ML20005B729
| ML20005B729 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 08/24/1981 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Pilant J NEBRASKA PUBLIC POWER DISTRICT |
| Shared Package | |
| ML20005B730 | List: |
| References | |
| TAC-12589, NUDOCS 8109020022 | |
| Download: ML20005B729 (3) | |
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Docket No. 298 August 24, 1981 Y
s Mr. J. H. P11 ant Director ll
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Licensing 4 Quality Assurance AUG 2 01981 Hebraska Public Power District ki ' g,s wy,muo j
P. O. Box 499 N*
Colunbus, Nebraska f;9601
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Dear ftr. Pilant:
Ml1 By letter dated Februarv 25, 1930 we informed all licensee / users of Vesting-I house icw-pressure turbines that stress corrosion cracks were being found I
in the keyway and bore areas of low-pressure discs. Pecause these cracks were considered to increase the probability of disc failure we requested thct you perforn ultrasonic inspections on your low-pressure discs and justify that your plant could continue to operate safely, f
All Vestinghouse low-pressure turbines at operating nuclear power plants have now been inspected, at least once, for keyway and bore cracks.
Indica-tion of one or both types of these cracks has been found at 20 plants. Al-though all factors related to cracking have not been positively established, operatir.g experience indicates that crack initiation and growth are related to disc tenperature and material characteristics. Westinghouse is continuing to evaluate the effect of other manufacturing and operational variables.
I.Intil a satisfactory solution can be found we believe that it would be pru-dent for you to continue inspecting your lo9-pressure turbine discs en a schedule designed to minimize the probability that a crack will form and grow to a depth that would cause a disc to rupture. Westinghouse has deve-loped a rethod to determine safe inspection and re-inspection frequencies and has submitted this information in Henorandum f4STG-1-P, June 1981 (Pro-prietary) for revicu by the HRC staff.
Our appraisal of the Westinghouse approach is presented in the enclosed Safety Evaluation. He conclude that inspet. tion schedules based on the recommendations in the Westinghouse Memoranduo will provide an acceptably bigh 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.
I In our Safety Evaluation we list four criteria for an acceptable inspection i
schedule.
I request that you cormit to use these criteria for future disc inspections. We believe that such a coeitnent will reduce the probability for a safety probico to such a degree thit the NRC staff would no longer need to monitor your turbine inspections except through the normal activi-ties of our Office of Inspection and Enforcerent. Your connitrent would i
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 7
by Westinghour 810902OO22 810824 h
PDR ADOCK 05000298 1
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. Your response to this request should be subnitted 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 nethodology described in these reports was used to provide its customers with estimates of the probability of disc rupture fron stress corrosion cracking and with analyses of potential missile energies. We shall provide Westinghouse with our evaluation of this riethodology as soon as our resources permit.
Sincerely, i
[
Thoras A. IppoIito, Chief Operating Reactors Branch #2 Division of Licensing
Enclosure:
Safety Evaluation cc w/ enclosure See next page Distribution:
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Mr. J..M. Pflant Nebra.ska Public Power District cc:
'Mr. G. D. Watson, General Counsel Nebraska Public Power District P. O. Box 499 Columbus, Nebraska. 68601 Mr. Arthur C. Gehr, Attorney Snell & Wilmer 3100 Valley Center Phoenix, Arizona. 85073 l
Coofer Nuclear Station ATTN: Mr. L. Lessor Station Superintendent P. O. Box 98 Brownville, Nebraska 68321 Auburn Public Library 118 - 15th Street Auburn, Nebraska 68305 Mr. Dennis Dubois USNRC Resident Inspector P.O. Box 218 Brownsville, NE 68321 a
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