U₃Si₂-SiC fuel performance analysis in BISON during normal operation

Highlights: • An empirically-fit thermal-conductivity damage model for SiC composite layer. • U3Si2-SiC fuel performance simulation in BISON under normal operation. • U3Si2 fuel pellet and SiC cladding deformation were compared to UO₂ and Zircaloy. - Abstract: U₃Si₂-SiC is an accident-tolerant fuel concept currently under development by Westinghouse that has potential to improve economic performance and safety of light water reactors. Since U₃Si₂ fuel suffers from poorer hydrothermal corrosion performance relative to UO₂, it is paramount in an U₃Si₂-SiC fuel rod to lower the stress in the cladding to prevent any inward leakage of coolant. This motivates a detailed fuel-clad analysis of U₃Si₂-SiC during normal operation. The SiC cladding is modeled with a layer of SiC_f/SiC composite followed by a layer of monolithic SiC. The dependence of thermomechanical properties for each SiC layer on temperature and neutron fluence is considered in the BISON fuel performance code. Particularly, pseudo-ductile deformation and anisotropic swelling models of SiC_f/SiC composite are updated. While SiC thermal conductivity is commonly known to decrease as a consequence of irradiation damage, its additional degradation by mechanical damage is also modeled. Owing to limited availability of U₃Si₂ irradiation behavior models and experimental data under power reactor conditions, several assumptions are made to perform the initial detailed assessment of the fuel system. The results show that the fuel rod designs with larger pellet radius, thinner SiC cladding and larger initial gap width (thus larger cladding inner radius) can be beneficial to lower cladding stress during power operation and reactor shutdown.