ML20010J511
| ML20010J511 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/21/1981 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8110050205 | |
| Download: ML20010J511 (2) | |
Text
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$ SMUG SACRAMENTO MUNICIPAL UTILITY DISTRICT O 626.' s Street, Rox 15830, Sacramento, California 95813 116) 452-3211 September 21, 1981 N.(/
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IA DIRECTOR OF NUCLEAR REACTOR REGULATION u,,' DEgou
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JOHN F STOLZ CHIEF OPERATING REACTORS BRANCH 4 f
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WASHINGTON DC 20555 DOCKET 50-312, RANCHO SEC0 NUCLEAR GENERATING STATION UNIT NO. I NRC LETTER, AUGUST 19, 1981, STOLZ TO MATTIM0E The District has carefully followed the problems related to the Westinghouse low pressure turbine stress corrosion cracks in the keyway and bore areas.
During our refuel ing shutdown in early 1981, we encountered problems with keyway cracks in the 11 L.P.
rotor.
This required removing the #1 disc f rom the generator end of the af fected rotor and ul t imately removing the first four stages of rotating blading f rom both the generator and the governor end. The #2 L.P. rotor tested satisfactorily. While at power on August 13, 1981, the modified #1 L.P. rotor failed as a result of blade failure.
We are currently completing the installation of a new universal rotor which incorporates the Westinghouse key plate design feature. This key plat design feature is supposed to significantly reduce the liklihood of cracks in the bore area of Westinghouse rotor discs.
We conclude that the Westinghouse memorandum will provide an acceptably high degree of assurance that discs will be inspected before cracks can grow to a size that coald cause disc failure. This schedule includes inspecti ~n of low pressure turbine discs to minimize the probability that a crack will not grou to a depth greater than 50 percent of the critical crack length.
Our future inspection schedule following Westinghouse recommendations will be:
- 1) The universal rotor currently installed in the #1 L.P. position will be inspected after five full years of operation.
2)
The #2 L.P.
rotor will be reinspected af ter an additional 3.6 years of operation calculated f rom the date that the unit went back on line in May of 1981.
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DIRECTOR OF NUCLEAR REACTOR REGULATION ATTN:
JOHN F STOLZ CHIEF
- 3) Any new discs which may be installed in the future will be inspected before any postulated crack would grow to more than one-half the critical crack depth.
4)
Discs operating with known and measured cracks will be inspected before the time calculated for any crack to grow to 50 percent of the critical crack length.
- 5) The above inspection schedules will be varied to coincide..ith scheduled outages.
6)
Changes to Westinghouse recommendations shall take precedence over the above schedule.
This inspection program will continue until problems related to turbine disc cracking have been satisfactorily resolved.
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" John'[.Mattimoe Assistant General Manager and Chief Engineer l
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