ML20084F788

AO 251-75-3:on 750304,steam Generator Protection Sys Channel II Low Steam Line Pressure Comparator Failed.Caused by Failed Capacitor in 15-volt Dc Instrument Power Supply. Comparator Replaced

ML20084F788
Person / Time
Site:	Turkey Point
Issue date:	03/14/1975
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Case E Office of Nuclear Reactor Regulation
Shared Package
ML20084F769	List: ML20084F767 ML20084F788
References
AO-251-75-3, NUDOCS 8304210277
Download: ML20084F788 (2)

Text

y P.O. BOX 3100 MIAMI MCalDA 33101

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March 14, 1975 i :

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Mr. Edson G. Case, Acting Director Office of Nuclear Reactor Regulation [2Y k(pg, g"Q (

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Dear Mr. Case:

,j / J ABNORMAL OCCURRENCE NO. 251-75-3 3 MARCH 12, 1975 '

OCCURRENCE DATE: MARCII 4, 1975 TURKEY POINT UNIT NO. 4

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STEAM GENERATOR PROTECTION SYSTEM ]

CHANNEL II - LOW STEAM LINE PRESSURE COMPARATOR FAILURE l

A. CONDITIONS PRIOR TO OCCURRENCE e The reactor was in steady-state power operation at 100% reactor power. stnam annavatnr Pen +ar' tion Syrtem Channel II ::: in the tripped mode to perform a periodic functional test on this channel.

c B. DESCRIPTION OF OCCURRENCE During the performance of the periodic functional test, the test I signal input did not trip Channel II low steam line pressure ]

comparator (PC-4-474A)-as the signal was decreased below the expected trip setpoint (equivalent to 600 psig). After the test signal was reduced significantly below the expected trip setpoint, the comparator tripped.

C. CAUSE OF OCCURRENCE Extensive tests of the comparator revealed a failed capacitor in the -15V d.c. instrument power supply. Failure of this ~

capacitor allowed an a.c. signal to be superimposed on the internal d.c. signal in the comparator.- This caused the failure of the comparator to trip at the expected setpoint value equivalent to 600 psig.

D. ANALYSIS OF OCCURRENCE The incidents analyzed and presented in the Turkey Point Unit Nos. 3 and 4 Final Safety Analysis Report assume conservative pfl o i

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Mr. Edson G. Case, Acting Director Page Two March 14, 1975 l values for instrument error in measuring pressure, time delays '

associated with tripping functions, and maximum trip setpoints assumed for analysis. In these analyses, actuation of one out l of two redundant protection channels or any two out of three redundant protection channels will initiate the necessary pro-tective actions.

Functional tests of the two redundant steam generator protection j system channels III and IV demonstrated that both of these pro-tection channels were operable.

Review, analyses, and evaluation of reactor operating conditions during this occurrence concluded that the reactor was protected at all times by two redundant operable protection channels. There-fore, neither reactor safety nor the health and safety of the public were jeopardized by this occurrence. f

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E. CORRECTIVE ACTION The faulty comparator was replaced with a calibrated spare com-parator. Functional tests performed after the spare comparator was installed, demonstrated that the comparator performance was satisfactory.

There was no evidence of generic failure. z F. FAILURE DATA Review of operating and failure reports show that on September 6, 1974, during the performance of a periodic functional test on No.

3C Steam Generator, the failure of low-low level comparator (LC-3-495A) was identified. Refer to A.O. 250-74-10 for further details.

The failed low steam line pressure comparator, PC-4-474A, was manufactured by IIagan Controls Corporation. Single Comparator, A.C. Output, Model No. 4111082-001.

Very truly yours, a

m Vice President Power Resources VTC/cpc ec: Mr. Norman C. Moseley Jack R. Newman, Esquire

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