ML20059D103
| ML20059D103 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 08/30/1990 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20059D100 | List: |
| References | |
| IEB-88-002, IEB-88-2, NUDOCS 9009060087 | |
| Download: ML20059D103 (2) | |
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-ENCLOSURE 1
. SAFETY EVALUATION REPORT PORTLAND GENERAL ELECTRIC COMPANY TROJAN NUCLEAR PLANT, l
L DOCKET NO. 50-344 L
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1.0 INTRODUCTION
' Portland General Electric Company (the licensee) submitted its response to NRC Bulletin 88-02, " Rapidly Propagating Fatigue Cracks in Steam Generator Tubes"-
l by letters dated March 11. April 1.-ano Mcember 23, 1988, and by letters
' dated March 19 and June 22, 1990..Bulletin 88-02 requested that licensees for 1
plants with Westinghouse steam generators employing carbon steel support plates take certain actions (specified in the bulletin) to minimize the potential for a steam generator tube rupture event caused by a rapidly propagating fatigue crack such as occurred at North Anna Unit 1 on July 15, 1987.
- 2.0 -DISCUSSION The licensee reports that the Trojan steam generators exhibit' indications of denting at the uppermost support plate.
Accordingly, items C.1 and C.2 of the bulletin are applicable to Trojan.
a In accordance with item C.1 of the bulletin, the licensee has implemented an enhanced primary-to-secondary leak rate monitoring program which is described
j in the' licensee's March 11 and April 1, 1988 submittals. This enhanced leak rate monitoring program is an interim compensatory measure pending completion i
of the' actions requested in item C.2 of the bulletin and NRC staff review and approval of these actions.
The licensee has implemented the generic program developed by Westinghouse to resolve item C.2 of the bulletin. The licensee's implementation of this program for Trojan is described in Westinghouse reports WCAP-12024 (Proprietary version) and WCAP-12023 (Non-Proprietary version)_ which were i
submitted with the licensee's letter dated December 23, 1988.
These reports describe the analyses which were conducted to establish the susceptibility _of the Trojan, steam generator. tubes to rapidly propageting fatigue cracks and to' identify any needed corrective actions.
The staff has reviewed the Westinghouse generic program and documented its tevalua. tion in Reference 1.
The staff concluded in= Reference 1 that the Westinghouse program is an-acceptable approach for resolving item C.2 of the Bulletin. The staff further concluried that the Westinghouse program, if
- properly implemented, will provide reasonable assurance against further 0
failures'of the kind which occurred at North Anna Unit 1.
The safety evaluation herein incorporates the staff's generic Reference 1 evaluation 'by
- reference.
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lThe asialysesWr the' Trojan steam generators conservatively assumed that all unsupported tubes are dented at the uppemost support plate.
In addition, the stress ratio and fatigue estimates were based on the assumption of a full mean stress effect (i.e., yield stress), consistent with staff findings in Reference 1.
Stability ratios for the Trojan steam generators tubes were detemined from
-the FASTVIB computer code using thermal-hydraulic input from a 3-D ATHOS model H
for assumed referer.ce o>erating conditions (e.g., steam pressure and flow, l:
circulation ratio)~ whic are conservative for current operating cycle l
anti-vibration bar (AYB)g factors were determined for the actualinsertion configurati parameters.
Flow peakin 9
results from air model tests.
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The staff requested additional infomation from the licensee concerning the-l l
conservatism of the flow peaking factor estimates by letter dated January 30,
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.1990._ On behalf of the licensee, Westinghouse reevaluated the AVB insertion configurations and identified a number of revisions. These revisions were reflected in an updated assessment of flow peaking factors which were provided T
to the !!aff by letters dated March 19 and June 22, 1990. This updated assessment included en additional air model test of a potentially limiting l
AVB configuration. The staff finds that these submittals adequately resolve L
the issues raised in the staff's January 30, 1990 letter.
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The analyses documented in WCAP-12023 show that all unsupported tubes in the l
Trojan steam generators satisfy the Westinghouse stress ratio criterion and are acceptable for continued service. The fatigue usage factor for the most limiting tube remaining in service is calculated to be 0.18 for a 40 year operating period with the assumed reference operating parameters.
3.0 C0hCLUSION
.The' staff concludes that the actions taken by the licensee resolve the issues identified in Bulletin 88-02 and are, therefore, acceptable.
Consistent with
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staff finding No.11 in Reference 1, the above findings are subject to the 4
development of administrative controls by the licensee to ensure that updated i
stress ratio and fatigue usage calculations are perfomed in the event of any significant changes to the steam generator operating parameters (e.g., steam pressure and flow, circulation ratio) relative to the reference parameters assumed in the analyses for Trojan.
4.0~ REFERENCE 1.
Safety Evaluation Report, " Evaluation of Westinghouse Methodology to Address Item C.2 of 11RC Bulletin 88-02" which was transmitted to 4
- Westinghouse by letter dated October 2, 1989.
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