Strategy analysis of beyond design basis accident for typical 1000 MWe NPPs

The time windows for operators under different scenarios of beyond design basic accidents are calculated by RELAP5 and MAAP code, based on small break loss of coolant accident (SBLOCA). The results show that, the time window for SBLOCA without core melt is 1800 s and the time window for the activation of the containment spray is 5400 s. The operator should depressurize the primary loop under severe accidents. According to different prevention purposes, the time window to avoid the core melt is 200 s and the time window to avoid the pressure vessel failure is 3000 s. Through calculation and analysis, the safety features for different scenarios of beyond design basic accident and operator time windows are provided. (authors)