ML19294B677

Ro:On 791229,loss of Main Control Board Annunciators Occurred.Fourteen Power Supplies That Are Paralleled to Provide Voltages for Annunciator Electronics,Lamps & Field Contacts Failed.Surveillance Implemented

ML19294B677
Person / Time
Site:	Millstone
Issue date:	01/23/1980
From:	Opeka J NORTHEAST UTILITIES
To:
References
MP-2-4269, NUDOCS 8003050287
Download: ML19294B677 (2)

Text

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1V January 23, 1980 MP 4269 Mr. Boyce H. Grier, Director Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Comission 631 Park Avenue King of Prussia, Pennsylvania 19406

Dear Sir:

This letter is provided for your information concerning the lass of the main control board annunciators at Millstone Unit 2 on December 29, 1979.

The information is presented in sequence and includes the events leading to the loss of annunciators, the loss of annunciators, immediate corrective action, and the short term actions to prevent recurrence.

During the evening of Friday, December 28, 1979 an ancmaly occurred in the Annunciator System in that certain alarm windows (one or two) began to flash withouc any audible alarm. The flashing windows would extinguish (return to normal) upon depressing the annunciator reset pushbutton. This occurrence was not considered to require imediate attention and the Operators on shift submitted a main-tenance request to the Instrument and Control Department.

During the evening of December 29 a similar event occurred. This time the window (s) could not be reset and at 2320 all annunciator windows began to flash and eventually all windows went out.

The Shift Supervisor inspected the Annunciator System cabinets and although he detected no physical damage he did detect the smell of overheated electrical components. He directed the supply breaker to be opened.

Upon investigating the failure of the Annunciator System it was detennined that of the twenty eight Rochester Instrument System (RIS) Model AN-159 power supplies that are paralleled to provide the voltages required for the annunciator electronics, lamps and field contacts, fourteen had failed. This condition resulted in the remaining power supplies being overloaded. The design of the power supply is such that once sufficiently overloaded, the supply will automatically shut down. When this happened the Annunciator System was disabled.

8003050 2h /

U.S. Nuclear Regulatory Comission Mr. Boyce H. Grier Page 2 At 0542 on December 30, 1979 following replacement of the fourteen failed supplies the Annunciator System was re-energized and declared operable.

Short term actions to prevent recurrence have been taken. They include the implementation of a Surveillance Procedure to periodi-cally verify the operability of all Annunciator System power supplies and discussions with the supply manufacturer to determine if the supply can be upgraded through component changes.

Long term actions to prevent recurrence are being considered. When they have been determined, the Resident Inspector will be made aware of our program. If additional information or clarification is necessary, please contact us.

Very truly yours, bd n F.']peka Station Superintendent Millstone Nuclear Po.ter Station JF0/ECF:kaf cc: J. T. Shedlosky