ML19317F089

AO-287/74-10:on 741119,ac Vital Instrumentation Bus Energized from Improper Source.Caused by Personnel Error. Inverter Replaced by Use of Regulated Ac Source. Interpretation of Tech Spec Reviewed W/Operating Personnel

ML19317F089
Person / Time
Site:	Oconee
Issue date:	12/04/1974
From:	DUKE POWER CO.
To:
Shared Package
ML19317F086	List: ML19317F085 ML19317F089
References
NUDOCS 8001080780
Download: ML19317F089 (2)

Text

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Report No.: _AO-287/74-10 1 Report Date: December-4, 1974 l

Occurrence Date: November 19, 1974 Facility: Oconee Unit 3, Seneca, South Carolina Identification of occurrence: AC vital instrumentation bus energized from

' improper source 1: Conditions Prior to Occurrence: Unit at 75 percent full power Description of Occurrence:

On November.19, 1974, as a result of the incident reported in Abnormal Occurrence Report A0-270/74-18, an inspection of Oconee Unit 3 static I

inverters was conducted. The 3DID static inverter manual selector switch was discovered in the " Regulated AC" position rather than the normal " Inverter" position. Thus, one of the four AC vital panelboards was being energized from the regulated AC bus rather than through the battery, diode, static inverter string as intended in Technical Specification 3.7.1. The inverter selector switch was immediately returned to the " Inverter" position to supply

- the AC vital panelboard from the inverter.. ?f Designat*.oa of Apparent Cause of Occurrence:

Operations personnel felt that it was not necessary that the inverter supply the vital panelboa-d because Technical Specification 3.7.1 does not specifi-cally state that the inverters be-operable and supplying the AC vital panel-boards. All other' components in the electrical string from the batteries l

to the AC vital panelboards are specifically identified in the Technical

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Specifications and the operating procedures.

- Analysis of Occurrence:

The function of the 3DID inverter was replaced by use of the regulated AC source to supply the 3KVID AC vital panelboard. The regulated AC source is 1

E -from.a non-load shed~ circuit and the inverter loads would havs been temporarily deenergized, until the emergency power source was energized, had a loss of all

' Unit 3 AC power occurred while the inverter was bypassed. In the event.the bus had been deenergized, the RPS Channel D would have been deenergized and given a tripped indication.: . This would place the remaining RPS channels in a one-out-of-three logic' state necessary for a trip. This is a more conservative mode of operation for the Reactor Protective System. It is concluded that the health and safety of'the public was not affected.

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Corrective Action:

The interpretation of Technical Specification 3.7.l'has been reviewed with operating personnel. The Normal Power Lineup Electrical Checklist OP/1107/02 for each Oconee unit has been revised to specify that all four AC vital instrumentation panelboards be supplied from their respective inverters prior to exceeding 200 F. This procedure is followed at the beginning of .

each unit startup.

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