The effect of the light reactor water environment on fatigue damage is referred to as environmentally assisted fatigue (EAF). This effect is accounted for by applying an environmental fatigue correction factor, Fen, to calculated fatigue usage. In providing guidelines for calculation of Fen, Revision 0 of NUREG/CR-6909  permits temperature averaging for the case of a constant strain rate and linear temperature response, and permits it in other cases as well, but only if the average temperature used produces results that are consistent with the modified rate approach [1, p. A.5]. Revision 1 of NUREG/CR-6909  modifies this slightly, requiring that the threshold temperature be used in averaging instead of the minimum if the minimum is below the threshold [2, p. A-6]. In both cases, the benchmark for accuracy is the modified rate approach [2, Section 4.4].
In this paper, we use real world examples to compare Fen values based on the modified rate approach with those using average strain rate and temperature. We also examine how to select the rise time used to calculate average strain rate in those cases where it is not obvious. We find that temperature averaging is conservative if rise time and other parameters are correctly selected.