Investigation of the distortion suction flow on the performance of the canned nuclear coolant pump

In AP1000 reactor system, two canned motor pumps are directly attached to the cold side of the steam generator. In order to investigate the effect of the velocity distortion generated by the steam generator on the performance of the two pumps, CFD method is used to simulate the model pump with three different suction flows, one comes from the straight pipe and the other two come from the cold side of the steam generator. The results show that the head of the pump under the left channel head increases by 1.1% while the head under the right channel head decreases by 2.2% when compared to the straight pipe case at design point. The efficiency of the pumps under the steam generator decreases. 3-D flow field at the inlet of the impeller and in the channel head is studied in details and the circumferential velocity induced by the complex geometry upstream in the discharge pipe of the steam generator is analysed which causes the change of the head. The results suggest that the nozzle dam brackets should be installed in the discharge pipe of the steam generator to improve the performance of the pump.