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 containin g different amounts of fission products, a series of mixed oxides of ThO2 a nd oxides of some major fission products (Ba2+, Sr2+ and Y3+) were prepared and characterized by powder XRD. The upper solubility limit of these dopan ts was determined by following the change in lattice parameters as a functi on of their content. The bulk thermal expansion of the each product was inv estigated from ambient temperature to 1123 K using a dilatometer. The subst itution of alkaline-earth ions and Y3+ was shown to have the opposite effec ts on thermal expansion behaviour of ThO2; e.g., in the presence of 12.5 mo l% of Y3+, the average linear thermal expansion coefficient <(<alpha>)over bar> (293-1123 K) of ThO2 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 Ba2+, the <(<alpha>)o ver bar> (293-1123 K) of ThO2 increased to 9.65 x 10(-6) K-1. (C) 2001 Else vier Science B.V. All rights reserved.