Abstract The oxidation of UO 2 in Ar–O 2 atmospheres was studied at temperatures between 350 °C and 600 °C and for oxygen partial pressures (pO 2 ) between 0.20 atm and 0.70 atm. The experiments were carried out on both powder samples and discs cut from sintered pellets. Oxidation kinetics were monitored by TGA and the oxides formed were characterised by XRD, SEM and specific surface area (SSA) measurements. Whatever the temperature or pO 2 tested, total oxidation of UO 2 to U 3 O 8 was systematically observed. At all temperatures studied, the conversion of UO 2 to U 3 O 8 seemed to involve the formation of an intermediate oxide, which could be U 3 O 7 . Experiments carried out on powders with different SSA appeared to show that the effect of solid texture predominates over the effect of temperature in the formation (or non-formation) of intermediate oxides. An increase in pO 2 systematically led to an increase in the UO 2 oxidation rate. On the other hand, an increase in the oxidation temperature seemed to cause a decrease in the density of cracks propagating through the samples, probably due to an increase in the plasticity of U 3 O 8 . The inert marker experiment also showed an inward growth of U 3 O 8 involving anionic sublattice point defects.
Berenguer-Besnard et al. (Wed,) studied this question.