ML073300013
| ML073300013 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 11/19/2007 |
| From: | Bezilla M FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 3380, TAC MD4452 | |
| Download: ML073300013 (7) | |
Text
FENOC ,"oft% 5501 North State Route 2 FirstEnergyNuclear OperatingCompany Oak Harbor,Ohio 43449 419-321-7676 Mark B. Bezilla Fax: 419-321-7582 Vice President - Nuclear Docket Number 50-346 License Number NPF-3 Serial Number 3380 November 19, 2007 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Supplemental Information Regarding Proposed Alternative to American Society of Mechanical Engineers Code Section XI Repair Requirements (TAC No.
MD4452)
Ladies and Gentlemen:
By letter dated February 15, 2007, as supplemented by letters dated June 28, 2007 and September 28, 2007, the FirstEnergy Nuclear Operating Company (FENOC) requested Nuclear Regulatory Commission (NRC) approval of a proposed alternative to American Society of Mechanical Engineers Code Section XI requirements in support of weld overlay repairs for the Davis-Besse Nuclear Power Station (DBNPS).
During a teleconference on October 30, 2007, the NRC noted items that need to be clarified before the request can be approved. To aid the review process, FENOC is supplementing the initial request with replacement pages to address the NRC's concerns.
Attachment 1 contains the replacement pages.
As stated in the February 15, 2007 letter, FENOC requests approval of this proposed alternative to allow installation of the pressurizer weld overlays during the next maintenance and refueling outage, which is currently scheduled to commence in December 2007.
As indicated in Attachment 2, the regulatory commitments associated with the February 15, 2007 request-remain in effect, and no additional commitments are established in this letter. If there are any questions or if additional information is required, please contact Mr. Thomas A, Lentz, Manager - FENOC Fleet Licensing, at (330) 761-6071.
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Docket Number 50-346 License Number NPF-3 Serial Number 3380 Page 2 of 2 Very truly yours, Mark B. Bezilla, Vice Prec,!dent-Nuclear Attachments: 1. Revised Pages for Proposed Alternative to American Society of Mechanical Engineers Code Section XI Repair Requirements
- 2. Commitment List cc: Regional Administrator, NRC Region III NRC/NRR Project Manager NRC Senior Resident Inspector Utility Radiological Safety Board C. O'Claire, Ohio Emergency Management Agency
Docket Number 50-346 License Number NPF-3 Serial Number 3380 Page 1 of 4 Revised Pages for Proposed Alternative to American Society of Mechanical Engineers Code Section XI Repair Requirements The following pages are replacement pages for the Proposed Alternative to American Society of Mechanical Engineers Code Section XI Repair Requirements previously submitted to the NRC on February 15, 2007, as supplemented by correspondence dated June 28, 2007 and September 28, 2007. The specific revised pages are intended to take the place of the relevant pages as indicated below.
Page to be Removed Page to be Inserted 4 of 53 4 of 53 32 of 53 32 of 53 45 of 53 45 of 53
Docket Number 50-346 License Number NPF-3 Serial Number 3380 Page 4 of 53 overlays. The use of weld overlay filler materials that are resistant to PWSCC (Alloy 52/52M), weld overlay procedures that create compressive residual stress profiles in the original weld, and post overlay preservice and inservice inspections provides assurance that the structural integrity of these welds will be maintained for the life of the plant. The applicable stress limits from ASME Section III are applicable to the weld overlays. Crack growth evaluations for PWSCC and fatigue of any as-found (or conservatively postulated) flaws demonstrate that structural integrity of the welds will be maintained.
FENOC intends to install the preemptive weld overlays using Alloy 52M filler metal.
However, experience at one plant has shown that Alloy 52M can be susceptible to hot cracking when excessive concentrations of surface impurities, such as sulfides, silicates or phosphates, exist in the underlying stainless steel piping or safe-end. If high levels of impurities are discovered in the nozzle welds to be overlaid, FENOC intends to apply a 308L stainless steel buffer layer over the stainless steel piping or safe-end. The buffer layer would be installed using a machine Gas Tungsten Arc Welding process and installed up to, but not touching, the dissimilar metal butt weld joining the safe-end to the low alloy steel nozzle. Stainless steel weld deposits have been shown to be substantially more resistant to hot cracking resulting from impurity effects than austenitic nickel based filler materials, such as Alloy 52M. After dye penetrant surface examination of the buffer layer, the first Alloy 52M weld overlay layer would be deposited, using proven and demonstrated overlay welding parameters, over the buffer layer and continuing over the dissimilar metal weldment and the low alloy steel nozzle material. Individual qualifications would be used for the stainless steel buffer layer and the Alloy 52M weld overlay, and a mockup would be prepared to validate the entire process for the range of configurations that may be used. If the austenitic stainless steel buffer layer is installed, the buffer layer would not be included in the structural weld overlay thickness, and the effect of the buffer layer would be reconciled in the weld overlay design and residual stress analyses. The thickness of the buffer layer would be typical of that used for structural weld overlay layers (0.080 to 0.100 inches), with specific welding parameters to be defined during the aforementioned procedure qualification and mockup programs.
WELD OVERLAY DESIGNAND VERIFICATION The fundamental design basis for full structural overlays is to maintain the original safety margins, with no credit taken for the underlying PWSCC susceptible weldments. The assumed design basis flaw for the purpose of structural sizing of the overlays is 3600 and 100% through the original wall thickness of the dissimilar metal welds. For the crack growth analyses, initial flaw sizes will be assumed based upon Performance Demonstration Initiative (PDI) qualified inspection of the overlay at the conclusion of the weld overlay process, including the outer 25% of the original weld or susceptible base material.
Following is a list of the specific analyses and verifications that will be performed.
- 1. Nozzle specific stress analyses will be performed to establish a residual stress profile in the nozzle. Inside diameter (ID) weld repairs will be assumed in these analyses to effectively bound any actual weld repairs that may have occurred in the nozzles. The analysis will then simulate application of the weld overlays to
Docket Number 50-346 License Number NPF-3 Serial Number 3380 Page 32 of 53 Nonmandatory Appendix Q Proposed Overlay Alternative Comments (b) The weld overlay examination volume in Fig. - <3 EXAMINATION AND INSPECTION (c)> Equivalent requirements 4300-1 shall be ultrasonically examined to (2) The weld overlay examination volume in determine if any new or existing cracks have Fig. 2 shall be ultrasonically examined to propagated into the upper 25% of the pipe base determine if any new or existing cracks material or into the overlay. The angle beam have propagated into the upper 25% of shall be directed perpendicular and parallel to the base material or into the overlay. The the pipe axis, with scanning performed in four angle beam shall be directed directions. perpendicular and parallel to the piping axis, with scanning performed in four directions.
(c) The inservice examination acceptance standards <3 EXAMINATION AND INSPECTION (c)> Equivalent requirements. Additional statement of Table IWB-3514-2 shall be satisfied for the (3) The inservice examination acceptance regarding PWSCC flaws provides clarification weld overlay. Alternatively, for Class 1, 2, or 3 standards of Table IWB-3514-2 shall be but does not alter the requirements.
piping systems, the acceptance criteria of IWB- met for the weld overlay. If the 3600, IWC-3600, or IWD-3600, as applicable, acceptance criteria of Table 3514-2 shall be satisfied for the weld overlay. Cracks in cannot be met, the acceptance criteria of the outer 25% of the pipe base metal shall meet IWB-3600, IWC-3600, or IWD-3600, as the design analysis requirements of P-3000. applicable, shall be met for the weld overlay. Cracks in the outer 25% of the base metal shall meet the design analysis requirements of 2. In no circumstance will the requirements of IWX-3600 be used to disposition PWSCC flaws.
Docket Number 50-346 License Number NPF-3 Serial Number 3380 Page 45 of 53 Code Case N-638-1 Proposed Overlay Alternative Comments
<1-3 WELDING PROCEDURE REQUIREMENTS> Provides options for measuring interpass (e) The interpass temperature shall be determined temperatures. No change to the maximum by the method described in Paragraph 3(e)(1). interpass temperature is made.
If it is impractical to use the interpass temperature measurements described in Paragraph 3(e)(1) due to situations where the weldment area is not accessible, such as internal bore welding or when there are extenuating radiological concerns, either Paragraphs 3(e)(2) or 3(e)(3) may be used.
(1) temperature measurement (e.g.
pyrometers, temperature-indicating crayons, and thermocouples) during welding.
(2) heat flow calculations using the variables listed below as a minimum:
(a) welding heat input (b) initial base material temperature (c) configuration, thickness, and mass of the item being welded (d) thermal conductivity and diffusivity of the materials being welded (e) arc time per weld pass and delay time between each pass (f) arc time to complete the weld (3) measurement of the maximum interpass temperature on a test coupon that is equal to or less than the thickness of the item to be welded. The maximum heat input of the welding procedure shall be used in the welding of the test coupon.
Docket Number 50-346 License Number NPF-3 Serial Number 3380 Page 1 of 1 COMMITMENT LIST The following list identifies those actions committed to by the FirstEnergy Nuclear Operating Company in this document. Any other actions discussed in the submittal represent intended or planned actions by FENOC. They are described only for information and are not regulatory commitments. Please contact Mr. Thomas A. Lentz, Manager - FENOC Fleet Licensing, at (330) 761-6071 with any questions regarding this document or associated regulatory commitments.
COMMITMENTS DUE DATE The regulatory commitments associated with the Not Applicable.
February 15, 2007 request remain in effect, and no additional regulatory commitments are established in this letter.