Dynamic structural characteristics of rotor components during the start-up transition of the LFR main coolant pump

The delivery medium of the LFR main coolant pump (MCP) is lead-bismuth eutectic (LBE). During startup, the MCP's impeller encounters direct interaction forces with the high-density LBE, subjecting the rotor to substantial stress. The MCP system utilizes an electric motor with variable current intensities to enable a controlled and gradual startup mode. Accurate prediction of the structural behavior of the MCP during this transient process is critical to ensuring the safe operation of the entire reactor unit. In this paper, we theoretically deduce the transient changes in flow and rotational speed of the MCP under different start-up models. We analyze the transient structural load characteristics of the rotor components using the fluid-structure interaction method. This includes examining the radial and axial loads on the rotor, the stress distribution in critical zones of the rotor, and the transient dynamic stress evolution. The results show that during the start-up process, the highest stress concentration area is located at the root of the impeller blade. The maximum deformation occurs at the intersection of the suction surface of the blade and the hub-covered/shroud-covered area near the blade outlet. A larger start-up torque corresponds to greater start-up acceleration, causing substantial torsional impact on the rotor components. The maximum high-stress zone is primarily found at the junction between the blade and the hub-covered area. Furthermore, the real-time maximum stress value of the impeller during start-up is directly related to the instantaneous speed of the MCP.