Development of coupled analysis system for PWR design basis accidents using RETAC and ATHROC

Abstract

A coupled analysis framework based on RETAC and ATHROC was developed to support the safety evaluation of pressurized water reactors under design-basis accident conditions. The framework considers two coupling interfaces: one between the primary coolant system and the containment, and the other between the safety injection system and the primary system. Through data exchange between the two codes, the transient behavior of the reactor coolant system and the containment can be evaluated in an integrated manner. The proposed RETAC–ATHROC coupling scheme was applied to a CPR1000 small-break loss-of-coolant accident accompanied by auxiliary feedwater failure. The results show that the coupled calculation preserves the main thermal-hydraulic response of the primary coolant system predicted by RETAC, while the containment pressure, gas temperature, refueling water storage tank level, and sump water level follow trends consistent with ATHROC predictions. These results indicate that the coupled program can reasonably reproduce the interaction between the primary system and the containment during accident progression. Therefore, the developed method provides a useful tool for integrated safety analysis of PWR plants and supports transient thermal-hydraulic evaluation under coupled system conditions.