ML20043B661

LER 90-006-00:on 900426,control Room Ventilation Sys Actuated to Recirculation Mode Due to High Level Trip of Vinyl Acetate Channel on Gas Analyzer.Caused by Failure of electro-mechanical Positioner.Part replaced.W/900525 Ltr

ML20043B661
Person / Time
Site:	South Texas
Issue date:	05/25/1990
From:	Ayala C, Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-006, LER-90-6, ST-HL-AE-3464, NUDOCS 9005310077
Download: ML20043B661 (5)

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' compting Houseon Lig er PoweranySouth Teans Project P.O. SosElectric Generating 289 Wadeworth Team 17483 $t May 25, 1990 ,

ST HL AE 3464  :

File No : G26 10CFR50.73 L

-U. S. Nuclear Regulatory Commission [

Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 2 '

Docket No. STN 50 499 Licensee Event Report 90 006 Regarding ,

Control Room Ventilation Actuation to Recirculation Mode Due to a Failure of a Toxic Cas Analvrer r

1%rsuant to 10CFR50.73, Houston Lighting & Power Company (HL&P) submits the attached Licensee Event Report (LER 90 006) regarding a control room ventilation actuacion to the recirculation mode due to a failure of a toxic gas analyzer. The safety systems performed as designed and the event did not ,

have any adversa impact on the health and safety of the public.

If you should have any questions on this matter, please contact l Mr. C. A. Ayala at (512) 972-8628 or myself at (512) 972-7921.

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O. E. Vaugh Vice President Nuclear Generation RAD /n1 l

Attachment:

LER 90 006 (South Texas, Unit 2) l 1

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A1/LER006U2.M1 A Subsidiary of Houston Industries incorporated M

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, ST.HL.AE. 3464 l h..,. Heuno'n Lighting & Power Company File No.: C26 .

South Texas Project Electric Generating Station Page 2 .i L i cc : . 1 Regional Aaministrator, Region IV Rufus S. Scott Nuclear Regulatory Commission ' Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company S Arlington,-TX 76011 P. 0. Box 61867 i . .

Houston, TX- 77208 ,

George Dick, Project Manager' ,

U.S. Nuclear Regulatory Commission INPO ,

Washington, DC 20555. Records Center t 1100 Circle 75 Parkway l J. I. Tapia Atlanta, CA' 30339 3064 l Senior Resident Inspector 'l c/o V. 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 .'

hewman & Holtzinger, P.C. Texas Department of Health

1615 L Screet, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78704 i D. E. Ward /R. P. Verret j Central Power & Light Company 3 P. O. Box;2121 Corpus Christi, TX 78403  :

J. C. Lanier I

' Director of Generation.

City of Austin Electric Utility 721 Barton Springs Road

-Austin, TX 78704  ;

i R.' J. Costello/M. T. Hardt 4 City Public Service Board '

P. O. Box 1771 ,

San Antonio, TX 78296 '

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the control room ventilation system actuated to the recirculation mode as a result of a high level trip of the Vinyl Acetate channel on a toxic gas analyzer. The redundant analyzer did not actuate. Further investigation determined that the cause of this event was a failure of an electro mechanical positioner within the analyzer. The analyzer has been replaced. Engineering

i. is pursuing modifications which will improve the reliability of the toxic gas

analyzer.

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0l0 0l2 0' Ol3 DESCRIPTION OF EVENT!

On April 26, 1990, Unit 2 was in Mode 1 at 100 percent power. At 0057 hours6.597222e-4 days <br />0.0158 hours <br />9.424603e-5 weeks <br />2.16885e-5 months <br />, the control room ventilation system actuated to the recirculation mode as a i

result of a high level trip of the Vinyl Acetate channel on a toxic gas analyzer (XE.9326). The redundant analyzer did not actuate. The NRC was notified at 0153 hours0.00177 days <br />0.0425 hours <br />2.529762e-4 weeks <br />5.82165e-5 months <br /> on April 26, 1990.

Toxic gas analyzer XE.9326 indicated an abnormally high concentration of Vinyl Acetate which caused the actuation, but the analyzer also indicated high erroneous readings on the Ammonia, Hydrochloric Acid, and Naptha channels.

The toxic gas analyzers each utilize a spectrum analyzer to determine the concentration of five toxic gases in samples of control room intake air. To accomplish this, a movable infrared light filter is positioned by a microprocessor controller and an electro mechanicel positioning system to select the proper wavelength for analysis of each of the five toxic gas channels. Diagnostic testing revealed that the positioning system was unable to consistently repeat the position of the infrared filter from one sample to l

the next. This prevented the analyzer from accurately determining the l concentration of the various gases in the sample.

,. No personnel were observed working on or near the analyzer when the actuation occurred. The analyzer was installed on August 7, 1989, replacing an analyzer with a similar failure.

CAUSE OF EVENT!

l The cause of this event was a failure of the electro mechanical positioning system on toxic gas analyzer XE 9326. Although the exact cause of the failure could not be conclusively determined, the most likely cause is degradation of its feedback signal due to accumulation of dust or other contaminants in the feedback potentiometer.

I ANALYSIS OF EVENT 1 Unplanned actuation of an Engineered Safety Feature is reportable pursuant to 10CFR50.73(a)(2)(iv). The control room ventilation system actuated to the recirculation mode as required. No toxic gas was determined to be present and this event did not affect normal operation of the unit. ,

t While any unnecessary challenge to an Engineered Safety Feature is undesirable, actuation of the control room ventilation system to the recirculation mode represents a minimal hazard since it could not cause, worsen, or prevent mitigation of an accident.

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01 0 013 0F 01 3 v.n v . .e an.wnn CORRECTIVE ACTION!

The following corrective actions are being taken as a result of this event:

1. Toxic gas analyzer XE 9326 has been replaced. j

2. Engineering is pursuing modifications to the manufacturer's design -

to improve the reliability of the toxic gas analyzer. This ,

investigation will be completed by August 1, 1990. ,

ADDITIONAL INFORMATION  !

l There has been one previous event regarding an ESF actuation as a result of a failure of the electro mechanical positioning system of a toxic gas analyzer, ,

LER 89 018 Control Room Ventilation Actuation to Recirculation Mode Due to a Failure of

a. Toxic Gas Analyzer .l Several other events involving the toxic gas analyzers have been reported and .

L numerous correctiva actions have been implemented to improve the reliability l.

I of the Foxboro Miran 981 Analyzers.. 4 i

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