ML071570458

Pressurizer Surge, Spray, Safety, and Relief Nozzle Weld Susceptibility to Primary Water Stress Corrosion Cracking

ML071570458
Person / Time
Site:	Millstone
Issue date:	07/18/2007
From:	Catherine Haney Plant Licensing Branch III-2
To:	Christian D Dominion Nuclear Connecticut
Hughey J, NRR/DORL, 301-415-3204
References
TAC MD4161
Download: ML071570458 (4)

Text

July 18, 2007 Mr. David A. Christian Sr. Vice President and Chief Nuclear Officer Dominion Nuclear Connecticut Innsbrook Technical Center 5000 Dominion Boulevard Glenn Allen, VA 23060-6711

SUBJECT:

MILLSTONE POWER STATION UNIT 2 - PRESSURIZER SURGE, SPRAY, SAFETY, AND RELIEF NOZZLE WELD SUSCEPTIBILITY TO PRIMARY WATER STRESS CORROSION CRACKING (TAC NO. MD4161)

Dear Mr. Christian:

This letter acknowledges the receipt of information from Dominion Nuclear Connecticut, Inc.

pertaining to the pressurizer surge, spray, safety, and relief nozzle and safe end welds at Millstone Power Station Unit 2 (MPS2).

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 12, 2007 (Agencywide Documents Access and Management System Accession Number ML070440188), you stated that the pressurizer at MPS2 has been replaced. The new pressurizer utilizes stainless steel nozzle safe ends and weld material that are resistant to stress corrosion cracking. As a result, your response adequately addresses the concerns that the NRC has at this time regarding PWSCC susceptibility of these welds.

D. Christian This completes the NRC staff efforts on TAC No. MD4161 for the review associated with this issue. If you have any questions regarding this matter, please contact the MPS2 Project Manager, John Hughey at 301-415-3204.

Sincerely,

/ra/

Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336 cc: See next page

ML071570458 OFFICE CPNB LPL1-2/PM LPL1-2/PM LPL1-2/LA NAME TLupold GEMiller JHughey RSola DATE 07/16/07 06/06/07 06/06/07 06/08/07 OFFICE LPL1-2/BC CPNB/BC DORL/D NAME HChernoff TChan CHaney DATE 07/12/07 07/16/07 07/18/07 Millstone Power Station, Unit No. 2 cc:

Lillian M. Cuoco, Esquire Mr. J. W. "Bill" Sheehan Senior Counsel Co-Chair NEAC Dominion Resources Services, Inc. 19 Laurel Crest Drive Building 475, 5th Floor Waterford, CT 06385 Rope Ferry Road Waterford, CT 06385 Mr. Evan W. Woollacott Co-Chair Edward L. Wilds, Jr., Ph.D. Nuclear Energy Advisory Council Director, Division of Radiation 128 Terry's Plain Road Department of Environmental Protection Simsbury, CT 06070 79 Elm Street Hartford, CT 06106-5127 Ms. Nancy Burton 147 Cross Highway Regional Administrator, Region I Redding Ridge, CT 00870 U.S. Nuclear Regulatory Commission 475 Allendale Road Mr. Chris L. Funderburk King of Prussia, PA 19406 Director, Nuclear Licensing and Operations Support First Selectmen Dominion Resources Services, Inc.

Town of Waterford Innsbrook Technical Center 15 Rope Ferry Road 5000 Dominion Boulevard Waterford, CT 06385 Glen Allen, VA 23060-6711 Charles Brinkman, Director Mr. David W. Dodson Washington Operations Nuclear Services Licensing Supervisor Westinghouse Electric Company Dominion Nuclear Connecticut, Inc.

12300 Twinbrook Pkwy, Suite 330 Building 475, 5th Floor Rockville, MD 20852 Rope Ferry Road Waterford, CT 06385 Senior Resident Inspector Millstone Power Station Mr. Joseph Roy, c/o U.S. Nuclear Regulatory Commission Director of Operations P.O. Box 513 Massachusetts Municipal Wholesale Niantic, CT 06357 Electric Company Moody Street Mr. J. Alan Price P.O. Box 426 Site Vice President Ludlow, MA 01056 Dominion Nuclear Connecticut, Inc.

Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385