Peculiar Behavior of (U,Am)O2鈭捨?/sub> Compounds for High Americium Contents Evidenced by XRD, XAS, and Raman Spectroscopy

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• 作者：Florent Lebreton ; Denis Horlait ; Richard Caraballo ; Philippe M. Martin ; Andreas C. Scheinost ; Andre Rossberg ; Christophe J茅gou ; Thibaud Delahaye
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 19, 2015
• 年：2015
• 卷：54
• 期：20
• 页码：9749-9760
• 全文大小：709K
• ISSN：1520-510X

文摘

In U_1鈥?i>xAm_xO_2卤未 compounds with low americium content (x 鈮?20 atom %) and oxygen-to-metal (O/M) ratios close to 2.0, Am^III+ cations are charge-balanced by an equivalent amount of U^V+ cations while the fluorite structure of pure U^IV+O₂ is maintained. Up to now, it is unknown whether this observation also holds for higher americium contents. In this study, we combined X-ray diffraction with Raman and X-ray absorption spectroscopies to investigate a U_0.5Am_0.5O_2卤未 compound. Our results indicate that americium is again only present as Am^III+, while U^V+ remains below the amount required for charge balance. Unlike lower americium contents, this leads to an overall oxygen hypostoichiometry with an average O/M ratio of 1.92(2). The cationic sublattice is only slightly affected by the coexistence of large amounts of reduced (Am^III+) and oxidized (U^V+) cations, whereas significant deviations from the fluorite structure are evidenced by both extended X-ray absorption fine structure and Raman spectroscopies in the oxygen sublattice, with the observation of both vacancies and interstitials, the latter being apparently consistent with the insertion of U₆O₁₂ cuboctahedral-type clusters (as observed in the U₄O₉ or U₃O₇ phases). These results thus highlight the specificities of uranium鈥揳mericium mixed oxides, which behave more like trivalent lanthanide-doped UO₂ than U_1鈥?i>xPu_xO_2卤未 MOX fuels.