UPDATED U3SI2 thermal creep model and sensitivity analysis of the U3SI2-SIC accident tolerant FUEL

Abstract U3Si2 is a candidate accident tolerant fuel (ATF) replacement for UO2. U3Si2’s high uranium density and high thermal conductivity are favorable properties in steady-state and accident conditions. Low power performance of this U3Si2-SiC concept fuel is compared to that of UO2-Zr4 fuels by implementing models that describe the properties of U3Si2 and SiC-SiC into Idaho National Laboratory's (INL) fuel performance code, BISON. Included in these material models is a thermal creep model for U3Si2 based on compressive creep data. The simulated results are in keeping with community knowledge that the U3Si2-SiC concept fuel may serve as a replacement for UO2-Zr4 fuels during steady-state operation, provided the mSiC layer remains under compression. Through a moderate power history and three 24-month fuel cycles, the mSiC layer remains under compressive stress through a burnup of 80 MWd/kgU. During low power operation, failure of the mSiC layer generally occurs prior to significant thermal creep in U3Si2. Generally, U3Si2 creep is temperature sensitive and of little importance at the temperatures and stresses simulated during steady operation and during fuel-to-cladding contact. A parameter variation study including 11,520 individual simulations with variations in nominal fuel thermal creep rate, cladding thermal conductivity, cladding irradiation creep and swelling, cladding gap size, and cladding thickness demonstrated that research priorities for this ATF should revolve around reducing cladding thickness as a means to minimize cladding failure. Generally, despite advances in SiC-SiC compliance, the brittle nature of mSiC excludes U3Si2-SiC for use where fuel cladding contact may occur.