05000346/LER-1979-107-03, /03L-0:on 791105,unit Experienced Loss of Essential Instrumentation Distribution Panel Y2 & Did Not Enter Action Statement in Mode 5.Caused by Blown Preinverter YV2 Output Fuse.Repaired Inverter

/03L-0:on 791105,unit Experienced Loss of Essential Instrumentation Distribution Panel Y2 & Did Not Enter Action Statement in Mode 5.Caused by Blown Preinverter YV2 Output Fuse.Repaired Inverter

ML19260B513
Person / Time
Site:	Davis Besse
Issue date:	12/04/1979
From:	Naylor R TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19260B507	List: 05000346/LER-1979-107, Forwards LER 79-107/03L-0 05000346/LER-1979-107-03, /03L-0:on 791105,unit Experienced Loss of Essential Instrumentation Distribution Panel Y2 & Did Not Enter Action Statement in Mode 5.Caused by Blown Preinverter YV2 Output Fuse.Repaired Inverter
References
LER-79-107-03L, LER-79-107-3L, NUDOCS 7912100288
Download: ML19260B513 (2)

LER-1979-107, /03L-0:on 791105,unit Experienced Loss of Essential Instrumentation Distribution Panel Y2 & Did Not Enter Action Statement in Mode 5.Caused by Blown Preinverter YV2 Output Fuse.Repaired Inverter

Event date:
Report date:
3461979107R03 - NRC Website

text

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8 EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h10 1320 hours0.0153 days <br />0.367 hours <br />0.00218 weeks <br />5.0226e-4 months <br /> tTie unit experienced a loss of essential instru-l On November 5, 1979, at o

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-122_

DATE OF EVENT: November 5, 1979 FACILITY: Davis-Besse Unit 1 Loss of essential instrumentation distribution panel IDENTIFICATION OF OCCURRENCE:

Y2 The unit was in Mode 5, with Power (MNT) = 0, and Conditions Prior to Occurrence:

Load (Gross MWE) = 0.

On November 5, 1979 at 1320 hours0.0153 days <br />0.367 hours <br />0.00218 weeks <br />5.0226e-4 months <br />, the unit experienced Description of Occurrence _:

a loss of essential instrumentation distribution panel Y2 caused by a blown fuse on Being in Mode 5, the unit did not enter the Action the pre-inverter YV2 output.

Statement of Technical Specification 3.8.2.2 as it only requires three of the 120 volt This occurrence is being reported to docu-AC essential buses operable in this mode.

ment a component failure.

The cause of the blown fuse is not yet Designation of Apparent Cause of Occurrence:

fully understood but it appears to be related to an open resistor in the power supply to the inverter.

The resistor functioned as a buffer on the input of inverter YV2.

When open, the output of the inverter fails low causing the loss of the bus.

There was no danger to the health and safety of the public Analysis of Occurrence _1 The unit was shutdown and the three redundant channels or to station personnel.

Essential instrumentation distribu-were operable while the inverter was inoperable.

tion panci Y2 was re-energized from its alternate power source.

79-3487, On November 5, 1979 under Maintenance Work Order (MWO)

Corrective Action

When the an investigation was conducted to determine :he cause of the blown fuse.

On 79-3504 was written to repair the inverter.

open resistor was discovered, MWO Power Engineering November 8, 1979, the inverter was tested and returned to service.

and Construction is investigating the relationship between the open resistor and blown fuse with the vcndor.

There have been previous failures of fuses but non due to buffer Failure Data:

resistor failure.

. LER #79-107 I521 315