Comparison of Numerical Analysis Methods of Coolant Environmental Fatigue Based on Strain Rate Control

Abstract

In this paper, the transformed strain rate of environmental fatigue correction factor (Fen), which is used to consider the influence of PWR primary coolant environment on material fatigue, is studied. EPRI’s guideline and the AFCEN’s probationary phase rule (RPP) No.3 of Volume VI in RCC-M 2017 edition provide two different calculation methods of transformed strain rate separately. NUREG CR-6909 gives two versions of prediction models of Fen for Low alloy steel, nickel base alloy and austenitic stainless steel which are the three main materials of the primary circuit system. In this paper, the model and transients of Sample 2 in EPRI’s guideline are selected for calculation and comparison, so as to verify whether the analysis method is reasonable. Firstly, the fatigue analysis in air is carried out, and then based on the combination, the detailed calculation of strain rate is carried out to calculate environmental fatigue results. The analysis results are compared with the results of guideline, and the valuesare close. Then, the main pipeline safety injection nozzle components with small fatigue margin in PWR are selected to carry out environmental fatigue analysis. In the analysis, different methods of calculating modified strain rates are used, and different prediction models in CR-6909 are used. The coefficient of Fen integrated in RPP3 isconsidered, and the effects of various calculation methods on the results are compared. The results show that for austenitic stainless steel, the results of RCC-M RPP3 method are mostly less than those of EPRI guidelines. Compared with the prediction model of NUREG CR-6909 version 0, the prediction model version 1 greatly decreases the Fen results.