ML071070076

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

ML071070076
Person / Time
Site:	Kewaunee
Issue date:	05/03/2007
From:	Catherine Haney Plant Licensing Branch III-2
To:	Christian D Dominion, Dominion Energy Kewaunee
Kuntz, Robert , NRR/DLPM, 415-3733
References
TAC MD4158
Download: ML071070076 (4)

Text

May 3, 2007 Mr. David A. Christian Senior Vice-President and Chief Nuclear Officer Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711

SUBJECT:

KEWAUNEE POWER STATION - PRESSURIZER SURGE, SPRAY, SAFETY, AND RELIEF NOZZLE WELD SUSCEPTIBILITY TO PRIMARY WATER STRESS CORROSION CRACKING (TAC NO. MD4158)

Dear Mr. Christian:

This letter acknowledges the receipt of information from Dominion Energy Kewaunee, Inc.

pertaining to the pressurizer surge, spray, safety, and relief nozzle and safe end welds at Kewaunee Power Station (KPS).

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 & Management System (ADAMS) Accession Number ML070440188), you stated that the pressurizer surge, spray, safety, and relief nozzle and safe end welds do not contain Alloy 82/182 material at KPS. As a

result, your response adequately addresses the concerns that the NRC has at this time regarding PWSCC susceptibility of these welds.

Sincerely,

/RA/

Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-305 cc: See next page

ML071070076 OFFICE CPNB LPL3-1/PM LPL3-1/LA NAME TLupold RKuntz THarris DATE 4/30/07 5/2/07 4/18/07 OFFICE LPL3-1/BC CPNB/BC DORL/D NAME LRaghavan TChan CHaney DATE 5/3/07 4/30/07 5/1/07 Kewaunee Power Station cc:

Resident Inspectors Office U.S. Nuclear Regulatory Commission N490 Hwy 42 Kewaunee, WI 54216-9510 Regional Administrator, Region III U.S. Nuclear Regulatory Commission Suite 210 2443 Warrenville Road Lisle, IL 60532-4351 Ms. Leslie N. Hartz Dominion Energy Kewaunee, Inc.

Kewaunee Power Station N 490 Highway 42 Kewaunee, WI 54216 Mr. Chris L. Funderburk Director, Nuclear Licensing and Operations Support Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711 Mr. Thomas L. Breene Dominon Energy Kewaunee, Inc.

Kewaunee Power Station N490 Highway 42 Kewaunee, WI 54216 Ms. Lillian M. Cuoco, Esq.

Senior Counsel Dominion Resources Services, Inc.

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