ML19317E045

RO 269/77-31:on 771229,leakage of Less than 1 Gallon Per Minute Noted.Caused by Failure of Switch 1PS-364 Diaphragm. Switch 1PS-364 to Be Replaced During Future outage.1PT-21P Switch Recalibr & Returned to Svc

ML19317E045
Person / Time
Site:	Oconee
Issue date:	01/26/1978
From:	DUKE POWER CO.
To:
Shared Package
ML19317E043	List: ML19317E041 ML19317E045 ML19317E046
References
RO-269-77-31, NUDOCS 7912110823
Download: ML19317E045 (2)

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DUKE POWER COMPANY OCONET UNIT 1 'f' Report No.: 'RO-269/77-31 ." ,

Report Date: January 26,'1978 .

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7 occurrence Date: Dheember 29, 1977 .

e Facility: Oconee Uniti, Seneca, South Carolina .

IdentificationofOccurrgee: RCS Pressure Channel Inoperable Conditions' Prior to Ocet ence: 90 percent full power Description of Occurrence: '?,

On December 27, 1977, unidentified Reactor Coolant System leakage of less than 1 gpm was detected. At 2131 RPS Channel A tripped on low pressure /

temperature and was placed in manual bypass. At 0200 on December 28 the previously detected leak was determined to be coming from the area of ~

Engineered Safeguard' Channel 1and RPS Channel A Pressure Transmitter. A reactor shutdown was initiated at-0209 due to high Reactor Building (RB) activity. At 0600 personnel entered the RB and determined that pressure switch 1 PS-364 was leaking and valved it out. Reactor power reduction was stopped at 39 percent full power and with the isolation of 1PS-364, RPS Channel A.was returned to service..

At 2400 during PT/l&2/0600/01, it was determined that RC Loop A wide range (WR) pressure was indicating high. Further investigation determined that ES Analog Channel 1 WR pressure was indicating high and would not trip at required setpoints. ES Analog Channel 1 was placed in trip condition.

. Pressure transmitter IPT-21P, which is located approximately 5 feet from and slightly below IPS-364 was recalibrated and ES Analog Channel 1 was returned to service.

Apparent Cause of Occurrence:

The diaphragm of pres.sure switch IPS-364 evidently failed as steam was seen blowing from the switch. This failure caused RPS Channel A to trip.

The steam f, rom the switch failure evidently impacted on and shifted the zero setting of pressure transmitter IPT-21P. The zero shift caused the high reading-on ES Analog Channel 1.

Analysir'of Occurrence:

-Pressure switch 1PS-364 provides a signal to prevent valves LP-1, -2 from opening with RCS pressure greater than 400 psig. The failed diaphragm caused RPS Channel A to trip. RPS Channels B, C & D remained fully opera-tional during-the incident as required by Technical Specifications 3.5.1.

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Valves LP-1, -2 had been tagged shut prior to this incident..

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- The zero:setpoint of pressure. transmitter 1PT-21P shifted when it was-heated.by steam from the switch failure. ES Analog Channel 1 which ,

,provides a signal-for LPI and EPI initiation became inoperable, however, channels l2 and 3 remained fully operational as required by Technical Specification 3.5.1. TheLhealth and safety of-the public were not endangered'by this incident.

. Corrective Action:

Pressure' switch 1PS-364 is presently valved out and will be replaced

, during a^ future outage.. Pressure transmitter'1PT-11P was~recalibrated and returned to service.

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