Document: NRC Regulatory Guide
Document ID: 40fb588c-37f6-474f-b12a-d7be81beefe5
Document Type: regulatory_guide
Title: Guidelines for Evaluating Fatigue Analyses Incorporating the Life Reduction of Metal Components Due to the Effects of the Light-Water Reactor Environment for New Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1417/ML14171A584.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.207
CFR Part: 
CFR Title: 

Content:
e materials, because their use will yield the same or more conservative results. Fen calculations for carbon, low-alloy, austenitic stainless, and Ni-Cr-Fe alloy steels need only consider the types of stress cycles or load set pairs that exceed the strain threshold criteria. The evaluation options depend on the complexity of the analyzed transient conditions and the details of the evaluation. For example, in an evaluation in which the results of detailed transient analyses are available to determine the necessary parameters (strain rate, temperature, and others), the “modified rate approach” (presented and cited in Section 4.1.14 of Revision 1 of NUREG/CR-6909) is an acceptable method for determining the Fen values. This method involves a strain-based integral to evaluate conditions for which temperature and strain rate change, resulting in the variation of Fen over time. This detailed approach calculates the Fen values based on the strain history for each load set in the fatigue analysis evaluation, considering the effects of strain rate and temperature variations for each incremental segment in the strain history. Such results may be used to reduce the conservatism in the calculated Fen values. For a simplified calculation yielding more conservative results for complex or poorly defined transients, the strain rate is equal to the average strain rate in the transient or segment, and the temperature is equal to the maximum temperature in the transient or segment. For such simplification, care should be taken in the selection of temperature, as discussed in Section 4.1.14 of Revision 1 of NUREG/CR-6909. Appendix C to Revision 1 of NUREG/CR-6909 provides a sample problem showing one method of calculating and applying Fen to a CUF calculation. Harmonization with International Standards The NRC staff searched for available guidance from the International Atomic Energy Agency (IAEA) and the International Organization for Standardization (ISO), and did not identify