ML070800004

Confirmatory Action Letter Alloy 82/182 Butt Welds in the Pressurizers (TAC Nos. MD4181 and MD4182)

ML070800004
Person / Time
Site:	San Onofre
Issue date:	03/22/2007
From:	Dyer J Office of Nuclear Reactor Regulation
To:	Rosenblum R Southern California Edison Co
Kalyanam N, NRR/DORL/LP4, 415-1480
References
TAC MD4181, TAC MD4182, NRR-07-025
Download: ML070800004 (5)

Text

March 22, 2007CAL No. NRR-07-025Mr. Richard M. RosenblumSenior Vice President and Chief Nuclear Officer Southern California Edison Company San Onofre Nuclear Generating Station P. O. Box 128 San Clemente, CA 92674-0128

SUBJECT:

SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 AND 3 -CONFIRMATORY ACTION LETTER (TAC NOS. MD4181 AND MD4182)

Dear Mr. Rosenblum:

This letter confirms commitments by the Southern California Edison Company (SCE) regardingAlloy 82/182 butt welds in the pressurizers at the San Onofre Nuclear Generating Station (SONGS), 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 safetyconcerns based on the size and location of the indications. At Wolf Creek, three indicationswere in the pressurizer surge nozzle-to-safe end weld, and two separate indications were in thesafety and relief nozzle-to-safe end welds. These findings also indicated that significantconcerns might exist with the inspection schedules for addressing the pressurizer weldconcerns issued by the industry-sponsored Materials Reliability Program (MRP), in "PrimarySystem Piping Butt Weld Inspection and Evaluation Guideline (MRP-139)."The Nuclear Regulatory Commission (NRC) is concerned about the pressurizer surgenozzle-to-safe end weld indications, as this is the first time that multiple circumferential primarywater stress-corrosion cracking (PWSCC) indications have been identified in a weld. Thiscondition calls into question the degree of safety margin present in past structural integrityevaluations for flawed DM welds susceptible to PWSCC, since multiple stress-corrosioncracking flaws may grow independently and ultimately grow together, significantly reducing thetime from flaw initiation to leakage or rupture. The size of the relief nozzle-to-safe end flaw isalso of concern, as this flaw has a much larger aspect ratio than those assumed in theestimates used to establish the basis for completing the baseline inspections required by theindustry-sponsored MRP. Larger aspect ratios could result in achieving a critical flaw size andrupture before the onset of detectable leakage. The long-term resolution of this issue is expected to involve changes to the American Society ofMechanical Engineers Boiler and Pressure Vessel Code (ASME Code), and will involvechanges 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, R. Rosenblum-2-whether the rule adopts the ASME Code standards or defines separate requirements, will likelybenefit from additional operating experience, continuing assessments, and analysis beingconducted by the NRC and the MRP. Until NRC regulations are revised, it is necessary to establish a minimum set of enhancedreactor coolant system (RCS) DM butt weld inspection expectations for nickel-basedAlloy 82/182 pressurizer surge, spray, safety, and relief nozzle butt welds, including safe endwelds, to supplement existing inspection and other requirements of the ASME Code and NRCregulations. In addition, enhanced monitoring of RCS leakage is needed to promptly identifyany through-wall flaws in the pressurizer surge, spray, safety, or relief nozzle DM butt welds orsafe end DM butt welds to prevent additional degradation from occurring. The above actionsprovide reasonable assurance that there is no undue risk to the health and safety of the publicwhile the NRC regulations are revised. The NRC communicated the need for near-term enhancements to the industry through publicmeetings held on November 30, 2006, December 20, 2006, and February 2, 2007. Licenseessubmitted letters voluntarily committing to the enhanced inspection and leakage monitoringrequirements. After teleconferences with specific licensees held between February 12 throughFebruary 23, 2007, the licensees submitted supplemental commitment letters addressing theNRC staff's concerns regarding inspection, compensatory actions, and reporting.In your letter dated March 7, 2007 (Agencywide Documents Access and Management System(ADAMS) Accession Number ML070680042) you described actions you will take at the SONGS, 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 andcommitments 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 inspection schedule and reporting. *SCE is committing that neither SONGS Unit 2 nor Unit 3 will operate pastDecember 31, 2007, without meeting the MRP-139 requirements for pressurizerDMWs [dissimilar metal welds]. MRP-139 will be met through mitigation ofthe surge line nozzle welds.*The NRC will be informed in writing if SCE revises the commitment to theenhanced leakage monitoring program described herein, reporting requirements, or the commitment to have all pressurizer DMWs compliant withMRP-139, prior to operation after December 31, 2007.These clarifications were discussed with and agreed upon by your staff during a telephonediscussion on March 20, 2007, between Edward Scherer, Manager of Nuclear Regulatory Affairs and Michael Cheok, Deputy Director, Division of Operating Reactor Licensing.

R. Rosenblum-3-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; and3)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 formalizingthe 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 andyour response will be made available electronically for public inspection in the NRC PublicDocument Room or from the NRC's ADAMS, accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html. To the extent possible, your response should notinclude 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 RegulationDocket Nos. 50-361 and 50-362 License Nos. NPF-10 and NPF-15 cc: See next page

ML070800004OFFICECPNBDCILPL4/PMLPL4/LALPL4/BCTECH EDDIRS/TANAMETLupoldESullivanNKalyanamLFeizollahiDTeraoHChangRPascarelliDATE3/21/073/21/073/21/073/21/073/21/072/28/073/21/07 OFFICECPNB/BCDRP/D RGN 4DORL/DDCI/DADES/ADNRR/D NAMETChanAHowell, III: via e-mailCHaney:JWL for CHMEvansJGrobeJDyerDATE3/21/073/19/073/21/073/21/073/22/073/22/07 March 2006San Onofre Nuclear Generating Station Units 2 and 3 cc:Mr. Daniel P. Breig Southern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92674-0128Mr. Douglas K. Porter, EsquireSouthern California Edison Company 2244 Walnut Grove Avenue Rosemead, CA 91770Mr. David Spath, ChiefDivision of Drinking Water and Environmental Management P.O. Box 942732 Sacramento, CA 94234-7320Chairman, Board of SupervisorsCounty of San Diego 1600 Pacific Highway, Room 335 San Diego, CA 92101Mark L. ParsonsDeputy City Attorney City of Riverside 3900 Main Street Riverside, CA 92522Mr. Gary L. Nolff Assistant Director - Resources City of Riverside 3900 Main Street Riverside, CA 92522Regional Administrator, Region IVU.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064Mr. Michael R. OlsonSan Diego Gas & Electric Company 8315 Century Park Ct. CP21G San Diego, CA 92123-1548Director, Radiologic Health BranchState Department of Health Services P.O. Box 997414, MS 7610 Sacramento, CA 95899-7414Resident Inspector/San Onofre NPS c/o U.S. Nuclear Regulatory Commission Post Office Box 4329 San Clemente, CA 92674Mayor City of San Clemente 100 Avenida Presidio San Clemente, CA 92672Mr. James T. Reilly Southern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92674-0128Mr. James D. Boyd, CommissionerCalifornia Energy Commission 1516 Ninth Street (MS 31)

Sacramento, CA 95814Mr. Ray Waldo, Vice PresidentSouthern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92764-0128Mr. Brian KatzSouthern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92764-0128Mr. Steve HsuDepartment of Health Services Radiologic Health Branch MS 7610, P.O. Box 997414 Sacramento, CA 95899Mr. A. Edward SchererSouthern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92674-0128