Fatigue Assessment of Class 1 Nuclear Power Piping According to ASME BPV Code: Why Other Alternatives?

In this paper, fatigue assessment of Class 1 nuclear power piping according to ASME Boiler and Pressure Vessel Code, Section III, NB-3600, is discussed. Key parameters involved in the fatigue assessment, i.e. the alternating stress intensity S_alt, the penalty factor K_e and the cumulative damage factor U, are addressed. In particular, a so-called simplified elastic-plastic discontinuity analysis for alternative verification when basic fatigue requirements found unsatisfactory, and the procedures for evaluating the alternating stress intensity S_alt, is reviewed. Factors that can significantly affect the reliability and accuracy of the fatigue assessment are examined. It is illustrated that there is a great need of other alternatives to this simplified elastic-plastic analysis procedure. An alternative based on non-linear finite element analysis is suggested. This paper is a continuation of our work presented in ICONE16-21, which attempted to categorize design rules in the code into linear and non-linear rules and to clarify corresponding requirements that can be used in combination with non-linear finite element analysis.