ML19253C317

LER 79-023/03L-0:on 791016,level Switch LIS 2-263-72A Failed to Trip During Calibr.Caused by Failure of One Mercury Wetted Magnetic Switch Encl in Level Indicator.New Switch Installed & Tested Satisfactorily

ML19253C317
Person / Time
Site:	Quad Cities
Issue date:	11/14/1979
From:	Hannum D COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19253C316	List: ML19253C315 ML19253C317
References
LER-79-023-03L-03, LER-79-23-3L-3, NUDOCS 7911300507
Download: ML19253C317 (2)

Text

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1 8 60 61 DOCKET NUMBER 68 69 EVENT DATE 74 75 REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h O 2 ! While performing the Reactor Low-Low Water Level Calibration, procedure QlS 11-1, l o 3 level switch LIS 2-263-72A failed to trip when given a low-low reactor water signal l

[T] il l (T.S.3.2). The other three switches were found to be fully operable and would have l 0 s I given the proper ECCS initiation signal had a low-low reactor water level occurred. g Lo 6 Subsequently, the automatic initiation capability of ECCS wa's always operable. l 0 7 I l 0 a !

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[ g 41 lY[g lNlg lYl0l1[0lg 40 42 43 44 4y CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i o l The cause of this occurrence was the failure of one of four mercury wetted magnetic l i- l i j i switches enclosed in Yarway level indicator LIS 2-263-72A. Corrective action was to

, 7 l replace the switch with a like switch. The new switch was installed and tested l i 3 satisfactory on October 16, 1979 l 1 4 l 1 7 8 9 go ST S  % POWER OTHER STATUS ISCOV RY DISCOVERY DESCRIPTION lt s lE @ 0 l 5 l 0 l@l NA J Blgl Routine Test l ACTIVITY CC TENT RELEASED OF RELE ASE AVOUNT OF ACTIVITY LOCATION OF RE6 EASE 1

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l. LER NUMBER: LER/R0 79-23/03L-0 II. LICENSEE NAME: Commonwealth Edison Compsav Quad-Cities Nuclear Power Station 111. FACILITY NAME: Unit Two IV. DOCKET NUMBER: 050-265 V. EVENT DESCRIPTION:

At 11:00 AM on October 16, 1979, while performing the Reactor Low-Low Water Level Calibration, procedure QlS 11-1, level switch LIS-2-263-72A failed to trip when given a low-low reactor water level signal.

VI. PROBABLE CONSEQUENCES OF THE OCCURRENCE:

Level switch LIS 2-263-72A is one of four low-low level switches which initiate the Emergency Core Cooling System (ECCS) Logic.

The other three switches were tested during the same calibration and were found to be fully operable. These switches are arranged in a one-out-of-two-twice logic. The other three operable switches would have given the proper ECCS initiation signal had a low-low reactor water level occurred. Subsequently the automatic initiation capability of ECCS was always operable and safe reactor operation was not af' ;ted by this occurrence.

Vll. CAUSE:

The level indicating switch that failed, LIS-2-263-72A, is one of four mercury wetted magnetic switches enclosed in the Yarway level indicator. A magnet moves on the arm of the level indicator causing each of these switches to close. The switch that failed was the one that closes on low-low reactor water level. There was no observed physical damage to the switch.

Vill. CORRECTIVE ACTION:

Corrective action taken was to replace the switch with a like switch. The new switch was installed and tested satisfactorily on October 16, 1979 144lf'081