ML20084F415

AO 250-75-8:on 751026,MSIV C Malfunctioned.Cause Not Determined.Msiv Stem Packing & Pneumatic Cylinder Inspected. Investigation of Cause Continuing

ML20084F415
Person / Time
Site:	Turkey Point
Issue date:	11/05/1975
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20084F373	List: ML20084F397 ML20084F415
References
AO-250-75-8, NUDOCS 8304210125
Download: ML20084F415 (3)

Text

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. November 5,.1975

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ne g Office of Inspection and Enforcement ,,( t f U. S. Nuclear Regulatory Commission l']

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ABNORMAL OCCURRENCE 250-75-8 '~

TURKEY POINT UNIT 3 DATE OF OCC.URRENCE, OCTOBER 26, 1975 MALFUNCC' ION 'OF "C" MAIN STEAM

'lSOLATION VALVE A. Conditions Prior to Occurrence The reactor was critical below the power range with -5 intermedia'te range nuclear instrumentation indicating-10 amps. Preparations were being made to shutdown the reactor-i for a scheduled r.cfueling outage.

B. Description of Occurrence At about 1:05 A.M. (Eastern Standard Time) on October 26, 1 1975, the Control Room switch which operates the "C" Main Steam Isolation Valve (MSIV) was placed in the "CLOSF," '

position but the valve did not close. Immediate corrective action taken to closr- the valve was unsuccessful. The

applicable Instrumentation and Control drawings were being studied to determine possible followup action when, at about 2

30 A.M., the valve went closed.

C. Designation of Apparent Cause of Occurrence The exact cause of the occurrence has not been determined.

Inspection.of related electrical and air system components and other valve externals has revealed'no reason for the  ;

valve having remained open.  :

! D. Analysis of Occurrence The analysis of_FSAR Section 14.2.5 i,s applicable-to this occurrence. The analysis states that each of three main-

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l Mr. Norman C. Moseley, Director, Region II-i Page Two j November 5, 1975 i -

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. steam lines has a fast closing stop valve (MSIV).and a ,

check valve. These six valves are arranged to prevent 1

i blowdown of more than one steam generator for any main

! steam line break location even if one valve-doe.s not close.

The analysis then considers an uncontrolled steam release l

' from one steam generator. caused by pipe rupture or valve malfunction. The results presented are a_ conservative j indication of the events which could occur because th'e analysis assumes the most pessimistic combination of

circumstances which could lead to an undesirable power transient following a steam line break. The analysis concludes that no i

1 DNB would occur in the core and that the core would be ultimately shut down by the boric acid in the boron injection tank and the refueling water storage _ tank. Therefore, based on the safety analysis of FSAR Section 14.2.5 and the-fact that there was no steam line break during the mal-function of the "C" MSIV, the health and safety of_the public i

were not adversely.affected by this occurrence.

j E. Corrective Action '

i The "C" MSIV consists of a swing disc which is opened and held open by air pressure acting on a' piston in a pneumatic ^

cylinder. The valve is shut by air pressure _ assisted by spring force. Air flow is controlled by solenoid-operated '

air valves which are energized to open and deenergized to close

the MSIV.

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The immediate corrective action was to ' pull the fuses _to' one-i pair of solenoid operated air valves to ensure that they_were deenergized. When this did not cause the MSIV to close,_the.

fuses were reinstalled and the air lines were disconnected 3

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from the pneumatic cylinder to release any air-which may;have.

i been ' trapped in the cylinder by blockage of the' air lines.

There was no air-trapped in the cylinder and the MSIV remained open. The air lines were then reconnected to the pneumat'ic cylinder. .

l Followup corrective action _was to inspect'the MSIV stem- .  :

packing and-the pneumatic cylinder internals for signs;of' 1

' mechanical binding. No indication'of binding _was found in ,

i either case. ,

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I l ,The valve has been satisfactorily cycled'approximat'ely-nine '

times since the occurrence. The inve,stigation to determine the cause of the occurrence is continuing. .

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4 Mr. Norman C. Moseley, Director, Region II.

~ Page Three November 5, 1975 '

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F. Failure Data i 'The "C" MSIV is.a 26 inch, 600.lb. A.S.A. Main Steam Line l- Trip Valve manufactured by Schutte and Koerting Company.

] There have been no previous Abnormal Occurrences involving-d i a MSIV.

j Very truly yours, l A

Al.D.Y/s~ chmidt

) Vice President

Power Resources l MAS /cpc -

i-l cc: Jack R. Newman, Esquire ,

Director, Office of Inspection and Enforcement. (40) i Director,. Office of Management Information and

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