ML20062F825

Ro:On 901118,control Room Alarms Annunciated Failure of Inverter Associated W/One of Four 118-volt Ac Safeguards Instrument Buses.Caused by Failed Components within Scr/Diode Assembly

ML20062F825
Person / Time
Site:	Comanche Peak
Issue date:	11/20/1990
From:	William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-901037, NUDOCS 9011280190
Download: ML20062F825 (2)

Text

- - . - - - . . . . -. -- -. .__ _ _

i c g ..-

U. ,

Log # TXX-901037 i

==

File # 10013

~ ~

10125 Ref. # 10CFR50.72(a)(i) 1 nlELECTRIC

-November 20, 1990 ,

Wliliam J. Cebill, Jr.

herwive n y hesera U. S. Nuclear Regulatory Commission ,

Attn: Document Control Desk .

Washington, D.C. 20555

SUBJECT:

COMANCHE PEAK STEAR ELECTRIC STATION (CPSES)

DOCKET NO. 50-446'S TRANSMITTAL OF' REPORT FOLLOWING A NOTIFICATION OF UNUSUAL EVENT (NUREG-0654)

Gentlemen:

~

1 As specified in the CPSES Emergency Plan, TV Electric hereby transmits the attached report which summarizes the incident which occurred on November 19,  !

1990. As stated in the corrective action,- an_ evaluation is in process and a Licensee Event Report (LER) will be submitted:in accordance with 10CFR50.73 by December 19, 1990. -

Sincerely,

?

' William J. Cahill, Jr. -

DEN /bm  ;

c - Mr. R. D. Martin, Region IV Mr. J. H. Wilson, NRR l Resident' Inspectors, CPSES (3) .

~i Mr. Robert Lansford, Division of Emergency Management .

l l

l 9011280190 901120 PDR ADOCK 05000445

, 1 g

(, w v *' '

l P. O. Box 1002 ' Glen Rose. Texas 7600-1002

e

~

Enclosure TXX 901037 Page 1 of 1 TU Electric.

Comanche Peak Steam Electric Station, Unit 1 Docket No. 50-445 Notification of Unusual Event as a Result ofInitiating a Plant Shutdown Required by Technical Specification Action Statement ,

Reoort Reoutrement This report is being submitted as recommended by NUREG-0654, " Criteria fbr Preparation and' -;

Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear.

Power Plants" and in accordance with Comanche Peak Steam Electric Station (CPSES) Emergency Plan Procedures. The CPSES Emergency Plan procedures require that a written summary be submitted within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of the closcout of the Notification of Unusual Event (NOUE) ' ,

l Event Descrlotton On November 18,1990, at 0243 CST, CPSES Unit I was in Mode 1. Power Operations, with reactor power at approximately 48 percent. Control Room alarms annunciated the failure of the inverter associated with one of four 118 vcIt A.C. Safeguards instrument busses. 'Ihe bus was re energized j from its bypass distribution sour ce,'and Control Room personnel initiated a Limiting Condition for Operation Action Requiremen, to track the condition. The related Technical Specification requires that the instrument bus le energized from its associated inverter connected to its associated D.C. bus within 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> s, or the plant must be placed in Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown withia the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

By 0200 on November 19, the failed nyerter had not yet been restored to service. At that time th'e Emergency Plan was activated with the Notification of Unusual Event and commencement of a ;

reactor shutdown. Notification of the Nuclear Regulatory Commission and the appropriate offsite agencies was accomplished in accordance with the applicable regulatory and procedural requirements.

The plant entered Mode 3. Hot Standby, at 0754. At 1938, with the Reactor Coolant System at 450

. degrees F and 1160 psig, on the way to Mode 5, Cold Shutdown, the inverter was restored to service.

At 2302 the inverter was declared operable, and at 2342 the NOUE was terminatedi Initial review 1

of the event indicates that all Technical Specification action requirements were satisfied and all systems functioned as designed.

, Immediate Cause l The inunediate cause of the inverter failure has been attributed to failed components within the SCR/ Diode assembly which caused an internal power fuse to blow. Following rep!acement of the assembly, the inverter was successfully started and loaded. The root cause of the failure is still-under invesugation.

i i Corrective Actions Inunediate corrective actions were focused on troubleshooting the cause of the inverter failure and restoring the inverter to service. Subsequent actions were taken to place the plant in a condition t allowed by the related Technical Specification. Additional actions will be determined based on '

, the results of the findings of the plant incident investigauon of this event. The details of the event, including root cause determination and recommendations for corrective actions, will be included in the Licensee Event Report to be submitted to the Commission in accordance with 10CFR50.73; J

M

- - ,. , . . . . , , 4 v---