title: Actinide Oxidation State and O/M Ratio in Hypostoichiometric Uranium-Plutonium-Americium U0.750Pu0.246Am0.004O2-x Mixed Oxides.
abstract: Innovative americium-bearing uranium-plutonium mixed oxides U1-yPuyO2-x are envisioned as nuclear fuel for sodium-cooled fast neutron reactors (SFRs). The oxygen-to-metal (O/M) ratio, directly related to the oxidation state of cations, affects many of the fuel properties. Thus, a thorough knowledge of its variation with the sintering conditions is essential. The aim of this work is to follow the oxidation state of uranium, plutonium, and americium, and so the O/M ratio, in U0.750Pu0.246Am0.004O2-x samples sintered for 4 h at 2023 K in various Ar + 5% H2 + z vpm H2O (z = ∼ 15, ∼ 90, and ∼ 200) gas mixtures. The O/M ratios were determined by gravimetry, XAS, and XRD and evidenced a partial oxidation of the samples at room temperature. Finally, by comparing XANES and EXAFS results to that of a previous study, we demonstrate that the presence of uranium does not influence the interactions between americium and plutonium and that the differences in the O/M ratio between the investigated conditions is controlled by the reduction of plutonium. We also discuss the role of the homogeneity of cation distribution, as determined by EPMA, on the mechanisms involved in the reduction process.
authors.affiliation: CEA, DEN, DTEC, Centre d'études nucléaires de Marcoule, Bagnols-sur-Cèze F-30207, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Vauchy
authors.affiliation: CEA, DEN, DEC, Centre d'études nucléaires de Cadarache, Saint Paul Lez Durance F-13108, France.
authors.forename: Renaud C
authors.initials: RC
authors.lastname: Belin
authors.affiliation: CEA, DEN, DEC, Centre d'études nucléaires de Cadarache, Saint Paul Lez Durance F-13108, France.
authors.forename: Anne-Charlotte
authors.initials: AC
authors.lastname: Robisson
authors.affiliation: CEA, DEN, DTEC, Centre d'études nucléaires de Marcoule, Bagnols-sur-Cèze F-30207, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Lebreton
authors.affiliation: CEA, DEN, DEC, Centre d'études nucléaires de Cadarache, Saint Paul Lez Durance F-13108, France.|CEA, DEN, DTN, Centre d'études nucléaires de Cadarache, Saint Paul Lez Durance F-13108, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Aufore
authors.affiliation: Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, P.O. Box 510119, 01314 Dresden, Germany.|BM20 Rossendorf Beamline at European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France.
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Scheinost
authors.affiliation: CEA, DEN, DTEC, Centre d'études nucléaires de Marcoule, Bagnols-sur-Cèze F-30207, France.|CEA, DEN, DEC, Centre d'études nucléaires de Cadarache, Saint Paul Lez Durance F-13108, France.
authors.forename: Philippe M
authors.initials: PM
authors.lastname: Martin