Preventive Measures to Avoid Core Uncovering in Cold Shutdown for Pressurized Water Reactor Nuclear Power Plants

During cold shutdown,the loss of residual removal function（unavailable of the RHR pump） due to the vortex suction or cavitations distinctly increases the core uncovering possibility,which might lead to core meltdown.In order to prevent the core uncovering accident during cold shutdown,the water motion in the reactor primary circuit and the RHR degrade incidents occurred in nuclear power plants in the world are analyzed and the three following preventive measurement are proposed: RCP water level measurement,RHR pump vortex detection and water makeup after loss of RHR function.The measures are based on experiences of Daya Bay nuclear power plant.The Probability Risk Analysis indicates that these three modifications decrease core uncovering efficiently.