Experimental and numerical investigation on the dynamic response of reactor coolant pump rotor under different inflow conditions

In pressurized water reactors, a reactor coolant pump (RCP) is crucial for circulating coolant through the primary loop. However, in advanced passive (AP) reactors, the steam generator and RCP are not connected by a long pipeline, creating a transition section that leads to a non-uniform inflow at the pump inlet. The non-uniform inflow can affect the operational status of a pump, which in turn affects the motion state of the rotor. In this study, the variation of the axis orbit under non-uniform inflow was analyzed through experiments, and it was found that the shape of the axis orbit had undergone significant changes, and the amplitude of the orbit had also increased significantly, particularly in the y direction, where it increased by 88.6%. Subsequently, a combined approach of pump computational fluid dynamics (CFD) analysis and rotor finite element analysis was used to analyze the cause of the axis orbit change. The study revealed the existence of a vortex with a pulsating frequency of approximately 16.4 Hz at the inlet of the non-uniform inflow. This vortex caused the impeller's attack angle to deviate from the design value, resulting in flow separation inside the impeller, an increase in the impeller's radial force, and radial force pulsation at the same frequency as the vortex. The change in the axis orbit was caused by the superposition of the rotor's unbalance mass and radial force pulsation under non-uniform inflow.