ML17339B073

LER 80-007/01T-0:on 800507,while Performing Planned Maint as Result of Problem on Unit 3 (LER 250-79-31),disc Stud Nut Was Discovered Missing from 4A Main Steam Check Valve.Caused by Failure of Associated Locking Device

ML17339B073
Person / Time
Site:	Turkey Point
Issue date:	05/21/1980
From:	Schoppman M FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17339B072	List: ML17339B071 ML17339B073
References
LER-80-007-01T, LER-80-7-1T, NUDOCS 8006030456
Download: ML17339B073 (4)

Text

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'n a'result of a problem initially detected on Unit No. 3 '(see LER 250-79-31), the disc stud nut

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was discovered to be missing from the 4A main steam check valve. The nut was recovered from the turbine control valve.. The disc and disc stud'ere in"the proper. position and the valve was fully operable as found although the disc stud had sustained some wear damage from the loose flat

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VRPR'JSLJQ 41 CAUSS GSSCRIPTION ANO CORRSCTIVS A~iQNS

~i o The cause of the stud nut dislod ing from the disc stud was f'ailure of the associated locking device.. Examination of .the other two HSCVs revealed minor disc stud dama e. Disc st d w'e renlaced d an im roved lockin device will be installed on all. three NSCVs rior S~

to starting up from cold shutdown. MSIVs were also examined.

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REPORTABLE OCCURRENCE 251-80-07 LICENSEE EVENT REPORT PAGE THO Additional Event Descri tion and Probable Conse uences:

On >lednesday, May 7, 1980, in the course of performing planned maintenance scheduled as a result of a problem initially detected on Unit No. 3 (see LER 250-79-31),

the disc stud nut was discovered missing from the 4A bin steam check valve (MSCV).

The disc and disc stud were in the proper position -~nd the valve was fully operable as found. The disc stud nut was subsequently recovered from the turbine control valve. The 4A MSCV disc stud had sustained some wear damage from the loose washer which had remained in place. The 4B and 4C MSCVs were inspected and the disc stud nuts were found in place although some distress was noted on the disc stud. Addition-ally, the main 'steam isolation valves'HSIVs) were inspected.

Additional Cause Descri tion and Corrective Actions:

The cause of the disc stud nut dislodging from the disc stud ~~as failure of its associated locking device. Vibration 'resulted in the disc stud nut "backing off" the disc stud. The disc studs and disc stud nuts on all three MSCVs will be replaced and an improved locking device will be installed prior to starting up from cold shutdown. The improved locking device has been installed on all three MSIVs.

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