New insight into self-irradiation effects on local and long-range structure of uranium-americium mixed oxides (through XAS and XRD)


New insight into self-irradiation effects on local and long-range structure of uranium-americium mixed oxides (through XAS and XRD)

Lebreton, F.; Martin, P. M.; Horlait, D.; Bes, R.; Scheinost, A. C.; Rossberg, A.; Delahaye, T.; Blanchart, P.

Uranium-americium mixed oxides could be used as transmutation targets to lower Am inventory in spent nuclear fuels. Due to 241Am activity, these materials are subjected to α-self-irradiation which provokes structural damages. 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 Am-bearing targets 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 U1-xAmxO2± solid solutions (x = 0.15 and 0.2) aged of 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. Obtained results show that the fluorite-type structure of U-Am mixed oxides withstands 241Am α-irradiation without major damage. Even though an increase of interatomic distance and structural disorder was observed during the first year of storage, the present results show that no further evolution occurs. Furthermore, comparison between long-range and local evolution suggests that α-self-irradiation-induced defects are mainly located in low-ordered domains. The major difference between samples was even found to be related to differences in fabrication conditions. Based on these results, no detrimental factors have been identified for several-year storage of U-Am transmutation targets before irradiation.

Keywords: nuclear fuel; transmutation; uranium; americium; EXAFS; XRD

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Publ.-Id: 20189