Raman spectroscopy characterization of actinide oxides (U1−yPuy)O2: Resistance to oxidation by the laser beam and examination of defects

Structural changes in four (U1−yPuy)O2 materials with very different plutonium concentrations (0 ⩽ y ⩽ 1) and damage levels (up to 110 dpa) were studied by Raman spectroscopy. The novel experimental approach developed for this purpose consisted in using a laser beam as a heat source to assess the reactivity and structural changes of these materials according to the power supplied locally by the laser. The experiments were carried out in air and in water with or without hydrogen peroxide. As expected, the material response to oxidation in air depends on the plutonium content of the test oxide. At the highest power levels U3O8 generally forms with UO2 whereas no significant change in the spectra indicating oxidation is observed for samples with high plutonium content (239PuO2). Samples containing 25 wt.% plutonium exhibit intermediate behavior, typified mainly by a higher-intensity 632 cm−1 peak and the disappearance of the 1LO peak at 575 cm−1. This can be attributed to the presence of anion sublattice defects without any formation of higher oxides. The range of materials examined also allowed us to distinguish partly the chemical effects of alpha self-irradiation. The results obtained with water and hydrogen peroxide (a water radiolysis product) on a severely damaged 238PuO2 specimen highlight a specific behavior, observed for the first time.