Study on the transient evolution law of internal flow field and dynamic stress of reactor coolant pump under rotor seizure accident

Abstract

When the reactor coolant pump (RCP) operates under rated conditions, the rotor is suddenly forced to stop rotating in a very short time because of the great resistance moment. This nuclear accident is called rotor seizure accident and is the most extreme nuclear accident in a nuclear power plant. After the rotor seizure accident, the coolant flow rate of the primary circuit system drops sharply, the core temperature rises, and the fuel rod is forced in a danger of deviating from the bubble core boiling (DNB). In this paper, the AP1000 reactor coolant pump is taken as the research object, and the transient transition process under the rotor seizure condition are studied. Firstly, the simulation calculation of bidirectional fluid-structure coupling was verified by experiments. Then on the basis of considering the bidirectional fluid-solid coupling, the numerical simulation method is applied to study the flow law inside the reactor coolant pump and the deformation and stress distribution of the blade under the rotor seizure condition. The results show: the rotor seizure accident condition is a transient transition from a normal pump condition to a reverse turbine condition; when the rotor seizure accident occurs, the high specific pressure energy zone in the pump is gradually transferred from the volute to the inlet section; due to the direct impact of the liquid flow, the impeller is a concentrated area of high stress; high pivot dynamic stress was generated easily at the juncture between the inlet and outlet edges and the front and back cover plates of the impeller, which would transfer with the evolution of the rotor seizure accident.