ML19260B513

LER 79-107/03L-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

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: ML19260B506 ML19260B513
References
LER-79-107-03L, LER-79-107-3L, NUDOCS 7912100288
Download: ML19260B513 (2)

Text

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? 8 00 61 DOCKET NUYBER EVENT DESCRIPTION AND PROB 1320 ABLE hoursCONSEQUENCES tTie unit experienced h10 a loss of essential instru-  ;

o 2 l On November 5, 1979, at Being in Mode 5, the unit did not enter the Action [

y j ; mentation distribution panci Y2.

j Statement of Technical Specification 3.8.2.2, as it only requires three of the 120 g o , ,, , g There was no danger to the health and l o 3  ; volt AC essential buses operable in the mode.

This occurrence is being reported to docu--l l o is ] l safety of the public or station personnel.

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40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i o [Under Maintenance Work Order (>NO) 79-3487, the loss of Y2 was found to be caused by a The blown fuse appears to be related to j

, , [ blown fuse on the pre-inverter YV2 output.

FNO 79-3504 was written to

_ g , , , , l an open resistor ir the power supply of inverter YV2.

On November 8, 1979, the inverter was tested and returned to j

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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.

Description of Occurrence _:

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 a loss of essential instrumentation distribution panel Y2 caused by a blown fuse on the pre-inverter YV2 output. Being in Mode 5, the unit did not enter the Action Statement of Technical Specification 3.8.2.2 Thisas it only requires occurrence three is being of theto120 reported volt 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 into thethe power supply inverter.

of inverter YV2. The resistor functioned as a buffer on the input When open, the output of the inverter fails low causing the loss of the bus.

Analysis of Occurrence _1 There was no danger to the health and safety of the public or to station personnel. The unit was shutdown and the three redundant channels were operable while the inverter was inoperable. Essential instrumentation distribu-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 Power inverter.

Engineering open resistor was discovered, MWO 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.

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

. LER #79-107 I521 315