Performance evaluation of accident tolerant Cr-coated Zr alloy cladding under accident conditions based on a refined degradation model

A refined coating degradation model that comprehensively considers the phenomena of coating oxidation, diffusion, reduction, and volatilization is used to evaluate the performance of accident tolerant Cr-coated zirconium alloy cladding under accident conditions. The typical accident types of Station Blackout (SBO) and Large Break Loss of Coolant Accident (LBLOCA) are analyzed, with the consideration of three modes of coating failure: Failure in coating oxidation stage, Failure in oxide layer reduction stage, Failure caused by eutectic reaction. For the SBO accidents with relatively long time, the initial coating thickness of 9∼10 μm is recommended, which could provide good protection for zirconium alloy throughout the entire process and trigger the reduction of Cr₂O₃ before reaching Cr–Zr eutectic temperature to inhibit the occurrence of eutectic reaction. For the LBLOCA accidents where the cladding is rapidly heated, eutectic reaction is the dominant factor leading to coating failure, so how to avoid eutectic reaction failure remains to be further studied.