Raman spectroscopic study of the structural change of uranium–thorium-mixed oxides before and after oxidation

Abstract

UO2 pellets doped with 1, 5 and 10 mol% Th before and after oxidation were analyzed by using Raman spectroscopy to investigate the Th doping effect on the structural changes during oxidation of UO2. While the Raman spectra of all sample pellets showed a close-to-perfect fluorite structure before oxidation, those of oxidized (U1−yTh y )O2+x (0.03 ≤ x ≤ 0.06) pellets showed distinct defect structures after oxidation at 1150 °C with CO/CO2 = 0.001. The increasing relative ratio of first-order longitudinal optical modes of (U1−yTh y )O2+x with increasing doping levels should represent the defect structure due to the Th doping effect.