ML19354E727

Responds to 891129 Ltr Re NRC Bulletin 88-002, Rapidly Propagating Fatigue Cracks in Steam Generator Tubes.

ML19354E727
Person / Time
Site:	Sequoyah
Issue date:	01/24/1990
From:	Michael Ray TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-88-002, IEB-88-2, TAC-67323, TAC-67324, TAC-R00328, TAC-R00329, TAC-R328, TAC-R329, NUDOCS 9002010204
Download: ML19354E727 (9)

Text

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, TENNEOSEE VALLEY AUTHORITY

, CH ATTANOOGA. TENNESSEE 37401 SN 1578 Lookout Place JAN 241990 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen: .

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT (SQN) - NRC BULLETIN 88-02, RAPIDLY ~ PROPAGATING FATIGUE i CRACKS IN STEAM GENERATOR TUBES

Reference:

NRC letter to TVA dated November 29, 1989, " Request for Information, NRC Bulletin 88-02 (TAC Nos. R00328/67323 and R00329/67324) - Sequoyah Nuclear Plant, Units 1 and 2" In response to the referenced letter, the enclosure provides TVA's reply to $

NRC's questions. This response was discussed with Emmett Murphy, of your-organization, on January 4 and 9, 1990. '

No commitments are contained in this submittal. Please direct' questions concerning this issue to K. S. Whitaker at (615) 843-6172.

Very truly yours,

! TENNESSEE VALLEY AUTHORITY' r

Manage , Nuclea teensing and Regulatory Affairs -

Enclosure cc: See page 2 f

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An Equal Opportunity Employer h'

. U.S. Nuclear Regulatory Commission JAN84 W i

cc (Enclosure):

Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. A. Wilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379

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1 ENCLOSURE 1

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Electric Corporation Mr. P. G. Trudel TVA-90-523 Sequoyah Project Engineer January 11, 1990 Tennessee Valley Authority Sequoyah Nuclear Power Plant, DSC-A PO Box 2000 Soddy Daisy. TN 37379 Tennessee Valley Authority Sequoyah Nuclear Power Plant Response to NRC Ouestions - TVA

Dear Mr. Trudel:

The attached text material sumarizes responses to NRC questions regarding l

the '88-02' analysis for Sequoyah Units 1 and 2. These responses were jointly developed between TVA and Westinghouse personnel during meetings held at the Westinghouse Energy Center January 3 and 4,1990; and in '

subsequent telecons between T. A. Pitterle, D. Goetcheus, and Emit Murphy (NRC) Jan. 4, 1990. The responses also incorporate changes in text developed to support the telecon between TVA and Emit Murphy Jan. 9, 1990.

We trust TVA will find the attached consistent with recent discussions.

Please advise Westinghouse if there are questions.

Very truly yours, WESTINGHOUSE ELECTRIC CORPORATION k- N M . J. Garry, M nager l

TVA Sequoyah Project Customer Projects Department cc: D. Goetcheus, IL, 1A D. M. Lafever, IL, IA R.. Smith. IL, IA R. Davis, IL, IA M. Hodge, IL, IA 1

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,, Westinghouse Proprietary Attachment 1: Response to the Request for Additional Information relating to WCAP-12289, (Sequoyah Unit 1 Writeup) ,

1. *...Were these pkts the only information provided to Westinghouse concemitig the AVB insertion j depths ?"

t Response: In addition to providing FiOures 6 2 through 6 5. TVA had numerous discussions with [

l Westin0 house regarding the technique involved in establishing the AVB locations. The TVA l graphical projection method provides a physical representation of the AVB projection measurements, and was determined to provide the same level of accuracy as the Westin0 house arithmetic AVB projection methodology.

a. *Were pro}edion' measurements provided (such as those given in FQures 6-6 thmugh 6 9)?'

4-Response: The AVB maps provided in fiDures 6 2 through 6 5 are based on the graphical projection method (above). These maps show the AVB centertine insertion distance and are based on the best estimate values. Where inconsistencies are apparent in the eddy current data, the structurally '

conservative ' minimum AVB insertion distance' interpretation is used.

b. "Was information concoming the uncertainties associated with the pro}ection measurements ,

communicated to the Westinghouse personnelwho estimated flowpeaking factors?' '

Response: The AVB maps are based on oddy current calls from multiple tubes within each column.

These were plotted to establish AVB projection depths and to segregate the AVBs on the right and l ieft sides of each tube. Communication between TVA and Westinghouse provided adequate L

information to conservatively assess the flow peaking. The flow peaking assessment selectively l considered variations in AVB insertion distance relative to the values mapped in figure 6 2 through t i 6-5 so as to maximize the flow peaking potential forthe various locations.

!- To furth~er confirm the conservatism of the Sequoyah Unit 1 evaluation, fourteen tubes were selected for re evaluation based on their potential sensitivity to flow peaking. This evaluation was performed jointly by TVA and Westinghouse personnel. The tubes evaluated were:

l SG Row Column 1 10 44 9 4 l 8 34 l 8 59 l 2 9 10 9 84 8 24 8 35 3 9 60 8 35 8 60 4 9 91 8 59 8 80 1

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s Westinghouse Proprietary-These tubes were re evaluated based on AUB placements which would produce

• maximum flow peaking". All fourteen tubes rem 1ued to be 4eptable, ,

Four, previously listed as unsupporteu, were identified as being supported. - Tube R8035 in SG 2 is an example of this. It had been listed as unsupported with a peakin0 factor of 1.37.

One tube out of the 14 was found to have less peakin0 when the AVB locations were reviewed.

This tube, R10C44 in SG 1 had been identified for corrective action, and had been stabilized during the June 1988 outa0s. Although unsupported, the flow peakin0 value was reduced -

from 1.20 to 1.00.

Six of the 14 tubes showed no change in support condition or flow peakin0 ,

Using the " maximum peakin0* approach, three tubes were found to have the potential for increased flow peaking; but all remained below the allowable peaking l6mit and continued to be acceptable.

This 14 tube re-evaluation Indcates that the methods described in WCAP 12289 are acceptable and that the critical tubes have been property identified.

2. "Are the AVB insertion plots in Figures 62 through 6 5 based on the positbn of the centerline of the .

AVB7 (or are they based on the position of the bottom surface of the AVB7). Was the answer to this question known to the Westinghouse personnel who performed the flow peakir:0 estimeles7' Response: The AVB maps show the AVB centertine location. This information was provided to Westin0 house prior to the flow peakin0 evaluation.

. 3. 'Are the AVB insertion plots in FQures 6-2 through 6-5 based on the best estimate AVB insertion estimates, or clo they reflect adjustinents to account for AVB insertion uncertainties so as to yield .

conservative estimates of ikw peaking factors ?'

Response: As noted above, the AVB maps show the best estimate AVB locations. Where inconsistencies are apparent in the eddy current data, the structurally conservative ' minimum AVB insertion distance' interpretation is used.

4.

• Please confirm that the followiry statement appearing on page 815 of WCAP-12289 is applicable to Sequoyah Unit 1. 'For AVB pattems leading to significant peaking factors, AVBs were positioned within uncertainties to maximize the flowpeaking factor'.*

Response: The flow peaking assessment selectively considered minor AVB adjustmerts relative to the AVB maps in figure 6 2 through 6-5 so as to maximize flow peaking. As noted above, conservative -

consideration of the AVB locations was reconfirmed in the 14 tube re-evaluation.

2

Westinghouse Proprttary ,

Attachment 2: Response to the Request for Additional Information relating to WCAP 12289 (Sequayah Unit 2 Writeup)  ;

'The staff requests...Information be provided...to demonstrate that (tube R09/C35)...is acceptable for continued service,' ,

i Response: In response to the request for additional information regarding the evaluation of tube R09fC35 in Sequoyah Unit 2 SG 2. Wettinghouse has performed a detailed re evaluation of the AVB positioning used as the basis for the flow peaking model of that tube (See Figure 1)

As a result of the re-evaluation, a new test geometry, now identified as configuration 8o (Figure '

2) was identified P.s defining this geometry and tested in the air, cantilever model at the Westinghouse Science and Technology Center. The test results indicate that the critical velocity which triggers fluideiastic instability for this tube is approximately 25 ft. I sec, it should be noted that the critical velocity for R09C51 in North Anna Unit 1 is 8.9 ft. I sec. Based on these critical velocities, a flow peaking factor of 1.00 is obtained for tube R09/C35 of Sequoyah Unit 2, Steam Generator 2. This tube is acceptable for continued service.

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