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Sample records for oklo natural fission

  1. Fission yields of molybdenum in the Oklo natural reactor

    International Nuclear Information System (INIS)

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

  2. The Oklo natural reactor: Cumulative fission yields and retentivity of the symmetric mass region fission products

    Science.gov (United States)

    De Laeter, J. R.; Rosman, K. J. R.; Smith, C. L.

    1980-10-01

    Solid source mass spectrometry has been used to determine the relative cumulative fission yields of five elements in three samples of uranium ore from reactor zones in the Oklo mine site. Eighteen fission chains covering the mass range from 105 ? A ? 130 have been measured for Pd, Ag, Cd, Sn and Te. These measurements have enabled a number of nuclear parameters to be calculated including the relative proportions of 235U, 238U and 239Pu involved in the fission process. The concentration of the five elements in the Oklo samples have also been measured using the stable isotope dilution technique. These values have then been compared to the estimates of the amount of these elements produced by fission under the conditions that are appropriate to the three samples. This procedure enables the retentivity of the elements in the reactor zones to be evaluated. Our work confirms the fact that Pd and Te are retained almost in their entirety in the samples, whereas the other three elements have been partially lost from the reactor site. Almost all the Cd fission products have been lost, and more than 50% of the Ag and Sn fission-produced material has been removed.

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  6. Conclusions from studies of Oklo natural reactors

    International Nuclear Information System (INIS)

    After a description of the geological formation of the OKLO mine and a review of the main parameters of the natural nuclear reactors, all the data concerning the evolution of the most important fission products and transuranian elements in the OKLO reactors are given. Conclusions from these studies are presented that can be related to the problem of radioactive waste storage

  7. Nuclear fission is no invention of humans: The natural reactor of Oklo two billion years ago

    International Nuclear Information System (INIS)

    On 7 July 1972, in a routine isotopic analysis of a sample of uranium ore that was sent from the west African state of Gabon to the French isotope separation plant Pierrelatte, a content of only 0.7171 atomic per cent (at.%) of 235U, instead of 0.7202, was determined. The technicians who carried out the analyses were very exact, and they checked the analysis records of previous batches from the Oklo mine. They then noticed greater departures (eventually finding contents as low as 0.296 at.%!). These showed that the isotope depletions were greater for higher total uranium contents. Since geochemical isotope effects in such heavy elements are excluded, the only explanation was that nuclear fission was somehow involved. Thereupon analyses were undertaken of associated elements, e.g. neodymium, that is formed in high yield in nuclear fission. Here anomalies in the isotope composition relative to natural neodymium were explained on the basis of their known nuclear fission yields. Clear proofs for nuclear fission were also shown in other elements from zinc (atomic number (Z) = 30) to dysprosium (Z = 66). The clearest is the low abundance of 142Nd, since it is not formed in fission. The uranium content of ores from Oklo was especially high, so one can imagine that the entrance of rainwater could have started a self-sustaining chain reaction, initiated by neutrons from the spontaneous fission of 238U or by neutrons formed by secondary reactions of cosmic radiation. From changes in isotope ratios, however, with modern mass spectrometry one can learn a lot about the migration of fission products. Thus it is possible to obtain a 'glimpse' of a final repository after millions of years, a better picture than any computer simulation has been able to provide. And although no technical barriers and no optimized geological conditions hindered the migration of fission products and plutonium, this picture shows that uranium, neptunium, plutonium, niobium, yttrium, technetium, zirconium and the rare earth metals have remained in their original places. Elements that have migrated are alkali metals, e.g. rubidium and caesium, the alkaline earth metals barium and strontium, the noble gases, molybdenum, cadmium, lead and iodine. It must also be noted that, in this historical final repository, the heat production of approximately 50 W/m2 (through the intermittent chain reaction) was many times higher than in the final repositories planned today for highly radioactive waste

  8. XPS and XRD studies of samples from the natural fission reactors in the Oklo uranium deposits

    International Nuclear Information System (INIS)

    Mineral samples from the natural fission reactors 10 and 13 in the Oklo uranium deposits were studied using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to gain information about the long-term behaviour of UO2 fuel in a geological disposal vault. Two samples from reactor zone 10 (samples No. D81N-190292 and D73-88) and one sample from reactor zone 13 (sample No. SD37-S2/CD) were analysed. Low-resolution XPS spectra were recorded to determine the major elements present in the ore. High-resolution spectra were recorded to gain information about the chemical state of the elements present in the mineral samples. The samples show low values for the U6+/U4+ ratio. The oxidation state of uranium in these samples is even lower than that in U4O9.The binding energies of the Pb 4f bands indicate most of the Pb is in the +2 oxidation state in these samples. The C ls band indicates the presence of organic carbon. XRD analysis shows that the main uranium-bearing phase is uraninite and lead is present mainly as galena. The significance of the results for nuclear fuel waste management is discussed

  9. Migration of fission products into micro-minerals of the Oklo Natural Reactors

    International Nuclear Information System (INIS)

    Isotopic characterization of two kinds of unique micro inclusions, metallic aggregate and apatite, in reactor core samples at the Oklo uranium ore in Republic of Gabon was studied. In order to investigate the migration and retention mechanism of fission products, in-situ isotopic analyses by secondary ion mass spectrometry (SIMS), and precise isotopic measurements by thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS) were carried out. The results of isotopic analyses led to the following observations: (1) fissiogenic Ru, Pd and Te are enriched in the micrometallic inclusions, and (2) micro apatites contain fissiogenic alkaline, alkaline earth, and rare earth elements (REE). Moreover, the geochemical behaviour of long-lived radionuclides 99Tc and 137Cs could be estimated from the precise isotopic determination of fissiogenic Ru and Ba, respectively. Fissiogenic REE have fractionated chemically during the migration processes from the uraninite matrix inot an apatite structure. (orig.)

  10. The Oklo natural reactor, Gabon

    International Nuclear Information System (INIS)

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

  11. 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

  12. 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

  13. 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

  14. Reappraisal of the limit on the variation in ? implied by the Oklo natural fission reactors

    Science.gov (United States)

    Davis, Edward D.; Hamdan, Leila

    2015-07-01

    Background: A signature of many dynamical models of dark energy is that they admit variation in the fine structure constant ? over cosmological time scales. Purpose: We reconsider the analysis of the sensitivity of neutron resonance energies Ei to changes in ? with a view to resolving uncertainties that plague earlier treatments. Methods: We point out that with more appropriate choices of nuclear parameters, the standard estimate (from Damour and Dyson) of the sensitivity for resonances in Sm is increased by a factor of 2.5. We go on to identify and compute excitation, Coulomb, and deformation corrections. To this end, we use deformed Fermi density distributions fitted to the output of Hartree-Fock (HF) + BCS calculations (with both the SLy4 and SkM* Skyrme functionals), the energetics of the surface diffuseness of nuclei, and thermal properties of their deformation. We also invoke the eigenstate thermalization hypothesis, performing the requisite microcanonical averages with two phenomenological level densities which, via the leptodermous expansion of the level density parameter, include the effect of increased surface diffuseness. Theoretical uncertainties are assessed with the inter-model prescription of Dobaczewski et al. [J. Phys. G: Nucl. Part. Phys. 41, 074001 (2014), 10.1088/0954-3899/41/7/074001]. Results: The corrections diminish the revised Sm sensitivity but not by more than 25%. Subject to a weak and testable restriction on the change in mq/? (relative to the change in ? ) since the time when the Oklo reactors were active (mq is the average of the u and d current quark masses, and ? is the mass scale of quantum chromodynamics), we deduce that | ?Oklo-?now|atomic clock experiments. Conclusions: The order of magnitude of our Oklo bound on changes in ? is reliable. It is one order of magnitude lower than the Oklo-based bound most commonly adopted in earlier attempts to identify phenomenologically successful models of ? variation.

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

    Science.gov (United States)

    Hidaka, Hiroshi; Holliger, Philippe

    1998-01-01

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

  16. Coupled processes at the Oklo Natural reactor

    International Nuclear Information System (INIS)

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

  17. 3D modelling of thermal and fluid transfers around a natural fission reactor (Oklo, Gabon)

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  19. Physiochemical studies of uraninite from an Oklo natural reactor

    International Nuclear Information System (INIS)

    Two billion years ago, over a span of a few hundred thousand years, the only known natural occurrence of sustained nuclear fission radically altered the isotopic, chemical, and mineralogical composition of the surrounding rocks. Today remnants of the event exist as lenses within the Oklo uranium mine in the African Republic of Gabon. Fission product abundances in one of the reactor zones revealed a striking relationship between the fission products Ruy, Pd, Te, and Mo. Eight samples contain widely varying quantities of these fission products but retain equal proportions, which leads to the conclusion that these elements make up a distinct secondary phase which should be detectable. They report here the results of that search by electron microscopy and EXAFS techniques. Another aspect of their study investigates the relationship between the distribution of iron(II) and iron(III) and the degree of fission-induced radiolysis, using EXAFS and Mossbauer spectroscopy

  20. 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

  1. Swedish activities in the Oklo natural analogue project

    International Nuclear Information System (INIS)

    Presently, many countries are concerned about the need for a safe method to dispose of high-level nuclear wastes. The various national regulatory agencies involved generally require quantitative predictions for at least the first 104 years after disposal, and qualitative predictions of repository safety performance for up to 106 years. Predicting what this future behaviour will be can be considerably facilitated by comparison with the evolution of parallel natural geochemical systems, particularly those rich in radioelements. Such natural systems, or natural analogues, therefore provide a unique opportunity to test, by observation and measurement, many of the geochemical processes that are expected to influence the predicted reliability of high-level radioactive waste containment deep in the bedrock for long periods of geological time, thus providing direct and indirect validation support for some of the models and data used in performance assessment. Oklo, by virtue of representing a fossil natural reactor which achieved criticality some 2 000 Ma ago, provides a unique opportunity to show whether the stable nuclear fission end-products have remained, in the near-vicinity of the reactor zone subsequent to fission. Furthermore, the materials found in the Oklo reactors resemble closely important waste forms such as spent nuclear fuel and bitumised residue and have been subject to extreme geochemical reactions and radiolysis when related to expected site disposal conditions, and for a much longer time. In order to study such effects, not only do the reactor zones require further detailed mineralogical, geochemical and radiochemical study, but equally the geological setting and hydrological environment of the reactor zones also need to be understood. For this reason SKB are interested to study the spatial distribution of the reactor zones at Oklo, Okelobondo and Bagombe in the context of the large-and small-scale groundwater hydraulics of the host sedimentary rocks. (author). 7 refs., 1 fig

  2. The deposit of Oklo and its natural nuclear reactors

    International Nuclear Information System (INIS)

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

  3. Inception and evolution of Oklo natural nuclear reactors

    International Nuclear Information System (INIS)

    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 235U. 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)

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

    International Nuclear Information System (INIS)

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

  5. 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

  6. The nonlinear dynamics of the Oklo natural reactor

    International Nuclear Information System (INIS)

    An analysis of the Oklo natural reactor, a self-sustaining and self-regulating critical assembly that existed some 2 billion years ago in Gabon, Africa, is presented. Nonlinear continuous dif ferential and nonlinear discrete iterative formulations are established and selected parameter characterizations identified. Conceivable power oscillations are calculated and discussed. Some implications of nonlinear mappings for nuclear simulation are suggested

  7. 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)

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

    International Nuclear Information System (INIS)

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

  9. What we learn from the nuclear data in Oklo natural reactor

    International Nuclear Information System (INIS)

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

  10. Lutetium thermometry for Oklo natural reactors: a new look at old data

    CERN Document Server

    Gould, C R; 10.1103/PhysRevC.85.024610

    2012-01-01

    Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures $T_O$ which in turn impacts bounds on time variation of the fine structure constant $\\alpha$. We revisit results for reactor zone RZ10 in light of new measurements of the isomer branching ratio $B^g$ in $^{175}$Lu neutron capture at 5 and 25 keV. We recalculate predictions for $T_O$ as a function of $B^g$ using realistic models of the Oklo neutron flux. We find $T_O = 100 \\pm 30$ C using a new value of $B^g$, in contrast to $350 < T_O < 500 $ C using the evaluated value at thermal energy. Lutetium thermometry can be applicable to analyses of Oklo reactor data, but a better measurement of $B^g$ with thermal neutrons is needed to confirm the reliability of temperature predictions.

  11. Lutetium thermometry for Oklo natural reactors: a new look at old data

    OpenAIRE

    Gould, C R; Sharapov, E.I.

    2012-01-01

    Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures $T_O$ which in turn impacts bounds on time variation of the fine structure constant $\\alpha$. We revisit results for reactor zone RZ10 in light of new measurements of the isomer branching ratio $B^g$ in $^{175}$Lu neutron capture at 5 and 25 keV. We recalculate predictions for $T_O$ as a function of $B^g$ using realistic models of the Oklo ...

  12. Search for fission-produced Rb, Sr, Cs and Ba at Oklo

    International Nuclear Information System (INIS)

    Five samples from the 2'P' cross-section, Oklo Mine, Gabon have been analysed to determine the isotopic composition of Rb, Sr, and Ba in order to search for the presence of fission-produced isotopes of these elements, as well as 135Ba and 137Ba which may be enriched due to fission-produced Cs. Three of the samples were powders and the other two U-rich segments of core; all five contain abundant total U (40 to 55%) and are depleted in 235U (0.52 to 0.41% of total U). Further, all samples are mixed to various degrees with silicate plus oxide gangue material. Even on the core samples the gangue is present along grain edges, in cracks, and is virtually impossible to separate from the uraninite. Presumably this gangue material is rich in alkali and alkaline earth elements and thus acts as a diluent for any fission-produced material. Rb, Sr, and Ba were separated by ion-exchange chromatographic techniques following cleansing by leaching with HCl and standard HF:HClO4 dissolution and their isotopic compositions determined by mass spectrometric thermionic emission. The leachate fractions of four of the five samples contain more Rb, Sr, and Ba of normal isotopic composition than the insoluble residues for which three of the five samples indicate the presence of fission-produced Cs (now as Ba isotopes) and Rb; further, increasing (135Ba/137Ba) correlates with decreasing (85Rb/87Rb). All five samples indicate the presence of fission-produced 88Sr as reflected in very low (86Sr/88Sr) ratios; available data suggest correlation between increase in fission 88Sr and depletion in 235U. The collective data suggest that fission-produced Rb, Sr, and Cs (now as Ba isotopes) are present in these samples but highly diluted by large amounts of the normal elements. Enrichment in 138Ba has not been demonstrated; which may be attributed to the high Ba content (i.e. 0.2-0.3%). (author)

  13. Oklo - natural analogue for transfer processes in a geological repository: present status of the programme

    International Nuclear Information System (INIS)

    The uranium ore body in Oklo is a unique subject in the world, as natural fission reactions occurred there two billion years ago. It provides opportunities for the study of natural analogy with deep radioactive waste disposal, specially radionuclide mass transfer processes to the surface. The ongoing program is co-funded by the CEC, and it involves several directorates in the CEA, that is to say the IPSN, plus DTA and DCC. Other, non-CEC agencies also take part in the studies, such as SKB (Sweden), AECL and ONTARIO-HYDRO (Canada). It can be subdivided into several different tasks: 1. In situ sampling, in close collaboration with the mining company (C.O.M.U.F., Compagnie des Mines d'Uranium de Franceville, Mounana, Gabon). 2. Study and characterization of the source term (mostly in CEA laboratories). 3. Studies on the geochemical systems ruling the migrations, implying collaboration between CEA laboratories and other institutions: CREGU (Centre de Recherches sur la Geologie des matieres premieres minerales et energetiques, formerly 'de l'Uranium', Nancy), Centre de Geochimie de la surface (CNRS, Strasbourg), and Ecole Nationale Superieure des Mines de Paris (ENSMP, Centre de Geologie Generale et Miniere and Centre d'Informatique Geologique, Fontainebleau). 4. Modelling: Part of the modelling will take place in each laboratory involved, but the final coupling of models will be the responsibility of IPSN and ENSMP. 1 fig

  14. Oklo, natural analogue for transfer processes in a geological repository: an overview

    International Nuclear Information System (INIS)

    The uranium ore body in Oklo is a unique subject in the world, as natural fission reactions occurred there two billion years ago. It provides opportunities for the study of natural analogy with deep radioactive waste disposal, specially radionuclide mass transfer processes to the surface. The ongoing program is co-funded by the CEC, and it involves several directorates in the CEA, that is to say the IPSN, plus DTA and DCC. Other, non-CEC agencies also take part in the studies, such as SKB (Sweden), AECL and ONTARIO-HYDRO (Canada). It can be subdivided into several different tasks: (1) In situ sampling, in close collaboration with the mining company (C.O.M.U.F., Compagnie des Mines d'Uranium de Franceville, Mounana, Gabon). (2) Study and characterization of the source term (mostly in CEA laboratories). (3) Studies on the geochemical systems ruling the migrations, implying collaboration between CEA laboratories and other institutions: CREGU (Centre de Recherches sur la Geologie des matieres premieres minerales et energetiques, formerly ''de l'Uranium'', Nancy), Centre de Geochimie de la Surface (CNRS, Strasbourg), and Ecole Nationale Superieure des Mines de Paris (ENSMP, Centre de Geologie Generale et Miniere and Centre d'Informatique Geologique, Fontainebleau). (4) Modelling: Part of the modelling will take place in each laboratory involved, but the final coupling of models will be the responsibility of IPSN and ENSMP. (author). 1 fig

  15. The neutron balance of the natural reactors at Oklo

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    2005-01-01

    Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Mult...

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

    International Nuclear Information System (INIS)

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

  18. The geochemical behavior of radioactive nuclides at the Oklo natural reactor

    International Nuclear Information System (INIS)

    The Oklo uranium mine in the Republic of Gabon, West Africa, has been known as fossil fission reactor. Such a unique phenomenon brings us to not only geochemical information but also practical knowledge about radioactive waste disposal. In this study, isotopic compositions and abundances of various elements (Rb, Sr, Zr, Mo, Ru, Pd and rare earth elements) deeply associated with nuclear reactions were precisely measured with mass spectrometer. On the basis of these data, the authors could investigate the geochemical behavior of fission product nuclides. Zr, Ru, Pd and rare earth elements (except La and Ce) were difficult to move and have been relatively preserved in the reactor. On the other hand, Rb, Sr have almost perfectly disappeared out of the reactor. It is particularly interesting that La and Ce had behaved differently from other rare earth elements and partly removed in spite of chemical similarity among rare earth elements

  19. The Oklo reactors

    International Nuclear Information System (INIS)

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

  20. 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

  1. 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

  2. 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.

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

    International Nuclear Information System (INIS)

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

  4. Effects of organic matter on the containment of uranium and fissiogenic isotopes in the Oklo natural reactors

    International Nuclear Information System (INIS)

    Several of the Proterozoic natural fission reactors at Oklo in the Republic of Gabon contain abundant organic matter. Organic petrography including reflectance measurements, Rock-Eval pyrolysis, microfocused-laser Raman spectrometry, pyrolysis-gas chromatography-organic mass spectrometry, pyrolysis-high resolution organic mass spectrometry, ion microprobe and thermal ionization isotope mass spectrometry, backscattered scanning electron microscopy and electron microprobe analyses were used to characterize the organic matter and its associated minerals in and in the vicinity of the organic-rich reactors 7-9. Non-uraniferous organic samples distant from the reactors were also examined by most of these analytical techniques. There are two types of organic matter in the natural reactors and in the distant sedimentary rocks: solid bitumen and kerogen. Both of these organic substances consist of a condensed aromatic hydrocarbon macromolecular matrix which contains dispersed fine-grain size, cryptocrystalline graphite. Liquid bitumen was generated during criticality through reaction mechanisms involving water at elevated temperatures. Later the liquid bitumen became a solid. The liquid bitumen helped to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite which incorporated fissiogenic isotopes. These uraninite crystals were coated and enclosed in bitumen, which held them immobile after its solidification. This mechanism prevented 235U and fission product losses for long periods of time. Organic matter in the natural reactors and uranium ores have a less tightly bound macromolecular matrix than organics in the non-uraniferous and distant sedimentary rocks, but the looser molecular matrix did not hinder 235U and fission product retention. (author). 19 refs., 2 tabs

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

    Science.gov (United States)

    Moxham, Robert M.

    1976-01-01

    About 20 years ago, Kuroda theorized that a high-grade uranium deposit emplaced about 2x109 years ago could achieve criticality and sustain a nuclear chain reaction, given a sufficient thickness of high-grade ore and an appropriate water content. Such a natural reactor was found in 1972 at the Oklo deposit, Gabon. The ore contains as much as 60 percent uranium, but the isotopic abundance of 235U is as little as 0.4 percent in contrast to the normal abundance of 0.7110 percent 235U. A sample from the Oklo deposit containing about 0.51 atom percent 235U (by mass spectrometer) was analyzed by a gamma-ray spectrometer system, using a high-purity planar germanium detector. The 235U was determined from its daughter's (234Th) 63.3 keV photopeak; the 235U was determined from its 143.8 and 163.4 keV photopeaks. The ratios of these photopeaks were compared with that from a standard having normal uranium isotopic content; the resulting calculations give a 235U abundance of 0.54 atom percent in the Oklo sample. The gamma-ray spectrum also contains lines from five other isotopes in the uranium series, which indicate the Oklo sample to be at or near secular equilibrium, as the time elapsed since the nuclear reaction ended was sufficient to permit the daughters to achieve equilibrium.

  6. 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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  11. 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)

  12. The discovery and study of the nuclear reactor in Oklo

    International Nuclear Information System (INIS)

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

  13. Oklo stable isotopes

    International Nuclear Information System (INIS)

    It is generally accepted that the fission reactions at Oklo resulted in convective circulation of the water heated up in the reactor zones. These convective currents were likely the main cause for the redistribution of some of the uranium of the reactor zones and most of the migration of the fission products possibly occurred at this stage. In order to derive generic conclusions applicable to the problems of nuclear waste disposal one has to identify the pattern of circulation of the convective currents and relate the observed distribution of elements around the reactor zones to the patterns left behind by the paleohydrogeological regime. The objective of this project is to discern and delineate the pathways of elemental migration by determining the deuterium and oxygen signature in the rocks confining the reactor zones. Furthermore the stable isotope analysis provides insights regarding water-rock interaction. In pursuit of this objective the Toronto team is concentrating on measurements of deuterium while F. Gauthier-Lafaye of Strasbourg is responsible for the analysis of the oxygen isotopes. In the final synthesis of the results beyond the main objective we intend to evaluate the differences in migration between the various members of the decay chains by means of a semi-analytical 3 dimensional model. (author). 8 refs., 1 fig., 1 tab., 2 appendices

  14. Oklo as a natural analogue. Reconstruction of ancient fluid circulations using trace-element geochemistry from near to far field

    International Nuclear Information System (INIS)

    The natural nuclear reactors located in the Oklo uranium ore deposit (Gabon) represent one of the best analogy of what could be the interaction of a site of radioactive wastes storage with geological medium. It is under this view of natural analogue that reaction zones and uranium ore deposit are studied in part of european program coordinated by C.E.A. The aim of the thesis is to characterize the ancient fluid circulation which have induced some elementary redistributions from near field to far field. Tracing fluid phase geochemistry have been made by study of several mineral populations (apatite, zircon, pyrite chalcopyrite). Fluids escaping from reaction zones during their critically have been identified by isotopic and elementary compositions of apatites located in 'argiles de pile'. Geochemical feature of those fluids have not been founded in the bearing sandstones. Although, mineralogical observations, chemical analysis on whole rocks and analysis of trace elements of zircons and apatites allowed to characterize an early hydrothermal stage which predates criticality in reaction zones. At the scale of uranium ore deposit, study of sulfur allowed to identify several hydrothermal stages. All those stages are later with respect to criticality in reaction zones. The principal fluid circulation stage, present both in pyrites and galena is interpreted as a resulting from mixing between a locally induced fluid and a regional circulation. A second stage is certainly later and correspond to a reworking of lead in galena and precipitation of pyrites and chalcopyrites. (author)

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Damour, T. [Institut des Hautes Etudes Scientifiques, 91 - Bures-sur-Yvette (France)]|[Institute for Advanced Study, Princeton, NJ (United States). School of Natural Sciences]|[DARC, Obs. de Paris, CNRS, Meudon (France); Dyson, F. [Institute for Advanced Study, Princeton, NJ (United States). School of Natural Sciences

    1996-11-25

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

  17. The Oklo phenomenon

    International Nuclear Information System (INIS)

    Until recently, scientists believed that the chemical elements were synthesized only in stars. The discovery of the Oklo phenomenon in the Republic of Gabon in 1972 has revealed, however, that a nuclear ''fire'' had existed on the earth and large-scale transmutations of the elements were occurring on our planet 1.7x109 years ago. The formation of natural (or Pre-Fermi) reactors is closely related to the appearance of life on our planet earth. The Pre-Fermi reactors were probably never formed until about 2x109 years ago, when oxygen was injected into the earth's atmosphere by a new generation of living organisms carrying out photosynthesis. (orig.)

  18. Oklo reactors and implications for nuclear science

    CERN Document Server

    Davis, E D; Sharapov, E I

    2014-01-01

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

  19. 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)

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

    International Nuclear Information System (INIS)

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

  1. 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.)

  2. 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 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

  3. Geochemical behaviour study of radionuclides and their radiogenic daughters in the vicinity of Oklo 10 and 13 natural nuclear reactors (Gabon) - Application to high-level radioactive waste disposal

    International Nuclear Information System (INIS)

    Since 1981, the discovery of new and almost unaltered natural nuclear reactors in the uranium mine of Oklo (Gabon) renewed the interest of scientific community. Indeed, due to their specific features, these reactors could be extensively investigated as natural analogues to better understand the geochemical processes which may occur in a high level nuclear waste repository. The aim of this PhD thesis is to determine the present distribution of a few radionuclides or their radiogenic daughters initially formed within the reaction zones and to infer their geochemical behaviour, subsequently to the stopping of nuclear reactions. Our study was focused on reactors 10 and 13 and their immediate sandstone surroundings in order to decipher the fate of U, Y and light rare earth elements which are assumed to be chemical analogues of actinides and fission products. Mineralogical observations, chemical and isotopic analyses on bulk rocks, led us to conclude that a part of radionuclides, as well as their daughters, remained confined within the reactions zones, in association with secondary mineral phases, whereas another part migrated towards tbe reactor rims. The radionuclides were concentrated at the reactor border or migrated within the first few metres of the surrounding sandstone, according to the intensity of nuclear reactors and the presence of the so-called 'facies argile de pile' which constitutes an intermediate facies between that of reactor cores and that of the surrounding sandstone. In the latter, long range elemental transfers occurred via fissures. Some of them, contemporaneous to the nuclear reactions drained radionuclides-rich fluids at temperatures of about 150-170 deg. C. More recent fissures, observed only in the environment of reactor 13, have allowed the transport of hotter hydrothermal fluids (about 310 deg. C), likely related to the nearby intrusion of dolerite dyke. The principal implications of this work for the disposal of nuclear wastes concern notably the long term stability of U dioxide in a reducing geological environment and its retention capability for various radionuclides. Our results also suggest that interfaces within the near field of a repository may act as sinks for radionuclides. Finally, this study confirms that fissures are likely to play an essential role in the transport of fluids and thus in the dispersion of radionuclides. (author)

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

    International Nuclear Information System (INIS)

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

  5. 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

  6. Bound on the variation in the fine structure constant implied by Oklo data

    CERN Document Server

    Hamdan, Leila

    2015-01-01

    Dynamical models of dark energy can imply that the fine structure constant $\\alpha$ varies over cosmological time scales. Data on shifts in resonance energies $E_r$ from the Oklo natural fission reactor have been used to place restrictive bounds on the change in $\\alpha$ over the last 1.8 billion years. We review the uncertainties in these analyses, focussing on corrections to the standard estimate of $k_\\alpha\\!=\\!\\alpha\\,dE_r/d\\alpha$ due to Damour and Dyson. Guided, in part, by the best practice for assessing systematic errors in theoretical estimates spelt out by Dobaczewski et al. [in J. Phys. G: Nucl. Part. Phys. 41, 074001 (2014)], we compute these corrections in a variety of models tuned to reproduce existing nuclear data. Although the net correction is uncertain to within a factor of 2 or 3, it constitutes at most no more than 25% of the Damour-Dyson estimate of $k_\\alpha$. Making similar allowances for the uncertainties in the modeling of the operation of the Oklo reactors, we conclude that the rela...

  7. Fission fragment tracks in natural glasses

    International Nuclear Information System (INIS)

    The fission fragment track age of the natural glasses - two specimens of tektites - indochinites Tailand and one specimen of volcanic glass from Armenia (pearlite) - has been determined. The glass specimens have been placed in the epoxy resin, then etched in 10% HF during 6-8 min at 20 deg C, then spontaneous fission track density and track diameters have been measured. For uranium concentration measurements these glasses have been irradiated with thermal neutron fluxes 1.1x1015 cm-2 (tektites) and 5.7x1015 cm-2 (pearlite), then etched in HF and scanned under the microscope. The track age of indochinite glasses has been determined as (7.50.8)x105 years, the age of pearlite - (2.60.3)x105 years. 8 refs.; 2 figs

  8. 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.)

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  11. Petrographic study of organic matter from Oklo

    International Nuclear Information System (INIS)

    Coal petrography techniques were applied to Oklo samples and various types of organic material were determined around the reactor and throughout the region as a whole: e.g. interstratified autochthonous organic material of the coal type, with maximum reflectance in the oil, reaching 6.90%; secondary-filler organic material of the bitume type, with reflectance varying around 2%, which is the type of organic material that is associated with the reactor; and natural coke organic material with fine-grain anisotropy between crossed nicols. An attempt has been made, with a 600-m series intersected by a borehole, to estimate the intensity of the thermal palaeoflux. The research is still only at the initial stage and should be continued. (author)

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

    International Nuclear Information System (INIS)

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

  13. Search for an ''Oklo Phenomenon'' in the Northeastern regions of Brazil

    International Nuclear Information System (INIS)

    Rocks samples from the Northeastern region of Brazil were analysed for their 235U isotopic abundance, in search for the occurrence of an ''Oklo Phenomenon'' here. The samples were collected in locations that could have been connected to the African continent, according to the continental-drift theory, in accordance to the Francevillian formations in the Gabon Republic, in which place the Oklo natural fossil reactor is situated. Two methods were used for the determination of the 235U abundance: activation analysis followed by high resolution gamma-ray spectrometry and activation analysis by delayed neutron counting. No evidence of 235U depletion was found in the rock samples analysed. (author)

  14. 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)

  15. 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

  16. Reconstitution of fluid paleo-circulations and element migrations in the environments of Oklo's natural nuclear reactors (Gabon) and of Tournemire's argillites (France)

    International Nuclear Information System (INIS)

    To better characterize the mobilization and migration process in rocks, a petrological and geochemical study of fluid paleo-circulation through fractures has been made in two different sites: (1) The environment of natural nuclear reactors from Proterozoic Oklo uranium ores (Gabon). The Archean basement typical of TTG series and the sandstones-pelites series of the Franceville basin are affected by a fracturing mainly filled by quartz-daphnite-calcite-sulfides and barren ou mineralized bitumens. Three paragenetic stages has been correlated to three regional structural phases. During the first extensional phase, a low saline (1.7-6.5 wt% NaCl), heated in the basement (190-210 deg. C) and impoverished in 18O meteoric recharge is injected into the basin, along major N-S faults. It was responsible of silicification. The circulation of diagenetic brines is able to leach U, Pb, Zr, REEs and P resulting from accessory minerals alteration, at the basin-scale between 2104 Ma and 1719 Ma (Pb/Pb isochrone obtained on galena incorporated in zircons). These brines are responsible of anomalous Th/La ratios (1.8) of FA silicified sandstones higher than those (0.25) of most of Archean and Proterozoic metasediments. They are highly chlorine, calco-sodic ([Cl] > 6 m, from 28 wt% NaCl to 30 wt% CaCl2), equilibrated with carbonate and evaporitic layers of FA sandstones, with low temperatures (130 deg. C) and rich in Ca, Li and Br. They are expulsed laterally due to the compaction of FA sandstones, and upwards along sub-vertical fractures. During the second extensional phase, the mineralization stage, mainly controlled by N-S faults corresponds to a mixing (155-220 deg. C) between the brines, the meteoric recharge and hydrocarbons C9 and C10-rich fluids derived from organic matter maturation in the FB pelites. The interaction of the three fluids is responsible of the mineralization in sandstones and in calcites displaying an organic carbon origin (δ13C=-10 to -15 0/00 vs. PDB). The low to moderately saline (3-18 wt% NaCl) fluids with higher temperatures (200-550 deg. C), containing traces of O2, CH4 and CO2 are related to the reactors functioning and cooling with local silicification events. During the last compressional phase, the fluid paleo-circulations are mainly responsible of barren calcite crystallization (δ13C= 0 to -5 0/00 vs. PDB). (2) The Toarcian shales from experimental IPSN site in the Tournemire tunnel (Aveyron, France). Four mineral parageneses (calcite, calcite and framboidal pyrite, calcite and cubic pyrite, and calcite and barite) have been distinguished in fractures induced by compressional Pyrenean tectonic activities. The major- and trace-element contents, and the 87Sr/86Sr isotopic ratios (0.70847-0.70852) of the vein calcite are buffered by the surrounding shales, strongly suggesting short-distance migrations of the elements considered. Low uranium and high iron contents of the vein calcite suggest circulation of reducing fluids. However, an external origin for the carbonate fillings of the main fault, obtained with 87Sr/86Sr isotopic ratios (0.70841 and 0.70858), and of positive Eu anomalies in the REE patterns, cannot be excluded. This study shows that the competition between chemical aggressiveness of diagenetic fluids and buffering from surrounding rocks, with P-T conditions control determine or regulate the scale of element migration which has been important at Oklo and moderate at Tournemire. (author)

  17. 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

  18. Geochemistry of actinides and fission products in natural aquifer systems

    International Nuclear Information System (INIS)

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

  19. Interpretation of chemical and isotopic analysis of ruthenium carried out on Oklo ore samples and various geological samples

    International Nuclear Information System (INIS)

    Isotopic compositions of ruthenium from various terrestrial sources were compared between them and with ruthenium from a sample of the meteorite of Canyon Diablo. It was not possible to detect any isotopic anomalies, beyond precision of measurement, this result shows that less than 0.5% of the earth crust uranium participated in Oklo type nuclear reactions, in the hypothesis of a complete rehomogeneization of ruthenium in the earth crust. Chemical and isotopic analysis of fission ruthenium along the SC 36 boring of zone II show a noticeable differenciation between ruthenium and technetium at the time of nuclear reaction and a ruthenium distribution slightly narrower in comparison with that of fission neodymium

  20. 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)

  1. 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.

  2. Implications of the Oklo Phenomenon in a Chiral Approach to Nuclear Matter

    International Nuclear Information System (INIS)

    It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant α over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both α and the average mq of the u and d current quark masses, and which makes explicit the dependence on mass number A and atomic number Z. (Recent model independent results on hadronic σ -terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivity to changes in the pion mass Mπ of a single nucleon potential determined by an in-medium chiral perturbation theory (χPT) calculation which includes virtual Δ-excitations. Subject to some reasonable assumptions about low-energy constants, we confirm that the mq-contribution to resonance shifts is enhanced by a factor of 10 or so relative to the α-term and deduce that the Oklo data for Sm imply that |mq(Oklo)−mq(now)|≲10−9 mq(now) . (author)

  3. The Nature of Singlet Exciton Fission in Carotenoid Aggregates

    OpenAIRE

    Musser, Andrew J.; Maiuri, Margherita; Brida, Daniele; Cerullo, Giulio; Friend, Richard H.; Clark, Jenny

    2015-01-01

    Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains...

  4. The nature of singlet exciton fission in carotenoid aggregates.

    Science.gov (United States)

    Musser, Andrew J; Maiuri, Margherita; Brida, Daniele; Cerullo, Giulio; Friend, Richard H; Clark, Jenny

    2015-04-22

    Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission. PMID:25825939

  5. The discovery of the Oklo reactors

    International Nuclear Information System (INIS)

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

  6. 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

  7. The origin of the chemical elements and the Oklo phenomenon

    International Nuclear Information System (INIS)

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

  8. Production of fission molybdenum by using irradiated natural uranium targets

    International Nuclear Information System (INIS)

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

  9. Chemical concentration of a new natural spontaneously fissionable nuclide from solutions with low salt background

    International Nuclear Information System (INIS)

    The results of experiments on further concentration of a new natural spontaneously fissionable nuclide, the concentrates of which form the Cheleken geothermal brines have been obtained, are presented. The conclusions are drown about the chemical nature of a new spontaneously fissionable nuclide. It is a chalcophile element which copreipitates with sulphides of copper, lead, arsenic and mercury from weakly acid solutions. The behaviour of the new nuclide in sulphide systems in many respects is similar to the behaviour of polonium, astatine and probably of bismuth. The most probable stable valence of the new nuclide varies from +1 up to +3. The data available on the chemical behaviour of the new nuclide as well as the analysis over contamination by spontaneously fissionable isotopes permit to state that the new natural spontaneously fissionable nuclide does not relate to the known isotopes

  10. Analysis of possibility of reactors occurring in nature

    International Nuclear Information System (INIS)

    A historical account is presented of the sequence of events which led to the 1956 prediction by the author that nuclear reactors should have existed in nature approximately 2 billion years ago. Following a brief review of the natural reactor theory, some of the results from recent studies of the Oklo Phenomenon are discussed. The report consists of the following chapters: I. Introduction, II. Natural Reactor Theory, III. The Oklo Phenomenon-Models of Natural Reactors, IV. Possibility of the Graphite-type Natural Reactor, V. The Sudbury Phenomenon, and VI. Conclusion. The Chap. IV deals with the studies on the occurrence of fissiogenic xenon isotopes in the carbon-rich mineral thucholite from the Besner Mine, Parry Sound, Ontario, Canada. The thucholite contained fissiogenic xenon isotopes from 238U spontaneous fission, but not from 235U neutron-induced fission. The Chap. V deals with the studies of the abundance pattern of Ne, Ar, Kr and Xe in several granite samples, including the Red Rock granite from the Sudbury structure, Ontario, Canada, which, according to Dietz (1964), was formed by the impact of an asteroid about 1.7 billion years ago. No unusual concentration of fissiogenic xenon isotopes was detected in the Red Rock granite, but the observed rare gas abundance pattern resembled that in meteorites, rather than the terrestrial rare gas abundances. (auth.)

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

    International Nuclear Information System (INIS)

    Escape of the products from the Oklo reactor proceeds, first, by escape from the uraninite (UO2) grains and, second, by transport out of the gangue. Escape from the grain by fission recoil accounts for prompt deposition in the gangue of 5 to 10 percent of the products. Escape by volume diffusion is very slow. The rate of loss by diffusion was highest during the operating period of the reactor and may have been of the order of 10-6 fraction/a for the most volatile elements. The least volatile elements have been retained in the grains. Their diffusion rates are less than 5 x 10-10/a. If similar loss rates can be achieved in synthetic uraninite (or thorianite), the overall rate of transport of most reactor products would be sufficiently limited by diffusion to insure that essentially all of the radioactive species would decay in situ. The principal geochemical requirements for a suitable storage site are those that insure the survival of the UO2 matrix, particularly that the pH and Eh are similar to the values at Oklo. Previous work has demonstrated wide variations in the rates of transport of Oklo products out of the reactor zones. Quantitative or semiquantitative estimates of these rates can be made for those elements which were retained in significant amounts but the estimates become qualitative for the very mobile elements. On a relative scale the losses are lowest in a group of elements including Zr, Nb, Ru, Pd, Ag, Te, the rare earths, Bi, Th, U, and Pu, and are high in a group including Sr, Mo, Ba, Kr, Xe, Rb, and Cs. Retention of the various reactor products varied from greater than or equal to 90 percent down to approximately 0.01 percent

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  14. 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

  15. Summary of the mineralogical and petrographic studies of the Oklo ores, their gangues and the country rock

    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 hand 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

  16. 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 μm) 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 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

  17. Study on natural deposition of fission product aerosol in severe accidents

    International Nuclear Information System (INIS)

    Aerosol natural deposition model of gravitational sedimentation, diffusionphoresis, inertial impaction and thermophoresis are established based on integrated safety analysis model for 600 MW pressurized water reactor. Typical severe accidents are chosen, and natural deposition phenomenon of fission product aerosol is analyzed. Additionally, gravitational sedimentation model of MELCOR is coupled into integrated safety analysis model, and fraction of gravitational sedimentation is compared. The results show that gravitational sedimentation is the most important deposition mechanism, and deposition effect of gravitational sedimentation model in this paper is stronger than MELCOR. (authors)

  18. Does a new natural spontaneously fissioning nuclide concentrate in ocean concentrations concentrate in ocean concentrations

    International Nuclear Information System (INIS)

    To search for superheavy elements (SHE) in nature iron-manganese concentrations deposited at the bottom of the Pacific Ocean have been studied. Using the carbonate leaching method selective uranium extraction from the concentrations is carried out. Concentration of a new natural spontaneously fissioning nuclide is measured. Comparison of the new nuclide content with the content of the known elements in the cancentrations is made. It is shown that the low degree of the nuclide extraction in the concretions does not contradict the forecast of SHE chemical properties and consequently the supposition on the nuclide attribution to SHE

  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. Cumulative fission yields of short-lived isotopes under natural-abundance-boron-carbide-moderated neutron spectrum

    Energy Technology Data Exchange (ETDEWEB)

    Finn, Erin C.; Metz, Lori A.; Greenwood, Lawrence R.; Pierson, Bruce; Wittman, Richard S.; Friese, Judah I.; Kephart, Rosara F.

    2015-04-09

    The availability of gamma spectroscopy data on samples containing mixed fission products at short times after irradiation is limited. Due to this limitation, data interpretation methods for gamma spectra of mixed fission product samples, where the individual fission products have not been chemically isolated from interferences, are not well-developed. The limitation is particularly pronounced for fast pooled neutron spectra because of the lack of available fast reactors in the United States. Samples containing the actinide isotopes 233, 235, 238U, 237Np, and 239Pu individually were subjected to a 2$ pulse in the Washington State University 1 MW TRIGA reactor. To achieve a fission-energy neutron spectrum, the spectrum was tailored using a natural abundance boron carbide capsule to absorb neutrons in the thermal and epithermal region of the spectrum. Our tailored neutron spectrum is unique to the WSU reactor facility, consisting of a soft fission spectrum that contains some measurable flux in the resonance region. This results in a neutron spectrum at greater than 0.1 keV with an average energy of 70 keV, similar to fast reactor spectra and approaching that of 235U fission. Unique fission product gamma spectra were collected from 4 minutes to 1 week after fission using single-crystal high purity germanium detectors. Cumulative fission product yields measured in the current work generally agree with published fast pooled fission product yield values from ENDF/B-VII, though a bias was noted for 239Pu. The present work contributes to the compilation of energy-resolved fission product yield nuclear data for nuclear forensic purposes.

  1. Bulk Segregant Analysis Reveals the Genetic Basis of a Natural Trait Variation in Fission Yeast.

    Science.gov (United States)

    Hu, Wen; Suo, Fang; Du, Li-Lin

    2015-12-01

    Although the fission yeast Schizosaccharomyces pombe is a well-established model organism, studies of natural trait variations in this species remain limited. To assess the feasibility of segregant-pool-based mapping of phenotype-causing genes in natural strains of fission yeast, we investigated the cause of a maltose utilization defect (Mal(-)) of the S. pombe strain CBS5557 (originally known as Schizosaccharomyces malidevorans). Analyzing the genome sequence of CBS5557 revealed 955 nonconservative missense substitutions, and 61 potential loss-of-function variants including 47 frameshift indels, 13 early stop codons, and 1 splice site mutation. As a side benefit, our analysis confirmed 146 sequence errors in the reference genome and improved annotations of 27 genes. We applied bulk segregant analysis to map the causal locus of the Mal(-) phenotype. Through sequencing the segregant pools derived from a cross between CBS5557 and the laboratory strain, we located the locus to within a 2.23-Mb chromosome I inversion found in most S. pombe isolates including CBS5557. To map genes within the inversion region that occupies 18% of the genome, we created a laboratory strain containing the same inversion. Analyzing segregants from a cross between CBS5557 and the inversion-containing laboratory strain narrowed down the locus to a 200-kb interval and led us to identify agl1, which suffers a 5-bp deletion in CBS5557, as the causal gene. Interestingly, loss of agl1 through a 34-kb deletion underlies the Mal(-) phenotype of another S. pombe strain CGMCC2.1628. This work adapts and validates the bulk segregant analysis method for uncovering trait-gene relationship in natural fission yeast strains. PMID:26615217

  2. Des analogues naturels de sites de stockage de dchets nuclaires vieux de 2 milliards d'annes : les racteurs de fission nuclaire naturels du Gabon (Afrique)

    Science.gov (United States)

    Gauthier-Lafaye, Franois

    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 Bangomb (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.

  3. From the natural reactor to the neutron bomb

    International Nuclear Information System (INIS)

    On the basis of several geological phenomena the theory of Kuroda on the existence of the natural reactor may be considered as confirmed. The existence of the Oklo phenomenon is supported by several facts in connection with the changes in uranium concentration. The output of the natural reactor is equal to that of an experimental reactor. It is also an evidence for the spontaneous fission of heavy elements and the spontaneous fusion of light elements in nature (the process of energy generation in the stars). The neutron bomb, or the Enhanced Radiation Warhead as called originally, has a high specific radiation effect as compared with other nuclear warheads. The possibilities of protection are based on the radiation attenuation factors of various materials. (R.P.)

  4. Neutronic study of an innovative natural uranium–thorium based fusion–fission hybrid energy system

    International Nuclear Information System (INIS)

    Highlights: • An innovative fusion-fission hybrid reactor blanket design is presented. • The blanket adopts seed–blanket concept to improve overall neutron economy. • The blanket is designed with two types of modules, i.e. uranium and thorium module. • The reactor could reach multi operating system purpose. - Abstract: An innovative design for a water cooled fusion–fission hybrid reactor (FFHR), aiming at efficiently utilizing natural uranium and thorium resources, is presented. The major objective is to study the feasibility of this concept balanced with multi-purposes, including energy gain, tritium breeding and 233U breeding. In order to improve overall neutron economy of the system, the fission blanket is designed with two types of modules, i.e. the natural uranium modules (U-modules) and thorium modules (Th-modules), which are alternately arranged in the toroidal and poloidal directions of the blanket. This innovative design is based on a simple intuition of neutron distribution: with the alternate geometrical arrangement, energy multiplication by uranium fission, tritium breeding and 233U breeding are performed separately in different sub-zones in the blanket. The uranium modules which has excellent neutron economy under the combined neutron spectrum, plays the dominant role in the energy production, neutron multiplication and tritium breeding. Excess neutrons produced by the uranium modules are then used to drive the thorium modules (which have poor neutron economy) to breed 233U fuel. Therefore, it creates a new free dimension to realize the blanket’s balanced design. The COUPLE code developed by INET of Tsinghua University is used to simulate the neutronic behavior in the blanket. The simulated results show that with the volumetric ratio of thorium modules about 0.4, the balanced design for multi purposes is achievable, with energy multiplication M ⩾ 9, tritium breeding ratio TBR ⩾ 1.05, and at the end of the five years refueling cycle, the 233U enrichment in thorium modules exceeding 1.0%. The neutronic analysis results also show that the preliminary design of this innovative FFHR is of great potential to utilize the bred 233U effectively after the initial fuel load of the first ten-year operation

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

    CERN Document Server

    Flambaum, V V

    2008-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    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...

  8. 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.

  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. Searches for superheavy elements in nature: Cosmic-ray nuclei; spontaneous fission

    Science.gov (United States)

    Ter-Akopian, G. M.; Dmitriev, S. N.

    2015-12-01

    There is little chance that superheavy nuclei with lifetimes of no less than 100 million years are present on the stability island discovered at present. Also, pessimistic are the results of estimates made about their nucleosynthesis in r-process. Nevertheless, the search for these nuclei in nature is justified in view of the fundamental importance of this topic. The first statistically significant data set was obtained by the LDEF Ultra-Heavy Cosmic-Ray Experiment, consisting of 35 tracks of actinide nuclei in galactic cosmic rays. Because of their exceptionally long exposure time in Galaxy, olivine crystals extracted from meteorites generate interest as detectors providing unique data regarding the nuclear composition of ancient cosmic rays. The contemporary searches for superheavy elements in the earth matter rely on knowledge obtained from chemical studies of artificially synthesized superheavy nuclei. New results finding out the chemical behavior of superheavy elements should be employed to obtain samples enriched in their homologues. The detection of rare spontaneous fission events and the technique of accelerator mass spectrometry are employed in these experiments.

  12. 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.

  13. 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

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

    International Nuclear Information System (INIS)

    - Microscopic flux measurements in reactor Aquilon have allowed to investigate the thermal and epithermal flux distribution in natural uranium rods, then to obtain the neutron spectrum variations in uranium, Wescott 'β' term of the average spectrum in the rod, and the ratio of epithermal to therma fissions. A new definition for the infinite multiplication factor is proposed in annex, which takes into account epithermal parameters. (authors)

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

    Energy Technology Data Exchange (ETDEWEB)

    Iunes, P.J.

    1990-06-01

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

  16. Resolution of the nature of the coupling in subthreshold fission in 238U+n

    International Nuclear Information System (INIS)

    The analysis of a recent high-resolution neutron capture measurement at 152 m has provided the first evidence that the strong fission resonance at 721 eV is a class-II resonance. This conclusion is based on the measured capture width of 4.7 +- 0.6 MeV, which is considerably smaller than the average capture width of 23.5 MeV for the neighboring resonances. Furthermore, after analyzing the fission widths for the 721- and 1211-eV clusters, we conclude for the J/sup π/ = 1/2+ fission barrier in 239U that the inner barrier is lower than the outer barrier by approx.1.5 MeV

  17. 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

  18. 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)

  19. 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

  20. 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 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.)

  1. Isotopic and gravimetric analyses of rare earths in Oklo ore samples

    International Nuclear Information System (INIS)

    Seven ore samples were chosen for the study of perturbations and migrations of elements. The following elements were analysed: neodymium, europium, samarium, gadolinium and uranium. The following samples were chosen: No. 612, as reference sample; No. 1294, in which 235U depletion was greatest and which was chosen with a view to seeing whether the fission-product balance remained consistent with the reference case; No. 882/1 (a compact uraninite nodule) and No. 882/2 (the clay surrounding No. 882/1), which were chosen with a view to obtaining information - by comparison of the two samples - about possible leaching of the fission products and of the uranium; Nos 1323, 1326 and 1332, chosen with a view to studying the transport of the fission products and the level of the fluence received as one moves away from the core (Nos 1323 and 1332 were only partially analysed). The analytical method used was thermal-ionization mass spectrometry, together with isotopic dilution for the determinations. To achieve complete but rapid separation of the rare earths, the authors used chromatography on ion-exchange paper, with development by autoradiography and recovery by calcination. The main difficulties of interpretation are due to the need to estimate the proportion of natural elements among the fission products and the extent of neutron capture. The relative proportions of the natural elements, the fluences, the spectral indices and the conversion coefficients are on the whole consistent. Similarly, the numbers of fissions observed are related to the fission yields and proportional to the fluences. Sample No. 882 indicates that there was migration of the uranium without movement of the fission products. Samples Nos 1326 and 1323, on the other hand, indicate simultaneous transport of the uranium and the rare earths

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-08-01

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

  3. 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)

  4. Thermal fission rates with temperature dependent fission barriers

    CERN Document Server

    Zhu, Yi

    2016-01-01

    \\item[Background] The fission processes of thermal excited nuclei are conventionally studied by statistical models which rely on inputs of phenomenological level densities and potential barriers. Therefore the microscopic descriptions of spontaneous fission and induced fission are very desirable for a unified understanding of various fission processes. \\item[Purpose] We propose to study the fission rates, at both low and high temperatures, with microscopically calculated temperature-dependent fission barriers and mass parameters. \\item[Methods] The fission barriers are calculated by the finite-temperature Skyrme-Hartree-Fock+BCS method. The mass parameters are calculated by the temperature-dependent cranking approximation. The thermal fission rates can be obtained by the imaginary free energy approach at all temperatures, in which fission barriers are naturally temperature dependent. The fission at low temperatures can be described mainly as a barrier-tunneling process. While the fission at high temperatures ...

  5. 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

  6. 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.

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

    International Nuclear Information System (INIS)

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

  8. 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

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

    OpenAIRE

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

    2005-01-01

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

  10. Entrance-channel dependence of fission transients

    OpenAIRE

    Charity, R.J.

    2004-01-01

    Fission transients describe the fission rate as it evolves towards the quasistationary value given by Kramers' formula. The nature of fission transients is dependent on the assumed initial distribution of the compound nuclei along the fission coordinate. Although the standard initial assumption of a near-spherical object leads to a transient suppression of the fission rate (fission delay), a moderate initial fissionlike deformation can reduce the magnitude of this suppression. For still large...

  11. Delayed fission

    International Nuclear Information System (INIS)

    Delayed fission is a nuclear process that couples beta decay and fission. In the delayed fission process, a parent nucleus undergoes beta decay or electron capture and thus populates excited states in the daughter nucleus. This review covers experimental methods for detecting and measuring delayed fission. Experimental results (ECDF activities and beta-DF activities) and theory are presented. The future prospects for study of delayed fission are discussed. 50 refs., 8 figs., 2 tabs

  12. Cumulative fission yields of short-lived isotopes under natural-abundance-boron-carbide-moderated neutron spectrum

    International Nuclear Information System (INIS)

    This work expands the availability of energy-resolved short-lived cumulative fission product yields for 235,238,233U, 239Pu, and 237Np subjected to a 2$ pulse in the Washington State University TRIGA reactor. A boron carbide capsule tailored the neutron spectrum, creating a spectrum with an average energy of 700 keV, similar to fast reactor spectra and approaching that of 235U fission. Unique gamma spectra were collected from 4 min to 1 week after fission using high purity germanium detectors. Measured cumulative fission product yields generally agree well with published fast pooled fission product yield values from ENDF/B-VII, though a bias was noted for 239Pu. (author)

  13. 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)

  14. 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)

  15. Nuclear fission

    International Nuclear Information System (INIS)

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

  16. 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

  17. Isotopic composition and neutronics of the Okelobondo natural reactor

    Science.gov (United States)

    Palenik, Christopher Samuel

    The Oklo-Okelobondo and Bangombe uranium deposits, in Gabon, Africa host Earth's only known natural nuclear fission reactors. These 2 billion year old reactors represent a unique opportunity to study used nuclear fuel over geologic periods of time. The reactors in these deposits have been studied as a means by which to constrain the source term of fission product concentrations produced during reactor operation. The source term depends on the neutronic parameters, which include reactor operation duration, neutron flux and the neutron energy spectrum. Reactor operation has been modeled using a point-source computer simulation (Oak Ridge Isotope Generation and Depletion, ORIGEN, code) for a light water reactor. Model results have been constrained using secondary ionization mass spectroscopy (SIMS) isotopic measurements of the fission products Nd and Te, as well as U in uraninite from samples collected in the Okelobondo reactor zone. Based upon the constraints on the operating conditions, the pre-reactor concentrations of Nd (150 ppm +/- 75 ppm) and Te (samples (0.7 to 13.8 GWd/MTU), the final fission product inventories of Nd (90 to 1200 ppm) and Te (10 to 110 ppm) were calculated. By the same means, the ranges of all other fission products and actinides produced during reactor operation were calculated as a function of burnup. These results provide a source term against which the present elemental and decay abundances at the fission reactor can be compared. Furthermore, they provide new insights into the extent to which a "fossil" nuclear reactor can be characterized on the basis of its isotopic signatures. In addition, results from the study of two other natural systems related to the radionuclide and fission product transport are included. A detailed mineralogical characterization of the uranyl mineralogy at the Bangombe uranium deposit in Gabon, Africa was completed to improve geochemical models of the solubility-limiting phase. A study of the competing effects of radiation damage and annealing in a U-bearing crystal of zircon shows that low temperature annealing in actinide-bearing phases is significant in the annealing of radiation damage.

  18. 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

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

    DEFF Research Database (Denmark)

    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; Bähler, Jürg; Beyer, Andreas

    2014-01-01

    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...

  20. 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

  1. Spontaneous Fission

    Science.gov (United States)

    Segre, Emilio

    1950-11-22

    The first attempt to discover spontaneous fission in uranium was made by [Willard] Libby, who, however, failed to detect it on account of the smallness of effect. In 1940, [K. A.] Petrzhak and [G. N.] Flerov, using more sensitive methods, discovered spontaneous fission in uranium and gave some rough estimates of the spontaneous fission decay constant of this substance. Subsequently, extensive experimental work on the subject has been performed by several investigators and will be quoted in the various sections. [N.] Bohr and [A.] Wheeler have given a theory of the effect based on the usual ideas of penetration of potential barriers. On this project spontaneous fission has been studied for the past several years in an effort to obtain a complete picture of the phenomenon. For this purpose the spontaneous fission decay constants {lambda} have been measured for separated isotopes of the heavy elements wherever possible. Moreover, the number {nu} of neutrons emitted per fission has been measured wherever feasible, and other characteristics of the spontaneous fission process have been studied. This report summarizes the spontaneous fission work done at Los Alamos up to January 1, 1945. A chronological record of the work is contained in the Los Alamos monthly reports.

  2. Ternary fission

    International Nuclear Information System (INIS)

    Since its discovery in 1946, light (charged) particle accompanied fission (ternary fission) has been extensively studied, for spontaneous as well as for induced fission reactions. The reason for this interest was twofold: the ternary particles being emitted in space and time close to the scission point were expected to supply information on the scission point configuration and the ternary fission process was an important source of helium, tritium, and hydrogen production in nuclear reactors, for which data were requested by the nuclear industry. Significant experimental progress has been realized with the advent of high-resolution detectors, powerful multiparameter data acquisition systems, and intense neutron and photon beams. As far as theory is concerned, the trajectory calculations (in which scission point parameters are deduced from the experimental observations) have been very much improved. An attempt was made to explain ternary particle emission in terms of a Plateau-Rayleigh hydrodynamical instability of a relatively long cylindrical neck or cylindrical nucleus. New results have also been obtained on the so-called open-quotes trueclose quotes ternary fission (fission in three about-equal fragments). The spontaneous emission of charged particles has also clearly been demonstrated in recent years. This chapter discusses the main characteristics of ternary fission, theoretical models, light particle emission probabilities, the dependence of the emission probabilities on experimental variables, light particle energy distributions, light particle angular distributions, correlations between light particle accompanied fission observables, open-quotes trueclose quotes ternary fission, and spontaneous emission of heavy ions. 143 refs., 18 figs., 8 tabs

  3. 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

  4. Calculations of fission rates for r-process nucleosynthesis

    OpenAIRE

    Panov, I. V.; Kolbe, E.; Pfeiffer, B; Rauscher, T.; Kratz, K. -L.; Thielemann, F.-K.

    2004-01-01

    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 neverthe...

  5. Time-variability of the fine-structure constant expected from the Oklo constraint and the QSO absorption lines

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, Yasunori

    2003-10-30

    The data from the QSO absorption lines indicating a nonzero time-variability of the fine-structure constant has been re-analyzed on the basis of a 'damped-oscillator' fit, as motivated by the same type of behavior of a scalar field, dilaton, which mimics a cosmological constant to understand the accelerating universe. We find nearly as good fit to the latest data as the simple weighted mean. In this way, we offer a way to fit the more stringent result from the Oklo phenomenon, as well.

  6. The discovery of fission

    International Nuclear Information System (INIS)

    In this article by the retired head of the Separation Processes Group of the Chemistry Division, Atomic Energy Research Establishment, Harwell, U.K., the author recalls what he terms 'an exciting drama, the unravelling of the nature of the atomic nucleus' in the years before the Second World War, including the discovery of fission. 12 references. (author)

  7. 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

  8. 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.

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

    International Nuclear Information System (INIS)

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

  10. Ternary fission

    Indian Academy of Sciences (India)

    M Balasubramaniam; K R Vijayaraghavan; C Karthikraj

    2015-09-01

    We present the ternary fission of 252Cf and 236U within a three-cluster model as well as in a level density approach. The competition between collinear and equatorial geometry is studied by calculating the ternary fragmentation potential as a function of the angle between the lines joining the stationary middle fragment and the two end fragments. The obtained results for the 16O accompanying ternary fission indicate that collinear configuration is preferred to equatorial configuration. Further, for all the possible third fragments, the potential energy surface (PES) is calculated corresponding to an arrangement in which the heaviest and the lightest fragments are considered at the end in a collinear configuration. The PES reveals several possible ternary modes including true ternary modes where the three fragments are of similar size. The complete mass distributions of Si and Ca which accompanied ternary fission of 236U is studied within a level density picture. The obtained results favour several possible ternary combinations.

  11. A study of 239Pu production rate in a water cooled natural uranium blanket mock-up of a fusion-fission hybrid reactor

    Science.gov (United States)

    Feng, Song; Liu, Rong; Lu, Xinxin; Yang, Yiwei; Xu, Kun; Wang, Mei; Zhu, Tonghua; Jiang, Li; Qin, Jianguo; Jiang, Jieqiong; Han, Zijie; Lai, Caifeng; Wen, Zhongwei

    2016-03-01

    The 239Pu production rate is important data in neutronics design for a natural uranium blanket of a fusion-fission hybrid reactor, and the accuracy and reliability should be validated by integral experiments. The distribution of 239Pu production rates in a subcritical natural uranium blanket mock-up was obtained for the first time with a D-T neutron generator by using an activation technique. Natural uranium foils were placed in different spatial locations of the mock-up, the counts of 277.6 keV γ-rays emitted from 239Np generated by 238U capture reaction were measured by an HPGe γ spectrometer, and the self-absorption of natural uranium foils was corrected. The experiment was analyzed using the Super Monte Carlo neutron transport code SuperMC2.0 with recent nuclear data of 238U from the ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0u2, JEFF-3.2 and CENDL-3.1 libraries. Calculation results with the JEFF-3.2 library agree with the experimental ones best, and they agree within the experimental uncertainty in general with the average ratios of calculation results to experimental results (C/E) in the range of 0.93 to 1.01.

  12. Benchmarking Nuclear Fission Theory

    OpenAIRE

    Bertsch, G. F.; Loveland, W.; 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.

  13. Benchmarking nuclear fission theory

    Science.gov (United States)

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

    2015-07-01

    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.

  14. Fission Spectrum

    Science.gov (United States)

    Bloch, F.; Staub, H.

    1943-08-18

    Measurements of the spectrum of the fission neutrons of 25 are described, in which the energy of the neutrons is determined from the ionization produced by individual hydrogen recoils. The slow neutrons producing fission are obtained by slowing down the fast neutrons from the Be-D reaction of the Stanford cyclotron. In order to distinguish between fission neutrons and the remaining fast cyclotron neutrons both the cyclotron current and the pusle amplifier are modulated. A hollow neutron container, in which slow neutrons have a lifetime of about 2 milliseconds, avoids the use of large distances. This method results in much higher intensities than the usual modulation arrangement. The results show a continuous distribution of neutrons with a rather wide maximum at about 0.8 MV falling off to half of its maximum value at 2.0 MV. The total number of netrons is determined by comparison with the number of fission fragments. The result seems to indicate that only about 30% of the neutrons have energies below .8 MV. Various tests are described which were performed in order to rule out modification of the spectrum by inelastic scattering. Decl. May 4, 1951

  15. Singlet Fission

    Czech Academy of Sciences Publication Activity Database

    Smith, M. B.; Michl, Josef

    2010-01-01

    Roč. 110, č. 11 (2010), s. 6891-6936. ISSN 0009-2665 Grant ostatní: Department of Energy (US) DE-FG36-08GO18017 Institutional research plan: CEZ:AV0Z40550506 Keywords : solar energy conversion * photovoltaics * singlet fission Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 33.033, year: 2010

  16. 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.)

  17. From transmutation to fission

    International Nuclear Information System (INIS)

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

  18. Fission meter

    Science.gov (United States)

    Rowland, Mark S.; Snyderman, Neal J.

    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.

  19. 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.

  20. Fission theory and actinide fission data

    Energy Technology Data Exchange (ETDEWEB)

    Michaudon, A.

    1975-10-01

    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 ..gamma.. 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 ..gamma..-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, ..gamma.., 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. 17 figures, 56 ref. (auth)

  1. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Perez Morales, I.

    2000-07-01

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

  3. Fission Research at IRMM

    OpenAIRE

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

    2010-01-01

    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.

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

    Science.gov (United States)

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

    2005-02-01

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

  5. 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. Gnnenwein ... [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. Sillanp ... [et al.]. MYRRHA, a new fast spectrum facility / H. At 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.

  6. 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)

  7. Fine structure in the fission fragment yields

    International Nuclear Information System (INIS)

    Discussed are the most interesting experiments on the fine structure of fission product yields of U, Pu, Th, Cf, Es, Cm, Fr, Np isotopes. Modern comprehension of the fine structure nature in connection with other problems of fission dynamics is considered. It is noted, that the fine structure results from pairing correlations in a nucleus. The conclusion is drawn, that the available set of experimental data is not sufficient to elucidate the fine structure nature

  8. 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.

  9. Nuclear fission induced by Pi mesons

    International Nuclear Information System (INIS)

    Pi mesons are an important part of the interactions among strongly-interacting particles, and their reactions with complex nuclei involve reactions with a wide range of interactions and time scales, with the slowest being the familiar fission process. Decades of effort have produced a wide range of fission data with stopped and energetic charged beams, both positive and negative. These results are the result of many uncoordinated studies, but in total can give a very good view of pion-induced fission. This review will compare and combine the measurements, with comparisons to a range of theoretical expectations. It is found that the nature of fission induced by pi mesons is not significantly different from fission induced by other energetic particles, in spite of the special features of the mesonic beam. This specific arena of nuclear science may now be considered complete. (author)

  10. Fission Mass Yield Studies

    International Nuclear Information System (INIS)

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

  11. 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.

  12. Dynamics of Coulomb fission

    OpenAIRE

    Kruse, Hans; Pinkston, W. T.; Greiner, Walter, 1935-; 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 θc.m.=180° is increased by a factor of 3....

  13. Ternary Fission. A Review

    International Nuclear Information System (INIS)

    Experimental results in the field of light-particle-accompanied fission (including fission accompanied by 'scission neutrons') - and in relation to fission into three fragments of comparable mass - are reviewed over the last four years. These results are set against the background of previously ascertained fact, and certain empirical regularities are noted. (author)

  14. 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

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

    International Nuclear Information System (INIS)

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

  16. 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 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 together numerous experimental facts, and c

  17. 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)

  18. Study on effect of fission delayed gamma quanta in measuring fission neutron spectra by means of time-of-flight method

    International Nuclear Information System (INIS)

    The effects of the delayed fission γ - rays on the results of measuring the fission neutron spectra have been investigated by time-of-flight method. Some conclusions have been drawn on the nature of these effects

  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. Complex fission phenomena

    OpenAIRE

    Poenaru, Dorin N.; Gherghescu, Radu A.; Greiner, Walter, 1935-

    2005-01-01

    Complex fission phenomena are studied in a unified way. Very general reflection asymmetrical equilibrium (saddle point) nuclear shapes are obtained by solving an integro-differential equation without being necessary to specify a certain parametrization. The mass asymmetry in binary cold fission of Th and U isotopes is explained as the result of adding a phenomenological shell correction to the liquid drop model deformation energy. Applications to binary, ternary, and quaternary fission are ou...

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

    International Nuclear Information System (INIS)

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

  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. 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.

  5. Is channeling of fission tracks taking place?

    International Nuclear Information System (INIS)

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

  6. 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)

  7. Fission gas detection system

    Science.gov (United States)

    Colburn, Richard P.

    1985-01-01

    A device for collecting fission gas released by a failed fuel rod which device uses a filter to pass coolant but which filter blocks fission gas bubbles which cannot pass through the filter due to the surface tension of the bubble.

  8. Fission Xenon on Mars

    Science.gov (United States)

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

    2002-01-01

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

  9. The nuclear fission

    International Nuclear Information System (INIS)

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

  10. Principles of fission

    International Nuclear Information System (INIS)

    This short animated film introduces the principles of nuclear fission as applied to 'thermal' nuclear reactors and 'fast' reactors. It explains nuclear fission, the properties of Uranium 235 and 238, how a chain reaction works and the need for a moderator in thermal reactors. The film shows how Plutonium is created and used to provide even more energy when used in Fast Reactors. (author)

  11. Study of hypernuclei fission

    International Nuclear Information System (INIS)

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

  12. Biomodal spontaneous fission

    Energy Technology Data Exchange (ETDEWEB)

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

    1989-09-26

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

  13. 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

  14. Feasibility of Producing Molybdenum-99 on a Small Scale Using Fission of Low Enriched Uranium or Neutron Activation of Natural Molybdenum. Companion CD-ROM

    International Nuclear Information System (INIS)

    This publication documents the work performed within the IAEA coordinated research project (CRP) on developing techniques for small scale indigenous molybdenum-99 production using low enriched uranium (LEU) fission or neutron activation. The CRP enabled participating institutions to gain the knowledge necessary for indigenous molybdenum-99 production. The outcome serves to capture the steps participants undertook in examining the feasibility of becoming small scale 99Mo producers. Most participants carried out work related to the entire production process, from target assembly through irradiation, planning for target disassembly in hot cells, chemical processing of targets, quality control practices, and managing waste streams. Some participants focused on one particular area, for example, testing new methods for production of LEU foil for targets and the production of gel generators from 99Mo solution. The publication aggregates all of the work undertaken as part of the CRP in order to present the results as a whole. The accomplishments of participating institutions are detailed in individual country reports on this CD-ROM

  15. 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)

  16. Geochemical constraints on accumulation of actinide critical masses from stored nuclear waste in natural rock repositories. Technical report, April 1, 1978--August 31, 1978 (plus supplemental time to December 31, 1978)

    International Nuclear Information System (INIS)

    Results of a literature search of abundant data on lanthanide and actinide individual and joint systematics are presented. Covered were several papers/reports about uranium solution chemistry, uranium deposits, a natural fission reactor, rare-earch deposits, manganese nodules, bedded and dome salt deposits, and miscellaneous items. This literature search is not complete but represents efforts of seven individuals attempting to gather data relevant to the objectives defined in this report. Many foreign articles, as well as many English language articles are absent. Approximately 800 articles were inspected; 69 are included in the References cited. The data search for actinides and lanthanides in natural rocks indicated that only limited segregation of the actinides U, Np, Pu, Am, and Cm from the lanthanides is possible should high-level waste be released from canisters stored in various geomedia. Supporting this were studies of Oklo and other uranium deposits, manganese nodules, monomineralic and concretion formation rates, and actinide and lathanide transport in brines. The fact that some waste canisters may, under certain conditions, contain several critical masses of one or more actinides is countered by the facts that (a) most actinides have very short half-lives and would decay before release from canisters, (b) released actinides and lanthanides, although dispersed, would be transported and deposited as a group, thus preventing point concentration of any actinides, and (c) 235U has a much longer half-life than the other actinides, thus allowing greater time for possible reaccumulation and criticality; such a scenario would demand that 235U be segregated effectively from other elements in the lanthanide-actinide groups.No mechanism to do this is consistent with the natural occurrences studied or the theoretical Eh-pH diagrams considered

  17. 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

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

    International Nuclear Information System (INIS)

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

  19. Fission Fragments Discriminator

    International Nuclear Information System (INIS)

    Nuclear fission reaction between Uranium-235 nucleus and thermal neutron caused the high energy fission fragments with uncertainly direction. The particle direction discrimination was determined. The 2.5 x 3.0 mm2 polyethylene gratings with 1-6 mm thickness were used. The grating was placed between uranium screen that fabricated from ammonium-diurinate compound and polycarbonate nuclear track film recorder irradiated by neutron from Thai Research Reactor (TRR-1/M1) facility. The nuclear track density was inversely with grating thickness. It's only fission fragments normal to uranium screen pass through film recorder when grating thickness was 4-6 mm

  20. Nucleon-induced fission at intermediate energies

    International Nuclear Information System (INIS)

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

  1. Study on Fission Blanket Fuel Cycling of a Fusion-Fission Hybrid Energy Generation System

    International Nuclear Information System (INIS)

    Full text: Direct application of ITER-scale tokamak as a neutron driver in a subcritical fusion-fission hybrid reactor to generate electric power is of great potential in predictable future. This paper reports a primary study on neutronic and fuel cycle behaviors of a fission blanket for a new type of fusion-driven system (FDS), namely a subcritical fusion-fission hybrid reactor for electric power generation aiming at energy generation fueled with natural or depleted uranium. Using COUPLE2 developed at INET of Tsinghua University by coupling the MCNP code with the ORIGEN code to study the neutronic behavior and the refueling scheme, this paper focuses on refueling scheme of the fissionable fuel while keeping some important parameters such as tritium breeding ratio (TBR) and energy gain. Different fission fuels, coolants and their volumetric ratios arranged in the fission blanket satisfy the requirements for power generation. The results show that soft neutron spectrum with optimized fuel to moderator ratio can yield an energy amplifying factor of M> 20 while maintaining the TBR > 1.1 and the CR > 1 (the conversion ratio of fissile materials) in a reasonably long refueling cycle. Using an in-site fuel recycle plant, it will be an attractive way to realize the goal of burning 238U with such a new type of fusion-fission hybrid reactor system to generate electric power. (author)

  2. Feasibility of Producing Molybdenum-99 on a Small Scale Using Fission of Low Enriched Uranium or Neutron Activation of Natural Molybdenum

    International Nuclear Information System (INIS)

    This publication documents the work performed within the IAEA coordinated research project (CRP) on Developing Techniques for Small Scale Indigenous Molybdenum-99 Production Using LEU Fission or Neutron Activation. The project allowed participating institutions to receive training and information on aspects necessary for starting production of molybdenum-99 (99Mo) on a small scale, that is, to become national level producers of this medical isotope. Stable production of 99Mo is one of the most pressing issues facing the nuclear community at present, because the medical isotope technetium-99m (99mTc), which decays from 99Mo, is one of the most widely used radionuclides in diagnostic imaging and treatment around the world. In the past five years, there have been widespread shortages of 99Mo owing to the limited number of producers, many of which use ageing facilities. To assist in stabilizing the production of 99Mo, and to promote the use of production methods that do not rely on the use of highly enriched uranium (HEU), the IAEA initiated the abovementioned CRP on small scale 99Mo production using low enriched uranium (LEU) fission or neutron activation methods. The intention was to enable participating institutions to gain the knowledge necessary to become national level producers of 99Mo in the event of further global shortages. Some of the institutions that participated in the CRP have continued their work on 99Mo production, and are enlisting the assistance of other CRP members and the IAEA’s technical cooperation programme to set up a small scale production capability. In total, the CRP was active for six years, and concluded in December 2011. During the CRP, fourteen IAEA Member States took part; four research coordination meetings were held, and four workshops were held on operational aspects of 99Mo production, LEU target fabrication and waste management. Most participants carried out work related to the entire production process, from target assembly to irradiation (most only performed the thermal and hydraulic calculations necessary for irradiation), to planning for target disassembly in hot cells, chemical processing of targets, quality control practices and managing waste streams. However, some participants focused on one particular area, for example, testing new methods for production of LEU foil for targets or the production of gel generators from 99Mo solution. This publication aggregates all of the work undertaken as part of the CRP in order to present the results as a whole; the accomplishments of participating institutions are detailed in individual country reports on the attached CD-ROM. In addition to presenting the work performed within the CRP, this publication is intended to serve a wide readership that includes nuclear authorities, regulators and any institution that may have an interest in becoming a small scale producer of 99Mo using non-HEU production methods. The details presented here could serve as a template for a feasibility study to be carried out by an institution or State wishing to produce 99Mo; special care has been taken to note areas that were particularly challenging for participants and therefore may not be feasible for other small scale producers without significant investment in human resources or infrastructure

  3. Study of a fission neutron detector and application to the measurement of the 241Am fission cross-section

    International Nuclear Information System (INIS)

    This work describes a fission neutron detector particularly suited to the measurement of the fission cross sections of highly radioactive nuclei. It is made of a cylinder containing 45 liters of NE 213 liquid scintillator. The fission neutrons are detected through the scintillation emitted by the recoiling proton in the scintillator. They are discriminated from γ rays by a shape discrimination of the photomultiplier pulses. Since the detector is insensitive to α particles from natural radioactivity it can be used with several grams of fissile materials as needed when the fission cross section is quite small. As an example, the 241Am fission cross section measurement is presented. In this experiment an americium target with an activity of 1011α/sec was bombarded by the neutron beam provided by the 60 MeV Saclay/linear accelerator. The fission cross section and the resonance parameters have been measured up to 40 eV

  4. Fission - Innovative Systems

    International Nuclear Information System (INIS)

    The nuclear data needs of the fission energy application in the future were presented from the user's viewpoint. The fields considered were fast reactors (INPRO, Gen-IV, FaCT), accelerator driven systems (ADS), and next-generation light water reactors (NG-LWR). In fission applications, nuclear data already have an established place in the industry, having moved well beyond the status of an art into nuclear science. This fact implies strong requirements for both the quality and the quantity of nuclear data, leading, in particular, to the need for important aspects such as covariances, and the verification and validation (V and V) system. Typical areas to be improved in fission applications would be: minor actinides, fission products, thermal scattering, and so on

  5. Fission fragment angular distributions

    International Nuclear Information System (INIS)

    The first fission fragment angular distributions were observed by Winhold et al. in 1952 for the photofission of thorium. They found angular distributions peaked towards 90 degrees with respect to the ?-beam direction. Corresponding angular distribution measurements were soon reported for fission induced by neutrons and charged particles (see Vaz and Alexander and Bond and references therein). The customary theory gives for all fragments the same angular distribution independent of their masses, yields, and kinetic energies. This subject will be treated in Section II. Recently, measurements by Wilke and Wilke et al. for photofission and by Gokhberg et al. for neutron-induced fission showed mass dependences of the fission fragment angular distributions. If these measurements are confirmed, then the contemporary theory has to be extended. Such a possible direction of extension is proposed in Section III. 16 refs., 1 fig

  6. Spontaneous fission and clusterization

    International Nuclear Information System (INIS)

    We study the very exotic cluster configurations of atomic nuclei defined by the spontaneous fission channels. Our treatment applies effective U(3) symmetry labels corresponding to the quadrupole deformation of the nuclei. We study in detail the Mo emission of the 252Cf, which was observed in a recent experiment. The effect of the microscopic structure turns out to be nonuniform for different fission channels. (author)

  7. Microscopic Theory of Fission

    Science.gov (United States)

    Younes, W.; Gogny, D.

    2008-04-01

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

  8. 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)

  9. 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.

  10. Modernizing the fission basis

    International Nuclear Information System (INIS)

    The first TUNL-LANL-LLNL collaborative experiment under the program of high precision measurements of neutron induced product yields as a function of incident neutron energy was carried out at the 10-MV FN Tandem Accelerator at the Triangle Universities Nuclear Laboratory. The activation measurements were performed at 9 MeV neutrons produced from the D(d,n)3He reactions on 235U and 238U targets. The main objective of the experiment was to demonstrate the capability to measure characteristic γ rays from specific fission products and to study the background from room scattered neutrons. The neutron flux was measured using the different monitor foils such us Al, In and Au. In addition, time of flight measurements were performed using a neutron-monitor (NE 213) and two 3He counters. After this successful run, the second experiment under this program was completed in September 2011 with 9 MeV neutron beam using the dual fission chamber for 235U, 238U and 239Pu targets. The dual fission chamber design permits simultaneous exposure of absolute fission fragment emission rate and fission activation foils. The results will be coupled with theoretical analysis to provide a more fundamental understanding of the fission process. (author)

  11. 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

  12. 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)

  13. A study on the association of two iodine isotopes, of natural 127I and of the fission product 129I, with soil components using a sequential extraction procedure

    International Nuclear Information System (INIS)

    Sequential extraction techniques have been utilized in order to investigate the degree of binding or association of natural iodine 127I and the radioactive iodine isotope 129I with soil components. The results indicate that only a small fraction of natural iodine (2.5-4%) but a large fraction of the recently added radioactive 129(38-49%) is water-soluble. The other forms of iodine which were determined for both iodine isotopes were exchangeable iodine, iodine bound to metal-oxides and iodine bound to organic matter. (author). 34 refs., 4 tabs

  14. Potential operating orbits for fission electric propulsion systems driven by the SAFE-400

    International Nuclear Information System (INIS)

    Safety must be ensured during all phases of space fission system design, development, fabrication, launch, operation, and shutdown. One potential space fission system application is fission electric propulsion (FEP), in which fission energy is converted into electricity and used to power high efficiency (Isp>3000s) electric thrusters. For these types of systems it is important to determine which operational scenarios ensure safety while allowing maximum mission performance and flexibility. Space fission systems are essentially non-radioactive at launch, prior to extended operation at high power. Once high power operation begins, system radiological inventory steadily increases as fission products build up. For a given fission product isotope, the maximum radiological inventory is typically achieved once the system has operated for a length of time equivalent to several half-lives. After that time, the isotope decays at the same rate it is produced, and no further inventory builds in. For an FEP mission beginning in Earth orbit, altitude and orbital lifetime increase as the propulsion system operates. Two simultaneous effects of fission propulsion system operation are thus (1) increasing fission product inventory and (2) increasing orbital lifetime. Phrased differently, as fission products build up, more time is required for the fission products to naturally convert back into non-radioactive isotopes. Simultaneously, as fission products build up, orbital lifetime increases, providing more time for the fission products to naturally convert back into non-radioactive isotopes. Operational constraints required to ensure safety can thus be quantified

  15. Potential Operating Orbits for Fission Electric Propulsion Systems Driven by the SAFE-400

    Science.gov (United States)

    Houts, Mike; Kos, Larry; Poston, David; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Safety must be ensured during all phases of space fission system design, development, fabrication, launch, operation, and shutdown. One potential space fission system application is fission electric propulsion (FEP), in which fission energy is converted into electricity and used to power high efficiency (Isp greater than 3000s) electric thrusters. For these types of systems it is important to determine which operational scenarios ensure safety while allowing maximum mission performance and flexibility. Space fission systems are essentially nonradioactive at launch, prior to extended operation at high power. Once high power operation begins, system radiological inventory steadily increases as fission products build up. For a given fission product isotope, the maximum radiological inventory is typically achieved once the system has operated for a length of time equivalent to several half-lives. After that time, the isotope decays at the same rate it is produced, and no further inventory builds in. For an FEP mission beginning in Earth orbit, altitude and orbital lifetime increase as the propulsion system operates. Two simultaneous effects of fission propulsion system operation are thus (1) increasing fission product inventory and (2) increasing orbital lifetime. Phrased differently, as fission products build up, more time is required for the fission products to naturally convert back into non-radioactive isotopes. Simultaneously, as fission products build up, orbital lifetime increases, providing more time for the fission products to naturally convert back into non-radioactive isotopes. Operational constraints required to ensure safety can thus be quantified.

  16. The fission TPC project

    International Nuclear Information System (INIS)

    New high-precision fission experiments have become a priority within the nuclear energy community due to a growing, world wide, interest in nuclear reactors. In particular, the design of the next generation reactors requires a reduction in the errors on a number of cross section measurements. Most of the required nuclear data has been measured over the last 50 years, although improvements in the accuracy of the data appear unlikely with the current technology. A potential breakthrough is the deployment of a detector developed within the particle physics community called the Time Projection Chamber (TPC). A group of 6 universities and 3 national laboratories have undertaken the task of building the first TPC for this purpose. In this talk I will present the fission TPC concept, and why we think we can make an improvement on 50 years of fission study. (author)

  17. 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.

  18. The Fission TPC Project

    Science.gov (United States)

    Hill, Tony; Klay, Jenn; Heffner, Mike

    2008-10-01

    New high-precision fission experiments have become a priority within the nuclear energy community due to a growing, world wide, interest in nuclear reactors. In particular, the design of the next generation reactors requires a reduction in the errors on a number of cross section measurements. Most of the required nuclear data has been measured over the last 50 years, although improvements in the accuracy of the data appear unlikely with the current technology. A potential breakthrough is the deployment of a detector developed within the particle physics community called the Time Projection Chamber (TPC). A group of 6 universities and 3 national laboratories have undertaken the task of building the first TPC for this purpose. In this talk we will present the fission TPC concept, and why we think we can make an improvement on 50 years of fission study.

  19. Fission modelling with FIFRELIN

    International Nuclear Information System (INIS)

    The nuclear fission process gives rise to the formation of fission fragments and emission of particles (n,γ, e-). The particle emission from fragments can be prompt and delayed. We present here the methods used in the FIFRELIN code, which simulates the prompt component of the de-excitation process. The methods are based on phenomenological models associated with macroscopic and/or microscopic ingredients. Input data can be provided by experiment as well as by theory. The fission fragment de-excitation can be performed within Weisskopf (uncoupled neutron and gamma emission) or a Hauser-Feshbach (coupled neutron/gamma emission) statistical theory. We usually consider five free parameters that cannot be provided by theory or experiments in order to describe the initial distributions required by the code. In a first step this set of parameters is chosen to reproduce a very limited set of target observables. In a second step we can increase the statistics to predict all other fission observables such as prompt neutron, gamma and conversion electron spectra but also their distributions as a function of any kind of parameters such as, for instance, the neutron, gamma and electron number distributions, the average prompt neutron multiplicity as a function of fission fragment mass, charge or kinetic energy, and so on. Several results related to different fissioning systems are presented in this work. The goal in the next decade will be i) to replace some macroscopic ingredients or phenomenological models by microscopic calculations when available and reliable, ii) to be a support for experimentalists in the design of detection systems or in the prediction of necessary beam time or count rates with associated statistics when measuring fragments and emitted particle in coincidence iii) extend the model to be able to run a calculation when no experimental input data are available, iv) account for multiple chance fission and gamma emission before fission, v) account for the scission neutrons. Several efforts have already been made to replace macroscopic ingredients and phenomenology by microscopic ingredients provided in various nuclear parameter libraries such as electric dipole photon strength functions or HFB level densities. First results relative to theses aspects are presented in this work. (orig.)

  20. Characteristics of Coulomb fission

    OpenAIRE

    Oberacker, Volker; Greiner, Walter, 1935-; 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 might...

  1. Low energy nuclear fission

    International Nuclear Information System (INIS)

    In these lectures the liquid drop model of fission is presented and some of its predictions compared with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. It is shown how a synthesis of the liquid drop model and of the shell model can be made using the Strutinsky shell averaging procedure. Some experimental data related to the existence of shape isomers are presented and discussed. We conclude by discussing some aspects, both experimental and theoretical, of fission dynamics

  2. 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

  3. 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.

  4. 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

  5. Theory of macroscopic fission dynamics

    Science.gov (United States)

    Adeev, G. D.; Pashkevich, V. V.

    1989-10-01

    Recent advances in the theory of macroscopic fission dynamics are outlined with special emphasis on the diffusion model with realistic inertia and friction parameters, used to describe the fission fragment distributions.

  6. Theory of macroscopic fission dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Adeev, G.D. (Omskij Gosudarstvennyj Univ. (USSR)); Pashkevich, V.V. (Joint Inst. for Nuclear Research, Dubna (USSR). Lab. of Theoretical Physics)

    1989-10-09

    Recent advances in the theory of macroscopic fission dynamics are outlined with special emphasis on the diffusion model with realistic inertia and friction parameters, used to describe the fission fragment distributions. (orig.).

  7. Nucleus-nucleus coherent Bremsstrahlung in 252Cf spontaneous fission

    International Nuclear Information System (INIS)

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

  8. Status of fission yield measurements

    International Nuclear Information System (INIS)

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

  9. Discoveries of isotopes by fission

    Indian Academy of Sciences (India)

    M Thoennessen

    2015-09-01

    Of the about 3000 isotopes presently known, about 20% have been discovered in fission. The history of fission as it relates to the discovery of isotopes as well as the various reaction mechanisms leading to isotope discoveries involving fission are presented.

  10. 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.

  11. Fission dynamics of hot nuclei

    Indian Academy of Sciences (India)

    Santanu Pal; Jhilam Sadhukhan

    2014-04-01

    Experimental evidence accumulated during the last two decades indicates that the fission of excited heavy nuclei involves a dissipative dynamical process. We shall briefly review the relevant dynamical model, namely the Langevin equations for fission. Statistical model predictions using the Kramers’ fission width will also be discussed.

  12. 50 years of nuclear fission

    International Nuclear Information System (INIS)

    The article tells the story of the discovery of nuclear fission in Berlin 50 years ago by Otto Hahn and Fritz Strassmann in cooperation with Lise Meitner. 50 years later nuclear fission is still a subject of research. Some question remain unanswered. Selected new research results are used to discuss the dynamics of the collective movement of the elementary nuclear fission process. (orig.)

  13. Deformation, clusterization and fission

    International Nuclear Information System (INIS)

    The relation of the quadrupole deformation and clusterization is discussed from the microscopic viewpoint. A connection can be established via the shell model not only for harmonic oscillator, but also for more realistic interactions. The effects of the microscopic structure on the (exotic) cluster radioactivity and on the binary fission are investigated. (author)

  14. 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

  15. Fission yields in the thermal neutron fission of plutonium-239

    International Nuclear Information System (INIS)

    Fission yields for 27 mass numbers were determined in the thermal neutron fission of 239Pu using high resolution gamma ray spectrometry and radiochemical method. The results obtained using gamma ray spectrometry and from the investigations on the fission yield of 99Mo using radiochemical method were reported earlier. These data along with fission yields for 19 mass numbers determined using radiochemical method formed a part of Ph.D. thesis. The data given here are a compilation of all the results and are presented considering the neutron temperature correction to 239Pu fission cross-section which is used for calculating the total number of fissions in these studies. A comparison is made of the resulting fission yield values with the latest experimentally determined values and those given in two recent compilations. (author)

  16. Elastocapillary Instability in Mitochondrial Fission

    Science.gov (United States)

    Gonzalez-Rodriguez, David; Sart, Sébastien; Babataheri, Avin; Tareste, David; Barakat, Abdul I.; Clanet, Christophe; Husson, Julien

    2015-08-01

    Mitochondria are dynamic cell organelles that constantly undergo fission and fusion events. These dynamical processes, which tightly regulate mitochondrial morphology, are essential for cell physiology. Here we propose an elastocapillary mechanical instability as a mechanism for mitochondrial fission. We experimentally induce mitochondrial fission by rupturing the cell's plasma membrane. We present a stability analysis that successfully explains the observed fission wavelength and the role of mitochondrial morphology in the occurrence of fission events. Our results show that the laws of fluid mechanics can describe mitochondrial morphology and dynamics.

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

    International Nuclear Information System (INIS)

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

  18. Dynamical features of nuclear fission

    Indian Academy of Sciences (India)

    Santanu Pal

    2015-08-01

    It is now established that the transition-state theory of nuclear fission due to Bohr and Wheeler underestimates several observables in heavy-ion-induced fusion–fission reactions. Dissipative dynamical models employing either the Langevin equation or equivalently the Fokker–Planck equation have been developed for fission of heavy nuclei at high excitations (T ∼1 MeV or higher). Here, we first present the physical picture underlying the dissipative fission dynamics. We mainly concentrate upon the Kramers’ prescription for including dissipation in fission dynamics. We discuss, in some detail, the results of a statistical model analysis of the pre-scission neutron multiplicity data from the reactions 19F+194,196,198Pt using Kramers’ fission width. We also discuss the multi-dimensional Langevin equation in the context of kinetic energy and mass distribution of the fission fragments.

  19. Statistical theory of nuclear fission

    International Nuclear Information System (INIS)

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

  20. Fission modes of mercury isotopes

    CERN Document Server

    Warda, M; Nazarewicz, W

    2012-01-01

    Recent experiments on beta-delayed fission in the mercury-lead region and the discovery of asymmetric fission in $^{180}$Hg [1] have stimulated renewed interest in the mechanism of fission in heavy nuclei. Here we study fission modes and fusion valleys in $^{180}$Hg and $^{198}$Hg using the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals. We show that the observed transition from asymmetric fission in $^{180}$Hg towards more symmetric distribution of fission fragments in $^{198}$Hg can be explained in terms of competing fission modes of different geometries that are governed by shell effects in pre-scission configurations. The density distributions at scission configurations are studied and related to the experimentally observed mass splits.

  1. 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

  2. Fission engine concepts.

    Science.gov (United States)

    Thom, K.

    1971-01-01

    Discussion of numerous approaches to exploitation of fission energy for special applications in more beneficial ways than can be achieved by conventional reactor technology. It is *hown that, for space propulsion, the high temperature plasma core reactor is most desirable. But fissioning plasmas may find applications beyond this. Because of the criticality to be achieved in high temperature gaseous uranium fuel, plasma core reactors would operate at very high pressures, up to a thousand atmospheres, and their power would range from 5000 to 50,000 megawatts. However, apart from obvious technological difficulties, basic physics problems have to be solved before the feasibility of plasma core reactors can be demonstrated. These problems and their implications are discussed.

  3. Fusion-fission dynamics

    International Nuclear Information System (INIS)

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

  4. Fission physics, transuranium elements and fundamentalism crisis

    International Nuclear Information System (INIS)

    The most acute problem of the heavy nuclei fission physics and searching of transuranium elements is the problem of the separate island existence of of super-heavy nuclei near Z=114 and N=84. it is suggested, that the world does not forming additively from some fundamental elements, and it is non-linear. the present paper is devoted to the nature of this non-linearity

  5. Naturalness

    OpenAIRE

    Cvetko-Orenik, Varja

    2015-01-01

    The framework of the paper is Natural Syntax initiated by Janez Orenik in thetradition of (morphological) naturalness as established by Wolfgang U. Dressler and Willi Mayerthaler. The basic tenets of Natural Syntax are described at the beginning of the paper. Natural Syntax is here applied to aspects of Old Indian synchronic verbal morphonology and verbal morphosyntax: (1) Causative -ya- verbs in Rig Veda and Atharva Veda. The root vowel a is short in closed syllables and long in open sylla...

  6. Extended optical model for fission

    Science.gov (United States)

    Sin, M.; Capote, R.; Herman, M. W.; Trkov, A.

    2016-03-01

    A comprehensive formalism to calculate fission cross sections based on the extension of the optical model for fission is presented. It can be used for description of nuclear reactions on actinides featuring multi-humped fission barriers with partial absorption in the wells and direct transmission through discrete and continuum fission channels. The formalism describes the gross fluctuations observed in the fission probability due to vibrational resonances, and can be easily implemented in existing statistical reaction model codes. The extended optical model for fission is applied for neutron induced fission cross-section calculations on 234,235,238U and 239Pu targets. A triple-humped fission barrier is used for U,235234(n ,f ) , while a double-humped fission barrier is used for 238U(n ,f ) and 239Pu(n ,f ) reactions as predicted by theoretical barrier calculations. The impact of partial damping of class-II/III states, and of direct transmission through discrete and continuum fission channels, is shown to be critical for a proper description of the measured fission cross sections for 234,235,238U(n ,f ) reactions. The 239Pu(n ,f ) reaction can be calculated in the complete damping approximation. Calculated cross sections for U,238235(n ,f ) and 239Pu(n ,f ) reactions agree within 3% with the corresponding cross sections derived within the Neutron Standards least-squares fit of available experimental data. The extended optical model for fission can be used for both theoretical fission studies and nuclear data evaluation.

  7. The evaluation of fission product yields for 238U fission

    International Nuclear Information System (INIS)

    The cumulative fission yields for 45 fission product nuclides of 238U fission induced by neutron of fast reactor spectrum and high energy (around 14.0 MeV) neutron have been evaluated. The results were compared with the ENDF/B-6, JENDL-3/FY, CENDL-FY (86) and JEF-2/FY. It was found that in the total 68 evaluated values, the most of present results (88 percent in total) are in agreement with at least one of the main fission yield libraries within the quoted error limits

  8. Fission yields measured with target materials in contact with solid state track detectors

    International Nuclear Information System (INIS)

    The configuration of the contact of fissionable target materials with dielectric track detectors is reviewed in order to obtain fission yields corrected for fragment self-absorption in fission sources of different thicknesses and for optical magnification for the observation of etched fission tracks. The total detection efficiency and 'effective' thickness of the target sample are obtained in the case of formation of cone-shaped tracks by etching. A number of useful forumlae for evaluation of fission yields in both induced and spontaneous fission experiments are reported. The method can be extended and applied also to fission-related problems, natural and induced emission of nuclear fragments, as well as nuclear reaction studies. (author)

  9. 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 δ28, 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 δ28 which can be measured: ϵ =1 + Cδ28 , where C is a constant involving nuclear properties of U238 and U235: Previous methods of measuring δ28 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 δ28 a is generally attributed to the fission chamber calibration. The method developed at MIT avoids the need for a fission chamber calibration and is accomplished directly with foils irradiated within a fuel rod in the lattice. Two foils of differing U235 concentration are irradiated and allowed to cool for at least a week. The relative activity of the 1.60 MeV gamma ray of the fission product La140 is determined for the two foils. This ratio, the foil weights and atomic densities, and the ratio of fission yields β25/β28 for La140 are then used to determine δ28. This value of δ28 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 β25/β28 La140). In addition, the results can be improved as better fission product yield ratio data become available, and the method facilitates comparison of δ28 values obtained by different laboratories. (author). (author)

  10. General view on nuclear fission

    OpenAIRE

    Schmidt, K.-H.; Jurado, B; Amouroux, C.

    2014-01-01

    A general approach to nuclear fi ssion is described which explains the complex appearance of fission observables by universal principles of theoretical models and considerations on the basis of fundamental laws of physics and mathematics. The approach reveals a high degree of regularity and provides a considerable insight into the physics of the fission process. Fission observables can be calculated with a precision that comply with the needs for applications in nuclear technology. The releva...

  11. Fission barriers of light nuclei

    International Nuclear Information System (INIS)

    Experimental fission excitation functions for compound nuclei /sup 52/Fe, /sup 49/Cr, /sup 46/V, and /sup 44/Ti formed in heavy-ion reactions are analyzed in the Hauser-Feshbach/Bohr-Wheeler formalism using fission barriers based on the rotating liquid drop model of Cohen et al. and on the rotating finite range model of Sierk. We conclude that the rotating finite range approach gives better reproduction of experimental fission yields, consistent with results found for heavier systems

  12. Fission in Rapidly Rotating Nuclei

    Directory of Open Access Journals (Sweden)

    A. K. Rhine Kumar

    2014-02-01

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

  13. Fission approach to cluster radioactivity

    Indian Academy of Sciences (India)

    D N Poenaru; R A Gherghescu

    2015-09-01

    Fission theory is used to explain decay. Also, the analytical superasymmetric fission (ASAF) model is successfully employed to make a systematic search and to predict, with other models, cluster radioactivity. The macroscopic–microscopic method is illustrated for the superheavy nucleus 286Fl. Then a few results of the theoretical approach of decay (ASAF, UNIV and semFIS models), cluster decay (ASAF and UNIV) and spontaneous fission dynamics are described with Werner–Wheeler and cranking inertia. UNIV denotes universal curve and semFIS the fission-based semiempirical formula.

  14. Hidden systematics of fission channels

    International Nuclear Information System (INIS)

    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. (authors)

  15. 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)

  16. Energy from nuclear fission(*

    Directory of Open Access Journals (Sweden)

    Ripani M.

    2015-01-01

    Full Text Available The main features of nuclear fission as physical phenomenon will be revisited, emphasizing its peculiarities with respect to other nuclear reactions. Some basic concepts underlying the operation of nuclear reactors and the main types of reactors will be illustrated, including fast reactors, showing the most important differences among them. The nuclear cycle and radioactive-nuclear-waste production will be also discussed, along with the perspectives offered by next generation nuclear assemblies being proposed. The current situation of nuclear power in the world, its role in reducing carbon emission and the available resources will be briefly illustrated.

  17. The SPIDER fission fragment spectrometer for fission product yield measurements

    International Nuclear Information System (INIS)

    The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E–2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using 229Th and 252Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of 252Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from 252Cf spontaneous fission products are reported from an E–v measurement

  18. Fission decay properties of ultra neutron-rich uranium isotopes

    Indian Academy of Sciences (India)

    L Satpathy; S K Patra; R K Choudhury

    2008-01-01

    The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier properties and neutron emission characteristics in the fission process. 233U and 235U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich uranium isotopes is examined here. The neutron number = 162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium isotopes around it with = 154-172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics; a manifestation of the close shell nature of = 162 (or 164). We consider here the thermal neutron fission of a typical representative 249U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that 250U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory, this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties will have important implications in stellar evolution involving -process nucleosynthesis.

  19. Calculation of the fast fission factor from basic nuclear data

    International Nuclear Information System (INIS)

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

  20. 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.

  1. Study of fission dynamics in fusionfission reactions

    International Nuclear Information System (INIS)

    Highlights: ? A modified wall and window dissipation was used in Langevin equations. ? Prefission multiplicities of particles were calculated for 200Pb. ? Fission probabilities were calculated for 200Pb and compared with the experimental data. -- Abstract: One-dimensional Langevin equations were applied to study the fission dynamics of compound nucleus 200Pb formed in heavy ion-induced fusion reactions in an intermediate range of excitation energies. A modified wall and window dissipation with a reduction coefficient, ks, has been used in the Langevin equations. The average pre-fission multiplicities of neutrons, light charged particles and fission probabilities were calculated for 200Pb and results compared with the experimental data. It was shown that the results of the calculations are in good agreement with the experimental data of neutron and charged particles (p and alphas) multiplicities and fission probabilities by using values of ks in the range 0.27 ? ks ? 0.48.

  2. 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.)

  3. Fission Dynamics of Compound Nuclei

    OpenAIRE

    Iwata, Yoritaka; Heinz, Sophia

    2012-01-01

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

  4. Fission fragment driven neutron source

    Science.gov (United States)

    Miller, Lowell G.; Young, Robert C.; Brugger, Robert M.

    1976-01-01

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

  5. Fission of Halving Edges Graphs

    OpenAIRE

    Khovanova, Tanya; Yang, Dai

    2013-01-01

    In this paper we discuss an operation on halving edges graph that we call fission. Fission replaces each point in a given configuration with a small cluster of k points. The operation interacts nicely with halving edges, so we examine its properties in detail.

  6. Fission throughout the periodic table

    International Nuclear Information System (INIS)

    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

  7. 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.)

  8. Status of fission yield data

    International Nuclear Information System (INIS)

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

  9. 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

  10. Ternary fission of nuclei into comparable fragments

    International Nuclear Information System (INIS)

    The problem of nuclear fission into three comparable fragments is considered. A mechanism of true ternary fission is proposed. In contrast to sequential fission, where the three fragments arise upon two sequential events of binary fission, the mechanism in question relies on a scenario that originally involves fission into three fragments. This mechanism is driven by a hexadecapole deformation of the fissioning nucleus, in contrast to binary fission associated with quadrupole vibrations of the nuclear surface. The fragment-mass ratios are estimated. The dynamics of formation of collinear fragments and their subsequent motion in opposite directions is traced. The calculated probability of true ternary fission complies with observed values

  11. Activity decay of fission products produced by fast fissions

    International Nuclear Information System (INIS)

    After an introduction presenting the calculation of the gamma activity in fission products either after the pile shutdown or after a certain cooling time, the authors report the determination of the gamma activity of each radioactive nuclide formed during fission. They present the calculation method which uses the most recent data for each nuclide (decay period, fission efficiency, gamma ray energy emitted by each disintegration, emission percentage). Results are presented under the form of activity decay curves for each group and for each nuclide after a 30-day or infinite irradiation

  12. Spontaneous fission activities

    International Nuclear Information System (INIS)

    For several years, the Nuclear Data Project has been using a standard computer-readable format to organize the results of data evaluations published in Nuclear Data Sheets. Adopted values for level energies, spins, half-lives, radiation properties, and spectroscopic factors are recorded in standard blocks of information, which are then filed onto indexed direct-access storage. The resulting Evaluated Nuclear Structure Data File (ENSDF) is then available as a standard source of nuclear structure information. Computer organization of selected data into pages has been a feature of Nuclear Data Sheets since 1975. As an illustration of the power and potential usefulness of the ENSDF system, we present a collection of nuclear levels for which the spontaneous fission has been studied. The values tabulated have appeared in recent issues of Nuclear Data Sheets. The selection of values and arrangement into a table has been done completely automatically. We welcome comments and criticisms about the form or content of this table

  13. Automatic fission track counting using quantiment 720

    International Nuclear Information System (INIS)

    Several sets of Makrofol SSTR were irradiated on the natural uranium shell of the NISUS assembly at the University of London Reactor CONSORT. In each set pairs of films were placed one on the outer surface of the shell and the other on the inner surface. The ratio of the fission rates in the two positions were calculated by ANISN transport code and found to be 10,86. The etched films were counted by the Quantimet 720 and by eye using an optical microscope. The results showed that for the six pairs satisfactorily counted by eye the mean fission ratio was 10,31 with standard deviation of 1,4%. The mean fission ratio for the same pairs satisfactorily counted by the Quantimet was 10.53 with standard deviation of 2.3%. The relative efficiency of the Quantimet to eye was found to be 0.975+-0.005 (random). This value is subject to a systematic error of +-2% attributable to the calibration of the fields of view. (orig.)

  14. 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.)

  15. 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.

  16. 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.

  17. The spectroscopy of fission fragments

    International Nuclear Information System (INIS)

    High-resolution measurements on γ 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)

  18. Fission-product source terms

    International Nuclear Information System (INIS)

    This presentation consists of a review of fission-product source terms for light water reactor (LWR) fuel. A source term is the quantity of fission products released under specified conditions that can be used to calculate the consequences of the release. The source term usually defines release from breached fuel-rod cladding but could also describe release from the primary coolant system, the reactor containment shell, or the site boundary. The source term would be different for each locality, and the chemical and physical forms of the fission products could also differ

  19. Recent progress in theories of nuclear fission

    International Nuclear Information System (INIS)

    The lecture focuses on the characteristics of the fission process related to the potential energy surface around the fission barrier configuration. In particular, the calculations of fission barrier heights by macroscopic-microscopic method, fission probabilities and cross sections are discussed, as well as the theory of fragment angular distributions. 52 refs, 31 figs

  20. 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)

  1. 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)

  2. Chemical effects of fission recoils

    International Nuclear Information System (INIS)

    The production of nitrogen from nitrous oxide at high density was employed to investigate the energy deposition efficiency of fission recoils produced from fission of U235 in uranium-palladium foils clad with platinum. Nitrogen production varied linearly with fission recoil dose from 1.1 x 1020 to 9.0 x 1020 eV, and was independent of density between 12.5 and 127.5 g l-1 N2O. 16.2 +- 0.8% of the fission recoil energy was deposited external to the foil. Electron microprobe analysis showed some unevenness of new foil and polymer buildup on the surface after irradiation of ethylene-oxygen mixtures. Subsequent irradiation in the presence of nitrous oxide restored some of the original efficiency. This is ascribed to chemical oxidation of the polymer induced by reactive intermediates produced from nitrous oxide. (author)

  3. 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.

  4. 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

  5. Fission of rotating fermium isotopes

    International Nuclear Information System (INIS)

    In this paper we discuss the process of fission of even fermium isotopes, on the basis of their rotational states. The nuclear intrinsic vorticity and its coupling to the global rotation of the nucleus are used to simulate the interaction between the rotational motion and the pairing field, and lead to pairing quenching in the case of higher angular momentum states. The rotation leads to a decreasing of the fission barrier heights. The ingredients of the modelground state fission barriers, pairing correlation energies and the cranking moments of inertiaare obtained within the self-consistent HartreeFockBogoliubov framework using the Skyrme SkM? energy density functional. Fission barriers and half-lives are estimated for spins I up to I = 16?

  6. Measurement of fission cross sections

    International Nuclear Information System (INIS)

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

  7. 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.

  8. Fission modes of mercury isotopes

    Science.gov (United States)

    Warda, M.; Staszczak, A.; Nazarewicz, W.

    2012-08-01

    Background: Recent experiments on β-delayed fission in the mercury-lead region and the discovery of asymmetric fission in 180Hg [A. N. Andreyev , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.252502 105, 252502 (2010)] have stimulated theoretical interest in the mechanism of fission in heavy nuclei.Purpose: We study fission modes and fusion valleys in 180Hg and 198Hg to reveal the role of shell effects in the prescission region and explain the experimentally observed fragment mass asymmetry and its variation with A.Methods: We use the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals.Results: The potential energy surfaces in multidimensional space of collective coordinates, including elongation, triaxiality, reflection-asymmetry, and necking, are calculated for 180Hg and 198Hg. The asymmetric fission valleys—well separated from fusion valleys associated with nearly spherical fragments—are found in both cases. The density distributions at scission configurations are studied and related to the experimentally observed mass splits.Conclusions: The energy density functionals SkM* and D1S give a very consistent description of the fission process in 180Hg and 198Hg. We predict a transition from asymmetric fission in 180Hg toward a more symmetric distribution of fission fragments in 198Hg. For 180Hg, both models yield 100Ru/80Kr as the most probable split. For 198Hg, the most likely split is 108Ru/90Kr in HFB-D1S and 110Ru/88Kr in HFB-SkM*.

  9. Dynamin-mediated membrane fission

    OpenAIRE

    Morlot, Sandrine

    2012-01-01

    Membrane fission is required for vesicular traffic between intracellular compartments. Dynamin is a GTPase implicated in vesicle scission during Clathrin-mediated endocytosis. It polymerizes into a helix at the neck of endocytic buds. Upon GTP hydrolysis, conformational changes reduce the helical radius and pitch showing that fission proceeds through a constriction mechanism. We show that the deformation of Dynamin helices is highly concerted and damped by the friction between membrane and Dy...

  10. Fission hindrance and nuclear viscosity

    Indian Academy of Sciences (India)

    Indranil Mazumdar

    2015-08-01

    We discuss the role of nuclear viscosity in hindering the fission of heavy nuclei as observed in the experimental measurements of GDR -ray spectra from the fissioning nuclei. We review a set of experiments carried out and reported by us previously [see Dioszegi et al, Phys. Rev. C 61, 024613 (2000); Shaw et al, Phys. Rev. C 61, 044612 (2000)] and argue that the nuclear viscosity parameter has no apparent dependence on temperature. However, it may depend upon the deformation of the nucleus.

  11. 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.

  12. 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.

  13. The Microscopic Theory of Fission

    Energy Technology Data Exchange (ETDEWEB)

    Younes, W; Gogny, D

    2009-06-09

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

  14. 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)

  15. Energy released in ternary fission

    International Nuclear Information System (INIS)

    From time to time (at best once per about 1000 fission events) a spontaneous (or induced) fission of a nucleus leads to three fragments, usually one light particle (which is more frequently 4 He or some Be, C, or O isotope) and two fragments of sizes not very different from those resulting from binary fission. Even less probable is a process in which the three fragments are almost identical. As with other cold spontaneous fission processes, ?-decay and cluster radioactivities, we can get some idea about the most probable particles emitted in ternary fission by looking at the released energy corresponding to different competing fragmentations. We have plotted both the liquid drop deformation energy estimations and the 'exact' calculations using different mass tables. Also, shown is a comparison for fissioning parent nuclei lying on the Green approximation for the line of ?-stability. We have calculated Q values for the cold splitting of even-even nuclei into three particles of equal size, as well as a various fission processes accompanied by light-particle emission for nuclides with Z = 90-116. Four possibilities to emit the light particle 4,6,8 He, 6,8,10,12 Be, 10,12,14,16,18 C, and 14,16,18,20,22,24 O are analyzed: from the most probable light fragment, from its corresponding heavy fragment, and as half a particle from each fragment of an asymmetric or symmetric binary fission; the two processes having the largest Q values are listed with each of the 18 light particles. Data for a larger set of parent nuclei (including odd proton and neutron numbers) are available in a computer-readable file

  16. Microscopic Description of Nuclear Fission Dynamics

    OpenAIRE

    Umar, A. S; Oberacker, V. E.; Maruhn, J. A.; Reinhard, P.-G.

    2010-01-01

    We discuss possible avenues to study fission dynamics starting from a time-dependent mean-field approach. Previous attempts to study fission dynamics using the time-dependent Hartree-Fock (TDHF) theory are analyzed. We argue that different initial conditions may be needed to describe fission dynamics depending on the specifics of the fission phenomenon and propose various approaches towards this goal. In particular, we provide preliminary calculations for studying fission following a heavy-io...

  17. 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)

  18. The binary fission origin of the moon

    Science.gov (United States)

    Binder, Alan B.

    1986-01-01

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

  19. Binary fission origin of the moon

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  1. 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)

  2. Alpha Particle Emission in Fission

    International Nuclear Information System (INIS)

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

  3. 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

  4. 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 ν-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)

  5. 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.)

  6. Sequential Detection of Fission Processes for Harbor Defense

    Energy Technology Data Exchange (ETDEWEB)

    Candy, J V; Walston, S E; Chambers, D H

    2015-02-12

    With the large increase in terrorist activities throughout the world, the timely and accurate detection of special nuclear material (SNM) has become an extremely high priority for many countries concerned with national security. The detection of radionuclide contraband based on their γ-ray emissions has been attacked vigorously with some interesting and feasible results; however, the fission process of SNM has not received as much attention due to its inherent complexity and required predictive nature. In this paper, on-line, sequential Bayesian detection and estimation (parameter) techniques to rapidly and reliably detect unknown fissioning sources with high statistical confidence are developed.

  7. Fission product solvent extraction

    Energy Technology Data Exchange (ETDEWEB)

    Moyer, B.A.; Bonnesen, P.V.; Sachleben, R.A. [and others

    1998-02-01

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

  8. Temperature transients of a fusion-fission ITER pebble bed reactor in loss of coolant accident

    International Nuclear Information System (INIS)

    In this preliminary scoping study, post-accident temperature transients of several fusion-fission designs utilizing ITER-FEAT-like parameters and fission pebble bed fuel technology are examined using a 1-D cylindrical MATLAB heat transfer code along with conventional fission decay heat approximations. Scenarios studied include systems with no additional passive safety features to systems with melting reflectors designed to increase emissivity after reaching a specified temperature. Results show that for a total fission power of ∼1400-2800 MW, two of the realistic variants investigated are passively safe. The crucial time, defined as the time when either any structural part of the fusion-fission tokamak reaches melting point, or when the pebble fuel reaches 1873 K, ranges from 5.7 to 76 h for the unsafe configurations. Additionally, it is illustrated that, fundamentally, the LOCA characteristics of pure fission pebble beds and fusion-fission pebble beds are different. Namely, the former depends on the pebble fuel's large thermal capacity, along with external radiation and natural convective cooling, while the latter depends significantly more on the tokamak's sizeable total internal heat capacity. This difference originates from the fusion-fission reactor's conflicting goal of having to minimize heat transfer to the magnets during normal operation. These results are discussed in the context of overall fusion-fission reactor design and safety

  9. Reference Reactor Module for the Affordable Fission Surface 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 requirements of many surface power applications allow the consideration of systems with much less development risk than most other space reactor applications, because of modest power (10s of kWe) and no driving need for minimal mass (allowing temperatures 2-fueled, liquid metal-cooled 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. One of the important 'affordability' attributes is that the concept has been designed to minimize both the technical and programmatic safety risk

  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 4π γ-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 γ-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 γ 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 α particles, which is important for experiments with α-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 α'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 α'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. Terracentric Nuclear Fission Reactor: Background, Basis, Feasibility, Structure, Evidence, and Geophysical Implications

    OpenAIRE

    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 ...

  13. Separation of fission Molybdenum for production of technetium generator

    International Nuclear Information System (INIS)

    There are two basically different methods for Mo-99 productions: Activation of Mo-99 contained at about 24% in natural isotopic mixtures. Mo-98 enriched targets are irradiated in high-flux reactors in order to achieve the highest possible specific activity of the product. Idolisation of fission molybdenum from irradiated nuclear fuel targets which have undergone short-term cooling. Maximum fission yield can be attained by irradiation of uranium-235 with the highest possible enrichment. On account of its approximately 1000 times higher specific activity. Fission molybdenum has almost replaced worldwide the product fabricated by activation. However, fission molybdenum-99 production has as its prerequisite a suitably advanced technology by which the production process taking place under high activity conditions can be controlled. An integral part of the process consist in the retention of the fission gases the recycling of non-consumed fuel and the treatment of the waste streams arising. This publication will deal with the individual steps in the process

  14. Prompt Emission in Fission Induced with Fast Neutrons

    Science.gov (United States)

    Wilson, J. N.; Lebois, M.; Halipr, P.; Oberstedt, S.; Oberstedt, A.

    Prompt gamma-ray and neutron emission data in fission integrates a large amount of information on the fission process and can shed light on the partition of energy. Measured emission spectra, average energies and multiplicities also provide important information for energy applications. While current reactors mostly use thermal neutron spectra, the future reactors of Generation IV will use fast neutron spectra for which little experimental prompt emission data exist. Initial investigations on prompt emission in fast neutron induced fission have recently been carried out at the LICORNE facility at the IPN Orsay, which exploits inverse reactions to produce naturally collimated, intense beams of neutrons. We report on first results with LICORNE to measure prompt fission gamma-ray spectra, average energies and multiplicities for 235U and 238U. Current improvements and upgrades being carried out on the LICORNE facility will also be described, including the development of a H2 gas target to reduce parasitic backgrounds and increase intensities, and the deployment of 11B beams to extend the effective LICORNE neutron energy range up to 12 MeV. Prospects for future experimental studies of prompt gamma-ray and neutron emission in fast neutron induced fission will be presented.

  15. Energy production using fission fragment rockets

    International Nuclear Information System (INIS)

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

  16. The latest progress of fission track analysis

    International Nuclear Information System (INIS)

    Fission track analysis as a new nuclear track technique is based on fission track annealing in mineral and is used for oil and gas exploration successfully. The west part of China is the main exploration for oil and gas. The oil and gas basins there experienced much more complicated thermal history and higher paleotemperature. In order to apply fission track analysis to these basins, following work was be carried out: 1. The decomposition of grain age distribution of zircon fission tracks. 2. Study on thermal history of Ordos basin using zircon fission track analysis. 3. The fission track study on the Qiang Tang basin in tibet

  17. Contribution to the study of nuclear fission

    International Nuclear Information System (INIS)

    The author proposes an overview of his research activity during the past fifteen years and more particularly that dealing with nuclear fission. The first part reports works on nucleus physics at the scission via the investigation of ternary fission (experimental procedure, influence of fission modes, influence of resonance spin, influence of excitation energy of the fissioning nucleus, emission probabilities, energy spectra of ternary alphas and tritons, emission mechanism). The second part reports measurements and assessments of neutron-induced fission cross sections. The third part reports the investigation of some properties of fission products (efficiencies, branching ratios of the main delayed neutron precursors)

  18. Nuclear fission and neutron-induced fission cross-sections

    CERN Document Server

    James, G D; Michaudon, A; Michaudon, A; Cierjacks, S W; Chrien, R E

    2013-01-01

    Nuclear Fission and Neutron-Induced Fission Cross-Sections is the first volume in a series on Neutron Physics and Nuclear Data in Science and Technology. This volume serves the purpose of providing a thorough description of the many facets of neutron physics in different fields of nuclear applications. This book also attempts to bridge the communication gap between experts involved in the experimental and theoretical studies of nuclear properties and those involved in the technological applications of nuclear data. This publication will be invaluable to those interested in studying nuclear fis

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

    International Nuclear Information System (INIS)

    Fission fragment mass distribution has been measured from the decay of 246Bk nucleus populating via two entrance channels with slight difference in mass asymmetries but belonging on either side of the Businaro Gallone mass asymmetry parameter. Both the target nuclei were deformed. Near the Coulomb barrier, at similar excitation energies the width of the fission fragment mass distribution was found to be drastically different for the 14N+ 232Th reaction compared to the 11B+ 235U reaction. The entrance channel mass asymmetry was found to affect the fusion process sharply. (authors)

  20. 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)

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

    International Nuclear Information System (INIS)

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

  2. 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.)

  3. Status of fission yield data

    International Nuclear Information System (INIS)

    In this paper we summarize the current status of the recent US evaluation for 34 fissioning nuclides at one or more neutron incident energies and for spontaneous fission. Currently there are 50 yields sets, and for each we have independent and cumulative yields and uncertainties for approximately 1100 fission products. When finalized the recommended data will become part of Version VI of the US ENDF/B. Other major evaluations in progress that are included in a recently formed IAEA Coordinated Research Program are also summarized. In a second part we review two empirical models in use to estimate independent yields. Comparison of model estimates with measured data is presented, including a comparison with some recent data obtained from Lohengrin (Cf-249 T). 18 refs., 13 figs., 3 tabs

  4. Cranking mass parameters for fission

    CERN Document Server

    Mirea, M

    2009-01-01

    A formalism for semi-adiabatic cranking mass parameters is presented. For the fission process of 234U, the time-dependent pairing equations of motion were used to calculate the excitation energy and to extract values of the cranking inertia. A fission barrier is determined by minimizing the action trajectory in a five dimensional configuration space spanned by elongation, necking, deformations of fragments and mass-asymmetry. The deformation energy is computed in the the frame of the microscopic-macroscopic model. The two center shell model with Woods-Saxon potentials is used in this context. Values of the inertia for excited fissioning systems are reported. A dependence between the cranking mass parameters and the intrinsic excitation energy is evidenced.

  5. Fission Yields in the Iodine Region

    International Nuclear Information System (INIS)

    Independent yields of all iodine isotopes from l118 to I134 except I122 (short-lived), I127(stable) and I129(long-lived) resulting from irradiating natural uranium with 590-MeV and 19-GeV protons have been measured. In addition, cross-sections (mostly cumulative) of many xenon and tellurium isotopes have been obtained. In the experiments extensive use has been made of an electromagnetic isotope separator, constructed at CERN for nuclear reaction studies, by which the iodine (or tellurium) isotopes were separated from samples chemically isolated from the irradiated targets. In the study of xenon isotopes the uranium target was heated in a small oven connected to the separator via a cold trap to stop unwanted activities. After the separation, the activity of the samples was measured by counting methods. In certain cases (I118, I119, I120,I121, Xe118, Xe119, Xe120, Xe121) spectroscopic investigations were performed to provide information for the conversion of the counting data to absolute counting-rates needed for the determination of the fission yields. The experiments show a significant shift in the isotopic cross-section distribution when the 19-GeV results are compared with those obtained at the lower irradiation energy. The yields far out ai the neutron-deficient wing increase considerably whereas the other part of the distribution is depressed. A comparison with spallation data indicates that the neutron-deficient part of the distribution might result from the spallation of uranium. Spallation gives negligible yields in the iodine regional 590 MeV, but at 19 GeV these cross-sections a re expected to be much larger. The competition with spallation decreases the probability for fission, and consequently the yields of the fission products will decrease. (author)

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

    International Nuclear Information System (INIS)

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

  7. Velocity fluctuations of fission fragments

    CERN Document Server

    Llanes-Estrada, Felipe J; Martinez, Jose L Muñoz

    2015-01-01

    We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramer-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.

  8. Velocity fluctuations of fission fragments

    Science.gov (United States)

    Llanes-Estrada, Felipe J.; Carmona, Belén Martínez; Martínez, Jose L. Muñoz

    2016-02-01

    We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.

  9. Spontaneous fission of superheavy nuclei

    Indian Academy of Sciences (India)

    R A Gherghescu; D N Poenaru

    2015-09-01

    The macroscopic–microscopic method is extended to calculate the deformation energy and penetrability for binary nuclear configurations typical for fission processes. The deformed two-centre shell model is used to obtain single-particle energy levels for the transition region of two partially overlapped daughter and emitted fragment nuclei. The macroscopic part is obtained using the Yukawa-plus-exponential potential. The microscopic shell and pairing corrections are obtained using the Strutinsky and BCS approaches and the cranking formulae yield the inertia tensor. Finally, the WKB method is used to calculate penetrabilities and spontaneous fission half-lives. Calculations are performed for the decay of 282,292120 nuclei.

  10. NEACRP thermal fission product benchmark

    International Nuclear Information System (INIS)

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

  11. The wastes of nuclear fission

    International Nuclear Information System (INIS)

    In this paper the author presents the problems of the radioactive wastes generated by the nuclear fission. The first part devoted to the fission phenomenon explains the incident neutron energy and the target nuclei role. The second part devoted to the nuclear wastes sources presents the production of wastes upstream of the reactors, in the reactors and why these wastes are dangerous. The third part discusses the radioactive wastes management in France (classification, laws). The last part details the associated research programs: the radionuclides separation, the disposal, the underground storage, the transmutation and the thorium cycle. (A.L.B.)

  12. 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.

  13. Neutronics for critical fission reactors and subcritical fission in hybrids

    International Nuclear Information System (INIS)

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

  14. 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

  15. Fission properties of the heaviest elements

    International Nuclear Information System (INIS)

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

  16. Absolute calibration technique for spontaneous fission sources

    International Nuclear Information System (INIS)

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

  17. Fission products measurements in the SLOWPOKE 2 reactor at the University of Toronto

    International Nuclear Information System (INIS)

    During 1995 and 1996 new measurements on fission and activation products in the water and air of the SLOWPOKE 2 nuclear reactor at the University of Toronto were performed. Due to the age of the fuel, small quantities of fission products are released during normal operation of the reactor. Low concentrations of fission and activation products can be measured in the water and air of the reactor. Studying the behaviour of fission and activation products in their natural conditions inside the reactor is very useful, both for improving the understanding of their real chemical and physical properties and for the development and evaluation of analytical methodologies. Adsorption and desorption of noble gases on charcoal can play an important role during any release of fission and activation products from containment to the atmosphere following a reactor accident. Experiments conducted at the SLOWPOKE 2 Reactor permitted the study of these phenomena

  18. 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.

  19. Fission properties of the BCPM functional

    OpenAIRE

    Giuliani, Samuel A.; Robledo, Luis M.

    2013-01-01

    We explore the properties of the Barcelona Catania Paris Madrid (BCPM) energy density functional concerning fission dynamics. Potential energy surfaces as well as collective inertias relevant in the fission process are computed for several nuclei where experimental data exists. Inner and outer barrier heights as well as fission isomer excitation energies are reproduced quite well in all the cases. The spontaneous fission half lives $t_{\\textrm{\\textrm{SF}}}$ are also computed using the standa...

  20. Superfluid fission dynamics with microscopic approaches

    OpenAIRE

    Simenel C.; Scamps G.; Lacroix D.; Umar A.S.

    2016-01-01

    Recent progresses in the description of the latter stage of nuclear fission are reported. Dynamical effects during the descent of the potential towards scission and in the formation of the fission fragments are studied with the time-dependent Hartree-Fock approach with dynamical pairing correlations at the BCS level. In particular, this approach is used to compute the final kinetic energy of the fission fragments. Comparison with experimental data on the fission of 258Fm are made.

  1. 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.

  2. Formation and dynamics of fission fragments

    OpenAIRE

    Simenel, C.; Umar, A. S

    2013-01-01

    Although the overall time-scale for nuclear fission is long, suggesting a slow process, rapid shape evolution occurs in its later stages near scission. Theoretical prediction of the fission fragments and their characteristics are often based on the assumption that the internal degrees of freedom are equilibrated along the fission path. However, this adiabatic approximation may break down near scission. This is studied for the symmetric fission of $^{258,264}$Fm. The non-adiabatic evolution is...

  3. Microscopic Theory of Nuclear Fission: A Review

    OpenAIRE

    Schunck, N; Robledo, L M

    2015-01-01

    This article reviews how nuclear fission is described within nuclear density functional theory. In spontaneous fission, half-lives are the main observables and quantum tunnelling the essential concept, while in induced fission the focus is on fragment properties and explicitly time-dependent approaches are needed. The cornerstone of the current microscopic theory of fission is the energy density functional formalism. Its basic tenets, including tools such as the HFB theory, effective two-body...

  4. Nuclear fission in covariant density functional theory

    Science.gov (United States)

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

    2013-12-01

    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.

  5. Nuclear fission in covariant density functional theory

    Directory of Open Access Journals (Sweden)

    Afanasjev A.V.

    2013-12-01

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

  6. Fission, fusion and photonuclear physics. Chapter 2

    International Nuclear Information System (INIS)

    The effect of the even-odd character of the fission fragment charges on their yields and excitation energies may provide some informations on the dynamics of the fission process. Several even-even fissioning systems have been studied. Preliminary results are presented

  7. Microscopic description of nuclear fission

    OpenAIRE

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

    1981-01-01

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

  8. Brownian shape dynamics in fission

    Directory of Open Access Journals (Sweden)

    Randrup Jørgen

    2013-12-01

    Full Text Available It was recently shown that remarkably accurate fission-fragment mass distributions are obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potentialenergy surfaces; the current status of this novel method is described here.

  9. Search for singlet fission chromophores

    Czech Academy of Sciences Publication Activity Database

    Havlas, Zdeněk; 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

  10. Hybrid nuclear cycles for nuclear fission sustainability

    International Nuclear Information System (INIS)

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

  11. 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)

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

    OpenAIRE

    Boeckstiegel, C.; Steinhaeuser, S.; Schmidt, K.-H.; Clerc, H. -G.; Grewe, A.; Heinz, A.; M. de Jong; Junghans, A. R.; Mueller, J.; Voss, B.

    2007-01-01

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

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

    OpenAIRE

    Rios Huguet, A; Stevenson, PD; Goddard, P.

    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. Met...

  14. Intrinsic energy partition in fission

    International Nuclear Information System (INIS)

    The intrinsic energy partition between the 2 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 2 conditions. One of them fixes the number of particles and the other one separates the pairing active spaces associated with the 2 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. It is not possible to extract directly the energy partition from experimental data. Nevertheless, the main de-excitation process is the neutron evaporation. Therefore, indirect information can be obtained from neutron multiplicities, for which accurate results are available in literature. The excitation energy of each fragment can be computed and it is shown that several experimental features are reproduced by theoretical data. The deeply minimum in the neutron multiplicity occurs close to the mass of the doubly magic nucleus 132Sn. A maximal value of the neutron multiplicity is obtained for the mass 116, that is in the symmetric fission region. In general, the excitation energy of the light fragment is larger than that of the heavy one. As for neutron multiplicities, excepting the strong fluctuations related to the large mass asymmetries, the results agree qualitatively well with the experimental data. It is a first microscopic description of the intrinsic energy partition in a wide range of fission channels that succeed to reproduce the main behavior of the neutron multiplicities

  15. The decay and fission of uranium

    International Nuclear Information System (INIS)

    According to the Bernai liquid drop alpha particle model, the nuclear structure of uranium contains a core of 38 alpha particles comprised of 5 concentric layers. The innermost core of 4 alpha particles corresponding to the oxygen 16 nuclide is enclosed by 4 more alpha particles giving the structure of the sulphur 32 nuclide. The third layer of 6 alpha particles completes the 14 alpha particle model of nickel 56. The fourth and fifth layers each contain 12 alpha particles. It will be shown that the fifth layer forms a barrier to the natural radioactive decay of uranium isotopes. Furthermore, it appears that whist the fourth layer sets a limit on the minimum size of the larger daughter fragment of the thermal neutron induced fission of a uranium isotope, the third layer sets a limit on the minimum size of the smaller fragment

  16. Theory of nuclear fission. A textbook

    International Nuclear Information System (INIS)

    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.)

  17. The Fission of Thorium with Alpha Particles

    Energy Technology Data Exchange (ETDEWEB)

    Newton, Amos S.

    1948-04-15

    The fission distribution of fission of thorium with alpha particle of average energy 37.5 Mev has been measured by the chemical method. The distribution found shows that the characteristic dip in the fission yield mass spectrum has been raised to within a factor of two of the peaks compared to a factor of 600 in slow neutron fission of U{sup 235}. The raise in the deip has caused a corresponding lowering in fission yield of these elements at the peaks. The cross section for fission of thorium with 37.5 Mev alphas was found to be about 0.6 barn, and the threshold for fission was found to be 23 to 24 Mev.

  18. 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.)

  19. 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.

  20. The nucleon phase of binary fission

    International Nuclear Information System (INIS)

    Full text: The main step of the fission process is a sharing-out of nucleons, within a 'nucleon-phase', between the valence shells of the primordial cluster of the internally-dissociated fissioning system and the valence shells of the 'A =126 nucleon core' of the nascent heavy fragment. The formation of an 'A = 82 nucleon core' in the nascent light fragment explains the asymmetric fission mode of the light actinide nuclei. The nucleon partition in the nucleon phase can be understood in the framework of chemical thermodynamics. The formation of an 'A = 126 nucleon core' in the nascent light fragment of heavier fissioning systems explains the symmetric fission mode of 258Fm and that of heavier nuclei. But the new phenomenon of 'barrier-free' fission, discovered in 258Fm (s.f.), plays in this system and all symmetrically fissioning superheavy nuclei a very important role. (author)

  1. 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

  2. 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

  3. A fission fragment detector for correlated fission output studies

    International Nuclear Information System (INIS)

    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

  4. A fission fragment detector for correlated fission output studies

    Energy Technology Data Exchange (ETDEWEB)

    Mosby, S., E-mail: smosby@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Tovesson, F.; Couture, A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Duke, D.L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States); Kleinrath, V. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Idaho State University, Pocatello, ID 83201 (United States); Meharchand, R.; Meierbachtol, K.; O' Donnell, J.M.; Perdue, B.; Richman, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Shields, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States)

    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.

  5. 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.

  6. DSP Algorithms for Fission Fragment and Prompt Fission Neutron Spectroscopy

    International Nuclear Information System (INIS)

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

  7. The risks of the nuclear fission fuel cycle

    International Nuclear Information System (INIS)

    An overview is given of the title subject in comparison with other electric power generating techniques. This overview is based on reports from several foreign institutes (UNSCEAR, EPRI, US-DOE, EC, and ORNL) and Dutch institutes (VROM, COVRA, URENCO, and ECN). It appears that the Dutch nuclear power plants (Dodewaard and Borssele) and other installations of the nuclear fission fuel cycle in the Netherlands show a lower individual risk than the risk values estimated by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The risks, outlined by UNSCEAR, is mainly determined by ore exploration and processing, the reactor operation and the breeder conversion. The total global risk of the nuclear fission fuel cycle (with 200 GWej and 100% recycling) is a factor 10,000 lower than the risk, caused by natural radiation. The main cause of risks of the cycle by accidents are nuclear power plant accidents (varying in the literature from circa 95% to more than 99%). For normal operational conditions nuclear fission, natural gas, wind and thermal solar energy are more favourable than coal, oil and photovoltaic solar cells. It is expected that the use of hydro power (dam collapse and floods) and coal (mine disasters) on average per GWje will cause the largest amount of immediate victims. A separate abstract has been prepared for the appendices in which descriptions are given of all the processes of the nuclear fission fuel cycle: mining and extraction, refining and conversion, enrichment, fission fuel elements fabrication, reactor operation, reprocessing, aboveground storage facilities, ultimate storage, and transport. 4 figs., 14 refs., 2 appendices, 17 refs

  8. From transmutation to fission. Far-reaching discovery

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, B.

    1988-12-01

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

  9. Nuclear Dissipation from Fission Time

    Energy Technology Data Exchange (ETDEWEB)

    Gontchar, I.; Morjean, M.; Basnary, S. [GANIL DSM/CEA, IN2P3/CNRS, BP 5027, 14076 Caen Cedex 5 (France)

    2000-04-21

    Fission times, pre-scission neutron multiplicities and GDR pre-scission {gamma}-ray multiplicities measured for uranium or thorium nuclei formed with temperatures T {approx} 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 k{sub red} {approx} 0.45 {+-} 0.10 applied to the wall term for the mononuclear configuration. (authors)

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

    International Nuclear Information System (INIS)

    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 < or similar A < or similar 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. (orig.)

  11. JEFF-3T. Decay data and fission yield libraries

    International Nuclear Information System (INIS)

    Comprehensive decay-data and fission-yield libraries provide important input to a wide range of nuclear physics codes for nuclear applications. A new initiative has begun under the auspices of the NEA/OECD to generate improved data sets that will constitute the JEFF-3 libraries in ENDF-6 format, primarily for nuclear power, fuel reprocessing and waste management needs. Various sources of decay data have been accessed in order to assemble these files: NUBASE, ENSDF, UKPADD-6 and UKHEDD-2. Efforts have also focused on the evaluation of decay data for a number of important short-lived fission products, so that artificial adjustments to some of the relevant decay data and fission yields are not required to accommodate a previous lack of such data. Fission yields were adopted from UK evaluations recently undertaken to create the UKFY3 library. Decay-data files for 3 755 nuclides have been prepared, including sets of data for the stable nuclides (i.e. mass, natural abundance, spin and parity). Problems in the assignment of ENDF material numbers were addressed, while format and consistency tests were made using CHECKR and FIZCON, respectively. The assembly processes are discussed and reviewed, and the contents of the JEFF-3T starter libraries are described. (author)

  12. 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

  13. The fast fission as a dissipative regime in heavy ion reactions

    International Nuclear Information System (INIS)

    We present a macroscopic dynamical model for dissipative collisions in heavy ion reactions. The relative motion and the nucleon exchanges are described in the framework of the local harmonic approximation. The deformations and the rearrangement of densities inside the composite system are introduced by means of a time dependent hamiltonian. In such a description the fast fission process appears naturally. After we recall the experimental studies concerning fast fission phenomenon we compare the calculated distributions with the experimental ones

  14. Metrology for new generation nuclear power plants - MetroFission

    OpenAIRE

    Johansson, L; FILTZ J.-R.; De Felice, P.; SADLI M.; Plompen, Arjan; HEYSE JAN; HAY, Bruno; Dinsdale, A.; POMME Stefaan; CASSETTE P.; KEIGHTELY John

    2013-01-01

    This EMRP (European Metrology Research Programme) project, MetroFission, has been looking at solving metrological problems related to a new generation of nuclear power plants. The proposed Generation IV power plants are designed to run safely, make efficient use of natural resources, minimize the waste and maintain proliferation resistance. In order to reach these goals, the reactor operation involves higher temperatures, high-energy neutron fluence, different types of fuel where the minor ac...

  15. 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.)

  16. Sexual differentiation in fission yeast

    DEFF Research Database (Denmark)

    Egel, R; Nielsen, O; Weilguny, D; Nielsen, Olaf

    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....

  17. Thomas-Fermi fission barriers

    International Nuclear Information System (INIS)

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

  18. Fission tracks dating for obsidian

    International Nuclear Information System (INIS)

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

  19. The VERDI fission fragment spectrometer

    Directory of Open Access Journals (Sweden)

    Frgeau 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.

  20. The VERDI fission fragment spectrometer

    International Nuclear Information System (INIS)

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

  1. 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.

  2. The discovery of uranium fission

    International Nuclear Information System (INIS)

    Uranium was discovered 200 years ago. Its radioactive character was first demonstrated in 1896 and two years later radium was extracted from uranium minerals. In 1911 studies with alpha rays from radioactive decay led to the unexpected discovery of the atomic nucleus. Exposure of beryllium to alpha rays yielded neutrons, first detected in 1932. Starting in 1934, neutron irradiation of uranium produced radioactive substances erroneously attributed to transuranium elements but with confusing properties. Painstaking experiments by chemists left no doubt on 17 December 1938 that barium was produced by these irradiations: the neutrons had split some uranium nuclei. The physics of the fission process was understood two weeks later; after a few months, neutron multiplication was found to be probable. This review deals with the eminent scientists involved, their successes, errors and disappointments, and the unexpected insights which occurred on the paths and detours of scientific research. It is, therefore, instructive also to discuss how fission was not discovered. The momentous discovery must be considered inevitable; the great tragedy was that Germany started World War II just at the time when the possibility of nuclear chain reactions and bombs became known. The consequences and anxieties that remain after 50 years of nuclear fission demand that mankind act with reason and conscience to maintain peace. (author)

  3. Fission throughout the periodic table

    International Nuclear Information System (INIS)

    The explicit treatment of the mass asymmetry degree of freedom has allowed us to extend the concept of fission to statistical processes involving the emission of fragments of any size. This generalization makes fission a process that extends throughout the periodic chart and that incorporates as special cases both traditional fission and light particle evaporation. Despite the extensive research covered in this presentation, a lot if not most of the work remains yet to be done. The experimental determination of the conditional barriers is so far limited to one isotope, and even that is incomplete. A systematic study of the conditional barriers is clearly necessary to test the validity (or to define the parameters) of the macroscopic models like the finite range model. As it has been done for the symmetric barriers in heavy systems, it should be possible to isolate the shall effects from the macroscopic part of the conditional barriers. Furthermore, the knowledge of the conditional barriers is essential for the predictions of cross sections and reaction rates

  4. Fission product yields from 22 MeV neutron-induced fission of 235U

    International Nuclear Information System (INIS)

    The chain yields of 28 product nuclides were determined for the fission of 235U induced by 22 MeV neutrons for the first time. Absolute fission rate was monitored with a double-fission chamber. Fission product activities were measured by HPGe γ-ray spectrometry. Time of flight technique was used to measure the neutron spectrum in order to estimate fission events induced by break-up neutrons and scattering neutrons. A mass distribution curve was obtained and the dependence of fission yield on neutron energy is discussed

  5. Fission product yields from 19.1 MeV neutron induced fission of 238U

    International Nuclear Information System (INIS)

    36 chain yields were determined for the fission of 238U induced by 19.1 MeV neutrons for the first time. Absolute fission rate was monitored with a double-fission chamber. Fission product activities were measured by HPGe γ-ray spectrometry. Threshold detector method was used to measure the neutron spectrum in order to estimate the fission events induced by break-up neutrons and scattering neutrons. A mass distribution curve was obtained and the dependence of fission yield on neutron energy was discussed

  6. 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)

  7. Have Superheavy Elements been Produced in Nature?

    OpenAIRE

    Petermann, I.; Langanke, K.; Martínez-Pinedo, G.; Panov, I. V.; Reinhard, P.-G.; Thielemann, F.-K.

    2012-01-01

    We discuss the possibility whether superheavy elements can be produced in Nature by the astrophysical rapid neutron capture process. To this end we have performed fully dynamical network r-process calculations assuming an environment with neutron-to-seed ratio large enough to produce superheavy nuclei. Our calculations include two sets of nuclear masses and fission barriers and include all possible fission channels and the associated fission yield distributions. Our calculations produce super...

  8. The resonance neutron fission on heavy nuclei

    International Nuclear Information System (INIS)

    A new approach to the description of the fission, similar to the well-known reaction theory and based on the helicity representation for the exit fission channels, is briefly summarized. This approach allows one to connect the multimodal fission representation with A. Bohr's concept of the fission transition states and to obtain formulae for the partial and differential fission cross sections. The formulae are used for analysis of the angular anisotropy of fragments in the neutron resonance induced fission of aligned 235U nuclei and of the P-even angular forward-backward and right-left correlations of fragments oe the P-odd correlations caused by the interference of s- and p-wave neutron resonances

  9. 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.

  10. Radiochemical studies on nuclear fission at Trombay

    Indian Academy of Sciences (India)

    Asok Goswami

    2015-08-01

    Since the discovery of nuclear fission in the year 1939, both physical and radiochemical techniques have been adopted for the study of various aspects of the phenomenon. Due to the ability to separate individual elements from a complex reaction mixture with a high degree of sensitivity and selectivity, a chemist plays a significant role in the measurements of mass, charge, kinetic energy, angular momentum and angular distribution of fission products in various fissioning systems. At Trombay, a small group of radiochemists initiated the work on radiochemical studies of mass distribution in the early sixties. Since then, radiochemical investigations on various fission observables have been carried out at Trombay in , , and heavy-ion-induced fissions. An attempt has been made to highlight the important findings of such studies in this paper, with an emphasis on medium energy and heavy-ion-induced fission.

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

    International Nuclear Information System (INIS)

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

  12. Thermal Performance of Deep-Burn Fusion-Fission Hybrid Waste in a Repository

    Energy Technology Data Exchange (ETDEWEB)

    Blink, J A; Chipman, V; Farmer, J; Shaw, H; Zhao, P

    2008-11-25

    The Laser Inertial Confinement Fusion Fission Energy (LIFE) Engine [1] combines a neutron-rich but energy-poor inertial fusion system with an energy-rich but neutron-poor subcritical fission blanket. Because approximately 80% of the LIFE Engine energy is produced from fission, the requirements for laser efficiency and fusion target performance are relaxed, compared to a pure-fusion system, and hence a LIFE Engine prototype can be based on target performance in the first few years of operation of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). Similarly, because of the copious fusion neutrons, the fission blanket can be run in a subcritical, driven, mode, without the need for control rods or other sophisticated reactivity control systems. Further, because the fission blanket is inherently subcritical, fission fuels that can be used in LIFE Engine designs include thorium, depleted uranium, natural uranium, spent light water reactor fuel, highly enriched uranium, and plutonium. Neither enrichment nor reprocessing is required for the LIFE Engine fuel cycle, and burnups to 99% fraction of initial metal atoms (FIMA) being fissioned are envisioned. This paper discusses initial calculations of the thermal behavior of spent LIFE fuel following completion of operation in the LIFE Engine [2]. The three time periods of interest for thermal calculations are during interim storage (probably at the LIFE Engine site), during the preclosure operational period of a geologic repository, and after closure of the repository.

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

    Science.gov (United States)

    Johansson, Lena; Samuelsson, Christer; Holm, Elis

    1999-03-01

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

  14. 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 ...

  15. Migration and transfer of transuranium elements (Pu, Am) and longliving fission products (Sr, Ru, Sb, Cs, Ce, Eu) in natural forest ecosystems of the 30-km-zone around Chernobyl

    International Nuclear Information System (INIS)

    In the framework of the C.E.C. research project ECP-5 entitled ''The behaviour of radionuclides in natural and semi-natural ecosystems'' our institute carried out investigations on selected sites of forest ecosystems in the 30-km-zone of Chernobyl in cooperation with research instituts of the C.I.S. states Russia and Ukraine. Our research is concentrated on the transfer of radionuclides from soil to plants of the understorey, especially species of farns and berries, as this plants take up their nutrients mainly from the upper organic horizons. (orig.)

  16. 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.

  17. Pion-induced fission of actinide targets

    International Nuclear Information System (INIS)

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

  18. 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.)

  19. Superfluid dynamics of 258Fm fission

    OpenAIRE

    Scamps, Guillaume; Simenel, Cédric; 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 theor...

  20. Fission dynamics at low excitation energy

    OpenAIRE

    Aritomo, Y.; Chiba, S.

    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 vibrati...

  1. 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.

  2. Benchmarking the LAHET trademark fission models

    International Nuclear Information System (INIS)

    There has been considerable interest in improving the fission models in the LAHET Monte Carlo code for the transport and interaction of nucleons, pions, muons, light ions, and antinucleons. Although subactinide fission contributes little to neutron production in lead or tungsten targets, it can be significant for simulation of target activation and fission product contamination. The availability of new data permits new comparisons to be made between experiment and calculation

  3. 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

  4. 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.)

  5. Mechanisms of Mitochondrial Fission and Fusion

    OpenAIRE

    van der Bliek, Alexander M.; Shen, Qinfang; Kawajiri, Sumihiro

    2013-01-01

    Mitochondria continually change shape through the combined actions of fission, fusion, and movement along cytoskeletal tracks. The lengths of mitochondria and the degree to which they form closed networks are determined by the balance between fission and fusion rates. These rates are influenced by metabolic and pathogenic conditions inside mitochondria and by their cellular environment. Fission and fusion are important for growth, for mitochondrial redistribution, and for maintenance of a hea...

  6. Nuclear fission with a Langevin equation

    International Nuclear Information System (INIS)

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

  7. 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. τdef >> τnucleon (τdef is the descent time, τnucleon ∼ n/ΔEnucleon, and ΔEnucleon is the distance between the nucleon levels). In this case nucleonic shells are formed before scission. At the same time τdef rot, i.e. the process of descent is fast with respect to the rotational degrees of freedom (τrot h/ΔErot) - In the case of fission of an excited nucleus with fairly high excitation energy at the saddle point, ΔEnucleon may be so low that not only τdef rot but also τdef 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)

  8. International conference on fifty years research in nuclear fission

    International Nuclear Information System (INIS)

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

  9. Some problems concerning the investigation of spontaneously fissioning isomers

    International Nuclear Information System (INIS)

    Some experiments throwing light on the understanding of spontaneously fissioning isomers (SFI) and fission processes are discussed. Photofission below the fission barrier is treated. The formation of SFI at the beta decay is investigated. The measurement of the mean number of fission neutrons for the fission below the barrier is dealt with. Finally, SFI in isobaric analogue resonances are discussed

  10. Fission-track dating using object-based image analysis

    International Nuclear Information System (INIS)

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

  11. Fission dynamics within time-dependent Hartree-Fock: boost-induced fission

    OpenAIRE

    Goddard, P M; Stevenson, P. D.; 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 induced fission processes, using quadrupole boosts in the nuclide $^{240}$Pu as an example. Method...

  12. 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

  13. Some aspects of fission and quasifission processes

    Indian Academy of Sciences (India)

    B B Back

    2015-08-01

    The discovery of nuclear fission in 1938–1939 had a profound influence on the field of nuclear physics and it brought this branch of physics into the forefront as it was recognized for having the potential for its seminal influence on modern society. Although many of the basic features of actinide fission were described in a ground-breaking paper by Bohr and Wheeler only six months after the discovery, the fission process is very complex and it has been a challenge for both experimentalists and theorists to achieve a complete and satisfactory understanding of this phenomenon. Many aspects of nuclear physics are involved in fission and it continues to be a subject of intense study even three quarters of a century after its discovery. In this talk, I will review an incomplete subset of the major milestones in fission research, and briefly discuss some of the topics that I have been involved in during my career. 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, some of the circumstances around the establishment of large-scale nuclear research in India will be discussed.

  14. Process for the extraction of fission products

    International Nuclear Information System (INIS)

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

  15. FISSION PRODUCT REMOVAL FROM ORGANIC SOLUTIONS

    Science.gov (United States)

    Moore, R.H.

    1960-05-10

    The decontamination of organic solvents from fission products and in particular the treatment of solvents that were used for the extraction of uranium and/or plutonium from aqueous acid solutions of neutron-irradiated uranium are treated. The process broadly comprises heating manganese carbonate in air to a temperature of between 300 and 500 deg C whereby manganese dioxide is formed; mixing the manganese dioxide with the fission product-containing organic solvent to be treated whereby the fission products are precipitated on the manganese dioxide; and separating the fission product-containing manganese dioxide from the solvent.

  16. Fission properties for r-process nuclei

    OpenAIRE

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

    2011-01-01

    We present a systematics of fission barriers and fission lifetimes for the whole landscape of super-heavy elements (SHE), i.e. nuclei with Z>100. The fission lifetimes are also compared with the alpha-decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parameterizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. Th...

  17. Photon- and electron-induced fission

    International Nuclear Information System (INIS)

    This chapter begins with a discussion of electromagnetic probes and nuclear fission. Section II concentrates on fission fragment angular distributions from the viewpoints of formalism and experiments. Section III discusses photofission cross sections and fission probabilities for deep subbarrier fission, the barrier region, and the giant resonance, quasideuteron, and ?-resonance region. Section IV is devoted to the fragment characteristics in photofission. Finally, Section V examines electrofission cross sections (inclusive electrofission cross sections and exclusive (e,e',f) coincidence experiments). 194 refs., 49 figs., 9 tabs

  18. Formal theory of neutron induced fission

    Energy Technology Data Exchange (ETDEWEB)

    Barabanov, A.L. [Kurchatov (I.V.) Inst. of Atomic Energy, Moscow (Russian Federation); Furman, W.I. [Joint Inst. for Nuclear Research, Dubna (Russian Federation)

    1997-05-01

    General expression for differential cross section of neutron induced fission is derived with account of arbitrary spin orientation of colliding particles. A covariant description of angular dependence of fission cross section is proposed. Helicity representation for fission fragments is considered in details and limits of its validity are investigated. It is shown that this representation makes reliable basis for description of interference effects in total and differential cross sections of fission induced by slow neutrons. A relation between total fragment helicity K and A.Bohr quantum number K is discussed. (orig.). With 2 figs.

  19. 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)

  20. Fission investigations and evaluation activities at IRMM

    International Nuclear Information System (INIS)

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

  1. 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 λf∼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)

  2. Time Variation of the Fine Structure Constant Driven by Quintessence

    OpenAIRE

    Anchordoqui, Luis; Goldberg, Haim

    2003-01-01

    There are indications from the study of quasar absorption spectra that the fine structure constant $\\alpha$ may have been measurably smaller for redshifts $z>2.$ Analyses of other data ($^{149}$Sm fission rate for the Oklo natural reactor, variation of $^{187}$Re $\\beta$-decay rate in meteorite studies, atomic clock measurements) which probe variations of $\\alpha$ in the more recent past imply much smaller deviations from its present value. In this work we tie the variation of $\\alpha$ to the...

  3. Spectroscopy of heavy fissionable nuclei

    Indian Academy of Sciences (India)

    S K Tandel

    2015-09-01

    Structural studies of heavy nuclei are quite challenging due to increased competition from fission, particularly at high spins. Nuclei in the actinide region exhibit a variety of interesting phenomena. Recent advances in instrumentation and analysis techniques have made feasible sensitive measurements of nuclei populated with quite low cross-sections. These include isomers and rotational band structures in isotopes of Pu ( = 94) to Rf ( = 104), and octupole correlations in the Th ( = 90) region. The obtained experimental data have provided insights on various aspects like moments of inertia and nucleon alignments at high spins, quasiparticle energies and evolution of quadrupole and octupole collectivity, among others. An overview of some of these results is presented.

  4. 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 ω of periodic perturbation. In particular, the intensity of the first peak in RTD has a sharp maximum at certain nuclear temperature depending on ω. This maximum should be considered as fist-hand manifestation of stochastic resonance in nuclear dynamics

  5. Fission fragment excited laser system

    Science.gov (United States)

    McArthur, David A.; Tollefsrud, Philip B.

    1976-01-01

    A laser system and method for exciting lasing action in a molecular gas lasing medium which includes cooling the lasing medium to a temperature below about 150 K and injecting fission fragments through the lasing medium so as to preferentially excite low lying vibrational levels of the medium and to cause population inversions therein. The cooled gas lasing medium should have a mass areal density of about 5 .times. 10.sup.-.sup.3 grams/square centimeter, relaxation times of greater than 50 microseconds, and a broad range of excitable vibrational levels which are excitable by molecular collisions.

  6. Microscopic theory of fission dynamics

    International Nuclear Information System (INIS)

    A microscopic theory of fission is presented in which a Feynman path integral is used to understand tunneling. The idea of an instanton in the case of a Boson field theory is generalized to many Fermions and used to determine the dynamical path self-consistently. The essential roles of Fermion nodal surfaces and symmetry breaking are emphasized. The theory is applied to a solvable pedagogical model, which demonstrates its quantitative accuracy and the importance of solving for the optimal collective path. Similar features are observed in a more realistic calculation of a 32-Fermion system in three dimensions. (orig.)

  7. Microscopic theory of fission dynamics

    Science.gov (United States)

    Negele, John W.

    1989-10-01

    A microscopic theory of fission is presented in which a Feynman path integral is used to understand tunneling. The idea of an instanton in the case of a Boson field theory is generalized to many Fermions and used to determine the dynamical path self-consistently. The essential roles of Fermion nodal surfaces and symmetry breaking are emphasized. The theory is applied to a solvable pedagogical model, which demonstrates its quantitative accuracy and the importance of solving for the optimal collective path. Similar features are observed in a more realistic calculation of a 32-Fermion system in three dimensions.

  8. Microscopic theory of fission dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Negele, J.W. (Massachusetts Inst. of Tech., Cambridge (USA). Center for Theoretical Physics; Massachusetts Inst. of Tech., Cambridge (USA). Dept. of Physics)

    1989-10-09

    A microscopic theory of fission is presented in which a Feynman path integral is used to understand tunneling. The idea of an instanton in the case of a Boson field theory is generalized to many Fermions and used to determine the dynamical path self-consistently. The essential roles of Fermion nodal surfaces and symmetry breaking are emphasized. The theory is applied to a solvable pedagogical model, which demonstrates its quantitative accuracy and the importance of solving for the optimal collective path. Similar features are observed in a more realistic calculation of a 32-Fermion system in three dimensions. (orig.).

  9. Symmetric fission of 24Mg

    International Nuclear Information System (INIS)

    In this contribution we present preliminary results of a measurement of the fission of 24Mg into two 12C nuclei following inelastic excitation of 24Mg projectiles scattered from a light target. The use of a heavy ion inelastic scattering reaction preserves the connection to the 24Mg ground state configuration, and the high initial 24Mg momentum provides considerable kinematic focussing, yielding high efficiency for detecting the breakup fragments. The data show distinct structure as a function of 24Mg excitation over an energy range similar to that observed in 12C + 12C scattering

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

    Energy Technology Data Exchange (ETDEWEB)

    Kessler, Guenter

    2012-07-01

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

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

    International Nuclear Information System (INIS)

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

  12. 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

  13. 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

  14. HIV-1 Protease in the Fission Yeast Schizosaccharomyces pombe

    Science.gov (United States)

    Benko, Zsigmond; Elder, Robert T.; Li, Ge; Liang, Dong; Zhao, Richard Y.

    2016-01-01

    Background HIV-1 protease (PR) is an essential viral enzyme. Its primary function is to proteolyze the viral Gag-Pol polyprotein for production of viral enzymes and structural proteins and for maturation of infectious viral particles. Increasing evidence suggests that PR cleaves host cellular proteins. However, the nature of PR-host cellular protein interactions is elusive. This study aimed to develop a fission yeast (Schizosaccharomyces pombe) model system and to examine the possible interaction of HIV-1 PR with cellular proteins and its potential impact on cell proliferation and viability. Results A fission yeast strain RE294 was created that carried a single integrated copy of the PR gene in its chromosome. The PR gene was expressed using an inducible nmt1 promoter so that PR-specific effects could be measured. HIV-1 PR from this system cleaved the same indigenous viral p6/MA protein substrate as it does in natural HIV-1 infections. HIV-1 PR expression in fission yeast cells prevented cell proliferation and induced cellular oxidative stress and changes in mitochondrial morphology that led to cell death. Both these PR activities can be prevented by a PR-specific enzymatic inhibitor, indinavir, suggesting that PR-mediated proteolytic activities and cytotoxic effects resulted from enzymatic activities of HIV-1 PR. Through genome-wide screening, a serine/threonine kinase, Hhp2, was identified that suppresses HIV-1 PR-induced protease cleavage and cell death in fission yeast and in mammalian cells, where it prevented PR-induced apoptosis and cleavage of caspase-3 and caspase-8. Conclusions This is the first report to show that HIV-1 protease is functional as an enzyme in fission yeast, and that it behaves in a similar manner as it does in HIV-1 infection. HIV-1 PR-induced cell death in fission yeast could potentially be used as an endpoint for mechanistic studies, and this system could be used for developing a high-throughput system for drug screenings. PMID:26982200

  15. The use of recoil for the separation of uranium fission products; Utilisation du recul pour la separation des produits de fission de l'uranium

    Energy Technology Data Exchange (ETDEWEB)

    Henry, R.; Herczec, C. [Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires

    1959-07-01

    The recoil distance of fission fragments in U{sub 3}O{sub 8} is about 8 microns. By using highly diluted suspensions of uranium oxide particles having dimension much smaller than this figure (mean diameter 0,5 micron), we were able to study the re-adsorption of fission products on uranium oxide. Separation results have been studied as a function of the nature of the irradiation medium (solid or liquid) and the separation medium, of particle size and of concentration of particles in the dispersing medium. Decay curves can be used to discriminate between {sup 239}Np and mixed fission products. Most of the {sup 239}Np is found in the U{sub 3}O{sub 8} particles. The location of fission products in solid dispersing media has been determined, fission products being found always inside the dispersing medium particles. The results obtained can be applied to the rapid separation of short-lived fission products from a uranium-free starting material. (author) [French] Le parcours de recul des fragments de fission est en moyenne de 8 microns dans l'U{sub 3}O{sub 8}. En prenant des suspensions d'oxyde d'uranium dont les particules, tres diluees, ont des dimensions nettement inferieures a cette valeur (diametre moyen 0,5 micron), on a pu etudier directement la readsorption des produits de fission sur l'oxyde d'uranium. Les resultats de separation ont ete etudies en fonction de la nature du milieu d'irradiation (solide ou liquide) et du milieu de separation, de la taille des particules d'oxyde et de leur concentration dans le milieu dispersant. Les courbes de decroissance permettent de determiner la perturbation apportee dans les mesures par le {sup 239}Np qui reste en majorite dans les grains d'U{sub 3}O{sub 8}. On a determine enfin l'emplacement des produits de fission dans le cas des melanges solides; ils se trouvent toujours a l'interieur des grains du milieu recepteur. Les resultats obtenus permettent d'envisager la separation rapide de produits de fission a periode courte a partir d'un milieu debarrasse d'uranium. (auteur)

  16. 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

  17. 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)

  18. Effect of inertia parameters on static fission path

    International Nuclear Information System (INIS)

    Properties of static (minimum potential) fission path in the formalism of Hofmann are investigated. It is pointed out that the inertial parameters greatly affect the fission path and hence the penetrability. The difficulty of determining fission path is discussed

  19. Least squares analysis of fission neutron standard fields

    International Nuclear Information System (INIS)

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

  20. Okulo natural reactors

    International Nuclear Information System (INIS)

    French CEA has reported in 1972 that natural nuclear reactors existed in Okulo uranium deposit in Gabon in Africa, that caused nuclear fission chain reaction (Okulo phenomena) spontaneously two billion years ago. The fission products and transuranic elements produced by the natural reactors have been preserved in strata without movement while subjected to geological phenomena for such very long years. 16 zones of the natural reactors have been discovered so far. The geological features of the Okulo uranium deposit are explained. The total amount of 235U lost by the chain reaction was estimated to be about 6t, and the fission products were about 6t. The Okulo phenomena offered the valuable results of the synthetic formation disposal test that the nature has carried out for such long years. The significance of the study on natural analog is discussed. Organic substances and the mechanism of holding and movement of uranium and fission nuclides, the stability of uraninite and the age measurement of the deposit by Nd-Sm process are reported as the main results. (K.I.)

  1. 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)

  2. Spectroscopy of selected fission fragments

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-10-22

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

  3. Spectroscopy of selected fission fragments

    International Nuclear Information System (INIS)

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

  4. Isoscaling of the Fission Fragments with Langevin Equation

    OpenAIRE

    Wang, K; Ma, Y.G.; Wei, Y. B.; Cai, X.Z.; Chen, J G; Fang, D.Q.; Guo, W.; Ma, G.L.; Shen, W.Q.(Shanghai Institute of Applied Physics, Shanghai, 201800, China); Tian, W.D.; Zhong, C.; Zhou, X. F.

    2004-01-01

    Langevin equation is used to simulate the fission process of $^{112}$Sn + $^{112}$Sn and $^{116}$Sn + $^{116}$Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. Isoscaling behavior has been observed from the analysis of fission fragments of both reactions and the isoscaling parameter $\\alpha$ seems to be sensitive to the width of fission probability and the beam energy.

  5. 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

  6. 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

  7. Dissipation and friction in nuclear fission

    International Nuclear Information System (INIS)

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

  8. Nuclear Power from Fission Reactors. An Introduction.

    Science.gov (United States)

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

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

  9. Fission stability diagram of 240Pu

    OpenAIRE

    Garcias, Francisca; Barranco Gómez, Manuel; Wio, Horacio S.; Ngô, Christian; Nemeth, J.

    1989-01-01

    We have used an axially symmetric deformed Thomas-Fermi model to evaluate the fission barrier of 240Pu as a function of the quadrupole moment Q2 for different values of the angular momentum L and temperature T. The fission stability diagram of this nucleus is investigated.

  10. Influence of nuclear forces on Coulomb fission

    OpenAIRE

    Holm, Hartmut; Greiner, Walter, 1935-

    2006-01-01

    The Coulomb-fission cross sections for 132Xe and 148Nd incident on 238U are calculated in a dynamical classical model. In particular the influence of nuclear forces on the cross sections is studied. Since they are counteracting the Coulomb force, they diminish the cross sections for Coulomb fission significantly and shift the Coulomb barrier towards lower energies.

  11. Broadband amplifier assembly for fission chamber

    International Nuclear Information System (INIS)

    This report presents and describes an amplifier assembly which has been designed to solve the problem of discrimination of fission impulsions with respect to α impulsions in a fission chamber. It notably comprises a signal shaping by means of a short-circuited delay line. The assembly comprises a pre-amplifier and an amplifier. Response curves and circuit layouts are presented

  12. Correlation measurements of fission-fragment properties

    Directory of Open Access Journals (Sweden)

    Oberstedt A.

    2010-10-01

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

  13. Collective and relative motion of fission fragments

    International Nuclear Information System (INIS)

    A classical dynamical calculation has been performed to study the time evolution of deformation, kinetic energy, and internal excitation in post-scission motion of the fission fragments. The model has been applied to the spontaneous fission of 252Cf and results compare favourably with experiment. (author)

  14. Correlation measurements of fission-fragment properties

    International Nuclear Information System (INIS)

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

  15. Correlation measurements of fission-fragment properties

    Science.gov (United States)

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

    2010-10-01

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

  16. Fission cross section calculations for Pa isotopes

    International Nuclear Information System (INIS)

    Based on the recently measured cross-section values for the neutron-induced fission of 231Pa and our experience gained with other isotopes, new self consistent neutron cross section calculations for n+231Pa have been performed up to 30 MeV. The results are quite different to the existing evaluations, especially above the first chance fission threshold. (authors)

  17. 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

  18. 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

  19. 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

  20. 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

  1. Options for Affordable Fission Surface Power Systems

    International Nuclear Information System (INIS)

    Fission surface power systems could provide abundant power anywhere on the 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. (authors)

  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 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

  4. 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.

  5. 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.

  6. Contained fissionly vaporized imploded fission explosive breeder reactor

    International Nuclear Information System (INIS)

    Disclosed is a nuclear reactor system which produces useful thermal power and breeds fissile isotopes wherein large spherical complex slugs containing fissile and fertile isotopes as well as vaporizing and tamping materials are exploded seriatim in a large containing chamber having walls protected from the effects of the explosion by about two thousand tons of slurry of fissile and fertile isotopes in molten alkali metal. The slug which is slightly sub-critical prior to its entry into the centroid portion of the chamber, then becomes slightly more than prompt-critical because of the near proximity of neutron-reflecting atoms and of fissioning atoms within the slurry. The slurry is heated by explosion of the slugs and serves as a working fluid for extraction of heat energy from the reactor. Explosive debris is precipitated from the slurry and used for the fabrication of new slugs

  7. 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)

  8. Systematics of Fission-Product Yields

    Energy Technology Data Exchange (ETDEWEB)

    A.C. Wahl

    2002-05-01

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

  9. Systematics of Fission-Product Yields

    International Nuclear Information System (INIS)

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

  10. 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.

  11. Fission gas behaviour in water reactor fuels

    International Nuclear Information System (INIS)

    During irradiation, nuclear fuel changes volume, primarily through swelling. This swelling is caused by the fission products and in particular by the volatile ones such as krypton and xenon, called fission gas. Fission gas behaviour needs to be reliably predicted in order to make better use of nuclear fuel, a factor which can help to achieve the economic competitiveness required by today's markets. These proceedings communicate the results of an international seminar which reviewed recent progress in the field of fission gas behaviour in light water reactor fuel and sought to improve the models used in computer codes predicting fission gas release. State-of-the-art knowledge is presented for both uranium-oxide and mixed-oxide fuels loaded in water reactors. (author)

  12. Theory of neutron emission in fission

    International Nuclear Information System (INIS)

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

  13. Theory of neutron emission in fission

    Energy Technology Data Exchange (ETDEWEB)

    Madland, D.G.

    1988-01-01

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

  14. Theory of neutron emission in fission

    Energy Technology Data Exchange (ETDEWEB)

    Madland, D.G.

    1989-01-01

    Following a summary of the observables in neutron emission in fission, a brief history is given of theoretical representations of the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity /bar /nu///sub p/. This is followed by descriptions, together with examples, of modern approaches to the calculation of these quantities including recent advancements. Emphasis will be placed upon the predictability and accuracy of the modern approaches. In particular, the dependence of N(E) and /bar /nu///sub p/ on the fissioning nucleus and its excitation energy will be discussed, as will the effects of and competition between first-, second- and third-chance fission in circumstances of high excitation energy. Finally, properties of neutron-rich (fission-fragment) nuclei are discussed that must be better known to calculate N(E) and /bar /nu///sub p/ with higher accuracy than is currently possible. 17 refs., 11 figs.

  15. 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.

  16. Theoretical study of fission dynamics with muons

    International Nuclear Information System (INIS)

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

  17. Fission dynamics with systems of intermediate fissility

    Indian Academy of Sciences (India)

    E Vardaci; A Di Nitto; P N Nadtochy; A Brondi; G La Rana; R Moro; M Cinausero; G Prete; N Gelli; E M Kozulin; G N Knyazheva; I M Itkis

    2015-08-01

    A 4 light charged particle spectrometer, called 8 LP, is in operation at the Laboratori Nazionali di Legnaro, Italy, for studying reaction mechanisms in low-energy heavy-ion reactions. Besides about 300 telescopes to detect light charged particles, the spectrometer is also equipped with an anular PPAC system to detect evaporation residues and a two-arm time-of-flight spectrometer to detect fission fragments. The spectrometer has been used in several fission dynamics studies using as a probe light charged particles in the fission and evaporation residues (ER) channels. This paper proposes a journey within some open questions about the fission dynamics and a review of the main results concerning nuclear dissipation and fission time-scale obtained from several of these studies. In particular, the advantages of using systems of intermediate fissility will be discussed.

  18. 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 ν-bar (3 papers), multiplicity distribution of fission neutrons (3 papers), competition between neutron and γ-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

  19. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

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

  20. Fission of doubly ionized calcium clusters

    Science.gov (United States)

    Blaisten-Barojas, Estela; Chien, Chang-Hong; Pederson, Mark R.; Mirick, Jeff W.

    2004-09-01

    Cluster ions, CaN+ and CaN2+, containing up to N = 8 atoms are studied within density functional theory. Ground and first excited states, and ionization energies are reported for all sizes. At zero temperature Ca32+ and Ca42+ are linear, whereas Ca52+ through Ca72+ undergo structural transitions from 3D-configurations into linear ions below 600 K. As a consequence, fission that occurs above 600 K starts from linear configurations. Ca82+ has an hexagonal bipyramidal structure. The preferred fission channels are CaN2+?Ca++CaN-1+ with fission barriers smaller than the evaporation energy up to Ca72+. However, Ca82+ presents a large fission barrier and would rather evaporate one atom than undergo fission.

  1. Nuclear Fission as a Markov Process

    International Nuclear Information System (INIS)

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

  2. Microscopic Theory of Nuclear Fission: A Review

    CERN Document Server

    Schunck, N

    2015-01-01

    This article reviews how nuclear fission is described within nuclear density functional theory. In spontaneous fission, half-lives are the main observables and quantum tunnelling the essential concept, while in induced fission the focus is on fragment properties and explicitly time-dependent approaches are needed. The cornerstone of the current microscopic theory of fission is the energy density functional formalism. Its basic tenets, including tools such as the HFB theory, effective two-body effective nuclear potentials, finite-temperature extensions and beyond mean-field corrections, are presented succinctly. The EDF approach is often combined with the hypothesis that the time-scale of the large amplitude collective motion driving the system to fission is slow compared to typical time-scales of nucleons inside the nucleus. In practice, this hypothesis of adiabaticity is implemented by introducing (a few) collective variables and mapping out the many-body Schr\\"odinger equation into a collective Schr\\"odinge...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-05-15

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

  4. 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

  5. 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

  6. Nuclear fission industry in Japan

    International Nuclear Information System (INIS)

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

  7. 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

  8. Coulomb effects in cold fission

    International Nuclear Information System (INIS)

    The structures in the mass and total kinetic energy (TKE) distributions in cold fission of 234U and 236U are interpreted in terms of the Coulomb interaction energy (C) between fragments at the scission point. The maximal value of C (Cmax) corresponding to the most compact scission configuration, is calculated for several mass fragmentations. It is shown that Cmax increases, if one increases the charge asymmetry for a given primary fragmentation and Q being constant. This dependence produces oscillations with a period of approximately 5 amu of C as a function of the light fragment mass which are correlated with the observed oscillations of the maximal value of TKE. Moreover, it follows that the yields of the more asymmetric charge fragmentation of the same system are increased, that is for the more compact configuration. (orig.)

  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. 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.

  11. 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...

  12. Comparison of fission signatures from β− delayed γ-ray and neutron emissions

    International Nuclear Information System (INIS)

    The delayed γ-ray and neutron fission signals utilized in active inspection techniques were measured simultaneously in order to directly compare their detection sensitivities. Fissionable and non-fissionable targets were irradiated by a 15-Hz pulsed bremsstrahlung beam operating at endpoint energies from 7 to 22 MeV. The fissionable mass detection limits for both these signals decreased approximately three orders of magnitude as the irradiation energy was increased with the delayed γ-ray limits 4.3–8.2 times smaller. The signals from the non-fissionable targets were consistent with the natural passive backgrounds for irradiation energies up to 16 MeV. At higher bremsstrahlung energies, there was a target independent active background in the delayed γ-ray signal that accounted for 35% of the gross yield. In addition, these higher irradiation energies resulted in products from 9Be(γ,p)8Li and 18O(γ,p)17N reactions interfering with the delayed γ-ray and neutron fission signals, respectively

  13. Optimal deuteron energy for a neutron rich nuclei source based on fission

    International Nuclear Information System (INIS)

    A neutron rich nuclei source can be conceived by using the neutron induced fission process. A high neutron flux can be obtained through the deuteron break-up reaction in the so--called converters. The number of fission events and their isotopic distributions produced in a uranium target depends on the deuteron incident beam energy, characteristics of the converter and geometry of the combination. A theoretical approach is presented in order to optimize the number of fission events in the uranium target as function of the above mentioned parameters. The initial kinetic energy of the deuteron beam, the nature of the converter and its geometry determines the angular and energy distributions of the emerging neutrons. The models used to simulate these distributions are essentially based on the Serber's approximation. The fission is treated in a microscopic-macroscopic approach using the two center shell model. A new concept is used to determine the isotopic distribution of the fission fragments as a function of the neutron energy. A steep dumping of the neutron energy is produced in the compound nucleus which modifies the two humped fission barrier and produces changes of the penetrabilities associated to each binary partition and therefore, in the isotopic distribution. Finally, our results show that a good value of the incident deuteron energy suitable for the production of neutron rich beams is closed to 80 MeV. (authors)

  14. 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

  15. Multimodal nuclear fission model and its application

    International Nuclear Information System (INIS)

    As the nuclear fission models, the following are explained: random-neck rupture model; nuclear fission channel theory; breakpoint model, especially breakpoint model by Wilkins et al.; and multimodal random-neck rupture model. In addition, the prompt neutron spectrum analysis of multimodal model, and the application to the energy-dependent analysis of delayed neutron yield are also described. In the random-neck fracture model proposed by S. L. Whetstone, a nucleus has a form like 'elongated gourd' just before the rupture, and the mass distribution is determined by the part of the neck where cleavage occurs. The division of mass and charge in nuclear fission, according to the nuclear fission channel theory, is considered to be determined by which transition state the saddle point of fission barrier is passed through. On the other hand, the model, where the deformation of nucleus further proceeds and the division is determined by the breakpoint just before the division to two fissure pieces, is called the breakpoint model. The multimodal nuclear fission model is the concept to consider that there are several deformation channels for nucleus, and that each of them leads to a different rupture state. The model that combines the random-neck rapture model and multimodal fission model is the multimodal random-neck rupture model. (J.P.N.)

  16. Neutron and gamma emission in fission

    International Nuclear Information System (INIS)

    The total kinetic energy freed by the mass rearrangement in binary low-energy nuclear fission is roughly of the order of 180 to 240 MeV, depending on the fissioning system. This energy is distributed at the end of the fission process between the total kinetic energy of the two fragments, the energy released by neutron and ?-ray emission, and lastly by the ? or electron conversion decay which is accompanied by the delayed emission of neutrons and ?-rays. In general, 75 to 85% of the total available energy is present as fragment kinetic energy, whereas about 10% and 3 to 4% are contained in the prompt neutron and ?-ray emission processes. A fraction of about 8% of the total available energy from the whole mass rearrangement down to stable isotopes is released in the ? decay and electron conversion and subsequent delayed ?-ray and neutron emission. This chapter discusses time scale in fission, the integral fission neutron energy spectrum, early neutrons, neutron multiplicities, the dependence of neutron emission on excitation energy, prompt neutron emission in the resonance region, neutron emission in ternary fission, prompt gamma emission in fission, and delayed neutron and gamma emission. 132 refs., 29 figs., 3 tabs

  17. 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)

  18. Fission studies at the IGISOL facility

    International Nuclear Information System (INIS)

    Studies of the properties of the fission products ant the induced fission reaction mechanism have been a significant part of the nuclear physics research program at the IGISOL for more than 20 years. For example, one of the key motivations behind the commitment of the JYFLTRAP was isobaric separation of the fission products for spectroscopic studies. Such experiments have indeed been performed, however, the JYFLTRAP twin trap has turned out to be even more versatile instrument anyone dared dream of in advantage. The precision atomic mass measurements of neutron rich fission products has thus far resulted in considerably improved mass value for more than 150 neutron-rich isotopes, on top of which becomes the work on proton rich side. The purification Penning trap has also proven to be an excellent tool for independent fission cross section measurements. This novel method employs ion counting after JYFLTRAP and is described in a detailed way. The method takes advantage of the fact that JYFLTRAP can be used as a mass filter with a precision such that it allows an unambiguous identification of most of the fragments produced in the low-energy fission of 238U. A satisfactory agreement with previous measurements was found for independent yields of Cs isotopes in 50 MeV proton induced fission

  19. 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

  20. Our 50-year odyssey with fission

    International Nuclear Information System (INIS)

    On the occasion of this International Conference of 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 dumbbell-like systems. 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. Future challenges include devising experiments to unambiguously distinguish dissipative effects from analogous effects caused by collective degrees of freedom and computing fission directly from the underlying hadronic interaction. (orig.)