ML19317D840

Abnormal Occurrence Rept AO-269/74-14:on 741005,pressure Switch 1PS-364 Found Leaking.Caused by Defective Diaphragm. Switch Removed & Piping Capped.No Adverse Effects on Health & Safety

ML19317D840
Person / Time
Site:	Oconee
Issue date:	10/18/1974
From:	DUKE POWER CO.
To:
Shared Package
ML19317D830	List: ML19317D829 ML19317D840
References
NUDOCS 7912100570
Download: ML19317D840 (2)

Text

._

s m

~

k' 8

) _

}

DUKE POWER COMPANY OCONEE UNIT 1 -

Report No.: A0-269/74-14 Report Date: October 18, 1974 Occurrence Date: October 5, 1974 Facility: Oconee Unit 1, Seneca, South Carolina Identificatico of Occurrence: Failure of Pressure Switch 1PS-364 , .

Conditions Prior to Occurrence: Unit at 75 Percent of Full Power Description of Occurrence:

At 1350 October 5, 1974, a 4 gpm reactor coolant leak was detected on Oconee Unit 1. A reactor shutdown commenced im=ediately after discovery. During the shutdown, at 1441, the Channel A Engineered Safeguards (ES) and Reactor Protective Systems (RPS) tripped indicating low reactor coolant system pressure. The reactor was suberitical by 1547, however, personnel entry to the Reactor Building was not possible until 0600 October 6, 1974. Pressure Switch 1PS-364, interlock for valve ILP-2, was found leaking and was isolated. Channel A ES and RPS pressure transmitter IPT-21P was found to be damaged due to steam from 1PS-364.

Designation of Apparent Cause of Occurrence:

The reactor coolant leakage from pressure switch 1PS-364 was the result of a defective diaphragm. This was the first failure of this type of valve at Oconee. The valve is proof tested to 4500 psi.

The failure of pressure transmitter 1PT-21P was due to electronic component failure induced by heat from the steam being impinged on it.

l Analysis of Occurrence:

i l Pressure switch LPS-364 creates an electrical interlock to the operation of l valve ILP-2, decay heat re= oval from the reactor coolant system, which l prevents opening with reactor coolant pressure greater than 410 psi. This will prevent inadvertent overpressurization of the low pressure injection piping. The failure of the pressure switch resulted in the proper action of preventing .the opening of valve ILP-2.

Valve ILP-1 serves as a redundant isolation valve to prevent overpressurization of the low pressure injection system. This valve is interlocked using a pressure signal from the integrated control syste' which prevents operation l with reactor coolant pressure in excess of 200 psi. Valve ILP-1 was not affected by this incident.

7 912100 f70

2- -

t i

Pressure transmitter IPT-21P supplies pressura infor=ation to Channel A ES

• and RPS. The failure of this transmitter gave a "zero" pressure indication ,

to ES and RPS Channel A and resulted in a channel trip. The pressure switch failed in a conservative manner by giving a channel trip.

The maximum level of contamination in the Reactor Building was 2.1 x 10~7 pCi/mi of 131 I Personnel radiation exposure was minimized during this incident. All entries into the Reactor Building were controlled by health physics personnel. No activity was released to the environment. It is concluded that the health and safety ci the public was not affected.

Corrective Action:

Pressure switch IPS-364 was isolated and removed. The piping was capped because a spare pressure switch was not in stock. The breakers for valve ILP-2 and redundant valve ILP-1 were red tagged to prevent inadvertent actuation.

Pressure transmitter IPT-21P was replaced with a new transmitter and was properly calibrated.

Failure Data:

Pressure switch IPT-364 is a Custom Component, Type 6045GX4 (200-400 psi range, 4500 psi proof pressure, 35 psi deadFand).

Pressure transmitter IPT-21P is a Motorola Type 56 PH.

I l

?

l

} -