title: New insight into self-irradiation effects on local and long-range structure of uranium-americium mixed oxides (through XAS and XRD).
abstract: Uranium-americium mixed oxides could be used as transmutation targets to lower Am inventory in spent nuclear fuels. Due to (241)Am activity, these materials are subjected to α-self-irradiation which provokes crystallographic disorder. Previous studies on U-Am mixed oxides gave first insight into α-radiation tolerance of these compounds, but have never been carried out for more than a year, whereas these compounds might be stored up to a few years between fabrication and irradiation. In this work, we study effects of self-irradiation on the structure of U(1-x)Am(x)O(2±δ) solid solutions (x = 0.15 and 0.20) aged 3 to 4 years. Especially, X-ray diffraction and X-ray absorption spectroscopy are combined to observe these effects from both long-range and local perspectives. Results show that the fluorite-type structure of U-Am mixed oxides withstands (241)Am α-irradiation without major damage. Despite the increase of interatomic distances and crystallographic disorder observed during the first months of storage, the present results show that a steady state is then reached. Thus, no detrimental factors have been identified in this study in terms of structural damage for several-year storage of U(1-x)Am(x)O(2±δ) pellets before irradiation. Furthermore, comparison between long-range and local evolution suggests that α-self-irradiation-induced defects are mainly located in low-ordered domains. Based on literature data and present results, the steady state appears related to the equilibrium between radioinduced defect formation and material self-healing.
authors.affiliation: DTEC/SDTC/LEMA, DEN, CEA , F-30207 Bagnols-sur-Cèze Cedex, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Lebreton
authors.forename: Philippe M
authors.initials: PM
authors.lastname: Martin
authors.forename: Denis
authors.initials: D
authors.lastname: Horlait
authors.forename: René
authors.initials: R
authors.lastname: Bès
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Scheinost
authors.forename: Andre
authors.initials: A
authors.lastname: Rossberg
authors.forename: Thibaud
authors.initials: T
authors.lastname: Delahaye
authors.forename: Philippe
authors.initials: P
authors.lastname: Blanchart