ML19327B803
| ML19327B803 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 11/03/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19327B800 | List: |
| References | |
| IEB-88-002, IEB-88-2, NUDOCS 8911130359 | |
| Download: ML19327B803 (2) | |
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SAFETY EVALUATION BY THE OFFICE OF flVCLEAR REACTOR REGULATION CLOSEOUT OF BULLETIN 88-02 ISSUES DUKE PCVER COMPAt:Y MCGUIRE t UCLEAR STATION, UNIT 1 DOCKET NO. 50-369 l
i 1.0 INTF:0D0CT10N Duke Power Company (the licensee) submitted its response to NRC Bulletin 88-02,
'Ptpidly Propagating Tatigue Cracks in Steam Generator Tebes" by letters dated March 24, April 25, and June 10, 1988 and by letter dated January 16, 1989.
Bulletin E8-02 requested that licensees for plants with Westinghouse steam generators unploying carben steel support plates take certain specified actions to minimize the potential for a steam generator tube rupture event caused by a rapidly propagatir.g fatigue crack such as cccurred at North Anna Unit 1 on July 15,.1987.
2.0 DISCUSSION The licensee re> orts that the McGuire Unit 1 steam generaturs exhibit evidence of denting at tie uppermost support plate.
Accordingly, items C.1 and C.2 of j
the bulletin are applicable to McGuire Unit 1.
In accordance with item C.1 of the bulletin, the licensee has implemented an i
enhanced primary-tc-secondary leak rate monitering program which is described in the licensee's June 10, 1988, letter.
This enhanced leak rate monitoring program is an interim compensatory measure pending completion of the actions requested in item C.2 of the bulletin and i:RC staf f review and approval of these actions.
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The licensee hos implemented the generic program developed by Westinghouse to resolve item C.2 of the bulletin.
The licensee's implementation of this program l
is described in Westinghouse report WCAP-12060 (Proprietary) which was subr.iitted i
with the licensee's letter. This report describes the analyses which were con.
l ducted to establish the susceptibility of the FcGuire steam generator tubes to l
rapidly prcpagating fatigue cracks and to identify any needed corrective actions.
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The staff has reviewed the Westinghouse generic program and documented its evalu-i stion in Reference 1.
The staff concluded in Reference 1 that the Pestinghouse l
program is an acceptable approach for resolving item C.2 cf the Bulletin.
The l
staff further concluded that the Westinghouse program, if properly innplemented, i
8911130359 891103 l'
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will provide reasonable assurance against further failures of the kind which l
occurred at North Anna Unit 1.
The safety evaluation herein ir.ccrporates the staff's gent:ric Reference 1 evaluation by reference.
The analyses for the McGuire Unit I steam generators conservatively assumed that all unsupported tubes tre dented at the uppermust support plate.
In addition, the strtss ratio End fatigue estimates were based on the assumption of a full u en stress effect (i.e., yield stress), censistent with staff fir. dings in Reference 1.
l Stability ratios for the McGuire Unit I steara generator tubes were determined from detailed analyses prfornwd for PcGuire Unit 2 whose thermal-hydraulic conditions are slightly more limiting than those for Unit 1.
These analyses included tube instability analyses performed with the FAS1VIB computer code using thermal-hyoraulic input from a 3-D ATHOS model.
Flow peaking factors were determined for l
the actual anti-vibration bar geometry et McGuire l' nit 1 on the basis of results i
from air model tests.
The analyses documented in WCAP-12060 show that all unsuppcrted tubes in the I
P.cGuire Unit 1 steam generators satisfy the Westinghouse stress ratio criterion.
The fatigue usage factor for the most liraiting tube is calculated to be 0.95 for a 40-year o rating period with the current fuel cycle parameters (e.g., steam pressure and flow, circulation ratic).
Thus, the licensee has concluded that all tubes in the McGuire Unit I steam generstors are acceptable for continued service i
and that no h6rcVare modifications, preventive tube plugging, or other reasures arc necessary to precludt fatigue cract initiation.
3.0 CONCLUSION
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The staff concludes that the cctions talen by the licensee resche the issues identified in Bulletin 88-02 and are, therefore acceptable. Consistent with l
staff finding bc.11 in Reference 1, the tbove fincirgs are subject to the l
develcpment of administrative controls by the licensee to ensure that updated stress ratio and fatigue usage calculattens are performed in the tvent of any I
significant changes to the steam generator cperating parameters (e.g., steam pressure and flew, circulttien ratio) relative to the reference parametcrs
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essumed in the McGuire Unit 1 onalyses.
4.0 REFERENCE 1.
Safety Evaluation Report. " Evaluation of Westirthouse Methodology to l
l Aodress Item C.2 of NRC Bulletin 88-02* which was transmitted to Westinghouse by NRC letter dated October 2,1967.
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