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Effect of the fission products on the kinetics of dissolution of uranium dioxide

Abstract : Studies dedicated to the chemical durability of spent nuclear fuel are usually based on the overall inventory of elements present in solution under various dissolution conditions. However, these studies do not allow identifying and quantifying the role of the different phases present in the solid on the dissolution rates. Therefore, it is necessary to evidence separately the effect of the main fission products incorporated in the uranium dioxide structure or precipitated at grain boundaries on the evolution of the microstructure and the dissolution rates. First of all, different model compounds containing fission products were synthesized from oxalic and hydroxide precursors [1]. Uranium dioxide based compounds with lanthanides molar ratio in the range 1 to 10 mol. % were prepared (with 13 % La; 7.4 % Y; 25.6 % Ce; 12 % Pr; 42 % Nd). Divalent (Ba, Sr) or monovalent (Cs, Rb) cations were also incorporated separately in the UO2 matrix. Finally, samples of uranium dioxide containing 0.6 to 3 mol. % of precipitated platinoids (with 55 % Ru; 9.6 % Rh; 35.4 % Pd) were also obtained. Then, the starting precursors were converted into oxides, pelletized and sintered. The aim of these syntheses and heat treatments was to obtain pellets with fission products amounts, structure and microstructure representative of spent nuclear fuel. Different characterizations have been done. On the one hand, concerning Uranium dioxide based compounds with lanthanides, XRD analyzes allowed to identify the crystal lattice as the CaF2 fluorite structure Pm3 et773;m, characteristic of (+IV) uranium dioxide. On the other hand, concerning the other kinds of fission products, an additional phase was present in addition of the CaF2 fluorite structure Pm3 et773;m. Furthermore to control the total incorporated amount of fission products in the UO2 matrix, X-EDS analyzes on oxides and ICP-AES analyzes of oxides total dissolution were done. A multiparametric study of the dissolution was achieved in concentrate nitric acid in order to simulate the reprocessing conditions and to highlight the effect of the fission products on the overall dissolution rates. Furthermore, the microstructural evolution of the pellets during the dissolution was monitored by ESEM. The aim of the study was to identify the preferential dissolution zones and to allow a better understanding of the impact of the fission products on the dissolution mechanisms.
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Submitted on : Tuesday, March 17, 2020 - 10:52:35 AM
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  • HAL Id : cea-02509794, version 1

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T. Cordara, Stephanie Szenknect, L. Claparede, A. Mesbah, Bruno Corso, et al.. Effect of the fission products on the kinetics of dissolution of uranium dioxide. ATALANTE 2016, Jun 2016, Montpellier, France. ⟨cea-02509794⟩

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