Abstract
The sintering behaviour of freeze-granulated UO2-PuO2 powders containing 33 and 15 mol% Pu/(U+Pu) was investigated under reducing conditions up to 1700 °C. For both compositions, the grain size versus relative density trajectory was constructed. All the experimental points form a single trajectory meaning that a relative density/grain size pair obtained after sintering is independent of the thermal path (heating rate, soak time, soak temperature) and of the Pu content. Exploiting the grain size versus relative density trajectory enabled also to propose that densification was controlled by grain boundary diffusion and grain growth by the grain boundaries. An activation energy around 510 kJ/mol was obtained for densification, which was close to the value reported for the grain boundary diffusion of plutonium cations in U1-xPuxO2 polycrystals. Whatever the Pu content, the sintered microstructure of 98% dense samples appeared homogeneous regarding the distribution of the plutonium and uranium cations.