ML20040D454

LER 81-048/03L-0:on 811223,pressure Differential Switch Which Controls Reactor Bldg to Suppression Chamber Vacuum Breaker Cv 4305 Tripped at Out of Tech Spec Value.Caused by Instrument Drift.Switch Recalibr & Functionally Tested

ML20040D454
Person / Time
Site:	Duane Arnold
Issue date:	01/22/1982
From:	Varner D IES UTILITIES INC., (FORMERLY IOWA ELECTRIC LIGHT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20040D453	List: ML20040D452 ML20040D454
References
LER-81-048-03L, LER-81-48-3L, NUDOCS 8202010311
Download: ML20040D454 (2)

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DUAHE ARNOLD ENERGY CENTER

. Iowa Electric Light and Power Company Licensee Event Report - Supplemental Data e'

Docket No. 050-0331 Licensee Event Report Date: 1-22-82 Reportable.0ccurrence No.: 81-048 Event Description During nornal operation while performing surveillance testing, the pressure differential switch which controls reactor building to suppression chamber vacuum breaker CV 4305 tripped at an out of specification value. The switch, PDIS 4305, tripped at 0.2 psid, which is conservatively low. Technical Specification 3.7.A.3.a. requires the setpoint to be 0.5 psid. PDIS 4304, which controls redundant vacuum breaker CV 4304, was operating properly.

There have been five previous similar occurrences (see A0 75-33, R0 77-55, -

R0 78-32, RO 79-18, and R0 80-23).

Cause Description The cause is attributed to instrument drift. A contributing cause is the relatively large range of the switch, which results in decreased setpoint accuracy and difficulty in calibration. PDis 4305 is a Barton pressure differential switch Model 288A.

Corrective Action F

The switch was.recalibrated and functionally tested with satisfactory results.

To increase the accuracy or setpoint repeatability and make calibration less difficult, a design' change has been initiated to decrease the range of switches PDIS 4304 and 4305. This will be accomplished by replacing the bellows unit ,

assembly on each switch. Increased surveillance testing is continuing.

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