EXPERIMENTAL STUDY ON THE EFFECT OF NON-UNIFORM FLOW ON THE VIBRATION CHARACTERISTICS OF THE REACTOR COOLANT PUMP

In AP nuclear power plants, the reactor coolant pump is connected with steam generator directly instead of a straight pipe section. However, this simplification will cause the flow field at the pump inlet to be non-uniform, which is likely to influence the performance of the pump and cause special vibrations, which will seriously affect the nuclear power plant safe operation. Therefore, it is of great necessity to perform a vibration test in terms of non-uniform flow for pump model. Studies have shown that non-uniform inflow conditions can cause the pump's head and efficiency to drop and the vibration to increase. In the previous test results that we did, experiments are combined with numerical simulations to investigate the influence of the non-uniform flow on the main pump, in which the steady state performance and pressure pulsation characteristic of the pump were compared under two conditions. The vibration data at the pump outlet and the upper bearing are obtained. It was observed from the acceleration time-domain signal, that the amplitude of the acceleration signal of the non-uniform incoming flow in three directions is significantly higher than that of the uniform incoming acceleration signal. The analysis of the velocity signal reveals that the amplitude of the velocity signal flowing nonuniformly in the horizontal direction perpendicular to the pump axis is higher, and the amplitude of the velocity signal of the uniform inflow is lower, but the opposite is true in the direction of the pump axis. Comparing the two inflow conditions, the acceleration amplitude is more than 46 times in the direction of the exit, and the velocity amplitude is more than 21 times. Under uniform flow conditions, there is almost no vibration in the exit direction at the measured point, but a certain vibration is generated under non-uniform inflow conditions. The frequency domain analysis of the vibration signal reveals that low frequency vibration will occur under non-uniform inflow conditions. And the main frequency characteristic of the pump under uniform flow conditions is rotating frequency conversion, while rotating frequency multiplication is observed under uniform flow conditions.