ML20024H438

Discusses Closeout of Bulletin 88-09, Thimble Tube Thinning in Westinghouse Reactors

ML20024H438
Person / Time
Site:	Catawba
Issue date:	05/16/1991
From:	Martin R Office of Nuclear Reactor Regulation
To:	Tuckman M DUKE POWER CO.
References
IEB-88-009, IEB-88-9, TAC-72651, TAC-72652, NUDOCS 9106040029
Download: ML20024H438 (4)

Text

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A i NUCLEAR REGULATORY COMMISSION i-O WASHINGTON. D.C. 20586

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May 16, 1991 Docket Nos. 50-413-and 50-414 Mr. M. S. Tuckman Vi_ce President Nuclear Operations Duke Power Company P. O. Box 1007 Charlotte, NC_ 28201-1007

SUBJECT:

CATAWBA UNITS 1 AND 2 - CLOSE0VT OF BULLETIN 68-09,

" THIMBLE-TUBE THINNING IN WESTINGHOUSE REACTORS" (TAC NOS. 72651 AND 72652)

By letters dated March 16, lo89, April 18,1989, October 1, 1990 and December 6, 1990,. Duke Power Company (DPC) responded to NRC Bulletin 88-09, " Thimble Tube Thinning in Westinghouse Reactors", for Catawba Nuclear Station Units 1 and 2.

The bulletin requested that licensees of operating Westinghouse plants establish and implement an inspection program to periodically confirm incore neutron monitoring system thimble tube integrity. The acceptance criterion of 60%

through-wall wear _ adopted by DPC was based on peak-stress intensities calculated for.a wall-thinning.model generated by Westinghouse.

Thimble tubes were initially examined for wear by:an eddy current method during refueling outages af ter cycle'3 for Unit 1 and after cycle _2 for-Unit 2.

For Unit 1, only a single thimble showed detectable wear. The observed 55%

through-wall wear approached the 60% acceptance criterion, so the defective

~ tube was isolated by-capping it above the. seal table. DPC plans the next Unit'l thimble tube ekaminations after cycle 6.

For Unit 2, thimble-tube wear af te.r two fuel cycles was more severe. Twenty-two (22) of the fif ty-eight (58) thimble tubes showed measurable wear, ranging from 17% to-a maximum of 48% through-wall wear. The ten (10) thimble tubes with through-wall wear greater than 30% were. repositioned by withdrawing them 2 to.3 inches in their guide tubes. By this means the more severely worn l_

area of each tube was_ moved to a core depth where less wear was observed.-

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Both the amount and distribution of thimble wear were generally consistent with y

expectations for a constant or decreasing wear rate at each core position and l

depth. _ Two thimbles showed higher.than-expected wear in cycle 3 and were L

capped. _ For the remaining thimbles, on_the basis of constant wear rates,

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DPC estimated that wall loss would not exceed the 60% criterion for~ Unit 2-ll operation through cycle 4.

DPC plans the next Unit 2 thimble tube examinations l

-af ter cycle 4.

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Mr. M. S. Tuckman May 16, 1991 The DPC submittals state that future action to assure thimble tube integrity (e.g., repositioning, capping or replacement) will be determined by the results of future re-inspections and the reconnendations of the Westinghouse Owners Group Report of the subject. We have reviewed DPC's thimble tube inspection program and find that it responds acceptably to the recommendations of Bulletin 88-09. This completes the staff's actions on this issue as accounted for pursuant to TAC Hes. 72651 and 72652.

Sincerely, o er E. Martin, Sr. Project Manager Project Directorate 11-3 Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation cc: See next page l

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Mr. M. S. Tuckman May 16, 1991 The DPC submittals state that future action to assure thimble tube integrity (e.g., repositioning, capping or replacement) will be determined by the results of future re-inspections and the recommendations of the Westinghouse Owners Group Report of the subject. We have reviewed DPC's thimble tube iaspection program and find that it responds acceptably to the reconmendations of Bulletin 88-09.

This completes the staff's actions on this issue as accounted for pursuant to TAC Nos. 72651 and 72652.

Sincerely,

/s/

Robert E. Martin, Sr. Project Manager Project Directorate 11-3 Division of Reactor Projects - 1/II Office of Huclear Reactor Regulation cc:

See next page DISTRIBUTION:

Docket File NRC & Local PDRs PDII-3 R/F G. Lainas D. Matthews B. Clayton J. Ramsey B. Buckley J. Norberg S. Kirslis Catawba R/F S. Varga

• See Previous Concurrence OFC LA:PDII-3*

PE:PDII-3*

PM:PDII-2*

EMEB*

OGCB*

NAME BClayton/'1\\"

SKirslis:sl BBuckley JNorberg JRamsey M'

4/18/91 4/18/91 4/22/91 4/22/91 DATE 4/17/91 in OFC PM:PDK33 J)gIghb3 NAME -$thrtin:sl i{Matthews 4/h/91 4//h/91 DATE 0FFICIAL RECORD COPY Document Name: CLOSE0VT OF BULLETIN 8809

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0 Mr. M.S. Tuckman Catawba Nuclear Station Duke Power Company cc:

Mr. A.V. Cat r, Esq.

North Carolina Electric Membership Duke Power Company Corp.

422 South Church Street P.O. Box 27306 Charlotte, North Carolina 28242-0001 Raleigh, North Carolina 27611 J. Michael McGarry, 111, Esq.

Saluda River Electric Cooperative, Winston and Strawn Inc.

1400 L Street, N.W.

P.O. Box 929 Washington, D. C.

20005 Laurens, South Carolina 29360 Senior Resident inspector North Carolina MPA-1 Route 2, Box 179N Suite 600 York, South Carolina 29745 P.O. Box 29513 Raleigh, North Carolina 27626-0513 Regional Administrator, Region 11 U.S. Nuclear Regulatory Counission Mr. Frank Modrak 101 Marietta Street, NW, Suite 2900 Project Manager. Mid-South Area Atlanta, Georgia 30323 ESSD Projects Westinghouse Electric Corp.

Mr. Heyward G. Shealy, Chief MNC West Tower - Bay 241 Bureau of Radiological Health P.O. Box 355 South Ccrolina Department of Health Pittsburgh, Pennsylvania 15230 and Environmental Control 2600 Bull Street County Manager of _ York County Columbia, South Carolina 29201 York County Courthouse York, South Carolina 29745 Ms. Karen E. Long Assistant Attorney General Richard P. Wilson, Esq.

N.C. Department of Justice Assistant Attorney General P.O. Box 629 S.C. Attorney General's Office Raleigh, North Carolina 27602 P.O. Box 11549 Columbia, South Carolina 29211 Mr. J. W. Hampton, Station Manager Duke Power Company Piedmont Municipal Power Agency Catawba Nuclear Station 121 Village Drive 4800 Concord Road Greer, South Carolina 29651 York, South Carolina 29745 Mr. Alan R. Herdt, Chief Mr. R.L. Gill, Jr.

Project Branch #3 Nuclear Production Department U.S. Nuclear Regulatory Commission Duke Power Company 101 Marietta Street, NW, Suite 2900 P.O. Box 1007 Atlanta, Georgia 30323 Charlotte, North Carolina 28201-1007