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EVETEMENERGY |'REEDUNCEE, INC..

jo m G CES E JRoneco May 31, 1989vNuckxy Licenung

U.S. Nuclear Regulatory CommissionMail Station P1-137Washington, D.C. 20555 |

Attention: Document Control Desk-

Gentlemen: i

SUBJECT: Grand Gulf Nuclear Station ;

Unit 1 '

Docket No. 50-416 ,

License No. NPF-29Special Report 88-007/1Diesel Generator 11 ShutdownDuring Testing ,

AECM-89/0104 ;

On February 17, 1989 System Energy Resources, Inc. (SERI) received NRCletter dated February 10,1989(MAEC-89/0047) concerning SERI's submittal of ,

Special Report 88-007/0 dated January 13,1989(AECM-89/0008). In response to jthis NRC letter, attached is SERI's update to Special Report 88-007/0. This !

Special Report is submitted pursuant to Technical Specification 4.8.1.1.3. j

If you have any questions concerning this update report, please advise. |

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Yours truly, j

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JGC:mcg -

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8906060075 890531PDR ADOCK 05000416 /ds PDC sf f

P O BOX 233D | JACXSON M;SS:SSIPPt 39225300 | (cct) cur;219 .

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AECM-89/0104Page 2.

cc: Mr. W. T. Cottle (w/a)Mr. T. H. Cloninger (w/a)Mr. R. B. McGehee (w/s)Mr. N. S. Reynolds (w/a)Mr. H. L. Thomas (w/o)Mr. H. O. Christensen (w/a)

Mr. Stewart D. Ebneter (w/a)Regional AdministratorU.S. Nuclear Regulatory CommissionRegion II101 Marietta St. , N.W. , Suite 2900Atlanta, Georgia 30323

Mr. L. L. Kintner, Project Manager (w/a)Office of Nuclear Reactor RegulationU.S. Nuclear Regulatory CommissionMail Stop 14B20Washington, D.C. 20555

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AECM-89/0104Page 2'

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cc: Mr. W. T. Cottle (w/a)Mr. T. H. Cloninger (w/a)Mr. R. B. McGehee (w/a)-Mr. N. S. Reynolds (w/a)Mr. H. L.-Thomas (w/o)Mr-. H. O. Christensen (w/a)

Mr. Stewart D. Ebneter (w/a)Regional AdministratorU.S. Nuclear Regulatory ConmissionRegion II101' Marietta St. , N.W. , Suite 2900Atlanta, Georgia 30323

Mr. L. L. Kintner, Project Manager (w/a)Office of Nuclear Reactor RegulationU.S. Nuclear Regulatory CommissionMail Stop 14B20Washington, D.C. 20555

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- Special Report 88-007/1-

0n December. 14, 1988 at 2109_ hours Diesel Generator 11 was manually started toa perform the monthly. functional surveillance. The Diesel Generator successfully

started'and loaded. Operators increased load at 1000 kilowatt intervals per.

normal procedure..;When the load reached 5000 kilowatts, field amps, line amps'and generator MVARs began oscillating. The operator at the. Control Room panelreported that. field volts were' oscillating from 150 to 175 volts, field amps.wereoscillating from 700 to 800' amps, and generator MVAR's were oscillating from 1.0to 1.5..

..The diesel generator .which had been loaded to the bus for approximately 32-minutes, was shutdown as a precautionary measure.- The cause of the oscillatingindications was determined.to be the No. I rectifier bridge circuit. Theredundant No. 2 rectifier. bridge circuit was placed into service. The dieselgenerator was restarted,' loaded, and the functional. surveillance successfullycompleted.

.DieselLGenerator 11 was: removed from service on January 17, 1989 to replacesuspect | diodes in the No. I rectifier bridge circuit. All six diodes.werereplaced and the' diesel generator was successfully retested. Resistance readingsof the-six diodes revealed that none of the diodes had failed open. The actualextent and direct.cause of the malfunction has not been determined.

A review of the event revealed that indications noted by the operator at the,

Control Room panel and indications documented by an engineer at the local panel-differed. From a. review of the data and the' range of.the instruments SERI| concludes that-the field volt and field amp values. reported by the operator'

.were"probably field amps and AC line amps respectively.

' The available data is not sufficient to positively determine if the dieselgenerator would have powered ESF loads in response to a bonafide signal.

-Therefore, SERI considers the test a valid failure. This is the. fourth validfailure in the'last 100 valid tests and the first in the:last 20. The testingfrequency remains at once per 31 days in accordance with the test schedule of. Technical Specification Table 4.8.1.1.2-1. This Special Report is submittedpursuant to Technical. Specification 4.8.1.1.3.,

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