Uraninites of the Oklo Reactors: O Isotopes and Mineralogical Data

1997 ◽  
Vol 506 ◽  
Author(s):  
L. Pourcelot ◽  
F. Gauthier-Lafaye
Keyword(s):  
Spent Nuclear Fuel ◽  
Fission Products ◽  
Ore Deposits ◽  
Unique Case ◽  
X Ray ◽  
Isotopic Analyses ◽  
O Isotopes ◽  
Clay Matrix ◽  
Oxygen Isotopic ◽  
Fission Reactors

Natural fission reactors located in the uranium ore deposits of Oklo-Okélobondo and Bangombé (Gabon) are a unique case of natural nuclear waste disposal. The Reactor Zones (RZ) (up to fifteen) cores are made of 60% uranium (UO2) embedded in a clay matrix [1]. The uraninites are depleted in 235U and contain fission products. Therefore, they are considered to be good analogues for spent nuclear fuel matrix [2]. The aim of this work is to study the conditions of preservation over a long periode of time of the uraninites which have been sumitted to interraction with fluid having different oxidizing potential. For this purposes mineralogical (X-ray powder diffraction), chemical (electron microprobe) and oxygen isotopic analyses were performed on uraninites from various RZs.

scholarly journals A Review of In Situ Isotopic Studies of the Oklo and Bangombé Natural Fission Reactors Using Microbeam Analytical Techniques

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1060
Author(s):  
Hiroshi Hidaka
Keyword(s):  
Nuclear Reactions ◽  
Fission Products ◽  
Analytical Techniques ◽  
Laser Probe ◽  
The Past ◽  
Isotopic Analyses ◽  
Isotopic Studies ◽  
Reactor Materials ◽  
Fission Reactors

Isotopic analyses of elements in the natural reactor materials have often been performed to understand the distribution behaviors of the fission products and to evaluate the function of nuclear reactions since the first discovery of a natural reactor in 1972. Several types of unique microminerals, including significant amounts of fission products, have been found in and around the Oklo and the Bangombé natural reactors. In the past two decades, microbeam techniques using ion and laser probe facilities have been effectively applied for the in situ isotopic analyses of individual microminerals to investigate the migration behaviors of fissiogenic radioisotopes produced in the reactors. This paper presents a review of interpretations of the isotopic results of microminerals found in and around the natural reactors.

In Situ Isotopic Analysis of Uraninite Microstructures from the Oklo-Okélobondo Natural Fission Reactors, Gabon

2002 ◽  
Vol 713 ◽  
Author(s):  
Mostafa Fayek ◽  
Keld A. Jensen ◽  
Rodney C. Ewing ◽  
Lee R. Riciputi
Keyword(s):  
Spatial Resolution ◽  
Spent Nuclear Fuel ◽  
Spatial Scales ◽  
Ionization Mass ◽  
Near Surface ◽  
Chain Reactions ◽  
Isotopic Analyses ◽  
Fission Reactors

ABSTRACTUranium deposits can provide important information on the long-term performance of radioactive waste forms because uraninite (UO2+X) is similar to the UO2 in spent nuclear fuel. The Oklo-Okélobondo U-deposits, Gabon, serve as natural laboratory where the long-term (hundreds to billions of years) migration of uranium and other radionuclides can be studied over large spatial scales (nm to km). The natural fission reactors associated with the Oklo- Okélobondo U-deposits occur over a range of depths (100 to 400 m) and provide a unique opportunity to study the behavior of uraninite in near surface oxidizing environments versus more reducing conditions at depth. Previously, it has been difficult to constrain the timing of interaction between U-rich minerals and post-depositional fluids. These problems are magnified because uraninite is susceptible to alteration, it continuously self-anneals radiation damage, and because these processes are manifested at the nm to μm scale. Uranium, lead and oxygen isotopes can be used to study fluid-uraninite interaction, provided that the analyses are obtained on the micro-scale. Secondary ionization mass spectrometry (SIMS) permits in situ measurement of isotopic ratios with a spatial resolution on the scale of a few μm. Preliminary U-Pb results show that uraninite from all reactor zones are highly discordant with ages aaproaching the timing of fission chain reactions (1945±50 Ma) and resetting events at 1180±47 Ma and 898±46 Ma. Oxygen isotopic analyses show that uraninite from reactors that occur in near surface environments (δ18O= −14.4‰ to −8.5‰) have reacted more extensively with groundwater of meteoric origin relative to reactors located at greater depths (μ18O= −10.2‰ to −7.3‰). This study emphasizes the importance of using in situ high spatial resolution analysis techniques for natural analogue studies.

Weathering Conditions and Behavior of Fission Products in Oklo Reactors

1997 ◽  
Vol 506 ◽  
Author(s):  
L. Pourcelot ◽  
F. Gauthier-Lafaye
Keyword(s):  
Fission Products ◽  
Fission Reactions ◽  
Clay Layer ◽  
Ore Deposit ◽  
Uranium Ore ◽  
Clay Matrix ◽  
High Concentrations ◽  
And Behavior ◽  
Fission Reactors

Two billion years ago, natural fission reactions occured in the uranium ore deposit of Oklo (Gabon), mainly due to the high concentrations of fissile 235U. At that time, high uranium contents (40-60 % U) allowed reaching criticality when oxidised uranium bearing fluids met reduced fluids accompanying the migration of hydrocarbons. Natural fission reactors consist of a core made of uraninite crystals embedded in a clay matrix (mainly chlorites). The thickness of the clay layer range between few centimetres to 2 meters. Fission products are mostly located in the uraninite grains but newly crystallised minerals such as phosphate minerals, clays and metallic aggregates retain some proportions of migrated fissiogenic elements [1].

Segregation and speciation in the Neogene planktonic foraminiferal clade Globoconella

Paleobiology ◽  
1999 ◽  
Vol 25 (3) ◽  
pp. 383-395 ◽  
Author(s):  
Cynthia E. Schneider ◽  
James P. Kennett
Keyword(s):  
Morphological Evolution ◽  
Evolutionary Divergence ◽  
Clinal Variation ◽  
Near Surface ◽  
Surface Warming ◽  
Isotopic Analyses ◽  
Oxygen Isotopic ◽  
Morphological Differences ◽  
Middle Pliocene ◽  
Water Depths

The origin of the Neogene planktonic foraminifer Globorotalia (Globoconella) pliozea in the subtropical southwest Pacific has been attributed to its isolation resulting from intensification of the Subtropical Divergence (Tasman Front). Oxygen isotopic analyses suggest that, although the Subtropical Divergence may have played a role, the evolution of Gr. (G.) pliozea was facilitated by depth segregation of Gr. (G.) conomiozea morphotypes (low and high conical) during an interval of near-surface warming and increasing thermal gradient. Oxygen isotopic analyses suggest that low conical morphotypes of Gr. (G.) conomiozea inhabited greater depths than high conical morphotypes. Low conical forms of Gr. (G.) conomiozea are considered ancestral to the low conical species, Gr. (G.) pliozea. Oxygen isotopes indicate that Gr. (G.) pliozea inhabited greater depths than its ancestor, Gr. (G.) conomiozea.These data are consistent with depth-parapatric and depth-allopatric models, but not with a sympatric model of speciation. In the allopatric model, reproduction at different water depths acts as a barrier between morphotypes. In the parapatric model, clinal variation along a depth gradient acts as a barrier between morphotypes living at the limits of the gradient. Depth segregation in both models results in genetic isolation and evolutionary divergence. Our data support a correlation between morphological evolution and habitat changes in the Globoconella clade, implying separation of populations as a driving force for morphological evolution.Ecological segregation of morphotypes and species may be related to morphology (height of the conical angle), based on the data from Gr. (G.) conomiozea and Gr. (G.) pliozea. However, morphological differences alone do not necessarily produce depth differences. Large morphological differences between Gr. (G.) pliozea and closely related Gr. (G.) puncticulata did not result in isotopic and therefore depth differences between these species. These species coexisted at the same water depths for nearly 1 m.y. Thus, it is unlikely that the extinction of Gr. (G.) pliozea in the middle Pliocene resulted from competition with Gr. (G.) puncticulata, as previously suggested.

scholarly journals Mineralogy and chemistry of archaeological ceramic fragments from archaeological Dark Earth site in Colombian Amazon

2011 ◽  
Vol 64 (1) ◽  
pp. 17-23 ◽  
Author(s):  
Marcondes Lima da Costa ◽  
Gaspar Morcote Rios ◽  
Mônia Maria Carvalho da Silva ◽  
Glayce Jholy da Silva ◽  
Uliana Molano-Valdes
Keyword(s):  
Brazilian Amazon ◽  
Chemical Characteristics ◽  
Amazon Forest ◽  
X Ray Diffraction ◽  
Aluminium Phosphate ◽  
X Ray ◽  
Clay Matrix ◽  
Archaeological Ceramic ◽  
Colombian Amazon ◽  
Grey Colour

Several Archaeological Dark Earth (ADE) sites have been already found in the Colombian Amazon forest showing high content of archaeological ceramic fragments similarly to those in the Brazilian Amazon represented by Quebrada Tacana site. Their fragments are yellow to grey colour, display a burned clayey matrix which involves fragments of cariapé and coal and ash particles, besides grains of quartz and micas. The clay matrix is made of metakaolinite, quartz, and some mica flakes, chlorite and sepiolite. Cariapé and cauixi spicules are constituted of cristobalite, which is also the main mineral component of the coal and ashes. Although not detected by X-ray diffraction, the phosphate minerals should be present, since the contents of phosphor reach up to 2.90 Wt.% P2O5. Possibly it occurs as aluminium-phosphate, since Ca contents fall below 0.1 Wt.%. These mineralogical and chemical characteristics allow to correlate these ceramic fragments with those found in the ADE in Brazil and reinforce phosphor as an important chemical component, which indicates human activity by the daily use of pottery all over the Amazon region.

scholarly journals X-RAY FLUORESCENCE AND STABLE ISOTOPES ANALYSES OF IKPESHI MARBLE, SOUTH SOUTHERN NIGERIA

2020 ◽  
Vol 10 ◽  
pp. 102
Author(s):  
Phillips Reuben Ikhane ◽  
Olalekan Olayiwola Oyebolu ◽  
Afolabi Omotayo Alaka
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Precipitation Process ◽  
Dolomitic Marble ◽  
X Ray ◽  
Humid Condition ◽  
Major Oxides ◽  
Chemical Index ◽  
Isotopic Analyses ◽  
Chemical Index Of Alteration

Integration of X-ray fluor escence and stable isotope spectrometric techniques for quality assessment and provenance study of exposed marble deposit at Fakunle Quarry, Ikpeshi, South Western Nigeria constitute the fundamental aims of this research. Fourteen fresh (14) marble samples obtained at different localities within the quarry were subjected to geochemical and isotopic analyses to ascertain the quantitative abundance of major oxides and stable isotopes using X-Ray Fluorescence and Thermo Fisher mass spectrometer respectively. The major oxides revealed by XRF analysis of the marble samples are CaO, MgO, SiO2, Al2O3, Fe2O3 and Na2O with percentage composition ranging between 11.66 – 13.25, 7.75 – 9.65, 41.36 – 47.55, 12.36 – 15.23, 7.79 – 10.55 and 1.44 – 1.75respectively. Na2O + K2O value ranges between 1.48 and 1.78.The classification of marble in relation to percentage of calcite-dolomite indicate a percentage range of -5 to 4% and 93-103% for Calcite and Dolomite respectively. Chemical Index of Alteration (CIA) ranges from 45.16 to 51.59 % and Chemical Index of Weathering (CIW) ranges from 46.19 to 52.30 %. Stable isotope ( ? –180) of marble ranges from -10.50 to -7.00 with a corresponding value from 25.50 to 55.33.Interpretation of the overall results indicates an impure quartz-rich dolomitic marble; metamorphosed from a low carbonate sedimentary/meta sedimentary protolith which shallowly precipitated within a passive marginal marine environment under humid condition. The high silica impurity can however be attributed to the inordinate influx of terrigenous sediments during the precipitation process. Weathering effect is minimal on the marble deposit. Conclusively, strong correlation is apparent between the obtained geochemical result and the basement geology of the study area.

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