ML20006E458

LER 90-001-00:on 900117,technician Mirror Contacted Bare Power Supply Terminal & Shorted Terminal to Ground,Causing Power Supply to Trip & Isolation of Outside Air to Control Room.Exposed Wire Terminal Points covered.W/900216 Ltr

ML20006E458
Person / Time
Site:	Prairie Island
Issue date:	02/16/1990
From:	Hunstad A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
LER-90-001, LER-90-1, NUDOCS 9002230219
Download: ML20006E458 (4)

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3 February 16, 1990 10 CFR Part 50

! Section 50,73  ;

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Director of Nuclear Reactor Regulation  :

U S Nuclear Regulatory Commission '

Attn: Document Control Desk Washington, DC 20555 i

l' PRAIRIE ISLAND NUCLEAR GENERATING PIANT '

Docket Nos, 50 282 License Nos. DPR 42 50-306 DPR 60 .

Automatic Control Room Isolation and Start of Control  ;

Room Cleanuo Fan Due to Personnel Error Durine Surveillance Test The Licensee Event Report for this occurrence is attached.

This event was reported via the Emergency Notification System in accordance with 10 CFR Part 50, Section 50.72, on January 17, 1990. Please contact us if

- you require additional information related to this event.

Thomas M Parker Manager

' Nuclear Support Servicts c: Regional Administrator - Region III, NRC NRR Project Manager, NRC

-Senior Resident Inspector, NRC .f MPCA Attn: Dr J W Ferman Attachment ADOCK 0500 2 ,/'.

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... . ., ,., .. . -.,. . , o s i On January 17,1990, Unit 1 was shutdown for refueling and Unf.t 2 was at 100%

power. SP1698, Chlorine Monitor Weekly Check, was in progress. This surveillance procedure cleans and checks operation of the chlorine monitors.

An 160 technician uses a small mirror on a handle to see parts of the optics block of the monitor. At 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, while the I&C technician was working in the monitor cabinet, his mirror contacted a bare power supply terminal and shorted it to ground, tripping the power supply. Since both monitors on the affected train share the power supply, the failure caused the outside air to the control room to be isolated and No. 122 control room cleanup fan to start.

The system was returned to normal in about 20 minutes.  !

The chlorine monitors were returned to service in about 20 minutes. Exposed wire terminal points in the monitor cabinets will be covered to prevent a similar occurrence. This work will be completed by April 1, 1990. Long term corrective action involves replacement of the present chlorine monitors with now, more trouble free monitors, each having its own power supply.

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EVENT DESCRIPTION -

On January 17, 1990, Unit 1 was shutdown for refueling and Unit 2 was at 100% ,

power. SP1698, Chlorine Monitor Weekly Check, was in progress. This surveillance procedure cleans and checks operation of the chlorine monitors (EIIS Component Identifier: HON). An 160 technician uses a small mirror on a handle to see parts of the optics block of the monitor. At 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, while the 16C technician was working in the monitor cabinet, his mirror contacted a bare power supply terminal and shorted it to ground, tripping the power supply. Since both monitors on the affected train share the power supply, the failure caused the outside air to the control room to be isolated and No. 122 control room cleanup fan (EIIS Component Identifier: FAN) to start. The system was returned to normal in about 20 minutes.

CAUSE OF THE EVENT The cause of the event was personnel error in that the tool used by the I&C technician shorted a bare power supply terminal to ground. Since the power supply is shared by two chlorine monitors in the same train, loss of power to the affected train caused the outside air to the control room to be isolated and one control room cleanup fan to start.

ANALYSIS OF THE EVENT The functional response of the automatic actuation of the control room cleanup fan and isolation of the outside air to the control room was according to design. The purpose of this isolation is to protect control room personnel from chlorine leaks. Since this occurrence was not triggered by the presence of chlorine in the atmosphere, there was no threat to the operation of the plant. The affected chlorine monitor train failed to the safe condition.

Therefore, this event did not affect the health and safety of the public.  ;

CORRECTIVE ACTION The chlorine monitors were returned to service in about 20 minutes.

Exposed wire terminal points in the monitor cabinets will be covered to prevent a similar occurrence. This work will be completed by April 1, 1990.

Long term corrective action being considered involves replacement of the present chlorine monitors with new, more trouble free monitors, each having its own power supply.

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PREVIOUS SIMIIAR EVENTS ,

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• Several automatic actuations of the control room isolation and cleanup system have occurred and were reported as LER's 89 006, 89 009, 89 012, 89 015 and 89 020.

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