ML20024H206

LER 91-003-00:on 910423,auto-start Occurred of One Train of Auxiliary Bldg Special Ventilation Sys.Cause Unknown.Plant Mod Initiated Removing Unnecessary Wiring That Could Short Monitor module.W/910523 Ltr

ML20024H206
Person / Time
Site:	Prairie Island
Issue date:	05/23/1991
From:	Hunstaf A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-003-01, LER-91-3-1, NUDOCS 9105300152
Download: ML20024H206 (4)

Text

{{#Wiki_filter:- _ f - - . Northern Statco Power Company 414 Nicollet Mall M.nneapolis, Minnesota 55401 1927 Telephone (612) 330-5500 May 23, 1991 10 CFR Part 50 Section 50.73 U S Nuclear Regulatory Commission Attn: Document Control Desk Vashington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50 282 License Nos. DPR-42 50-306 DPR-60 Auto-start of one Train of Auxiliary Building Sriecial Ventilation System Due to Unknown Cause 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 April 23, 1991.        Please contact us if you require additional information related to this event.

Tw 4 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 V Ferman l Attachment 9105300152 910523 PDR ADOCK 05000282 1522 S POR / l

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• est a acr u. , ,. um - u. -. w., . e ,,- . , o o On April 23, 1991, both units were operating at full power. At 0938 control room operators observed annunciation of a RADIATION MONITOR DOWNSCALE FAILURE, and noticed that No. 121 Auxiliary Building Special Ventilation System was runnir.g.

Inspection of the control room radiation monitoring panel showed a failure alarm for radiation mon! tor 2R-37, which actuates the Auxiliary Building Special Ventilation System en a high radiation signal. No high radiation alarms were received, and normal background response was indicated on the panel meter and also by-the redundant monitor 1R-37. Since there was no high radiation condition in the Auxiliary Building, the control room operator reset the alarm on the l radiation monitor and returned the Auxiliary llullding Special Ventilation System to the normal standby condition and returned the Auxiliary dullding Normal Ventilation S*ystem to service The system engineer was contacted and an investigation of the downscale failure was begun. l Testing by the plant and by the manufacturer have identified no cause for the l actuation. L l l \

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0 l5 l0 l0 l0 l 2l8 l 2 )]! - 0 l0 l 3 - 0 l0 0p OF 0 l3 rm w ~ a w. , ~ nne ra,,, w.o nn l EVENT DESCRIPTl_O)fi 1 On April 23, 1991, both units were operating at full power. At 0938 control room i operators observed annunciation of a RADI ATION MONITOR DOWNSCALE FAILURE, and noticed that No. 121 Auxiliary Building Special Ventilation System was running. Inspection of the control room radiation monitoring panel showed a failure alarm , for radiation monitor 2R-37, which actuates the Auxiliary Building Special j Ventilation System on a high radiation signal. No high radiation alarms were i I received, and normal background response was indicated on the panel meter and also by the redundant monitor 1R-37. Since there was no high radiation condition in the Auxiliary Building, the control room operator reset the alarm on the i radiation monitor (EIIS Component Identifier MON) and returned the Auxiliary Building Special Ventilation System to the normal standby condition and returned the Auxiliary Building Normal Ventilation System to service. The system engineer was contacted and an investigation of the downscale failure was begun. CAUSE OF THE FVENT Testing by the plant and by the manufacturer have identified no cause for the j actuation. ANAL.YSIS OF THE EVENT The functional response of the auto-start actuation of the Auxiliary Building Special Ventilation System was according t.o design, which is to deactivate the Auxiliny Building Normal Ventilation and actuate the Auxil.iary Building Special Ventilation System. The Auxiliary Building Special Ventilation System is used to decrease radiological impact of a radiological release to the Auxiliary Building through increased filtration and monitoring af the air in the vent.llation system. Since this event was not triggered by a radiological event, there were no radiological concerns and there was no offeet on the health and l safety of the public. This event is reportable pursuant to 10C FR50. 73 ( a ) ( 2 ) ( iv) since there was an unplanned actuation of Engineered Safety Feature equipment.

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Prairie Island Nuc Gen Plant Unit 1 l0 l5 l0 l0 l0 l 2l8 l 2 9 l1 - 0 l Oi 3 - 0l0 0l3 M 0l3 Tm w . , - ==e w w.mn CORRECTIVE ACTION ' A new monitor module had just recently been installed in Radiation Monitor 2R-37. A Work Request was written immediately to test the 2R-37 module and external relays, and to replace the new rnodule CRM-84 with its old style module CRM-71. The new module was functionally tested in place, then removed, inspected and bench-tested; no problems were identified. The module was returned to the manufacturer for further testing. To date no problems with the module have been identified. The external relays that actuate the Engineered Salety Feature equipment and control room high radiation annunciator were tested and inspected; no problems were identified. Evaluation of the module circuitry that pr mides the Engineered Safety Feature actuation was done. That evaluation indicates that the only failures that could cause a downscale failure in conj unc tion with an Engineered Safety Feature actuation are misoperation of the relay that proviacs the 12V power to the external relays, or interruption of the 12V power supply itself. Testing of this circuitry identified no problems. The manufacturer is investigating possible software problems. A plant modification has been initiated to remove unnecessary wiring that could potentially short the monitor module's 12V power supply. FAII.ED C05 3NENT IDENTIFICATION Nuclear Measurements Corporation Model APM-625 gas monitor with CRM-84 module. PREVIOUS SIMIlAR EVENTS Engineered Safety Feature auto-starts from similar monitors have been reported as Unit 1 LER's 88-007, 88-011, 89-008, 89-016, 89-018, 90-005 and 91-002. ==C,- ma u i}}