ML20086D932

Updated AO 73-28:on 730910,microswitch Installed in Differential Pressure Indicating Switch 2-129B Failed to Actuate at Required Setpoint.Complete Assembly Replaced When Insp Revealed Excessive Binding in Switch Actuating Arm

ML20086D932
Person / Time
Site:	Vermont Yankee
Issue date:	09/18/1973
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086D933	List: ML20086D932 ML20086D935
References
AO-73-28, VYV-3026, NUDOCS 8312050679
Download: ML20086D932 (2)

Text

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Director Y Di re c to ra te of 1.iccasinp g unnedSnaesAlescenJrnyC-tssion g. RECENED -

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Abnor rul Occurrence No. A0-73-28 fad secu.n 9/ *

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Gentlemen: U1 As defined by Technical Specifications for the Vermont Yanime

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Abno rru l Occurrence as AU- / _i- as .

At approximately 1330 on September 10, 1973, while perf orcing a monthly functieaal tent on the Low P re:,n u re Coolant Injection Syutem (LPC1) break detect ion logic (i.'., A>ll d/p acrow riset s) , a microswi tch

. mtalled in DPIS 2-12913 failed to tetuate at the required setpoint of 1 (+J.5) psid aa specified in Table 3. 2.1 of t.he Technical Specifications.

The mim oswit.ch actuating arm uas mechanically bound and fniled to drop into the cam valley. Function.tlly , this swi t ch ope rat es in conjunction wi t h DP f S 2-129D to act.uat e a relay in thei r respect he logic strings to close t he Loop "il" LPCI valve and actuate the Loop "A" Recircu lation val vea .

Th. reactor was shut down at the time of this incident.

The nensor wa'. nade operable by replacing the r:icroswitch assembly t;hi ch includen the suitch, the switch actuatiin arm and backplate assembly.

Operation was natislactory af ter repeated actuations and the inatrument channel was declared operable at 1619 on f>eptembe r 10, 1973.

The Plant Operations Review Commit tee (PORC) , r..eet ing t o revjew the ineident, noted that this was the samt 11arton swit ch and actunt ing assemb.ly which h.td f ailed twice previously during aurvell]nnce t e s t. in g . These incidents were reported as A0-73-09 and A0-7 3-21.

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/~\ \p h ) .I VERMONT YA$KEC NUCLEAR POWCR CCT4 F'ORATIOT Directorate r.1 Licensing September 18, 1973 Page 2 Whe rais , in the previous two incidents, corrective action consisted of replacement of the nicrosult h only and/or re :'.ignment of the actuating, arn, in this case, the complete subasseubly was replaced when inspection revealed excessive binding f ra the switch actuating arm.

The committee ar, reed that this more extensive rep lacement should correct the probh n and reccamended that the defective assembly be returned to the vendor for analysis to determine the cause of the mechanical binding.

Very truly yours, VERMONT YANKEE NUChEAR POWER CORPORATION bb3 .

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Bradford W. Riley -

Plant Superintendant WFC/hbd i

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