Study on the Fatigue Analysis Technology of the Control Rod Drive Mechanism Considering the Coolant Environment

The US Nuclear Power Management Guidelines RG1.207 require that the design of a new nuclear reactor considered the coolant environment effect on the fatigue life of Class 1 components. Its conventional analysis was first carried out on the lower joint of the control rod drive mechanism of nuclear equipment with ANSYS software. For more reasonable assessment of the fatigue life, the fatigue analysis technology was studied to improve its calculation accuracy. Based on the RCC-M edition 2002 specification, the elastoplastic correction factor (K_e) is modified by separating thermal and mechanical parts. The temperature and pressure transient grouping is considered in the calculation because some transients will not be combined in operation process, which can reduce the conservative margin of the analysis results. Based on the types of environmental fatigue life prediction models, the effect on structural fatigue life was compared. The results show that the modified K_e can significantly reduce the conservatism of fatigue results when the secondary stress amplitude is high and the thermal part dominates. The coolant environment has obvious influence on the fatigue results of austenitic stainless steel, and the results obtained by the NUREG/CR-6909 method are found to be smaller than the one by the JNES method.