Research on gradient optimization design method for Q-H curve changes of nuclear reactor coolant pump based on energy loss analysis

Variations in the primary circuit temperature of a nuclear reactor can lead to changes in coolant pressure, thereby altering the operating conditions of the reactor coolant pump (RCP). To enhance operational safety, this study introduces the gradient of the Q–H curve variation as a quantitative indicator for evaluating the safety performance of the RCP. Pressure pulsation characteristics at various circumferential positions on the RCPM casing were obtained through model testing, and then analyzed the internal flow structures under different flow conditions. By examining the distribution of entropy production, the primary regions of hydraulic loss in various structural components under off-design conditions were identified. Based on this analysis, a structural optimization method was proposed in which the guide vanes are offset from the centerline of the pump outlet. The optimization results demonstrate that this approach effectively reduces the number of vortices within the pump casing, lowers overall turbulence intensity, and mitigates flow losses under low-flow conditions. Consequently, the hydraulic efficiency has increased by 1.08 %, and the slope of the Q-H curve has increased by 30 %, thereby enhancing the RCP's operational stability and adaptability to varying conditions. These findings provide theoretical support and design guidance for the structural optimization and efficient operation of reactor coolant pumps.