Analysis and Optimization of Primary Circuit Pressure Drop Caused by RCP Inching for the First Time after Refueling Overhaul in Nuclear Power Plant

After the refueling overhaul of pressurized water reactor nuclear power plant, the first inching of the reactor coolant pump (RCP) will cause a significant decrease in the primary circuit pressure. If the pressure drops below the operating range specified in the technical specifications, there is a risk of RCP cavitation and shaft seal damage, which threatens the safety of the core. In this paper, the mechanism that the primary pressure drops sharply when the RCP is inched for the first time after refueling overhaul in nuclear power plant is analyzed theoretically, and three optimization methods are put forward to control the pressure drop, including determining the timing and principles for shutting down the RCP, determining the starting sequence of the RCP, setting the initial pressure of the primary circuit and using the primary pressure regulating valve to automatically respond quickly. The practical results show that the optimized and improved control method for the inching of RCP can reduce the pressure drop in the primary circuit by 0.2 MPa. The optimized and improved control method of inching RCP established in this study can reduce the risk of cavitation and shaft seal damage of RCP.