Impact of the cationic homogeneity on Th0.5U0.5O2 densification and chemical durability

Abstract In order to study the effects of cationic homogeneity on the life cycle of Th 1- x U x O 2 ceramics, including sintering and reprocessing (dissolution) steps, five different ways of preparation were set up, going from the most homogenous oxalic co-precipitation to a mechanical mixture of the parent oxides. Dilatometric experiments evidenced a better sintering capability for the most homogenous compounds obtained through wet chemistry methods while dry chemistry routes led to poor density values (between 80 and 90 %TD). However, the introduction of an additional mechanical grinding step prior to the powders sintering systematically led to the homogenization of the systems. Improved homogeneity also provide a better chemical durability associated with the congruent release of thorium and uranium in solution during dissolution tests of Th 0.5 U 0.5 O 2 samples. However, heterogeneous samples led to incongruent behaviors that can be lowered by introducing a grinding step before the sintered samples preparation. Since the impact of the cationic homogeneity must be followed carefully during dissolution, in operando observations of evolving solid/solution interface by ESEM were performed. They allowed imaging the preferential dissolution of uranium-enriched zones and confirmed the significant impact over dissolution rate of the presence of chemical heterogeneities at the interface.