Influence of O/M ratio on sintering behavior of (U0.8, Pu0.2)O2±x

The shrinkage of (U0.8, Pu0.2)O2±x pellets was investigated with the help of a thermal dilatometer in isothermal and isochronal heating tests. During shrinkage measurements in isothermal heating, the oxygen-to-metal ratio of the pellets was maintained at a constant value by controlling the oxygen potential in the sintering atmosphere. The influence of the oxygen-to-metal ratio on the sintering behavior was evaluated from the measurement results. Mainly two mechanisms dominated the sintering of mixed oxide pellets. When the oxygen-to-metal ratio was close to the stoichiometric composition, pellet shrinkage progressed at low temperatures of 1200-1600 K, and the shrinkage rate of the pellets drastically changed with a small deviation from stoichiometric composition. The result showed that a diffusion process was dominated during the sintering of near-stoichiometric compositions. On the other hand, the sintering of reduced mixed oxide pellet proceeded at high temperatures of 1600-1900 K, and the shrinkage rate was very low as compared with stoichiometric mixed oxide.