Document: NRC Regulatory Guide
Document ID: a4944d20-ef6e-480b-a45d-14425bedd2e5
Document Type: regulatory_guide
Title: ASME Code Cases Not Approved for Use (Rev. 8)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2219/ML22196A065.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.193
CFR Part: 
CFR Title: 

Content:
ble 2 of the Code Case) are not acceptable because sufficient technical basis has not been provided. • These curves are developed based on a factor of 10 on cycles and a factor of 2 on stress, which are not in agreement with the factor of 12 on cycles and a factor of 2 on stress, as established in NUREG/CR-6909, “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials,” (Ref. 11). The factor of 10 on cycles is technically inconsistent with the factor of 12 in NUREG/CR-6909. The proposed curves are nonconservative relative to the estimates based on the NUREG/CR-6909 procedure. The use of a different set of factors for the consideration of the LWR coolant environmental effects (i.e., a factor of 10 on cycles and a factor of 2 on stress) for the environmental fatigue correction factor (Fen) approach versus the environmental fatigue curves approach is inconsistent from a technical and regulatory perspective. • The technical basis document for the proposed Code Case does not describe the step-by-step process, from beginning to end, on how final design curves for an LWR environment are obtained. The technical basis document does not provide the expression for the best-fit S-N curve of the experimental data and the details of the mean stress correction for each curve and how the proposed design curves were obtained. • The proposed Code Case contains five environmental fatigue curves for carbon and low-alloy steels and five for stainless steels (i.e., the air curve, the worst-case environmental curve, and three other curves for different strain rates). These environmental curves are not consistent with the experimental data. The strain rate dependence for the first three curves is much lower than that observed in experimental data on smooth 9/20/10 DG-1408, Page 8 CODE CASE NUMBER TABLE 1 UNACCEPTABLE SECTION III CODE CASES SUMMARY DATE OR SUPPLEMENT/ EDITION cylindrical or tube specimens or even in the recent Electric Power Research Institute