Simulation on pellet-cladding mechanical interaction (PCMI) of accident tolerant fuel (ATF) with coated cladding

In this study, based on the code FROBA (Fuel ROd Behavior Analysis), a thermal-mechanical analysis code initially developed for traditional UO2-Zr fuel elements by our research group, a modified version named FROBA-ATF was developed to perform the fuel performance simulation of ATFs with different claddings, including Zr-4, SiC and Zr-4 coated with SiC. Compared with initial version, the cladding could be divided into arbitrary number control volumes with different materials in the new code, so it can be used to perform the calculation for multilayer coatings. In addition, a new non-rigid PCMI calculation model was established in the new code. Neither of the cladding and the pellet was regarded as the rigid body in this study, which means it can provide more accurate prediction compared with the rigid-fuel model in the initial code when Pellet-cladding Mechanical Interaction (PCMI) happened. The FROBA-ATF code was used to predict PCMI performance of two kind fuels with coated claddings, including the internalsurface coating and external-surface coating. The calculation result indicates that because the coating surface was close to the inner surface of the clad where also was the PCMI surface, the absolute value of the combine pressure of internal-surface coated cladding was substantial larger than that of the externalsurface coated cladding, which might be harmful the coating behavior. However, the internal-surface coated mode can provide a protection for alloy due to the isolation from direct contact with fuel pellets, which can result in a much lower equivalent stress of zirconium body during the PCMI.