Raman study of the surface oxidation in (U, Pu)O$_2$ as a function of Pu content
Résumé
This work presents a systematic Raman study of the matrix oxidation in a variety of (U$_{1-y}$, Pu$_y$)O$_2$ compositions (0 ≤ y ≤ 0.46) at different temperatures, between 250 DC and 400 DC. 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 DC and 310 DC, on a time scale of several hours. M$_4$O$_9$ seems to be the most stable intermediate phase formed upon oxidation of all the investigated mixed oxides, before final oxidation to M$_3$O$_8$. 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.
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