05000457/LER-1990-006

LER 90-006-00:on 900521,containment Fuel Handling Incident Area Radiation Monitor Failed Automatic Checksource Test Due to Low Count Rate.Caused by Component Failure.Detector replaced.W/900618 Ltr

ML20055C829
Person / Time
Site:	Braidwood
Issue date:	06/18/1990
From:	Auer M, Querio R COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BW-90-0638, BW-90-638, LER-90-006-09, LER-90-6-9, NUDOCS 9006250211
Download: ML20055C829 (4)

LER-2090-006,

Event date:
Report date:
4572090006R00 - NRC Website

text

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) Commonwealth Edison Braldwood Nuct:sr Pati:r Stati:n

.(/N c; Route #1. Box 64 Braceville. lilinois 60407 N Telephone 815/458-2801 i

June 18,1990 BW/90-0638 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Dear Str:

The enclosed Licensee Event Report from Braldwood Generating Station is being transmitted to you in accordance with the requirements of 10CFR50.73(a)(2)(lv) which requires a 30-day written report.

This report is number 90-006-00; Docket No. 50-457.

Very truly yours,

't ,

l ylR. E. Querto Station Manager i Braldwood Nuclear Station l

REQ /JDW/sjs (7126z)

Enclosure:

Licensee Event Report No. 90-006-00 cc: NRC Region Ill Administrator l NRC Resident inspector INPO Record Center CECO Distribution List l

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_.__ 20.402(b) _. 20.405(c) 2. 50.73(a)(2)(iv) __ 73.71(b)

POWER _ 20.405(a)(1)(1) .__. 50.36(CHI) _ 50.73(aH2)(v) _ 73.71(c)

LEVEL _.__ 20.405(a)(1)(ll) 50.36(c)(2) __._ 50.73(a)(2)(vli) ____ Other (Specify

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At 1117 on May 21, 1990 a Containment - fuel Mandling incident Area Radiation Monitor failed its automatic ch;cksource test due to a low countrate. The checksource test is generated by the microprocessor circuitry of the monitor every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Upon failure, the monitor reverted to the Interlock position. This generated a C:ntainment Ventilation Isolation $lgnal for train A which resulted in the closure of Mint-Purge Exhaust valves and tripped the running Mint-Purge Exhaust Ian. 1he operator acknowledged the Checksource Failure Alarm and v: rifled all automatic actions. The cause of this event was component failure. The detector checksource circuit failed causing the Radiation Monitor to revert to the interlock condition which resulted in the Train A C:ntainment Ventilation Isolation. The Detector was replaced, recalibrated and returned to service. The cintainment fuel Handling Incident Radiation Honitor detectors are replaced on an 18 month frequency in accordance with the Environmental Qualification program. The f ailed detector in this event had been in service since April 26. 1990. A review of component failure histories did not identify any adverse trend concern for this type of detector. Previous corrective actions were not appilcable to this even'..

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. -PLANT CONDITIONS PRIOR TO EVENT:

Unit: Braldwood 2: Event Date: May 21, 1990; Event ilme: 1117; Mode: 4 - Hot $hutdown; Rx Power: 0%;

RCS (AB) Temperature /Prissure: NOT/NOTt

..DESCRIPIl0N OF EVENT:

There were no systems or components inoperable at the beginning of the event which contributed to the severity of th) event. Containment Release G-0102 was in progress.

At 1117 on May 21, 1990 the Containment - Fuel Handling Incident Area Radiation Honitor (AR) (IL), 2RT.AR01),

f ailed its automatic checksource test due to a low countrate. The checksource test is generated by the cicroprocessor circuitry of the monitor every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Upon f ailure of the self diagnostic test the monitor

. reverted.to the interlock position. This generated a Containment Ventilation isolation Signal for Train A which-resulted in the closure of Mint-Purge Exhaust (VQ) (VA) valves 2VQ005A and C, and tripped the running Hint-Purge Exhtust Fan.

The Unit 2 Nuclear Station Operator (N50) (Licensed Reactor Operator) acknowledged the Checksource railure Alarm and verified all automatic actions.

^lhe 2RT-AR011 wa' n elared inoperable and the appropriate Technical. Specification Action Statements were entered and compiled with.

The appropriate NRC notification via the ENS phone system was made at 1222 pursuant to 10CFR50.72(b)(2)(ii)..

An investigation revealed that the Detector Checksource circuit had f ailed. The Detector was replaced.

~

At 1050 on Hay 24,1990 the 2RT-AR011 was declared operable and the Technical Specificatiten Statements were exited.

This event is being reported pursuant to 10CFR50.73(a)(2)(iv) - any event of condition that resulted in manual or autonatic actuation of any Engineered Safety Feature, including the Reactor Protection System.

. CAUSE OF EVENT:

..The root cause of this event was component failure. The detector checksource circuit f ailed causing the Radiation

.Ho'nitor to revert to the interlock condition which resulted in the Train A Containment Ventilation Isolation.

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-lEXT Energy Industry identification System (Ells) codes are identified in the text as (XX)

~ D. SAFETY ANALYSIS:

This event had no effect on the safety of the plant or the public. All systems operated as designed, lhe monitor reverts to its Engineered Safety Feature (ESF) safe configuration upon detector checksource failure.

Th) redundant AR monitor, 2RT-AR012 was operable and available to provide indication and Train B Containment V:ntilation Isolation. l Under the worst case condition of total monitor f ailure there would still be no eflect. The radiation monitoring system is designed such that the monitor reverts to the tripped condition and the appropriate ESF actuation occurs upon failure of the monitor, detector, or automatic diagnostic testing as was the case in this event.

E. CORRECTIVE ACi10NS:

lhe Detector for 2RT-AR0ll was replaced. The monitor was recalibrated and returned to service.

The Containment fuel Handling incident Radiation Monitor detectors are replaced on an 18 month frequency in accordance with the Environmental Qualification program. The failed detector in this event had been in service since April 26, 1990. A review of component failure histories did not identify any adverse trend c ncern for this type of detector.

F. PREVIOUS OCCURRENCES:

There have been previous occurrences of radiation monitor f ailures resulting in ESF actuations. -The correttive actions were implemented addressing both root and contributing causes. Previous corrective actions are not applicable to this event.

G .' COMI'0HENT FAltVRE DATA:

Manufacturer Nomenclature Model Number /HFG Part Number

$;rrento Electronics Area Detector Assy 0281-0760-002 30302(061590)/4