ML070740294

Confirmatory Action Letter - Braidwood, Units 1 and 2

ML070740294
Person / Time
Site:	Braidwood
Issue date:	03/22/2007
From:	Dyer J Office of Nuclear Reactor Regulation
To:	Crane C Exelon Generation Co
kuntz, Robert , NRR/DORL, 415-3733
References
TAC MD4134, TAC MD4135, NRR-07-008
Download: ML070740294 (8)

Text

March 22, 2007 CAL No. NRR-07-008 Mr. Christopher M. Crane President and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

CONFIRMATORY ACTION LETTER - BRAIDWOOD STATION, UNITS 1 AND 2 (TAC NOS. MD4134 AND MD4135)

Dear Mr. Crane:

This letter confirms commitments by Exelon Generation Company, LLC and AmerGen Energy Company, LLC in regard to Alloy 82/182 butt welds in the pressurizer at Braidwood Station, Units 1 and 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.

C. Crane 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 21, 2007, (Agencywide Documents Access & Management System (ADAMS) ML070520499) you described actions you will take at Braidwood Station Units 1 and 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 7 of the actions/commitments as indicated in bold below regarding inspection schedule, RCS leak monitoring, and reporting.

• Exelon Generation Company, LLC (EGC) will complete mitigation activities on the pressurizer surge, spray, safety, and relief nozzle butt welds and safe end butt welds containing Alloy 82/182 material prior to December 31, 2007 for Braidwood Station Unit 1.

• Braidwood Station Unit 2 will develop contingency plans to shutdown [sic] in 2007 and perform mitigation. If the NRC agrees that the Materials Reliability Project sponsored refined crack growth project results provide reasonable assurance that there is sufficient time between leak and break, then EGC will complete inspection or mitigation activities on the pressurizer surge, spray, safety, and relief nozzle butt welds and safe end butt welds containing Alloy 82/182 material prior to the completion of Braidwood Station Unit 2 cycle 13 refueling outage.

• The pressurizer surge, spray, safety, and relief nozzle butt welds and safe end butt welds containing Alloy 82/182 material will be inspected within every 4 years, until mitigated.

C. Crane

• Once the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> evaluation period, i.e. the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> period of sustained increased leakage, is complete, and the leakrate is still elevated, Braidwood Station Unit 1 or Unit 2, as applicable, will be placed in MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in MODE 5 within 36 additional hours and a bare metal visual inspection of unmitigated Alloy 82/182 pressurizer nozzles will be performed.

• If a post-shutdown inspection identifies the source of the unidentified RCS leakage to originate from a source other than the pressurizer, a pressurizer BMV inspection would not be performed, provided the leak can be quantified and that quantity drops the unidentified RCS leakage below the appropriate threshold(s).

• Reports of any Alloy 82/182 pressurizer nozzle connections inspection results for Braidwood Station Unit 1 and Unit 2 will be submitted to the NRC within 60 days of the completion date of the inspection. This includes reports of any bare metal visual inspections as a result of increased RCS leak rate, and reports of any corrective or mitigative actions taken on the pressurizer surge, spray, safety, or relief nozzle butt welds and safe end butt welds containing Alloy 82/182 material.

• The NRC will be informed in writing prior to changing any of the commitments or actions above or in the referenced letter.

These clarifications were discussed with and agreed upon by your staff during a telephone discussion on March 16, 2007, between Thomas Coutu, Site Vice President, Braidwood Station, 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

C. Crane 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. 50-456 and 50-457 License Nos. NPF-72 and NPF-77 cc: See next page

ML070740294 NRR-106 OFFICE CPNB DCI LPL3-2/PM LPL3-2/LA LPL3-2/BC TECH ED DIRS/TA NAME TLupold ESullivan RKuntz EWhitt RGibbs HChang RPascarelli DATE 3/19/07 3/20/07 3/16/07 3/16/07 3/16/07 2/28/07 3/20/07 OFFICE CPNB/BC DRP/D RGN 3 DORL/D DCI/D AD:DES NRR/D NAME TChan MSatorius CHaney MEvans JGrobe JDyer DATE 3/19/07 3/19/07 3/21/07 3/20/07 3/22/07 3/22/07 Braidwood Station Units 1 and 2 cc:

Regional Administrator, Region III County Executive U.S. Nuclear Regulatory Commission Will County Office Building Suite 210 302 N. Chicago Street 2443 Warrenville Road Joliet, IL 60432 Lisle, IL 60532-4351 Attorney General Document Control Desk - Licensing 500 S. Second Street Exelon Generation Company, LLC Springfield, IL 62701 4300 Winfield Road Warrenville, IL 60555 Plant Manager - Braidwood Station Exelon Generation Company, LLC Mr. Dwain W. Alexander, Project Manager 35100 S. Rt. 53, Suite 84 Westinghouse Electric Corporation Braceville, IL 60407-9619 Energy Systems Business Unit Post Office Box 355 Site Vice President - Braidwood Pittsburgh, PA 15230 Exelon Generation Company, LLC 35100 S. Rt. 53, Suite 84 Ms. Bridget Little Rorem Braceville, IL 60407-9619 Appleseed Coordinator 117 N. Linden Street Senior Vice President - Operations Support Essex, IL 60935 Exelon Generation Company, LLC 4300 Winfield Road Howard A. Learner Warrenville, IL 60555 Environmental Law and Policy Center of the Midwest Chairman, Ogle County Board 35 East Wacker Dr., Suite 1300 Post Office Box 357 Chicago, IL 60601-2110 Oregon, IL 61061 U.S. Nuclear Regulatory Commission Manager Regulatory Assurance - Braidwood Braidwood Resident Inspectors Office Exelon Generation Company, LLC 35100 S. Rt. 53, Suite 79 35100 S. Rt. 53, Suite 84 Braceville, IL 60407 Braceville, IL 60407-9619 Ms. Lorraine Creek Director - Licensing and Regulatory Affairs RR 1, Box 182 Exelon Generation Company, LLC Manteno, IL 60950 4300 Winfield Road Warrenville, IL 60555 Illinois Emergency Management Agency Associate General Counsel Division of Disaster Assistance & Exelon Generation Company, LLC Preparedness 4300 Winfield Road 110 East Adams Street Warrenville, IL 60555 Springfield, IL 62701-1109

Braidwood Station Units 1 and 2 Senior Vice President - Midwest Operations Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Vice President - Regulatory Affairs Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Manager Licensing - Braidwood, Byron and LaSalle Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555