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

In order to study the effects of cationic homogeneity on the life cycle of Th1-xUxO2 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 Th0.5U0.5O2 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.