Prediction and Analysis of Pressure Pulsation Inside a Mixed-flow Diffuser Reactor Coolant Pump

The pressure pulsation inside reactor coolant pump (RCP) is much more complex than that inside a general mixed-fow pump due to its structure and actual operating conditions. It is necessary to understand the pressure pulsation behavior and figure out its characteristics at different operating conditions in order to meet the requirements of high reliability and safety in both design and operation phases. To seek the relationship between the pressure pulsation characteristics and operating conditions, pressure pulsation behavior inside the impeller and guide vanes was carefully investigated by using 3D transient flow simulations of the completed pump at 5 operating conditions, and the time-domain and frequency-domain characteristics of pressure pulsation at different locations inside the RCP were analyzed. It has been shown that the dominant frequency of pressure pulsation is mainly governed by the blade-passing frequency(BPF) due to rotor-stator interaction (RSI) between the impeller blades and guide vanes at all operating conditions, and the amplitude of pressure pulsation mainly depends on the operating discharges and reaches the smallest level in the design operating condition. For an RCP with spherical casing, the amplitude of pressure pulsations inside the impeller increases from inlet to outlet, which reaches the maximum value between the impeller and guide vanes, and then decreases from inlet to outlet of guide vanes. The behavior of pressure pulsations at the inlet of the impeller in circumferential direction is not the same and the pulsations are more intensive on the suction side than that 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 guide vanes. 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 diffusers under 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 pulsation inside the whole flow channel distinctly increases when the RCP is operating at extreme small discharge. The spherical casing does has influence on the pressure pulsation inside the impeller and guide vanes, the effect is great under small discharge operating conditions but is relatively poor inthe design and large discharge operating conditions.