Multiphysics analysis of thermal mechanical behavior and tritium migration in FeCrAl and Cr-coated Zircaloy cladding under PWR normal operating and transient conditions

Abstract

Both Cr-coated Zircaloy and the FeCrAl alloy have garnered attention as potential substitutes for PWR cladding materials, due to their impressive qualities, such as robust high-temperature oxidation and corrosion resistance. However, FeCrAl alloy is found to accelerate the tritium permeation throughout the cladding, this heightened tritium permeation prompts easier release from the cladding into the coolant. Consequently, the assessment of material tritium permeation becomes a crucial aspect in fuel performance analysis. In this work, the multiphysics models of Cr-coated Zircaloy and FeCrAl cladding are reviewed firstly. Then the multiphysics models are implemented in CAMPUS code and the validation of tritium migration model is presented. Subsequently, the fuel performance under normal and accident (LOCA and RIA) conditions and the tritium migration in three types of claddings are simulated and discussed. The simulation results show that the utilization of FeCrAl cladding, instead of Zircaloy, results in an overall reduction in fuel temperature under both normal and LOCA conditions. Furthermore, both the Cr-coated Zircaloy and FeCrAl cladding are found to effectively delay the cladding failure time under LOCA condition. However, the total strain of FeCrAl cladding is found to be significantly higher than that of the Cr-coated Zircaloy cladding under RIA condition. And the Cr-coated Zircaloy is found to have better tritium resistance effect than FeCrAl cladding, which greatly reduces the coolant contamination treatment. Therefore, based on the combined consideration of fuel performance and tritium resistance, Cr-coated Zircaloy emerges as the preferred candidate cladding over the FeCrAl cladding.