Dissolution of morphology-controlled Th1-xUxO2 model dioxides

The influence of the morphology of Th1-xUxO2 solid solutions on their chemical durability was evaluated considering two routes of preparation, involving either direct precipitation of a precursor or hydrothermal conditions. The great differences in terms of morphology and crystallization state of the so-obtained samples were correlated to an important variation of the specific surface area of the final dioxides then to the density of the sintered pellets fired at 1500 deg. C. In order to evaluate the chemical durability of such materials, leaching tests were undertaken. The dissolution of the samples was associated to low normalized dissolution rates typically ranging from 3.10-6 g.m-2.day-1 (HNO3 10-4 M) to 2 10-5 g.m-2.day-1 (HNO3 10-1 M) at 25 deg. C for x equals 0.25. The influence of the x value on the normalized dissolution rate was found to be limited due to the homogenization of the cationic distribution obtained through the precipitation process. Moreover, the good crystallization state initially obtained from hydrothermal conditions led to a higher chemical durability. (authors)