Overpressure Analysis of Second-Class Low Temperature Water Compaction in HPR1000

To meet the classification and acceptance requirements of HPR1000 overpressure conditions and to minimize radioactive release under second-class low-temperature water-dense overpressure conditions, a low-temperature brittle fracture limiting function for low-temperature water-dense conditions is proposed. High-reliability automation systems or equipment operated by control units are used in overpressure analysis to prevent the opening of Residual Heat Removal (RHR) safety valves and Pressurizer Safety Valves (PSV). Analysis using THEMIS software establishes an accident condition model and argues for the setting of the limiting function. The analysis results show that the low-temperature brittle fracture limiting function can provide effective overpressure protection for the pressure boundary of the primary circuit under low-temperature water compaction, ensuring the integrity of the reactor system pressure boundary under class II conditions and avoiding radioactive release.