ML20064G165

/03L-0 on 781110:during Critical Steady State Oper Alarms Showed High Steam Line Differential Pressure on Line B.Proper Bistables Tripped,Placing Plant in Safe Condition. Caused by Faulty Instru Loop Pwr Supply Card in Circuitry

ML20064G165
Person / Time
Site:	North Anna
Issue date:	12/01/1978
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20064G164	List: ML20064G161 ML20064G165
References
LER-78-119-03L, NUDOCS 7812070190
Download: ML20064G165 (2)

Text

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D ATE - 87 C 60 61 DOCKET NUMBER EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h 10 la l l During critical Steady State operation. alarms indicating high steam line differential I

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iO i3i I pressure were observed on Steamline B. Although this event placed the plant in a I l0 lci I degraded mode, the proper bistables were administrative 1y tripped, thereby placing i iO13i i the plant in a safe condition. Reportable under T.S. 6.9.1.9.b. j IO ls i i l 10171 l l I

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35 40 42 44 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l i l 0 l l The cause of this event was found to be a faulty instrument loop power supply card I i i l in the high steam line differential pressure protection circuitry. The card wes j g j I replaced and the instrument loop was recalibrated and- returned to service. , _ _j 1 3 l l li 141 I _-

l 7 8 9 80 STA 5  % POWE R OTHER STATUS dis O FY DISCOVERY DESCRIPTION l i I s l W@ l 0 [ 9 l 7 l@[_ N/A l l A l@l Operator Observation l CTIVITY CO TENT RELE ASED OF RE LE ASE AVOUNT OF ACTIVITY LOCATION OF RELE ASE 7

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Virginia Electric and Power Company North Anna Power Station, Unit #1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. LER 78-119/03L-0 Description of Event:

On 11/10/78, at approximately 0730, several control board alarms were actuated on Steamline Differential Pressure indicating low steam line pressure in Loop B. These alarms are for bistable trip status of the Engineered Safe-guard System logic.

f-Probuble Consequences of Occurrence:

This event caused a protection channel of the Engineered Safeguard Feature to sense a low steam line pressure which places the plant in a safer condition since only one additional channel would be required to respond to actuate a Safety Injection. Therefore, since this equipment failed in the

(. safe condition as well as having the normal redundant channel operable simul-taneous with the failure, the health and safety of the general public was preserved. ,

Cause of Occurrence:

1 This problem was caused by a faulty instrument loop power supply card in the high steam line differential pressure protection process circuitry.

Immediate Corrective Action:

The immediate corrective action was to place all the associated protection bistables in the tripped status to maintain a safer plant status while repairs in the form of trouble shooting, part replacement, recalibration and adjustments were performed. Upon completion of repairs, the channel was returned to service with all bistables in the normal mode. ,

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Scheduled Corrective Action:

No scheduled corrective action other than the regular periodic operability tests is considered necessary.

Action to Prevent Recurrence:

No action to prevent recurrence can be determined since this failure was  ;

an isolated incident.

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