Development of the environmental assisted fatigue assessment method for nuclear plants in digital twin

Abstract

The effect of reactor water for Environmental Assisted Fatigue (EAF) should be evaluated with caution in the fatigue assessment of the Class 1 components while the influence trend of strain rate on environmental correction factor (Fen) and on alternating stress values is often inconsistent. Currently, the influence of the load pairing method on the Fen factor is often ignored in the existing codes. In this paper, the EAF problem is introduced firstly, including the development of EAF and its evaluation methods. Although the main consideration focuses on the method of using the Fen factor to evaluate the EAF problem, the feedback of American experience, the modification of the latest RCC-M Code and the detailed process of EAF evaluation are also discussed. At the end of 2019, the sub-committee of RCC-M Code has launched a benchmark on the topic of the EAF problem based on the 2016 Edition of RCC-M Code which includes recent evaluations in fatigue assessment rules and the results of the benchmark. Then, the Digital Twin Technology (DTT) for the EAF are discussed. The DTT needs to accumulate the basic operating data, firstly. Through the Influence Function (IF) to automatically analyze stress data, the more reasonable operation parameters can be selected to reduce the effect of EAF. Based on the engineering cases, the reliability of the IF and the influence of different load pairing method on the fatigue damage value are analyzed. Lastly, the IF is showed to be accurate enough to be used in the DTT. The analysis case shows that when considering EAF, the existing code assessment method may produce non-conservative results.