ML20024H257

LER 91-014-00:on 910420,erratic Containment Extended Range Pressure Channel Output Occurred.Caused by Bad Control Card. Weekly Channel Checks Performed,Control Card Replaced & Channel calibrated.W/910524 Ltr

ML20024H257
Person / Time
Site:	South Texas
Issue date:	05/24/1991
From:	Ayala C, Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-014, LER-91-14, ST-HL-AE-3777, NUDOCS 9105310061
Download: ML20024H257 (6)

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The Light c o rn p a n y * '"' "' " ' '"*""E * "" "'

llouston 1ighting A Power May 24, 1991 ST HL AE 3777 File No.. 026 10CTR50.73 U. S. Nuclear Regulatory Conveission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50 498 Licensee Event Report 91 014 Regarding Erratic Containment Extended Range Pressure Chnnnel Outpn1 Pursuant to 10CFR50.73, Houst.on Lighting 6 Power Company (H1AP) submits the attached Licensee Event Report (LER 91 014) regarding erratic containment extended range pressure channel output. This event Uld not result in an adverse impact on the health and safety of the public.

An extension of the due date for this LER to May 24, 1991, was granted on May 21, 1991, by Mr. A. Howell of NRC Region IV.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972 8628 or me at (512) 972 7205.

') h.cxn . ' , u, o Villiam J. Jump Manager, Nuclear Licensing PLV/ amp

Attachment:

LER 91-014 (South Texas, Unit 1) I/

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ST i:L AE.3777

. Ifouston I.igittit.d Pown Conipu,y File No. C26 South Trsas 1%jed 1:ledric Genrreting Statian Page y cc:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Cortpany Arlington, 1DC 76011 P. O. Box 61867 Houston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INP0 Washington, DC 20$$$ Records Center 1100 Circle 75 Parkway

-J. 1. Tapia Atlanta, CA 30339 3064 Senior Resident Inspector 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. iacker J. R. Newman, Esquire _ Bureau of Radiation Control

-Newman 6-iloltzinger,-P.C. Texas Department of Health 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78756 3189 D. E. Ward /T. M. Puckett Central Power and Light Company P. O. Box-2121 Corpus Christi, TX 78403 J. C. Lanier/M. B. Lee City of Austin Electric Utility Department P.O. Box 1088 Austin, TX 78767 R. J. Costello/M. T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 78296

-Revised 01/29/91 L'4/NRC/

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3091 3 On April 20, 1991, (Jnit I was in mode 1 at 100% power. At 0406 hours0.0047 days <br />0.113 hours <br />6.712963e-4 weeks <br />1.54483e-4 months <br />, while conducting a containment supplemental purge to lower the containment pressure l in response to a Containment liigh Pressure alarm, contaitunent extended range pressure channel 9759 was found to read 5 psig while channel 9760 read 0 pstS.

Channel 9759 was_ declared inoperable at 0407 hours0.00471 days <br />0.113 hours <br />6.729497e-4 weeks <br />1.548635e-4 months <br />. Review of historical computer records indicated that the channel had been inoperabic in excess of the seven day allowed outage time. After initial recalibration, subsequent channel check surveillance revealed an additional erratic output signal by the

! transmitter. The transmitter control card was replaced and the transmitter was calibrated. Channel checks will be performed weekly for one month to confirm the channel is repaired.

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DESCRIPTION OF EVENT:

On April 20, 1991, Unit I was in mode 1 at 1004 power. At 0402 hours0.00465 days <br />0.112 hours <br />6.646825e-4 weeks <br />1.52961e-4 months <br />, the Containroent High Pressure annunciator was received in the Control Room. At 0406 hours0.0047 days <br />0.113 hours <br />6.712963e-4 weeks <br />1.54483e-4 months <br />, containment supplemental purge was conutenced to lower the containroent pressure. Periodic purging to control containment pressure is part of normal operation at South Texas. Contairunent pressure may increase due to warming of contaltunent air during plant heatup or due to norinal flow of instrument air into contaltunent. While monitoring the contaitument pressure indications, an operator noticed that contaitument extended range pressure channel 9759 read 5 psig and channel 9760 read 0 psig. The channel check acceptance value for the difference between the two channels is 4 psig. I consequently, at 0407 hours0.00471 days <br />0.113 hours <br />6.729497e-4 weeks <br />1.548635e-4 months <br />, extended range prest.ure monitor 9759 was declared 1 inoperabic based on channel check acceptance criteria.

Pressure transmitter 9759 was calibrated on April 21, 1991, and returned to service, it was declared operable at 2250 hours0.026 days <br />0.625 hours <br />0.00372 weeks <br />8.56125e-4 months <br /> on April 21. The loop was monitored for three days with no abnormal indications. The monthly channel check surveillance was performed on April 29, 1991, and channel 9759 again read about 5 psig. The channel was declared inoperable at 0819 hours0.00948 days <br />0.228 hours <br />0.00135 weeks <br />3.116295e-4 months <br />. The control card was replaced and the instrument was recalibrated.

Extended range containment pressure instrument ation is required to be operable by Technical Specification 3.3.3.6 for use in post accident monitoring. If one less than the two available channels is operable, the inoperable channel must be returned to service within seven days or the plant inust be shut down within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The channels are channel checked mont' ly and calibrated every refueling outage. Review of historical plant puter records revealed that channel 9759 had been erratic since Harel IP?1 and exceeded the channel check acceptance criteria on March 23,1 % 'owever, when the monthly channel check was performed on March 24, 1991, ., instrument had drifted back to specification limits and passed the channel check.

Since the erratic channel had existed for more than the seven days allowed, the NRC was notified at 0108 hours0.00125 days <br />0.03 hours <br />1.785714e-4 weeks <br />4.1094e-5 months <br /> on April 21, 1991.

The control card was examined and was found to have a cracked therrnistor; however, the erratic behavior of the press.ure transmitter cannot be positively attributed to this thermistor.

CAUSE OF EVENT:

This channel f ailed due to a bad cont rol card. The specific failure rnechanism for the control card is unknown, but may be due to a cracked thermistor, tt:k) 91127001.U1 aj e onw 3a..

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6NALYSIS OF EVENT:

Monitoring of containment press.ure is irnportant during an accident to ensure contaitunent integrity. The consequences of this instrument malfunction are an increased risk of inappropriate actions in an accident condition due to erroneous indication. However, instrument redundancy was provided by channel 9760. This event did not result in any advers< safety or radiological concerns, nor did it threaten the safety of the public at any time.

Reportability of this event van discussed with the Senior R(sident inspector and Mr. J. Crooks of the NRC. Since firin evidence in computer historical data was available regarding the length of time the channel was out of service, Question 2.3 of NUREG 1022, Supplement 1, was found to apply. Accordingly, this event represents operation in a condition prohibited by Technical Specifications, which is reportable pursuant to 10CI'R50.73(a)(2)(1)(It).

CORRECTIVE ACTIONS:

The following corrective actions are bein6 taken as a result of this event:

1. Af ter the first discovery of the inoperable channel, the channel was calibrated and returned to service on April 21, 1991.

2. After the second discovery of the inoperable channel, the channel was removed froin service, the control card was replaced, and the channel was returned to service on May 3, 1991.

3. Weekly channel checks will be performed until May 31, 1991, to verify that the channel has been repaired by the card replacement.

4. H1AP will evaluate the failure rate of Barton Model 752 pressure transmitters at STp as it compares to the industry failure rate. A supplemental report will be submitted by September 20, 1991, addressing apparent causes and corrective actions.

5. procedures will be clarified to ensure that plant operators check the extended rango containment pressure readings when Containment High pressure is annunciated in the Control Room. This action is being taken to minimize the potential for exceeding the allowed outage time of the extended range containment pressure channel. The changes will be effective by July 1, 1991.

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6ED1710NAL INP0f,tihl1QH:

The affected transtnitter is a Barton Model 752. No corrective realntenance has previously been required on the Barton Model 752 for contairutent pressure channel 9759. Necessary information will be submitted to NPRDS by September 1, 1991.

NPRDS includes seven previously reported failures at DTP which required transtaltter tepair or replacertient strice Decentber 1988, four irom STP Unit 1 and three from STP Unit 2.

There have been no previous Leks due to transmitter failure.

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