Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

Highlights: • Thermophysical properties of U_1-yTh_yO₂ have been systematically investigated by MD. • The potential parameters of thorium ion are determined by the three point method. • Thermophysical properties of U_1-yTh_yO₂ significantly depend on the Th content. • The U_1-yTh_yO₂ exhibits lower thermal conductivity than both pure UO₂ and ThO₂. • A series of consistent equations for thermophysical properties are recommended. The effect of thorium addition on the thermophysical properties of uranium dioxide has been systematically investigated by molecular dynamics (MD) simulation technique in the whole concentration range of thorium and in the temperature range from 300 K to 2100 K. The Born-Mayer-Huggins (BMH) interatomic potential with the partially ionic model (PIM) was used and the potential parameters of thorium ion are derived from the experimental lattice constants data of thorium dioxide by the three point method. The predicted lattice parameter, thermal expansion coefficient, enthalpy, specific heat capacity, and thermal conductivity for the U_1-yTh_yO₂ solid solution all agree well with the available experimental data. The results indicate a significant effect of thorium content on the thermophysical properties of the U_1-yTh_yO₂ solid solution. The lattice parameters are increasing with the thorium content and closely followed Vegard's law, while the thermal expansion coefficient and enthalpy as well as specific heat capacity decrease very clearly with the thorium content. On the other hand, it is found that the U_1-yTh_yO₂ solid solution exhibits lower thermal conductivity than both the pure UO₂ and ThO₂. Additionally, a series of consistent equations for the thermophysical properties of U_1-yTh_yO₂ solid solution are recommended based on the MD data.