ML20084G081

AO 251-75-1A:on 750103,zero Shift in Pressurizer Lead/Lag Controller PM-456A Occurred.Caused by Failure of Capacitor in Amplifier of Lead/Lag Controller.Controller Replaced W/ Calibr Spare Controller

ML20084G081
Person / Time
Site:	Turkey Point
Issue date:	02/14/1975
From:	FLORIDA POWER & LIGHT CO.
To:	Case E Office of Nuclear Reactor Regulation
Shared Package
ML20084G080	List: ML20084G077 ML20084G081 ML20084G086
References
AO-251-75-1A, NUDOCS 8304210406
Download: ML20084G081 (3)

Text

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Mr. Edson G. Case, Acting Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 6 ear Mr. Case:

ABNORMAL OCCURRENCE NO. 251-75-1A SUPPLEMENTAL REPORT DATE: FEBRUARY 14, 1975 OCCURRENCE DATE: JANUARY 3, 1975 PRESSURIZER PRESSURE PROTECTION CHANNEL II LEAD / LAG CONTROLLER FAILURE A. Introduction This supplemental report presents the results of tests performed to determine the cause of the Pressurizer Lead / Lag Controller fulluru.

B. Problem and Investigation Action ,

Background .

Abnormal Occurrence Report No. 251-75-1 reported the occurrence of a zero-shift in Pressurizer Lead / Lag Controller PM-456A.

The zero-shift was corrected by adjusting the controller.

Additional Investigative Action Approximately three weeks later, on January 27, 1975, results of functional tests on Controller PM-456A revealed that a zero-shift had occurred again. The measured controller output was 1.170 volts compared to an expected output of 1.075 volts.

Immediate corrective action was to adjust the controller and per-form tests'to demonstrate satisfactory operation.

Approximately six hours later, on January 27, 1975, the con-troller output was checked and a barely detectable zero-shift i noted. Although the magnitude of this zero-shift was small,

the controller was replaced with a calibrated spare controller..

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O O Mr. Edson G. Case, Acting Director Page Two February 14, 1975 Extensive tests of the failed controller determined that a capacitor in the amplifier had failed open. Failure of this capacitor would allow alternating current to be superimposed on the amplifier direct current signal. This would increase the amplifier output signal and cause a zero-shift in the controller output signal.

C. Designation of Apparent Cause of Occurrence Evaluation of test results concluded that the cause of Abnormal Occurrence No. 251-75-1 was the failure of a capacitor in the amplifier of the Lead / Lag Controller.

D. Analysis of Occurrence The maximum zero-shift error measured was'0.095 volts from the expected value of 1.075 volts. This is equivalent to an error of 19 psi at steady-state conditions.

If the pressure signal to the controller decreases rapidly, the Lead / Lag Controller output signal falls rapidly. This will canso a reactor trip at a higher pressure than the stead _y-state-setting.

The incidents analyzed and presenteB in the Turkey Point Unit Nos. 3 and 4 Final Safety Analysis Report assume a value of 30 psi for steady ' state fluctations in primary pressura and measuring error. A reactor trip is assumed to be actuated from any two out of three channels at a pressure of 1685 psig.

The reactor was protected at all times by two redundant, oper-able channels. Therefore, neither' reactor safety nor the health-and safety of the public were jeopardized by this occurrence.

E. Corrective Action The faulty Lead / Lag Controller was replaced with a calibrated spare controller.

F. Failure Data Review of Instrument and Control maintenance-records show'this I. was the'first failure of a Lead / Lag Controller caused by a 4

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i papacitor failure in the amplifier. There,was'no evidence-of a generic failure.

. Very truly yours, J

i A. D.'Schmidt Vice President Power Resources J

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! cc: Mr. Norman C. Moseley j Jack R. Newman, Esquire 1

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