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. •Raman spectroscopy is highly reliable for evaluating the (U, Pu)O2 fuel oxidation.•The higher the Pu content, the more the oxidation of the dioxide matrix is hindered.•M4O9 is the intermediate stable phase found before oxidising to M3O8 (M = U, Pu).