Thermodynamic modelling of thoria-urania and thoria-plutonia fuels: Description of the Th-U-Pu-O quaternary system

In this work, a thermodynamic treatment for (Th,U)O₂ and (Th,Pu)O₂ fuels has been developed using the CALPHAD method to describe phase diagram and thermodynamic data of the phases in the Th-U-Pu-O sub-systems. The treatment builds on previously reported assessments of the U-Pu-O ternary oxide system and of the Th-U-Pu ternary metallic system. The thermodynamic and phase diagram properties calculated by the models herein are in good agreement with available experimental data for the binary and ternary subsystems, as well as new phase diagram data for the Th-O binary reported here. This treatment is useful to predict thermodynamic behavior of thoria-based nuclear fuels at various temperatures and compositions.