ML13317A798
| ML13317A798 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/10/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Dietch R Southern California Edison Co |
| References | |
| TAC-12582 LSO5-81-12-033, LSO5-81-12-33, NUDOCS 8112290560 | |
| Download: ML13317A798 (3) | |
Text
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UNITED STATES.
NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 December 10, 1981 Docket No. 50-206 LS05-81-12-033 Mr. R. Dietch Vice President Nuclear.Engineering and bperations Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91270
Dear Mr. Dietch:
By letter'dated February 25, 1980 we informed aTT1licensee/users of Westing house low-pressure turbirts that stress corrosion cracks were being found in the keyway and bore areas of low-pressure discs. Because these cracks were considered to increa e the probability of disc failure we requested that you perform ultrasonic inspections on your low-pressure. discs-and justify that your plant could continue to operate safely.
All Westinghouse low-pressure turbines at operating nuclear power plants-have now been inspected, at least once, for keyway and bore cracks. Indta tion of one or both typesof these cracks has been found at 20 plants. }j' though all factors related to cracking have not been positively establishd operating experience indicates that crack initiation and growth are relat'd to disc temperature and material characteristics. Westinghouse is continuing to evaluate theieffect of other manufacturing apd operational variables.
Until a satisfactory solution can be found we.bdlieve that it would be pru dent for you to continue inspecting your low-pressure turbine discs on a schedule designed to minimize the probability that a crack will form and
.grow-to a depth that would cause a disc to ruptute. Westinghouse has deve loped a method to determine safe inspection and re-inspection frequencies and has submitted this information in Memorandum MSTG-1-P, June 1981 (Pro prietary) for review by the NRC staff.
Our appraisal of the Westinghouse approach is presented in the enclosed Safety Evaluation. We conclude that inspection schedules based on the recommendations in the Westinghouse Memorandum will provide an acceptably high degree of assurance that discs will be inspected before cracks can grow to a size that could cause disc failure at speeds up to design speed.
In our Safety Evaluation we list four criteria for an acceptable inspection schedule. I request that you commit to use these criteria for future disc inspections. We believe that such a commitment will reduce the probability for a safety problem to such a degree that the NRC staff would no longer
-need to monitor your turbine inspections except through the normal activi ties of our Office of Inspection and Enforcement. Your commitment would also eliminate the need for you to report these inspection results. to the staff or to transmit the computerized disc data sheets that are prepared by Westinghouse.
Mr.
December 10, 1981 Your response to this request should be submitted within 30 days of re ceipt of this letter.
I also take this opportunity to advise you that on June 11, 1981 Westing house transmitted two proprietary reports related to turbine missiles for NRC staff review and evaluation.
We have been advised by Westinghouse that the methodology described in these reports was used to provide its customers with estimates of the probability of disc rupture from stress corrosion cracking and with analyses of potential missile energies. We shall provide Westinghouse with our evaluation of this methodology as soon as our resources permit.
Sincerely, Original signed by Thomas V. Wambach for/
Dennis M. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing
Enclosure:
Safety Evaluation cc w/enclosure See next page DISTRIBUTION Docket
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December 10, 1981 cc Charles R. Kotheri Assistant General Counsel:
James Beoletto, Esquire Southern California Edison Company Post Office Box 800 Rosemead, Califorria 91770 David R. Pigott Orrick, Herrington-& Sutcliffe 600 Montgomery Street San Francisco, Caljfornia 94111 Harry B. Stoehr San Diego Gas & E14ctric Company P. 0. Box 1831 San'Diego, Califforrdia 92112 Resident InspectorbSan-Onofre NPS c/o U. S. NRC P. 0. Box 4329 San Clemente, California 92672 Mission Viejo Branch Library 24851 Chrisanta-Dri e Mission Viejo, California 92676 Mayor City of San Clemente San Clemente, California, 92672 Chairman Board of Supervisors County of San Diego San Diego, California 92101 California Department of Health ATTN:
Chief, Environmental Radiation Control Unit Radiological Health Section 714 P Street, Room 498 Sacramento, California 95814 U. S. Environmental Protection Agency Region IX Office ATTN:
Regional Radiation Representative 215 Freemont Street San Francisco, California 94111