ML20043E060

LER 90-005-00:on 900504,control Room Received High Radiation Alarm & Indication of Automatic Start of Spent Fuel Pool Special Exhaust Fan 121 on Two Occasions.Caused by Electrical Spike on Monitor.Modules replaced.W/900604 Ltr

ML20043E060
Person / Time
Site:	Prairie Island
Issue date:	06/04/1990
From:	Hunstad A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-005, LER-90-5, NUDOCS 9006120018
Download: ML20043E060 (4)

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414 N'r AM Mall Minneapolis, Minnesota 554011927.

Telephone (612) 330-5500 i

' June 4, 1990 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 CENERATING Y1 ANT Docket Nos, 50 282 License Nos. DPR 42 50 306 DPR 60 cl Auto-starts of-Spent Fuel Pool Special Ventilation System Due to Electrical Soiking of Radiation Monitor j 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 May 4, 1990 and May 14, 1990. Please contact us if-you require additional information related to these events.

J Cs J 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 Attachment 9006120018 900604 DR ADOCK0500gg2 t --

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~~~] vts In v., <m.m soucreo suswwoar QArus T] NO l l A T x ACT n . ., . . A . . ,.. ,, A n ,.,,. .-e e,-.mo , o ei During these events, both urtts were operating at 100% power. The control room received a high radiation alarm and indication of an automatic start of No.121 Spent Fuel Pool Special Exhaust Fan on two separate occasions: at 0733 hours0.00848 days <br />0.204 hours <br />0.00121 weeks <br />2.789065e-4 months <br /> on May 4, 1990; and at 0310 hours0.00359 days <br />0.0861 hours <br />5.125661e-4 weeks <br />1.17955e-4 months <br /> on May 14, 1990. These were non-ESF actuations of an ESF system. On the first occasion the actuation was caused by an electrical spike on spent fuel pool radiation monitor R 25 when an 160 technician turned off power to a nearby monitor for maintenance. On the second occasion the actuation was also caused by an electrical spike on the same monitor, for no apparent reason. In each case, radiation monitor R 25 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 spent fuel pool area, the control room operator reset the alarm on the radiation monitor and returned the Spent Fuel Pool Normal Ventilation System to service. These radiation monitor modules will be replaced with upgraded monitor modules.

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Ol0 012 0F 0 13 Terrn . anc - 4wnn EVENT DESCRIPTION During these events, both units were operating at 100% power. The control room received a high radiation alarm and indication of an automatic start of No.121 Spent Fuel Pool Special Exhaust Fan on two-separate occasions: at 0733, hours on i May 4,1990; and at 0310 hours0.00359 days <br />0.0861 hours <br />5.125661e-4 weeks <br />1.17955e-4 months <br /> on May 14, 1990. These were non Engineered Safety '

Feature actuations of an Engineered Safety Feature system. On the first occasion the actuation was caused by an electrical. spike on spent fuel pool radiation monitor R 25 (EIIS Component Code Identifier: MON) when an 160 technician turned _j off power to a nearby monitor for maintenance. On the second occasion the -

actuation was also caused by an electrical spike on the same monitor, for no-apparent reason. In each case, radiation monitor R 25 was found to be in alarm with a normal response indicated by the meter located on the monitor. Since l there was in fact no high radiation condition in the spent fuel pool area, the control room operator reset the alarm on the radiation monitor and returned the Spent Fuel Pool Normal Ventilation System to service.

CAUSE OF THE EVENT l Cause of each event was an electrical spike on the radiation monitor, causing the l high radiation alarm and actuation of No. 121 Spent Fuel Pool Special Exhaust L Fan. Cause of the spiking could not be conclusively identified, though the first l- event occurred while maintenance was taking place on a radiation monitor just adjacent to R-25 in the monitor rack. No maintenance activities were underway {

during the second event.

ANAINSIS OF THE EVENT The functional response of the auto-start actuation of the Spent Fuel Pool Special Exhaunt System was according to design, which is to deactivate the Spent Fuel Pool Normal Supply and Exhaust Fans and actuate the Spent Fuel Pool Special Exhaust Fans. The Spent Fuel Pool Special Ventilation System is used to decrease radiological impact of a radiological release in the Spent Fuel Pool through increased filtration and monitoring of the air in the ventilation system. Since these events were not triggered by radiological events, there were no radiological concerns and there was no effect on the health and safety of the 4 public, l

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0 l0 0'l3 0F 0 l3 tener . - a.c = an.uun CORRECTIVE ACT10h Corrective actions included troubleshooting and inspection of the radiation monitoring channel. The detector tube connector was found to be corroded and it was cleaned. _ One of the wires at.the detector tube connector was fraye,d and it .

was -repaired. The detector tube was replaced and the monitor was watched carefully for a few days. There has been no recurrence of spiking.

These radiation monitor modules will.be replaced by an upgraded monitor module manufactured by Nuclear Measurements Corporation. This upgrade will eliminate spiking caused by either intermittent component failure or poor connectors within the module. The new modules also provide circuitry that will-. prevent actuation of a control function even if a spike is generated within the radiation monitor channel. We expect the modificatins will be made by March 1991'.

~ FAILED COMPONENT IDENTIFICATION Nuclear Measurements Corporation Model IGM 912 gas monitor PREVIOUS SIMIIAR EVENTS Previous similar events were reported as Unit 1 LER's88-007. 88 011, 89 008,89-016 and-89-018.

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