Analysis of containment pressure control strategy in HPR1000 NPP under severe accidents

Containment is the last barrier of preventing the release of radioactive fission products in a nuclear power plant (NPP). It has the top priority of its strategy in a severe accident (SA) to ensure the integrity of containment. Generally, there are two ways for the containment heat removal. One is to set exchangers or sprays to cool the atmosphere in the containment like CPR1000. The other is to set sprays out of the steel containment to remove heat like AP1000. After Fukushima Daiichi nuclear accident, mitigation strategies after severe accidents are focused and specific systems of dealing with containment failure threat are required to design in new built NPPs. HPR1000 is a generation-Ⅲ PWR in China, which deployed the dedicated severe accident (SA) system of containment spray to address the above conditions. Containment spray in HPR1000 has two identical trains isolated physically, and each train is capable to reduce containment pressure after severe accidents. The containment spray system cannot start automatically, but only be started by operator during severe accidents. According to the lessons from Fukushima accident, it is hard for the operator to make the right choice in such a high-pressure environment during severe accidents, so the proper start-up time is better given in advance as possible. This paper assesses the effectiveness of the containment spray, conducts sensitive calculations of different start-up time, and discuss the negative effects of containment spray. Based on the calculation results, insights of containment spray strategy are gained for HPR1000 NPP and the proper start-up time for the strategy of containment spray in SAMG are put forward.