Raman study of the oxidation in (U, Pu)O2 as a function of Pu content

This work presents a systematic Raman study of the matrix oxidation in a variety of (U1-y, Puy)O2 compositions (0 ≤ y ≤ 0.46) at different temperatures, between 250 °C and 400 °C. Our results indicate that the increase in Pu content hinders the oxidation process of the dioxide matrix. Further oxidation of the uranium-plutonium mixed dioxides in air starts between 250 °C and 310 °C, on a time scale of several hours. M4O9 seems to be the most stable intermediate phase formed upon oxidation of all the investigated mixed oxides, before final oxidation to M3O8. In addition, X-ray diffraction measurements and SEM images confirm the trend observed by Raman spectroscopy, i.e. Pu stabilises the fcc structure of the dioxide.