Present study evaluates distribution of .sup.210Pb and .sup.210Po in soil around uranium mineralized region of East Singhbhum district, Jharkhand, India. The overall median activity concentration of ....sup.210Pb and .sup.210Po in soil was observed to be 95 ± 35 Bq kg.sup.-1 and 79 ± 35 Bq kg.sup.-1, respectively. Based on KS test, both the radionuclides follow normal distribution in the study area. The extent of disequilibrium in soil is evaluated using .sup.210Po/.sup.210Pb activity ratio. Also, comparison between cultivated and virgin (uncultivated) lands based on activity concentration of .sup.210Pb and .sup.210Po and .sup.210Po/.sup.210Pb activity ratio has been carried out. Higher median activity concentration of both the radionuclides were observed in cultivated soil compared to uncultivated soil. Comparison of .sup.210Po/.sup.210Pb ratio indicates higher degree of radioactive disequilibrium in cultivated soils (.sup.210Po/.sup.210Pb = 0.70) compared to uncultivated soils (.sup.210Po/.sup.210Pb = 0.99). Further, correlation study indicated significant difference between cultivated and uncultivated soils with respect to .sup.210Po and .sup.210Pb. The observed difference between cultivated and uncultivated soil could be due to physical and chemical alterations of cultivated land during farming practices.
Uranium speciation and physical-chemical characteristics were studied in solids precipitated from synthetic acidic to circumneutral wastewaters in the presence and absence of dissolved silica and ...phosphate to examine thermodynamic and kinetic controls on phase formation. Composition of synthetic wastewater was based on disposal sites 216-U-8 and 216-U-12 Cribs at the Hanford site (WA, USA). In the absence of dissolved silica or phosphate, crystalline or amorphous uranyl oxide hydrates, either compreignacite or meta-schoepite, precipitated at pH 5 or 7 after 30 d of reaction, in agreement with thermodynamic calculations. In the presence of 1 mM dissolved silica representative of groundwater concentrations, amorphous phases dominated by compreignacite precipitated rapidly at pH 5 or 7 as a metastable phase and formation of poorly crystalline boltwoodite, the thermodynamically stable uranyl silicate phase, was slow. In the presence of phosphate (3 mM), meta-ankoleite initially precipitated as the primary phase at pH 3, 5, or 7 regardless of the presence of 1 mM dissolved silica. Analysis of precipitates by U LIII-edge extended X-ray absorption fine structure (EXAFS) indicated that "autunite-type" sheets of meta-ankoleite transformed to "phosphuranylite-type" sheets after 30 d of reaction, probably due to Ca substitution in the structure. Low solubility of uranyl phosphate phases limits dissolved U(VI) concentrations but differences in particle size, crystallinity, and precipitate composition vary with pH and base cation concentration, which will influence the thermodynamic and kinetic stability of these phases.
"This book examines the prospects and challenges of a global phase-out of highly enriched uranium and the risks of this material otherwise being used by terrorists to make atom bombs. Terrorist ...groups, such as Al Qaeda, have demonstrated repeatedly that they seek to acquire nuclear weapons. Unbeknownst even to many security specialists, tons of bomb-grade uranium are trafficked legally each year for ostensibly peaceful purposes. If terrorists obtained even a tiny fraction of this bomb-grade uranium they could potentially construct a nuclear weapon like the one dropped on Hiroshima that killed tens of thousands. Nuclear experts and policymakers have long known of this danger but - so far - have taken only marginal steps to address it. This volume begins by highlighting the lessons of past successes where bomb-grade uranium commerce has been eliminated, such as from Argentina's manufacture of medical isotopes. It then explores the major challenges that still lie ahead: for example, Russia's continued use of highly enriched uranium (HEU) in dozens of nuclear facilities. Each of the book's thirteen case studies offers advice for reducing HEU in a specific sector. These insights are then amalgamated into eight concrete policy recommendations for U.S. and world leaders to promote a global phase-out of bomb-grade uranium. This book will be of much interest to students of nuclear proliferation, global governance, international relations and security studies"--
Uranium,as one of twenty-six kinds of important minerals in China,is strategic resource and energy mineral,which has been thoroughly investigated in the project of National Potential Evaluation of ...Uranium Resource.During the implementation of this project,the authors summarized the metallogenic regularity of uranium resource in China systematically,through the researches of geological characteristics of uranium resource,uranium deposits type（genetic and prediction type）,temporal and spatial distribution,and metallogenic series.Based on the investigation of present situation and progress in uranium exploration,this paper proposes the uranium deposits in China should be divided into 4 classes,9 types,21 subtypes in genetic,and 50 types in prediction;suggests to divide China into 29 uranium metallogenic belts and 20 uranium prospective area,and constructs 20uranium-polymetallic metallogenic series,through summarizing temporal and spatial distribution characteristics and metallogenic regularity of uranium deposits in China.The above research is beneficial to the comprehensive understanding of regional uranium metallogenic regularity,and will direct the uranium exploration in the future.
Small modular reactor's development provides an alternative option for potentially using nuclear power more economically and effectively. SMART is the world's first licensed, integral, small ...pressurised water reactor. However, it should still be optimised for the UK's energy market. This thesis has used the stochastic method Monte Carlo codes MONK and OpenMC to investigate the neutronic related behaviours and assess the proposed optimisations. The numerical models based on both codes have been validated and verified, especially to the open-source code OpenMC. The neutron transport simulation and depletion calculation results show that a beryllium-based reflector material would significantly improve fuel assemblies' utilisation rate at the core edge area. This would give higher power output and reduce the frequency of reactor shutdown and refuelling. In addition to the beryllium oxide reflector, three types of variant fuel layout were designed. They respectively occupy 57,44,28 high enrichment fuel assemblies at different positions. This thesis then proposes two hypothetical construction paths to the staggered build of a giga-watt scale,10 SMART unit power station by combining and switching the core layout. Both paths could self-sustain the reloading fuels and, most importantly, decrease the demand for fresh fuel in every refuelling period.
The eastern boundary region of the southeastern Pacific Ocean hosts one of the world's most dynamic and productive upwelling systems with an associated oxygen minimum zone (OMZ). The variability in ...downward export fluxes in this region, with strongly varying surface productivity, upwelling intensities and water column oxygen content, is however poorly understood. Thorium-234 (.sup.234 Th) is a powerful tracer to study the dynamics of export fluxes of carbon and other elements, yet intense advection and diffusion in nearshore environments impact the assessment of depth-integrated .sup.234 Th fluxes when not properly evaluated. Here we use vessel-mounted acoustic Doppler current profiler (VmADCP) current velocities, satellite wind speed and in situ microstructure measurements to determine the magnitude of advective and diffusive fluxes over the entire .sup.234 Th flux budget at 25 stations from 11 to 16.sup." S in the Peruvian OMZ. Contrary to findings along the GEOTRACES P16 eastern section, our results showed that weak surface wind speed during our cruises induced low upwelling rates and minimal upwelled .sup.234 Th fluxes, whereas vertical diffusive .sup.234 Th fluxes were important only at a few shallow shelf stations. Horizontal advective and diffusive .sup.234 Th fluxes were negligible because of small alongshore .sup.234 Th gradients. Our data indicated a poor correlation between seawater .sup.238 U activity and salinity. Assuming a linear relationship between the two would lead to significant underestimations of the total .sup.234 Th flux by up to 40 % in our study. Proper evaluation of both physical transport and variability in .sup.238 U activity is thus crucial in coastal .sup.234 Th flux studies. Finally, we showed large temporal variations on .sup.234 Th residence times across the Peruvian upwelling zone and cautioned future carbon export studies to take these temporal variabilities into consideration while evaluating carbon export efficiency.
Extraction of uranium from seawater is critical for the sustainable development of nuclear energy. However, the currently available uranium adsorbents are hampered by co-existing metal ion ...interference. DNAzymes exhibit high selectivity to specific metal ions, yet there is no DNA-based adsorbent for extraction of soluble minerals from seawater. Herein, the uranyl-binding DNA strand from the DNAzyme is polymerized into DNA-based uranium extraction hydrogel (DNA-UEH) that exhibits a high uranium adsorption capacity of 6.06 mg g
with 18.95 times high selectivity for uranium against vanadium in natural seawater. The uranium is found to be bound by oxygen atoms from the phosphate groups and the carbonyl groups, which formed the specific nano-pocket that empowers DNA-UEH with high selectivity and high binding affinity. This study both provides an adsorbent for uranium extraction from seawater and broadens the application of DNA for being used in recovery of high-value soluble minerals from seawater.
Uranium (U) is both chemically toxic and radioactive. Uranium mill tailings (UMTs) are one of the most important sources of U contamination in the environment, wherein the mechanisms that control U ...release from UMTs with different granularities have not yet been well understood. Herein, the release behaviours and underlying release mechanisms of U from UMTs with five different particle size fractions (<0.45, 0.45–0.9, 0.9–2, 2–6 and 6–10 mm) were studied with a well-defined leaching test (ANS 16.1) combined with geochemical and mineralogical characterizations. The results showed that the most remarkable U release unexpectedly emerged from UMT2–6 mm; in contrast, the smallest particle size UMT<0.45 mm contributed to the least U release. The predominant mechanism of U release from UMT2–6 mm was the oxidative dissolution of U-bearing sulfides, while abundant gypsum present in UMT<0.45 mm inhibited U release. The study highlights the importance of combined geochemical and mineralogical investigation when performing leaching tests of mineral-containing hazardous materials such as UMTs with consideration of particle size effects. The findings also indicate that elevating the content of gypsum and avoiding the oxidation of sulfides can effectively help immobilize and minimize the residual U release from the UMTs.
•U release capacity and mechanism from UMTs with five particle sizes were revealed.•Elevated U release emerged in UMTs with calcite and pyrite despite large grain size.•Inhibited U release occurred in UMTs with abundant gypsum despite small grain size.•The results have implications for the remedial measures towards UMTs leaching hazards.
Advances in the quantification of rare earth elements (REE) at the micrometric scale in uranium oxides by laser ablation‐inductively coupled plasma‐mass spectrometry are described. The determination ...of the best analytical conditions was tested using a uranium oxide (Mistamisk) the concentrations of REE in which were previously estimated by other techniques. Comparison between the use of U or Pb as an internal standard clearly showed a diameter‐dependent fractionation effect related to Pb at small crater diameters (16 and 24 μm), which was not found for U. The quantification of REE contents in uranium oxide samples using both matrix‐matched (uranium oxide) and non‐matrix‐matched (NIST SRM 610 certified glass) external calibrators displayed no significant difference, demonstrating a limited matrix effect for REE determination by LA‐ICP‐MS. Moreover, no major interferences on REEs were detected. The proposed methodology (NIST SRM 610 as external calibrator and U as internal standard) was applied to samples from uranium deposits from around the world. The results showed that LA‐ICP‐MS is a suitable analytical technique to determine REE down to the μg g−1 level in uranium oxides at the micrometre scale and that this technique can provide significant insights into uranium metallogeny.
Une avancée pour la quantification des éléments de terres rares (ETR) à l'échelle micrométrique dans les oxydes d'uranium par ablation laser couplée à un spectromètre de masse à source plasma est décrite dans le présent papier. La détermination des meilleures conditions analytiques est premièrement testée sur un oxyde d'uranium (Mistamisk) pour lequel les concentrations en ETR ont été antérieurement estimées par d'autres techniques. La comparaison entre l'utilisation de U ou Pb comme standard interne montre clairement un effet de fractionnement dépendent du diamètre pour Pb à petit diamètre (16 et 24 μm), ce qui n'a pas été observé pour U. La quantification des concentrations en ETR dans un oxyde d'uranium de composition connue en utilisant des materiaux de réferences externes de même matrice ou de matrice différente (verre silicaté certifié NIST SRM 610) ne montre pas de différence significative, démontrant des effets de matrice limités pour l'analyse des ETR par LA‐ICP‐MS. De plus, aucune interférence majeure n'a pu être détectée pour les ETR par LA‐ICP‐MS. La méthodologie proposée (NIST SRM 610 comme standard externe et U comme standard interne) est appliquée à des échantillons en provenance de différents types de gisements mondiaux d'uranium. Les résultats montrent que la technique LA‐ICP‐MS est actuellement une méthode d'analyse localisée efficace pour déterminer des concentrations en ETR, jusqu'à des teneurs de l'ordre du μg g−1, dans les oxydes d'uranium à l'échelle micrométrique, et que cette technique peut apporter des contributions significatives pour la métallogénie de l'uranium.
The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical ...conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria. To determine the effects of aqueous uranyl speciation on uranium bioreduction kinetics, incubations and viability assays with Shewanella putrefaciens strain 200 were conducted over a range of pH and dissolved inorganic carbon (DIC), Ca2+, and Mg2+ concentrations. A speciation-dependent kinetic model was developed to reproduce the observed time series of total dissolved uranium concentration over the range of geochemical conditions tested. The kinetic model yielded the highest rate constant for the reduction of uranyl non-carbonate species (i.e., the ‘free’ hydrated uranyl ion, uranyl hydroxides, and other minor uranyl complexes), indicating that they represent the most readily reducible fraction of U(VI) despite being the least abundant uranyl species in solution. The presence of DIC, Ca2+, and Mg2+ suppressed the formation of more bioavailable uranyl non-carbonate species and resulted in slower bioreduction rates. At high concentrations of bioavailable U(VI), however, uranium toxicity to S. putrefaciens inhibited bioreduction, and viability assays confirmed that the concentration of non-carbonate uranyl species best predicts the degree of toxicity. The effect of uranium toxicity was accounted for by incorporating the free ion activity model of metal toxicity into the bioreduction rate law. Overall, these results demonstrate that, in the absence of competing terminal electron acceptors, uranium bioreduction kinetics can be predicted over a wide range of geochemical conditions based on the bioavailability and toxicity imparted on U(VI) by solution composition. These findings also imply that the concentration of uranyl non-carbonate species, despite being extremely low, is a determining factor controlling uranium bioreduction at contaminated sites.
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