ST-HL-AE-4094, Special Rept:On 920408,SDG 21 Tripped When Released from Emergency Mode.Cause Has Not Been Determined.Further Analysis & Investigation Performed on Sdg 21.Supplemental Rept Will Be Submitted by 920730

Special Rept:On 920408,SDG 21 Tripped When Released from Emergency Mode.Cause Has Not Been Determined.Further Analysis & Investigation Performed on Sdg 21.Supplemental Rept Will Be Submitted by 920730

ML20096C915
Person / Time
Site:	South Texas
Issue date:	05/08/1992
From:	Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-4094, NUDOCS 9205150034
Download: ML20096C915 (4)

Text

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1 The Light companyS flouston Lighting & l'ower.. _?f3'Tes..projntynagg7nnagng siatign i>, g. nos :89 y.d.worit , Tes.3 774 83 May 8, 1992 ST-IIL-AE-4094 File No.: G02 10CFR$0 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Unit 2 Docket No. STN 50-499 Special Report Regarding A Non-Valid E011ure of Standby Diesel Gelterator #21 on ADril 8. 1992 P

Pursuant .to . the South Texas Project (STP) Technical Specifications 4.8.1.1.3 and 6.9.2, Houston Lighting & Power (llL&P) submits the attached Special Report regarding Standby Diesel Generator /21 non-valid failure which occurred on April 8, 1992.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8628 or no at (512) 972-7205.

) bnt. .

William J. Ju Manager, Nuclear Licensing MAC/1f

Attachment:

Special Report Regarding A Non-Valid Failure of SDG #21 on April 8, 1992

-t.200 YO surte2-11s, col I A Subsidiary of Ilouston industries incorporated k 9205'150034 920508 PDR L

'ADOCK 05000499 PDR JT

i 1 1

,' llouston Lighting & Power Company

, Snuth Teras Project Elecith Goiuating Station S fL "4 4 F o1 Pago 2 Col Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory-Commission Associate General Counsel Gil Ryan Plaza Drive, Sitite 400 Houston Lighting & Power Company .

Arlington, TX 76011 P. O. Box 61867  !

Houston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Conter 1100 Circle 75 Parkway J. I. Tapia Atlanta, GA 30339-3064 Senior Resident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrio Commission 50 Bo11 port Lane _

6 P. O. Box 91P Bellport, NY 11713 Bay City, TX .414 D. X. 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 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 X. J. Fiedler/M. T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 78296 i

Revised 10/11/91 L4/NRC/

( ,

Attachment ST-HL-AE-4094

,! Page 1 of 2 7

3 South Texas Project O Unit 2 t Docket No. STN 50-499 Special Report Regarding A Non-Valid

'1 4ure of Standby Diesel Generatpr #21 on W il 8. 1992 .

!' Q, 'lON OF EVENT:

\ M, Or- . JL 8, 1992, Unit 2 was in Mode 1 at 100% power. While 3

- .v Diesel Generator (SDG) #21 Operability Test was being

{

p .c d, the SDG tripped when released from the emergency n. ode. D Fu a; .as or relay fit.gs, which would indicate the cause of the

g trip w ce detected. In addition, when SDG #21 was started, none p 't the usual starting alarms (i.e., low . starting air pressure, ,

d ycket water standpipe level low) were received.

Troubleshooting or the SOG #21 electrical trig circuitry was >

performed with no problems found. The applicable fuses, relays and timers were verified for proper operation. Various connections '

were inspected which revealed a icose connector to the input side of the annunciator ,ower supply. This connection was repaired. 3 A failed annt u i wrt power supply (PS-2) was also identified. This power sapply vss ed.sequently replaced three times before the cause for thts power supply failures estid be determined. The failure of

( ,

this power supply was criginally thought to have been the cause for the trip - upce release from emergency mode. However, after axtensive troubleshooting, this conclusion could not be supported. j i

A functional check of the engine speed monitor and its associated trip setpoints were verifled. No abnormalities were noted.

.CAUSE OF EVENI:

The cause c' the SDG #21 trip upon release from the emergency mode has not been determined at this time. Previous occurrences of both SDG #21 and #23 trips upon release from the emergency code have been attributed to a loss of air pressure in the pneumatic shutdown header. This event ;s described in the attached correspondence ST-HL-AE-4065 dated April 30, 1992. In addition, undetected electrical faults co.1 .d also result in unannunciated trips upon release from the emergency mooo SREP)02 118,001

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4 Attachment ST-HL-AE-4094 Page 2 of 2 ANALYSIS OF EVENT:

This event has been classified as a non valid failure since the SDG

1. 21 . operated satisfactorily in the emergency mode and if ciglienged, would have performed its safety function.

CORRECTIVE ACTIONS:

1. Further analysis and investigation will be performed on SDG #21.

A supplemental report will be submitted by July 30,. 1992, identifying the cause, if determined, and the- necessary corrective actions.

ADDITIONAL INFORMATIOE:

At the time of the event, there were no valid failures in the last 20 valid tests and loss than 4 valid failures in the last 100 tests for SDG #S?.. Therefoce, the testing frequency will remain at once per 31 c' i s.

. The power supply is manufactured by Beta Products, Part No. 306930.

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SREPt92-118.001

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l The Light cllouston ompLight.ing any South

& l'ower Texas l'_r_

_ . Generating acct Electric _ . . . _Station

._ . _,_' .O.Ilon289 l. ...___ Wad worth. Tc m ai 774 81 April 30, 1992 ST-liL- AE- 4 0 6 5 File No.: G02 1 URSO U. S. Nuclear Regulatory Commission Attention: Document Control Desk _

Washington, DC 20555 South Texas Project Unit 2 Docket No. STN 50-499 Supplemental Special Report Regarding Two Diesel Generator N_on-Valid Failures ,

B.

Pursuant to the South Texas Project Electric Generating Station (STPECS) Tech '. ca l Specifications 4.8.1.1.3 and 6.9.2, Houston Lighting & Pove e submits the attached Supplemental Special Report regarding Standby Diesel Generators (SDG) #23 and #21 non-valid failures which occurred on Dscomber 6 and 7, 1991,

- respectively. A Special Report regarding the failure was provided 3, 1992, reference letter ST-HL-AE-3955.

to the NRC on January Please find attached a supplement to that report which provides additional information cor'erning investigative findings. Change bars have been added to highlight supplemental information. _

A separate Special Report regarding a non-valid failure of SDG #21 on December 24, 1991 was provided to the NRC on January 23, 1992, reference letter ST-HL-AE-3985. The attached report also provides additional information for HL&P letter ST-HL-AE-3985 that was due to the NRC by July 30, 1992.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8629 or myself 7 .

(512) 972-7205.

fhte William J. Jump 4

Manager, Nuclear Licensing JMP/sh Attachtr e nt : Supplemental Special Repert. degarding Two SDG Non-Valid failures SREP\92-b.3.001 A Subudiary of l{ousum NJustries hvorpm.ned

3. - q c; { ! (}~ s

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4 Ilouston Lighting & Power Company-- , ST-HL-AE-4065 South Texas Project Electric Generating Stanon File No.: G02 Page 2.

cc:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel dll Ryan Plaza Drive, Suite 400 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 George-Dick,-Project Manager U.S. Nuclear'.. Regulatory Commission INPO Washington, DC 20555. Records Center 1100 Circle 75-Parkway J. I. Tapia.

Atlanta, GA -30339-3064 Senior Resident Inspector c/o;U. S. Nuclear Regulatory Dr. Joseph M. Hendrie

' Commission- 50 Bellport Lano

.P. O. Box 910 Bellport, NY 11713 Bay-City, TX 77434 D. K. Lacker J':R. Newman, Esquire

. Bureau of Radiation Centrol Newman & Holtzinger, 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-Chrinti, TX -78403 J. C. Lanier/M. B. Lee" ._

City _ of Austin Electric' Utility Department

- P.O. Box 1088 ~

. Austin, TX--78767

-X. J. Fiedler/M. T. Hardt City Public Service Board-P. O.-Box 1771 San Antonio, TX 78296-Revised 10/11/91 L4/NRC/

Attachnent ST-IIL-A E-4 0 6 5 Page 1 of 3 South Texas Project Unit 2 DoLKet No. STN 50-499 Supplemental Special Report Regarding Two Diesel Generator Non-Valid Failures DESCRIPTION OF EVEliT:

On December 6, 1991, at 2301 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.755305e-4 months <br />, Standby Diesel Generator

/23 was started in the emergency mode following release of Equipment Clearance Order 2 '61 which was associated with a work document. Unit 2 was in Moce 4 during a refucling outage.

SDG #23 came up to rated speed, voltage, and frequency within 10 seconds. When the engine was released from emergency mode, SDG

/;.3 tripped with no test mode trips indicated. The engine was then restarted at 0030 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> on December 7 in the test mode with I&C, Electrical, and Mechanical Maintenance personnel present. The engine came up to rated speed, voltage, and frequency within the 10 second limit and was running satisfactorily. The engine was then started a third time at 0059 hours6.828704e-4 days <br />0.0164 hours <br />9.755291e-5 weeks <br />2.24495e-5 months <br /> in the emergcncy mode. The dierel generator was released from the emergency modo to the test mode without a trip. The Control Room then commenced the Standby Diesel Generator #23 Operability Test. The diesel performed

. ,atisfactorily during the one hour _ surveillance run and SDG #23 was

+1tclared operable at 0250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br />.

Standby-Diesel Generator /21 was started on December 7, 1991, at 0313 hours0.00362 days <br />0.0869 hours <br />5.175265e-4 weeks <br />1.190965e-4 months <br /> in the emergency mode to verify operability in accordance with Technical Specification Action Statement 3.8.1.1 and came up to rated speed, voltage, and- frequency within 10 seconds. When the engine was released from the emergency mode, SDG #21 tripped with no' test mode trips indicated. SDG #31 was restarted in the emergency mode a second time at 0323 hours0.00374 days <br />0.0897 hours <br />5.340608e-4 weeks <br />1.229015e-4 months <br />, released from the emergency mode to the test mode, and the engine functioned properly. At 0603 hours0.00698 days <br />0.168 hours <br />9.970238e-4 weeks <br />2.294415e-4 months <br />, th2 Control Room commenced SDG /21 operability test and declared SDG /21 operable at 0820 hours0.00949 days <br />0.228 hours <br />0.00136 weeks <br />3.1201e-4 months <br />.

Subsequent troubleshooting was performed on SDG /23 and SDG /21 on February 28, 1992, and January 15, 1992 respectively.

All electrical circuitry pertaining to the 86S relay trip circuit was verified for termination tightness, condition of lugs, and proper termination. In addition, a chart recorder was set up to monitor the 86S trip circuit loop voltages. L abnorcal indications were observed. I&C personnel also inspected the pneumatic control system by monitoring performance with test gauges, but did not disassemble any piping or components. Again, no problems were noted on either diesel.

$2 epi 92-098.001

Attachment ST-HL-AE-4065 Page 2 of 3 DESCRIZf_LON OF EVEST: (Continued)

The 86S relay on SDG #21 was again tested on March 3, 1992. The voltages vore monitored with a chart recorder during operation of the generator. One set of contacts were found to have a slightly out of tolerance resistance measurement. The relay was subsequently replaced. Evaluation of the 86S relay shows that the chance of circuit malfunction would be unlikely with the as-found value of resistance. The conservative approach was to replace the relay, as a considerably higher value of contact resistance (leading to contact failure) could cause this mode of diesel trip.

Inspection of- the pneumatic control circuits on both engines revealed foreign material in check valves SD-3207 (#21) and SD-3209 (123). These check valves prevent reverse airflow from the shutdown control air line into the reset air line. Foreign material-under the seat of these check valves causes a decrease in air line prassure and-at 20 psig, a shuttle valve will change state and cause the engine to trip with no indications, CAUSE OF EVENT The cause of these events can reasonably be attributed to foreign material under the' seat of the check valves allowing a decrease in air pressurof and ultimately causing the trips with no apparent indication.

ANALYSIS OF EVENT:

These two events have been classified as non-valid failures since - the diesel generators operated satisfactorily in the emergeacy mode and if challenged, would have performed their safety

'functlun. SDGs #21 and #23 were started in test mode on December 15, 1991 and both engines operated satisfactorily. Diesel generator /21 also successfully completed a valid test on December

~

19, 1991. SDGs #21 and #23 started and ran in the energency mode when ~ responding to a recent reactor trip and Safety - Injection-signal _on December 24, 1991. SDG /21 tripped when released from the emergency mode during the run on December 24. Subsequently,

'a separate report for this apparent non-valid failure was submitted addressing the cause of the SDG trip, reference letter ST-HL-AE-3985. Since these SDGs have operated correctly in the emergency mode, the diesel generators are considered capable of fulfilling their required safety functions.

SREP\92-098.001

Attachment ST-ItL-AE-4 0 6 5 Page 3 of 3 CORRECTIVE ACTIONfi:

1. Troubleshooting for SDG /23 and SDG l'J 1 have been completed.

2. Preventive maintenance instructions will be developed to clean the subject check valves periodically. This activity will be completed by July 15, 1992.

ADDITIONAL INFORMATION:

At the time of the event, there were no valid failures in the last 20 valid tests and less than 4 valid failures in the last 100 tests for SDG #21. The testing frequency remained at once per 31 days.

At the time of the event, there were no valid failur.:s in the last 20 valid tests and less than 4 valid failures in the last 100 tests for SDC #23. The testing frequency remailed at once per 31 days.

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I-SREP\92-093.001