ML19308B545

LER 78-008/03L-0:on 780305,power Range Detector Found Spiking.Reactor Protection Sys Channel a Bypassed,Preventing Spurious Trips.Cause Not Determined.Investigation to Resume Next Refueling or Next Spiking

ML19308B545
Person / Time
Site:	Oconee
Issue date:	04/04/1978
From:	Ken Wilson DUKE POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19308B538	List: ML19308B536 ML19308B545
References
LER-78-008-03L-01, LER-78-8-3L-1, NUDOCS 8001090540
Download: ML19308B545 (2)

Text

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SS 69 EVENT DATE 74 75 mEPCAT OATE 40 svENT cascalPTION ANO PACS A8LE CCNSECUENCES h 1o 121 l At 2039, during normal operation it was observed that Power Range Detector ,

la is t 1 (NI-5) was soiking. RPS Channel A, which it serves, was olaced in manual l iot.] [ bypass. An investigation was commenced to determine the cause of the spik ;

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DUKE POWER COMPANY OCONEE UNIT 3 Report Number: R0-287/78-8 Report Date: April 4, 1978 Occurrence Date: March 5, 1978 Facility: Oconee Unit 3, Seneca, South Carolina Identification of Occurrence: Reactor Protection System (RPS) Channel A Bypassed Due to Nuclear Instrumentation (NI)-5 Spiking Conditions Prior to occurrence: 100 percent Full Power Description of Occurrence:

On March 5, 1978, at 2039, Reactor Protection System (RPS) Channel A was placed in Manual Bypass. A spiking problem in Nuclear Instrumentation (NI)

Power Range Detector, NI-5, necessitated the bypass of the channel. An investigation of the spiking was initiated at 2200 and continued until 1000 on March 6, 1978 when the spiking had ceased. No further spiking has recurred and RPS Channel A has been left in the manual bypass mode.

Apparent Cause of Occurrence:

At this time the cause of the spiking has not been determined. The RPS Cabinet itsel( has been eliminated as a possibility but, the cause could lie anywhere from the cabinet to the detector itself. Further investiga-tion will continue at either the next occurrence of the spiking or during the next refueling outage.

Analysis of Occurrence:

The Reactor Protection System has four channels and normally trios on a two-out-of-four logic. With one RPS channel bypassed the remaining trip logic is two-out-of-three which is the minimum required by Technical Speci-fications (T.S. 3.5.1) . There is, tharefore, sufficient redundancy assured with one channel bypassed. Thus, the health and safety of the public are not endangered by continued operation in this mode.

2orrective Action:

No other corrective action can be taken until the cause is determined. The bypassing of the RPS channel prevents spurious RPS channel tr1.ps due to spiking in the NI channel.