Dynamic measurements on unsteady pressure pulsations and flow distributions in a nuclear reactor coolant pump

Abstract

The operational stability of the nuclear reactor coolant pump (RCP) will directly affect the safety of the nuclear power plants (NPPs). A comprehensive analysis of the dynamic characteristics of the internal flow structure in the RCP is extremely important to assess its operational stability. Because the unsteady pressure characteristics of the spherical casing wall of the RCP and the dynamic flow field inside the RCP are complicated, it is highly demanding to be accurately measured by a reliable approach. Dynamic pressure pulsation and Laser Doppler Velocimetry (LDV) measurements have been carried out on the spherical casing wall and internal flow of the RCP under different operating conditions. Based on the pressure pulsation measurement, it is convinced that different unsteadiness flow structures directly affect the pressure pulsation characteristics, which will generate various excitation signals. The intercoupling between rotor-stator interaction (RSI) and the collision of the fluid discharged from the diffuser with the circulating flow to the casing bottom is the main reason for leading to strong pressure pulsations. Dynamic LDV measurement result shows that there is a significant counterclockwise periodic vortex shedding from the diffuser blade trailing edge, especially under high flow rate (1.2QN), which is also the main reason of strong velocity pulsations. The core of this paper is to comprehensively elaborate the dynamic flow characteristics in such a complex hydraulic machinery through combining multiple dynamic measurement methods. Moreover, an exhaustive understanding of dynamic flow characteristics is the basis for optimizing the RCP. The experimental results can provide ideas and basis for the optimization of the RCP with stable operation characteristics.