Multiphysics Analysis of UN Fuel Performance With a Two-Layered SiC Cladding Under Multiple Operating Conditions in a Light Water Reactor

In recent years, UN fuels have emerged as potential alternatives to UO2 fuels, due to its superior thermophysical properties, such as high thermal conductivity, melting point and fission density. And SiC is considered as one of the new generations of accident-tolerant cladding materials because of its excellent high temperature strength, creep resistance, lower thermal expansion and better irradiation performance. In this paper, the thermal and mechanical properties of the two-layered SiC cladding and UN fuel are reviewed. Then, based on the developed fuel performance analysis code CAMPUS, the multiphysics models of two-layered SiC cladding and UN fuel are implemented into the CAMPUS code. After that, the fuel performance of three fuel cladding systems, UN-two-layered SiC cladding, UN-Zircaloy cladding and UO2-Zircaloy cladding, are simulated and analyzed under both normal operating and accident conditions of PWR. Our calculation results show that using UN fuel can significantly reduce the maximum temperature of the fuel under LOCA condition, resulting in a significant delay in cladding failure time. Thus, the safety margin of the reactor can be improved. After the two-layered SiC cladding is further assembled, the failure time of fuel rod under accident condition is found to be effectively delayed due to better mechanical properties of SiC.