ML20024H208

LER 91-015-00:on 910422,train C AFW Pump Inadvertently Started Due to Failure of Led in Sequencer Test Circuitry. Faulty Led Replaced & Blocking Circuit Satisfactorily tested.W/910522 Ltr

ML20024H208
Person / Time
Site:	South Texas
Issue date:	05/22/1991
From:	Ayala C, Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-015, LER-91-15, ST-HL-AE-3781, NUDOCS 9105300179
Download: ML20024H208 (6)

Text

-- ----

The Light cllouston o mp a ny 8""'h3' I"I 33"i' C'""ating station Lighting & Power I>. O. nox 289

_wadsworth. Tes ai 7748{}

May 22, 1991 ST.HL-AE-3781 File No.. G26 10CFR50.73 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 91-015 Regarding an Engineered Safety Feature Actuati2p Caused by a Failed Light Emittinn Diode Pursuant to 10CFR50.73, Houston Lighting & Power Company (HL&P) submits the attached Licensee Event Report (LER 90 015) regarding a Engineered Safety Feature actuation caused by a failed light emitting diode.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-862d or myself at (512) 972-7205.

) 4bn William J . Jump Manager, Nuclear Licensing SMH/kmd

Attachment:

LER 91-015 (South Texas, Unit 1) t m s.i m ot.ut 910530,179 910522 A Subsidiary of flouston industries incorporated 7Q PDR ADOCK 05000498 S PDR />/

/

_. . ~ _ _ _ _ _ _

ST-HL- AE- 3781 llouston Light.ing & Power C,ompany File No ' G26 South Texas Project Electric Generating Station Paga 2 cc Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel

-611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 Ceorge 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 Lane

-P., O. Box 910 Be11 port, NY 11713 Bay City 'D( 77414 D. R. 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 R.- J . Costello/M. T. Hardt

-City.Public Service Board P,.0. Box 1771-San Antonio, TX 78296 Revised 01/29/91 L4/NRC/

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

-* eRC f orm in4 U S NUCL8 AR RIOULA? Day COMMiESiON APPRoy10 OM4 No sito oios LICENSEE EVENT REPORT (LER) ' " a ' s * *' "

f ACILif V NAME iu Docu t Y NUMet a ni P A6E < 3, South Texas, Unit 1 o;s;o;o;og4 [9 ;8 i jorl 0; 4 tirLE m-Engineered Safety Feature Actuailon Caused by a Failed Light Emitting Diode IVENT oaf t ill Lin NvMeta tai at POR T Da f t 171 OTMER f ecatitits INv0LvtD 18 MONfw DAY YEAR $ lap

" [ "

((M MONTm Das vtAR C' u t , ha Man DOCA li NUM8t R:5>

0151010 1 0 1 1 1

~ -

m.

Ol4 2l2 91 9l1 0l 1 l5 0l 0 d5 2l2 9l 1 o isio l0 iog l l

, ,,,,,,, Twis a POmr is susMittt0 PunsuANT TO rmt atovintMENTs or to Ce a t icaA. . ., -o,. .* ea. <e"..-e nii

" ' " ' to 40m X so n..< 7s sii=> l 1 so ei.i ir i o ai.in n,i a n .nn no n.ia.i.i n m.>

no.

-+- 1 o io - ao ==in n.i o on. inn a so nwari so n. uni ..

so n.,an,ui so n.nau.. n&i Ov-

• w

..t a. ,<5e,,

.. A

7. . . N C. ,.<, .,.

no 406t.nt ness So 7 31 6f a nai to 731.nanvitinBI so ai.in n,i so n.:a na.i no n.uan.i LICE NSit CONT ACT POR THis Lim #1 6 NAME TattPesONE NUM6tR aat a CGot Charles Ayala - Supervising Licensing Engineer 512 972-8628 I I I I I I I , i COMPLE TE ONE LiNE 90R E ACH COMPONINT F A.LURI DESC#iSED IN YMit REPOm f 413i CAUSE 5t$1tp COvPCNENT $'a t Y N'ACS CAu$t Sv5 TEM COM*ONINY d't "OY PF 1  ! I I I I I I 1 i i i i I i F i 'i' i i i 7' *" i i i i i i i SUPPLlut NT AL REPORT E sPGCTE D (14# MONYa DAv vtAR L.0V 51'ON Yt$ tH vee camp,. s E M*ECTED SvowSSoON DA TE! %D l l l A....C,_.,.._.....-...,_,.._...-~~..,n.,

On April 22, 1991, Unit I was in Mode 1 operating at 100% power. At 0200, during performance of a Train C Engineered Safety Feature Sequencer surveillance test, the Train C Auxiliary Feedwater (AFW) Pump inadvertently started. The pump was secured at 0208. The cause of this event was failure of a Light Emitting Diode (LED) in the Sequencer test circuitry. The LED has been replaced. An evaluation has determined that a similar failure of an LED in the Sequencer actuation circuitry, rather than the test circuitry, would prevent actuation of the associated ESF component. The functionality of the sequencer is tested quarterly. In addition, if such a failure occurred, an alarm would indicate the affected component had failed to start and operator action could be taken to statt the component. Therefore, since there has been only one such failure at STP, no additional corrective action is planned.

LER)01130001.U1 NHC Foem J46 19 8 li

U S NUCLE A A RE GUL ATORY COMuttaiON hac f ees 3e4A d'" imavto oms o am om LICENSEE EVENT REPORT (LER) TEXT CONTINUATION i.. aii e u e

}

l #&ceta f f haeal pt poc a t f huses t a in g g , gggg g , ,,, pagg g3,

~~ "M;;' :2,T:

South Texas, Unit 1 o l5 l0 j o j o l 419 l 8 911 --

0l1l5 -

0l0 01 2 OF 0[4, nxv w = .- . -.v. -ac s wo n n DESCRIPTION OF EVENT:

On April 22, 1991, Unit I was in Mode 1 at 100 percent power. A surveillance test of the C train Engineered Safety Feature (ESP) Sequencer was being performed to check actuation relay function and circuit continuity. During performance of the test, C train Auxiliary Feedwater (AFW) Pump 13 inadvertently started at 0200. The ATV pump was secured at 0208. The incident was reported to the NRC at 0500.

The ESF sequencer surveillance test is performed in the Manual Local mode. In this mode, blocking relays are energized to prevent actuation of some of the sequenced loads. Output relay actuation is indicated on the Output Status Indicator display while circuit continuity is indicated on the External Circuit Continuity Monitor. Initially, all lights on both monitors are out.

As the output relays close for each load as it is sequenced, the corresponding lamp on the output Status Indicator illuminates and remains on for the remainder of the tes:. When this indication is received, a pushbutton on the External Circuit Continuity Monitor corresponding to the sequenced load is momentarily depressed allowing a current too low to operate the load to flow through the circuit. A light on this monitor illuminates to indicate circuit continuity and extinguishes when the pushbutton is released.

Dur'ng performance of the test, the lamp associated with AFW pump 13 on the External Circuit Continuity Monitor functioned properly while testing the continuity of the circuit. After all the output relays had sequenced but prior to resetting the sequencer at the end of the test, the lamp associated with the AFW pump lit and remained lit on the External Circuit Continuity Monitor. Actuation of the AFW pump followed. The light on the External Circuit Continuity Monitor for the AFW pump is illuminated by completing the circuit with the monitor pushbutton or by closure cf the blocking relay contacts.

Troubleshooting identified that a Light Emitting Diode (LED) in series with an optical isolator had failed open during the surveillance test. The optical isolator provides a current path for the blocking relay associated with the AFW circuit. Failure of the LED caused deenergization of the blocking relay for AFW pump 13, causing the AFW pump to start. The optical isolator was removed and installed on a new board containing a new LED. Functional testing of the blocking circuit was satisfactery.

Indication that blocking relays are energized is provided on the Sequencer Test / Status Control Panel. The blocking relay status contacts are connected in serie s to illuminate the indication. The indication will not illuminate if any one blocking relay fails to energize. Surveillance procedures require that test personnel verify that the lamp indicating that the blocking relays tDM91130301,U1 c cau ne.

Nic f eesa 384A , U S NUCL E Am REGut ATORY COMMISSION LICENSEE EVENT REPORT (LER) TEXT CONTINUATION A*eaovio oMe No 34so-oio4

( 3 PvRt $ $ '3135 P&CtkITV N Aut m Docu H NUMetR Qi tit NUM8t h (6s PAQt (35

_4*a "t'.W. #.70 South Texas, Unit 1 nn w ~ . w m .am.,anc w ma anm o l5 l 0 l o j o l4 l9 l 8 9l1 --

0l1l5 -

0l 0 0l3 or 0 l4 pESCRIPTION OF EVENT: (cont'd) are energized is illuminated. This is done after the sequencer is put into the Manual Local mode and before proceeding with the sequencing portion of the test. During the performance of this test, the blocking relays were successfully energized since the sequencing portion of the test had been completed without AFW actuation. This confirms that the LED failure and subsequent blocking relay deen 6erization occurred during the performance of the test.

LEDs are also used in the input and output relays that are part of the actuation citcuitry. Input and portions of the output relay circuits are continually tested while the sequencer is in the Auto Test mode. Detection of an open input or output circuit interrupts the Auto Test and generates a Trouble indication. Plant operations personnel perform a surveillance once per shift in Modes 1 through 4 to verify that the sequencer is functioning properly in the Auto Test Mode. A portion of the output ciretit, including the LED, is not tested in the Auto Test Mode. This portion of the output circuit is functionally tested during the quarterly surveillance performed at the time of this incident. Failure of an LED in the output circuit to the open position would prevent actuation of the associated component. Failure to actuate would be annunciated in the control room and the equipment can be manually started. Open circuit failure of an LED is an unusual condition.

More commonly, an IID will short, which affects indication but not circuit operability.

CAUSE OF EVENT:

The cause of this event was a failed open LED in the circuit associated with the blocking relay for the AFW pump. Failure of the LED created an open circuit which allowed the blocking relay to deenergize resulting in the start of the AFW pump ANALYSIS OF EVENT:

Unanticipated . zation of the AFW pump occurred during an ESF sequencer surveillance te . . Unplanned actuation of an Engineered Safety Feature is reportable in accordance with 10CFR30.73(a)(2)(iv). The LED that failed was part of a test circuit. Failure of this component would not have prevented proper operation of the ESF Sequencer under an actual emergency situation.

LEDs are used in the same configuration in other circuits suc'c as those associated with the input and output relays. Failure of an LED or any other component in these circuits to the open position would prevent receipt of a field input signal or. prevent closure of output relay contrcts to the tut \91130001.U1 a eo=M uem

nc e . ga u s mucie an mioutatomv cowwimc

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION areaoan ove No 2* oic

( R PiH{ $ $1]I1th

' ACete' V = AMt a u DOC R 41 NUMG4 R (26 LE K NUMet a les P AGE (J.

"aa " #fA,;'." 'Of.O South Texas, Unit 1 o l6 l0 [o j o l4l9 l 8 9l1 -

0l1p ,0 p 0l4 OF Ql4 t e xm <. . w. .- - ==e s- ma4 .i mi ANALYSIS OF EVENT: (cont'd) associated component. This component would not be actuated as required by the sequencer. This event did not result in any increased risk to the public or to safe operation of the plant.

CORRECTIVE ACTIONS:

The faulty LED was replaced and the blocking circuit satisfactorily tested, i As noted above, LEDs are included in the ac:uation circuitry of the sequencer.

Failure of any of these LEDs would prevent .ictuation of the associated ESF component. However, since the component can be manually started upon annunciation in the control room of the failure to actuate condition, coupled with the fact that this is the only such failure to have occurred in either unit's respective sequencers (6 total), no additional corrective actions are considered necessary.

ADDITIONAL INFORMATION:

A review of work history associated with the Unit 1 and Unit 2 ESF sequencer did not reveal a similar failure. A similar LED had previously failed in a shorted condition which prevented illumination of the LED but did not open the circuit.

tER\91130001,U1 l

% suaw me.