ML20042F219

LER 90-005-00:on 900329,feedwater Booster Pump 11 Tripped Upon Actuation of Ground Fault Relay & Standby Pump 13 Started But Did Not Deliver Sufficient Flow to Prevent Trip. Cause Not Found.Inlet Filters to Be cleaned.W/900502 Ltr

ML20042F219
Person / Time
Site:	South Texas
Issue date:	05/02/1990
From:	Ayala C, Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-005, LER-90-5, ST-HL-AE-3449, NUDOCS 9005080001
Download: ML20042F219 (6)

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I The Light co mapanySouth Texas Project Electric Generating Station . P. O. Bos 289 Houston Lighting & Power

' ' May.2,-1990 ST llL AE-3449 File No.: G26 1 10CFR50.73 1

U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 1-Docket No. STN 50 498 .!

Licensee Event Report 90-005 Regarding a Reactor Trip on Low j Steam Generator Level Due to a Feedwater Booster Pumn Trio -

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Pursuant to 10CFR50.73, llouston Lighting & Power Company (HIAP) submits j the attached LicenseeJEvent Report (LER 90 005) regarding reactor trip on low.

steam generator level due to a feedwater booster pump trip. This event did 1 not have any adverse impact on the health and safety of the public.  !

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

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G.'E. Vaughn Vice President Nuclear. Generation n

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Attachment:

LER 90-005 (South Texas, Unit 1) i

'h 9005080001 900502 PDR ADOCK 05000498 s PDC

.A1/LER005U1 LO1 A Subsidiary of Hauston Industries Incorporated

' ST HL-AE.3449- .

' Houston Lighting & Power Company - File No.: C26 t

. South Texas Project Eledric Generating Station Page 2  :

-cc:

Regional Administrator, Region IV .,Rufus S. Scott s

. Nuclear Regulatory Commission Associate General Counsel' 611 Ryan Plaza Drive, Suite'10001 Houston Lighting &. Power Company.

Arlington, TX 76011 P. 0. Box 61867-George Dick, Project Manager U.S.-Nuclear Regulatory Commission INPO Washington,fDC. 20555 Records Center i 1100 Circle 75 Parkway.

J. I. Tapia Atlanta, CA 30339-306t.

Senior Resident Inspector 4

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

Commission 50 Be11 port Lane  !

P. O. Box 910 - Be11 port, NY 11713 '

Bay City,-TX 77414 i 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 D..E. Ward /R. P,-Verret Central Power & Li ht S Company P. O. Box 2121 Corpus Christi, TX 78403 J. C. Lanier Director of Generation City of Austin Electric Utility 721 Barton Springs Road Austin, TX 78704 R. J. Costello/M. T. Hardt City Public Service Board l P. O. Box 1771 .

San Antonio, TX 78296 e

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l-l Revised 12/15/89 l-L4/NRC/

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• fi,CiLITY NAME til DOCEST NUMSER GI PAUa G South Texas, Unit 1 o is lo io j ol4 l9 l 8 i loFl 01 4 Reactor Trip on Low Steam Generator Level Due to a Feedwater Booster Pumn Trin avtNT oaf t m LER NvMeta i.i atroRT oaf t iT> ofwla e Acitl?its iNvotvlo ion  ;

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to 406:eH1Het 54 73talGHW to 734eH2Hal LICENSES CONT ACT 90R THIS L8R (121 NAMt itLIPHONE NUMetR Charles Ayala - Supervising Licensing Engineer ' " " ' '

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on March 29, 1990, Unit I was in Mode 1 at 100 percent power. At approximately 1443 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.490615e-4 months <br />, Feedwater Booster Pump (FBP) 11 tripped upon actuation of a ground fault relay. The standby pump, FBP 13, automatically started; but did not deliver sufficient flow to prevent Steam Generator Feedwater Pump 12 from tripping on low suction pressure. Attempts to maintain steam generator level were unsuccessful and the reactor tripped on low steam generator level. The plant waa brought to a stable shutdown in Mode 3. The cause of the FBP 11 trip has not yet been identified; however, it is believed that a weakness of the FBP 11 windings at Neder cables aggravated by moisture intrusion and dirt due to clogged air inler Jilters resulted in the ground fault. Corrective action is being taken to disassemble, inspect and clean the FBP 11 motor during the current refueling outage. The preventive maintenance  ;

activity to inspect the pump motor has been revised to periodically inspect and clean the cooling air filters. Backup FBP 13 did not provide adequate flow because the recirculation valve had been manually set in the open position until the valve controller could be repaired. Repair to the FBP 13 recirculation valve controller will be completed during the current refueling outage.

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0l 0 0l2 OF 0l4 DESCRIPTION OF EVENTi +

I On March 29, 1990, Unit I was in Mode 1 at 100 percent power. At '

I approximately 1443 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.490615e-4 months <br />, Feedwater Booster Pump (FBP) 11 tripped upon actuation of a' ground fault relay. The standby pump, FBP 13, automatically started; however, its recirculation valve was open resulting in reduced flow. ,

Steam Generator Feedwater Pump 12 subsequent 1y'eripped on low suction {

pressure. Control room' operators attempted to maintain steam generator level by reducing turbine load while an operator was dispatched to close the'FBP 13-recirculation valve. Before the FBP 13 recirculation valve could be closed, j the reactor trip},ed on low steam generator level. A feedwater isolation '

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signal was generated as expeted on low average reactor coolant system . y temperature; however, the Train A and D Feedwater Isolation Valves failed to

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close immediately. The Train A valve went to an intermediate position, and' '

subsequently closed after about two minutes and the Train D valve closed after, approximately 5 minutes. All other safety systems performed as required and the plant was brought to a stable shutdown in Mode 3. The NRC was notified of this event at 1741 hours0.0202 days <br />0.484 hours <br />0.00288 weeks <br />6.624505e-4 months <br />. Based upon initial troubleshooting of the Feedwater '

Isolation Valves, the decision was made to begin the scheduled Unit 1 refueling outage approximately one week early.

At the time of tha trip a heavy rainstorm was in progress. This pump has tripped previously during rainstorms. As a result of these events, troubleshooting was performed and corrective action was taken to prevent i

. recurrence. Troubleshooting included checks of the. circuitry and cables for- l the pump motor and corrective actions taken included sealing of the junction boxes and cable terminations to prevent moisture intrusion. Following a pump trip in October of 1989, troubleshooting identified a failed insulator.which was believed to have caused the ground faults. Following replacement of the insulator,-the pump ran satisfactorily and was believed to be fully repaired.

Following the Marcht29th event,-inspections were conducted on the motor connection box. Traces of moisture were found, but not enough to have caused a ground fault. The insulators and surge capacitors were inspected, tested, and found to be in good condition. The motor feeder cables were meggered and a polarization index and winding analysis.was performed on the motor with ,

satisfactory results. The ground fault relay was tested and scheme checked and the current transformer was inspected. No deficiencies were noted.

' The pump motor end covers were opened for an internal inspection. The four inlet air filters'were found to be severely dirty and approximately 50. percent clogged. Oil, dirt and water were found at the bottom and on the walls of the air chamber. Oil and dirt were found on the motor internals, including the stator windings. The location of the ground fault.was not found; however, it is believed that the dirty conditions combined with moisture which was drawn into the motor due to the clogged filters aggravated an existing weakness in the motor winding insulation resulting in the ground fault.

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' DESCRIPTION OF EVENT: (Cont'd.)

Both South Texas units are designed to tolerate a single FBP failure without a trip. However, in this case, the Unit i recirculation valve controller-associated with FBP 13 was inoperable pending receipt of repair parts. Since the: recirculation valve had been left in the open position for puny

, protection,=and the controller was inoperable, closure of the valve'could not l

be accomplished in time to prevent loss of suction pressure to the main Steam: 1 Cenerator Feedwater Pumps.

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CAUSE OF EVENT!

The reactor trip was initiated by the tripping of FBP 11 and failure of the backup FBP'13 to provide sufficient feedwater flow to the main. Steam Generator.

Feedwater Pumps. The most probable cause of the FBP 11~ trip was a defect or weakness in the FBP 11 motor windings or feeder cable insulation which periodically results in a Ground fault. This condition may have been.

aggravated by clogged inlet air filters which caused moisture and dirt to be drawn into the motor, y

The FBP 13 bypass valve failed to close' automatically due'to a controller which was inoperable.pending receipt of repair parts.

The cause of the Feedwater Isolation Valves failureito close was the breakdown

! of the hydraulic fluid under high temperature. A further discussion of the-l1 feedwater isolation valves is included in a 100FR21 teport submitted to the ';

l- NRC under HIAP letter number ST-HL AE-3430 dated April 11, 1990. _

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\ J ANALYSIS OF EVENT An unplanned reactor trip is reportable pursuant to 10CFR50.73(A)(2)(iv).

'During this event the reactor was_ brought to a stable shutdown in Mode 3.= l Other than the delayed closing of the. Train A and D Feedwater Isolation l

Valves, there were no unexpected post trip transients.

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CORRECTIVE ACTION:

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

1. The inlet air filters on the Feedwater Booeter Pumps will be inspected and cleaned prior to completion of the current Unit 1 refueling outage.

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j CORRECTIVE ACTION: (Cont'd.)

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2. The Feedwater Booster Pump 11 Motor will be disassembled, inspected and cleaned prior to startup from the current Unit 1

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refueling outage.

7 3. The preventive maintenance activity to inspect the Feedwater Booster Pumps has been revised to include inspection and cleaning

, of the intake air filters.

4. The Feedwater Booster Pump 13 recirculation valve controller will be repaired prior to startup from the current refueling outage._

ADDITIONAL INFORMATION

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There have been no previous events reported regarding a reactor trip due to failure of a feedwater booster pump.

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