Experimental Study on Transient Thermal–hydraulic Characteristics of an Open Natural Circulation for the Passive Containment Cooling System

Nuclear safety has attracted increasing global attention. Passive Containment Cooling System (PCCS) is one of the several passive safety systems designed to ensure the safety of nuclear power plants (NPPs). A large-scale test facility was built to simulate the PCCS for understanding the thermal–hydraulic characteristics with operating conditions in the start-up process. Parameter analysis is carried out to reveal the influences of various parameters on the thermal–hydraulic characteristics. Results show that the transient-state performance of the PCCS strongly depends on the initial containment pressure and air mass fraction. The air mass fraction has a greater effect on the transient heat transfer process. Meanwhile, the effect of cooling water temperature on the transient characteristics can be ignored. The response time, which is defined to characteristic the heat transfer ability of PCCS, is proposed. In addition, a non-dimensional empirical correlation for response time is developed to reveal the relationship between the heat transfer capacity of the natural circulation and forced circulation, while the deviation mostly within ±20%. Studies on the relevant physical processes or phenomena are helpful for the safety analysis or accident study related with PCCS.