Development of Green's Function Approach Considering Temperature-dependent Material Properties and its Application

Abstract

About 40% of reactors in the world are being operated beyond design life or are approaching the end of their life cycle. During long-term operation, various degradation mechanisms occur. Fatigue caused by alternating operational stresses interms of temperature or pressure change is an important damage mechanism in continued operation of nuclear power plants. To monitor the fatigue damage of components, Fatigue Monitoring System (FMS) has been installed. Most FMSs have usedGreen's Function Approach (GFA) to calculate the thermal stresses rapidly. However, if temperature-dependent materialproperties are used in a detailed FEM, there is a maximum peak stress discrepancy between a conventional GFA and a detailedFEM because constant material properties are used in a conventional method. Therefore, if a conventional method is used inthe fatigue evaluation, thermal stresses for various operating cycles may be calculated incorrectly and it may lead to anunreliable estimation. So, in this paper, the modified GFA which can consider temperature-dependent material properties isproposed by using an artificial neural network and weight factor. To verify the proposed method, thermal stresses by the newmethod are compared with those by FEM. Finally, pros and cons of the new method as well as technical findings from theassessment are discussed