Solubility limits and bulk thermal expansion of ThO 2:M n+ (M=Y 3+, Sr 2+ and Ba 2+)

Abstract

In order to simulate the bulk thermal expansion behaviour of ThO 2 containing different amounts of fission products, a series of mixed oxides of ThO 2 and oxides of some major fission products (Ba 2+, Sr 2+ and Y 3+) 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 Y 3+ was shown to have the opposite effects on thermal expansion behaviour of ThO 2; e.g., in the presence of 12.5 mol% of Y 3+, the average linear thermal expansion coefficient α (293–1123 K) of ThO 2 decreased from 9.04×10 −6 to 8.27×10 −6 K −1. On the other hand, in the presence of 10.0 mol% of Ba 2+, the α (293–1123 K) of ThO 2 increased to 9.65×10 −6 K −1.