ML070790113

Confirmatory Action Letter

ML070790113
Person / Time
Site:	Oconee
Issue date:	03/27/2007
From:	Dyer J Office of Nuclear Reactor Regulation
To:	Brandi Hamilton Duke Energy Carolinas, Duke Power Co
Olshan L N, NRR/DORL, 415-1419
References
MRP-139, TAC MD4166, TAC MD4167, NRR-07-022
Download: ML070790113 (6)

Text

March 27, 2007 CAL No. NRR-07-022 Mr. Bruce H. Hamilton Vice President, Oconee Site Duke Power Company LLC 7800 Rochester Highway Seneca, SC 29672

SUBJECT:

CONFIRMATORY ACTION LETTER - OCONEE NUCLEAR STATION, UNITS 2 AND 3 (TAC NOS. MD4166 AND MD4167)

Dear Mr. Hamilton:

This letter confirms commitments by Duke Power Company LLC, d/b/a Duke Energy Carolinas, LLC, regarding Alloy 82/182 butt welds in the pressurizers at the Oconee Nuclear Station, Units 2 and 3.

The discovery, in October 2006, of five circumferential indications in three 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. The size of the relief nozzle-to-safe end flaw is also of concern, as this flaw has a much larger aspect ratio than those assumed in the estimates used to establish the basis for completing the baseline inspections required by the industry-sponsored MRP. Larger aspect ratios could result in achieving a critical flaw size and rupture before the onset of detectable leakage.

The long-term resolution of this issue is expected to involve changes to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), and will involve changes to the NRC regulations in Title 10 of the Code of Federal Regulations (10 CFR),

Part 50, Section 50.55a, Codes and standards. The development of the NRC regulations,

whether the rule adopts the ASME Code standards or defines separate requirements, will likely benefit from additional operating experience, continuing assessments, and analysis being conducted by the NRC and the MRP.

Until NRC regulations are revised, it is necessary to establish a minimum set of enhanced reactor coolant system (RCS) DM butt weld inspection expectations for nickel-based Alloy 82/182 pressurizer surge, spray, safety, and relief nozzle butt welds, including safe end welds, to supplement existing inspection and other requirements of the ASME Code and NRC regulations. In addition, enhanced monitoring of RCS leakage is needed to promptly identify any through-wall flaws in the pressurizer surge, spray, safety, or relief nozzle DM butt welds or safe end DM butt welds to prevent additional degradation from occurring. The above actions provide reasonable assurance that there is no undue risk to the health and safety of the public while the NRC regulations are revised.

The NRC communicated the need for near-term enhancements to the industry through public meetings held on November 30, 2006, December 20, 2006, and February 2, 2007. Licensees submitted letters voluntarily committing to the enhanced inspection and leakage monitoring requirements. After teleconferences with specific licensees held between February 12 through February 23, 2007, the licensees submitted supplemental commitment letters addressing the NRC staffs concerns regarding inspection, compensatory actions, and reporting.

In your letter dated January 31, 2007 (Agencywide Documents Access & Management System (ADAMS) Accession Number ML070390049), as supplemented by letter dated February 22, 2007 (ADAMS Accession Number ML070600169), you described actions you will take at the Oconee Nuclear Station, Units 2 and 3, for the pressurizer dissimilar metal butt welds containing Alloy 82/182 material. These commitments address: 1) completion schedules for inspection/mitigation of the welds; 2) RCS leak monitoring frequency, action levels, and actions; and 3) reporting requirements.

The NRC staff has reviewed these actions and commitments and agrees the actions and commitments are appropriate to address the potential of PWSCC of the applicable pressurizer dissimilar metal butt welds containing Alloy 82/182 material with clarification on one of the commitments as indicated in bold below regarding reports to be provided to the NRC.

• Report to the NRC, within 60 days of unit restart, details of the inspection results of any unmitigated weld examinations and any corrective or mitigative actions taken on the pressurizer surge, spray, safety, or relief nozzle or safe end welds containing Alloy 82/182 material.

This clarification was discussed with and agreed upon by your staff during a telephone discussion on March 22, 2007, between Graham Davenport, Regulatory Compliance Manager, and Michele Evans, Director-Division of Component Integrity.

Pursuant to Section 182 of the Atomic Energy Act, 42 U.S.C. 2232, you are required to:

1) Notify me immediately if your understanding differs from that set forth above;

2) Notify me if for any reason you cannot complete the actions and commitments within the specified schedule and advise me in writing of your modified schedule in advance of the change; and

3) Notify me in writing when you have completed the actions and commitments addressed in this Confirmatory Action Letter.

Issuance of this Confirmatory Action Letter does not preclude issuance of an order formalizing the above commitments or requiring other actions on the part of the licensee; nor does it preclude the NRC from taking enforcement action for violations of NRC requirements that may have prompted the issuance of this letter. In addition, failure to take the actions addressed in this Confirmatory Action Letter may result in enforcement action.

In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter and your response will be made available electronically for public inspection in the NRC Public Document Room or from the NRCs ADAMS, accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html. To the extent possible, your response should not include any personal privacy, proprietary, or safeguards information so that it can be made available to the Public without redaction. If personal privacy or proprietary information is necessary to provide an acceptable response, then please provide a bracketed copy of your response that identifies the information that should be protected and a redacted copy of your response that deletes such information. If you request withholding of such material, you must specifically identify the portions of your response that you seek to have withheld and provide in detail the bases for your claim of withholding (e.g., explain why the disclosure of information will create an unwarranted invasion of personal privacy or provide the information required by 10 CFR 2.390(b) to support a request for withholding confidential commercial or financial information). If safeguards information is necessary to provide an acceptable response, please provide the level of protection described in 10 CFR 73.21.

Sincerely,

/RA/

J. E. Dyer, Director Office of Nuclear Reactor Regulation Docket Nos. 50-270, 50-287 License Nos. DPR-47, DPR-55 cc: See next page

ML070790113 OFFICE CPNB DCI LPL2-1/PM LPL2-1/LA LPL2-1/BC TECH ED DIRS/TA NAME TLupold ESullivan LOlshan MOBrien/OL for EMarinos HChang RPascarelli DATE 3/23/07 3/23/07 3/22/07 3/22 /07 3/26/07 2/28/07 3/26/07 OFFICE CPNB/BC DRP/D RGN 2 DORL/D DCI/D AD:DES NRR/D NAME TChan/ CCasto/per email CHaney JL for MEvans Jgrobe/PH for JDyer GG for Christensen DATE 3/26/07 3/23/07 3/26/07 3/26/07 3/27/07 3/27/07 Oconee Nuclear Station, Units 1, 2, and 3 cc:

Mr. Bruce H. Hamilton Mr. Leonard G. Green Vice President, Oconee Site Assistant Attorney General Duke Power Company LLC NC Department of Justice 7800 Rochester Highway P.O. Box 629 Seneca, SC 29672 Raleigh, NC 27602 Ms. Lisa F. Vaughn Mr. R. L. Gill, Jr.

Associate General Counsel and Managing Manager - Nuclear Regulatory Attorney Issues and Industry Affairs Duke Energy Carolinas, LLC Duke Power Company LLC 526 South Church Street - EC07H 526 S. Church St.

Charlotte, North Carolina 28202 Mail Stop EC05P Charlotte, NC 28202 Manager, LIS NUS Corporation Division of Radiation Protection 2650 McCormick Dr., 3rd Floor NC Dept of Environment, Health, & Natural Clearwater, FL 34619-1035 Resources 3825 Barrett Dr.

Senior Resident Inspector Raleigh, NC 27609-7721 U.S. Nuclear Regulatory Commission 7812B Rochester Highway Mr. Peter R. Harden, IV Seneca, SC 29672 VP-Customer Relations and Sales Westinghouse Electric Company Mr. Henry Porter, Director 6000 Fairview Road Division of Radioactive Waste Management 12th Floor Bureau of Land and Waste Management Charlotte, NC 28210 Dept. of Health and Env. Control 2600 Bull St. Mr. Henry Barron Columbia, SC 29201-1708 Group Vice President, Nuclear Generation and Chief Nuclear Officer Mr. Michael A. Schoppman P.O. Box 1006-EC07H Framatome ANP Charlotte, NC 28201-1006 1911 North Ft. Myer Dr.

Suite 705 Mr. Charles Brinkman Rosslyn, VA 22209 Director, Washington Operations Westinghouse Electric Company Mr. B. G. Davenport 12300 Twinbrook Parkway, Suite 330 Regulatory Compliance Manager Rockville, MD 20852 Oconee Nuclear Site Duke Energy Corporation Ms. Kathryn B. Nolan ON03RC Senior Counsel 7800 Rochester Highway Duke Energy Carolinas, LLC Seneca, SC 29672 526 South Church Street - EC07H Charlotte, NC 28202