ML071570267
| ML071570267 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 06/20/2007 |
| From: | Catherine Haney Plant Licensing Branch III-2 |
| To: | Gordon Peterson Duke Power Co |
| Stang J, NRR/DORL, 415-1345 | |
| References | |
| TAC MD4160 | |
| Download: ML071570267 (4) | |
Text
June 20, 2007 Mr. G. R. Peterson Vice President McGuire Nuclear Station Duke Power Company LLC 12700 Hagers Ferry Road Huntersville, NC 28078
SUBJECT:
MCGUIRE NUCLEAR STATION, UNIT 2 - PRESSURIZER SURGE, SPRAY, SAFETY, AND RELIEF NOZZLE WELD SUSCEPTIBILITY TO PRIMARY WATER STRESS CORROSION CRACKING (TAC NO. MD4160)
Dear Mr. Peterson:
This letter acknowledges the receipt of information from Duke Power Company, LLC pertaining to the pressurizer surge, spray, safety, and relief nozzle and safe end welds at McGuire Nuclear Station, Unit 2 (McGuire Unit 2).
The discovery, in October 2006, of five circumferential indications in three Alloy 82/182 dissimilar metal (DM) welds on the pressurizer at the Wolf Creek Generating Station (Wolf Creek) raised safety concerns based on the size and location of the indications. At Wolf Creek, three indications were in the pressurizer surge nozzle-to-safe end weld, and two separate indications were in the safety and relief nozzle-to-safe end welds. These findings also indicated that significant concerns might exist with the inspection schedules for addressing the pressurizer weld concerns issued by the industry-sponsored Materials Reliability Program (MRP), in Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139).
The Nuclear Regulatory Commission (NRC) is concerned about the pressurizer surge nozzle-to-safe end weld indications, as this is the first time that multiple circumferential primary water stress-corrosion cracking (PWSCC) indications have been identified in a weld. This condition calls into question the degree of safety margin present in past structural integrity evaluations for flawed DM welds susceptible to PWSCC, since multiple stress-corrosion cracking flaws may grow independently and ultimately grow together, significantly reducing the time from flaw initiation to leakage or rupture.
Based on discussions with the NRC staff, licensees of plants susceptible to this condition have committed to enhanced inspection frequency and reactor coolant system leakage monitoring until actions to mitigate the potential of PWSCC in the affected welds have been completed.
In your letter dated February 9, 2007 (Agencywide Documents Access & Management System (ADAMS) Accession Number ML070580244), you stated that the pressurizer surge, spray, safety, and relief nozzle-to-safe end welds containing Alloy 82/182 material have been mitigated through application of full structural weld overlay at McGuire Unit 2. As a
G. Peterson result, your response adequately addresses the concerns that the NRC has at this time regarding PWSCC susceptibility of these welds. This action closes TAC No. MD4160.
Sincerely,
/RA/
Catherine Haney, Director Division of Operating Reactor Licensing Docket No. 50-370 License No. NPF-17 cc: See next page
ML071570267 OFFICE CPNB NRR/LPL2-1/PM NRRLPL2-1/LA NRR/LPL2-1/BC CPNB/BC DORL/D NAME TLupold JStang:nc MOBrien EMarinos TChan CHaney DATE 6/18/07 6/18/07 6/18/07 6/20/07 6/18/07 6/20/07
McGuire Nuclear Station, Units 1 & 2 cc:
Vice President McGuire Nuclear Station Duke Power Company, LLC 12700 Hagers Ferry Road Huntersville, NC 28078 Associate General Counsel and Managing Attorney Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, North Carolina 28202 County Manager of Mecklenburg County 720 E. Fourth St.
Charlotte, NC 28202 Regulatory Compliance Manager Duke Energy Corporation McGuire Nuclear Site 12700 Hagers Ferry Road Huntersville, NC 28078 Senior Resident Inspector U.S. Nuclear Regulatory Commission 12700 Hagers Ferry Road Huntersville, NC 28078 Mecklenburg County Department of Environmental Protection 700 N. Tryon St Charlotte, NC 28202 Vice President Customer Relations and Sales Westinghouse Electric Company 6000 Fairview Road, 12th Floor Charlotte, NC 28210 NCEM REP Program Manager 4713 Mail Service Center Raleigh, NC 27699-4713 Assistant Attorney General NC Department of Justice P.O. Box 629 Raleigh, NC 27602 Manager Nuclear Regulatory Issues &
Industry Affairs Duke Energy Corporation 526 S. Church St.
Mail Stop EC05P Charlotte, NC 28202 Division of Radiation Protection NC Dept of Environment, Health & Natural Resources 3825 Barrett Dr.
Raleigh, NC 27609-7721 Owners Group (NCEMC)
Duke Energy Corporation 4800 Concord Road York, SC 29745 Group Vice President, Nuclear Generation
& Chief Nuclear Officer P.O. Box 1006-EC07H Charlotte, NC 28201-1006 Senior Counsel Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, NC 28202