ML19345E696

LER 81-001/03L-0:on 810101,MSIV 80B & 86A Closing Times Exceeded Tech Spec.Caused by Improper Adjustment of Hydraulic Dash Pot Closure Time Adjustment Mechanism in B & Broken Spring in Mechanism A.Pot Adjusted & Spring Replaced

ML19345E696
Person / Time
Site:	Vermont Yankee
Issue date:	01/30/1981
From:	Murphy W VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19345E695	List: ML19345E694 ML19345E696
References
LER-81-001-03L, LER-81-1-3L, NUDOCS 8102050564
Download: ML19345E696 (2)

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EVENT DESCRIPTION AND PLOBABLE CONSEQUENCES

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During routine surveillance testing at 38% reactor power, MSIV '

80 B and MSIV 86 A were found to close in 5.5 and 5.3 seconds respectively, which exceeds the Tech. Spec. limit of 5 seconds. As required by Tech.

, Spec. Section 3.7.D.2, MSIV 80 A and MSIV 86 B were closed.

Additionally, while testing MSIV 80 C, relay SA-K 3F failed to de-energize-i due to a failed limit switch in the closed position on >$IV 80 C.

Vermont Yankee incorrectly reported this occurrence a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> reportable occurrence (LER 81/01/IP). Further investigation has determined that 4 instrument channels per trip system were operable as required by Tech. i Spec. Table 3.1.1 since closure of MSIV 86 C did cause relay 5A-K3F to operate. RPS Limit swite'es on MSIV 80 C and MSIV 86 C'are redundant and it was determined that this instrument channel was operable bue ,

degraded. If a Group 1 isolation signal had occurred, a reactor scram would have resulted as required.

Since the second isolation valve in main steam lines A, B and C was

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operable as required by Tech. Spec., there were no potential consequences

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to the health and safety of the general public.. Similar slow MSIV closure times were reported in LER 79-29 and LER 78-32.-

CAUSE DESCRIPTION AND CORRECTIVE ACTION j

The cause of MSIV 80 B slow closure time was due to improper adjustment of the hydraulic dash pot closure time adjustment mechanism. . The valve actuator had been rebuilt and preventative maintenance had been performed

' during the annual refueling outage. The hydraulic dash. pot had been adjusted with the valve in the cold condition. Valve closure time was within Tech. '

Spec. req ~direments in the cold condition but changed slightly in the hot condition. Readjustment of the hydraulic dash pot returned MSIV 80.B to the' required-Tech. Spec. closing. time.

i The cauce of MSIV 86 A slow closure time was determined to be due to a  ;

broken spring in the hydraulic dash pot closure time adjustment mechanism '

(a Colorflow Control, 3/8 Range, manufactured by Manatol of Elyria, Ohio).

i The broken spring was replaced,l the hydraulic dash pot was reassembled and -

adjusted and MSIV 86 A was subsequently retim'ed and determined to close within the required Tech. Spec. closure time.

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