Effect of Head Loss on Flow Rate of Spray System and Containment Pressure

Abstract

The loss-of-coolant accident (LOCA) refers to the loss of a reactor coolant due to broken primary pipes in a nuclear power plant, which results in a rapid rise of containment temperature and pressure. The effused coolant flashes into steam because of the high core pressure, increasing the temperature and pressure inside the containment. To avoid the severe containment damage that may be caused by such a high temperature and pressure, a containment spray system is built at the top of the containment. When LOCA occurs, the core spray system will spray and condense the coolant to decrease the temperature and pressure inside the containment. However, as the operating time of the system increases, the water head of the pump built in the containment spray system decreases. A decrease in water head may result in reduction of water flow, and thus, suppress the capability of the spray system. Currently, there are limited studies on how head decline affects the internal pressure of a containment as well as on the safety measures to be employed when such a decrease in water head occurs. In this study, we are going to discuss whether containment spray systems are capable of adequately cooling and regulating the internal pressure of containments when experiencing a decrease in water head. In this study, an incident model LOCA caused by main streamline break was developed using GOTHIC. The heat loss of the wall was simulated by setting a heat sink. The model was validated by comparing it with the final safety analysis report (FSAR) of the Maanshan nuclear power plant (NPP).In this model, the containment spray system is composed of four height levels, each with different flow rates, based on the design of the Maanshan NPP. The boundary condition of the model was obtained by calculating the spraying flow rate of the containment spray system after the loss of water head using user-defined functions in computational fluid dynamics modeling. Then a precise model is built using GOTHIC. The simulation results show that the simulated flow rate is larger than that in the FSAR of Maanshan NPP. Even when the water head decreases, the peak pressure in the containment only increases by a small amount, which does not pose any potential damage to the containment.