Natural Reactor Research Articles

К истории открытия и изучения феномена Окло

The paper dwells on the brief history of the discovery and studies of the Oklo uranium deposit, a natural nuclear reactor, is considered. It was shown by French specialists in 1972. The discovery was made by studying the isotope ratio 235U§238U in ore. Several years earlier, such research was carried out at the All-Union Scientific Research Institute of Mineral Raw Materials (VIMS). Unfortunately, the application for the discovery of domestic scientists was rejected.

Effect of Extreme Variations of Fundamental Constants on the Structure of Atoms and Molecules.

The fundamental constants (FCs) of physics are promoted to dynamic quantities in modern theories. So far most of the literature focused on small fractional variations in the values of FCs. In this paper, we investigate the novel regime of extreme but transient variations of FCs. We focus on the speed of light (c) and show that its variation can dramatically change the electronic structure and chemistry of atoms and molecules. These changes are induced by increased relativistic effects when c is reduced from its nominal value. To model these changes, we solve the fully relativistic Dirac equation at different values of c. We show that at extreme variations of c, the periodic table is truncated, the nominal ground states of atoms can change, water fails to serve as a universal solvent, and the ammonia molecule becomes planar.

Isotopic variations of Sm, Gd, Er and Yb found in planetary materials caused by neutron-capture reactions in nature

The isotopic shifts of 149Sm–150Sm and 157Gd–158Gd have often been observed in meteorites and lunar surface materials, because they result from the neutron-capture reactions associated with secondary neutrons produced by cosmic-ray irradiation. While the Sm and Gd isotopic shifts can mainly be used for the estimation of thermal neutron fluences that of 167Er–168Er has recently been applied in the estimation of epithermal neutron fluences. The systematic isotopic dataset of Sm, Gd and Er helps us to consider the details of planetary materials’ cosmic-ray exposure conditions using the balance of the fluences between thermal and epithermal neutrons. This paper reviews a series of isotopic variations of Sm, Gd, and Er in association with neutron-capture reactions for the application of planetary sciences. As a new attempt and possibility for better understanding the neutron fluence and its energy distribution, the use of Yb isotopic variation is then discussed using two different data sources, namely lunar regolith and the Oklo natural reactors. Finally, the preliminary result for the precise isotopic measurement of Yb is presented from the viewpoint of chemical separation and instrumental improvement.

Petrological Evolution and Mass Redistribution in Basaltic Fault Zones: An Example From the Faroe Islands, North Atlantic Igneous Province

AbstractFault rock petrology exerts an important influence on the permeability structure and mechanical properties of fault zones. Slip‐related deformation on upper‐crustal faults in basaltic rocks is closely associated with fluid‐rock interaction, altering the distribution of physical properties within the fault. Here, we present quantitative descriptions of the geochemical and petrological evolution of basalt‐derived fault rocks from three passively exhumed fault zones in the Faroe Islands. Fault‐rock petrology is determined by optical petrography and automated phase identification based on micrometer‐scale chemical maps from scanning electron microscope X‐ray spectroscopy. Geochemical evolution is assessed from major and trace element composition measured by X‐ray fluorescence. The fault rocks show intense fluid‐mediated alteration from a tholeiitic basalt protolith in the damage zones, and mechanical mixing in the fault cores. Pervasive alteration occurs early during fault zone evolution, with incipient fault damage increasing permeability and allowing along‐fault percolation of carbonated meteoric water, increasing fluid‐rock ratios. Our results suggest that the only mobile species within the fault zones are Ca, Si, and Al, which are leached during the hydrolysis of volcanic glass and plagioclase, and CO2, which is added by percolating waters. These species are transported from the damage zones into the fault cores, where they precipitate as zeolite and calcite cement in veins and hydrothermal breccias. We propose that solutes are replenished by cement dissolution through pressure‐solution during cataclastic creep, during repeated cycles of hydrofracture and cementation. The fault zones are natural reactors for fluid‐mediated alteration by CO2 and water, while other species are redistributed within the fault zones.

The Oklo phenomenon, the discovery, first questions and first answers.

The discovery in Nature of 16 reactions zones where sustained fission chain reaction occurred 1.95 b.y ago raised numerous questions in many scientific fields. Fifty years later, some of them are still unanswered. This article recalls the history of this discovery and the scientific facts before discussing the present-day understanding of this complex phenomenon.

The influence of some rare earth elements as neutron absorbers on the inception of Oklo natural nuclear reactors.

A totally reflected core model was built to estimate the infinite multiplication factor ${{k}}_{{\infty}}$ as a parametric function using MCNP code. Thus, it was possible to evaluate the influence of a specific physical parameter on the criticality occurrence of the Oklo phenomenon, namely initial Poisons (IP: Gd, Sm and Nd). In fact, these rare earth elements, prior to criticality occurrence in Oklo reaction zones (RZs), are considered as a key parameter in the present study. Thus, it was possible to construct isocritical lines, ${{k}}_{{\infty}}\left({{V}}_{{UO}{2}},{{\varPhi}}_{{C}}\ \right)\cong{1}$, over a significant range of Uraninite volume fraction: ${{V}}_{{UO}{2}}\left[\%\right]{\in}\left[{0};{40}\right]$. The corresponding critical porosity ${{\varPhi}}_{{C}}$ is obtained for a given value of ${{V}}_{{UO}{2}}$ by Python-driven MCNP5 calculations. By including realistic measurements of IP for different RZs, it was possible to distinguish the corresponding inception circumstances for the natural RZs considered here.

Parallels between natural Oklo reaction zones and industrial reactors dynamics.

The first man-made nuclear reactor was developed by Fermi and collaborators at the University of Chicago and reached criticality in December 1942. This was the confirmation that men were able to use sustained fission reactions in order to produce energy. Following this success, nuclear reactors studies gave rise to several families of reactors corresponding to different orientations and technical choices. They are linked mainly to the choice of fuel (natural uranium, enriched uranium, plutonium, thorium), coolant (water, carbon dioxide, helium, sodium, ...) and moderator for slow neutron reactors (graphite, light water, heavy water). Out of all these choices, the pressurized water reactor (PWR) family is the closest to the Oklo natural reactors. Many intriguing similarities are observed and discussed in the present article. Our present-day understanding of the PWR operating conditions has been a great help for understanding the Oklo reactors.

Oklo natural fission reactors and dynamical models of dark energy.

Bounds on the cosmological variation of the fine structure constant α inferred from Oklo neutron capture dataare sometimes taken cum grano salis. It is possible to quantify uncertainties related to the treatment of excitation, deformation and the Coulomb interaction. On the basis of this analysis, it is concluded that Oklo data imply the relative change in α over the last 1.9 billion years is < 0.01ppm (95% CL). Accommodation of this constraint represents a challenge to dark energy models that predict that fundamental constants do change.

Oklo: historic and lessons learned

Abstract Two outstanding phenomena have taken place in earlier geological era where Gabon is now located: the presence of natural nuclear reactors and the appearance of a very elaborated form of life for its age. Calculations performed to establish the sustained fission history of Oklo site are presented first. Second, possible correlations between these two anomalies are discussed. Could the presence of ionizing radiation be the cause of genetic mutations? Today’s isotopic measurements allow us to improve our understanding of the irradiation suffered by organic matter over all times. The first objective is therefore to quantify the possible effects of such ionizing radiation. A second objective naturally appears: the storage of radioactive waste. Calculations issued from the first objective provide access to nuclear reactor waste formations and Oklo is the unique natural analogue of a long-term storage laboratory for nuclear waste. Returning to our primary objective, it is interesting to extend our reflections to other situations of naturally radioactive environments such as very old geological formations or lagoon.

Oklo, our scientific adventure with R. Naudet.

Following several years of studies of the Francevillian basin, I was a specialist of the Gabonese geology. Since the discovery of the Oklo phenomenon, I worked with Roger Naudet, Jean-Paul Pfiffelmann and François Gauthier-Lafaye on this exceptional scientific case. This article relates the beginning of this adventure.

From routine sample measurements in CEA to the Oklo phenomenon.

In 1972, before shipping natural uranium to the USSR for enrichment operations in 235U, the analysts at Pierrelatte plant noted a slight deficit in 235U: 0.7171 instead of 0.7202. The Direction des Productions of the CEA launched a vast campaign of analyses for the different mines exploited, at all stages of the elaboration of uranium; for this analysis campaign, the Direction des Productions relied on the analytical laboratory of the Pierrelatte plant and on the Central Analytical Laboratory of the CEA where I was in charge of analyses by mass spectrometry.

Investigation of clay and neutron absorbers’ roles in the genesis and evolution of Oklo natural nuclear reactors

Investigation of clay and neutron absorbers’ roles in the genesis and evolution of Oklo natural nuclear reactors

Spacetime variation of the s and c quark masses

Space-time variation of fundamental physical constants in expanding Universe is predicted by a number of popular models. The masses of second generation quarks are larger than first generation quark masses by several orders of magnitude, therefore space-time variation in quark masses may significantly vary between each generation. We evaluate limits on variation in the s and c quark masses from Big Bang nucleosynthesis, Oklo natural nuclear reactor, Yb+, Cs and Rb clock data. The construction of 229Th nuclear clock is expected to enhance these limits by several orders of magnitude. Furthermore, constraints are obtained on an oscillating scalar or pseudoscalar cold dark matter field, as interactions of the field with quarks produce variations in quark masses.

Intelligent Optimization Method for Core Flow Zoning of Long-Cycle Lead-Bismuth-Cooled Reactor

Flow zoning is an important way to achieve core outlet temperature flattening. Appropriate zoning can improve safety and economy. This study combines an artificial intelligence optimization algorithm with a parallel multi-channel model to develop a model for calculating reactor core flow zoning based on the modern optimization theory, convergence analysis of a genetic algorithm, differential evolution algorithm, and quantum genetic algorithm is carried out for long-life reactor flow partitioning. Using the optimized algorithm, two flow rates are determined using power distribution at the beginning of the core life as the sample data and the maximum power of each fuel assembly during the entire life as the sample data. Comparative analysis of two different flow zoning schemes is implemented on a small long-life natural circulation lead-bismuth fast reactor, SPALLER-100. The findings of this study show that the quantum genetic algorithm has the best convergence for the long-life reactor among the three intelligent optimization algorithms, and it can quickly provide optimal results. In flow zoning scheme calculations based on the core power distribution at the beginning of reactor life, the maximum outlet temperature of the fuel assembly exceeds the thermal safety limit of the reactor, and in the flow zoning scheme calculations based on the average core power distribution during the whole reactor life, the maximum outlet temperature of the fuel assembly is 140 K lower than the maximum outlet temperature obtained in the previous scheme, remaining below the thermal safety limit. The optimal number of partitions for the SPALLER-100 reactor is determined to be 5, and increasing the number of zones only slightly improved the thermal safety performance of the reactor.

A Thermal Natural Uranium Hyper-Breeder Reactor with Passive Safeguard Designs

A Thermal Natural Uranium Hyper-Breeder Reactor with Passive Safeguard Designs

Использование результатов изучения природных и исторических аналогов для оценки поведения материалов барьеров безопасности при обосновании безопасности захоронения радиоактивных отходов

The article discusses and substantiates the possibility and necessity of applying the findings of studies focused on natural and historical analogues in the development of radioactive waste disposal facilities (RWDF) and demonstration of their long-term safety. It explores the issues associated with the behavior of various structural materials used in the construction of RWDF, in particular, those used in the development of engineered safety barrier system (EBS). The article overviews available publications on natural and historical analogues of engineered barrier materials — silicate glasses, native and anthropogenic copper and bronze, iron, alkaline cements, uranium deposits, as well as the system of natural reactors in Oklo considered as an analogue of deep disposal facilities for radioactive waste. It evaluates natural conditions contributing to the preservation of their insulating properties and the containment of radionuclides contained in the radioactive waste (RW) in the system of engineered and natural RWDF barriers. The study concludes that the findings of the studies can and should be used to provide parametric support in computational modeling applied to assess the long-term safety of RW disposal systems.

A Defined Antigen Skin Test for Diagnosis of Bovine Tuberculosis in Domestic Water Buffaloes (Bubalus bubalis)

Bovine tuberculosis (bTB) remains endemic in domestic water buffaloes (Bubalus bubalis) in India and elsewhere, with limited options for control other than testing and slaughter. The prescribed tuberculin skin tests with purified protein derivative (PPD) for diagnosis of bTB preclude the use of Bacille Calmette-Guérin (BCG)-based vaccination because of the antigenic cross-reactivity of vaccine strains with Mycobacterium bovis and related pathogenic members of the M. tuberculosis complex (MTBC). For the diagnosis of bTB in domestic water buffaloes, we here assessed a recently described defined-antigen skin test (DST) that comprises overlapping peptides representing the ESAT-6, CFP-10 and Rv3615c antigens, present in disease-causing members of the MTBC but missing in BCG strains. The performance characteristics of three doses (5, 10 or 20 μg/peptide) of the DST were assessed in natural tuberculin skin test reactor (n = 11) and non-reactor (n = 35) water buffaloes at an organized dairy farm in Hisar, India, and results were compared with the single intradermal skin test (SIT) using standard bovine tuberculin (PPD-B). The results showed a dose-dependent response of DST in natural reactor water buffaloes, although the SIT induced a significantly greater (P < 0.001) skin test response than the highest dose of DST used. However, using a cut-off of 2 mm or greater, the 5, 10, and 20 μg DST cocktail correctly classified eight, 10 and all 11 of the SIT-positive reactors, respectively, suggesting that the 20 μg DST cocktail has a diagnostic sensitivity (Se) of 1.0 (95% CI: 0.72–1.0) identical to that of the SIT. Importantly, none of the tested DST doses induced any measurable skin induration responses in the 35 SIT-negative animals, suggesting a specificity point estimate of 1.0 (95% CI: 0.9–1.0), also identical to that of the SIT and compares favorably with that of the comparative cervical test (Se = 0.85; 95% CI: 0.55–0.98). Overall, the results suggest that similar to tuberculin, the DST enables sensitive and specific diagnosis of bTB in water buffaloes. Future field trials to explore the utility of DST as a defined antigen replacement for tuberculin in routine surveillance programs and to enable BCG vaccination of water buffaloes are warranted.

Long-term retention and chemical fractionation of fissionogenic Cs and Tc in Oklo natural nuclear reactor fuel

We present the results of a coordinated NAUTILUS and NanoSIMS isotopic study of epsilon (ε) phase metallic aggregates from the Oklo natural nuclear reactor zone (RZ) 13. We observed that fissionogenic Tc and Cs were heterogeneously sequestered within the aggregates. Isotopes of these elements are relevant for improving the safety of spent nuclear fuel storage and reactor operation on generational timescales. Like the noble metals, nearly all of the Tc was retained within the reactor, though its abundance relative to Ru in the metallic aggregates varied by a factor of 10. The neutron fluence estimated from the production of 100Ru from neutron capture on 99Tc was estimated to be up to 1.2 × 1021 n·cm-2. In contrast to Tc, nearly all of the fissionogenic Cs in the reactors was lost from the reactor fuel. The metallic aggregates contain the only phases yet identified to have sequestered radiocesium. Fissionogenic Cs isotopes decay over vastly different timescales, but were incorporated and retained within the ε-phase in proportions similar to stable 133Cs. This indicates that retention began during criticality and sequestration lasted billions of years, despite local geologic activity and the presence of nearby magmatic dikes. Using fissionogenic Ba isotopes, we estimated that the metallic aggregates continually incorporated their radioactive Cs parents during criticality, though the majority of Cs was flushed out of the reactor on a characteristic timescale of 2.7 ± 0.6 years. We found that the abundance of Bi was correlated to Rh and Pd, and speculate that this may have been due to primary Np–Rh and Np–Pd alloys forming during or shortly after criticality. Using Pb–Pb data from uraninite and galena grains surrounding the metallic aggregates, we also inferred a final Pb mobility age of 298 Ma for RZ13, which is more recent than most estimates from other RZs.

Limited expression of the Paleoproterozoic Oklo natural nuclear reactor phenomenon in the aftermath of a widespread deoxygenation event ~2.11–2.06 billion years ago

The only known case of natural fission reactors is hosted by high-grade uranium (U) deposits at Oklo-Okelobondo and Bangombé in sandstones of the ~2.1 Ga Francevillian Group, Gabon. However, the geochemical influence of the depositional environment on this unique natural nuclear phenomenon has not been clearly established. Localized, unusually high vanadium (V) enrichments are thought to have prevented such natural nuclear fission reactors from occurring in other Francevillian U deposits (e.g., Mounana, Boyindzi, and Mikouloungou). However, while U-bearing detrital monazite derived from Archean rocks surrounding the Francevillian basin is viewed as the main source of U, the source of V remains poorly constrained. Here, we combine petrographic and whole-rock geochemical data for the Francevillian Group sedimentary rocks, coupled with previously documented geochemical data for the Archean basement. These data suggest that, although ultramafic to mafic igneous rocks of the Mesoarchean Bélinga Group, and to some extent Archean granitoids, were likely important sources of V to the Francevillian U deposits, they were not the only source of the abnormally high V concentrations in the U deposits that did not produce natural nuclear reactors. Instead, hydrocarbon migration from V-rich black shales of the Upper Francevillian Group, deposited during widespread and protracted deoxygenation of the Paleoproterozoic ocean at the end of the Lomagundi Carbon Isotope Excursion (LE) at ~2.11–2.06 Ga, resulted in a redox front that precipitated the U deposits. These migrated V-rich hydrocarbons likely account for the high V concentrations, which ultimately prevented natural fission reactions from occurring in these U deposits. Similarities with other pyrobitumen-bearing Paleoproterozoic U deposits worldwide suggest that organic-rich source rocks, which deposited in open-marine settings under widespread hyper-euxinic conditions in the aftermath of the LE, played a key role in preventing the Oklo natural nuclear reactor phenomenon from reaching a larger extent.

Subsoil Natural Physico-chemical Reactor: The Property of Deep Abiogenic Methane-Containing High-Thermobaric Fluid to Form Coal Seams

Subsoil Natural Physico-chemical Reactor: The Property of Deep Abiogenic Methane-Containing High-Thermobaric Fluid to Form Coal Seams