ML19332C067

LER 89-021-00:on 891017,unplanned ESF Actuation of Control Room Ventilation Sys to Recirculation Mode Occurred.Cause Not Determined.Continued Surveillance Will Be Performed.W/ 891116 Ltr

ML19332C067
Person / Time
Site:	South Texas
Issue date:	11/16/1989
From:	Ayala C, Chewning R HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-021-01, LER-89-21-1, ST-HL-AE-3298, NUDOCS 8911220270
Download: ML19332C067 (5)

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! November 16, 1989 i

ST-HL-AE-3298 ,

File No.: G26 i

10CFR50.73 4

!. U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generatir.g Station Unit 1 Docket No. STN 50-498 Licensee Event Report 89-021 Regarding Unplanned Actuation of the Control Room Ventilation System Due to an Unknown Cause

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Pursuant to 10CFR50.73, Houston Lighting & Power (HL&P) submits the attached Licensee Event Report 89-021 regarding an unplanned actuation of the control room ventilation system due to an unknown cause. This event did not have any adverse impact on the health and safety of the public.

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

/R. W. Chewnin;;

Vice President Nuclear Operations RWC/BEM/n1 Attachment LER 89-021, South Texas, Unit 1 8911220270 891116 PDR ADOCK 05000498 S PDC HL.LER89021.U1 A Subsidiary of Ilouston Industries Incorporated / l g

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ST.HL. AE.3298 .

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

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i Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel l 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 1700 ,

Houston, TX 77001  !

Ceorge Dick, Project Manager ,

, U.S. Nuclear Regulatory Commission INPO '

Washington, DC 20555 Records Center

'; 1100 circle 75 Parkway J. I. Tapia Atlanta, CA 30339 3064

! Senior Resident Inspector

• c c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrie

Commission 50 Be11 port Lane

! P. O. Box 910 Be11 port, NY 11713 Bay City. TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger, P.C. Texas Department of Health 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78704 R. L. Range /R. P. Verret Central Power & Light Company P. O. Box 2121 Corpus Christi, TX 78403  :

I J. C. Lanier Director of Generations City of Auscin Electric Utility 721 Barton Springs Road

!- Austin, TX 78704 R. J. Costello/M. T. Hardt city Public Service Board  !

P. O. Box 1771  ;

San Antonio, TX 78296 l

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On October 17, 1989 Unit I was in Mode 1 at 7 percent power. At 1112 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23116e-4 months <br />, r an Engineered Safety Features, (ESF) actuation of the Control Room Ventilation System to the recirculation mode occurred. Inspections were performed of circuits which could have caused this event, however, we were unable to '

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

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i DESCRIPTION OF EVENT: ,

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

approximately 1112 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23116e-4 months <br />, an Engineered Safety Features (EST) Control Room  ?

Ventilation actuation occurred, causing the control room ventilation to go to the recirculation with filtered makeup mode of operation. Investigation at  ;

the time of the actuation did not reveal an apparent cause. The NRC was notified pursuant +.o 10CFR50.72 at 1155 hours0.0134 days <br />0.321 hours <br />0.00191 weeks <br />4.394775e-4 months <br />.

Subsequent investigation of the actuation did not reveal the specific cause of the 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 the control room ventilation system were actusted and no ESF actuation signals were present, the radiation monitoring system was determined to be the probable 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 for the control room vertilation radiation monitors, which are also located in i ZCP-023. Upon moatter failure or a high radiation alarm from either redundant radiation monitor, tae relay drivers deenergize the actuation relays causing all three trains of the Control Room Ventilation System to go to tne ,

recirculation with filtered makeup mode. If a problem had occurred with the relay 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 high radiation alarm or failure condition of the radiation monitor would be l l documented on the radiation monitoring and ERFDADS computer printouts. No  !

l record of a high radiation alarm or failure for either control room ventilation monitor was generated by ERFDADS or the radiation monitoring system.

Based on the above, the radiation monitor actuation relay wiring has been l inspected for loose connections or miswiring which may cause spurious actuations. No discrepancies have been noted. This event has been attributed to the spurious operation of a relay driver or actuation relay which has not recurred.

l CAUSE OF EVENT:

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! 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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...--,.--a.,m, ANALYSIS OF EVENT:  !

This event resulted in a spurious actuation of the Control Room Ventilation System 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 mode represents a minimal hazard since it could not cause, exacerbate or prevent mitigation of an accident, i

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

actuation occurred due to the control room ventilation radiation monitora.

CORRECTIVE ACTION: ,

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

corrective actions have been identified. Continued surveillance testing will l 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 system  !

to the recirculation with filtered makeup mode of operation. The actuation occurred during the performance of a Digital Channel Operation Test of the Spent Fuel Pool Radiation Monitors.

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