Long-term pressure and temperature analysis and suppression pool mixing of Lungmen ABWR containment

Lungmen Nuclear Power Plant in Taiwan is a twin-unit Advanced Boiling Water Reactor (ABWR) plant. The design-basis accident for the ABWR containment is a double-ended feedwater line break accident, and the long-term containment responses for this accident are calculated using GOTHIC in this study. The wetwell space is modeled in one dimension either in multi dimensions to investigate the pool mixing effect. The suppression pool is cooled by the Residual Heat Removal (RHR) system in a long-term accident. The RHR pumps have suction flow from the pool bottom. The suction flow is cooled by the heat exchangers, and then returns to the pool via the RHR return line. The long-term containment response using GOTHIC agrees with the Lungmen FSAR results. Significant stratification in the wetwell is observed using the one-dimensional model. However, the multi-dimensional wetwell models predict that the suppression pool and the wetwell airspace can be well mixed by the internal convection. The multi-dimensional results also show that using the wetwell spray to return the cooled water can reduce long-term wetwell pressure.