05000346/LER-1980-086-03, /03L-0:on 801203,while Performing ST 5030.12, Alligator Clip Slipped Off Terminal Studs 3 & 4 Causing Short Circuit.Caused by Design Error.St 5030.12 Modified & F101 Fuse Replaced

/03L-0:on 801203,while Performing ST 5030.12, Alligator Clip Slipped Off Terminal Studs 3 & 4 Causing Short Circuit.Caused by Design Error.St 5030.12 Modified & F101 Fuse Replaced

ML19340E223
Person / Time
Site:	Davis Besse
Issue date:	01/02/1981
From:	Werner B TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19340E218	List: 05000346/LER-1980-086, Forwards LER 80-086/03L-0 05000346/LER-1980-086-03, /03L-0:on 801203,while Performing ST 5030.12, Alligator Clip Slipped Off Terminal Studs 3 & 4 Causing Short Circuit.Caused by Design Error.St 5030.12 Modified & F101 Fuse Replaced
References
LER-80-086-03L, LER-80-86-3L, NUDOCS 8101060680
Download: ML19340E223 (3)

LER-1980-086, /03L-0:on 801203,while Performing ST 5030.12, Alligator Clip Slipped Off Terminal Studs 3 & 4 Causing Short Circuit.Caused by Design Error.St 5030.12 Modified & F101 Fuse Replaced

Event date:
Report date:
3461980086R03 - NRC Website

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6 EVENT DESCmPTION AND FROB ABLE CONSECUENCES h lo12]l(NP-33-SO-111) On 12/3/80 at approximately 1835 hours0.0212 days <br />0.51 hours <br />0.00303 weeks <br />6.982175e-4 months <br /> during testing in Reactor Pro-l terminal stud caus-l l tection System (RPS) Channel 3, an alligator clip slipped off the [o#3l l a l 4 ] l ing a short circuit between terminals 3 and 4.

A loss of power to the Y3 essential j

including RPS Chan-l ioI5l l power bus followed which in turn de-energized several instruments I; 161 l nel 3 and Safety Features Actuation Systen (SFAS) Channel 3.

This placed the unit in J J a l il l violation of T.S. 3.8.2.1.

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lwere continuously available as were the 120 VAC essential buses YI, Y2, and Y4.

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3 40 41 42 43 44 47 33 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS lilOllThe apparent cause of this occurrence is a design error. The short circuit was the l

ST 5030.12 was modit l result of utilizing alligator clips on oversized terminals studs.

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[,j3; l Order 80-3918 replaced the YV3 inverter input fuse F101 and the RPS trip circuit fuse.

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DVR 80-198

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TOLED0 EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-80-111 DATE OF EVENT:

December 3, 1980 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Loss of Instrument Bus Y-3 Conditions Prior to Occurrence:

T'ne unit was in Mode 3 with Power (MWT) = 0 and Load (Gross KJE) = 0.

Description of Occurrence: On December 3, 1980 at about 1835 hours0.0212 days <br />0.51 hours <br />0.00303 weeks <br />6.982175e-4 months <br /> while performing ST 5030.12, Control Rod Drive Trip Breaker Logic Functional Test in Reactor Protection System (RPS) Channel 3, one of a set of insulated alligator clips attached to terminal board 1-10-6 terminals 3 and 4 slipped of f causing a short circuit between terminals 3 and 4.

These terminals are used to monitor 115 VAC to the trip breaker undervoltage coil. The short circuit resulted in the RPS trip circuit fuse F2 and the YV3 inverter input fuse F101 blowing. The failure of YV3 fuse F101 caused a loss of power to the Y3 essential power bus de-energizing several instruments including RPS Channel 3 and Safety Features Actuation System (SFAS) Channel 3.

The loss of instrument bus Y3 caused the station to be placed in the action statement of Technical Specification 3.8.2.1.

The action statement requires the inoperable bus to b.

restored to operable status within eight hours or be in at least hot standby within the next six hours and in cold shutdown within the following thirty hours. Bus Y3 was manually transferred to its alternate source and the SFAS and RPS channels were re-energized.

Designation of Apparent Cause of Occurrence: The apparent cause of this occurrence was two-fold.

The short circuit was the result of too large a stud placed on these terminals, specifically for this surveillance test, such that the alligator clips utilized are almost entirely opened in order to grip the stud, thus preventing a secure, tensioned hold. These studs were put in place by Facility Change Request 79-273. The second cause is in the design in that the 200 amp inverter fuse blew, de-energizing the whole bus, before a 30 amp RPS supply fuse or the 25 amp RPS circuit breaker could pro-vide the necessary protection.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel.

RPS and SFAS Channels 1, 2, and 4 were continuoualy available as were 120 VAC essential buses Yl, Y2, and Y4

Corrective Action

Maintenance Work Order 80-3918 was issued to investigace the loss of the Y3 bus.

F101 was found blown and was replaced. There was no apparent damage to the inverter. The Y3 bus was transferred back to its normal source.

ST 5030.12 was modified to delete the requirement to measure the trip breaker voltage. Facility Change Request 80-217 was prepared in September of 1980 to correct the inverter fuse problem.

LER #80-086

P-TOLEDO EDIS0N COMPANY DAVIS-BESSE NUCLEAR PO'n'ER STATION UNIT ONE PAGE 2 SUPPLE >tENTAL INFOPJtATION FOR LER NP-33-80-111 Previous failures of 120 VAC essential power inverters due to accidental Failure Data:

shorting were reported in Licensee Event Reports NP-32-79-09, NP-33-79-13, and NP-33-80-70.

LER #80-086 I

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