Simulation on Pellet–Cladding Mechanical Interaction of Accident Tolerant Fuel With Coated Cladding

In this study, based on the code Fuel ROd Behavior Analysis (FROBA), a thermal–mechanical analysis code initially developed for traditional UO₂-Zr fuel elements by our research group, a modified version was developed to perform the fuel performance simulation of accident tolerant fuels (ATFs), named FROBA-ATF. 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 nonrigid pellet–cladding mechanical interaction (PCMI) calculation model was established in the new code. The FROBA-ATF code was used to predict PCMI performance of two kind fuels with coated claddings, including the internal surface coating and external surface coating. The calculation result indicates that because the coating surface was close to the inner surface of the cladding 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 external surface-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.