Thermal expansion and thermal conductivity of (Th,Ce)O2 mixed oxides: A molecular dynamics and experimental study

Thermal expansion and thermal conductivity of ThO2 and (Th,Ce)O2 mixed oxides (MOX) have been investigated by using molecular dynamics (MD) simulation and experimental study. The MD simulations have been performed on ThO2, CeO2 and (Th,Ce)O2 using Coulomb-Buckingham type potential function with partial ionic charges. The interatomic potentials of ThO2 and CeO2 are derived in this study and special quasirandom structures are employed to establish solid solution configurations. In order to evaluate the effect of inhomogeneous distribution of CeO2 in ThO2 matrix and change in oxygen to metal ratio (O/M) on thermal properties of MOX, the samples of (Th,Ce)O2 were prepared by conventional powder metallurgy route as well as coated agglomerate pelletization (CAP) route and sintered in air as well as Ar-H2 atmospheres. The thermal expansions of ThO2 and (Th,Ce)O2 (3, 5 and 8 wt% CeO2) are measured using dilatometry and thermal diffusivities of ThO2 and ThO2-5 wt% CeO2 were measured using a laser flash technique. The experimental results of thermal properties of (Th,Ce)O2 showed good correlation with those of MD simulations. It was found that the effect of inhomogeneity on thermal expansion and conductivity was not very significant, while porosity as well as O/M (stoichiometry) of the pellet majorly affected thermal properties.