ML043570323

Summary of Conference Call Regarding the 2004 Steam Generator Tube Inspections Performed at Diablo Canyon, Unit 2

ML043570323
Person / Time
Site:	Diablo Canyon
Issue date:	01/04/2005
From:	Shukla G NRC/NRR/DLPM/LPD4
To:	Rueger G Pacific Gas & Electric Co
SHUKLA G , NRR/DLPM/PD4, 415-8420
References
Download: ML043570323 (5)

Text

January 4, 2005 Mr. Gregory M. Rueger Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 3 Avila Beach, CA 93424

SUBJECT:

DIABLO CANYON POWER PLANT, UNIT 2 -

SUMMARY

OF CONFERENCE CALL REGARDING THE 2004 STEAM GENERATOR TUBE INSPECTIONS

Dear Mr. Rueger:

On November 16, 2004, the NRC staff participated in a conference call with the staff of Pacific Gas and Electric Company to discuss selected results of the steam generator tube inspections performed at the Diablo Canyon Power Plant, Unit 2 during the Fall 2004 refueling outage.

A summary of the information provided during the conference call is enclosed.

Sincerely,

/RA/

Girija S. Shukla, Project Manager, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-323

Enclosure:

Conference Call Summary cc w/encl: See next page

January 4, 2005 Mr. Gregory M. Rueger Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 3 Avila Beach, CA 93424

SUBJECT:

DIABLO CANYON POWER PLANT, UNIT 2 -

SUMMARY

OF CONFERENCE CALL REGARDING THE 2004 STEAM GENERATOR TUBE INSPECTIONS

Dear Mr. Rueger:

On November 16, 2004, the NRC staff participated in a conference call with the staff of Pacific Gas and Electric Company to discuss selected results of the steam generator tube inspections performed at the Diablo Canyon Power Plant, Unit 2 during the Fall 2004 refueling outage.

A summary of the information provided during the conference call is enclosed.

Sincerely,

/RA/

Girija S. Shukla, Project Manager, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-323 DISTRIBUTION:

PUBLIC

Enclosure:

Conference Call Summary PDIV-2 Reading RidsNrrDlpmLpdiv (HBerkow) cc w/encl: See next page RidsNrrDlpmLpdiv2 (RGramm)

RidsNrrPMGShukla RidsNrrLAEPeyton MMurphy KKarwoski JClark LLund RidsOgcRp RidsAcrsAcnwMailCenter RidsRegion4MailCenter (BJones)

• Input Accession No.: ML043570323 NRR-106 OFFICE PDIV-2/PM PDIV-2/LA EMCB/SC* PDIV-2/SC NAME GShukla:mp EPeyton LLund RGramm DATE 1/4/05 12/29/04 11/23/04 1/4/05 OFFICIAL RECORD COPY

Diablo Canyon Power Plant, Unit 2 cc:

NRC Resident Inspector Richard F. Locke, Esq.

Diablo Canyon Power Plant Pacific Gas & Electric Company c/o U.S. Nuclear Regulatory Commission P.O. Box 7442 P.O. Box 369 San Francisco, CA 94120 Avila Beach, CA 93424 Mr. David H. Oatley, Vice President Sierra Club San Lucia Chapter and General Manager c/o Henriette Groot Diablo Canyon Power Plant 1000 Montecito Road P.O. Box 56 Cayucos, CA 93430 Avila Beach, CA 93424 Ms. Nancy Culver City Editor San Luis Obispo The Tribune Mothers for Peace 3825 South Higuera Street P.O. Box 164 P.O. Box 112 Pismo Beach, CA 93448 San Luis Obispo, CA 93406-0112 Chairman Mr. Ed Bailey, Radiation Program Director San Luis Obispo County Board of Radiologic Health Branch Supervisors State Department of Health Services Room 370 P.O. Box 942732 (MS 178)

County Government Center Sacramento, CA 94234-7320 San Luis Obispo, CA 93408 Mr. James D. Boyd, Commissioner Mr. Truman Burns California Energy Commission Mr. Robert Kinosian 1516 Ninth Street (MS 31)

California Public Utilities Commission Sacramento, CA 95814 505 Van Ness, Room 4102 San Francisco, CA 94102 Mr. James R. Becker, Vice President Diablo Canyon Operations Diablo Canyon Independent Safety and Station Director Committee Diablo Canyon Power Plant ATTN: Robert R. Wellington, Esq. P.O. Box 3 Legal Counsel Avila Beach, CA 93424 857 Cass Street, Suite D Monterey, CA 93940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064

CONFERENCE CALL

SUMMARY

BETWEEN THE NRC AND PACIFIC GAS AND ELECTRIC COMPANY REGARDING THE 2004 STEAM GENERATOR TUBE INSPECTIONS PERFORMED AT THE DIABLO CANYON POWER PLANT, UNIT NO. 2 On November 16, 2004, the NRC staff participated in a conference call with the staff of Pacific Gas and Electric Company to discuss selected results of the steam generator tube inspections performed at Diablo Canyon Power Plant (DCPP), Unit 2 during the Fall 2004 refueling outage.

A summary of the information provided during the conference call is provided below.

DCPP Unit 2 has four Westinghouse model 51 steam generators. The mill annealed Alloy 600 steam generator tubes have an outside diameter of 7/8 inch and a nominal wall thickness of 0.050 inch. The tubes are explosively expanded (WEXTEX) for the full depth of the tubesheet at each end and are supported by a number of carbon steel tube support plates.

The purpose of the call was to notify the NRC staff pursuant to Technical Specifications 5.6.10.d.2 and 5.6.10.d.4 that axially-oriented primary water stress corrosion cracking indications and circumferential indications were detected at the tube support plate elevations. A total of three circumferential indications were detected. One of these three circumferential indications was also associated with an axially-oriented indication (i.e., a mixed mode indication). All three circumferential indications were considered small (i.e., low voltages). The axial and circumferential components of the mixed mode indication had sufficient separation to be considered non-interacting. Of the 64 axially-oriented primary water stress corrosion cracking indications detected, 53 were previously identified and 11 were new indications. Some of these axial indications required plugging since the depth of the indications outside the tube support plate area exceeded the 40 percent through-wall plugging limit. All of the flaws detected had adequate structural integrity.

The overall results of the inspection were within expectations. In fact, the results of the inspection were not category C-3. Four in-situ pressure tests were performed on indications within the tubesheet region (i.e., W* indications) and no leakage was observed.

During the outage, the licensee noticed that approximately five rolled plugs may be leaking.

This conclusion was based on visual examinations of the plugs which showed moisture and/or a ring of boron deposits around the plug. Each of the tubes involved had been plugged, deplugged and returned to service, and subsequently replugged after at least one cycle of operation.

The licensee attributed the leakage to primary water stress corrosion cracking in the parent tube at the location where the plug is rolled into the tube. In a prior outage at DCPP Unit 1, the licensee identified that tubes that were deplugged and returned to service could experience axial primary water stress corrosion cracking near the tube ends in the area containing residual stress from the original plug installation (approximately 1.5 inches above the tube end for plugs rolled into the tube).

The licensee assessed the potential for primary-to-secondary leakage to occur as a result of the cracks in the parent tube at the location of the plug and concluded that there would be no leakage. This conclusion was based on the location, size, and growth rates of the defects that resulted in these tubes being plugged a second time. The licensee also assessed whether the plug could perform its intended function and concluded that it would. This latter assessment considered whether the tube could become pressurized causing ejection of the plug from the tube. In future outages, the licensee plans to use a different type of rolled plug in tubes that were previously deplugged. The rolled region for this new type of plug will be above the original rolled region (i.e., the new rolled region will be above the location where primary water stress corrosion cracking could be occurring). The licensee plans to notify the industry of this experience.