ST-HL-AE-3985, Special Rept:On 911224,control Valve Failed Open Causing Reduction of Reactor Coolant Sys Pressure.Cause Can Not Be Determined.Verified No Loose Connections,High Resistant Contacts or Voltage Fluctuations Present

Special Rept:On 911224,control Valve Failed Open Causing Reduction of Reactor Coolant Sys Pressure.Cause Can Not Be Determined.Verified No Loose Connections,High Resistant Contacts or Voltage Fluctuations Present

ML20091M407
Person / Time
Site:	South Texas
Issue date:	01/23/1992
From:	Jump W HUDSON LIGHT & POWER DEPT.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3985, NUDOCS 9201290075
Download: ML20091M407 (4)

Text

o .

. The Light c o mp anySoutWesu Pn>Jni 11Nule Guinating $tallon Pg.110 289 Wadewarth, Tean 77483 ifouston Lighting & Power January 23, 1992 ST-ilL-AE-3 98 5 Filo lio.t G02 10CFR50 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Unit 2 Docket No. STN 50-499 Special Deport Regarding a Nonvalid Failuro of Standby Diosol Grngrator 21__on December 24, 1991 Pursuant, to the South Texas Project Electric Generating Station (STPEGS) Technical Specifications 4.8.1.1.3 and 6.9.2, llouston Lighting & Power submits the attached Special Report regarding a nonvalid failure of Standby Diesel Generator 21 which occurred on December 24, 1991.

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

914L%.e William J. Jump.

I 9 Managor, Nuclear Licensing JMP/lf

Attachment:

Special Report Regarding a Nonvalid Failure of SDG 21 on December 24, 1991 i

< 00 b '3 0 m nn na.o" A subsidiary of liousion indusuies incorporated

/

9201290015 9203g3

{DR ADOCK 05000499 PDR

l llaust}m I.lghting & Powtr Compan ' ST-llL+AE-3985

, South fesa6 Projnt I.initit Generating $tation Filo No. G02 Page 2 cc Regional' Administrator, Region IV llufus S. Scott Nuc1 car Regulatory Commission Associate General Counsel Gli Ryan Plata Drivo, Suito 400 llouston Lighting & Power company Arlington, TX 76011 P. O. Box G1867 Ilouston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Recorda contor 1100 circle 75 Parkway J. 1. Tapia Atlanta, GA 30339-3064 Senior Renident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. Ilondrio Commission 50 Dollport Lane P. O. Box 910 Dollport, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Howman, Esquiro Bureau of Radiation Control Newman & Ilolttingar, P.C. Texas Department of Iloalth 1615 L Street, N.W. 1100 Wout 49th Stroot

. 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 r

J. C. La"4er/M. D. Leo City of <.uutin Electric Utility Department P.O. Box 1088 Austin, TX. 78767 K. J. Fledler/M. T. liardt City Public Servico Board P. O. Box 1771 San Antonio, TX 78296 Revised 10/11/91 L4/NRC/

I Attachment ST-llL-AE-3985 i page 1 of 2 i South Texas Project .

Unit 2 ,

Dockot No. STN 50-499 Special Hoport Hogarding a Nonvalid Failuro of EtAnd2Y_D11A21_.GS119IAtDr_.21 on DeceInbor 2L ___1991 Dff9fRIPTION OF EVEliIt On Decomrer 24, 1991, Unit 2 was in Modo 1 at 30% reactor powor, during power anconsion from a recent refueling outago, when a control valvo failed open causing a reduction of Reactor Coolant System prosauro. Tho low pressurizer pressure caused a reactor trip and a safety injection signal. All thron Standby Diosol r Generators (SDGs) automatically started in the omorgency modo, as designed, on the safoty injection signal. Utilizing the performance of the Reactor Trip or Safoty injection Emergency Operating Proceduro, the SDGs woro released f rom the omorgency modo after the verification of availability of offsito power. The SDG 21 tripped instantly when it was released from the amorgency modo.

There woro no alarms or trip indications reco1ved on the SDG 21 trip.

On January 15, 1992, a chart recorder was not up at the local engine control panol to monitor the trip circuit loop voltagos during a test run of the SDG 21 i n an attempt to duplicate the event. No fluctuations were recorded by the chart recorder. A fluctuation would have indicated an interruption in the voltage due to a faulty contact, a loose connection or a component malfunction.

During the same test run of SDG 21 the pneumatic shutdown system was monitored using permanent instrumentation and a test

' instrument. The pneumatic regulators were found to be performing satisfactorily. However, one of the pneumatic regulators was found to be set low. The as found setting should not havo resulted in pressures low enough to cause a trip. The regulator was adjusted to the correct pressure.

CAUSE OF EVENT:

The cause of the ovent cannot bo determined at this timo. '

Further investigation is ongoing to troubleshoot the SDG 21 trip. .

Potential caustDs include the following

- trip circuit relay In1 function

- pneumatic contrsis malfunction l

. failure to reset the trip circuit prior to starting the l diosol.

SREH 92-014,001

. - . - ~-. , . ...w - . . . , , , , , . -. . < .

l

~

Attachmont ST-IIL-AE-3 9 8 5 Pago 2 of 2 CAUSE OF EVEliT (Continued)

SDG 23 and SDG 21 also tripped instantly when released from I the omorgoney modo on Docomber 6, 1991 and December 7, 1991, ,

respectively. Thoso SDG ovents woro classiflod as nonvalid l failures. These events were documented in an NRC Special Report submitted on January 3, 1992 (References ST-ilL-AE-3955) . The causo(s) of thoso events have not boon determined but their investigations are ongoing.

AN_LYSID A OF EVENT:

The SDG 21 automatically started in the emergency mode on a safety injection signal. The SDG 21 accelerated to rated speed, voltage, and frequency within the required ten seconds but was not t*

loaded because offsito power had not boon interrupted. The SDG 21 failure occurred vnen it was rolensed - from the amargency modo.

This indicates that the cause of the failure is in a non-omorgency component and/or circuit. This SDG 21 start was classified as a nonvalid failure. The SDG - 21 operated natisfactorily in the emergency modo and, if challonged, would have performed its design .

function.

CQRRCCTIVE ACT1QHgt

1. Initial troubleshooting was performed and verified that no loose connections, high resistant contacts, or voltage fluctuations woro present. Initial troubleshooting also verified that the pneumatic regulators, although one was found to be set low, were operating satisfactorily and . that the ,

pneumatic heador was maintaining adequato prosauro.

2. Troubleshooting will continuo during the schedulod train outage work weeks for SDG. 21 until a final resolution is dotormined. The results will be provided in a supplemental report which will include the necessary correctivo actions.

This report will be submitted to the NRC by July 30, 1992.

it . ' ADDILT1NAL..IEDIWATIol{1

'W , ,

1There have been mo valid.failurou in the last 20 valid tests U '

of'SDG 21. The number of- valid failures in the last 100 valid tests is loss than four. Therefore, the testing frequency for SDG 21 romains at once por 31 days.

Sk1M92-014.001

. - _ _ . _ , _ _ _ . _ _ _ ~ . ~ . _ , . . , _ - . . , _ _ - , - .

_