Room-temperature oxidation of hypostoichiometric uranium-plutonium mixed oxides U1−yPuyO2−x - A depth-selective approach

In the present work, TGA, XAS and XRD were used to evidence the spontaneous oxidation of biphasic U1−yPuyO2−x samples, with y = 0.28 and 0.45, at room temperature and upon exposure to low moisture and oxygen contents. The oxidation occurs within very short timescales (e.g. O/M ratio increasing from 1.94 to 1.98 within ∼1 μm surface layer in ∼50 h). The combined use of these three complementary methods offered a depth-selective approach from the sample's bulk to its surface and allowed a thorough understanding of the underlying processes involved during the formation of the oxidized layer and of its thickening with time. We believe our results to be of interest in the prospect of fabricating hypo-stoichiometric uranium-plutonium mixed oxides since mastering the oxygen content is a crucial point for many of the fuel properties.