Solubility limits and bulk thermal expansion of ThO2:Mn+ (M=Y3+, Sr2+ and Ba2+)

In order to simulate the bulk thermal expansion behaviour of ThO2 containing different amounts of fission products, a series of mixed oxides of ThO2 and oxides of some major fission products (Ba2+, Sr2+ and Y3+) were prepared and characterized by powder XRD. The upper solubility limit of these dopants was determined by following the change in lattice parameters as a function of their content. The bulk thermal expansion of the each product was investigated from ambient temperature to 1123 K using a dilatometer. The substitution of alkaline-earth ions and Y3+ was shown to have the opposite effects on thermal expansion behaviour of ThO2; e.g., in the presence of 12.5 mol% of Y3+, the average linear thermal expansion coefficient α-bar (293-1123 K) of ThO2 decreased from 9.04x10-6 to 8.27x10-6 K-1. On the other hand, in the presence of 10.0 mol% of Ba2+, the α-bar (293-1123 K) of ThO2 increased to 9.65x10-6 K-1