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Abstract  

This work studied a way to reclaim uranium from contaminated UO2 oxide scraps as a sinterable UO2 powder for UO2 fuel pellet fabrication, which included a dissolution of the uranium oxide scraps in a carbonate solution with hydrogen peroxide and a UO4 precipitation step. Dissolution characteristics of reduced and oxidized uranium oxides were evaluated in a carbonate solution with hydrogen peroxide, and the UO4 precipitation were confirmed by acidification of uranyl peroxo–carbonate complex solution. An agglomerated UO4 powder obtained by the dissolution and precipitation of uranium in the carbonate solution could not be pulverized into fine UO2 powder by the OREOX process, because of submicron-sized individual UO4 particles forming the agglomerated UO4 precipitate. The UO2 powder prepared from the UO4 precipitate could meet the UO2 powder specifications for UO2 fuel pellet fabrication by a series of steps such as dehydration of UO4 precipitate, reduction, and milling. The sinterability of the reclaimed UO2 powder for fuel pellet fabrication was improved by adding virgin UO2 powder in the reclaimed UO2 powder. A process to reclaim the contaminated uranium scraps as UO2 fuel powder using a carbonate solution was finally suggested.

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Abstract  

Feasibility of using fixed bed column of conventional ion exchangers/sorbent and chemical precipitation based processes have been examined for the effective removal of the very low levels of 106Ru activity from NH4NO3 effluent generated during wet processing of rejected sintered depleted uranium fuel pellets. Based on the results, a simple process involving precipitation of cobalt sulphide along with ferric hydroxide was selected and further optimization of process variables was carried out. The optimized process has been found to be highly efficient in reducing 106Ru activity down to extremely low levels.

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Abstract  

Recently authors demonstrated direct dissolution of g-level PHWR UO2 fuel pellet fragments and in situ extraction by TBP-HNO3 and TiAP-HNO3 solutions at atmospheric pressures. Extending the work, similar studies were performed on intact unirradiated PHWR UO2 fuel pellets (~15 g U) with varying compositions of organic solvate of tri-n-butyl phosphate (TBP). It was observed that extent of dissolution was a strong function of organic solution composition TBP·(HNO3)x(H2O)y. Complete dissolution of intact UO2 pellet in a reasonable time was observed only in case of a particular solvate composition.

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Abstract  

Analytical parameters sufficient for identification of nuclear materialof unknown origin have been assayed for a number of examples of uranium dioxidefuel. These parameters comprise isotopic composition of uranium and the morphologyfeatures of a fuel pellet. However, in practice, it occurs that a sample ofan industrial material corresponds frequently to the specification limitsof several suppliers. In order to narrow further a range for potential sources,additional analytical parameters are necessary, such as fuel pellet impuritylevels and surface roughness. In this study we utilise results from the followingnuclear analytical techniques: thermal-ionization mass spectrometry, glowdischarge mass spectrometry and profilometry. By way of example, we demonstratehow these results serve to differentiate the sources of confiscated, vagabondnuclear materials.

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Abstract  

Supercritical CO2 assisted dissolution of metals and metal-oxides and in situ extraction by TBP (or co-solvent) has been reported in literature. However, in this work, the dissolution and in situ extraction by nitric acid solvates of TBP and alternate solvent TiAP has been reported for g-level UO2 (essentially PHWR fuel pellet fragments) feeds at atmospheric pressure without requiring supercritical fluids. Encouraging results were obtained.

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Abstract  

Metal species that are dissolved in water can be transported in the environment, because they can be mobile. Microorganisms can affect metal mobility by excreting organic ligands with high metal affinity. Siderophores are organic ligands with high affinities for Fe3+. They are also able to form complexes with other metals such as actinides. Many countries plan to deposit spent nuclear fuel in deep geological repositories. Microorganisms are present in these subterranean environments and could potentially affect the repository. In this study, the effect of microbial siderophores on the dissolution behavior of two fragments of a spent nuclear fuel pellet was investigated. The commercial hydroxamate siderophore, deferoxamine mesylate (DFAM), and pyoverdin siderophores, isolated from cultures of Pseudomonas fluorescens (CCUG 32456A), were used. DFAM and lyophilized pyoverdins were dissolved in synthetic groundwater to final concentrations of 10 μM and 2.5·10−2 g·L−1, respectively. The fuel pellet fragments were kept in sealed pressure vessels at 10 bars of H2. The pyoverdin solution was first tested, followed by the DFAM solution and the pure synthetic groundwater. Samples were taken on 0, 1, 5, 9 and 14 days after changing the solution in the pressure vessels. The elemental composition of samples was analyzed by means of ICP-MS. The pyoverdin solution maintained significantly higher concentrations of Np and Pu than the pure synthetic groundwater. On the 14th day the concentrations of Np and Pu in the pure synthetic groundwater were 0.01 nM and 0.13 nM, respectively, compared to 0.02 nM and 0.31 nM in the pyoverdin solution. Furthermore, spent nuclear fuel samples were observed to release Ru in the presence of both pyoverdin and DFAM. Hence, it seems that siderophores can form complexes with elements present in spent nuclear fuel.

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glove box system. Besides being radiotoxic the mixed carbide fuel pellets are prone to oxidation and hydrolysis in the presence of oxygen and moisture as well as highly pyrophoric. Hence for carrying out the calorimetric measurements on these radioactive

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