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! November 16, 1989i ST-HL-AE-3298 ,

File No.: G26i 10CFR50.73 4

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!. U. S. Nuclear Regulatory CommissionAttention: Document Control DeskWashington, DC 20555

South Texas Project Electric Generatir.g StationUnit 1

Docket No. STN 50-498Licensee Event Report 89-021 Regarding Unplanned Actuation

of the Control Room Ventilation System Due to an Unknown Cause\'

Pursuant to 10CFR50.73, Houston Lighting & Power (HL&P) submits theattached Licensee Event Report 89-021 regarding an unplanned actuation of thecontrol room ventilation system due to an unknown cause. This event did nothave any adverse impact on the health and safety of the public.

If you should have any questions on this matter, please contactMr. C. A. Ayala at (512) 972-8628.

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R. W. Chewnin;;Vice PresidentNuclear Operations

RWC/BEM/n1

Attachment LER 89-021, South Texas, Unit 1

8911220270 891116PDR ADOCK 05000498S PDC

HL.LER89021.U1 A Subsidiary of Ilouston Industries Incorporated / | g

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ST.HL. AE.3298 .

' t Houston tighting & Power Company File No.: 026*9 South Texas Project Electric Generating Station Page 2

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i Regional Administrator, Region IV Rufus S. ScottNuclear Regulatory Commission Associate General Counsel |

611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company,

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Arlington, TX 76011 P. O. Box 1700'

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Houston, TX 77001!Ceorge Dick, Project Manager

U.S. Nuclear Regulatory Commission INPO,

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Washington, DC 20555 Records Center'; 1100 circle 75 Parkway

J. I. Tapia Atlanta, CA 30339 3064! Senior Resident Inspector *

c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendriec

: Commission 50 Be11 port Lane! P. O. Box 910 Be11 port, NY 11713

Bay City. TX 77414D. K. Lacker

J. R. Newman, Esquire Bureau of Radiation ControlNewman & Holtzinger, P.C. Texas Department of Health1615 L Street, N.W. 1100 West 49th StreetWashington, DC 20036 Austin, TX 78704

R. L. Range /R. P. VerretCentral Power & Light CompanyP. O. Box 2121Corpus Christi, TX 78403 :

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IJ. C. LanierDirector of GenerationsCity of Auscin Electric Utility721 Barton Springs Road

!- Austin, TX 78704

R. J. Costello/M. T. Hardtcity Public Service Board !P. O. Box 1771 ;

San Antonio, TX 78296|

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Revised 11/15/89

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On October 17, 1989 Unit I was in Mode 1 at 7 percent power. At 1112 hours, r

an Engineered Safety Features, (ESF) actuation of the Control Room VentilationSystem to the recirculation mode occurred. Inspections were performed of '

circuits which could have caused this event, however, we were unable to '

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determine the source of the actuation. Surveillance testing will continue andfuture actuations will be investigated if they occur.

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DESCRIPTION OF EVENT: ,

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On October 17, 1989, Unit I was in Mode 1 at 7 percent power. At ,

?approximately 1112 hours, an Engineered Safety Features (EST) Control RoomVentilation actuation occurred, causing the control room ventilation to go tothe recirculation with filtered makeup mode of operation. Investigation at ;

the time of the actuation did not reveal an apparent cause. The NRC wasnotified pursuant +.o 10CFR50.72 at 1155 hours.

:Subsequent investigation of the actuation did not reveal the specific cause ofthe actuation. High control room ventilation radiation or failure of the '

control room ventilation radiation monitors or ESF modes I, II or III are the i

only automatic actuations of the ESF control room ventilation system to the ,

recirculation mode with filtered makeup. Since all three trains of thecontrol room ventilation system were actusted and no ESF actuation signalswere present, the radiation monitoring system was determined to be theprobable cause of the actuation.

The radiation monitors actuate the ventilation system through relays located,

in radiation monitoring panel ZCP-023. These relays are kept normally !

energized by relay drivers from the microprocessor based indicator modules forthe control room vertilation radiation monitors, which are also located in iZCP-023. Upon moatter failure or a high radiation alarm from either redundantradiation monitor, tae relay drivers deenergize the actuation relays causingall three trains of the Control Room Ventilation System to go to tne ,

recirculation with filtered makeup mode. If a problem had occurred with therelay 24 Volt direct current (VDC) power supply inside the ZCP-023 panel,other ventilation actuations would have occurred since there is one common ,

24VDC power supply in the radiation monitoring panel ZCP-023. Also, the highradiation alarm or failure condition of the radiation monitor would be |

| documented on the radiation monitoring and ERFDADS computer printouts. No !

l record of a high radiation alarm or failure for either control roomventilation monitor was generated by ERFDADS or the radiation monitoringsystem.

Based on the above, the radiation monitor actuation relay wiring has been

| inspected for loose connections or miswiring which may cause spurious!

actuations. No discrepancies have been noted. This event has been attributedto the spurious operation of a relay driver or actuation relay which has notrecurred.

| CAUSE OF EVENT:1

! No cause has been established for this spurious actuation of the control room ,

vent ilation system to the recirculation with filtered makeup mode.

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ANALYSIS OF EVENT: !

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This event resulted in a spurious actuation of the Control Room VentilationSystem to the recirculation with filtered makeup mode. Had any radiation ,

release occurred, it would have had no effect on the control room environment.While any unnecessary challenge to an Engineered Safety Feature is

'undesirable, actuation of the Control Room Ventilation recirculation moderepresents a minimal hazard since it could not cause, exacerbate or preventmitigation of an accident,

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The event was reportable pursuant to 10CFR50.73(a)(2)(iv) since an ESF ,

actuation occurred due to the control room ventilation radiation monitora. '

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CORRECTIVE ACTION: ,

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Since no specific cause for this event has been determined, no further,

corrective actions have been identified. Continued surveillance testing will |be performed and this event will be used as input to evaluations of future ,'actuations should they occur.

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; ADDITIONAL INFORMATION:.

!LER 88-025 documented an ESF actuation of the control room ventilation systemto the recirculation with filtered makeup mode of operation. The actuationoccurred during the performance of a Digital Channel Operation Test of the

|Spent Fuel Pool Radiation Monitors.

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