ML070730518
| ML070730518 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 03/20/2007 |
| From: | Dyer J Office of Nuclear Reactor Regulation |
| To: | Morris J Duke Power Co |
| Stang J, NRR/DORL, 415-1345 | |
| References | |
| TAC MD4142, NRR-07-015 | |
| Download: ML070730518 (6) | |
Text
March 20, 2007 CAL No. NRR-07-015 Mr. J. R. Morris Site Vice President Catawba Nuclear Station Duke Power Company LLC 4800 Concord Road York, SC 29745
SUBJECT:
CONFIRMATORY ACTION LETTER - CATAWBA NUCLEAR STATION, UNIT 2 (TAC NO. MD4142)
Dear Mr. Morris:
This letter is confirms commitments by Duke Power Company LLC d/b/a Duke Energy Carolinas, LLC (Duke) regarding Alloy 82/182 butt welds in the pressurizer at Catawba Nuclear Station, Unit 2.
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.
J. Morris 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 February 26, 2007 (Agencywide Documents Access & Management System (ADAMS) Accession Number ML070650467) you described actions you will take at Catawba Nuclear Station, Unit 2 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 clarifications on 2 of the commitments as indicated in bold below regarding mitigation of the welds and reporting.
- For Unit 2, Catawba commits to either inspecting or mitigating the pressurizer nozzle welds containing Alloy 82/182 weld material no later than December 31, 2007.
- Follow-up correspondence required by Catawba's Request for Relief 07-GO-001 submittal will satisfy the 60-day reporting requirement for any corrective or mitigative actions taken. Results of Bare Metal Visual inspections, required due to RCS leakage, and any volumetric inspection results of unmitigated welds, if performed, will be reported to the NRC within 60 days of unit restart.
These clarifications were discussed with and agreed upon by your staff during a telephone discussion on March 14, 2007, between John W. Pitesa, Catawba Nuclear Station Plant Manager and John Lubinski, Deputy Director, Division of Operating Reactor Licensing.
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;
J. Morris 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 No. 50-414 License No. NPF-52 cc: See next page
ML070730518 OFFICE CPNB DCI LPL2-1/PM LPL2-1/LA LPL2-1/BC TECH ED DIRS/TA NAME TLupold ESullivan JStang MOBrien EMarinos HChang RPascarelli DATE 3/16 /07 3/16/07 03/16/07 03/16/07 3/16 /07 2/28/07 3/19/07 OFFICE CPNB/BC DRP/D RGN 2 DORL/D DCI/D AD:DES NRR/D NAME TChan CCasto CHaney MEvans JGrobe JDyer DATE 3/16/07 3/16/07 3/16 /07 3/16/07 3/20/07 3/20/07 Catawba Nuclear Station, Units 1 & 2 Page 1 of 2 cc:
Mr. Dhiaa Jamil North Carolina Electric Membership Corp.
Vice President P.O. Box 27306 Catawba Nuclear Station Raleigh, North Carolina 27611 Duke Power Company, LLC 4800 Concord Road Senior Resident Inspector York, SC 29745 U.S. Nuclear Regulatory Commission 4830 Concord Road Mr. Lee Keller, Manager York, South Carolina 29745 Regulatory Compliance Duke Energy Corporation Mr. Henry Porter, Assistant Director 4800 Concord Road Division of Waste Management York, South Carolina 29745 Bureau of Land and Waste Management Dept. of Health and Environmental Control Ms. Lisa F. Vaughn 2600 Bull Street Associate General Counsel and Managing Columbia, South Carolina 29201-1708 Attorney Duke Energy Carolinas, LLC Mr. R.L. Gill, Jr., Manager 526 South Church Street - EC07H Nuclear Regulatory Issues Charlotte, North Carolina 28202 and Industry Affairs Duke Energy Corporation North Carolina Municipal Power 526 South Church Street Agency Number 1 Mail Stop EC05P 1427 Meadowwood Boulevard Charlotte, North Carolina 28202 P.O. Box 29513 Raleigh, North Carolina 27626 Saluda River Electric P.O. Box 929 County Manager of York County Laurens, South Carolina 29360 York County Courthouse York, South Carolina 29745 Mr. Peter R. Harden, IV, Vice President Customer Relations and Sales Piedmont Municipal Power Agency Westinghouse Electric Company 121 Village Drive 6000 Fairview Road Greer, South Carolina 29651 12th Floor Charlotte, North Carolina 28210 Mr. Leonard G. Green Assistant Attorney General Mr. T. Richard Puryear North Carolina Department of Justice Owners Group (NCEMC)
P.O. Box 629 Duke Energy Corporation Raleigh, North Carolina 27602 4800 Concord Road York, South Carolina 29745 NCEM REP Program Manager 4713 Mail Service Center Ms. Kathryn B. Nolan Raleigh, North Carolina 27699-4713 Senior Counsel Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, NC 28202
Catawba Nuclear Station, Units 1 & 2 Page 2 of 2 cc:
Division of Radiation Protection NC Dept. of Environment, Health, and Natural Resources 3825 Barrett Drive Raleigh, North Carolina 27609-7721 Mr. Henry Barron Group Vice President, Nuclear Generation and Chief Nuclear Officer P.O. Box 1006-EC07H Charlotte, NC 28201-1006