ML071020046

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

ML071020046
Person / Time
Site:	Oconee
Issue date:	04/29/2007
From:	Catherine Haney Plant Licensing Branch III-2
To:	Brandi Hamilton Duke Power Co
Olshan L N, NRR/DORL, 415-1419
References
TAC MD4165
Download: ML071020046 (4)

Text

April 29, 2007 Mr. Bruce H. Hamilton Vice President, Oconee Site Duke Power Company LLC 7800 Rochester Highway Seneca, SC 29672

SUBJECT:

OCONEE NUCLEAR STATION, UNIT 1 - PRESSURIZER SURGE, SPRAY, SAFETY, AND RELIEF NOZZLE WELD SUSCEPTIBILITY TO PRIMARY WATER STRESS CORROSION CRACKING (TAC NO. MD4165)

Dear Mr. Hamilton:

This letter acknowledges the receipt of information from Duke Power Company LLC, d/b/a Duke Energy Carolinas, LLC (Duke), pertaining to the pressurizer surge, spray, safety, and relief nozzle and safe end welds at Oconee Nuclear Station, Unit 1.

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 RCS leakage monitoring until actions to mitigate the potential of PWSCC in the affected welds have been completed.

B. Hamilton In your letter dated January 31, 2007 (Agencywide Documents Access and Management System Accession Number ML070390049), you stated that the pressurizer surge, spray, safety, and relief nozzle and safe end welds containing Alloy 82/182 material have been mitigated through application of full structural weld overlay at Oconee Nuclear Station, Unit 1. As a result, your response adequately addresses the concerns that the NRC has at this time regarding PWSCC susceptibility of these welds.

This completes the NRC staff efforts on TAC No. MD4165 for the review associated with this issue. If you have any questions regarding this matter, please contact the Oconee Nuclear Station Project Manager, Leonard N. Olshan at 301-415-1419.

Sincerely,

/RA/

Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-269 cc: See next page

ML071020046 OFFICE CPNB NRR/LPL2-1/PM NRR/LPL2-1/LA NAME TLupold LOlshan:nc MOBrien DATE 4/25/07 4/19/07 4/12/07 OFFICE NRR/LPL2-1/BC CPNB/BC NRR/DORL/D NAME EMarinos TChan CHaney DATE 4/19/07 4/25/07 4/29/07 Oconee Nuclear Station, Units 1, 2, and 3 cc:

Mr. Bruce H. Hamilton P.O. Box 629 Vice President, Oconee Site Raleigh, NC 27602 Duke Power Company LLC 7800 Rochester Highway Mr. R. L. Gill, Jr.

Seneca, SC 29672 Manager - Nuclear Regulatory Issues and Industry Affairs Ms. Lisa F. Vaughn Duke Power Company LLC Associate General Counsel and Managing 526 S. Church St.

Attorney Mail Stop EC05P Duke Energy Carolinas, LLC Charlotte, NC 28202 526 South Church Street - EC07H Charlotte, North Carolina 28202 Division of Radiation Protection NC Dept of Environment, Health, & Natural Manager, LIS Resources NUS Corporation 3825 Barrett Dr.

2650 McCormick Dr., 3rd Floor Raleigh, NC 27609-7721 Clearwater, FL 34619-1035 Mr. Peter R. Harden, IV Senior Resident Inspector VP-Customer Relations and Sales U.S. Nuclear Regulatory Commission Westinghouse Electric Company 7812B Rochester Highway 6000 Fairview Road Seneca, SC 29672 12th Floor Charlotte, NC 28210 Mr. Henry Porter, Director Division of Radioactive Waste Management Mr. Henry Barron Bureau of Land and Waste Management Group Vice President, Nuclear Generation Dept. of Health and Env. Control and Chief Nuclear Officer 2600 Bull St. P.O. Box 1006-EC07H Columbia, SC 29201-1708 Charlotte, NC 28201-1006 Mr. Michael A. Schoppman Mr. Charles Brinkman Framatome ANP Director, Washington Operations 1911 North Ft. Myer Dr. Westinghouse Electric Company Suite 705 12300 Twinbrook Parkway, Suite 330 Rosslyn, VA 22209 Rockville, MD 20852 Mr. B. G. Davenport Ms. Kathryn B. Nolan Regulatory Compliance Manager Senior Counsel Oconee Nuclear Site Duke Energy Carolinas, LLC Duke Energy Corporation 526 South Church Street - EC07H ON03RC Charlotte, NC 28202 7800 Rochester Highway Seneca, SC 29672 Mr. Leonard G. Green Assistant Attorney General NC Department of Justice