ML16316A014
| ML16316A014 | |
| Person / Time | |
|---|---|
| Issue date: | 03/18/1986 |
| From: | Ward D Advisory Committee on Reactor Safeguards |
| To: | Stello V NRC/EDO |
| References | |
| D860318 | |
| Download: ML16316A014 (2) | |
Text
D860318 Mr. Victor Stello, Jr.
Acting Executive Director for Operations U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Mr. Stello:
SUBJECT:
ACRS COMMENTS ON DRAFT TECHNICAL REPORT ON GUIDELINES FOR BWR COOLANT PRESSURE BOUNDARY PIPING During its 311th meeting, March 13-15, 1986, the Advisory Committee on Reactor Safeguards heard a report of its Subcommittee on Metal Compo-nents regarding the draft report NUREG-0313, Rev. 2, "Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping" (manuscript completed September 1985). We have no objection to the issuance of this report for public comment, and we offer the following three comments on the proposed guidelines.
- 1. We recommend that NUREG-0313, Rev. 2, be modified to limit the fraction of welds in a piping system that can contain cracks larger than acceptable under ASME Section XI IWA-3500 (with or without repairs). This fraction might be set at 25 percent. Cracks in primary piping represent a degradation of the system. Even though each repair is evaluated conservatively, their multiple interaction cannot be treated with any certainty. At some level of cracking, the piping should be replaced instead of patched again.
- 2. Welds made with IGSCC resistant materials can still crack in service, especially in systems without good water chemistry. Thus, we would recommend that weldments not be given "Category A" status (least frequent inspection) unless the IGSCC resistant material is combined with an approved stress improvement treatment or hydrogen water treatment.
- 3. Table 1 of NUREG-0313, Rev. 2, sets the maximum allowable carbon level for sensitization resistant 347NG stainless as 0.08 percent.
This should be reduced to 0.035 percent to aid weldability and prevent the possibility of intense ("knife edge") corrosion at welds.
Subsequent to the public comment period, we expect to review this report together with the public comments and the NRC Staff's response to them.
Sincerely, David A. Ward Chairman
Reference:
Office of Nuclear Reactor Regulation, Division of Engineering, "Techni-
cal Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping," Draft NUREG-0313, Rev.2, manuscript completed September 1985.