Influence of the PuO2 content on the sintering behaviour of UO2-PuO2 freeze-granulated powders under reducing conditions

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 degrees 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 seems 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 whatever the Pu content. 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/(U + Pu) content, the sintered microstructure of 98 % dense samples possesses a homogeneous distribution of plutonium and uranium cations.

Automated summary

The sintering behavior of freeze-granulated UO2-PuO2 powders with different Pu content was studied, revealing that densification was controlled by grain boundary diffusion and grain growth by the grain boundaries. The sintered microstructure of samples with 98% density exhibited a homogeneous distribution of plutonium and uranium cations, independent of the Pu content.