05000369/LER-1981-171, Forwards LER 81-171/03L-0.Detailed Event Analysis Encl

Forwards LER 81-171/03L-0.Detailed Event Analysis Encl

ML20038C857
Person / Time
Site:	McGuire
Issue date:	11/30/1981
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20038C858	List: 05000369/LER-1981-171, Forwards LER 81-171/03L-0.Detailed Event Analysis Encl 05000369/LER-1981-171-03, /03L-0:on 811028,two Upper Head Injection Accumulator Discharge Isolation Valves Found Partially Closed During Investigation of Annunciator Alarm.Caused by Leaking Fitting from Low Leg Impulse Line to Level Switch
References
NUDOCS 8112140200
Download: ML20038C857 (3)

LER-1981-171, Forwards LER 81-171/03L-0.Detailed Event Analysis Encl

Event date:
Report date:
3691981171R00 - NRC Website

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3 Mr. J. P. O'Reilly, Director U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re: McGuire Nuclear Station Unit 1 Docket No. 50-369

Dear Mr. O'Reilly:

Please find attached Reportable Occurrence Report R0-369/81-171. This report concerns T.S.3.5.1.2, "Each Upper Head Injection Accumulator System Shall be Operable With:

a. The Isolation Valves Open,

". This incident was con-sidered to be of no significance with respect to the health and safety of the public.

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Very truly yours,

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DUKE POWER COMPANY McGUIRE NUCLEAR STATION REPORTABLE OCCURRENCE REPORT NO.: 81-171 REPORT DATE: November 30, 1981 FACILITY: McGuire Unit 1, Cornelius, NC IDENTIFICATION: Upper Head Injection (UHI) Accumulator Declared Inoperable due to the Discharge Isolation Valves Being Closed.

INTRODUCTION

On October 28, an annunciator alarm was received indicating that UHI isolation valves were not fully open. Prior to the occurrence, Unit #1 was in mode 1 at 30% power. The UHI accumulator discharge isolation valves were checked and valve 1NI-244B was found in the closed position and 1NI-242B in the intermediate position. This incident is reportable pursuant to Technical Specification 3.5.1.2; therefore, the plant entered into an action statement and immediately opened the valves.

Investigation discovered that there was a leak on an instrument line lead-ing to level switch 1 NILS 5730, and a work request was written to repair the leak.

There was some doubt about whether or not 1NI-242B was functioning properly because it was in the intermediate position, but it was determined that if the switch were closed momentarily then the valve would not have been able to go to its fully closed position.

Since the circuitry going from the switch to the valve was not a seal-in circuit it was confirmed that valve 1NI-242B had functioned properly.

The fitting from the low leg impulse line to the level switch was loose and had to be tightened.

The ferrule was checked prior to being tightened to verify that it was in-stalled correctly.

It is unknown as to why this instrument line came loose.

EVALUATION: 1NI-244B and 1NI-242B are hydraulically operated gate valves which are given a signal to close by 1 NILS 5730 and 1 NILS 5750 respectively, at low accumulator water level. The impulse lines which supply level instruments 1 NILS 5730 and 1 NILS 5750 both tap off a common line. The impulse line's fitting (a 1/2" Parker-Hannifin) came loose at 1 NILS 5730, which is the level switch to the valve, 1NI-244B, that closed.

It is not known, nor polatole to determine, why this fitting came loose. Also, it is doubtful that it was not tightened properly when it was last worked on; because, ac-cording to completed past work requests on the instrument, the instrument was repaired on April 16, 1981 and the tightness of all connections was checked at that time.

A possible reason for the actuated switches may have been due to an air bubble in

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the impulse line. When the leak developed, this air bubble moved toward the leaking l

fitting and was vented to atmosphere. The resulting pressure drop and then surge to fill the volume previously occupied by air caused the level switches to close as they did. The pressure drop would be greatest on the switch that developed the leak; there-fore, 1 NILS 5750, the switch which did not have the leak, only activated momentarily so that valve 1NI-242B did not close fully.

This appears to be an isolated incident; McGuire has not experienced failures of this type before. When an instrument is worked on, the instrument line is usually bled to l

remove any air bubbles from the instrument line. This prevents any erroneous instru-ment reading due to air in the system.

CORRECTIVE ACTION

In accordance with the action statement of Technical Specification 3.5.1.2, the valves were immediately returned to their fully open position. A work re-quest was written to have the leak repaired. Before the laaking fitting was tightened, the line was isolated and the ferrule on the fitting was checked to be sure that it

Report No.81-171 Page 2 was installed properly. Correct installation was verified, and the line was tightened and returned to service.

VERIFICATION:

Since the repair of the leak, there have been no.further spurious clos-ings of UHI discharge isolation valves. The fitting was checked, and it was verified that the fitting was not damaged or installed improperly.

SAFETY ANALYSIS

There are two discharge legs from the UHI water accumulator with 1NI-244B in one leg and 1NI-242B in the other. When the level. switches caused the loslation valves to change position, the flow path from the'UHI accumulator was re-

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i duced. Although the flow path was temporarily reduced, the ability to obtain a larger flow path was available by opening the affected valves, the valves apparently operated correctly under the conditions seen by their level switches. This has been an isolated incident and the valves' incorrect positions were immediately detected by an alarm. The degraded configuration of the plant was temporary (approximately one minute), and the capability to correct the situation was availabic.

Therefore, the health and safety of the public were not affected by this incident.

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