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Benarib S, Munoz M, Kieffer I, Hazemann JL, Dacheux N, Clavier N. Reductive hydrothermal conversion of uranyl oxalates into UO 2+x monitored by in situ XANES analyses. Dalton Trans 2024; 53:13982-13995. [PMID: 39101845 DOI: 10.1039/d4dt01451k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/06/2024]
Abstract
Hydrothermal conversion of actinide oxalates has recently gained attention as an innovative fabrication route for nuclear fuels but has remained mainly limited to tetra- or tri-valent cations. We report herein the reductive conversion of mixtures of uranyl and oxalate ions into UO2+x oxides under mild hydrothermal conditions (T = 250 °C). A multi-parametric study first led to specifying the optimal conditions in terms of pH, oxalate/U ratio and duration to provide a quantitative precipitation of uranium in the hyper-stoichiometric dioxide form with pH = 0.8; R = noxalate/nU = 3, and t = 72 hours. Particularly, pH was evidenced as a key parameter, with 3 different compounds obtained over a range of only 0.4 units. The mechanism leading to the formation of UO2+x was then investigated thanks to an in situ XANES study. Analysis of the supernatant showed that U(VI) was quickly reduced into U(IV) thanks to the presence of oxalates and/or their decomposition products in solution, following first-order kinetics. Tetravalent uranium was then hydrolysed, leading to the precipitation of UO2+x as the only crystalline phase. This study thus demonstrates that the hydrothermal conversion of actinide oxalates into oxides is an extremely versatile tool that can be implemented in a large variety of chemical systems, particularly in terms of the oxidation state of the cations initially present in solution.
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Affiliation(s)
- Sofian Benarib
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze, France.
| | - Maëva Munoz
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze, France.
| | - Isabelle Kieffer
- Université Grenoble Alpes, UAR CNRS 832, OSUG, 38041 Grenoble, France
| | | | - Nicolas Dacheux
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze, France.
| | - Nicolas Clavier
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze, France.
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Massonnet M, Claparede L, Martinez J, Martin PM, Hunault MOJY, Prieur D, Mesbah A, Dacheux N, Clavier N. Influence of Sintering Conditions on the Structure and Redox Speciation of Homogeneous (U,Ce)O 2+δ Ceramics: A Synchrotron Study. Inorg Chem 2023; 62:7173-7185. [PMID: 37133506 DOI: 10.1021/acs.inorgchem.2c03945] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Although uranium-cerium dioxides are frequently used as a surrogate material for (U,Pu)O2-δ nuclear fuels, there is currently no reliable data regarding the oxygen stoichiometry and redox speciation of the cations in such samples. In order to fill this gap, this manuscript details a synchrotron study of highly homogeneous (U,Ce)O2±δ sintered samples prepared by a wet-chemistry route. HERFD-XANES spectroscopy led to determining accurately the O/M ratios (with M = U + Ce). Under a reducing atmosphere (pO2 ≈ 6 × 10-29 atm at 650 °C), the oxides were found to be close to O/M = 2.00, while the O/M ratio varied with the sintering conditions under argon (pO2 ≈ 3 × 10-6 atm at 650 °C). They globally appeared to be hyperstoichiometric (i.e., O/M > 2.00) with the departure from the dioxide stoichiometry decreasing with both the cerium content in the sample and the sintering temperature. Nevertheless, such a deviation from the ideal O/M = 2.00 ratio was found to generate only moderate structural disorder from EXAFS data at the U-L3 edge as all the samples retained the fluorite-type structure of the UO2 and CeO2 parent compounds. The determination of accurate lattice parameters owing to S-PXRD measurements led to complementing the data reported in the literature by various authors. These data were consistent with an empirical relation linking the unit cell parameter, the chemical composition, and the O/M stoichiometry, showing that the latter can be evaluated simply within a ± 0.02 uncertainty.
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Affiliation(s)
- Malvina Massonnet
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze 30207, France
| | - Laurent Claparede
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze 30207, France
| | - Julien Martinez
- CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, Bagnols-sur-Ceze 30207, France
| | - Philippe M Martin
- CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, Bagnols-sur-Ceze 30207, France
| | | | - Damien Prieur
- Institute of Resource Ecology, Helmholtz Zentrum Dresden-Rossendorf (HZDR), 01314 Dresden, Germany
- The Rossendorf Beamline at ESRF - The European Synchrotron, 38043 Grenoble Cedex 9, France
| | - Adel Mesbah
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze 30207, France
- CNRS, IRCELYON, Univ Lyon, Université Claude Bernard Lyon 1, 69626 Villeurbanne, France
| | - Nicolas Dacheux
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze 30207, France
| | - Nicolas Clavier
- ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Bagnols/Cèze 30207, France
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Kvashnina KO, Butorin SM, Wang S, Shi W. Foreword to the special virtual issue on Actinide physics and chemistry with synchrotron radiation. JOURNAL OF SYNCHROTRON RADIATION 2022; 29:1131-1132. [PMID: 36073870 PMCID: PMC9455221 DOI: 10.1107/s1600577522007019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Foreword to the virtual special issue of Journal of Synchrotron Radiation on Actinide Physics and Chemistry with Synchrotron Radiation.
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Affiliation(s)
- Kristina O. Kvashnina
- The Rossendorf Beamline at ESRF, The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France
- Institute of Resource Ecology, Helmholtz Zentrum Dresden-Rossendorf (HZDR), PO Box 510119, 01314 Dresden, Germany
| | - Sergei M. Butorin
- Condensed Matter Physics of Energy Materials, X-ray Photon Science, Department of Physics and Astronomy, Uppsala University, PO Box 516, SE-75120 Uppsala, Sweden
| | - Shuao Wang
- State Key Laboratory of Radiation Medicine and Protection, School for Radiological and Interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, People’s Republic of China
| | - Weiqun Shi
- Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
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