ML20084C132

RO 251-74-6:on 741201,w/planned Shutdown in Progress,Turbine Tripped.Caused by Failure of Turbine Control Valve Spring Adjusting Bolt.Defective Bolt Replaced & Zyglo Testing of Remaining Three Bolts Performed

ML20084C132
Person / Time
Site:	Turkey Point
Issue date:	12/20/1974
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Case E US ATOMIC ENERGY COMMISSION (AEC)
References
RO-251-74-6, NUDOCS 8304070540
Download: ML20084C132 (2)

Text

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l} q f f m , x r- 3-or December 20, 1974 Mr. Edson G. Case, Acting Director /N Office of Regulation .W

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Directorate of Licensing ,C/ ' 'Vi U. S. Atomic Energy Commission .

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Dear Mr. Case:

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UNUSUAL EVENT NO. 251-74-6 \.

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5 TURKEY POINT PLANT UNIT NO. 4 j DOCKET NO. 50-251 0 FAILURE OF TURBINE CONTROL VALVE D SPRING ADJUSTING BOLT

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In accordance with Technical Specification 6.6.2b, the following unusual event is reported:

On December 1, 1974, planned shutdown of Turkey Point Unit No. 4 was in progress.

Problems were encountered in affecting complete shutdown, and the turbine was tripped at 6:40 A.M. Generator output at the time of the turbine trip was approximately 300 MNo. I Investigation of the turbino control problem revealed that No. 1 [;

turbine control valve spring adjusting bolt had failed causing ^

the control valve to remain ~open. With this one valve remaining open, continued governor adjustments resulted in the interceptor valves closing. This appeared as a turbine run-back to the operating personnel and the load decrease in conjunction with the opening of the reheat the turbine. safety valves was the reason for tripping The purpose of the control valve spring adjusting bolt is to compress the compression springs which hold the valve tightly on the seat when the valve is in the closed position. The failure

- of the bolt was in the threaded area and appeared to have occurred in several increments rather than all at once.

Immediate corrective action consisted of replacing the defective bolt and "Zyglo" testing the remaini.ng three bolts for No. 4 turbine.

No defects viere found in the other three bolts. The 8304070540 741220 12331 PDR ADOCK 05000251 S PDR COPY SENT ITGION >

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Mr. Edson G. Case, Acting Director Page Two December 20, 1974 ,

bolts for turbine No. 3, which was down for overhaul, were also "Zyglo" tested and one of these was found to be defective. The turbine vendor, Westinghouse, is analyzing the two defective bolts as to material and mode of failure. Permanent corrective action will be based on the Westinghouse analysis and recommenda-tions.

Very truly yours,

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s. D. Schmidt  ;

Vice President Power Resources GEL /cpc cc: Mr. Norman C. Moseley g, Jack R. Newman, Esquire e

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