Insight into the cationic charge distribution in U1 y zPuyAmzO2±x mixed oxides
Résumé
Uranium-plutonium mixed oxides, containing few mol.% of Am from the multi-recycling of Pu, are currently studied as fuel for Sodium Fast Reactors. The study of the O/M ratio of these fuels is of main interest, as its variation can be problematic for the reactor safety. For this purpose, four U1-y-zPuyAmzO2±x samples (0.235 ≤ y ≤ 0.39 and 0.005 ≤ z ≤ 0.02) were studied using EPMA, XRD and XAS experiments. EPMA analyses revealed a homogenous matrix phase with few U- and Pu-rich agglomerates. A matrix phase of fluorite structure (face centred cubic), as well as a UO2 phase of same structure, was evidenced for all the samples by XRD. The O/M ratios were calculated based on the obtained lattice parameters. XANES experiments highlighted the simultaneous presence of U5+ and Pu3+/Am3+ for all the samples, indicating a charge compensation mechanism even for stoichiometric samples. Based on the EPMA and XRD results, it was evidenced that this coexistence of U4+, U5+, Pu3+, Pu4+ and Am3+ was not originating from the U- and Pu-rich agglomerates but was rather a peculiarity of the U1 y zPuyAmzO2±x matrix phase.