Research on the energy characteristics of reactor coolant pump under flow coastdown transient

Abstract

In order to research the energy characteristics in impeller, guide vane and volute of reactor coolant pump under flow coastdown transient. In four typical states the variation laws of dynamic–static pressure energy and entropy generation in hydraulic components were analyzed under flow coastdown transient. The results show that after the occurrence of flow coastdown transient, the decreasing rate of energy conversion efficiency of impeller is similar that of the rotating speed. With the development of flow coastdown process, the high dynamic pressure energy distribution of impeller deviates to the outlet of impeller. After 0.25TQi, the energy retained by impeller is basically consumed. In guide vane passage, the change of dynamic pressure energy first increases and then decreases, and the static pressure energy firstly decreases and then increases. After 0.75TQi, the diffusivity of the guide vanes to the fluid decreases rapidly. With the development of flow coastdown process, the main working area of guide vane gradually shifts from the middle of guide vane to outlet. High static pressure energy area at guide vane inlet is enlarged and then reduced. With the development of flow coastdown process, the dynamic pressure energy of V2 and V4 at the monitoring points of volute changes alternately, and the dynamic pressure energy of right tongue region of volute gradually exceeds 11.20 m, and the energy conversion effect of volute gradually weakens, and the low static pressure energy region of the right tongue gradually disappears. Compared with other conditions, at 1.0TQi, the loss of dynamic pressure energy in volute is faster, while the reduction rate of static pressure energy is more stable. Entropy generation in reactor coolant pump varies in a similar manner to flow rate and speed, and is closely related to dynamic-static pressure energy. Both Total Entropy Generation (TEG) and per unit volume of entropy generation (Sˈ) eventually approach zero. Entropy generation ratio of volute is much larger than that of other areas, accounting for more than 60%. Guide vane area generates more per unit volume of energy loss than other areas. The flow in impeller under 0.5TQi condition is more stable than that under other conditions. The unstable flow in reactor coolant pump at the initial stage of flow coastdown transient is more severe and has a greater energy loss than under other conditions. After flow coastdown, great damage may occur in the impeller blade inlet area, the guide blade inlet area, the left area of the volute and the volute tongue area.