ML19317D932

Abnormal Occurrence Rept 269/75-01:on 750107,Channel a Reactor Coolant Pressure Buffer Amplifier Did Not Respond to Input.Caused by Faulty Operational Amplifier.Component Replaced

ML19317D932
Person / Time
Site:	Oconee
Issue date:	01/21/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19317D931	List: ML19317D930 ML19317D932
References
AO-269-75-01, AO-269-75-1, NUDOCS 7912100609
Download: ML19317D932 (2)

Text

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Duke Power Company Gh'a."! D::ketfik Oconee Unit 1

_ Report No.: A0-269/75-1 <

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l Report Date: January 21, 1975 Y

Occurrence Date: January 7, 1975 )

Facility: Oconee Unit 1,' Seneca, South Carolina Identification of Occurrence: Failure of Reactor Coolant Pressure Buffer Amplifier.

Conditions Prior to Occurrence: Unit in refueling shutdown.

Description of Occurrence:

On January 7, 1975, during surveillance testing of Oconee Unit 1 Reactor Protective System (RPS) Channel A, it was noted that the output of the Reactor Coolant (RC) pressure buffer amplifier would not respond properly to its input.

The buffer amplifier receives its input from the associated RC pressure trans-mitter and converts a current signal to a voltage signal compatible with the i

high and low pressure trip bistables and the pressure-temperature function generator. The buffer amplifier responded properly to inputs which correspond to pressures up to 2085 psig; however, it would not respond to inputs simulating greater pressure. The buffer amplifier was repaired, tested and returned to service. The Channel A buffer amplifier was last checked on December 20, 1974.

Der,ignation of Apparent Cause of Occurrence:

The nuse of the buffer amplifier failure was traced to a faulty operational amplifier in the circuit. This was the first failure of this component and is regarded as a random failure.

Analysis of Occurrence:

This buffer amplifier supplies inputs to the Channel A high and low pressure

! trips and the pressure-temperature trip. The nature of the failure would j have prevented a Channel A high pressure trip; however, a trip of two of the l

three remaining operable RPS Channels would have performed this function if l necessary. The Channel A low pressure trip would have operated properly as i the buffer amplifier failure did not affect the lower range of the amplifier.

l The pressure-temperature trip operates on decreasing pressure. If the unit had been at normal operating pressure and temperature, 1:.55 psig and 6010F, at the time of the failure of the amplifier, this Channel would have inadver-tently tripped. This would have been in a conservative direction. It is concluded that the health and safety of the public was not affected.

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f Corrective Action:

The cause of the buffer amplifier failure was isolated to a specific component in the circuit. This component was replaced and the amplifier was satisfactorily tested. The Oconee periodic surveillance program is considered adequate to identify random failures of this nature.

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