ML063390165

(Vogtle), Unit 1 - Summary of Conference Call Regarding the 2006 Fall Outage Steam Generator Tube Inspections

ML063390165
Person / Time
Site:	Vogtle
Issue date:	12/19/2006
From:	Martin R NRC/NRR/ADRO/DORL/LPLII-1
To:	Grissette D Southern Nuclear Operating Co
Martin R, NRR/DORL, 415-1493
References
TAC MD3371
Download: ML063390165 (5)

Text

December 19, 2006 Mr. D. E. Grissette Vice President Southern Nuclear Operating Company, Inc.

P.O. Box 1295 Birmingham, AL 35201-1295

SUBJECT:

VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 (VOGTLE) -

SUMMARY

OF CONFERENCE CALL REGARDING THE 2006 FALL OUTAGE STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD3371)

Dear Mr. Grissette:

On October 18, 2006, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with Southern Nuclear Operating Company, Inc., representatives regarding steam generator inspection findings during the fall 2006 refueling outage. The NRC staff is forwarding the enclosed summary for your information.

Sincerely,

/RA/

Robert Martin, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-424

Enclosure:

October 18 Conference Call Summary cc w/encl: See next page

ML063390165 NRR-106 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/LPL2-1/BC NAME RMartin MOBrien EMarinos DATE 12 /11 /06 12 /18 /06 12 / 19 /06

OCTOBER 18, 2006, CONFERENCE CALL

SUMMARY

STEAM GENERATOR TUBE INSPECTIONS VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 DOCKET NO. 50-424 On October 18, 2006, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with Southern Nuclear Operating Company, Inc., representatives, to discuss steam generator (SG) inspection activities at Vogtle Electric Generating Plant, Units 1 and 2, (Vogtle Unit 1 and Vogtle Unit 2), particularly those activities during the Vogtle Unit 1 fall refueling outage (designated 1R13). A summary of the information discussed during the call along with some background information is provided below.

Vogtle Unit 1 has four model F SGs designed and fabricated by Westinghouse. Each SG contains 5626 thermally treated Alloy 600 tubes with an outside diameter of 0.688 of an inch and a nominal wall thickness of 0.040 of an inch. The tubes are hydraulically expanded for the full depth of the tubesheet at each end and are supported by a number of stainless steel tube supports. In the U-bend region, the tubes are supported by anti-vibration bars. The tubes are arranged in a square pitch.

Vogtle Unit 1 SGs began commercial operation in 1987. In 2002, there was an inadvertent addition of phosphate to the Unit 1 and Unit 2 SGs. In the spring of 2004, Vogtle Unit 2 pulled two tubes to investigate crack-like indications at the expansion transition. A laboratory non-destructive examination of both of these tubes indicated that there was no cracking at the expansion transition. Destructive examination of one of these tubes confirmed there was no cracking at the expansion transition. In the spring of 2005, Vogtle Unit 1 identified cracking in bulges within the tubesheet. No crack-like indications were found during the fall 2005 inspection in Vogtle Unit 2. During the recently completed fall 2006 SG tube inspections at Vogtle Unit 1, crack-like indications were identified at the expansion transition. These findings are discussed below. The next Vogtle Unit 2 SG tube inspections are scheduled for the spring of 2007.

During the 1R13 outage, 100 percent of the tubes in SGs 2 and 3 were inspected with a bobbin coil. In addition, the U-bend region of 50 percent of the row 1 and 2 tubes, and 100 percent of the dings and dents greater than 5 volts in the hot leg in SGs 2 and 3 were inspected with a rotating probe. The SGs were chemically cleaned before the tube inspections and the SGs operate at a hot leg temperature of 618 o F.

During 1R13, +Point' inspections of the top of the tubesheet region were planned for 50 percent of the tubes in SGs 2 and 3. During this initial sample, indications of outside diameter stress corrosion cracking were found in several tubes at the bottom of the expansion transition region in both SGs. As a result of finding these indications, the scope of inspection at the top of the tubesheet was expanded to include 100% of the tubes in SGs 2 and 3 and 25 percent of the tubes in SGs 1 and 4. The extent of this inspection was from 3 inches above to 3 inches Enclosure

below the top of the tubesheet. As a result of finding indications in the initial sample inspection in SGs 1 and 4, the scope of the inspection at the top of the tubesheet was expanded to include 100 percent of the tubes. At the time of the conference call, 10 indications had been identified:

3 in SG 1, 2 in SG 2, 3 in SG 3, and 2 in SG 4. The licensee indicated that evaluations for other possible indications, some in the sludge pile region, were still ongoing in SG 4.

For SGs 1, 2 and 3, the indications are predominantly located in low row, high column tubes along the periphery (between rows 1 through 6 and between columns 103 through 119).

In order to confirm the indications, five different inspection methods were used: +Point',

Ghent, 3 Coil Delta, and the 0.080 and 0.115 pancake coil. All of the inspection methods confirmed the indications with the exception that some of the small amplitude signals were not identified with the 0.080 pancake coil. Given these results, the licensee concluded that these indications are cracks.

The largest crack-like indication was measured to have a circumferential extent of 180 degrees.

The maximum reported depth was 67 percent throughwall. The indication with the largest circumferential extent was not the same indication that had the maximum depth. The voltages associated with the indications were approximately 0.2 volts, although there were two indications that had voltages of 0.60 volts and 0.73 volts. A historical review of the +Point' data for the tubes in which the ODSCC indications were detected this outage was performed.

This review did not identify any precursor signals in these tubes.

The licensee stated that it had alerted the industry (other licensees of pressurized-water reactors) regarding this issue.

All tubes with crack-like indications will be plugged and stabilized. The licensee considered pulling a tube or tubes, but due to a major tube-pull project overseas, the licensee was not able to pull a tube given its outage schedule. The licensee will evaluate pulling a tube during the next refueling outage. Due to the location of the tubes with crack-like indications in relation to the divider plate, it is not clear whether pulling a tube is feasible. With respect to similar operating experience, the licensee indicated that Comanche Peak Unit 1 had first detected outside diameter circumferential cracks in a similar region of the tube bundle.

The licensee also stated there were indications near the top of the tubesheet that were identified with the +Point' probe but not confirmed with the Ghent, 3 Coil Delta probe or the 0.080 coil. These indications had voltages of approximately 0.06 volts to 0.08 volts.

In addition to crack-like indications found during the inspection, a volumetric flaw above the cold leg flow distribution baffle measuring 42 percent through-wall was detected in one tube.

The indication was attributed to a loose part. +Point' inspections were performed at this elevation for a 2-tube buffer surrounding this volumetric flaw. No possible loose parts were identified during this inspection. Given the location of the indication, visual inspections could not be performed. Other volumetric indications were observed in SG 2, however, they measured less than 10-percent through-wall.

Inspections were performed on a sample of bulges and overexpansion in the tubesheet region (i.e., from the top of the tubesheet to 17 inches below the top of the secondary face of the tubesheet). No indications were found during these inspections.

Based on the information provided, the NRC staff did not identify any technical issues that warranted follow-up action at this time.

Vogtle Electric Generating Plant, Units 1 & 2 cc:

Mr. Laurence Bergen Mr. D. E. Grissette, Vice President Oglethorpe Power Corporation Southern Nuclear Operating Company, Inc. 2100 East Exchange Place P.O. Box 1295 P.O. Box 1349 Birmingham, AL 35201-1295 Tucker, GA 30085-1349 Mr. N. J. Stringfellow Arthur H. Domby, Esquire Manager, Licensing Troutman Sanders Southern Nuclear Operating Company, Inc. Nations Bank Plaza P.O. Box 1295 600 Peachtree Street, NE Birmingham, AL 35201-1295 Suite 5200 Atlanta, GA 30308-2216 Mr. T. E. Tynan, General Manager Vogtle Electric Generating Plant Resident Inspector Southern Nuclear Operating Company, Inc. Vogtle Plant 7821 River Road 8805 River Road Waynesboro, GA 30830 Waynesboro, GA 30830 Mr. Jeffrey T. Gasser Office of the County Commissioner Executive Vice President Burke County Commission Southern Nuclear Operating Company, Inc. Waynesboro, GA 30830 P.O. Box 1295 Birmingham, AL 35201-1295 Mr. Steven M. Jackson Senior Engineer - Power Supply Municipal Electric Authority of Georgia 1470 Riveredge Parkway, NW Atlanta, GA 30328-4684 Mr. Reece McAlister Executive Secretary Georgia Public Service Commission 244 Washington St., SW Atlanta, GA 30334 Mr. Harold Reheis, Director Department of Natural Resources 205 Butler Street, SE, Suite 1252 Atlanta, GA 30334 Attorney General Law Department 132 Judicial Building Atlanta, GA 30334