05000271/LER-1979-021-03, /03L-0:on 790816,transmitters LT-16-19-38A/B Underwent zero-shift & Common Ref Leg Was Not Completely Filled.Caused by Loss of Water in Common Ref Leg of Transmitters Compounded by Apparent zero-shift

/03L-0:on 790816,transmitters LT-16-19-38A/B Underwent zero-shift & Common Ref Leg Was Not Completely Filled.Caused by Loss of Water in Common Ref Leg of Transmitters Compounded by Apparent zero-shift

ML19208B795
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	09/17/1979
From:	Conway W VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19208B790	List: 05000271/LER-1979-021, Forwards LER 79-021/03L-0 05000271/LER-1979-021-03, /03L-0:on 790816,transmitters LT-16-19-38A/B Underwent zero-shift & Common Ref Leg Was Not Completely Filled.Caused by Loss of Water in Common Ref Leg of Transmitters Compounded by Apparent zero-shift
References
LER-79-021-03L, LER-79-21-3L, NUDOCS 7909210409
Download: ML19208B795 (2)

LER-1979-021, /03L-0:on 790816,transmitters LT-16-19-38A/B Underwent zero-shift & Common Ref Leg Was Not Completely Filled.Caused by Loss of Water in Common Ref Leg of Transmitters Compounded by Apparent zero-shift

Event date:
Report date:
2711979021R03 - NRC Website

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NAME OF PREPARER

VTVYS1 05000271 LER 79-21/3L EVENT DESCRIPTION AND PROBABLE CONSEQUENCE 3 during routine surveillance testing of torus level transmitters LT-16-19-38A/B, it was determined that both transmitters had undergone a zero-shift and that the common reference leg was not completely filled.

Upon recalibration of the transmitters and filling the reference 1eg, it 3

was further determined that the torus water volume was 67,643 f t nicalSpecification3.7.A.l.erequiresaminimumvolumeof68,000ft}ech-Preparations for an orderly shutdown were commenced as necessitated by Technical Specification 3.7.A.2 as well as initiating efforts to refill the torus within required specifications. The necessary transfer was completed approximacely 30 minutes after the discovery.

Since the volume was reduced by less than.6% of the required volume and for only a short period of time, the potential consequences to the health and safety of the public were minimal. A similar reportable occurrence was reported as RO 78-35/3L.

CAUSE DESCRIPTION AND CORRECTIVE ACTION The cause of this occurrence is attributed to a loss of water in the common reference leg of the transmitters compounded by an apparent zero-shift of the transmitters. This resulted in an indicated higher than actual torus water level. The loss of water in the reference leg cannot be definitively determined.

In the future, the common reference leg will be checked and refilled on a weekly basis.

In addition, an in-vestigation is underway directed at improving this system and the relia-bility of torus water level indication.

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