Study on Function Extension of Pressurizer Fast Depressurization System for Gen III PWR NPPs

A nuclear power plant of Gen Ⅲ pressurized water reactor (PWR) in China has installed the pressurizer fast depressurization system for fast depressurization of the primary loop under severe accidents. With respect to this NPP, according to the general method and process of applying the probabilistic safety assessment (PSA) to the NPP design improvement, this study, focusing on the improvement plan of extending the pressurizer fast depressurization system function to the primary feed & bleed for depressurization to enable the use of this system as a standby pressure relief measure for the pressurizer safety valve, performs the PSA modeling and the feasibility evaluation and demonstration. Finally, this study shows that the improvement plan can reduce the core damage frequency of a NPP greatly, without any new negative effect, so the plan is feasible and can be implemented. Consequently, the NPPs should fully tap the potential of existing system equipment to further improve the safety and economical efficiency of NPPs.