Reliability Evaluation Method of Stress Corrosion Accelerated by Irradiation of Bolts in Reactor Internals
The connecting bolts of the reactor vessel internals are located near the core area of the primary circuit of the PWR.Due to its long-term operation in harsh working environments,bolt fracture events represented by irradiation assisted stress corrosion cracking(IASCC)occur from time to time.In order to analyze and evaluate the reliability of internal component bolts,a consider-ation bolt IASCC failure reliability assessment method.First,based on the criterion of stress intensity factor in fracture mechanics theory,the limit state functions of SCC and IASCC failure are constructed respectively,and the maximum equivalent stress in the function is solved by simulation analysis method.Secondly,considering the uncertainty of each parameter in the function,the first-order second-moment method is used to solve the reliability of the connecting bolts of internal components.Finally,the M16 bolts used in the pile are used as an example for calculation and analysis.The results show that the fracture toughness and the max-imum equivalent stress on the bolt have the greatest impact on the bolt reliability,followed by the crack propagation coefficient and the crack propagation index,and the initial crack size has the smallest impact on the reliability.This evaluation method can be used for the life prediction and reliability evaluation of various connection bolts in the design of the reactor structure,and can also help determine the safety inspection period and inspection focus of the reactor structure.
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