Negative pressure difference evaluation of Lungmen ABWR containment by using GOTHIC

Negative pressure difference of the pressure suppression containments means that the wetwell pressure is greater than the drywell pressure and is an undesired effect to the containment safety. The Wetwell-to-Drywell Vacuum Breakers (WDVBs) are check valves used to mitigate this adverse effect. The Lungmen Nuclear Power Plant in Taiwan is a twin-unit Advanced Boiling Water Reactor (ABWR) plant. There are totally 8 WDVBs in the ABWR containment. In this study, a GOTHIC model is developed to evaluate the negative pressure difference of the Lungmen plant. Sensitivity study on the operable WDVB number is also performed. The results show that there is sufficient margin against the negative pressure difference for the ABWR containment. The design value will not be exceeded unless only one WDVB is operable. Furthermore, the effect of the WDVB leakage on the drywell pressure is evaluated by performing the short-term containment analyses. The peak drywell pressure will be greater than the design value with leakage area greater than 50% of one WDVB area. Based on the results of this study, the current requirement that all WDVBs shall be closed and operable during normal operation ensures the Lungmen containment safety.