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, 2007Mr. Bruce H. HamiltonVice 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/aDuke 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 82/182dissimilar 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 havecommitted 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-2-In your letter dated January 31, 2007 (Agencywide Documents Access and ManagementSystem 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 thisissue. 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 RegulationDocket No. 50-269 cc: See next page

ML071020046 OFFICECPNBNRR/LPL2-1/PMNRR/LPL2-1/LANAMETLupoldLOlshan:nc MO'Brien DATE 4/25/07 4/19/07 4/12/07 OFFICENRR/LPL2-1/BCCPNB/BCNRR/DORL/D NAMEEMarinosTChanCHaney DATE 4/19/07 4/25/07 4/29/07 Oconee Nuclear Station, Units 1, 2, and 3 cc:

Mr. Bruce H. HamiltonVice President, Oconee Site Duke Power Company LLC 7800 Rochester Highway Seneca, SC 29672Ms. Lisa F. VaughnAssociate General Counsel and Managing Attorney Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, North Carolina 28202Manager, LISNUS Corporation 2650 McCormick Dr., 3rd Floor Clearwater, FL 34619-1035Senior Resident InspectorU.S. Nuclear Regulatory Commission 7812B Rochester Highway Seneca, SC 29672Mr. Henry Porter, DirectorDivision of Radioactive Waste Management Bureau of Land and Waste Management Dept. of Health and Env. Control 2600 Bull St.

Columbia, SC 29201-1708Mr. Michael A. SchoppmanFramatome ANP 1911 North Ft. Myer Dr.

Suite 705 Rosslyn, VA 22209Mr. B. G. DavenportRegulatory Compliance Manager Oconee Nuclear Site Duke Energy Corporation ON03RC 7800 Rochester Highway Seneca, SC 29672Mr. Leonard G. GreenAssistant Attorney General NC Department of JusticeP.O. Box 629Raleigh, NC 27602Mr. R. L. Gill, Jr.Manager - Nuclear Regulatory Issues and Industry Affairs Duke Power Company LLC 526 S. Church St.

Mail Stop EC05P Charlotte, NC 28202Division of Radiation ProtectionNC Dept of Environment, Health, & Natural

Resources 3825 Barrett Dr.

Raleigh, NC 27609-7721Mr. Peter R. Harden, IVVP-Customer Relations and Sales Westinghouse Electric Company 6000 Fairview Road 12th Floor Charlotte, NC 28210Mr. Henry BarronGroup Vice President, Nuclear Generation and Chief Nuclear Officer P.O. Box 1006-EC07H Charlotte, NC 28201-1006Mr. Charles BrinkmanDirector, Washington Operations Westinghouse Electric Company 12300 Twinbrook Parkway, Suite 330 Rockville, MD 20852Ms. Kathryn B. NolanSenior Counsel Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, NC 28202