Investigation of Unsteady Pressure Pulsations of Reactor Coolant Pump Passage under Flow Coast-down

In order to obtain the pressure pulsations of a reactor coolant pump during flow coast-down conditions, the time-domain characteristics of the flow passage under different times of flow coast-down were calculated by numerical calculation. Because the unsteady pressure pulsation signals in the RCP under flow coast-down are non-stationary and some phenomena may only occur in a short time, this paper analyzed them with the wavelet transform. The results show that the pressure fluctuation varies dramatically with the flow coast-down process and the variation rate of the pressure fluctuation coefficient can reach more than 60%. With the development of flow coast-down, there is a strong correlation between the pressure pulsation and number of impeller blades. The main frequency of the pressure pulsation gradually changes from high-frequency pulsation to low-frequency pulsation, and the regularity of the pressure pulsation is quickly destroyed, while the change in pressure pulsation regularity of the guide vane passage is more gentle than that of the impeller and pressurized water chamber. The change in wavelet intensity at the impeller outlet, guide vane inlet, and left side of the pressurized water chamber is more intense than at other areas.