ML19289D099

LER 78-137/03L-0 on 781228:during Mode I Operation,Turbine Automatic Stop Oil Low Pressure Signal Locked In.Caused by Loose Terminal Screw on PS-LO-609-4

ML19289D099
Person / Time
Site:	North Anna
Issue date:	01/25/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19289D098	List: ML19289D097 ML19289D099
References
LER-78-137-03L, LER-78-137-3L, NUDOCS 7901290224
Download: ML19289D099 (2)

Text

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LICENSEE EVENT REPORT E

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s' 7! 9!@ 80 7 8 80 81 DOCKET NUMBER 09 EV E> MTE EVENT DESCRIPTION AND PROBABLE CoNSEoUENCES h O 2 l Durina Mode 1 Operation CH I Turb Auto Ston 011 i nw PrRec Signal locked in. This

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O 2 I provided one of the 2/3 Reactor Trip Signals necessary for protective tripping of the l

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g treactor as a result of a turbine trip. This is conservative and thus the health and i O s safety of the general public were not endangered. This event is reportab1'e nder I T.S. 6.9.1.9.b. t g

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36 36 3# 40 41 42 43 44 CAUSE DESCRIPTION ANI. CORRECTIVE ACTIONS h

, O lThe CHI turb auto stop oil low press signal was caused by a loose terminal screw 1

, , (Terminal Ast 30) on PS-LO-609-4. The loose terminal screw was tightened as t

, described on maintenance report N17812281040. j

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NAME OF PREPARER W. R. Cartwright paous: 703-894-5151 {

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Virginia Electric and Power Company North Anna Power Station, Unit No. 1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. 78-137/03L-0 .

-icription of Event:

.

On 12-28-78 during nomal Mode 1 operation, Turb Auto Stop 011 Lo Press CH I annunciator locked in (IN-39) with a simultaneous alarm print out by the computer (P03960). An inspection of the oil system revealed no apparent problem so an emergency maintenance request was issued. Further investigation revealed the cause to be a loose terminal screw on PS-LO-609-4 (Teminal AST 30).

The teminal screw was tightened and the condition cleared.

Probable Consequence of Occurrence:

The Reactor Trip System required by T.S. 3.3.1.1 is provided to prevent damage to the fuel and loss of Reactor Coolant System integrity as a result of any anticipated malfunction. In this case, three pressure sensors are used to sense turbine auto stop oil pressure. A digital output is provided from each sensor when the oil pressure drops below a preset value. These three outputs are transmitted to two redundant two out of three matrices, either of which trips the reactor if above P-7.

With one trip signal initiated, on?y one additional trip'from either of the other pressure sensors,would be required to initiate a reactor trip.

This is more conservative than the normal two out of three coincidence required to generate a reactor trip and thus there was no danger to the health and safety of operating personnel or the general public.

Cause:

The cause for the CH I Turb Auto Stop 011 Low Press signal lock in was a loose terminal screw on PS-LO-609-4 resulting in an open circuit.

Imediate Corrective Action:

Visually inspected oil system, initiated emergency maintenance request and tightened the terminal screw, thereby correcting the problea within the time limit given per action 7 of T.S. 3.3.1.1.

Scheduled Corrective Action:

No further action required.

Action Taken to Prevent Recurrence:

No action required.

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