Multiphysics analysis of thorium-based fuel performance under reactor normal operating and accident conditions in a light water reactor

The ThO₂ fuel has higher thermal conductivity and melting boiling point than the UO₂ fuel, which is beneficial to the fast removal of heat and the improvement of fuel melt margin. In this paper, the material properties and thermodynamic behaviors of thorium-based fuel were firstly reviewed, and then the thermal physical properties and the fuel behavior models of Th_0.923U_0.077O₂ fuel and Th_0.923Pu_0.077O₂ fuel have been implemented in fuel performance analysis code FRAPCON and FRAPTRAN. Finally, the performances of Th_0.923U_0.077O₂ fuel, Th_0.923Pu_0.077O₂ fuel and UO₂ fuel under both normal operating conditions and transient conditions (both RIA and LOCA) are analyzed and compared. The thorium-based fuels are found to have lower fuel centerline temperature than that of the UO₂ fuel under normal operating condition, and a delayed pellet-cladding mechanical interaction (PCMI) under both normal operating and transient conditions. Furthermore, the fission gas release, cladding strain and internal fuel energy under transient conditions are found to be lower too. Lastly, the cladding displacement and temperature under transient conditions are also compared. The thorium-based fuel was found to have a higher safety margin and accident resistance than the UO₂ fuel under both normal operating condition and transient accident conditions.