ML20043C018

LER 90-005-00:on 900501,reactor Trip,Auxiliary Feedwater Actuation & Feedwater Isolation Occurred Due to Turbine Trip on Loss of Main Generator Stator Cooling Water.Caused by Blown Fuse.Fuse Replaced & Logic changed.W/900530 Ltr

ML20043C018
Person / Time
Site:	Callaway
Issue date:	05/30/1990
From:	Blosser J UNION ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-005, ULNRC-2218, NUDOCS 9006010187
Download: ML20043C018 (6)

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May 30, 1990

1 i U. S. Nuclear Regulatory Commission Document Control-Desk .j Washington, DC= 20555  ;

ULNRC-2218:

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DOCKET NUMBER 50-483 '

CALLAWAY PLANT UNIT 1 FACILITY OPERATING: LICENSE NPF-30 i LICENSEE EVENT REPORT 90-005-00 REACTOR TRIP DUE TO LOSS OF MAIN GENERATOR STATOR' COOLING WATER INSTRUMENTATION CAUSED BY A BLOWN FUSE The enclosed Licensee Event Report is submitted pursuant to '

10 CFR 50.73(a)(2)(iv) concerning an unplanned reactor trip which occurred during calibration of the main generator stator cooling water' inlet conductivity meter.  ;

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h J. Manager, D. Blosser I.

Callaway Plant

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1 9006010187 DR 900530 D ADOCK 0500o4g3 PDC

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cc' distribution =for ULNRC-2218: '

Mr; A.IBert Davis  :;Mr". Anthony T. Gody, Jr. - (2' copies)' l

. Regional = Administrator Office of Nuclear. Reactor Regulation U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission j]

Region:III -

= Mail:Stop:13-E-21 . .. i Washington, D.C.

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799 Roosevelt Road 20555- -j Glen Ellyn, IL '60137 '

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American Nuclear Insurers Mr. 0. Maynard c/o Dottie Sherman, Library  : Wolf Creek- Nuclear: Operating Corp.- .;

The Exchange Suite 245 P.10. Box 411'  ;

270 Farmington Avenue. Burlington, KS 66839; ,

.Farmington, CTL 06032 . 4 Mr. Merlin Williams' ~

'i Manager, Electric Departmentf . . -Supt. of: Regulatory; Qual 1ty;& l Missouri: Public Service Commission.. " Administrative Services "

P. O. Box'360 Wolf Creek Nuclear Operating-Corp.:

' Jefferson City,+f0 65102 P. 0.; Box 411. .

't Burlington,1KS .66839;

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a Records Center ' Mr . - R . ( L~.' Hague , .

' Institute of Nuc1 car Powery0perations' ' Chief, Project /Section 3C:-

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-U.SP Nuclear' Regulatory Commission 11100 circle-75' Parkway Region IIIL  ;

Atlanta, GAe'30339' 799-Roosevelt Road J!

Glen Ellyn, IL :60137 1

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_ b.CtLif Y NAME fil DOCRET NUMBE R (2) PAGE EJ8 Callaway Plant Unit 1 olslo10lol 4)8 13 1 lorl014

'"% actor Trip Duc To toss or nain Cenerator Stator Cooling Water instrumentation Caused By A Blown Fuse EVENT DAf t tSt LER NUMeta tal REPORT DATI 47: OTHER F ACILeilts INv0LytD tel sa DAY

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COMPLETE ONS LINE FOR ( ACH COMPONENT P AILURf DESCRISED IN THl$ REPORT H3)

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On 5/1/90 at 1331 CDT, a reactor trip, an Auxiliary Feedwater Actuation, and l a Feedwater Isolation occurred due to a turbine trip on a loss of main generator Stator Cooling Water (SCW) instrumentation. The. plant was in Mode 1 - Power Operations, 100 percent reactor power, at normal operating pressure and temperature.

The SCW low flow turbine trip signal and subsequent reactor trip signal were received during the calibration of the SCW inlet conductivity meter. During restoration of power to the conductivity meter, a conductive-foreign particle created a dead short across the power supply leads of the meter assembly.

The subsequent transient caused the failure of a 10 amp fuse resulting in a-loss of main generator SCW instrumentation power.. The loss of ,

instrumentation power initiated a turbine runback at 1328. With the " loss of SCW flow" signal still present, the main generator protection circuitry initiated a turbine trip at 1331.

l Several gene:rator protection SCW runback modifications are being implemented l to alleviate false activations and enhance the reliability of the system, i

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EASIS FOR REPORTABILITY on 5/1/90 at 1331 CDT, a turbine trip and Reactor Protection System (RPS)(I) reactor trip occurred during calibrat l

Water-(SCW) inlet conductivity meter. g of_the. mainof.the As.a result generator Stator Cooling.

RPS actuation, a D Feedwater Isolation and an Auxiliary Feedwater Actuation were generated by L design. Since the Engineered Safety Features:(ESP) actuation was not part of

• a preplanned sequence during reactorloperation or testing,;this event-is ,

reportable per 10CFR50.73(a)(2)(iv). -

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PLANT CONDITIONS AT TIME OF EVENT Mode 1-- Power Operations 100 percent Reactor Power Reactor' Coolant System (RCS){ ): temperature (average) 588 degrees; pressure - 2245:psig. q DESCRIPTION OF EVENT on 5/1/90, utility Instrument and Centrol -(I6C) technicians .were troubleshooting and calibrating the main generator SCW. inlet; conductivity meter. The meter had been removed in order to repair the high range' alarm.

l The technicians completed the meter calibration and were' reinstalling it.

Upon reconnecting the power supply, a number of local alarms were received. <

At 1328,.the Control Room licensed. operators were alerted to a= turbine runback initiation and observed'SCW pressure at-zero.. To, restore. proper pressure indication, the operators started the second SCW. pump.- SCW pressure indication remained at zero, however, the SCW o'tlet. u temperature indicated

! normal. After noting the operating conditions, the main-turbine generator.

was placed in standby to stop the runback. -The turbine runback was stopped. '

at 915 MW electrical. At 1331 after stabilizing power, a turbine trip occurred due to a locked-in SCW Icv flow signal per the generator protection circuit-design.

The subsequent reactor trip occurred due to a turbine' trip above=50 percent' J reactor power (e.g. P-9 interlock). The licensed operators stabilized the plant in accordance with plant procedures. ,

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w. .M a ma.inne r ass 4w nn ROOT CAUSE-The cause of 'this event was the creation of.a' dead short due to a conductive. ,

foreign particle across.the power supply leads of the SCW conductivity meter .I assembly. This was based on evidence of a short-circuit on the surface of ,

the input board power supply leads. 'The subsequent short circuit transient:

caused'the failure of a 10 amp fuse resulting in a loss of main generator SCW.  ;

instrumentation power-(i.e. a SCW low flow signal with'the current to flow comparator de-energized).

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A contributing factor was the lack of separation of.the. control and. 1 instrumentation power' source-and limited redundancy in-the SCW runback:- ,

circuits.

CORRECTIVE ACTIONS The blown fuse was replaced and the meter assembly was cleaned and' tested.' ,

In addition, a number.of measures are being implemented to enhance. system reliability and prevent a similar event.

a Corrective action to preclude recurrence of this: event will be prevented by: <

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L 1. TheSCgunbackcircuitrywillbeprovidedwithaseparate120VAC- ,

I- supply and will be removed from the alarm and indication supply- i source. ,

j Other corrective actions to be-taken to improve the main turbine generator reliability include *-

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1. The SCW low pressure runback wi11 be defeated based on redundancy of protection.

2. The SCW runback logic will be changed to require two of three l actuations for a runback to be initiated. This will be provided for SCW high temperature and SCW low flow conditions.

3. The SCW runback logic will be modified to not activate on a loss of

, instrument power. A loss of instrument power will-be alarmed in-

! the Control Room. I i

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-s l- The ESF systems (5) involved in:the event =perforned as required. 'There were ~

no detrimental effects on plant equipment as'a result of the actuations and this event posed no: threat 1to the health and safety of the public, i l .

PREVIOUS OCCURRENCES'

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FOOTNOTES The system and component codes listed below are;from IEEE Standards 805-1984 and 803A-1984, respectively. p .;

(1) System JC i l- (2)- System - TJ Component-MTR (3) System - AB (4) . System - JX i (5) System - JE i ..

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