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:
sing Appendix VIII-qualified 7/16/12 DG-1408, Page 20 CODE CASE NUMBER TABLE 2 UNACCEPTABLE SECTION XI CODE CASES SUMMARY DATE OR SUPPLEMENT/ EDITION procedures, equipment, and personnel to obtain the necessary data on flaws to ensure that the flaw density requirements of 10 CFR 50.61a are met. Although, under Code Case N-826, a licensee would have examined the full ½-t volume at least once in accordance with Appendix VIII, the NRC staff finds it unacceptable to allow reduction of the examination volume for later inservice examinations because of concerns about detection and sizing accuracy for smaller flaws using the current UT technology. Current UT technology cannot reliably detect and accurately size smaller flaws, which affects the validity of the comparison with the flaw density requirement of 10 CFR 50.61a. In addition, recent experiences at operating plants involving missed defects during examinations that used qualified methods and were conducted in compliance with Section XI, Appendix VIII, have raised concerns about the reliability of ultrasonic examinations. Finally, the reduction from ½ t to ½ inch originated with Code Case N-613. The purpose of the reduction in examination volume was to reduce the number of relief requests caused by the inability to examine the required volume for typical geometries of nozzle-to-vessel welds. The full-penetration vessel welds addressed by Code Case N-826 do not generally have similar geometric restrictions that would prevent an examination of the full ½-t volume. N-840 Cladding Repair by Underwater Electrochemical Deposition in Class 1 and 2 Applications, Section XI, Division 1 Code Case N-840 was developed specifically to address erosion/corrosion concerns in a Korean nuclear facility where cladding damage in the RPV has exposed low-alloy steels. If this were to occur in a U.S. nuclear facility the NRC staff would want to review the particular circumstances on a case-by- case basis. Any licensee that wants to use