ML19312C236

RO-269/78-07 & 09:on 780314 & 22,field Flashing Breaker Found Inoperable.Cause for Repeated Inoperability Has Not Been Determined.Faulty Relays Replaced Before 780322 Failure.Recorder Will Be Installed to Monitor Trip Circuits

ML19312C236
Person / Time
Site:	Oconee
Issue date:	04/21/1978
From:	DUKE POWER CO.
To:
Shared Package
ML19312C235	List: ML19312C234 ML19312C236 ML19312C237 ML19312C238
References
RO-269-78-07, RO-269-78-09, RO-269-78-7, RO-269-78-9, NUDOCS 7912110622
Download: ML19312C236 (2)

Text

_ _ _ _ _ _ _ _ -

DUKE POWER COMPANY OCONEE UNITS 1,2,3 Y

Report No.: R0-269/78-7; R0-269/78 Report Date: April 21, 1978 Occurrence Dates: March 14, 1978; March 22, 1978 Facility: Oconee Nuclear Station, Seneca, South Carolina Identification of Occurrence: Keowee Unit 2, Field Flashing Breaker Inoperable Conditions Prior to Occurrence: Unit i 100% Full Power Unit 2 100% Full Power Unit 3 100% Full Power (Both Occurrences)

Description of Occurrence:

This type of incident has occurred on four previous occasions and has been addressed in Reportable Occurrence Reports R0-269/77-29, 78-1, 78-3, and 78-6, transmitted by my letters of January 18, February 3, March 23, and April 7, 1978, respectively.

On March 14, 1978, the Keowee Unit 2 field flash breaker failed to peroperly function following an automatic start command from the Oconee Unit 1 and 2 Control Room. Following this incident, two faulty relays were found and replaced. No other abnormalities could be found during a complete check of the control circuits. Oconee Control Operators verified Keowee Unit 2 operable by initiating an automatic start suc-cessfully.

On March 22, 1978, the Keowee Unit 2 field flash breaker again failed to c. lose upon demand. Maintenance personnel checked the field flash breaker, control circuits and associated relays. The breaker was operated again under observation and was observed to trip upon closing.

The trip coil was causing a breaker trip for r.- known reason. All com-ponents were again inspected with no abnormalities observed.

Apparent Cause of Occurrence:

No apparent cause for the repeated breaker inoperability has been deter-mined. A special task force has been organized to investigate this re-curring problem. Investigation will continue until the cause can be l determined.

l l

7912110 [ M

~ "

Analysis of Occurrence:

The failure of the breaker to close caused Keowee 2 to become temporarily inoperable. During both instances, Keowee Unit I was fully op,erable and capable of supplying emergency power to 0conee, if required. The health and safety of the public were not endangered.

Corrective Action:

Two faulty relays were replaced after the March 14, 1978 incident, but this did not prevent the March 22 failure. A recorder will be installed to monitor the trip circuits and attempt to isolate the cause of these occurrences.

l l

e j

l

- i