamics, we treat the nuclear shape evolution in analogy with Brownian motion and perform random walks on five-dimensional fission potential-energy surfaces which were calculated previously and are the most comprehensive available. Test applications give good reproduction of highly variable experimental mass yields. This novel general approach requires only a single new global parameter, namely the critical neck size at which the mass partition is frozen in, and the results are remarkably insensitive to its specific value. In order to achieve a better understanding of these results, we have embarked on more involved calculations using the friction tensor implied by the one-body wall dissipation. Generally, an anisotropic friction deflects the multi-dimensional shape trajectory away from the directions of the the driving force provided by the deformation energy (and thus changes the shape evolution), but there are reasons to expect that this complication will have only a minor bearing on the mass partition. The results should be available at the time of the conference and, if so, they will be discussed as well. Relative to previously employed methods, the present approach represents a significant advance with regard to predictive power. Thus, it can be readily employed in regions of the nuclear chart that are of special astrophysical interest and it may, for example, help to clarify the importance of fission recycling for the r-process. Taking explicit account of the equilibration process, our treatment extends in a natural way the compound nucleus concept and it builds directly on the general picture of low-energy nuclear dynamics as being dissipation dominated

  13. The potential for large scale uses for fission product xenon

    International Nuclear Information System (INIS)

    Of all fission products in spent, low enrichment, uranium, power reactor fuels xenon is produced in the highest yield - nearly one cubic meter, STP, per metric ton. In aged fuels which may be considered for processing in the U.S. radioactive xenon isotopes approach the lowest limits of detection. The separation from accompanying radioactive 85Kr is the essential problem; however, this is state of the art technology which has been demonstrated on the pilot scale to yield xenon with pico-curie levels of 85Kr contamination. If needed for special applications, such levels could be further reduced. Environmental considerations require the isolation of essentially all fission product krypton during fuel processing. Economic restraints assure that the bulk of this krypton will need to be separated from the much more voluminous xenon fraction of the total amount of fission gas. Xenon may thus be discarded or made available for uses at probably very low cost. In contrast with many other fission products which have unique radioactive characteristics which make them useful as sources of heat, gamma and x-rays and luminescence as well as for medicinal diagnostics and therapeutics fission product xenon differs from naturally occurring xenon only in its isotopic composition which gives it a slightly higher atomic weight, because of the much higher concentrations of the 134X and 136Xe isotopes. Therefore, fission product xenon can most likrefore, fission product xenon can most likely find uses in applications which already exist but which can not be exploited most beneficially because of the high cost and scarcity of natural xenon. Unique uses would probably include applications in improved incandescent light illumination in place of krypton and in human anesthesia

  14. 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

  15. Fission product behavior

    International Nuclear Information System (INIS)

    During the TMI-2 accident, radioactive fission products were released from the fuel to the reactor coolant. Radionuclides were subsequently transported from the reactor primary system to the Reactor Building sump and into the Auxiliary Building. The residual radionuclide distributions have been studied to gain insight into the physical and chemical processes operative during and soon after the accident. Isotopes of (a) the radioactive noble gases (Kr and Xe), (b) radioiodine, (c) radiocesium, and (d) radiostrontium are of principal concern. The analyses of post-accident fluid and solid samples have identified 60--70 percent of the inventories of each of the four radionuclide categories. Except for the noble gases, the entire inventories are contained in the plant. The observed distributions indicate differences between the behavior of iodine and cesium, either during or after the accident

  16. 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)

  17. ICON, Reactor Operation Fission Products Inventory Calculation

    International Nuclear Information System (INIS)

    1 - Nature of physical problem solved: Determines complete fission product inventory for a reactor after a particular history of operating conditions taking into account the structure of the individual decay chains and also the effects of neutron capture. 2 - Method of solution: Each chain is fitted to a generalised decay scheme and the simultaneous differential equations, whose coefficient matrix is lower triangular, are solved. 3 - Restrictions on the complexity of the problem: In its present form up to 100 reactor cycles may be examined but this may be readily increased

  18. Methods for decorporation of important fission products

    International Nuclear Information System (INIS)

    Fission products incorporated into human body by accidents should be treated with an application of suitable decorporation method. Decorporation methods are divided into several groups according to their mechanism of action; 1) dilution of radio nuclide by its stable isotope or similar chemical behavior elements, 2) complex formation with chelating agents such as DTPA, 3) adsorption on insoluble materials such as charcoal, prussian blue, 4) disturbance of metabolism by medicine like hormone or deficient diet, and 5) others. The future research trends toward synthesis of new chelating agent and application of natural materials. Their effectiveness may be increased if they are applied in combination with other procedures. (author)

  19. Reaction rate calibration techniques at ZPPR for 239Pu fission, 235U fission, 238U fission, and 238U capture

    International Nuclear Information System (INIS)

    Reaction-rate calibration techniques used at ZPPR are described for 239Pu fission, 235U fission, 238U fission and 238U capture. In addition to these absolute reaction rates, calibration techniques are described for fission-rate ratios and the ratio of 238U capture to 239U capture to 239Pu fission. Uncertainty estimates are presented for all calibrations. Intercomparison measurements are reported which support the validity of the calibration techniques and their estimated uncertainties

  20. The spectroscopy of fission fragments

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-12-31

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

  1. Intrinsic energy partition in fission

    Directory of Open Access Journals (Sweden)

    Mirea M.

    2013-03-01

    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.

  2. 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

  3. Stationary operating mode of thermal reactor with high reproduction of fission materials

    International Nuclear Information System (INIS)

    Development of atomic power engineering requires intensive NFC power increasing, but using modern technologies fast expense of nature raw materials is happened. Fast development will be possible only under building of new generation reactors - reactors with high reproduction of fission materials using as uranium and thorium raw materials.The problem of thorium reactors startup is in absence of natural fission nuclides in thorium. Argument of possibility of such reactor startup without involvement of fast reactors technologies will increase attention on such thermal reactors. Process of accumulation of fission materials in reactor fuel on thermal neutrons operating in closed coupled uranium-thorium fuel cycle is examined. Five variants of reactor initial loading differed by technology of used fission materials production are worked out. Possibility of tested reactor variants startup is shown. Time of fission components in fuel starting composition is selected.(author)

  4. Fission nuclide identification using the photoneutrons and the fission neutrons

    International Nuclear Information System (INIS)

    Using the microtron M-30 at the electron energy of 8 MeV, the kinetic functions of 232Th, 235,238U, 237Np, 239Pu and those of the mixtures 232Th+238U, where the amount of the delayed neutrons is normalized to the summary photoneutron and prompt fission neutron yield, are determined. The kinetic functions are characterized by the discrimination relations ? 2 and that permits to identify the fission nuclides with error of ±0.1

  5. Fission and deep spallation characteristics in relativistic nuclear collisions

    International Nuclear Information System (INIS)

    Numbers of emitted fast charged particles associated with heavier nuclear fragments are employed as a graphic means of differentiating fission and spallation contributions to target fragment emission in relativistic nuclear collisions. The violent nature of the deep spallation mechanism is observed directly

  6. Simple diabatic model of induced fission

    International Nuclear Information System (INIS)

    A quantitative model describing fission is still not available although fission has been known for 50 years and an appreciable amount of experimental data exists. In the present paper a simple model accounting for the diabatic evolution of single particle states during fission is proposed. The model attempts to describe the measured distribution of masses to the fission fragments, for cases of induced fission in which the initial excitation energy is sufficiently large (approx-gt 10 MeV)

  7. 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

  8. ?-delayed fission from 230Ac

    International Nuclear Information System (INIS)

    ThO2 is irradiated with 60 MeV/u 18O beams. 230Ra is produced via the multi-nucleon transfer and dissipative fragmentation reactions of the target. 230Ra is radio-chemical separated from ThO2 and the other reaction products. The thin Ra sources are prepared. The mica fission track detectors are exposed to the Ra sources. ?-rays of Ra decay in the sources are measured by a HPGe detector. The mica foil is etched in HF solution. The etched mica foil is scanned with an optical microscope. The fission tracks that should come from ?-delayed fission of 230Ac are observed. The ?-delayed fission probability of 230Ac is determined to be (1.19 +- 0.85) x 10-8

  9. Background radiation from fission pulses

    Energy Technology Data Exchange (ETDEWEB)

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

    1988-05-01

    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.

  10. 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)

  11. Protactinium neutron-induced fission up to 200 MeV

    Directory of Open Access Journals (Sweden)

    Maslov V.

    2010-03-01

    Full Text Available The theoretical evaluation of 230-233Pa(n,F cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutroninduced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F, 232Th(n,2n and 238U(n,F, 238U(n,xn data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F reaction. Ratio surrogate data on fission probabilities of 232Th(6 Li,4 He234Pa and 232 Th(6 Li,d236U 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.

  12. Advanced Space Fission Propulsion Systems

    Science.gov (United States)

    Houts, Michael G.; Borowski, Stanley K.

    2010-01-01

    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.

  13. The microscopic theory of fission

    Science.gov (United States)

    Younes, W.; Gogny, D.

    2009-10-01

    Fission-fragment properties have been calculated for thermal neutron-induced fission on a 239Pu 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.

  14. The microscopic theory of fission

    CERN Document Server

    Younes, W

    2009-01-01

    Fission-fragment properties have been calculated for thermal neutron-induced fission on a $^{239}\\textrm{Pu}$ 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.

  15. Composition of fission product mixtures

    International Nuclear Information System (INIS)

    The report gives a compilation of the isotopic composition and specific activity of fission products produced by thermal neutron fission of U-235 and Pu-239. The composition was computed using an electronic computer ES 1040. The presentation comprises data of 27 elements at the end of a neutron irradiation of 3 years and after a time interval of 1, 4 and 10 years after the end of irradiation. (author)

  16. The microscopic theory of fission

    OpenAIRE

    Younes, W.; Gogny, D.

    2009-01-01

    Fission-fragment properties have been calculated for thermal neutron-induced fission on a $^{239}\\textrm{Pu}$ 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 multipliciti...

  17. Measurement of fission gas release from irradiated nuclear fuel elements

    International Nuclear Information System (INIS)

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

  18. 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

  19. Chemical reactions of fission products with ethylene using the gas jet technique

    International Nuclear Information System (INIS)

    An understanding of the nature of the chemical reactions taking place between fission products and their carrier gases, and the designing of a fast separation procedure were the purposes of this investigation. Chemical reactions of short-lived (less than one minute half-life) fission products with carrier gases lead to various chemical species which can be separated in the gas phase. The Gas Jet Facility at the Ford Nuclear Reactor was used to study the yields of volatile selenium and bromine fission products of 235U using a semi-automatic batch solvent extraction technique. Heptane and water were used as organic and inorganic solvents. A carrier gas mixture of ethylene to pre-purified nitrogen (1 : 3) was used to sweep the fission products from the target to the chemistry area for analysis. The results indicated that the volatile selenium products generated by the interaction of selenium fission fragments with ethylene were predominantly organic in nature (84%), possibly organoselenides. The selenium values were used to resolve the fractions of the bromine nuclides, which come from two major sources, viz., directly from fission and from the beta-decay of selenium. The data showed that the fractions of independent bromine fission products in the organic phase were much lower compared to selenium; the bromine values range from 10 to 22% and varied with mass number. Results indicated that the bromine products were inorganic in nature, as possibly hydrogen chlrganic in nature, as possibly hydrogen chloride. ((orig.))

  20. Modelling isothermal fission gas release

    International Nuclear Information System (INIS)

    The present paper presents a new fission gas release model consisting of two coupled modules. The first module treats the behaviour of the fission gas atoms in spherical grains with a distribution of grain sizes. This module considers single atom diffusion, trapping and fission induced re-solution of gas atoms associated with intragranular bubbles, and re-solution from the grain boundary into a few layers adjacent to the grain face. The second module considers the transport of the fission gas atoms along the grain boundaries. Four mechanisms are incorporated: diffusion controlled precipitation of gas atoms into bubbles, grain boundary bubble sweeping, re-solution of gas atoms into the adjacent grains and gas flow through open porosity when grain boundary bubbles are interconnected. The interconnection of the intergranular bubbles is affected both by the fraction of the grain face occupied by the cavities and by the balance between the bubble internal pressure and the hydrostatic pressure surrounding the bubbles. The model is under validation. In a first step, some numerical routines have been tested by means of analytic solutions. In a second step, the fission gas release model has been coupled with the FTEMP2 code of the Halden Reactor Project for the temperature distribution in the pellets. A parametric study of some steady-state irradiations and one power ramp have been simulated successfully. In particular, the Halden threshold for fission gas release and two simplified FUMEX cases have been computed and are summarised. (author)

  1. Fission profile in 256Fm

    International Nuclear Information System (INIS)

    The nuclear fission is one of the most challenging quantum many-body problems, due to the difficulty of finding a proper formulation of the evolution from a compound nucleus to fission fragments. The optimum trajectories, the associated shapes and energy in the fissioning nuclei at high angular momentum are studied. Hence the effect of angular momentum in the fission profile of a nucleus 256Fm is looked in to. Here the results for 256Fm, which was one among the most studied nuclei in various approaches are discussed. An independent-particle shell model with the mean field represented by the deformed Woods-Saxon potential is utilized. The main development in this work is the extension of Cassinian oval calculations to study the rotating nuclei. The properties of a fissioning nuclei at fixed spin is achieved by tuning the rotation frequency to get the desired angular momentum. The details about the calculations and the evolution of potential energy surfaces are explained in literature. The effect of spin in the fission profile is shown

  2. Fission fragment angular distributions and fission cross section validation

    International Nuclear Information System (INIS)

    The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n-TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) at the n-TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of the incident neutron above hundreds of MeV. The method based on the detection of the 2 fragments in coincidence allowed to clearly disentangle the fission reactions among other types of reactions occurring in the spallation domain. I will show the methods we used to reconstruct the full angular resolution by the tracking of fission fragments. Below 10 MeV our results are consistent with existing data. For example in the case of 232Th, below 10 MeV the results show clearly the variation occurring at the first (1 MeV) and second (7 MeV) chance fission, corresponding to transition states of given J and K (total spin and its projection on the fission axis), and a much more accurate energy dependence at the 3. chance threshold (14 MeV) has been obtained. In the spallation domain, above 30 MeV we confirm the high anisotropy revealed in 232Th by the single existing data set. I'll discuss the implications of this finding, related to the low anisotropy exhibited in proton-induced fission. I also explore the critical experiments which is valuable checks of nuclear data. The 237Np neutron-induced fission cross section has recently been measured in a large energy range (from eV to GeV) at the n-TOF facility at CERN. When compared to previous measurements, the n-TOF fission cross section appears to be higher by 5-7 % beyond the fission threshold. To check the relevance of n-TOF data, we simulate a criticality experiment performed at Los Alamos with a 6 kg sphere of 237Np. This sphere was surrounded by enriched uranium 235U so as to approach criticality with fast neutrons. The simulation predicts a multiplication factor keff in better agreement with the experiment (the deviation of 750 pcm is reduced to 250 pcm) when we replace the ENDF/B- VII.0 evaluation of the 237Np fission cross section by the n-TOF data. We also explore the hypothesis of deficiencies of the inelastic cross section in 235U which has been invoked by some authors to explain the deviation of 750 pcm. The large distortion that should be applied to the inelastic cross sections in order to reconcile the critical experiment with its simulation is incompatible with existing measurements. Also we show that the ?-bar of 237Np can hardly be incriminated because of the high accuracy of the existing data. Fission rate ratios or averaged fission cross sections measured in several fast neutron fields seem to give contradictory results on the validation of the 237Np cross section but at least one of the benchmark experiments, where the active deposits have been well calibrated for the number of atoms, favors the n-TOF data set. These outcomes support the hypothesis of a higher fission cross section of 237Np. (author)

  3. Properties and detection of ionizing radiation resulting from instantaneous fission and fission product mixture

    International Nuclear Information System (INIS)

    The different types of ionizing radiation accompanying fission and mixtures of fission products, their activity, the determination of the age of fission products and the biological hazard of radiation caused by instantaneous fission are described. The possibility is described of detection, and of the dosimetry of ionizing radiation resulting from instantaneous fission and emitted by a mixture of fission products, the determination of the dose of neutron radiation, surface contamination, internal contamination and the contamination of water and foods. (J.P.)

  4. 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

  5. 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)

  6. 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

  7. Separation of fission products by the use of recoil

    International Nuclear Information System (INIS)

    We have studied fission recoil in U3O8 organic solvent mixtures. The organic phase chosen was first naphtalene then terphenyl. Graphite and activated carbon were also tried out as recoil media. We first verified that the fission fragments are ejected from the uranium oxide particles under our experimental conditions. The retention phenomenon observed is due to an adsorption occurring either during irradiation or during the chemical treatment. Using naphthalene or terphenyl, the individual separation of the fission products has made it possible to show the influence of the chemical nature of the recoil medium on the retention of each fission product. We put forward a hypothesis concerning this phenomenon: experiments carried out using 'scavengers', together with kinetic studies make it possible to explain the retention phenomenon and to choose the most favorable conditions for reducing this retention to a low value. The thermal recombination kinetics demonstrate the influence of the fission ion charge on the final value of the retention for a given temperature. The origins of this thermal recombination are discussed. (author)

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

    International Nuclear Information System (INIS)

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

  9. Energy production using fission fragment rockets

    Science.gov (United States)

    Chapline, G.; Matsuda, Y.

    1991-08-01

    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 the efficiency if the fission fragment energy can be directly converted into electricity; reduction of the buildup of a fission fragment inventory in the reactor could avoid a Chernobyl type disaster; and collection of the fission fragments outside the reactor could simplify the waste disposal problem.

  10. 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 foequiring 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.

  11. Compact fission counter for DANCE

    Energy Technology Data Exchange (ETDEWEB)

    Wu, C Y; Chyzh, A; Kwan, E; Henderson, R; Gostic, J; Carter, D; Bredeweg, T; Couture, A; Jandel, M; Ullmann, J

    2010-11-06

    The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF{sub 2} crystals with equal solid-angle coverage. DANCE is a 4{pi} {gamma}-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 {gamma}-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 {gamma} 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 {alpha} particles, which is important for experiments with {alpha}-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 {alpha}'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 {alpha}'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.

  12. Projected-length distributions of fission-fragment tracks from U and Th thin film sources in muscovite

    Science.gov (United States)

    Guedes, S.; Jonckheere, R.; Iunes, P. J.; Hadler, J. C.

    2008-03-01

    Thin films of natural uranium and thorium deposited on muscovite were used as sources of neutron-induced fission fragments. Fragment energy loss in thin-source geometry is negligible. In this way, the observed fragment range results from the interaction of the fragment with the detector material. This characteristic enables the investigation of asymmetric fission and etching, through measurements of projected track length distributions in muscovite micas coupled with thin films. The means and standard deviations of the etchable length distributions of the heavy and light fission-fragment tracks were estimated by fitting a theoretical equation to the experimental data. The light fission-fragment accounts for ˜54% and the heavy fission-fragment for ˜46% of the etchable length of a full fission track. This average partition is the same for tracks from thermal-neutron-induced fission of 235U and fast-neutron-induced fission of 232Th. The mean etchable length of uranium fission tracks is ˜2.5% longer than that of thorium fission tracks. This difference is at the resolution limit of these measurements but correlates with the difference in the mean combined initial kinetic energies of the fission fragments. The mean etchable length of uranium fission tracks in muscovite is ˜5% shorter than their calculated latent track length, supporting earlier estimates of a length deficit of this magnitude. The length deficit and the standard deviation of the etchable length distribution of the light fission-fragment tracks are twice the equivalent values for the heavy fission-fragment tracks. This is interpreted in terms of a v t-profile (track etch rate) that depends on the mass of the track-forming particle.

  13. Fission fragment angular distribution and fission cross section validation

    OpenAIRE

    Leong, Lou Sai

    2013-01-01

    The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n_TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) at the n_TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of th...

  14. Change over from compound nuclear fission to quasi-fission

    International Nuclear Information System (INIS)

    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. (authors)

  15. Fission matrix capability for MCNP Monte Carlo

    International Nuclear Information System (INIS)

    The element Fij of the fission matrix is equal to the number of fission neutrons born in region i due to one average fission neutron starting in region j. The fission matrix is a spatially discretized Green's function for the next generation fission neutron source. 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

  16. 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.)

  17. 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)

  18. 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")

  19. Fission Matrix Capability for MCNP Monte Carlo

    Science.gov (United States)

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

    2014-06-01

    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.

  20. 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

  1. Fission transient time with quantum master equation

    International Nuclear Information System (INIS)

    Using a quantum master equation for the reduced density matrix, the influence of microscopical diffusion coefficients on the fission transient time and the probability of the first-chance fission are studied. (authors)

  2. Characteristics of fission products in fast reactor

    International Nuclear Information System (INIS)

    This paper discusses the charateristics of fission products in fast reactor. It is indicated that there are more important fission products in the fast reactor. The results obtained can help us to analyse charateristics of fast reactor.(Author)

  3. Ceramic Hosts for Fission Products Immobilization

    Energy Technology Data Exchange (ETDEWEB)

    Peter C Kong

    2010-07-01

    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.

  4. Search for Singlet Fission Chromophores

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-01-01

    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.

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

    International Nuclear Information System (INIS)

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

  6. 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)

  7. Fusion - fission dynamics: fragment mass distribution studies

    Science.gov (United States)

    Bhattacharya, S.; Chaudhuri, A.; Ghosh, T. K..; Banerjee, K.; Bhattacharya, C.; Kundu, S.; Mukherjee, G.; Rana, T. K.; Roy, P.; Pandey, R.; Bhattacharya, P.

    2015-01-01

    Using the major accelerator facilities available in India, detailed experimental studies have been made to understand the mechanism of quasi-fission and role of nuclear shell effect in heavy nuclei. Fission fragment mass distribution has been used as the probe to explore the role of entrance channel effects on fusion-fission and quasifission dynamics. Fission fragment mass distribution has also been demonstrated to be useful to identify the phenomenon of `washing out' of nuclear shell effect with excitation energy.

  8. Nuclear fission in covariant density functional theory

    OpenAIRE

    Afanasjev A.V.; Abusara H.; Ring P.

    2013-01-01

    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.

  9. Evaluation of the neutron temperatures in the Oklo reaction zones, based on a study of 176Lu/175Lu and 156Gd/155Gd isotope ratios

    International Nuclear Information System (INIS)

    Certain isotopes having particularly temperature-sensitive capture cross-sections with resonance in the thermal range can be used for estimating the equilibrium temperature between the neutrons generated by fission and the water acting as moderator. In this case the authors have chosen to work with lutetium-176 and gadolinium-155. For the theoretical calculation it is necessary to perform a number of approximations of the neutron spectrum in a range close to thermalization. One model consists in comparing the spectrum with a Maxwell spectrum, to which an asymptotic branch is added for the energies higher than a few kt; this asymptote takes into account corrections to the purely Maxwellian spectrum (ordinary contribution) as well as the epithermal contribution. This model is comparable to that of a heavy gas which corresponds suitably to the light-water moderator; the effective cross-sections used are defined in Westcott's terms, i.e. by sigma=sigma0(g+rs). The nuclear parameters are determined on the basis of the isotope pairs (143Nd-144Nd) and (147Sm-148Sm). The effective cross-sections used were deduced from Triton irradiations. The samples chosen must have fluences below a certain threshold beyond which the absorber nuclides disappear due to neutron capture. The fluence 0.23x1021n/cm2 of the sample SC 52 1472 (reaction zone No.3) seems to be perfect for determining neutron temperature; a tt for determining neutron temperature; a temperature of 2800C+-100C corresponds to a 176Lu/175Lu isotope ratio of 0.0107+-0.0001 without subsequent contamination with natural lutetium (4000C for 10% contamination). (author)

  10. Implication of fission yields data to fission process and their relevance to ADS

    International Nuclear Information System (INIS)

    Cumulative and independent fission yields of various fission products have been determined in the neutron induced fission of 229,232Th, 232,233,235,238U, 237Np,238,239,240,241Pu, 241,243Am and 244,245Cm as well as in the spontaneous fission of 244Cm and 252Cf. The fission yields data were used to carry out mass and charge distribution studies to understand the fission mechanism. Besides this, the data of fast neutron induced fission of minor long-lived actinides were discussed from the point of fast reactor design and their importance to ADS. (author)

  11. 248Cm spontaneous neutron fission spectrum

    International Nuclear Information System (INIS)

    Spontaneous fission neutron spectrum of 248Cm was measured by multidimensional time-of-flight spectrometer. 252Cf was used as a standard. The fission source was manufactured in form of thin platinum disc (0.1 mm thick), one side of which was coated with Cf and another one with Cm. Measurement results on neutron spectrum of 248Cm spontaneous fission are presented

  12. Fission yield data evaluation system FYDES

    International Nuclear Information System (INIS)

    Taking account of some features of fission yield data, to do the fission yield data evaluation conveniently, a fission yield data evaluation system FYDES has been developed for last two years. Outline of the system, data retrieval and data table standardization, data correction codes, data averaging code, simultaneous evaluation code and data fit programs were introduced

  13. Fission modes of heavy and superheavy nuclei

    International Nuclear Information System (INIS)

    Mass and energy distributions of fission fragments for spontaneous and low energy fission of nuclei with Z = 98-112 are discussed. The dependence of fragment characteristics (symmetric and asymmetric mass, low and high kinetic energy, bimodal) on nucleon composition of the compound nucleus and on the structure of fission fragments is investigated. (authors)

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

    CERN Document Server

    Kessler, Günter

    2012-01-01

    Unlike existing books of nuclear reactor physics, nuclear engineering and nuclear chemical engineering this book covers a complete description and evaluation of nuclear fission power generation. It covers the whole nuclear fuel cycle, from the extraction of natural uranium from ore mines, uranium conversion and enrichment up to the fabrication of fuel elements for the cores of various types of fission reactors. This is followed by the description of the different fuel cycle options and the final storage in nuclear waste repositories. In addition the release of radioactivity under normal and possible accidental conditions is given for all parts of the nuclear fuel cycle and especially for the different fission reactor types.

  15. Nuclear fission in reactor instrumentation

    International Nuclear Information System (INIS)

    The limitation in designing a high neutron sensitive fission counter comes from the alpha induced pulse pile-up with increase in coated quantity of 235U. The thicker coating reduces the number of fission fragments reaching the active volume and increase in coated surface area gives rise to higher capacitance resulting in severe alpha pile-up reducing the effective neutron sensitivity. The short resolving time (small capacitance) and small charge collection time (smaller electrode spacing) are the required features to overcome the problems associated with alpha pulse pile-up for achieving higher sensitivities. One such detector configuration using large number of electrodes connected in series as transmission line will achieve both the features. The adjacent signal electrodes are connected to each other through inductive elements thus each electrode constitutes a lumped-element transmission-line. The processing of pulses from each end of the transmission line to a time coincidence gate can improve discrimination. This configuration of fission detector can achieve sensitivity of about 6 cps/nv for detector of length 1 m and diameter 70 mm. The talk gives an overview of the fission detectors in reactor application and the recent developments

  16. Search for singlet fission chromophores.

    Czech Academy of Sciences Publication Activity Database

    Havlas, Zden?k; Akdag, Akin; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, Josef

    Philadelphia : American Chemical Society, 2012. 31PHYS. ISSN 0065-7727. [National Fall Meeting of the American Chemical Society /244./. 19.08.2012-23.08.2012, Philadelphia] Institutional support: RVO:61388963 Keywords : singlet fission * chromophores Subject RIV: CF - Physical ; Theoretical Chemistry

  17. Spontaneous fission of rutherfordium isotopes

    International Nuclear Information System (INIS)

    We have found several new spontaneous fission (SF) activities and suggested assignments for some of them to rutherfordium (element 104) isotopes. Their half-lives and production cross sections have been measured by collecting recoils on a moving nickel or steel tape and transporting them past stationary mica track detectors at known velocities. The following tentative assignments are based on several cross bombardments and comparisons between experimental and calculated production cross sections: 256Rf(9 +- 2 ms), 257Rf(3.8 +- 0.8 s, 14 +- 9% SF), 258Rf(13 +- 3 ms), 259Rf(3.4 +- 1.7 s, 9 +- 3% SF), 260Rf(21 +- 1 ms), and 262Rf(47 +- 5 ms). Presently we are unable to assign several other new spontaneous fission activities with half-lives of approx.15 ms, approx.22 ms, approx.100 ms (Z260Rf, in reactions in which we expected to produce this isotope. Our measurements support a shift in the spontaneous fission half-life systematics at element 104, first proposed by Flerov and Oganessian et al. and later predicted by Randrup et al. and Baran et al. and attributed to the disappearance of the second hump of the double-humped fission barrier and a weakening of the 152-ission barrier and a weakening of the 152-neutron subshell

  18. On epidote fission track dating

    International Nuclear Information System (INIS)

    The use of epidote in fission track dating was abandoned since the beginning of the 1980s due to difficulties like absence of a standard etching procedure, obtainment of different closure temperatures and the percentage of the datable samples. The results become much more reproducible when restricting fission track analysis to a peculiar kind of track. We are also studying confined track length, what makes possible to obtain information about fossil track annealing. Fission tracks in epidote were successfully etched with 48% HF at 35 deg. C for 12.5min. Dating samples by the external detector method was not possible due to problems in measuring the efficiency factor held between the number of fossil fission tracks and tracks induced in mica. Dating a sample from Brejui, RN, Brazil with the population method gave a corrected age of 510±69Ma, in agreement with published U/Th-Pb ages. From the fact that the fossil track length histogram was bimodal, we were able to infer that this sample registered a thermal episode during its history. These preliminary results indicate that epidote deserves further studies to establish whether it can be employed as a thermochronological tool

  19. 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.)

  20. 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

  1. Some aspects of fission and quasifission processes

    International Nuclear Information System (INIS)

    An incomplete subset of the major milestones in fission research are reviewed, and some of the related topics are briefly discussed . These include studies of vibrational resonances and fission isomers that are caused by the second minimum in the fission barrier in actinide nuclei, studies of heavy-ion induced fission in terms of the angular distributions and the mass-angle correlations of fission fragments. Some of these studies provided evidence for the importance of the quasifission process and the attendant suppression of the complete fusion process. Finally, the effect of suppression of complete fusion for systems used to synthesize super-heavy elements will be discussed

  2. Spontaneous fission. A many-body approach

    Energy Technology Data Exchange (ETDEWEB)

    Iwamoto, Akira; Bonasera, A. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1997-03-01

    We propose new model to calculate the fission phenomena in tunnel region. By the Vlasov equation and the imaginary time method, we could calculate actinides nuclear fission. This method makes possible to describe unified the motion of fission inside and outside of potential wall. The potential energy and mass parameters can be calculated by no means of the special model. The freedom of internal motion are calculated automatically both collective and a particle motion. Accordingly, particle released during fission process can be calculated. The kinetic energy of fragment after fission was very agreeable with the calculation results. (S.Y.)

  3. Core debris chemistry and fission product behavior

    International Nuclear Information System (INIS)

    Examinations are being performed to acquire data on the extent and nature of damage to the Three Mile Island Unit 2 (TMI-2) core. Six samples were obtained from the TMI core rubble bed in September 1983. Five of the six samples are being examined by EG and G Idaho, Inc., to acquire data on the postaccident condition of the core and the behaviour of radionuclides in the core region. A description of the sampling and analysis methods is presented, along with the results of chemical and radio-chemical examinations. Correlations are performed with the core structural composition and predicted fission product concentrations and inventories. The core debris is a mixture containing UO2 fuel, zircaloy cladding, and control materials (silver, indium, and cadmium); poison rod materials; and structural materials. Radionuclide concentrations are similar at all locations. The principal radionuclides measured are strontium-90, iodine-129, cesium-137, and cerium-144

  4. 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

  5. Recovery of noble metals from fission products

    International Nuclear Information System (INIS)

    Spent nuclear fuels contain significant quantities of three of the platinum-group metals--ruthenium, rhodium, and palladium--plus a related element, technetium, which is nearly absent in nature. Applications for the ruthenium, rhodium, and palladium are well established, and since the supply of these and other noble metals is largely from foreign sources, they are considered strategic materials. Thus, there is considerable incentive to recover them from nuclear fuels. The technical feasibility of using fission product (FP) noble metals extensively in industry depends on resolution of three major problems: 1. They must be thoroughly decontaminated from all other radioactive materials in the waste stream. 2. They must be separated from one another in very high purity because of internal decay processes. 3. Applications selected must provide appropriate control of radioactivity or the radioisotopes must be removed by isotope-separation techniques or normal decay

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

    International Nuclear Information System (INIS)

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

  7. Theory of nuclear fission. A textbook

    Energy Technology Data Exchange (ETDEWEB)

    Pomorski, Krzysztof [Lublin Univ. (Poland). Theoretical Physics Division; Krappe, Hans J.

    2012-07-01

    This book brings together various aspects of the nuclear fission phenomenon discovered by Hahn, Strassmann and Meitner almost 70 years ago. Beginning with an historical introduction the authors present various models to describe the fission process of hot nuclei as well as the spontaneous fission of cold nuclei and their isomers. The role of transport coefficients, like inertia and friction in fission dynamics is discussed. The effect of the nuclear shell structure on the fission probability and the mass and kinetic energy distributions of the fission fragments is presented. The fusion-fission process leading to the synthesis of new isotopes including super-heavy elements is described. The book will thus be useful for theoretical and experimental physicists, as well as for graduate and PhD students. (orig.)

  8. 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

  9. Fission dynamics at low excitation energy

    CERN Document Server

    Aritomo, Y

    2013-01-01

    The origin of mass asymmetry in the fission of uranium at a low excitation energy is clarified by a trajectory analysis of the Langevin equation. The positions of the peaks in the mass distribution of fission fragments are mainly determined by fission saddle points originating from the shell correction energy. The widths of the peaks, on the other hand, result from a shape fluctuation around the scission point caused by the random force in the Langevin equation. We found that a random vibration in the oblate direction of fissioning fragments is essential for the fission process. According to this picture, fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup. This is expected to lead to a new viewpoint of fission dynamics and the splitting mechanism.

  10. 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

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

    International Nuclear Information System (INIS)

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

  12. Dynamics of Cell Shape Inheritance in Fission Yeast

    OpenAIRE

    Abenza, Juan F.; Chessel, Anatole; Raynaud, William G.; Carazo-salas, Rafael E.

    2014-01-01

    Every cell has a characteristic shape key to its fate and function. That shape is not only the product of genetic design and of the physical and biochemical environment, but it is also subject to inheritance. However, the nature and contribution of cell shape inheritance to morphogenetic control is mostly ignored. Here, we investigate morphogenetic inheritance in the cylindrically-shaped fission yeast Schizosaccharomyces pombe. Focusing on sixteen different ‘curved’ mutants - a class of m...

  13. 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.)

  14. Monte Carlo based toy model for fission process

    International Nuclear Information System (INIS)

    There are many models and calculation techniques to obtain visible image of fission yield process. In particular, fission yield can be calculated by using two calculations approach, namely macroscopic approach and microscopic approach. This work proposes another calculation approach in which the nucleus is treated as a toy model. Hence, the fission process does not represent real fission process in nature completely. The toy model is formed by Gaussian distribution of random number that randomizes distance like the distance 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 (?CN, ?L, ?R), and standard deviation (?CN, ?L, ?R). By overlaying of three distributions, the number of particles (NL, NR) that are trapped by central points can be obtained. This process is iterated until (NL, NR) become constant numbers. Smashing process is repeated by changing ?L and ?R, randomly

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

    International Nuclear Information System (INIS)

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

  16. 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 froming 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)

  17. Fission yield covariance generation and uncertainty propagation through fission pulse decay heat calculation

    International Nuclear Information System (INIS)

    Highlights: • Fission yield data and uncertainty comparison between major nuclear data libraries. • Fission yield covariance generation through Bayesian technique. • Study of the effect of fission yield correlations on decay heat calculations. • Covariance information contribute to reduce fission pulse decay heat uncertainty. - Abstract: Fission product yields are fundamental parameters in burnup/activation calculations and the impact of their uncertainties was widely studied in the past. Evaluations of these uncertainties were released, still without covariance data. Therefore, the nuclear community expressed the need of full fission yield covariance matrices to be able to produce inventory calculation results that take into account the complete uncertainty data. State-of-the-art fission yield data and methodologies for fission yield covariance generation were researched in this work. Covariance matrices were generated and compared to the original data stored in the library. Then, we focused on the effect of fission yield covariance information on fission pulse decay heat results for thermal fission of 235U. Calculations were carried out using different libraries and codes (ACAB and ALEPH-2) after introducing the new covariance values. Results were compared with those obtained with the uncertainty data currently provided by the libraries. The uncertainty quantification was performed first with Monte Carlo sampling and then compared with linear perturbation. Indeed, correlations between fission yields strongly affect the uncertainty of decay heat. Eventually, a sensitivity analysis of fission product yields to fission pulse decay heat was performed in order to provide a full set of the most sensitive nuclides for such a calculation

  18. Cluster fission from the standpoint of nuclear fission

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-03-01

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

  19. A fission fragment detector for correlated fission output studies

    Science.gov (United States)

    Mosby, S.; Tovesson, F.; Couture, A.; Duke, D. L.; Kleinrath, V.; Meharchand, R.; Meierbachtol, K.; O'Donnell, J. M.; Perdue, B.; Richman, D.; Shields, D.

    2014-09-01

    A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup.

  20. Material synergism fusion-fission

    International Nuclear Information System (INIS)

    In fission and fusion reactors the common features such as operating temperatures and neutron exposures will have the greatest impact on materials performance and component lifetimes. Developing fast neutron irradiation resisting materials is a common issue for both fission and fusion reactors. The high neutron flux levels in both these systems lead to unique materials problems like void swelling, irradiation creep and helium embitterment. Both fission and fusion rely on ferritic-martensitic steels based on 9%Cr compositions for achieving the highest swelling resistance but their creep strength sharply decreases above ? 823K. The use of oxide dispersion strengthened (ODS) alloys is envisaged to increase the operating temperature of blanket systems in the fusion reactors and fuel clad tubes in fast breeder reactors. In view of high operating temperatures, cyclic and steady load conditions and the long service life, properties like creep, low cycle fatigue,fracture toughness and creepfatigue interaction are major considerations in the selection of structural materials and design of components for fission and fusion reactors. Currently, materials selection for fusion systems has to be based upon incomplete experimental database on mechanical properties. The usage of fairly well developed databases, in fission programmes on similar materials, is of great help in the initial design of fusion reactor components. Significant opportunities exist for sharing information on tities exist for sharing information on technology of irradiation testing, specimen miniaturization, advanced methods of property measurement, safe windows for metal forming, and development of common materials property data base system. Both fusion and fission programs are being directed to development of clean steels with very low trace and tramp elements, characterization of microstructure and phase stability under irradiation, assessment of irradiation creep and swelling behaviour, studies on compatibility with helium and developing fabrication and joining technologies for ferritic steels. There is also synergy in codifying mechanical design rules for high temperature structural materials. The rapid development of fusion requires a fundamental understanding and a robust predictive capability of radiation damage in materials located in high flux regions. A joint approach for solving material problems would bring significant benefits, including the acceleration of development of both areas. (orig.)

  1. 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 datahe 252Cf(SF) reaction with data available from literature.

  2. Nature

    Science.gov (United States)

    Heinhorst, Sabine; Cannon, Gordon

    1997-01-01

    The fact that two of the original articles by this year's Nobel laureates were published in Nature bears witness to the pivotal role of this journal in documenting pioneering discoveries in all areas of science. The prize for Physiology or Medicine was awarded to immunologists Peter C. Doherty (University of Tennessee) and Rolf M. Zinkernagel (University of Zurich, Switzerland), honoring work that, in the 1970s, laid the foundation for our current understanding of the way in which our immune system differentiates between healthy cells and virus-infected ones that are targeted for destruction (p 465 in the October 10 issue of vol. 383). Three researchers share the Chemistry award for their discovery of C60 buckminsterfullerenes. The work by Robert Curl, Richard Smalley (both at Rice University), and Harry Kroto (University of Sussex, UK) has led to a burst of new approaches to materials development and in carbon chemistry (p 561 of the October 17 issue of vol. 383). This year's Nobel prize in physics went to three U.S. researchers, Douglas Osheroff (Stanford University) and David M. Lee and Robert C. Richardson (Cornell University), who were honored for their work on superfluidity, a frictionless liquid state, of supercooled 3He (p 562 of the October 17 issue of vol. 383).

  3. Nuclear-fission studies with relativistic secondary beams: Analysis of fission channels

    International Nuclear Information System (INIS)

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

  4. Nuclear-fission studies with relativistic secondary beams: Analysis of fission channels

    Energy Technology Data Exchange (ETDEWEB)

    Boeckstiegel, C.; Steinhaeuser, S. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, 64289 Darmstadt (Germany); Schmidt, K.-H. [Gesellschaft fuer Schwerionenforschung m.b.H., Planckstrasse 1, 64291 Darmstadt (Germany)], E-mail: k.h.schmidt@gsi.de; Clerc, H.-G.; Grewe, A.; Heinz, A.; Jong, M. de [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, 64289 Darmstadt (Germany); Junghans, A.R. [Gesellschaft fuer Schwerionenforschung m.b.H., Planckstrasse 1, 64291 Darmstadt (Germany); Mueller, J. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, 64289 Darmstadt (Germany); Voss, B. [Gesellschaft fuer Schwerionenforschung m.b.H., Planckstrasse 1, 64291 Darmstadt (Germany)

    2008-04-01

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

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

    CERN Document Server

    Herndon, J Marvin

    2013-01-01

    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 ...

  6. Nuclear Dissipation from Fission Time

    International Nuclear Information System (INIS)

    Fission times, pre-scission neutron multiplicities and GDR pre-scission ?-ray multiplicities measured for uranium or thorium nuclei formed with temperatures T ? 1.8 MeV have been compared with calculations performed with CDSM2, a two-dimensional dynamical model combined with a statistical one. Among the three experimental approaches considered, fission times give access to the most precise pieces of information on nuclear dissipation at high excitation energy. For the temperature range under consideration, an agreement between the model and data is achieved if one-body dissipation is used with a strength factor kred ? 0.45 ± 0.10 applied to the wall term for the mononuclear configuration. (authors)

  7. Fission hindrance and nuclear viscosity

    International Nuclear Information System (INIS)

    Measurements of GDR gamma-rays in coincidence with fission fragments from medium heavy to very heavy systems are drawn. These measurements have shown excess yield of GDR gamma-rays from the fissioning compound nucleus than what is expected from simple transition state model. The excess yield of GDR gamma-rays is explained by incorporating dissipative mechanism through the Kramers formalism in the statistical model calculations. It will be shown, through a systematic analysis of different systems, namely, 16O+208Pb, and 32S+208Pb, over a wide range of excitation energy that the Kramers' viscosity parameter has ? no apparent temperature dependence. Instead, it may have some dependence on the angular momentum. The role of various parameters in the modified statistical model analysis, their importance and limitations, will be discussed

  8. The fusion-fission hybrid

    International Nuclear Information System (INIS)

    As the history of the development of fusion energy shows, a sustained controlled fusion reaction is much more difficult to produce than rapid uncontrolled release of fusion energy. Currently, the ''magnetic bottle'' technique shows sufficient progress that it might applied for the commercial fuel production of /sup 233/U, suitable for use in fission reactors, by developing a fusion-fission hybrid. Such a device would consist of a fusion chamber core surrounded by a region containing cladded uranium pellets cooled by helium, with lithium salts also present to produce tritium to refuel the fusion process. Successful development of this hybrid might be possible within 10 y, and would provide both experience and funds for further development of controlled fusion energy

  9. The Fission of thorium with Alpha Particles

    Energy Technology Data Exchange (ETDEWEB)

    Newton, Amos S.

    1948-10-15

    Soon after the discovery of fission, Meitner, Bretscher and Cook found differences in the decay of various chemical fractions separated from uranium irradiated with slow neutrons and thorium irradiated with fast neutrons respectively and suggested that a difference existed in the distribution of fission products in the two cases. In 1940, Turner suggested that the distribution in various modes of fission should be investigated. The fact that elements such as tin, cadmium, palladium, and silver were found in fast neutron and deuteron fission of uranium and thorium before they were found in slow neutron fission of uranium suggested that the middle region of the distribution was raised as the energy of the incident particle was increased. Since the compound nucleus formed in the fission of thorium with alpha particles is U{sup 236}, the same compound nucleus formed in the fission of U{sup 235} with neutrons, it is of interest to study the fission of thorium with alphas and compare the resulting distribution of fission products with that found with uranium with slow and thorium with fast neutrons. Any difference between the various results where the same compound nucleus is formed must be due to differences in energy content and possible differences in distribution of the nucleons in the compound nucleus at the time of fission.

  10. Sensitivity of Makrofol fission track detectors

    International Nuclear Information System (INIS)

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

  11. Theories of fission gas behaviour

    International Nuclear Information System (INIS)

    A review is presented of the theoretical developments and experimental evidence that have helped to evolve current models used to describe the behaviour of inert fission gases created during the irradiation behaviour of reactor fuel materials. The phenomena which are stressed relate primarily to steady state behaviour of fuel elements but are also relevant to an understanding of transient behaviour. The processes considered include gas atom solubility; gas atom diffusivity; bubble nucleation; and bubble growth, by bubble coalescence. (U.K.)

  12. Sexual differentiation in fission yeast

    DEFF Research Database (Denmark)

    Egel, R; Nielsen, O

    1990-01-01

    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.

  13. The VERDI fission fragment spectrometer

    Directory of Open Access Journals (Sweden)

    Frégeau M.O.

    2013-12-01

    Full Text Available 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.

  14. Fission fusion hybrids- recent progress

    Science.gov (United States)

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

    2012-03-01

    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.

  15. 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 e 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)

  16. Collective spectra along the fission barrier

    Directory of Open Access Journals (Sweden)

    Pigni M. T.

    2012-12-01

    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.

  17. MODELING AND FISSION CROSS SECTIONS FOR AMERICIUM.

    Energy Technology Data Exchange (ETDEWEB)

    ROCHMAN, D.; HERMAN, M.; OBLOZINSKY, P.

    2005-05-01

    This is the final report of the work performed under the LANL contract on the modeling and fission cross section for americium isotopes (May 2004-June 2005). The purpose of the contract was to provide fission cross sections for americium isotopes with the nuclear reaction model code EMPIRE 2.19. The following work was performed: (1) Fission calculations capability suitable for americium was implemented to the EMPIRE-2.19 code. (2) Calculations of neutron-induced fission cross sections for {sup 239}Am to {sup 244g}Am were performed with EMPIRE-2.19 for energies up to 20 MeV. For the neutron-induced reaction of {sup 240}Am, fission cross sections were predicted and uncertainties were assessed. (3) Set of fission barrier heights for each americium isotopes was chosen so that the new calculations fit the experimental data and follow the systematics found in the literature.

  18. Bimodal fission in binary and ternary spontaneous fission of 252Cf

    International Nuclear Information System (INIS)

    The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a ?-?-? coincidence cube for binary fission and LCP-gated ?-? matrix for ternary fission. By identifying the secondary fission fragments from their ?-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the 'hot mode' corresponding to ?3.1% of the total yield. In ? ternary fission, the first measurements of yields for specific fission splits are presented. The Te-?-Ru and Xe-?-Mo neutron yields fit well with a single mode, but the Ba-?-Zr split shows evidence for an enhanced hot mode with an intensity of ?13.8% of the normal mode

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

    Science.gov (United States)

    Clement, J. D.

    1973-01-01

    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.

  20. On the possibilities of the extraction and application of low-activity fission products from high-activity nuclear fuel wastes

    International Nuclear Information System (INIS)

    The possibilities of an economical extraction and technical application of low-activity fission products (krypton, xenon, rhodium, palladium, ruthenium, technetium) from radioactive wastes are shown. A survey is presented on the production, properties and quantities of fission products in nuclear fuel, on their application, the demand to be expected by the year 2000, and the supply from natural resources, as well as the economic prospects of pilot plants producing fission products. (author)

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

    International Nuclear Information System (INIS)

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

  2. 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)

  3. Fission barriers and half-lives

    International Nuclear Information System (INIS)

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

  4. Fission of nuclei far from stability

    International Nuclear Information System (INIS)

    The secondary-beam facility of GSI provided the technical equipment for a new kind of fission experiment. Fission properties of short-lived neutron-deficient nuclei have been investigated in inverse kinematics. The measured element distributions reveal new kinds of systematics on shell structure and even-odd effects and lead to an improved understanding of structure effects in nuclear fission. Prospects for further experimental studies are discussed. (orig.)

  5. Channel theory of fission with diffusive dynamics

    International Nuclear Information System (INIS)

    The channel theory of fission with diffusive dynamics is proposed based on Bohr channel theory of fission and Fokker-Planck equation. The main features of the theory proposed are illustrated both in analytical and numerical way. n + 238U as an example to calculate ?f by using the channel theory of fission with diffusive dynamics in the range of incident neutron energy from 1 to 9 MeV is presented. (2 figs.)

  6. Fission product retention in HTGR fuels

    International Nuclear Information System (INIS)

    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

  7. Measurements of Fission Cross Sections of Actinides

    CERN Multimedia

    Wiescher, M; Cox, J; Dahlfors, M

    2002-01-01

    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.

  8. Fission barriers and half-lives

    Energy Technology Data Exchange (ETDEWEB)

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

    1989-01-01

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

  9. Dynamics of incomplete fusion-fission reactions

    OpenAIRE

    Crouzen, Paulus Caorlus Nicolaas

    1988-01-01

    Fifty years after its first observation, nuclear fission is still a lively field of research. The contemporary interest in this well established phenomenon is mainly related to heavy-ion physics, where fission provides a valuable means for the study of reaction mechanisms. Until recently, most of the experiments on heavy-ion induced fission reactions were inclusive and often could not distinguish between complete and incomplete fusion. The present thesis work, however, was specifically focuss...

  10. Maximum entropy approach to nuclear fission processes

    International Nuclear Information System (INIS)

    The conservation of the number of nucleons is shown to be an important constraint that governs the nuclear fission process. Both cold and energy-rich fission processes are analyzed. Particular attention is paid to the role of pairing effects in governing the fine structure in the mass and charge distributions. Symmetric and asymmetric fission processes are studied using a maximal entropy procedure. The interpretation of the results in terms of the Planck potential of the nucleons is discussed. (orig.)

  11. Fission properties of einsteinium and fermium

    International Nuclear Information System (INIS)

    The systematics of the low energy fission of the fermium isotopes is studied considering half-lives, masss division, kinetic-energy release, and accompanying prompt neutron emission. It is shown that the low energy fission of the fermium isotopes is a microcosm of the fission process, exhibiting a wide range of half lives, mass and kinetic energy distributions and varying neutron emission. The trends in the fermium isotopes are considered. 23 references

  12. Future Scenarios for Fission Based Reactors

    International Nuclear Information System (INIS)

    The coming century will see the exhaustion of standard fossil fuels, coal, gas and oil, which today represent 75% of the world energy production. Moreover, their use will have caused large-scale emission of greenhouse gases (GEG), and induced global climate change. This problem is exacerbated by a growing world energy demand. In this context, nuclear power is the only GEG-free energy source available today capable of responding significantly to this demand. Some scenarios consider a nuclear energy production of around 5 Gtoe in 2050, which would represent a 20% share of the world energy supply. Present reactors generate energy from the fission of U-235 and require around 200 tons of natural Uranium to produce 1GWe.y of energy, equivalent to the fission of one ton of fissile material. In a scenario of a significant increase in nuclear energy generation, these standard reactors will consume the whole of the world's estimated Uranium reserves in a few decades. However, natural Uranium or Thorium ore, which are not themselves fissile, can produce a fissile material after a neutron capture (239Pu and 233U respectively). In a breeder reactor, the mass of fissile material remains constant, and the fertile ore is the only material to be consumed. In this case, only 1 ton of natural ore is needed to produce 1GWe.y. Thus, the breeding concept allows optimal use of fertile ore and development of sustainable nuclear energy production for several thousand yeaenergy production for several thousand years into the future. Different sustainable nuclear reactor concepts are studied in the international forum 'generation IV'. Different types of coolant (Na, Pb and He) are studied for fast breeder reactors based on the Uranium cycle. The thermal Thorium cycle requires the use of a liquid fuel, which can be reprocessed online in order to extract the neutron poisons. This paper presents these different sustainable reactors, based on the Uranium or Thorium fuel cycles and will compare the different options in term of fissile inventory, capacity to be deployed, induced radiotoxicities, and R and D efforts

  13. Future Scenarios for Fission Based Reactors

    Science.gov (United States)

    David, S.

    2005-04-01

    The coming century will see the exhaustion of standard fossil fuels, coal, gas and oil, which today represent 75% of the world energy production. Moreover, their use will have caused large-scale emission of greenhouse gases (GEG), and induced global climate change. This problem is exacerbated by a growing world energy demand. In this context, nuclear power is the only GEG-free energy source available today capable of responding significantly to this demand. Some scenarios consider a nuclear energy production of around 5 Gtoe in 2050, wich would represent a 20% share of the world energy supply. Present reactors generate energy from the fission of U-235 and require around 200 tons of natural Uranium to produce 1GWe.y of energy, equivalent to the fission of one ton of fissile material. In a scenario of a significant increase in nuclear energy generation, these standard reactors will consume the whole of the world's estimated Uranium reserves in a few decades. However, natural Uranium or Thorium ore, wich are not themselves fissile, can produce a fissile material after a neutron capture ( 239Pu and 233U respectively). In a breeder reactor, the mass of fissile material remains constant, and the fertile ore is the only material to be consumed. In this case, only 1 ton of natural ore is needed to produce 1GWe.y. Thus, the breeding concept allows optimal use of fertile ore and development of sustainable nuclear energy production for several thousand years into the future. Different sustainable nuclear reactor concepts are studied in the international forum "generation IV". Different types of coolant (Na, Pb and He) are studied for fast breeder reactors based on the Uranium cycle. The thermal Thorium cycle requires the use of a liquid fuel, which can be reprocessed online in order to extract the neutron poisons. This paper presents these different sustainable reactors, based on the Uranium or Thorium fuel cycles and will compare the different options in term of fissile inventory, capacity to be deployed, induced radiotoxicities, and R&D efforts.

  14. Recent advances in fusion-fission reactions

    International Nuclear Information System (INIS)

    Not only is the fission decay mode (the subject of this paper) uniquely important in reactions with heavy ions, but the authors have, after a decade of study and controversy, arrived at a quantitative understanding of the competition between fission and particle emission from compound nuclei, at least at relatively low bombarding energies. The author presents recently published conclusions on angular-momentum-dependent fission barriers. He presents unpublished results from the extension of these studies to higher energies. Finally, the author mentions measurements of neutron emission associated with fission and the potentially important role that such measurements play in the determination of the magnitude of nuclear dissipation

  15. 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

  16. Theoretical Description of the Fission Process

    Energy Technology Data Exchange (ETDEWEB)

    Witold Nazarewicz

    2003-07-01

    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.

  17. Attachment of gaseous fission products to aerosols

    International Nuclear Information System (INIS)

    Accidents may occur in which the integrity of fuel cladding is breached and volatile fission products are released to the containment atmosphere. In order to assess the magnitude of the subsequent radiological hazard it is necessary to know the transport behaviour of such fission products. It is frequently assumed that the fission products remain in the gaseous phase. There is a possibility, however, that they may attach themselves to particles and hence substantially modify their transport properties. This paper provides a theoretical assessment of the conditions under which gaseous fission products may be attached to aerosol particles. Specific topics discussed are: the mass transfer of a gaseous fission product to an isolated aerosol particle in an infinite medium; the rate at which the concentration of fission products in the gas phase diminishes within a container as a result of deposition on a population of particles; and the distribution of deposited fission product between different particle sizes in a log-normal distribution. It is shown that, for a given mass, small particles are more efficient for fission product attachment, and that only small concentrations of such particles may be necessary to achieve rapid attachment. Conditions under which gaseous fission products are not attached to particles are also considered, viz, the competing processes of deposition onto the containment walls and onto aerosol particles, and the possibility of the removal of aerosols from the containment by various deposition processes, or agglomeration, before attachment takes place. (author)

  18. Some Fission Problems Circa 1950 and 2008

    Science.gov (United States)

    ?wiatecki, W. J.

    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.

  19. Fusion and fission of heavy nuclei

    International Nuclear Information System (INIS)

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

  20. Cold valleys in fusion and fission

    International Nuclear Information System (INIS)

    The cold fission configuration after the preformation of the fragments resembles a short-lived dinuclear or quasi-molecular system. The most conceivable scission configuration is given by two fission fragments in touching with the symmetry axes aligned (pole-pole orientation). This conclusion was based on the simple argument that this configuration offers the optimal tunneling time, i.e. the difference between the Coulomb barrier and the decay energy Q is minimal. Other orientations are apparently precluded in cold spontaneous fission and should be regarded as quasi-fission doorways in the synthesis of superheavy elements by cold fusion. (orig.)

  1. Status of fission product yield data

    International Nuclear Information System (INIS)

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

  2. Theoretical Description of the Fission Process

    Science.gov (United States)

    Nazarewicz, Witold

    2006-10-01

    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.

  3. Beta-decay energy following fission

    International Nuclear Information System (INIS)

    A considerable uncertainty exists in the energy released following fission in the form of beta radiation from the fission products. Work supported in part by the UKAEA has been carried out at the Scottish Research Reactor Centre to measure the rate of decay of beta energy for times up to 105 s following irradiation of 235U for periods of 10 to 105 s. From the data it is possible to derive the total beta energy release and this is calculated to be 6.3 ± 0.5 MeV per fission. It is hoped to present data for 233U and 239Pu fission. (author)

  4. 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)

  5. Shell Effects in Nuclear Fission

    International Nuclear Information System (INIS)

    The important part played by shell effects in nuclear fission has been reliably established experimentally and forms the basis of the theory of asymmetry of fission and other properties of fission fragments. However, from the theoretical point of view there are certain difficulties in understanding these effects, since at the moment of scission the fragments axe considerably deformed. When the shell effects are calculated in succession, the energy of the fissioning nucleus before scission may be presented in the form of the sum of the energies of the spherical fragments taking shell effects into account, the Coulomb interaction energy of the fragments and their deformation energy. The deformation energy of the fragments should be calculated not using the elasticity values of the fragments according to the drop model, but, for very low deformations, the single particle elasticity values taking into account the magic effects, with a gradual transition to the drop values for deformations at which the levels of neighbouring shells intersect. The single-particle elasticity values can be obtained from the experimental data on the Coulomb excitation of the nuclei. In Vandenbosch's calculations of fragment deformation, the elasticity of the fragments was based on the condition of coincidence between the deformation energy of the fragments and the experimental values for their excitation energy. However, in this case the elasticity was assumed to be constant at all deformations, and for this reason, although the elasticity values found in Vandenbosch do show magic'effects, they differ considerably in magnitude from the experimental elasticity values (see above).. The calculations of Vandenbosch also failed to take into account the magic effects for non-deformed fragments that lead to a reduction in the energy of the magic nucleus. Therefore, according to these calculations fission should be symmetrical, since the elasticity and consequently also the deformation energy (at the same deformation) are greater for magic than for non-magic nuclei. In fact, since the energy gain for magic spherical fragments is greater than the loss resulting from the increase in elasticity, the formation of magic and near-magic fragments, i.e. asymmetrical fission, is energetically advantageous. This energy gain is essentially connected with the fact that because of the high elasticity value at low deformations the magic fragments are so little deformed that the deformation energy does not compensate for the difference in mass of magic and non-magic fragments. Apart from the deformation energy, the kinetic energy of the separating degrees of freedom at the moment of scission should be taken into account when calculating the excitation energy of fragments. For the shell effects of the fragments to play an important part in fission, the process of deformation of the nucleus on descending from the saddle point (in the case of threshold fission) must be, as in fact it is, fairly slow with respect to the nucleonic degrees of freedom, i.e. ?def >> ?nucleon (?def is the descent time, ?nucleon ? n/?Enucleon, and ?Enucleon is the distance between the nucleon levels). In this case nucleonic shells are formed before scission. At the same time ?def rot, i.e. the process of descent is fast with respect to the rotational degrees of freedom (?rot h/?Erot) - In the case of fission of an excited nucleus with fairly high excitation energy at the saddle point, ?Enucleon may be so low that not only ?def rot but also ?def nucleon, i.e. the process of descent is accelerated with respect to all the degrees of freedom. In this case the density matrix of the nucleus does not change on moving from the saddle point. This would seem to explain the fact that the theoretical angular distribution of fragments at fission of an excited nucleus agrees with the experimental value only when the parameters determining the rotational state of the nucleus (moment of inertia) at the saddle point and not at the scission point are used. (author). (author)

  6. Large-scale fission product containment tests

    International Nuclear Information System (INIS)

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

  7. Baby fission chambers; Etude de chambres a fission miniatures

    Energy Technology Data Exchange (ETDEWEB)

    Guery, U.; Tachon, J. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1957-07-01

    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) [French] Le present rapport se propose, d'une part, d'exposer les principales realisations de chambres a fission, d'autre part de faire une mise au point a caractere plus general sur ces detecteurs. Au depart, c'est surtout en vue des mesures de densite neutronique dans 'Proserpine' que les auteurs ont etudie ces chambres; au cours de la mise au point, il a paru interessant de developper leur etude pour des applications plus generales: mesures de densites de neutrons de differentes energies dans un element de volume tres reduit et avec faible perturbation locale. (auteur)

  8. Spontaneous fission decay constant of 238Pu

    International Nuclear Information System (INIS)

    Due to the high alpha-to-spontaneous fission back ratio of plutonium-238, previous attempts to measure its spontaneous fission rate were limited to few total fissions, with poor statistical accuracy resulting. Two independent techniques are used which have been able to surmount the alpha pile-up problem. In addition, a survey of current advances in the theory of spontaneous fission is presented. The first measurement technique involved the use of the mineral mica as a solid-state fission-track recorder. In one exposure spontaneous fission fragments are recorded. In the second exposure, tracks from thermal fissions in Pu-238 and Pu-239 as well as spontaneous fission are recorded. The spontaneous fission-decay constant may be calculated without knowledge of the source mass and absolute track-registration efficiency. By using the vendor's value of source isotopic ratio and measuring the thermal column flux with gold foils, a value is obtained for the spontaneous fission-decay constant of Pu-238. In terms of half-life, this value is 4.63 +- 0.12 x 1010 years. The second technique involved coincidence counting of fission fragments using silicon surface-barrier semiconductor detectors. The alpha rate of the source was measured by lower geometry alpha counting. The absolute counting efficiencies for both coincidence and alpha counting were calculated by a Monte Carlo computer program. The validity of the Monte Carlo calculation was checked by comparison with alphaation was checked by comparison with alpha counting of a standard alpha source. (U.S.)

  9. Stochastic resonance in nuclear fission

    International Nuclear Information System (INIS)

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

  10. Radiative Neutron Capture In Fissionable Nuclei

    International Nuclear Information System (INIS)

    Because of the great success of the (n, ?) method in nuclear structure studies, it is desirable to extend such measurements to fissionable target nuclei. A suitable spectrometer for investigating the high-energy radiative capture spectrum without significant interference from the fission process has been installed at the Karlsruhe research reactor FR- 2. The instrument is briefly discussed. First preliminary results are presented. (author)

  11. Calculation code of the fission products activity

    International Nuclear Information System (INIS)

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

  12. Independent Isotopic Fission Yield Studies with Jyfltrap

    Science.gov (United States)

    Penttilä, H.; Elomaa, V.-V.; Eronen, T.; Gorelov, D.; Hakala, J.; Jokinen, A.; Kankainen, A.; Karvonen, P.; Kolhinen, V. S.; Moore, I. D.; Rahaman, S.; Rinta-Antila, S.; Rissanen, J.; Rubchenya, V.; Saastamoinen, A.; Sonoda, T.; Weber, C.; Äystö, J.

    2014-09-01

    A technique to determine the independent isotopic fission yields utilizing the ability of a Penning trap to unambiguously identify the isotopes based on their mass has recently been developed at the IGISOL facility in the University of Jyväskylä. The analysis of proton induced fission of 238U at 25 MeV energy has been finalized. The results will be compared with theoretical models.

  13. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

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

  14. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

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

  15. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

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

  16. Qualitative specific features of nuclear fission dynamics

    International Nuclear Information System (INIS)

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

  17. Options for Affordable Fission Surface Power Systems

    Science.gov (United States)

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

    2006-01-01

    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.

  18. 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

  19. 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

  20. Spontaneous fission properties and lifetime systematics

    International Nuclear Information System (INIS)

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

  1. Induced-Fission Imaging of Nuclear Material

    International Nuclear Information System (INIS)

    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 ? ? + 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 cuntability, quality assurance, treaty confirmation, or homeland security applications.

  2. On prompt fission neutron spectrum in spontaneous fission of 252Cf

    International Nuclear Information System (INIS)

    Highlights: • We use simple analytical approach for PFNS in the laboratory system. • We compare our calculations with the observed PFNS in spontaneous fission of 252Cf. • LCL spectrum gives better representation of observed spectrum comparing with Watt spectrum. • A significant portion of scission neutrons can be described with our calculations. • Beside the Watt spectrum, LCL spectrum may also be used for representation of PFNS of 252Cf (sf). - Abstract: In this work we use simple representations of prompt fission neutron spectrum in both the center of mass system of fission fragments and the laboratory system which takes into account the multiple neutron emission from fission fragments. The laboratory spectra are compared with the observed spectrum of prompt fission neutrons in spontaneous fission of 252Cf. These forms of spectra, in addition to Watt spectrum, may be used for representation of observed prompt neutron spectrum of 252Cf spontaneous fission. The question on existence and quantity of scission neutrons is also discussed

  3. Cumulative fission product yields of fast-neutron fission of 232Th

    International Nuclear Information System (INIS)

    The cumulative yields of 33 fission products in fast-neutron induced fission of 232Th have been determined using direct gamma ray spectroscopic method. To obtain the absolute yields of fission products having half-lives ranging from 13 s to 32 days, a total of 66 multi-scaling gamma ray spectra with various irradiation and cooling periods were collected. Gamma rays and photopeak areas of interest were assigned to the fission products by their energies and half-lives. Fission product activities were evaluated from spectral data using growth and decay calculation, and fission yields were determined by normalizing the 140Ba yield to the average value from reported data. Results of the cumulative fission yields, among which 22 were measured for the first time, are compared with previous measurements and with recommended yields in recent evaluations. The agreements and some discrepancies of the comparisons are discussed, with the odd-even pairing effect emphasized. (orig.)

  4. 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)

  5. 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

  6. Nuclear Fission and Fission{minus}Product Spectroscopy: Second International Workshop. Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    Fioni, G. [Commissariat Energie Atomique, Saclay (France); Faust, H.; Oberstedt, S. [Institut Laue-Langevin, Grenoble (France); Hambsch, F. [Institute for Reference Materials and Measurements, Geel (Belgium)

    1998-10-01

    These proceedings represent papers presented at the Second International Workshop on Nuclear Fission and Fission{minus}Product Spectroscopy held in Seyssins, France in April, 1998. The objective was to bring together the specialists in the field to overview the situation and to assess our present understanding of the fission process. The topics presented at the conference included nuclear waste management, incineration, neutron driven transmutation, leakage etc., radioactive beams, neutron{minus}rich nuclei, neutron{minus}induced and spontaneous fission, ternary fission phenomena, angular momentum, parity and time{minus}reversal phenomena, and nuclear fission at higher excitation energy. Modern spectroscopic tools for gamma spectroscopy as applied to fission were also discussed. There were 53 papers presented at the conference,out of which 3 have been abstracted for the Energy,Science and Technology database.(AIP)

  7. Nuclear Fission and Fission-Product Spectroscopy: Second International Workshop. Proceedings

    International Nuclear Information System (INIS)

    These proceedings represent papers presented at the Second International Workshop on Nuclear Fission and Fission-Product Spectroscopy held in Seyssins, France in April, 1998. The objective was to bring together the specialists in the field to overview the situation and to assess our present understanding of the fission process. The topics presented at the conference included nuclear waste management, incineration, neutron driven transmutation, leakage etc., radioactive beams, neutron-rich nuclei, neutron-induced and spontaneous fission, ternary fission phenomena, angular momentum, parity and time-reversal phenomena, and nuclear fission at higher excitation energy. Modern spectroscopic tools for gamma spectroscopy as applied to fission were also discussed. There were 53 papers presented at the conference,out of which 3 have been abstracted for the Energy,Science and Technology database

  8. Fission models of population variability.

    Science.gov (United States)

    Thompson, E A

    1979-10-01

    Most models in population genetics are models of allele frequency, making implicit or explicit assumptions of equilibrium or constant population size. In recent papers, we have attempted to develop more appropriate models for the analysis of rare variant data in South American Indian tribes; these are branching process models for the total number of replicates of a variant allele. The spatial distribution of a variant may convey information about its history and characteristics, and this paper extends previous models to take this factor into consideration. A model of fission into subdivisions is superimposed on the previous branching process, and variation between subdivisions is considered. The case where fission is nonrandom and the locations of like alleles are initially positively associated, as would happen were a tribal cluster or village to split on familial lines, is also analyzed. The statistics developed are applied to Yanomama Indian data on rare genetic variants. Due to insufficient time depth, no definitive new inferences can be drawn, but the analysis shows that this model provides results consistent with previous conclusions, and demonstrates the general type of question that may be answered by the approach taken here. In particular, striking confirmation of a higher-than-average growth rate, and hence smaller-than-previously-estimated age, is obtained for the Yan2 serum albumen variant. PMID:535728

  9. Quark bags and their fission

    International Nuclear Information System (INIS)

    The aim of this work is to gain more insight into the physics of hadrons and to develop a theoretical framework for the treatment of hadronic fission. The description of hadronic matter in terms of quantum chromodynamics, which is generally accepted as the fundamental theory of strong interactions, is intimately connected with the concept of colour confinement. Since this phenomenon is a property of the vacuum state, much effort has been invested into trying to understand it in analogy with the occurence of the condensed ground state in the theory of superconductivity. In Chapter II, we therefore go back to non-relativistic physics, discuss the methods used there, and report in Chapter III on various attempts to apply these methods in quantum field theories, in particular in connection with the so-called 'dynamical symmetry breaking'. Although the fundamental problem of the 'true' vacuum state has not yet been solved, its solution has been anticipated in the so-called bag models which are discussed in great detail in Chapter IV. In Chapter V, we finally seek to understand the microscopic process of fission of hadrons. (orig./HSI)

  10. Theoretical Description of the Fission Process

    Energy Technology Data Exchange (ETDEWEB)

    Witold Nazarewicz

    2009-10-25

    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.

  11. 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.

  12. Fission

    International Nuclear Information System (INIS)

    Progress is reported in the areas of radiation physics; radiation dosimetry and radiation biophysics; microdosimetry of internal sources; dosimetry of internal emitters; real-time measurement of Pu in air at below-MPC levels; analytical techniques for measurement of 99Tc in environmental samples; and radiation instrumentation--radiological chemistry

  13. Fission dynamics at low excitation energy. 2

    CERN Document Server

    Aritomo, Y; Ivanyuk, F A

    2014-01-01

    The mass asymmetry in the fission of U-236 at low excitation energy is clarified by the analysis of the trajectories obtained by solving the Langevin equations for the shape degrees of freedom. It is demonstrated that the position of the peaks in the mass distribution of fission fragments is determined mainly by the saddle point configuration originating from the shell correction energy. The width of the peaks, on the other hand, results from the shape fluctuations close to the scission point caused by the random force in the Langevin equation. We have found out that the fluctuations between elongated and compact shapes are essential for the fission process. According to our results the fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup, but is accompanied by the fluctuations between elongated and compact shapes. This picture presents a new viewpoint of fission dynamics and the splitting mechanism.

  14. Theoretical study on spontaneous fission of actinides

    International Nuclear Information System (INIS)

    The spontaneous fission half-lives of the actinides are calculated by the WKB approximation and the potential barriers are constructed by a General Liquid Drop Model (GLDM) including the proximity energy, the mass and charge asymmetry, and an accurate nucleus radius. The microscopic shell correction which plays a key role for the spontaneous fission barrier is considered for the first time. The two-parameter quasi-molecular shape and the proximity are described in details within the GLDM. The effects of the microscopic shell correction and proximity energy for fission barrier are discussed separately. The calculated spontaneous fission half-lives for the actinides reasonably accord with the experimental data, implying the present GLDM combined with the microscopic shell correction can be used to study the spontaneous fission properties of heavy nuclei successfully. (authors)

  15. Superfluid dynamics of 258Fm fission

    CERN Document Server

    Scamps, Guillaume; Lacroix, Denis

    2015-01-01

    Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258Fm nucleus are studied. The resulting fission fragment characteristics show a good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle/quasi-particle picture is underlined and qualitatively studied.

  16. Fission Surface Power Technology Development Status

    Science.gov (United States)

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

    2010-01-01

    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.

  17. Standards for the fission yields measurements

    International Nuclear Information System (INIS)

    Two main methods are now used for the determination of fission yields. The gamma spectrometry, without or with radiochemical separations and the mass spectrometry using isotopic dilution. Fission yields are needed in burn up determination, dosimetry, safeguards and also in basic science (study of the fission mechanism). The 235U thermal neutron induced fission yields have been extensively studied. Complete and up to date evaluations for this system are available. The development of the most important of these fission yields, as standards, could be a good solution. They are easily measured and they allow the fulfilment of all the applications. A short review of all data available will be given. Only the gamma spectrometry method will be described. Some recommended decay data will be discussed. The experimental method will be also shortly described

  18. Experimental studies of fission barrier properties

    International Nuclear Information System (INIS)

    A review is presented of the experimental techniques for the determination of fission barrier properties including fission isomer and fission probability measurements. Microscopic statistical models for the extraction of barrier parameter estimates from the experimental data are described. The importance of nuclear symmetry effects on the calculation of fission widths is demonstrated. Evidence is presented for the fragmentation of the mass asymmetric second barrier in the thorium region and the axial asymmetric first barrier in the californium region. Detailed analyses of experimental data suggest the presence of two parallel second barriers; the normal mass asymmetric, axial symmetric barrier and a slightly higher mass symmetric, axial asymmetric barrier. Experimental barrier parameters are determined systematically and compared to calculations from various theoretical models. Techniques for expanding fission probability measurements to higher energies are discussed. (author)

  19. Physics of neutron emission in fission

    International Nuclear Information System (INIS)

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

  20. Improved Calculation of Thermal Fission Energy

    CERN Document Server

    Ma, X B; Wang, L Z; Chen, Y X; Cao, J

    2013-01-01

    Thermal fission energy is one of the basic parameters needed in the calculation of antineutrino flux for reactor neutrino experiments. It is useful to improve the precision of the thermal fission energy calculation for current and future reactor neutrino experiments, which are aimed at more precise determination of neutrino oscillation parameters. In this article, we give new values for thermal fission energies of some common thermal reactor fuel iso-topes, with improvements on two aspects. One is more recent input data acquired from updated nuclear databases. The other, which is unprecedented, is a consideration of the production yields of fission fragments from both thermal and fast incident neutrons for each of the four main fuel isotopes. The change in calculated antineutrino flux due to the new values of thermal fission energy is about 0.33%, and the uncertainties of the new values are about 30% smaller.

  1. Accidental and long-term safety assessment of fission and fusion power reactors

    International Nuclear Information System (INIS)

    Fusion is seen as a much cleaner energy than fission, and a resource for clean Energy in the far future. However, being a nuclear energy, fusion shares with fission most of its Safety problems. This study concerns the assessment of both the short term and the long term Hazards associated with fusion, compared with the same figures for fission reactors. For accidental Release of radioactive nuclide, fission data derive from well-known PWR safety assessments, and In particular from the Italian project PUN. Fusion data derive from the latest findings of the European SEAFP programme. Concerning inadvertent intrusion in a radioactive waste disposal Site: for fusion. This analysis was performed by the authors in the frame of the SEAFP-2 studies, While for fission data are taken from typical European waste disposal sites. Finally, for long-term Migration of radioactive nuclides due to natural waste package degradation, both fission and Fusion reactor cases are addressed. In all relevant cases, evaluation of associated risks is carried Out, with a comparison of the obtained results

  2. Empirical description of beta-delayed fission partial half-lives

    CERN Document Server

    Ghys, L; Antalic, S; Huyse, M; Van Duppen, P

    2015-01-01

    Background: The process of beta-delayed fission (bDF) provides a versatile tool to study low-energy fission in nuclei far away from the beta-stability line, especially for nuclei which do not fission spontaneously. Purpose: The aim of this paper is to investigate systematic trends in bDF partial half-lives. Method: A semi-phenomenological framework was developed to systematically account for the behavior of bDF partial half-lives. Results: The bDF partial half-life appears to exponentially depend on the difference between the Q value for beta decay of the parent nucleus and the fission-barrier energy of the daughter (after beta decay) product. Such dependence was found to arise naturally from some simple theoretical considerations. Conclusions: This systematic trend was confirmed for experimental bDF partial half-lives spanning over 7 orders of magnitudes when using fission barriers calculated from either the Thomas-Fermi or the liquid-drop fission model. The same dependence was also observed, although less p...

  3. Fission product measurements in the inpile fission product loop

    International Nuclear Information System (INIS)

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

  4. Fissioned triangular schemes via sharply 3-transitive groups

    CERN Document Server

    Ma, Jianmin

    2011-01-01

    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...

  5. Radiation Specifications for Fission Power Conversion Component Materials

    Science.gov (United States)

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

    2011-01-01

    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.

  6. Thermal stability of fission tracks in apatite and sphene: using confined-track-length measurements

    International Nuclear Information System (INIS)

    Confined track lengths have been used to monitor the annealing behaviour of fission tracks in Durango apatite and in two natural sphene samples subjected to laboratory annealing treatment. The residual track length and residual track density in apatite are found not to follow a linear one-to-one relationship. Comparison of the spontaneous and induced fission track lengths in sphene samples shows no evidence for the natural fading as is observed in apatite. No significant difference is found between the stability of neutron-induced and spontaneous fission track lengths in sphene over the temperature and time combinations employed. The behaviour of confined track lengths in sphene is found to follow Arrhenius law over the experimental domain investigated. On the basis of the Arrhenius law, our results indicate that, corresponding to a time-period of 106 yr, the closure temperature would be 123 +- 10 C for Durango apatite and 423 +- 27 C for the sphene sample investigated. (author)

  7. Fission gas bubble behaviour in uranium dioxide

    International Nuclear Information System (INIS)

    A theoretical model developed to study the gas bubble evolution in nuclear materials has been used to analyze experiments on uranium dioxide irradiated to low burnups (0.1 and 0.4 at%), in which fission gas bubble size distributions were measured following out-of-pile isothermal anneals. Following irradiation, the UO2 was annealed for 1 or 6 h each at temperatures between 1303 and 1973 K and then thinned for transmission electron microscopy observation of the bubble size distributions. The model is based on the assumption, that the coalescence of the moving bubbles is the main mechanism defining gas porosity development under these conditions. The gas bubbles are assumed to be in equilibrium and their motion is assumed to be caused by random migration. The calculations show that the observed bubble size distributions may be reproduced on the base of the bubble growth mechanisms considered. The joint action of bubble surface and volume diffusion mechanisms can explain both the general nature of the experimental distributions and their perculiarities, in particularly the bimodal bubble size distribution observed after annealing at 1673 K. The choice of appropriate values as input parameters into the model is discussed. (orig.)

  8. Potential for large-scale uses for fission-product Xenon

    International Nuclear Information System (INIS)

    Of all fission products in spent, low-enrichment-uranium power-reactor fuels, xenon is produced in the highest yield - nearly one cubic meter, STP, per metric ton. In aged fuels which may be considered for processing in the US, radioactive xenon isotopes approach the lowest limits of detection. The separation from accompanying radioactive 85Kr is the essential problem; however, this is state-of-the-art technology which has been demonstrated on the pilot scale to yield xenon with pico-curie levels of 85Kr contamination. If needed for special applications, such levels could be further reduced. Environmental considerations require the isolation of essentially all fission-product krypton during fuel processing. Economic restraints assure that the bulk of this krypton will need to be separated from the much-more-voluminous xenon fraction of the total amount of fission gas. Xenon may thus be discarded or made available for uses at probably very low cost. In contrast with many other fission products which have unique radioactive characteristics which make them useful as sources of heat, gamma and x-rays, and luminescence - as well as for medicinal diagnostics and therapeutics - fission-product xenon differs from naturally occurring xenon only in its isotopic composition which gives it a slightly hgiher atomic weight, because of the much higher concentrations of the 134Xe and 136Xe isotopes. Therefore, fission-product xenon can most Therefore, fission-product xenon can most likely find uses in applications which already exist but which can not be exploited most beneficially because of the high cost and scarcity of natural xenon. Unique uses would probably include applications in improved incandescent light illumination in place of krypton and in human anesthesia

  9. Geology behind nuclear fission technology

    International Nuclear Information System (INIS)

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

  10. 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

  11. 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 (10000 to 2000C) had been imposed. Deposition on the wall of the duct occurred by vapor condensation in the higher temperature regions and by aerosol deposition in the remainder of the duct. Reactions in the gas stream between CsOH and CsI and between CsOH and Te had an effect on the vapor condensation. The aerosol was characterized by the use of impingement tabs placed in the gas stream

  12. 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

  13. 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

  14. On the mechanism of fission neutron emission

    International Nuclear Information System (INIS)

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

  15. 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

  16. Fission following fusion of Ni+Sn

    International Nuclear Information System (INIS)

    Excitation functions for fission were measured for /sup 58,64/Ni beams incident on the even /sup 112//sup --//sup 124/Sn targets at energies extending from well below to about 1.5 times the Coulomb barrier. Fission was identified by kinematic coincidence between fission fragments. Angle integrated fission cross sections were obtained from angular distributions taken at several energies for all systems. From these and the previously measured cross sections for evaporation residues, we obtain the total fusion cross sections and fission probabilities over the energy range 150 approx. < E/sub c.m./approx. <240 MeV. The competition between particle evaporation and fission in the compound nuclei is compared to statistical model calculations. A good description of the data for all 14 systems is achieved with the use of a single set of parameters. The model includes fission barriers with finite range and nuclear diffuseness effects, and partial-wave distributions for fusion that are qualitatively consistent with those from microscopic reaction model calculations. The fusion excitation functions are analyzed in terms of the dynamical fusion model of Swiatecki et al. Within this model we extract new values for the ''extra-push'' parameters

  17. Asymmetric fission from egg shape deformation

    International Nuclear Information System (INIS)

    Asymmetric mass distributions have proved to be one of the most persistent puzzles in the fission process. The asymmetric fission of heavy nucleus is considered to occur because of the shell effects. In the fissioning process however, at some point of deformation the nucleus has to assume an asymmetrical shape in the fissioning direction. Simplest asymmetrical shape is like an egg. This egg shape is obtained basically from two hemi-ellipsoids of revolution (about the major axis, b and c with equal minor axis, a), by joining the equal circular faces. With the increase of b and c values the value of a decreases so as to conserve the total volume. The fission occurs when the joint is snapped as a result of the total surface energy increasing beyond the total surface energy of the spherical fragments. It is important that the fission process or the cleavage starts in this proceedings of elongation at a point where the surface curvature is least and it is at the joint of the two hemi-ellipsoids. For the first time the Coulomb energy of this egg shaped 235U92 nucleus has been evaluated. Most importantly the Coulomb energy for various fragment combinations is seen to decreases from that of the symmetric fission. This behaviour will lead to lower Coulomb barriers and shapes varying around the saddle point. So far this aspect of P3(cos?) deformation has not been investigated and present work indicates smaller amount of shell corrections (due to smaller fission barriers) to be applicable in the asymmetric fission

  18. Analysis of fission with selective channel scission model

    International Nuclear Information System (INIS)

    The mass distributions of fission product yields for neutron-induced fissions of 232Th, 235U, 239Pu and 241Pu were calculated by the selective channel scission model with simple assumptions. Although the present calculation is a rough estimation, it is applicable to the wide range of fissionable nuclei without the adjustable parameters for each fission channel. (author)

  19. Future challenges for nuclear data research in fission (u)

    Energy Technology Data Exchange (ETDEWEB)

    Chadwick, Mark B [Los Alamos National Laboratory

    2010-01-01

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

  20. Fission cross section measurements for minor actinides

    Energy Technology Data Exchange (ETDEWEB)

    Fursov, B. [IPPE, Obninsk (Russian Federation)

    1997-03-01

    The main task of this work is the measurement of fast neutron induced fission cross section for minor actinides of {sup 238}Pu, {sup 242m}Am, {sup 243,244,245,246,247,248}Cm. The task of the work is to increase the accuracy of data in MeV energy region. Basic experimental method, fissile samples, fission detectors and electronics, track detectors, alpha counting, neutron generation, fission rate measurement, corrections to the data and error analysis are presented in this paper. (author)

  1. Emission probabilities of light nuclei in fission

    International Nuclear Information System (INIS)

    The emission probabilities of the various light nuclei emitted in fission were investigated on the basis of a model in which particle-emission results from a rapid change of potential energy in the 'neck' region of the fissioning nucleus. The nucleus was treated by means of a one-dimensional potential well of infinite depth. The relative emission probabilities and kinetic energies of the neutrons, protons and the other light nuclei emitted in fission were investigated as a function of the rise time and shape of the rising potential. (author)

  2. Theory of nuclear fission by stopped pions

    International Nuclear Information System (INIS)

    Nuclear fission by stopped pions is analyzed in a two-step model in which the pion is absorbed on a nucleon pair, followed by the prompt emission of one nucleon and compound nucleus formation by the other. This simple picture yields agreement with observed prompt neutron spectra and average nucleon multiplicities. The analysis of nuclear fission in a statistical framework is shown to provide valuable corroboration of the expected properties of a highly excited compound nucleus and of one's understanding of the pion absorption mechanism. The ratio of fission to neutron level density parameters is shown to exceed unity in all cases studied. (Auth.)

  3. Accidental fission product release from the plant

    International Nuclear Information System (INIS)

    The accidental risk emanating from the HTR-Modul is decisively determined by the fission products accumulating outside the core in the primary loop during normal operation; release of these proceeds only under conditions created by the incidents of water ingress, or depressurization. The trend analysis therefore investigates the fission products depositing within the primary loop and their release and conditions of transport for the case of steam generator leakage, or leak in the primary loop pipework. The investigation is made for the radiologically important fission products cesium, strontium, and iodine. (orig./DG)

  4. Annealing studies of fission damages in muscovite

    International Nuclear Information System (INIS)

    Arrhenius plots of fission damages in muscovite have been plotted under laboratory conditions and the data have been extrapolated to geologically significant times and temperatures. Fossil fission tracks in muscovite will start fading if it remained at approximately 60degC for 100 m.y. whereas in the same period, all the tracks will be annealed at a temperature of approximately 160degC. The activation energy of fission damages in the mineral ranges from 1.4 to 1.8 ev. (author)

  5. Advanced fission models in nuclear data calculations

    International Nuclear Information System (INIS)

    Transition states at the saddle points and superdeformed or hyperdeformed states in the secondary wells of multiple-humped potential barriers play an important role in low-energy fission processes. In the present work discrete collective spectra at large nuclear deformations are predicted by means of the dinuclear model and combined with the optical model for fission of the Empire-3 system of codes. The formalism is applied to the 233U(n, f) reaction and the computed cross section compared with recent experimental results of the nTOF Collaboration. Angular anisotopies of fission fragments are evaluated with an improved version of the scission-point model.

  6. Fission induced by nucleons at intermediate energies

    Science.gov (United States)

    Lo Meo, S.; Mancusi, D.; Massimi, C.; Vannini, G.; Ventura, A.

    2015-01-01

    Monte Carlo calculations of fission of actinides and pre-actinides induced by protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Liège Intranuclear Cascade Model, INCL++, coupled with two different evaporation-fission codes, GEMINI++ and ABLA07. In order to reproduce experimental fission cross sections, model parameters are usually adjusted on available (p , f) cross sections and used to predict (n , f) cross sections for the same isotopes.

  7. The chemistry of the fission products

    International Nuclear Information System (INIS)

    This is a review of chemistry of some chemical elements in fission products. The elements mentioned are krypton, xenon, rubidium, caesium, silver, strontium, barium, cadmium, rare earth elements, zirconium, niobium, antimony, molybdenum, tellurium, technetium, bromine, iodine, ruthenium, rhodium and palladium. The chemistry of elements and their oxides is briefly given together with the chemical species in aqueous solution. The report also contains tables of the physical properties of the elements and their oxides, of fission products nuclides with their half-life and fission yields and of the permissible concentrations. (author)

  8. Fission gas analysis of MOX fuel

    International Nuclear Information System (INIS)

    As a part of post irradiation studies on mixed oxide (MOX) (U,Pu)O2 fuel, atom ratios of two important gaseous fission products namely krypton and xenon have been determined employing electron impact-quadrupole mass spectrometry (EI-QMS). From the isotopic and the yield ratios of these fission gases, it was possible to conclude that majority of fissions could have occurred in 239Pu. An attempt has also been made to estimate the period of cooling from the measured 85Kr/84Kr atom ratio. (author)

  9. Fission track geochronology of Eastern Ghats

    International Nuclear Information System (INIS)

    Fission track geochronology of Eastern Ghats has been established by using fission track technique in dating micaceous and accessory minerals occurring in the region. Annealing studies confirm that radiation damage fossil tracks can be erased in minerals under intense metamorphic episodes thus resetting the geological clock. The fission track ages of the minerals range between 450 +- 5 m.y. to 622 +- 148 m.y. It is concluded that f.t. ages of the minerals date the last metamorphic event of the Eastern Ghats, known as the Indian Ocean Cycle. (author)

  10. Nuclear fission as resonance-mediated conductance

    OpenAIRE

    Bertsch, G. F.

    2014-01-01

    For 75 years the theory of nuclear fission has been based on the existence of a collective coordinate associated with the nuclear shape, an assumption required by the Bohr-Wheeler formula as well as by the R-matrix theory of fission. We show that it is also possible to formulate the theory without the help of collective coordinates. In the new formulation, fission is facilitated by individual states in the barrier region rather than channels over the barrier. In a certain li...

  11. Fission induced by nucleons at intermediate energies

    CERN Document Server

    Meo, Sergio Lo; Massimi, Cristian; Vannini, Gianni; Ventura, Alberto

    2014-01-01

    Monte Carlo calculations of fission of actinides and pre-actinides induced by protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Li\\`ege Intranuclear Cascade Model, INCL++, coupled with two different evaporation-fission codes, GEMINI++ and ABLA07. In order to reproduce experimental fission cross sections, model parameters are usually adjusted on available (p,f) cross sections and used to predict (n,f) cross sections for the same isotopes.

  12. Relative defect-production efficiency for fission fragments, alpha decay and electron irradiation in apatite and glass, and absorption spectroscopy age method

    International Nuclear Information System (INIS)

    Radiation damage induced in natural fluorapatite and artificial sodium silica glass by fission fragments, alpha decay and electron irradiation has been studied by optical absorption spectroscopy of the respective color centers as a function of the radiation dose. Relative production efficiencies obtained are approx. 3 x 10-7 for alpha/fission in apatite, approx. 3 x 10-5 for alpha/fission in glass, approx. 20 for electrons/alpha in apatite and approx. 2 for electrons/alpha in glass, respectively. The values obtained for alpha/fission are orders of magnitude lower than values calculated from a purely collisional model. Moreover, absorption spectroscopy of defects in natural apatite is proposed as a new (alternative to the fission track) method for the determination of mineral cooling ages. (author)

  13. Effects of fissioning nuclei distributions on fragment mass distributions for high energy fission

    Directory of Open Access Journals (Sweden)

    Rossi P C R

    2012-02-01

    Full Text Available We study the effects of fissioning nuclei mass- and energy-distributions on the formation of fragments for fission induced by high energy probes. A Monte Carlo code called CRISP was used for obtaining mass distributions and spectra of the fissioning nuclei for reactions induced by 660 MeV protons on 241Am and on 239Np, by 500 MeV protons on 208Pb, and by Bremsstrahlung photons with end-point energies at 50 MeV and 3500 MeV on 238U. The results show that even at high excitation energies, asymmetric fission may still contribute significantly to the fission cross section of actinide nuclei, while it is the dominante mode in the case of lead. However, more precise data for high energy fission on actinide are necessary in order to allow definite conclusions.

  14. Fission Matrix Capability for MCNP Monte Carlo

    International Nuclear Information System (INIS)

    In a Monte Carlo criticality calculation, before the tallying of quantities can begin, a converged fission source (the fundamental eigenvector of the fission kernel) is required. Tallies of interest may include powers, absorption rates, leakage rates, or the multiplication factor (the fundamental eigenvalue of the fission kernel, keff). Just as in the power iteration method of linear algebra, if the dominance ratio (the ratio of the first and zeroth eigenvalues) is high, many iterations of neutron history simulations are required to isolate the fundamental mode of the problem. Optically large systems have large dominance ratios, and systems containing poor neutron communication between regions are also slow to converge. The fission matrix method, implemented into MCNP[1], addresses these problems. When Monte Carlo random walk from a source is executed, the fission kernel is stochastically applied to the source. Random numbers are used for: distances to collision, reaction types, scattering physics, fission reactions, etc. This method is used because the fission kernel is a complex, 7-dimensional operator that is not explicitly known. Deterministic methods use approximations/discretization in energy, space, and direction to the kernel. Consequently, they are faster. Monte Carlo directly simulates the physics, which necessitates the use of random sampling. Because of this statistical noise, common convergence acceleration methods used in deterministic methodstion methods used in deterministic methods do not work. In the fission matrix method, we are using the random walk information not only to build the next-iteration fission source, but also a spatially-averaged fission kernel. Just like in deterministic methods, this involves approximation and discretization. The approximation is the tallying of the spatially-discretized fission kernel with an incorrect fission source. We address this by making the spatial mesh fine enough that this error is negligible. As a consequence of discretization we get a spatially low-order kernel, the fundamental eigenvector of which should converge faster than that of continuous kernel. We can then redistribute the fission bank to match the fundamental fission matrix eigenvector, effectively eliminating all higher modes. For all computations here biasing is not used, with the intention of comparing the unaltered, conventional Monte Carlo process with the fission matrix results. The source convergence of standard Monte Carlo criticality calculations are, to some extent, always subject to the characteristics of the problem. This method seeks to partially eliminate this problem-dependence by directly calculating the spatial coupling. The primary cost of this, which has prevented widespread use since its inception [2,3,4], is the extra storage required. To account for the coupling of all N spatial regions to every other region requires storing N2 values. For realistic problems, where a fine resolution is required for the suppression of discretization error, the storage becomes inordinate. Two factors lead to a renewed interest here: the larger memory available on modern computers and the development of a better storage scheme based on physical intuition. When the distance between source and fission events is short compared with the size of the entire system, saving memory by accounting for only local coupling introduces little extra error. We can gain other information from directly tallying the fission kernel: higher eigenmodes and eigenvalues. Conventional Monte Carlo cannot calculate this data - here we have a way to get new information for multiplying systems. In Ref. [5], higher mode eigenfunctions are analyzed for a three-region 1-dimensional problem and 2-dimensional homogenous problem. We analyze higher modes for more realistic problems. There is also the question of practical use of this information; here we examine a way of using eigenmode information to address the negative confidence interval bias due to inter-cycle correlation. We apply this method mainly to four problems: 2D pressur

  15. Potential Energy Calculations for Collinear Cluster Tripartition Fission Events

    Science.gov (United States)

    Unzhakova, A. V.; Pashkevich, V. V.; Pyatkov, Y. V.

    2014-09-01

    Strutinsky shell correction calculations were performed to describe the recent experimental results on collinear ternary fission. Collinear Cluster Tripartion fission events were studied experimentally in neutron induced fission of 235U, where the missing mass in the detected binary decay was suggested to characterize fission event as a collinear tripartition; and in spontaneous fission of 252Cf, where the direct detection of the three fission fragments has been used to confirm the existence of the Collinear Cluster Tripartition channel with a probability of 4.7×10-3 relative to the binary fission events.

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

    International Nuclear Information System (INIS)

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

  17. The role of non-fission neutron sources in a fission reactor economy

    International Nuclear Information System (INIS)

    The expected supply of intense non-fission neutron sources suggests the possibility of enhancing the performance characteristics of existing fission converter reactors and of increasing the fissile fuel supply by neutron-induced transmutations. This potential is explored with an emphasis on the type of neutron sources and their mode of integration with fission reactors. Particular emphasis is placed on the achievement of self-sufficiency of a converter reactor with respect to fissile fuel. As a general result, it appears that neutronically efficient converter reactors combined with relatively modest external neutron contributions can have a significant effect on the long-term fissile fuel logistics of a fission reactor economy. (orig.)

  18. Microscopic description of complex nuclear decay: multimodal fission

    CERN Document Server

    Staszczak, A; Dobaczewski, J; Nazarewicz, W

    2009-01-01

    Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fission for some rutherfordium, seaborgium, and hassium isotopes.

  19. Microscopic description of complex nuclear decay: Multimodal fission

    Science.gov (United States)

    Staszczak, A.; Baran, A.; Dobaczewski, J.; Nazarewicz, W.

    2009-07-01

    Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fission for some rutherfordium, seaborgium, and hassium isotopes.

  20. Geometrical and statistical factors in fission of small metal clusters

    OpenAIRE

    Obolensky, O. I.; Lyalin, A. G.; Solov Yov, A. V.; Greiner, W.

    2005-01-01

    Fission of metastable charged univalent metal clusters has been studied on example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density functional theory methods. Energetics of the process, i.e. dissociation energies and fission barriers, as well as its dynamics, i.e. fission pathways, have been analyzed. The dissociation energies and fission barriers have been calculated for the full range of fission channels for the Na_{10}^{2+} cluster. The impact of cluster stru...

  1. Electron spectra from decay of fission products

    International Nuclear Information System (INIS)

    Electron spectra following decay of individual fission products (72 less than or equal to A less than or equal to 162) are obtained from the nuclear data given in the compilation using a listed and documented computer subroutine. Data are given for more than 500 radionuclides created during or after fission. The data include transition energies, absolute intensities, and shape parameters when known. An average beta-ray energy is given for fission products lacking experimental information on transition energies and intensities. For fission products having partial or incomplete decay information, the available data are utilized to provide best estimates of otherwise unknown decay schemes. This compilation is completely referenced and includes data available in the reviewed literature up to January 1982

  2. Feasibility study on fission moly target development

    International Nuclear Information System (INIS)

    A multi-purpose research reactor, HANARO has been operated on the beginning of 1995 and can be utilized for production of various radioisotopes. And a R and D program for fission Mo production was established, and the technical and economical feasibility study has been performed for fission Mo production in Korea. In this study the process for fission Mo production was recommended as follows; 1. Target : UO2 of annulus type. 2. Separation and purification : Nitric acid dissolution ? Alumina adsorption ? Benzoin oxime precipitation ? Alumina adsorption. And more desirable plan for steady supply of fission Mo were suggested in following viewpoints; 1. Technical collaboration with foreign company. 2. Backup supply system. 3. Marketing arrangement. (Author)

  3. Fission cross section measurements at intermediate energies

    International Nuclear Information System (INIS)

    The activity in intermediate energy particle induced fission cross-section measurements of Pu, U isotopes, minor actinides and sub-actinides in PNPI of Russia is reviewed. The neutron-induced fission cross-section measurements are under way in the wide energy range of incident neutrons from 0.5 MeV to 200 MeV at the GNEIS facility. In number of experiments at the GNEIS facility, the neutron-induced fission cross sections were obtained for many nuclei. In another group of experiments the proton-induced fission cross-section have been measured for proton energies ranging from 200 to 1000 MeV at 100 MeV intervals using the proton beam of PNPI synchrocyclotron. (author)

  4. Singlet fission: The chromophores and their coupling.

    Czech Academy of Sciences Publication Activity Database

    Wen, Jin; Havlas, Zden?k; Michl, Josef

    Santiago : -, 2014. IC119. [WATOC 2014. Congress of the World Association of Theoretical and Computational Chemists /10./. 05.10.2014-10.10.2014, Santiago] Institutional support: RVO:61388963 Keywords : singlet fission * chromophores * coupling Subject RIV: CF - Physical ; Theoretical Chemistry

  5. A new neutron counter for fission research

    International Nuclear Information System (INIS)

    A new neutron counter for research experiments on nuclear fission has been developed. This instrument is designed for the detection of prompt fission neutrons within relatively high levels of gamma and neutron background. It is composed of a set of 3He proportional counters arranged within a block of polyethylene which serves as moderator. The detection properties have been studied by means of Monte Carlo simulations and experiments with radioactive sources. These properties are confirmed by an experiment on neutron-induced fission of 238U at the WNR facility of the Los Alamos Neutron Science Center during which the mean prompt fission neutron multiplicity, or ?¯ has been measured from 1 to 20 MeV of incident neutron energy

  6. Ternary fission induced by polarized neutrons

    International Nuclear Information System (INIS)

    Ternary fission of (e,e) U- and Pu- isotopes induced by cold polarized neutrons discloses some new facets of the process. In the so-called ROT effect shifts in the angular distributions of ternary particles relative to the fission fragments show up. In the so-called TRI effect an asymmetry in the emission of ternary particles relative to a plane formed by the fragment momentum and the spin of the neutron appear. The two effects are shown to be linked to the components of angular momentum perpendicular and parallel to the fission axis at the saddle point of fission. Based on theoretical models the spectroscopic properties of the collective transitional states at the saddle point are inferred from experiment. (authors)

  7. Advanced modeling of prompt fission neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Talou, Patrick [Los Alamos National Laboratory

    2009-01-01

    Theoretical and numerical studies of prompt fission neutrons are presented. The main results of the Los Alamos model often used in nuclear data evaluation work are reviewed briefly, and a preliminary assessment of uncertainties associated with the evaluated prompt fission neutron spectrum for n (0.5 MeV)+{sup 239}Pu is discussed. Advanced modeling of prompt fission neutrons is done by Monte Carlo simulations of the evaporation process of the excited primary fission fragments. The successive emissions of neutrons are followed in the statistical formalism framework, and detailed information, beyond average quantities, can be inferred. This approach is applied to the following reactions: {sup 252}Cf (sf), n{sub th} + {sup 239}Pu, n (0.5 MeV)+{sup 235}U, and {sup 236}Pu (sf). A discussion on the merits and present limitations of this approach concludes this presentation.

  8. Nuclear viscosity from GDR -- fission studies

    International Nuclear Information System (INIS)

    Using ? emission from the Giant Dipole Resonance in a hot fissioning nucleus as a clock, it has been possible to study the time delay of the fission process at nuclear temperatures between 1 and 2 MeV. In addition, the correlation of the emitted ? rays relative to the spin axis of the intermediate system yields the deformation of the ? emitting system. By comparing the ? spectra observed in heavy transuranic nuclei with those of light actinides it is possible to determine the fission delay time inside the fission barriers and on the path from saddle to scission separately. In each regime, large delay times are observed that indicate a strongly overdampened mass motion and a large friction constant. From saddle to scission, the viscosity equals full one-body dissipation at T = 2 MeV. The same experimental methods can also be used to study formation and life time of the mono-nucleus and such results are presented

  9. Development of fission Mo-99 production technology

    International Nuclear Information System (INIS)

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

  10. Fast neutron fission of 241Am

    International Nuclear Information System (INIS)

    For the fission of 241Am induced by fast neutrons from a 239Pu critical assembly, we have determined the mass-yield distribution and measured independent fission yields and one isomer ratio. The mass-yield distribution curve was constructed from the results for 29 total chain yields which were derived from measurements of fission products ranging from 91Y to 161Tb. Absolute fission yields were obtained with an accuracy of 4% by the requirement of unit total yield in each half of the mass-yield distribution curve and by use of the 235U(n,f) and 238U(n,f) monitor reactions. The peak-to-valley ratio is about 60. Several independent fractional chain yields were measured. Values of Z/sub p/, the most probable charge for a given mass number, inferred from these measurements are in good agreement with those estimated from independent-yield systematics

  11. Fast neutron fission of /sup 240/Pu

    Energy Technology Data Exchange (ETDEWEB)

    Myers, W.A.; Kantelo, M.V.; Osborne, R.L.; Prindle, A.L.; Nethaway, D.R.

    1978-10-01

    We have measured the mass-yield distribution from the fission of /sup 240/Pu induced by fast neutrons from a plutonium metal critical assembly. Measurements were made for 44 fission products from /sup 72/Zn to /sup 169/Er, from which we calculated total chain yields for 36 mass numbers and constructed a mass-yield curve. Absolute fission yields were obtained with an accuracy of about 5% by using the /sup 235/U (n,f) monitor reaction and by the requirement of unit total yield in each half of the mass-yield distribution. The peak-to-valley ratio is about 150. Several independent fission yields were measured and Z/sub p/ values inferred from these measurements are in good agreement with those estimated from independent-yield systematics.

  12. Fast neutron fission of 240Pu

    International Nuclear Information System (INIS)

    We have measured the mass-yield distribution from the fission of 240Pu induced by fast neutrons from a plutonium metal critical assembly. Measurements were made for 44 fission products from 72Zn to 169Er, from which we calculated total chain yields for 36 mass numbers and constructed a mass-yield curve. Absolute fission yields were obtained with an accuracy of about 5% by using the 235U (n,f) monitor reaction and by the requirement of unit total yield in each half of the mass-yield distribution. The peak-to-valley ratio is about 150. Several independent fission yields were measured and Z/sub p/ values inferred from these measurements are in good agreement with those estimated from independent-yield systematics

  13. Fast neutron fission of /sup 241/Am

    Energy Technology Data Exchange (ETDEWEB)

    Sigg, R.A.; Kantelo, M.V.; Sisson, D.H.; Prindle, A.L.; Nethaway, D.R.

    1983-01-01

    For the fission of /sup 241/Am induced by fast neutrons from a /sup 239/Pu critical assembly, we have determined the mass-yield distribution and measured independent fission yields and one isomer ratio. The mass-yield distribution curve was constructed from the results for 29 total chain yields which were derived from measurements of fission products ranging from /sup 91/Y to /sup 161/Tb. Absolute fission yields were obtained with an accuracy of 4% by the requirement of unit total yield in each half of the mass-yield distribution curve and by use of the /sup 235/U(n,f) and /sup 238/U(n,f) monitor reactions. The peak-to-valley ratio is about 60. Several independent fractional chain yields were measured. Values of Z/sub p/, the most probable charge for a given mass number, inferred from these measurements are in good agreement with those estimated from independent-yield systematics.

  14. What can we learn from fission times?

    International Nuclear Information System (INIS)

    Fission times have been measured by the blocking technique in single crystal for uranium nuclei and for super-heavy elements with Z = 120. The fission times measured for uranium nuclei can be reproduced by statistical calculations following the Bohr and Wheeler approach only if a friction coefficient increasing with temperature is considered. In the super-heavy element domain, a discrimination between the fast quasi-fission process and the slow fusion-fission one has been achieved from reaction time measurements. A minimum cross-section ? = 22 mb for formation of Z 120 compound nuclei in 238U+Ni reactions at 6.62 MeV/A has been inferred. (authors)

  15. A new neutron counter for fission research

    Science.gov (United States)

    Laurent, B.; Granier, T.; Bélier, G.; Chatillon, A.; Martin, J.-F.; Taieb, J.; Hambsch, F.-J.; Tovesson, F.; Laptev, A. B.; Haight, R. C.; Nelson, R. O.; O'Donnell, J. M.

    2014-05-01

    A new neutron counter for research experiments on nuclear fission has been developed. This instrument is designed for the detection of prompt fission neutrons within relatively high levels of gamma and neutron background. It is composed of a set of 3He proportional counters arranged within a block of polyethylene which serves as moderator. The detection properties have been studied by means of Monte Carlo simulations and experiments with radioactive sources. These properties are confirmed by an experiment on neutron-induced fission of 238U at the WNR facility of the Los Alamos Neutron Science Center during which the mean prompt fission neutron multiplicity, or ?¯ has been measured from 1 to 20 MeV of incident neutron energy.

  16. Neutron energy spectra of spontaneous fission sources

    International Nuclear Information System (INIS)

    Some characteristics of energy distributions of neutrons from spontaneous fission sources are presented. The data on neutron energy spectrum of 252Cf are considered in detail. Main properties of neutron source on the basis of 252Cf are discussed. (author)

  17. "UCx fission targets oxidation test stand"

    CERN Document Server

    Lacroix, Rachel

    2014-01-01

    "Set up a rig dedicated to the oxidation of UCx and define a procedure for repeatable, reliable and safe method for converting UC2 fission targets into an acceptable uranium carbide oxide waste for subsequent disposal by the Swiss Authorities."

  18. A revised calculational model for fission

    International Nuclear Information System (INIS)

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

  19. Time resolved fission in metal clusters

    OpenAIRE

    Dinh, P. M.; Reinhard, P. -g; Suraud, E.

    2004-01-01

    We explore from a theoretical point of view pump and probe (P&P) analysis for fission of metal clusters where probe pulses are generalized to allow for scanning various frequencies. We show that it is possible to measure the time the system needs to develop to scission. This is achieved by a proper choice of both delay and frequency of the probe pulse. A more detailed analysis even allows to access the various intermediate stages of the fission process.

  20. Our 50-year odyssey with fission: Summary

    International Nuclear Information System (INIS)

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

  1. Thermal Fission Pathways in 232Th

    International Nuclear Information System (INIS)

    Two-dimensional thermal potential energy surfaces have been investigated for 232Th using the finite temperature HF+BCS approach with Skyrme energy density functional SkM*. At low excitation energy, the calculated static fission path goes through families of triaxial and reflection-asymmetric shapes. With increasing excitation energy, the shallow third minimum associated with a nonzero octupole moment becomes washed out, and the static fission valley moves towards the axial and reflection-symmetric limit.

  2. Predicting the Fission Yeast Protein Interaction Network

    OpenAIRE

    Pancaldi, Vera; Sarac?, O?mer S.; Rallis, Charalampos; Mclean, Janel R.; Pr?evorovsky?, Martin; Gould, Kathleen; Beyer, Andreas; Ba?hler, Ju?rg

    2012-01-01

    A systems-level understanding of biological processes and information flow requires the mapping of cellular component interactions, among which protein–protein interactions are particularly important. Fission yeast (Schizosaccharomyces pombe) is a valuable model organism for which no systematic protein-interaction data are available. We exploited gene and protein properties, global genome regulation datasets, and conservation of interactions between budding and fission yeast to predict fiss...

  3. Modeling Fission Product Sorption in Graphite Structures

    International Nuclear Information System (INIS)

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

  4. Formation and transport of fission product aerosols

    International Nuclear Information System (INIS)

    The calculation of fission product retention is the primary system of light water reactors requires the knowledge of the size distribution of the particles formed from the condensation of the volatile fission product vapors released in LWR accidents. To this end, a computer model RAFT (Reactor Aerosol Formation and Transport) is being developed to predict the size distribution and composition of the condensed cesium, iodine and tellurium containing aerosols

  5. Mitochondrial Fission: Regulation and ER Connection

    OpenAIRE

    Lee, Hakjoo; Yoon, Yisang

    2014-01-01

    Fission and fusion of mitochondrial tubules are the main processes determining mitochondrial shape and size in cells. As more evidence is found for the involvement of mitochondrial morphology in human pathology, it is important to elucidate the mechanisms of mitochondrial fission and fusion. Mitochondrial morphology is highly sensitive to changing environmental conditions, indicating the involvement of cellular signaling pathways. In addition, the well-established structural connection betwee...

  6. Fission of oriented nuclei by neutrons

    International Nuclear Information System (INIS)

    The available experimental data on fission of 235U and 233U oriented nuclei by resonance and fast neutrons are consideped. Serious difficulties in corbined interpretation of experimental results on fission of even-even compound nuclei formed in reactions at spinless targets and nuclei with a different from the zero spin are pointed out. As a possible physical cause of these divergences conservation of quantum number K (moment projection on symmetry axis) at various stages of the process is discussed

  7. MCNP6 Fission Multiplicity with FMULT Card

    International Nuclear Information System (INIS)

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

  8. A revised calculational model for fission

    Energy Technology Data Exchange (ETDEWEB)

    Atchison, F.

    1998-09-01

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

  9. Our 50-year odyssey with fission: Summary

    Energy Technology Data Exchange (ETDEWEB)

    Nix, J.R.

    1989-01-01

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

  10. Energy partition in low energy fission

    OpenAIRE

    Mirea, M.

    2011-01-01

    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 another separates the pairing active spaces associated to the two fragments in the vicinity of the scission configuration. The fission path is obtained in the frame of the macroscopic-microscopic model. The single particle level schemes are obtain...

  11. Modeling Fission Product Sorption in Graphite Structures

    Energy Technology Data Exchange (ETDEWEB)

    Szlufarska, Izabela [University of Wisconsin, Madison, WI (United States); Morgan, Dane [University of Wisconsin, Madison, WI (United States); Allen, Todd [University of Wisconsin, Madison, WI (United States)

    2013-04-08

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

  12. Fission Barriers of Compound Superheavy Nuclei

    OpenAIRE

    Pei, J. C.; Nazarewicz, W.; Sheikh, J. A.; Kerman, A. K.

    2008-01-01

    The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work, we investigate the isentropic fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for [superscript 264]Fm, [superscript 272]Ds, [superscript 278]112, [sup...

  13. Prompt fission neutron emission: Problems and challenges

    OpenAIRE

    -j, Hambsch F.; Bry? T.; Gamboni T.; Geerts W.; Göök A.; Matei C.; Oberstedt S.; Vidali M.

    2013-01-01

    This paper presents some of the challenges ahead of us even after 75 years of the discovery of the fission process and large progress made since then. The focus is on application orientation, which requires improved measurements on fission cross-sections and neutron and ?-ray multiplicities. Experimental possibilities have vastly improved the past decade leading to developments of highly sophisticated detector systems and the use of digital data acquisition and signal processing. The develop...

  14. License requirements for the MITR fission converter

    International Nuclear Information System (INIS)

    The Massachusetts Institute of Technology Nuclear Reactor Laboratory recently designed and constructed a fission converter that operates in conjunction with its 5 MW research reactor, the MITR. This fission converter, which provides an excellent epithermal neutron beam for neutron capture therapy, is a subcritical facility. Nevertheless , its use requires both a safety analysis report and technical specifications. A summary is given of these documents. (author)

  15. Fission product source term research in LOFT

    International Nuclear Information System (INIS)

    The basis for fission product source term research in LOFT to support the NRC Severe Accident Research Program is presented. Probabilistic risk assessments are reviewed to identify risk-dominant accident sequences and an overview of source term research is presented. Experiment requirements and specific test design recommendations for a severe fuel damage test in LOFT, representative of a station blackout (TMLB'), for the purpose of confirming the fission product source term data base are presented

  16. Fission of 209Bi, natPb and 197Au in the particle field of a fast accelerator driven system

    International Nuclear Information System (INIS)

    Highlights: ? Fission rates of Bi, Pb and Au were measured in a particle field similar to that of fast ADS. ? The experimental results on fission rates are in agreement with MCNPX calculations. ? The most up to date fission cross-sections and related parameterizations were used. ? New parameterizations were produced from the published cross-section data. - Abstract: Accelerator driven systems (ADS) are expected to have particle spectra of significantly greater energy range than that of current power reactors. The Energy plus Transmutation (EpT) set-up of the Joint Institute for Nuclear Research, Dubna, Russia, is designed to emulate the neutron spectrum in a fast ADS through the use of a spallation target surrounded by a blanket of natural uranium. The spectrum is further modified by a reflective layer of polyethylene and an internal absorbing layer of cadmium. The spallation target of EpT was irradiated with a beam of 4 GeV deuterons, and the fission rates of bismuth, lead and gold samples, placed in the target-blanket region were recorded using a fission track detector technique. The fission rates were also calculated using the MCNPX Monte Carlo code with the INCL4 cascade model and cross sections for nucleon induced fission obtained from literature. Agreement between the measured and calculated results indicates the model’s ability to predict the particle spectra and spatial distribution

  17. Progress on the conceptual design of a mirror hybrid fusion--fission reactor

    International Nuclear Information System (INIS)

    A conceptual design study was made of a fusion-fission reactor for the purpose of producing fissile material and electricity. The fusion component is a D-T plasma confined by a pair of magnetic mirror coils in a Yin-Yang configuration and is sustained by neutral beam injection. The neutrons from the fusion plasma drive the fission assembly which is composed of natural uranium carbide fuel rods clad with stainless steel and helium cooled. It was shown conceptually how the reactor might be built using essentially present-day technology and how the uranium-bearing blanket modules can be routinely changed to allow separation of the bred fissile fuel

  18. Measurements of the U-235 fission atomic percentage by thermoionic mass spectroscopy

    International Nuclear Information System (INIS)

    The most widely used methods in precise measurements of uranium isotopic abundance and uranium-235 percent fission for the purpose of burnup determination, are based on thermoionic mass spectrometry. Employing a surface ionization mass spectrometer coupled with a data processing system, uranium ratios have been obtained from irradiated and non-irradiated dilute solutions of natural uranium oxide sinterized pellets. The fission products separation and uranium chemical purification have been carried out by anion exchange. Detailed description of irradiation, dissolution, chemical separation and purification, deposition, data collecting and processing procedures is given. (Author)

  19. Realization of a flat fission power density in a hybrid blanket over long operation periods

    Energy Technology Data Exchange (ETDEWEB)

    Sahin, S.; Erisen, A.; Cebi, Y.

    1989-01-01

    A straightforward numerical graphical method is applied to achieve a flat fission power density (FPD) in a hybrid blanket by using a mixed fuel (ThO/sub 2/ and natural UO/sub 2/) with variable fractions of the fuel components in the radial direction. The neutronic analysis is carried out on a blanket with a hard neutron spectrum in the fissionable zone by simply omitting the moderating beryllium neutron multiplier. Mainly due to this precaution in the blanket design, the FPD could be kept quasi-constant over a relatively long plant lifetime.

  20. Realization of a flat fission power density in a hybrid blanket over long operation periods

    International Nuclear Information System (INIS)

    A straightforward numerical graphical method is applied to achieve a flat fission power density (FPD) in a hybrid blanket by using a mixed fuel (ThO2 and natural UO2) with variable fractions of the fuel components in the radial direction. The neutronic analysis is carried out on a blanket with a hard neutron spectrum in the fissionable zone by simply omitting the moderating beryllium neutron multiplier. Mainly due to this precaution in the blanket design, the FPD could be kept quasi-constant over a relatively long plant lifetime

  1. Overview of experimental support for fission-product transport analyses at Oak Ridge National Laboratory

    International Nuclear Information System (INIS)

    The program was designed to determine fission product and aerosol release rates from irradiated fuel under accident conditions, to identify the chemical forms of the released material, and to correlate the results with experimental and specimen conditions with the data from related experiments. These tests of PWR fuel were conducted and fuel specimen and test operating data are presented. The nature and rate of fission product vapor interaction with aerosols were studied. Aerosol deposition rates and transport in the reactor vessel during LWR core-melt accidents were studied. The Nuclear Safety Pilot Plant is dedicated to developing an expanded data base on the behavior of aerosols generated during a severe accident

  2. Accurate Fission Data for Nuclear Safety

    Science.gov (United States)

    Solders, A.; Gorelov, D.; Jokinen, A.; Kolhinen, V. S.; Lantz, M.; Mattera, A.; Penttilä, H.; Pomp, S.; Rakopoulos, V.; Rinta-Antila, S.

    2014-05-01

    The Accurate fission data for nuclear safety (AlFONS) project aims at high precision measurements of fission yields, using the renewed IGISOL mass separator facility in combination with a new high current light ion cyclotron at the University of Jyväskylä. The 30 MeV proton beam will be used to create fast and thermal neutron spectra for the study of neutron induced fission yields. Thanks to a series of mass separating elements, culminating with the JYFLTRAP Penning trap, it is possible to achieve a mass resolving power in the order of a few hundred thousands. In this paper we present the experimental setup and the design of a neutron converter target for IGISOL. The goal is to have a flexible design. For studies of exotic nuclei far from stability a high neutron flux (1012 neutrons/s) at energies 1 - 30 MeV is desired while for reactor applications neutron spectra that resembles those of thermal and fast nuclear reactors are preferred. It is also desirable to be able to produce (semi-)monoenergetic neutrons for benchmarking and to study the energy dependence of fission yields. The scientific program is extensive and is planed to start in 2013 with a measurement of isomeric yield ratios of proton induced fission in uranium. This will be followed by studies of independent yields of thermal and fast neutron induced fission of various actinides.

  3. Modelisation of the fission cross section

    International Nuclear Information System (INIS)

    The neutron cross sections of four nuclear systems (n+235U, n+233U, n+241Am and n+237Np) are studied in the present document. The target nuclei of the first case, like 235U and 239Pu, have a large fission cross section after the absorption of thermal neutrons. These nuclei are called 'fissile' nuclei. The other type of nuclei, like 237Np and 241Am, fission mostly with fast neutrons, which exceed the fission threshold energy. These types of nuclei are called 'fertile'. The compound nuclei of the fertile nuclei have a binding energy higher than the fission barrier, while for the fissile nuclei the binding energy is lower than the fission barrier. In this work, the neutron induced cross sections for both types of nuclei are evaluated in the fast energy range. The total, reaction and shape-elastic cross sections are calculated by the coupled channel method of the optical model code ECIS, while the compound nucleus mechanism are treated by the statistical models implemented in the codes STATIS, GNASH and TALYS. The STATIS code includes a refined model of the fission process. Results from the theoretical calculations are compared with data retrieved from the experimental data base EXFOR. (author)

  4. Novel roles for actin in mitochondrial fission.

    Science.gov (United States)

    Hatch, Anna L; Gurel, Pinar S; Higgs, Henry N

    2014-11-01

    Mitochondrial dynamics, including fusion, fission and translocation, are crucial to cellular homeostasis, with roles in cellular polarity, stress response and apoptosis. Mitochondrial fission has received particular attention, owing to links with several neurodegenerative diseases. A central player in fission is the cytoplasmic dynamin-related GTPase Drp1, which oligomerizes at the fission site and hydrolyzes GTP to drive membrane ingression. Drp1 recruitment to the outer mitochondrial membrane (OMM) is a key regulatory event, which appears to require a pre-constriction step in which the endoplasmic reticulum (ER) and mitochondrion interact extensively, a process termed ERMD (ER-associated mitochondrial division). It is unclear how ER-mitochondrial contact generates the force required for pre-constriction or why pre-constriction leads to Drp1 recruitment. Recent results, however, show that ERMD might be an actin-based process in mammals that requires the ER-associated formin INF2 upstream of Drp1, and that myosin II and other actin-binding proteins might be involved. In this Commentary, we present a mechanistic model for mitochondrial fission in which actin and myosin contribute in two ways; firstly, by supplying the force for pre-constriction and secondly, by serving as a coincidence detector for Drp1 binding. In addition, we discuss the possibility that multiple fission mechanisms exist in mammals. PMID:25217628

  5. Statistical model investigation of nuclear fission

    International Nuclear Information System (INIS)

    To assist in the improvement of fission product yield data libraries, the statistical theory of fission was investigated. Calculation of the theory employs a recent nuclear mass formula and nuclear density of states expression. Yields computed with a simple statement of the theory do not give satisfactory results. A slowly varying empirical parameter is introduced to improve agreement between measured and calculated yields. The parameter is interpreted as the spacing between the tips of the fragments at the instant of scission or as the length of a neck in the fissioning nucleus immediately prior to scission. With this spacing parameter semi-quantitative agreement is obtained between calculated and measured mass chain yields for six cases investigated, 233U(n/sub th/, f), 235U(n/sub th, f), 239Pu(n/sub th/, f), 235U(n+14, f), 238U(n+14, f), and 252Cf(sf). An indication of the source of mass asymmetry in fission is presented. The model developed predicts a mass and energy dependence of some of the parameters of models currently in use in data generation. A procedure for the estimation of the fission product yields for an arbitrary fissioning system is proposed. 63 references

  6. JNDC nuclear data library of fission products

    International Nuclear Information System (INIS)

    The JNDC (Japanese Nuclear Data Committee) FP (Fission Product) nuclear data library for 1172 fission products is described in this report. The gross theory of beta decay has been used extensively for estimating unknown decay data and also some of known decay data with poor accuracy. The calculated decay powers of fission products using the present library show excellent agreement with the latest measurements at ORNL (Oak Ridge National Laboratory), LANL (Los Alamos National Laboratory) and UTT (University of Tokyo, Tokai) for cooling times shorter than 103 s after irradiation. The calculated decay powers by the existing libraries showed systematic deviations at short cooling times; the calculated beta and gamma decay powers after burst fission were smaller than the experimental results for cooling times shorter than 10 s, and in the cooling time range 10 to 103 s the beta-decay power was larger than the measured values and the gamma decay power smaller than the measured results. The present JNDC FP nuclear data library resolved these discrepancies in the short cooling time ranges. The decay power of fission products has been calculated for ten fission types and the results have been fitted by an analytical function with 31 exponentials. This permits the easy application of the present results of decay power calculations to a LOCA (Loss-of-Coolant Accident) analysis of a light water reactor and so on. (author)

  7. Dynamics in heavy ion fusion and fission

    International Nuclear Information System (INIS)

    Dynamical aspects of heavy ion fussion and fission, mainly the aspect of damping which is meant as the dissipation of kinetic energy and the aspect of the effective mass of the fission motion, are discussed. Two categories of evidence of damping effects are given. One relates to the damping of the fission motion for the ground state shape and for the isomeric more elongated shape. The other relates to the damping of the fission motion from the last barrier to the scission point. The dependence of the effective mass associated with the fission motion on the deormation of nucleus is shown. As the elongation of the nucleus increases the effective mass of the fission motion varies strongly from being about forty times greater than the reduced mass in the beta-vibrational state of the ground state shape to being equal to the reduced mass in the moment of scission. Damping effects are expected to be propartional to the difference between the effective mass and the reduced mass. It is concluded that the damping in fussion reactions is relatively weak for lighter products and quite strong for superheavy products like 236U or 252Cf. (S.B.)

  8. Spontaneous fission of /sup 259/Md

    Energy Technology Data Exchange (ETDEWEB)

    Hulet, E.K.; Wild, J.F.; Lougheed, R.W.; Baisden, P.A.; Landrum, J.H.; Dougan, R.J.; Mustafa, M.; Ghiorso, A.; Nitschke, J.M.

    1979-05-04

    The mass and kinetic energy distributions of fission fragments from the spontaneous fission of th newly discovered nuclide /sup 259/Md were obtained. /sup 259/Md was identified as the E. C. daughter of /sup 259/No, and was found to decay entirely (> 95%) by spontaneous fission with a 95-min half-life. From the kinetic energies measured for 397 pairs of coincident fragments, a mass distribution was derived that is symmetric with sigma = 13 amu. /sup 259/Md, together with /sup 258/Fm and /sup 259/Fm, form a select group of three nuclides whose mass division in spontaneous fission is highly symmetric. Unlike the total-kinetic-energy (TKE) distributions of /sup 258/Fm and /sup 259/Fm, which peak at approx. = to 240 MeV, this distribution for /sup 259/Md is broad and is 50 MeV lower in energy. Analysis of the mass and energy distributions shows that events near mass symmetry also exhibit a broad TKE distribution, with one-third of the symmetric events having TKEs less than 200 MeV. The associated of low TKEs with symmetric mass division in the fission of very heavy actinides is anomalous and inconsistent with theories based upon the emergence of fragment shells near the scission point. Either three-body fragmentation or peculiar fragment shapes are assumed as the cause for the large consumption of Coulomb energy observed for a significant fraction of symmetric fissions in /sup 259/Md. 6 figures.

  9. Fission product release during U02 oxidation

    International Nuclear Information System (INIS)

    As part of a general program on fission product source term research we have measured the release of fission products from U02 oxidized in air. Three types of measurement were made: 1) volatile fission products carried in the gas stream, 2) condensible fission products deposited in the thermal gradient of the furnace tube, and 3) direct measurement of non-volatile fission products which remained with the oxidized U02. Xenon, cesium and iodine were detected in the gas stream. Cesium and iodine also deposited in the thermal gradient of the furnace tube. They were released from the fuel independently, not as CsI. Ruthenium was also deposited, as an oxide, within the thermal gradient. Release was strongly dependent on the oxidation temperature and by 1100 degrees Celsius 100% of these fission products were released. Reactive elements such as barium and the rare earths did not move from the fuel, probably because they reacted with oxygen to form highly stable, high melting point, oxides

  10. Theoretical description of cold fission modes

    International Nuclear Information System (INIS)

    In the spontaneous fission of 252 Cf two or more fragments emerge from the reaction. A limiting case of this process is represented by the so-called cold fission in which the decay products have very low excitation energy, in any case bellow the neutron emission threshold. The close resemblance between this phenomenon and the cluster radioactivity prompted the investigation of the cold fission from the standpoint of a cluster model with fragments deformations taken into account. This model describes the cold fission as the decay of a quasi-bound giant nuclear aggregate (molecule) or dinuclear system, the fragments being in their ground states with quadrupole, octupole and hexadecapole deformations. The interaction between the fragments is simply the sum of nuclear and Coulomb contributions. In the articles that our group published in last years, we took in the description of 252 Cf cold fission, the M3Y and Migdal interaction for the nuclear part. We outline the applications of this model to several channels of cold fission occurring in 252 Cf. Topics like calculation of the half-lives of the alpha-like trinuclear molecules, the preformation of light clusters on the surface of the hyperdeformed mother nucleus, the collective modes for the 10 Be-like trinuclear molecules and the shift of the first 2+ state of 10 Be in the quasi-molecular configuration are discussed. (author)ed. (author)

  11. Spontaneous fission of the heaviest elements

    International Nuclear Information System (INIS)

    Although spontaneous fission was discovered in 238U in 1940, detailed studies of the process were first made possible in the 1960's with the availability of milligram quantities of 252Cf. The advent of solid-state detectors made it possible to perform measurements of coincident fission fragments from even very short-lived spontaneous fission activities or those available in only very small quantities. Until 1971 it was believed that the main features of the mass and kinetic-energy distributions were essentially the same as those for thermal neutron-induced fission and that all low-energy fission proceeded via asymmetric mass division with total kinetic energies which could be derived by linear extrapolation from those of lighter elements. In 1971, measurements of 257Fm showed an increase in symmetric mass division with anomalously high TKE's. Subsequent experiments showed that in 258Fm and 259Fm, the most probable mass split was symmetric with very high total kinetic energy. Measurements for the heavier elements have shown symmetric mass distributions with both high and low total kinetic energies. Recent results for spontaneous fission properties of the heaviest elements are reviewed and compared with theory. 31 refs., 8 figs., 1 tab

  12. Spontaneous fission of the heaviest elements

    International Nuclear Information System (INIS)

    Although spontaneous fission was discovered in 238U in 1940, detailed studies of the process were first made possible in the 1960's with the availability of milligram quantities of 252Cf. The advent of solid-state detectors made it possible to perform measurements of coincident fission fragments from even very short-lived spontaneous fission activities or those available in only very small quantities. Until 1971 it was believed that the main features of the mass and kinetic-energy distributions were essentially the same as those for thermal neutron-induced fission and that all low-energy fission proceeded via asymmetric mass division with total kinetic energies which could be derived by linear extrapolation from those of lighter elements. In 1971, measurements of 257Fm showed an increase in symmetric mass division with anomalously high TKE's. Subsequent experiments showed that in 258Fm and 259Fm, the most probable mass split was symmetric with very high total kinetic energy. Measurements for the heavier elements have shown symmetric mass distributions with both high and low total kinetic energies. Recent results for spontaneous fission properties of the heaviest elements are reviewed and compared with theory

  13. DIRECT ENERGY CONVERSION (DEC) FISSION REACTORS - A U.S. NERI PROJECT

    Energy Technology Data Exchange (ETDEWEB)

    D. BELLER; G. POLANSKY; ET AL

    2000-11-01

    The direct conversion of the electrical energy of charged fission fragments was examined early in the nuclear reactor era, and the first theoretical treatment appeared in the literature in 1957. Most of the experiments conducted during the next ten years to investigate fission fragment direct energy conversion (DEC) were for understanding the nature and control of the charged particles. These experiments verified fundamental physics and identified a number of specific problem areas, but also demonstrated a number of technical challenges that limited DEC performance. Because DEC was insufficient for practical applications, by the late 1960s most R&D ceased in the US. Sporadic interest in the concept appears in the literature until this day, but there have been no recent programs to develop the technology. This has changed with the Nuclear Energy Research Initiative that was funded by the U.S. Congress in 1999. Most of the previous concepts were based on a fission electric cell known as a triode, where a central cathode is coated with a thin layer of nuclear fuel. A fission fragment that leaves the cathode with high kinetic energy and a large positive charge is decelerated as it approaches the anode by a charge differential of several million volts, it then deposits its charge in the anode after its kinetic energy is exhausted. Large numbers of low energy electrons leave the cathode with each fission fragment; they are suppressed by negatively biased on grid wires or by magnetic fields. Other concepts include magnetic collimators and quasi-direct magnetohydrodynamic generation (steady flow or pulsed). We present the basic principles of DEC fission reactors, review the previous research, discuss problem areas in detail and identify technological developments of the last 30 years relevant to overcoming these obstacles. A prognosis for future development of direct energy conversion fission reactors will be presented.

  14. Fission dynamics in 132Ce composite nuclei: study within a stochastic approach

    International Nuclear Information System (INIS)

    It is well known that nuclear viscosity plays a fundamental role in the fission process. Although much experimental and theoretical work has been devoted to this subject, many questions still remain open. They mainly refer to a precise determination of the fission time scale as well as to the nature of the dissipation. At issue is whether nuclear dissipation proceeds primarily by means of individual two-body collisions (two-body friction), as in the case of ordinary fluid, or by means of nucleons colliding with a moving potential wall (one-body friction). The modified statistical model as well as dynamical models based on the Lagrange, Fokker Planck and Langevin equations have been used in order to gain insight on these aspects of fission dynamics. The lack of constraints to the models appears to be, in several cases, the main source of controversies. In this framework, we are carrying on a research program with 8?LP apparatus at LNL, aimed at studying the fission dynamics in systems of intermediate fissility. These systems, compared to the heavier ones, have larger prescission charged particle multiplicities as well as comparable fission and evaporation residue (ER) cross sections. Therefore, the measurements of the relevant quantities in both channels allow to put severe constraints on the models, providing more reliable estimates of fission delay and of viscosity parameter. We report on the system 32S + 100Mo at Elab=200 MeV which produces the composite system 132Ce at Ex=122 MeV. The analysis of the pre-scission charged particles was already described in a previous report. We have proceeded in the analysis of this system extracting the charged particle multiplicities in the ER channel as well as the ER and fission cross sections. The whole set of extracted quantities has been compared with the predictions of a dynamical model based on the Langevin equation

  15. DIRECT ENERGY CONVERSION (DEC) FISSION REACTORS - A U.S. NERI PROJECT

    International Nuclear Information System (INIS)

    The direct conversion of the electrical energy of charged fission fragments was examined early in the nuclear reactor era, and the first theoretical treatment appeared in the literature in 1957. Most of the experiments conducted during the next ten years to investigate fission fragment direct energy conversion (DEC) were for understanding the nature and control of the charged particles. These experiments verified fundamental physics and identified a number of specific problem areas, but also demonstrated a number of technical challenges that limited DEC performance. Because DEC was insufficient for practical applications, by the late 1960s most R and D ceased in the US. Sporadic interest in the concept appears in the literature until this day, but there have been no recent programs to develop the technology. This has changed with the Nuclear Energy Research Initiative that was funded by the U.S. Congress in 1999. Most of the previous concepts were based on a fission electric cell known as a triode, where a central cathode is coated with a thin layer of nuclear fuel. A fission fragment that leaves the cathode with high kinetic energy and a large positive charge is decelerated as it approaches the anode by a charge differential of several million volts, it then deposits its charge in the anode after its kinetic energy is exhausted. Large numbers of low energy electrons leave the cathode with each fission fragment; they are suppressed by negatively biased on grid wires or by magnetic fields. Other concepts include magnetic collimators and quasi-direct magnetohydrodynamic generation (steady flow or pulsed). We present the basic principles of DEC fission reactors, review the previous research, discuss problem areas in detail and identify technological developments of the last 30 years relevant to overcoming these obstacles. A prognosis for future development of direct energy conversion fission reactors will be presented

  16. Spontaneous fission properties of 258Fm, 259Md, 260Md, 258No, and 260]: Bimodal fission

    Science.gov (United States)

    Hulet, E. K.; Wild, J. F.; Dougan, R. J.; Lougheed, R. W.; Landrum, J. H.; Dougan, A. D.; Baisden, P. A.; Henderson, C. M.; Dupzyk, R. J.; Hahn, R. L.; Schädel, M.; Sümmerer, K.; Bethune, G. R.

    1989-08-01

    We have measured the mass and kinetic-energy distributions from the spontaneous fission of 258Fm, 258No, 259Md, 260Md, and 260]. All are observed to fission with a symmetrical division of mass. The total-kinetic-energy distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the total-kinetic-energy distributions are resolved into two Gaussians, the constituent peaks lie near 200 and 233 MeV. We conclude that both low- and high-energy fission modes occur in four of the five nuclides studied. We call this property ``bimodal fission.'' Even though both modes are possible in the same nuclide, one generally predominates. We offer an explanation for each mode based on shell structures of the fissioning nucleus and of its fragments. The appearance of both modes of fission in this region of the nuclide chart seems to be a coincidence in that the opportunity to divide into near doubly magic Sn fragments occurs in the same region where the second fission barrier is expected to drop in energy below the ground state of the fissioning nucleus. Appropriate paths on the potential-energy surface of deformation have been found by theorists, but no physical grounds have been advanced that would allow the near equal populations we observe traveling each path. We suggest that this failure to find a reason for somewhat equal branching may be a fundamental flaw of current fission models. Assuming the proposed origins of these modes are correct, we conclude the low-energy, but also mass-symmetrical mode is likely to extend to far heavier nuclei. The high-energy mode will be restricted to a smaller region, a realm of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in 132Sn. We present some concluding remarks on the present state of fission theory and indicate a potential redirection that might be taken.

  17. Exploiting fission event detection in thick disks to develop a high efficiency fast neutron threshold detector

    International Nuclear Information System (INIS)

    Experiments at the Naval Research Laboratory (NRL) show that 1mm thick 238U disks backed by charged particle detectors have a significant count rate increase when exposed to a fast (MeV energy range) neutron flux. This count rate is higher than would be expected considering only detection of the short range primary fission fragments, which are detected in a standard fission chamber neutron detector. The authors believe the excess count rate can be understood in terms of longer range particles resulting from the highly energetic and prolific nature of the fission reaction and the decay of its daughter products, which yield many neutrons, ?'s, ?'s, etc. They are investigating exploiting these results to develop a fast neutron detector with an efficiency of several percent

  18. Determination of the fission coefficients in thermal nuclear reactors for antineutrino detection

    International Nuclear Information System (INIS)

    The nuclear reactors in operation periodically need to change their fuel. It is during this process that these reactors are more vulnerable to occurring of several situations of fuel diversion, thus the monitoring of the nuclear installations is indispensable to avoid events of this nature. Considering this fact, the most promissory technique to be used for the nuclear safeguard for the nonproliferation of nuclear weapons, it is based on the detection and spectroscopy of antineutrino from fissions that occur in the nuclear reactors. The detection and spectroscopy of antineutrino, they both depend on the single contribution for the total number of fission of each actinide in the core reactor, these contributions receive the name of fission coefficients. The goal of this research is to show the computational and mathematical modeling used to determinate these coefficients for PWR reactors. (author)

  19. Determination of the fission coefficients in thermal nuclear reactors for antineutrino detection

    Energy Technology Data Exchange (ETDEWEB)

    Araujo, Lenilson M. [Coordenacao dos Programas de Pos-Graduacao de Engenharia (PEN/COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Cabral, Ronaldo G., E-mail: rgcabral@ime.eb.b [Instituto Militar de Engenharia (IME), Rio de Janeiro, RJ (Brazil); Anjos, Joao C.C. dos, E-mail: janjos@cbpf.b [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil). Dept. GLN - G

    2011-07-01

    The nuclear reactors in operation periodically need to change their fuel. It is during this process that these reactors are more vulnerable to occurring of several situations of fuel diversion, thus the monitoring of the nuclear installations is indispensable to avoid events of this nature. Considering this fact, the most promissory technique to be used for the nuclear safeguard for the nonproliferation of nuclear weapons, it is based on the detection and spectroscopy of antineutrino from fissions that occur in the nuclear reactors. The detection and spectroscopy of antineutrino, they both depend on the single contribution for the total number of fission of each actinide in the core reactor, these contributions receive the name of fission coefficients. The goal of this research is to show the computational and mathematical modeling used to determinate these coefficients for PWR reactors. (author)

  20. The problem of gas fission products released in nuclear fuel rot with liquid metal filling

    International Nuclear Information System (INIS)

    The theoretical bases of the ways removal of gas fission products from fuel to gas-storage through fuel-shell valve filling liquid metal are considered. An analyses of possible ways of transitions allows making following conclusions: - diffusion could not provides removal gas fission products by reactor working because of gas weak solubility in liquid metal; - the natural alternative mechanism allows provide gas removal such is heterogeneous generation of gas bubbles on the fuel's surface and its the growth and the isolation and coming off; the main factors controlling bubble's dimensions such detachment from fuel surface are fuel wettability by metal and value of surface tension in metal. It is necessary reduce detach diameter of bubble for safety working fuel elements with liquid filling; bubble mechanism of gas fission provides reducing its yield to coolant by sealing fuel element's shell