Investigation of pressure pulsations in a reactor coolant pump with mixed-flow vaned diffuser and spherical casing

Abstract

Pressure pulsations are an important factors that cause unstable phenomena such as vibration and noise in the reactor coolant pump (RCP), which is much more complex than inside a general mixed-flow pump due to its structure and actual operating conditions. It is necessary to figure out its characteristics at different operating conditions in order to meet the high requirements of reliability and safety in both design and operation phases. Pressure pulsations inside the impeller and diffuser vanes was carefully investigated by using 3D unsteady flow simulations of the completed pump at 5 operating conditions. To seek the relationship between the pressure pulsations characteristics and operating conditions, the time-domain and frequency-domain characteristics of pressure pulsations at different locations inside the RCP were analyzed. It has been shown that the dominant frequency of pressure pulsations is mainly governed by the blade-passing frequency due to rotor-stator interaction (RSI) between the impeller and diffuser vanes at all operating conditions, and the amplitude of pressure pulsations mainly depends on the operating discharges. The influence on the peak amplitude of its higher harmonics can be neglected when operating at the design discharge, but cannot be negligible for operating at the smaller discharge. The behavior of pressure pulsations at the inlet of the impeller in circumferential direction is not the same and more intensive on the suction side than the pressure side of a blade at different operating conditions, but it is almost the same at the outlet of the impeller as the interaction between the impeller and diffuser vanes. The maximum amplitude of pressure pulsations mainly depends on the operating discharge and reaches the smallest level at the design operating condition. Due to geometric features of the spherical casing, the vortex flow inside the spherical casing leads to the highly irregular and unsteady pressure pulsations inside flow channel of the impeller and diffuser under the smaller discharge operating conditions, and the amplitude of pressure pulsations in higher frequencies increases with the decreasing of the operating discharge. The amplitude of pressure pulsations inside the whole flow channel distinctly increases when the RCP is operating at the extreme small operating discharge. The spherical casing does have influence on the pressure pulsations inside the impeller and diffuser vanes, the effect is stronger under smaller discharge operating conditions than at larger ones.