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

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 a (293-1123 K) of ThO 2 decreased from 9.04 x 10 6 to 8.27 x 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 x 10 6 K -1 .