05000298/LER-1981-010, Forwards LER 81-010/03L-0

Forwards LER 81-010/03L-0

ML20009A532
Person / Time
Site:	Cooper
Issue date:	06/03/1981
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20009A533	List: 05000298/LER-1981-010, Forwards LER 81-010/03L-0 05000298/LER-1981-010-03, /03L-0:on 810505,static Inverter 1A Spike Suppressor Capacitor Failed Causing Inverter to Become Inoperable.Caused by Aging & Effects of High Ripple Charger
References
CNSS810327, NUDOCS 8107130282
Download: ML20009A532 (2)

LER-1981-010, Forwards LER 81-010/03L-0

Event date:
Report date:
2981981010R00 - NRC Website

text

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> <umoNE son 8 sae n CNSS810327 June 3, 1981

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7 Mr. K. V. Seyfrit, Director

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U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement

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Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.3 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurcence that was discovered on May 5, 1981. A licensee event report f o rti is also enclosed.

Report No.:

50-298-81-10 Report Date:

June 3, 1981 Occurrence Date: May 5, 1981 Facility:

Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

An observed inadequacy in a procedural control whien could threaten to cause a reduction of degree of redundancy provided in the No Break Power System (NBP), an engineered safety feature system.

Conditions Prior to Occurrence:

The reactor was in the cold shutdown condition for refueling.

Description of Occurrence:

During performance of Surveillance Procedure 6.3.15.2, Station Battery Rated Load Test, a capacitor f ailed in the suppressor cir-cuit of 1A static inverter causing the inverter to become inoper-able.

Designation of Apparent Cause of Occurrence:

The principle contributors to the electrolytic caoacitor's failure were aging and the affects of high ripple DC voltage from the battery charger supplying the inverter.

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8107130282 810603 PDR ADOCK 05000298 S

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F Mr. K. V. Seyfrit June 3, 1981 Page 2.

Analysis of Occurrence:

1A static inverter converts DC voltage to AC voltage which supplies the station No Break Power Circuit. The DC bus supplying the 1A inverter is fed by a bank of batteries which are being charged continual!y by a battery charger.

When the battery bank is in the circuit, it acts as a large filter between the charger and static inverter filtering out the AC ripple voltage over the DC effective voltage. During the station battery load test the batteries are required to be disconnected from the DC bus.

The batteries were disconnected from the DC bus under load.

The inverter operatea directly from the charger for a period of time.

The load was then removed from the inverter, but it remained energized. Approximately 15 minutes later, the capacitor in the inverter's spike suppression circuit failed making the inverter inoperable. The sts*.ic inverter was then taken out of service.

The failed system was inspected and it was found that one silicon control rectifier (SCR) had failed in the charger supplying the inverter.

The failure of the SCR caused excessive AC ripple thus causing the capacitor in the inverter to become hot and fail. The age of the electrolytic capacitor could possibly have contributed to its failure.

This occurrence presented no adverse affects from the standpoint of public health and safety.

Corrective Action

A procedure change has been initiated to specify that prior to a battery discharge test, the battery charger will be verified to be operating properly, and that the load on the inverter will be shifted to an alternate source. This LER will be routed to approp-riate personnel.

Sincerely,

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