ML082100120

Evaluation Regarding the Steam Generator Tube Inspection Reports for the 2007 (IR14) Outage

ML082100120
Person / Time
Site:	Diablo Canyon
Issue date:	08/01/2008
From:	Wang A NRC/NRR/ADRO/DORL/LPLIV
To:	Conway J Pacific Gas & Electric Co
Wang, A B, NRR/DORL/LPLIV, 415-1445
References
GL-04-002, TAC MD6690
Download: ML082100120 (5)

Text

August 1, 2008 Mr. John Conway Senior Vice President - Station Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 770000 San Francisco, CA 94177-0001

SUBJECT:

DIABLO CANYON POWER PLANT, UNIT NO. 1- EVALUATION REGARDING THE STEAM GENERATOR TUBE INSPECTION REPORTS FOR THE 2007 (1R14) OUTAGE (TAC No.: MD6690)

Dear Mr. Conway:

By letters dated August 27, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML072420339 and ML072470561), November 26, 2007 (ML073390290), and June 6, 2008 (ADAMS Accession No. ML081700278), Pacific Gas and Electric Company (PG&E, the licensee), submitted information summarizing the results of the 2007 steam generator (SG) tube inspections at Diablo Canyon Power Plant, Unit No. 1 (DCPP-1). These inspections were performed during the fourteenth refueling outage (1R14). In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2007 SG tube inspections at DCPP-1 in an NRC letter to DCPP-1 dated August 8, 2007 (ADAMS Accession No. ML072130034).

The NRC staff has completed its review of these reports and concludes that the licensee provided the information required by their technical specifications. The NRC staff review of the reports is enclosed.

If you have any questions regarding this matter, please contact me at (301) 415-1445.

Sincerely,

/RA by Jack Donohew for/

Alan B. Wang, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-275 cc: See next page

ML081700278), Pacific Gas and Electric Company (PG&E, the licensee), submitted information summarizing the results of the 2007 steam generator (SG) tube inspections at Diablo Canyon Power Plant, Unit No. 1 (DCPP-1). These inspections were performed during the fourteenth refueling outage (1R14). In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2007 SG tube inspections at DCPP-1 in an NRC letter to DCPP-1 dated August 8, 2007 (ADAMS Accession No. ML072130034).

The NRC staff has completed its review of these reports and concludes that the licensee provided the information required by their technical specifications. The NRC staff review of the reports is enclosed.

If you have any questions regarding this matter, please contact me at (301) 415-1445.

Sincerely,

/RA by Jack Donohew for/

Alan B. Wang, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-323 cc: See next page DISTRIBUTION:

PUBLIC LPLIV Reading RidsNrrPMAWang Resource RidsNrrDorl Resource RidsNrrLAGLappert RidsNrrDorlLpl4 Resource RidsAcrsAcnwMailCenter Resource RidsRegion4MailCenter Resource RidsOgcRp Resource KKarwoski ACCESSION NO.: ML082100120

• memo OFFICE LPL4/PM LPL4/LA CSGB/BC LPL4/BC (A) LPL4/PM NAME AWang JDonohew GLappert AHiser* MThadani AWang for JDonohew for 7/31/08 7/30/08 07/18/08 8/01/08 8/01/08 DATE U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGUALTION

SUMMARY

OF STAFF REVIEW OF 2007 STEAM GENERATOR TUBE INSPECTIONS DIABLO CANYON POWER PLANT, UNIT NO. 1 TAC No. MD6690 DOCKET No. 50-275 By letters dated August 27, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML072420339 and ML072470561), November 26, 2007 (ADAMS Accession No. ML073390290), and June 6, 2008 (ADAMS Accession No. ML081700278),

Pacific Gas and Electric Company (PG&E, the licensee) submitted information summarizing the results of the 2007 steam generator (SG) tube inspections at Diablo Canyon Power Plant, Unit No. 1 (DCPP-1). These inspections were performed during the fourteenth refueling outage (1R14). In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff additional information concerning the 2007 SG tube inspections at DCPP-1 in an NRC letter to DCPP-1 dated August 8, 2007 (ADAMS Accession No. ML072130034).

The SGs at DCPP-1 are Westinghouse model 51 SGs. Each SG contains 3,388 mill-annealed Alloy 600 tubes. Each tube has a nominal outside diameter of 0.875 inch and a nominal wall thickness of 0.050 inch. The tubes are supported by a number of carbon steel tube support plates and Alloy 600 anti-vibration bars. The tubes were explosively expanded into the tubesheet at both ends for the full length of the tubesheet.

The licensee provided the scope, extent, methods, and results of their SG tube inspections in the documents referenced above. In addition, the licensee described corrective actions (i.e., tube plugging) taken in response to the inspection findings.

As a result of the review of the reports, the NRC staff has the following comments/observations:

No crack-like flaws have ever been identified in the tubes at cold-leg tube support plate elevations where distorted outside diameter bobbin indicators have been reported.

Approximately 31 percent of the inferred bobbin voltages (from the rotating probe data) were non-conservative when compared to the measured bobbin voltages. Some of these indications had measured bobbin voltages of approximately 2 volts.

Sludge lancing was not performed during the 2007 outage, in part, because of the small amount of sludge removed during the previous outage (1R13) and the chemical cleaning performed in the 1R12 outage in which about 19,000 pounds of sludge and scale were removed from the steam generators.

A detailed review of the condition monitoring and operational assessment was not performed for the degradation mechanisms that are not addressed by an alternate tube repair criteria (such as axial primary water stress corrosion cracking indications at tube support plate elevations).

However, the results of these assessments appear reasonable given the plug-on-detection approach for crack-like indications and past inspection results.

The 2007 steam generator tube inspections were the last planned tube inspections for these steam generators since the licensee plans to replace them during their next DCPP-1 outage (in 2009).

Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by their technical specifications. In addition, the NRC staff concludes that there are no technical issues that warrant follow-up action at this time since the inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.

Diablo Canyon Power Plant, Units 1 and 2 cc:

NRC Resident Inspector City Editor Diablo Canyon Power Plant The Tribune c/o U.S. Nuclear Regulatory Commission 3825 South Higuera Street P.O. Box 369 P.O. Box 112 Avila Beach, CA 93424 San Luis Obispo, CA 93406-0112 Sierra Club San Lucia Chapter Mr. Ed Bailey, Chief ATTN: Andrew Christie Radiologic Health Branch P.O. Box 15755 State Department of Health Services San Luis Obispo, CA 93406 P.O. Box 997414 (MS 7610)

Sacramento, CA 95899-7414 Ms. Nancy Culver San Luis Obispo Mr. James D. Boyd, Commissioner Mothers for Peace California Energy Commission P.O. Box 164 1516 Ninth Street (MS 31)

Pismo Beach, CA 93448 Sacramento, CA 95814 Chairman Mr. James R. Becker, Vice President San Luis Obispo County Board of Diablo Canyon Operations Supervisors and Station Director Room 370 Diablo Canyon Power Plant County Government Center P.O. Box 3 San Luis Obispo, CA 93408 Avila Beach, CA 93424 Mr. Truman Burns Jennifer Tang Mr. Robert Kinosian Field Representative California Public Utilities Commission United States Senator Barbara Boxer 505 Van Ness, Room 4102 1700 Montgomery Street, Suite 240 San Francisco, CA 94102 San Francisco, CA 94111 Diablo Canyon Independent Safety Committee ATTN: Robert R. Wellington, Esq.

Legal Counsel 857 Cass Street, Suite D Monterey, CA 93940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavillion 612 E. Lamar Blvd, Suite 400 Arlington, TX 76011-4125 Richard F. Locke, Esq.

Pacific Gas & Electric Company P.O. Box 7442 San Francisco, CA 94120