ML070730620
| ML070730620 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 03/20/2007 |
| From: | Dyer J Office of Nuclear Reactor Regulation |
| To: | Blevins M TXU Power |
| Thadani, M C, NRR/DORL/LP4, 415-1476 | |
| References | |
| TAC MD4143, TAC MD4144, NRR-07-007 | |
| Download: ML070730620 (5) | |
Text
March 20, 2007 CAL No. NRR-07-007 Mr. M. R. Blevins Senior Vice President and Chief Nuclear Officer TXU Power Comanche Peak Steam Electric Station ATTN: Regulatory Affairs Department P.O. Box 1002 Glen Rose, TX 76043
SUBJECT:
CONFIRMATORY ACTION LETTER - COMANCHE PEAK STEAM ELECTRIC STATION, UNITS 1 AND 2 (TAC NOS. MD4143 AND MD4144)
Dear Mr. Blevins:
This letter confirms commitments by TXU Generation Company LP in regard to Alloy 82/182 butt welds in the pressurizers at Comanche Peak Steam Electric 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
M. Blevins 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 February 20, 2007 (Agencywide Documents Access AND Management System (ADAMS) Accession Number ML070530211), you described actions you will take at Comanche Peak Steam Electric 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 two of the commitments as indicated in bold below regarding RCS leak monitoring actions and reporting.
TXU Generation Company LP will inform the NRC in writing prior to any revision of the pressurizer butt weld inspection schedules or commitments described in this letter.
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 period of sustained leakage increase, is complete and the leak rate is still elevated, place the unit 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 Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and perform a bare metal visual inspection of unmitigated Pressurizer surge, safety, spray, and relief nozzle butt welds and safe-end butt welds containing Alloy 82/182 material.
These clarifications were discussed with and agreed upon by your staff during a telephone discussion on March 15, 2007, between Rafael Flores, Site Vice President, and William Bateman, Deputy Director, Division of Component Integrity.
M. Blevins 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. 50-445 and 50-446 License Nos. NPF-87 and NPF-89 cc: See next page
ML070730620 OFFICE CPNB DCI LPL4/PM LPL4/LA LPL4/BC TECH ED DIRS/TA NAME KHoffman ESullivan:MGE for ES MThadani JBurkhardt DTerao HChang RPascarelli DATE 3/19/07 3/19/07 3/16/07 3/16/07 3/16/07 2/28/07 3/19/07 OFFICE CPNB/BC DRP/D RGN4 DORL/D DCI/D AD:DES NRR/D NAME TChan via e-mail CHaney:JL for CH MEvans JGrobe JDyer DATE 3/19/07 3/16/07 3/19/07 3/19/07 3/20/07 3/20/07
December 2004 Comanche Peak Steam Electric Station cc:
Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 2159 Glen Rose, TX 76403-2159 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 Mr. Fred W. Madden, Director Regulatory Affairs TXU Generation Company LP P.O. Box 1002 Glen Rose, TX 76043 George L. Edgar, Esq.
Morgan Lewis 1111 Pennsylvania Avenue, NW Washington, DC 20004 County Judge P.O. Box 851 Glen Rose, TX 76043 Environmental and Natural Resources Policy Director Office of the Governor P.O. Box 12428 Austin, TX 78711-3189 Mr. Richard A. Ratliff, Chief Bureau of Radiation Control Texas Department of Health 1100 West 49th Street Austin, TX 78756-3189 Mr. Brian Almon Public Utility Commission William B. Travis Building P.O. Box 13326 1701 North Congress Avenue Austin, TX 78701-3326 Ms. Susan M. Jablonski Office of Permitting, Remediation and Registration Texas Commission on Environmental Quality MC-122 P.O. Box 13087 Austin, TX 78711-3087 Terry Parks, Chief Inspector Texas Department of Licensing and Regulation Boiler Program P.O. Box 12157 Austin, TX 78711