Effect of interface control on pressurization deterioration and gas-phase distribution characteristics of a multistage mixed flow nuclear main pump

In case of emergencies such as loss-of-coolant accident (LOCA), high gas volume fractions (GVF) leads to severe pressurization deterioration and failure in mixed flow nuclear main pump (MFNMP), threatening nuclear engineering stability and safety. Two test methods and numerical simulation based on PBM model are used to study the effects of parameters including the interface condition, inlet GVF, rotational speed, and inlet pressure on the overall and inter-stage performance of the multistage MFNMP. The results show that the critical GVF of the pump at its rated rotational speed increases by 74.3 % compared to when pumping tap water by reducing the surface tension at the flow rate of 1.0 Q_BEP. With the increase of booster stage, the gas-phase distribution along the axis presents the characteristics of ‘single peak’ and ‘double peak’, indicating the great difference in the gas accumulation position inside different impellers. When the mass flow rate of the gas phase is small, although the pressurization of the MFNMP decreases with the increase of the liquid flow rate due to the intensification of flow separation, the amplitude of the decrease is smaller than the increase in pressurization amplitude resulting from the elimination of gas accumulation within the impeller. Therefore, the trend of distinct sudden rise in the pressurization curve is observed in the mapping test. Reducing surface tension significantly broadens the range of liquid flows that enable the pump to operate effectively at high pressures. A correlation equation considering fluid physical properties for predicting critical GVF for MFNMP pump is presented.