ML20024B838

LER 83-060/03L-0:on 830606,following Turbine Trip & Scram Due to High Vibration on Main Turbine,Reactor Recirculation Breaker 4B Closed.Cause Undetermined.Auxiliary Contacts cleaned.W/830705 Ltr

ML20024B838
Person / Time
Site:	LaSalle
Issue date:	07/05/1983
From:	Diederich G, Renwick J COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
LER-83-060-03L, LER-83-60-3L, NUDOCS 8307110488
Download: ML20024B838 (3)

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EVERETDESCRIPTION AND PROSA8LE CONSEQUENCES h tol2l l Ora June 6,1983 Uni t one was operating at 1435 MWt (44% power) when an indication g

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CAL 15E DESCRIPTION AND CORRECTIVE ACTIONS 27 11101I RR Pumo B breaker 3B ooened but redundant breaker 4B did not. The cause of the i 1

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g1 3s times and the loolc was also tested satisfactorilv. On 14 June 1983. the Main I turbine t rioned at Hioh Power and the 4B breaker functinned correctiv. I iiisi I

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l. LERNUMBER[ 83-060/03L-0 1I, LASALLE COUNTY STATION: Unit 1 III. DOCKET NUMBER: 050-373 IV. EVENT DESCRIPTION: i On 6 June 1983 with Unit I at .1435 W thermal and 443 MW electric, - '

the main turbine tripped due to a spurious eletrical spike on the number 8 bearing. The reastor scramed promptly on Turbine Stop Valve Closure Signal. ,

~ EOC-RPT functioned to shift the RR pumps to slow speed. The 4B breaker >  :

to RR Pump B did not open as did the 3B breaker, RR Pump A breakers 3A and 4A -

did open promptly.

V. PROBABLE CONSEQUENCES '0F THE OCCURRENCE: . A Reactor Power and Pressure followed expected trends on a turbine trip at high power. EOC-RPT did go to completion by means of the 3A, 4A'and '3B opening.

Breaker 4B which is redundant to the 3B breaker was tripped from the. control r room. The plant was maintained in a safe condition at all times and the health and safety of the pubile was not affected.

VI. CAUSE:

The exact cause of the failure of the 4B breaker to open could not be' determined.. The EOC-RPT logic did function properly.because the 3A breaker g__ _ _ opened at_the E0_C-RPT signal. The . redundant- logic for the 3B and 4A breakers functioned properly. .The 48 breaker was manufactured by ITE Model Number.

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n VII. CORRECTIVE ACTION Prior to restart of Unit 1 an On Site Review of this event,was conducted (83-36). The following items were conducted as a result o'f the On Site Review in order to. determine the cause of Breaker 4B failure toNopen.

1. Response time test for EOC-RPT conducted on 13 May 83 was reviewed and found to be satisfactory (LIS-RP-04) '

2. Circuit Breaker 4B was -tested 4 times and. tripped successfully each time e a simulated EOC-RPT signal. Twice in Test Position and twice Fully racked in.

3. Auxiliary contacts were cleaned.

4. Turbine stop valve EOC-RPT logic was tested satisfactorily. -

The cause of the 4B breaker failure to open could not be determined and .

based on the above actions, the breaker was declared operable.

On 14 June 1983, the Unit one turbine tripped at high power and EOC-RPT functioned properly.

Prepared by .i. C. Renwick O

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N Commonwealth Edison c.

-, ) Rural Route #1, Box 220LaSalle County Nuclear Station b' Marseilles, Illinois 61341 Telephone 815/357-6761 July 5, 1983 l

l James G. Keppler Regional Administrator Region ill U. S. Nuclear Regulatory Commission  !

799 Roosevelt Road f Glen Ellyn, IL 60137 i

Dear Sir:

Reportable Occurrence Report #83-060/03L-0 Docket #050-373 is being submitted to your office in accordance with LaSalle County Nuclear Power Station Technical Specification 6.6.B.2 (b), conditions leading i to operation in a degraded mode permitted by a limiting condition for

! operation or plant shutdown required by a limiting condition for operation.

l l

G J. Diederich Superintendent LaSalle County Station GJD/GW/sJc ,

Enclosure cc: Director of Inspection & Enforcement Director of Management Information & Program Control U. S. NRC Document Management Branch inpo-Records Center File /NRC ,

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