Abstract Environmental penalty factors (Fen) are used for assessment of Environmentally Assisted Fatigue (EAF) in NPP primary circuit components. The Fen factors are regression fitted based on reduced fatigue endurances of laboratory specimens tested in simulated reactor coolant environments and presented as functions of temperature and strain rate for relevant material types and water chemistries. The laboratory results are directly applied in fatigue management to adjust the allowable numbers of fatigue transients in reactor components. Plant operation experience and true ε-N data suggest that excessive conservatism is embedded in the environmental factors determined through stroke-controlled testing of stainless steels and/or transferability of the results (Fen per NUREG/CR-6909). Challenges in determining Fen factors and their transferability to plant operation are discussed in this paper. Possibilities for improvements by mechanism-based modelling of environmental effects are considered.
Seppänen et al. (Sun,) studied this question.