ML18094B414

Outlines Plan & Basis for Plan to Update Steam Generator Tube Fatigue Evaluations Performed by Westinghouse in Response to NRC Bulletin 88-002

ML18094B414
Person / Time
Site:	Beaver Valley, Salem
Issue date:	03/27/1990
From:	Johnson W WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	Richardson J Office of Nuclear Reactor Regulation
Shared Package
ML18094B415	List: ML18094B414
References
IEB-88-002, IEB-88-2, NS-NRC-90-3498, NUDOCS 9004230506
Download: ML18094B414 (3)

Text

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U.S. Nuclear Regulatory Commission NS-NRC-90-3498 ATTN: Document Control Desk March 27, l 990 Washington, D.C. 20555 ATTENTION: Mr. J.E. Richardson Director, Division of Engineering Technology

Subject:

Steam Generator Tube Fatigue Evaluations Update

Dear Mr. Richardson:

This letter outlines a plan and the basis for this plan to update steam generator tube fatigue evaluations performed by Westinghouse in response to NRC Bulletin 88-02. As these evaJuations prog~essed from late 1987 to, in particular, late 1988, methods for defining AVB position uncertainties improved and a larger flow peaking test data base showed. i~creased sensitivity to AVB positions. On this basis, it i~

prudent to review some of the earlier completed analyses ..

To date, reevaluations of earlier reports have been completed for six plants and a reevaluation partially completed for*a seventh plant. These efforts have led to the identification of a total of two tubes requiring corrective action that were not included in the original assessment. In one case, Diablo Canyon Unit 1, a tube was identified for corrective action as a consequence of an error in transposing graphical AVB data that was supplied by another vendor. Following this occurrence, all other plants that used graphical input to prepare AVB maps were reviewed and no other case of a transposition error was identified. For plants

• having the eddy current review for AVB positions performed by Westinghouse, AVB depth projections are used as an independent check on AVB positions which further minimizes the potential for an AVB mapping error.

For Salem Unit 1, the reassessment ~ompleted to date has identified one additional tube requiring corrective action. In this case, increased adjustments of AVB positions further away from the best estimate positions to account for position uncertainties resulted in a higher flow peaking factor than the original evaluation. The larger data base on flow peaking factors permits identification of more limiting AVB positions than possible for the earlier assessments. This situation forms the basis for the planned review of the tube fatigue evaluations completed prior to November 1988. Evaluations completed since this date have included increased efforts to establish AVB positions to maximize flow peaking based on extensive flow peaking tests. Consequently, these later evaluations do not require a reevaluation.

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Jhe existing C'~luations completed prior to November 1988 have ide~tified the most probable, limiting tubes relative to tube fatigue sensitivity .

. T-he later ass.;os11ients and planned reevaluations more extensiv'?1y incorporate lo,,g;.. probability AVB positions in the evaluation to increase the confidence t~~t all potentially affected tubes nave been identified.

A total of 3 t~ 4 months are necessary to complete the reevalu~tion. In the interim, w~stinghouse is not recommending that any action be taken by the identified plants.

To identify the tube fatigue analyses requiring review, the plants for which Westinghouse has completed the evaluations have been grouped into six categories. These categories are identified in Table 1 (attached).

Categories 1 to 4 do not require reevaluation for the reasons noted in the table; therefore, the associated plant names are not listed. The reevaluations have been completed for the Category 5 plants and the results transmitted to tbe respective utilities. As noted above, one tube in Diablo Canyon Unit 1 for the Category 5 plants was identified for corrective action. There are 9 plants in Category s*for which reevaluation will be performed. To date in this group, one tube in Salem Unit 1 has been identified for corrective action.

Westinghouse intends to complete the reevaluation for the Category 6 plants over the next 3 to 4 months. A letter summarizing the results of these assessments will be transmitted to the plant owners upon completion of these activities.

If there are any questions on this transmittal, please contact T.A. Lordi (412-374-4311) of my staff.

n, Manager fety Department

c I TABLE 1 PLANT CATEGORIES FOR TUBE FATIGUE EVALUATION CATEGORY PLANTS

1. Plants with AVB Modifications o Performed with projections o Small uncertainty on AVB positions o Negligible flow peaking effects o Reevaluation not required

2. Plants with large margins o Reevaluation not required

3. Plants with round bars o Round bars do ~ot show high peaking factors or sensitivity.

as found for square bars o Reevaluation not required

4. Evaluation performed since late 1988 o Sensitivity to AVBs fully recognized o Conservative evaluations performed o Reevaluation not required

5. Reevaluation already completed o Sensitivity analysis performed Oiablo Canyon 1 and 2 Sequoyah l and 2 Trojan Point Beach Z

6. Reevaluation should be performed o Evaluation performed prior to 11/88 Indian Point Z o Sensitivity analysis to be performed Kewaunee o 9 plants Zion l McGuire Z Beaver Valley 1 and 2 Salem l and Z Ginna