ML070320194

Summary of Conference Call Regarding Steam Generator Tube Inspections

ML070320194
Person / Time
Site:	Sequoyah
Issue date:	02/06/2007
From:	Moroney B NRC/NRR/ADRO/DORL/LPLII-2
To:	Singer K Tennessee Valley Authority
Moroney B, NRR/DORL, 415-3974
Shared Package
ML070320259	List: ML070320194 ML070330020
References
TAC MD3534
Download: ML070320194 (6)

Text

February 6, 2007Mr. Karl W. SingerChief Nuclear Officer and Executive Vice President Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

SUBJECT:

SEQUOYAH NUCLEAR PLANT, UNIT 2 -

SUMMARY

OF CONFERENCECALL REGARDING STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD3534)

Dear Mr. Singer:

On December 11, 2006, the U.S. Nuclear Regulatory Commission (NRC) staff participated in aconference call with Tennessee Valley Authority (TVA) representatives regarding the steam generator tube inspection activities during the 2006 refueling outage at Sequoyah Unit 2.

Enclosed is a brief summary of the conference call prepared by the NRC staff. The materials provided by TVA in support of the call are attached to this summary. If you have any questions regarding this material, please contact me at (301) 415-3974.Sincerely,/RA/Brendan T. Moroney, Project ManagerPlant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor RegulationDocket No. 50-328

Enclosure:

As stated cc w/enclosure: See next page

ML070320194Package: ML070320259 Attach: ML070330020 NRR-106OFFICELPL2-2/PMLPL2-2/LACSGB/BCLPL2-2/BC(A)NAMEBMoroneyRSolaEMurphy for AHiseras signed onMChernoffDATE2/6/072/5/0701/29/072/6/07 Enclosure

SUMMARY

OF DECEMBER 11, 2006 CONFERENCE CALLSTEAM GENERATOR TUBE INSPECTIONSSEQUOYAH NUCLEAR PLANT, UNIT 2DOCKET NO. 50-328On December 11, 2006, the Nuclear Regulatory Commission staff participated in a conferencecall with representatives of the Tennessee Valley Authority (the licensee) regarding the results of the steam generator (SG) tube inspections performed during the 2006 refueling outage at Sequoyah Unit 2. A summary of the information provided during the call is discussed below.The four SGs at Sequoyah Unit 2 are Westinghouse model 51. Each SG containsapproximately 3400 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. Each tube is roll-expanded for approximately 2.75 inches from the bottom of the tubesheet, and is secured into the remaining portion of the tubesheet by the Westinghouse Explosive Tube Expansion process. The tubesheet is approximately 21 inches thick and each tube is expanded for essentially the full thickness of the tubesheet. Each SG contains seven carbon steel tube support plates with drilled holes through which the tubes pass.In addition to a depth-based tube repair criteria, the licensee is authorized to apply the voltage-based tube repair criteria for predominantly axially-oriented outside diameter stresscorrosion cracking (ODSCC) within the tube support plates. The licensee is also authorized toleave flaws within the tubesheet region in service, provided they satisfy the W* repair criterion. Prior to the call, the licensee was provided with discussion points to help facilitate the phoneconference. In support of the phone call, the licensee provided the attached document that addressed the discussion points and provided inspection status as of 10:30 a.m. on December 11, 2006. At the time of the call, the eddy current inspections were nearly 100 percent complete. No unusual degradation or unexpected conditions were detected during the inspections. Additional clarifying information or information not included in the document provided by thelicensee is summarized below.Acronyms used by the licensee in the material they provided include:RFO (refueling outage), HTS (hotleg tubesheet), TSP (tube support plate), AVB (antivibration bar), MBM (manufacturing burnish mark), DSI (distorted support indication), OXP (overexpansion), BLG (bulge), ET (eddy current testing).The rotating pancake coil (RPC) probe used for the examination of the hot leg top oftubesheet region included a + Point TM coil.At the time of the call, 42 tubes had been preliminarily identified to be plugged; however,the tube plugging list was still being finalized. The licensee was planning to pull a tube this outage as part of implementing thevoltage-based repair criteria. The tube selected to be pulled had a 4.74-volt bobbin coil indication.Possible Loose Parts (PLPs) identified in SG 3 were determined to be deposits bridgingbetween the tubes.The enhanced technique for loose part wear detection referenced in the materialprovided by the licensee is the use of a three frequency (turbo) mix.The Foreign Object Search and Retrieval inspections included the annulus region, tubelane, and the blowdown lane at the top of tubesheet. In addition, one column in each of the four quadrants in the SG was to be visually inspected for hard sludge. Visual inspections were also planned for all locations with PLPs. All of the identified PLPs were at the top of tubesheet. Radiological dose was also considered in determining the need for a visual inspection.All four SGs were scheduled to be sludge lanced.

The circumferential ODSCC indication identified in SG 1 (in the tube located in row 45,column 39) was associated with a 35-volt dent.There were no crack-like indications identified on the cold leg side of the SGs, but therewere some cold leg thinning indications identified.An outside diameter volumetric indication was detected in SG 2. The rotating probeeddy current indication hasn't changed in appearance; however, the bobbin coil signal rotated in the upward direction when compared to the 2003 data. Since the indication may be a crack, the tube was scheduled to be plugged.The number of Primary Water Stress Corrosion Cracking (PWSCC) indications in thetubesheet region was within projections. Voltages of the dents associated with the axial PWSCC indications identified near TSPswere approximately 3 to 6 volts.All axial and circumferential PWSCC indications identified in the U-bend region were intubes in row 4 or less. As a result, the licensee did not expand the scope of the inspections.One tube (row 12, column 56) in SG 3 had two circumferential indications at the seventhhotleg tube support plate (TSP). The indications were associated with a 4.09-volt dent.

The indications were very small (less than 5 percent of the cross sectional area of the tube was affected).Only a few of the axial ODSCC indications were listed in the material supplied by the licensee. Two freespan axial ODSCC indications were identified. The indications werecharacterized as being very small. One of the indications (SG 2, row 8, column 2) was associated with a 6.18 volt dent. The indication was not initially detected by bobbin and part of the indication extended into the TSP region. Given the potential for cracks to grow outside the tube support plate region, the rotating probe data for all of the DSI with bobbin voltages greater than 1 volt were evaluated to confirm the indications stayed within the TSP.There are little clusters of dented tubes around the periphery of the SGs. Theseclusters are located approximately every 60-degrees around the SG and are associated with blocks/wedges used to position and support the TSPs.The staff did not identify any issues that required follow-up action at the time of the call;however, the staff asked to be notified in the event that any unusual conditions were detected during the remainder of the outage.

Attachment:

TVA Info Mr. Karl W. SingerSEQUOYAH NUCLEAR PLANTTennessee Valley Authority cc: Mr. Ashok S. Bhatnagar, Senior Vice President Nuclear Operations Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Preston D. Swafford, Senior Vice PresidentNuclear Support Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801Mr. Larry S. Bryant, Vice PresidentNuclear Engineering & Technical Services Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801General CounselTennessee Valley Authority 6A West Tower 400 West Summit Hill Drive Knoxville, TN 37902Mr. John C. Fornicola, ManagerNuclear Assurance Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801Ms. Beth A. Wetzel, ManagerCorporate Nuclear Licensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801Mr. Robert H. Bryan, Jr., General ManagerLicensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801Mr. Randy Douet, Site Vice PresidentSequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37384-2000Mr. Glenn W. Morris, ManagerLicensing and Industry Affairs Sequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37384-2000Mr. David A. Kulisek, Plant ManagerSequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37384-2000Senior Resident InspectorSequoyah Nuclear Plant U.S. Nuclear Regulatory Commission 2600 Igou Ferry Road Soddy Daisy, TN 37379Mr. Lawrence E. Nanney, DirectorDivision of Radiological Health Dept. of Environment & Conservation Third Floor, L and C Annex 401 Church Street Nashville, TN 37243-1532County MayorHamilton County Courthouse Chattanooga, TN 37402-2801Ms. Ann P. Harris341 Swing Loop Road Rockwood, TN 37854