Analysis of coasting-down hydrodynamic characteristics of sodium pump in the primary circuit of fast reactor

Abstract

The variation of coasting-down hydrodynamic characteristics of the sodium pump in the primary circuit of fast reactor is related to the safe and stable operation of nuclear power plant. In order to explore the variation rule of performance parameters during the coasting-down process, the prototype of the sodium pump (Vertical double suction coaxial in and out submersible pump) in the primary circuit of fast reactor was taken as the research object in this paper. Based on the N-S equation and the RNG k-ε turbulence model, the Fluent software was used. The UDF function was written to carry out unsteady numerical calculation on the coasting-down process of sodium pump, and the variation rule of rotating speed, flow rate, head, torque and pressure with time in the coasting-down process was obtained. The results show that during the coasting-down process，the time for the model pump rotating speed to drop to half (296.5 r/min) is more than 15 s, and the time to drop to the minimum (112 r/min) is more than 74 s, which meets the nuclear safety standards. The flow rate ratio and the rotating speed ratio have the same change law, the head ratio and the torque ratio have the same change law, and the decline speed of the head ratio and torque ratio is greater than the rotating speed ratio and the flow rate ratio, which conforms to the similarity law of the pump. During the coasting-down process, the energy of the model pump pressure pulsation is mainly concentrated at middle and low frequencies. With the increase of the coasting-down time, the amplitude of pressure pulsation decreases gradually, and the uniformity of pressure distribution at circumferential direction decreases gradually. In addition, under the influence of pressure pulsation and the complexity of flow passage of the flow components, the head has a pulsating downward trend.