ML20084C555

AO 250-74-10:on 740906,one Steam Generator C lo-lo Water Level Comparator Would Not Trip at Required Value.Caused by Failure of 15 Volt Dc Power Supply Filter Capacitor. Comparator Replaced W/Calibr Spare Unit

ML20084C555
Person / Time
Site:	Turkey Point
Issue date:	09/16/1974
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Case E Office of Nuclear Reactor Regulation
References
AO-250-74-10, NUDOCS 8304080104
Download: ML20084C555 (2)

Text

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FLORIDA P0.".EH & UGH r CGMNNY September 16 1974 c

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f M Mr. Edson G. Case, Acting Director I* i bENO l97d* k~

Directorate of Licensing Office of Regulation f U.

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U.S. Atomic Energy Commission Washington, D. C. 20545 k b.

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Dear Mr. Case:

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ABNORMAL OCCURRENCE NO. 250-74-10 SEPTEMBER 16, 1974 OCCURRENCE DATE: SEPTEMBER 6, 1974 TURKEY POINT UNIT 3 FAILURE OF STEAM GENERATOR LO-LO LEVEL COMPARATOR A. CONDITION PRIOR TO OCCURRENCE The reactor was in routine operation at 98% power.

B. DESCRIPTION OF OCCURRENCE At 3:00 a.m. on September 6, 1974, performance of the periodic test of the steam generator protection channels revealed that one of the C steam generator Lo-Lo water level comparators would not trip at the required value. Each steam generator has three Lo-Lo water level protection channels which trip at a level of 15%. The individual trips feed into a 2/3 logic which produces a reactor trip and start of the auxiliary feed-water pumps.

The other two channels of the C steam generator tripped as

-required when tested.

Periodic testing of the steam generator protection channels is performed on a monthly basis. The testing consists of placing

'the channel in the test mode and verifying trip actuation using

_ a transmitter simulator, digital voltmeter and installed in- .

dicating lights.

I C. CAUSE OF THE OCCURRENCE I 1

Bench testing of the defective comparator revealed that the

' 15 volt,DC power supply filter capacitor had failed.

This caused erratic operation of the comparator near the setpoint.

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o i Mr. Edson G. Case

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Page 2 September 16, 1974 The comparator did not indicate trip until the input was considerably below the setpoint. Evidence of trip actuation at setpoint was not demonstrated by the indicating light although there was an indication that the output relay may have operated as required.

D. ANALYSIS OF THE OCCURRENCE The comparator failure represents a single failure in a re-dundant system. For protective functions where two-out-of-three redundant. actuation is provided, a single channel failure is not considered to impair the protective function. Con-sequently, neither reactor safety nor the health and safety of the public was endangered by this occurrence.

E. CORRECTIVE ACTION Corrective Action consisted'of replacing the defective ccm-parator with a calibrated spare unit which was functionally tested with satisfactory results.

At this time, there is no indication that the comparator failure is a generic problem. For this reason, additional action was not deemed necessary.

! F. FAILURE DATA This occurrence represents the-first non-failsafe failure of a comparator in an'uclear safety related system since startup of the plant.

! Very truly yours,

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1. Ast-A. D. Schmidt l Director of Power Resources cc: Mr. Norman C. Moseley l.

Jack R. Newman, Esquire -

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