Alpha Self-irradiation effects on structural properties of (U, Am)O_2±δ materials - 03005

One of the main effects of α radiation in crystallized materials is a structural swelling. U_1-xAm_xO_2±δ compounds with different Am/(U+Am) ratios (7.5 ≤ x ≤ 50 at.%) were monitored by X-ray diffraction (XRD) after a heat treatment during several months to observe their lattice parameter evolution with time. The results obtained first evidenced that the fluorite-type structure (Fm-3m) of the compounds remains stable all along the study. The swelling kinetics logically increases with the Am content, but similar kinetics are obtained for all samples after normalization by the sample α activity. The effects of α self-irradiation in terms of structural disorder were also studied based on XRD and XAS data. Micro-strain determined from XRD by the Williamson-Hall method did not exhibit any significant evolution with time (whereas it increases with the Am content). Studies were also dedicated to the behavior of He atoms produced during α decay of ²⁴¹Am. A 5- year-old U_0.85Am_0.15O_2±δ sample was heat-treated up to 1500 K in a Knudsen cell coupled with a mass spectrometer (MS) allowing the quantification of released He. Results show that a first He release occurs around 1000 K, followed by a main one around 1350 K The total quantity of He released during this heat treatment was estimated to represent about 75 % of the He produced by α disintegrations during the sample storage. This short paper is followed by the slides of the presentation