ML19351A468

LER 89-020-00:on 891108,17,20,23,1201 & 08,automatic Isolation of Control Room Supply & Exhaust Occurred.Caused by Malfunctions of Chlorine Gas Detectors.Addl Monitors Installed & Actuation Logic modified.W/891211 Ltr

ML19351A468
Person / Time
Site:	Prairie Island
Issue date:	12/11/1989
From:	Hunstad A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-020, LER-89-20, NUDOCS 8912180070
Download: ML19351A468 (5)

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414 Nicollet Mall Minneapohs Minnesota $54011927 Telephone (612) 530 5500 l

December 11, 1989 10 CFR Part 50

Section 50.73 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT e-Docket Nos. 50 282 License Nos. DPR 42 50 306 DPR-60 Automatic Control Room Isolations and Starts of Control Room Cleanun Fans Due to Failures of Chlorine Gas Monitors The Licensee Event Report for these occurrences is attached.

These events were reported via the Emergency Notification System in accordance with 10 CFR Part 50, Section 50.72, on November 9, 1989, November 17, 1989, November 20, 1989, November 23, 1989, December 1, 1989, and December 8, 1989.

Please contact us if you require additional information related to these events, y -

Thomas M Parker Manager Nuclear Support Services c: Regional Administrator - Region III, NRC NRR Project Manager, NRC Senior Resident Inspector, NRC MPCA Attn: Dr J W Ferman I

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.oo ,,. .-. ,, . . , n ei Atsi . Ac r ,t-, . . . .,,,.. , A, This event consists of six similar occurrences. On November 8, 1989, November 17, 1989, November 20, 1989, November 23, 1989, December 1, 1989, and December 8, 1989, automatic isolation of the control room supply and exhaust occurred.

Each isolation was caused by malfunctions of chlorine gas detectors. Three different detectors malfunctioned, each causing a spurious high chlorine signal.

Corrective action to be taken include the installation of additional monitors and a modification of the actuation logic which initiates the automatic actuation.

The control room ventilation system entered its safeguards mode of operation as designed.

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On November 9, 1989, the " chlorine gas present" alarm came in, the 121 control room cleanup filter fan (EIIS Component Code Identifier: FAN) started, and the outside air to the control room automatically isolated. An operator was sent to investigate. It.was determined that there was no chlorine present and 111  ;

chlorine monitor (EIIS Component Code Identifier: MON) was placed in bypass, t The chlorine sensitive tape was torn, it was replaced and the monitor was tested, and the monitor was returned to service November 16, 1989 '

On November 17, 1989, the " chlorine gas present" alarm came in, the 111 control room cleanup filter fan started, and the outside air to the control room automatically isolated. An operator was sent to investigate. It was determined that there was no chlorine present and 111 chlorine monitor was placed in bypass.

An alarm card capacitor was replaced and the card contacts were cleaned. The monitor was tested and then it was returned to service November 22, 1989.

On November 20, 1989, the " chlorine gas present" alarm came in and the outside air to the control room automatically isolated. An operator was sent to investigate. It was determined that there was no chlorine present and 112 chlorine monitor was placed in bypass. The optics block was cleaned and replaced and the monitor was tested and returned to service November 22, 1989.

On November 23, 1989, the " chlorine gas present" alarm came in and the outside air to the control room automatically isolated. An operator was sent to investigate. It was determined that there was no chlorine present and 112 chlorine monitor was placed in bypass. The sample pump motor was found burned out. The pump problem may have been caused by debris entering the pump through the sample line. The sample line was cleaned out and the pump was replaced.

The monitor was tested and returned to service November 27, 1989.

On December 1, 1989, the " chlorine gas present" alarm came in, the 122 control room cleanup filter fan started and the outside air to the control room automatically isolated. An operator was sent to investigate. It was determined that there was no chlorine present and 122 chlorine monitor was placed in bypass.

The optics block was cleaned and replaced and the monitor was tested and returned to service December 5, 1989.

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On December 8, 1989, the " chlorine gas present" alarm came in, the 121 control room cicanup filter fan started, and the outside air to the control room automatically isolated. An operator was sent to investigate. It was determined that there was no chlorine present and 111 chlorine monitor was placed in bypass.

The chlorine sensitive tape was jammed in the optics block. The tape was replaced, the monitor was tested, and it was returned to service December 11, 1989.

CAUSE OF THE EVENTS The automatic control room ventiletion isolations and starts of cleanup fans were caused in each case by a malfunction of one of the chlorine gas monitors. The system logic is such that virtually any malfunction of any of these monitors will cause the conservative action of isolating the control room from outside air.

ANALYSIS OF THE EVENTS The functional response of the automatic actuation of the control room clean up 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 none of these occurrences was triggered by the presence of chlorine in the atmosphere, there was no threat to the operation of the plant. In all occurrences, the affected chlorine monitor failed to the safe condition.

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

1 CORRFCTIVE ACTIONS l

l The three chlorine detectors were repaired and returned to service as noted.

l l The logic is designed such that a spurious high chlorine signal on any one of the four detectors will actuate engineered safety features. An interim modification to the mor.itoring system logic, including the installation of 2 additional detectors, is currently being made to reduce the probability of spurious actuation of these engineered safety features. The details of this logic change were reported in LER 1 89 15.

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To improve the reliability of the chlorine detection system for the long term, >

the following investigations are underway:

Investigate the removal of the onsite liquid / gas chlorine source and determine the effect of that change on the necessity of chlorine detection capability.

Investigate the availability of qualified detectors with higher reliability than those presently installed. ,

Investigate the installation of a system which is capable of sampling chlorine from either #121 or #122 control room ventilation system trains.

This would allow the use of only four detectors and a 2 out of 4 logic. '

This requires reanalysis of the response times involved to insure timely isolation of the control room.

COMPONENT TDENTIFICATION MDA Scientific Chlorine Detection System, Model 7040 FAN PREVIOUS SIMIIAR EVENTS Previous similar events were reported as Unit 1 LERS 89 006,89-009, 89 012, and 89 015.

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