05000298/LER-1979-038, Forwards LER 79-038/03L-0

Forwards LER 79-038/03L-0

ML19257C584
Person / Time
Site:	Cooper
Issue date:	12/28/1979
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19257C585	List: 05000298/LER-1979-038, Forwards LER 79-038/03L-0 05000298/LER-1979-038-03, /03L-0:on 791130,during Normal Operation, Suppression Chamber Level Instrument PC-LI-12 Failed Downscale.Caused by Failure of Power Supply.Power Supply Replaced & Proper Indication Verified
References
CNSS790677, NUDOCS 8001290441
Download: ML19257C584 (2)

LER-1979-038, Forwards LER 79-038/03L-0

Event date:
Report date:
2981979038R00 - NRC Website

text

.

m COOPER NUCLEAR STATION Nebraska Public Power District

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5 CNSS790677 December 28, 1979 Mr. K. V. Seyfrit U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on November 30, 1979. A licensee event report form is also enclosed.

Report No.:

50-298-79-38 Report Date:

December 28, 1979 Occurrence Datc: tiovember 30, 1979 Facility:

Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which lead to operation in a degraded mode permitted by a limiting condition established in Table 3.2.F of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was operating at a steady state power level of approx-imately 937. of rated thermal power.

Description of Occurrence:

During normal operation, suppression chamber level indicator PC-LI-12 was observed to be operating erratically and then failed down-scala.

Designation of Apparent Cause of Occurrence:

The failure of torus level indicator PC-LI-12 was due to an in-terncl short in the instrumentation loop power supply. This short caused the power supply transformer to overheat and fail.

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8001290

Mr. K. V. Seyfrit December 28, 1979 Page 2.

Analysis of Occurrence:

Torus level is monitored by four independent level indicators and two level switches. There are three narrow range level indicators and a wide range level recorder. Alarms are provided from two of the level indicators and from the two level switches.

PC-LI-12 is one of the three narrow range level indicators for torus level.

Power supply PC-ES-12 provides power for the current loop con-sisting of level transmitter PC-LT-12, Hi/ Low level alarm PC-LA-12 and level indicator PC-LI-12.

Failure of the power supply caused the level indicator to indicate downscale and the low level alarm to annunciate. At the time of the occurrence, torus level was normal and all other indicators and alarms were functioning prop-erly.

The subject power supply is a co=monly used unit for various types of instrumentation systems.

It is found in numerous applications at Cooper Nuclear Station and is considered a nonrepairable type item after failure. There have been approximately five previous failures noted during the previous five years of operation at Cooper Nuclear Station. Considering the large number of this type power supply currently in use, the previous failures dictate an extremely low failure incidence rate.

Therefore, this failure is believed to be within the expected electronic component failure spectrum and no further analysis of this occurrence is warranted.

This occurrence presented no adverse consequences from the stand-point of public health and safety.

Corrective Action

The power supply was replaced with an identical replacement.

Proper operation of the indicator was then verified.

Sincerely,

/

L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Attach.

1829$356