ML20028H046

LER 89-018-03:on 891024,automatic Start of Auxiliary Bldg Ventilation Sys Occurred.Caused by Electronic Spike on Radiation Monitor.Radiation Monitor Modules Will Be Replaced by Upgraded Monitor module.W/900927 Ltr

ML20028H046
Person / Time
Site:	Prairie Island
Issue date:	09/26/1990
From:	Hunstad A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-018-01, LER-89-18-1, NUDOCS 9010050302
Download: ML20028H046 (4)

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September 27, 1990 10 CFR Part 50 Section 50.73 )

Dire.: tor of Nuclear Reactor Regulation i U S Nuclear Regulatory Commission Attn: Document Control Desk ,

Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50 282 License Nos. DPR 42 1 50 306 DPR 60 Auto starts of Auxiliary Building Special l yentilation System As a Result of Radiation Monitor Soikes J l

The Updated Licensee Event Report for these occurrences is attached. This update -)

includes a revised completion dat. for the modifications intended to prevent 1 recurrence. We had revised this completion date previously because of delivery problems with our vendor. Delivery problems necessitate another revision to the j completion date. They are scheduled to ship the necessary modules October 5, l 1990, later than our previous committed date. In addition, the necessary seismic ,

testing on the modified equipment has to be completed prior to installation.  !

Please contact us if you require additional information related to this event.

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Thomas M Parker Manager Nuclear Support Services

l. c: Regional Administrator - Region III, NRC )

H NRR Project Manager, NRC I Senior Resident Inspector, NRC MPCA Attn: Dr J V Ferman l

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During these events, both units were operating at 100% power. The control room received a High Radiation alarm, which initiated an automatic start of the Auxiliary Building Special Ventilation Sy* tem on four separate occasions:

at 1320 hours0.0153 days <br />0.367 hours <br />0.00218 weeks <br />5.0226e-4 months <br /> on October 24, 1989; at 1626 hours0.0188 days <br />0.452 hours <br />0.00269 weeks <br />6.18693e-4 months <br /> on October 25, 1989; at 1210 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.60405e-4 months <br /> on October 31, 1989; and at 0659 hours0.00763 days <br />0.183 hours <br />0.00109 weeks <br />2.507495e-4 months <br /> on November 12, 1989. These were non ECF actuations of an ESF system. In each case one of the radiation monitors which actuates the Auxiliary Building Special Ventilation System, was found to be in alarm with a normal response indicated by the meter located on the monitor. Since there was in fact no high radiation condition in the Auxiliary Building, the control room operator reset the alarm on the radiation monitor and returned the Auxiliary Building Special Ventilation System to the normal standby condition and returned the Auxiliary Building Normal Ventilation System to service. These radiation muitor modules will be replaced with upgraded monitor modules.

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EVENT DESCRIPTION -

During the events, both units were operating at 100% poser. The control room  ;

received a liigh Radiation alarm, which initiated an automatic start of the i Auxiliary Building Special Ventilation System on four separate occasi'ons: at 1320 hours0.0153 days <br />0.367 hours <br />0.00218 weeks <br />5.0226e-4 months <br /> on October 24, 1989; at 1626 hours0.0188 days <br />0.452 hours <br />0.00269 weeks <br />6.18693e-4 months <br /> on Octe er 25, 1989; at 1210 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.60405e-4 months <br /> on October 31, 1989; and at 0659 hours0.00763 days <br />0.183 hours <br />0.00109 weeks <br />2.507495e-4 months <br /> on November 12, 1989. These were '

non ESF actuations of an ESF system. In each case one of the radiation monitors (EIIS Component Code Ident*fier MON), which actuates the Auxiliary Building Special Ventilation System, was found to be in alarm ,ith a normal response indicated by the meter located on the monitor.,Since there was in fact no high radiation condition in the Auxiliary Building, the control room operator reset the alarm on the radiation monitor and returned the Auxiliary Building Special Ventilation System to the normal standby condition an<l r rcturned the Auxiliary Building aormal Ventilation System to service.

GAUSE OF THE EVENT Cause of each event was an electronic spike on the radiation monitor, causing a high radiation alarm and actuation of the Auxiliary Building Special Ventilation System, Cau , of the spiking could not be conclusively +

identified, though the first two events occurred while maintenance was taking place on an adjacent radiation monitoring channel.

I, ANAINSIS OF THE EVENT The functional response of the auto start actuation of the Auxiliary Building Special Ventilation System was according to design, which is to deactivate the Auxiliary Building Normal Ventilation and actuate the Auxiliary Building Special Ventilation System. The Auxiliary Building Special Ventilation System is used to decrease radiological impact of a radiologi. cal release to the ~

l Auxiliary Building through increased filtration and monitoring of the air in the ventilation system. Since this event was not triggered by a radiological event, there were no radiological concerns and there was no effect on the health and safety of the public. ,

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013 0l3 013 von se- . w. ==c s.= asanvim CORRECTIVE ACTION Immediate actions included troubleshooting and inspection of the radiation monitoring channel. .

These radiation teonitor modules wil'. be replaced by an upgraded monitor module manufactured by Nuclear Measuremen'.s Corporation (NMC). This upgrade will eliminate spiking caused by either intermittent couponent failure or poor connectors within the module. The new modules also provide circuitry that will prevent actuation of a contral function even if a spike is generated within the radiation monitor chant el. We expect the modifications to be coaplete by March 1991.

COMPONENT IDENTIFICATION Nuclear Measurements Corporation Model APM-625 gas monitor with totalizer PREVIOUS *i1MILAR EVENTS Previous similar events were reported as Unit 1 LFA's 88 007, 88 011 and 89 008, caused by monitor 1R 37, and LER 89 016 caused by moniter 2R 30, t

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