05000298/LER-1993-008

LER 93-008-00:on 930328,4,160-volt Breakers 1BG,1GB & 1GE Tripped Due to Actuation of 1GS Breaker Lockout Relay.Caused by Oversight in Design Change Installation Instructions. Work Stopped & Design Change Implemented

ML20056C209
Person / Time
Site:	Cooper
Issue date:	04/22/1993
From:	Reeves D NEBRASKA PUBLIC POWER DISTRICT
To:
Shared Package
ML20056C207	List: 05000298/LER-1993-007 05000298/LER-1993-008 ML20056C206
References
LER-93-008, LER-93-8, NUDOCS 9305110007
Download: ML20056C209 (3)

LER-2093-008,

Event date:
Report date:
2982093008R00 - NRC Website

text

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I N ferai 3es us. NUCLEAR REGULATORY COMutSssON APPROVED OME hO 3150 410s LICENSEE EVENT REPORT (LER) 8 '"* * ' '8= l i

FActLITY NAME (13 DOCatET NUMeER (2) PAGE63, i

Cooper Nuclear Station 0 l5 t o l0 l 0 l219 I 8 1 lorl013 TITLE 148 Loss of 4160 VAC 1G Bus During Design Change Installation Due To Inadvertent Trip Circuit Actuation EVENT DATE 151 LER NUMBER tsi REPORT DATE (71 OTHER 8 ACILITitt INvDLVED (BI ha SAL t DAY f ACf LtTV Se Augg DOCKET NUMBERLSI MONTH DAY YEAR YEAR a . i u MONTH YEAR Ol5{0l0l0g l l f 4

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Donald L. Reeves, Jr.

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On March 28, 1993, at 3:46 pm, during installation of an overvoltage relay on j 4160 VAC breaker IGS control cubicle door, 4160 VAC breakers IBG, 1GB and ICE were tripped due to actuation of the 1GS breaker lockout relay. The relay was  !

inadvertently tripped when one of the three phase overcurrent (51) protective relays  !

< located on the IGS control cubicle door actuated. The trip of the ICB breaker ,

resulted in.the 4160 VAC 1G Bus being de-energized for approximately 10 minutes and .l a corresponding 1/2 Group 1 Isolation,1/2 scram, and Groups 2. 3, 6, and 7

• Isolations. Additionally, Spent Fuel Fool cooling was interrupted for an approximate five minute time frame. At the time of the event, the plant was in Cold ,

Shutdown for the 1993 Refueling Outage. .

i The cause of the event was due to an oversight in the Design Change (DC) .

l installation instructions. When the instructions were written, operation of the 51-  !

relays caused by cabinet vibration or jarring during overvoltage relay installation  !

was judged to not be a problem as 51 relay operation requires disc rotation of  !

approximately 90 degrees to achieve contact closure. Considering relay disc j rotation to not be of concern, installation instructions did not specify de- .j energizing the relay logic circuit until electrical installation of the overvoltage '

relay was to begin.

The step de-energizing the lockout circuit was moved ahead of the steps addressing  ;

overvoltage relay installation. The relay installations were completed.In both l divisions without further incident. This event will be reviewed with design i engineers to emphasize the.need for conservative decision making. j l

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NMC forms 366Q UK NUCLEAR REGULOTO21 COMMISSIOni LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Aeovto oMe No siso-mo.

EXPtRES; B131/8B FOCILITY hAME (1) _ DOCKET NUMBLR (23 LER NUMBER 16) PAGE (3) vtaa  :

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0l 0 0l2 0F g l3 TEXT (F nme moce m segumt arse sadmonst A/AC Form 356A W t1M A. Event Description on March 28, 1993, at 3:46 pm, during installation of an overvoltage relay on 4160 VAC breaker 1GS control cubicle door, 4160 VAC breakers 1BG,1GB and IGE tripped due to actuation of the 1GS breaker lockout--

relay. The 1GS breaker lockout relay was inadvertently tripped during overvoltage relay installation when one of the three phase overcurrent (51) protective relays located on the 1GS control cubicle door actuated.

The overvoltage relay was being installed in accordance with Emergency Transformer Replacement Design Change (DC) installation instructions.

The breaker trips resulted in the 4160 VAC 1G Bus being de-energized for approximately 10 minutes and a corresponding 1/2 Group 1 Isolation, 1/2 scram, and Groups 2, 3, 6, and 7 Isolations (Primary Containment, Reactor Water Cleanup (RUCU), Secondary Containment, including Standby Gas Treatment (SGT) initiation, and Reactor Water Sampling).

Additionally, Spent Fuel Pool cooling was interrupted for approximately five minutes.

B. Plant Status Gold Shutdown for the 1993 Refueling Outage. At the time of the trip, Diesel Generator (DG) No. 2 was paralleled to the grid and loaded at 1000 KW in preparation for a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run conducted as post-maintenance testing (PMT).

C. Basis for Report An unplanned automatic actuation of ESF Groups 2, 3, 6, and 7 Isolations, reportable in accordance with 10CFR50.73(a)(2)(iv).

D. Cause Design; specifically, the DC installation instructions. The possibility that the 51 protective relays might trip during overvoltage relay installation was misjudged. These GE IAC53 type relays operate on an induction disk principle. One trip contact is mounted on the shaft of an induction disk. With the existing setting of these relays, this. disk must rotate approximately 90 degrees to provide a trip signal. When the design change installation instructions were written, disk rotation resulting in an inadvertent trip was judged to be implausible during overvoltage relay installation. However, during installation, the jarring and vibration of the cubicle door unexpectedly caused one of the three relay disks to rotate so that its contacts closed.

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NRC Feth 3044 U2. NUCLE AR 9tEGULATOftV COMMIS$ SON LICENSEE EVENT REPORT (LER) TEXT CONTINUATION -4eeRoveo ous NO. mo_om i LKPIRES: 8/31/88 FActLITY,NAME (1) . DOCKET NUMBER (2) LER NUMBER 40) eAGE (31

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i E. Safety Si rnifi cance l

The safety significance of the 4160 VAC 1G Bus (Division II) being de-energized was minimal. The plant was in Cold Shutdown with fuel removed from the vessel. While the Division II electrical system was in ,

service, it was not considered the primary power source since DG No. 2 had not yet been returned to service following overhaul. As previously-noted, the DG had been started and was operating in parallel with the >

grid at 1000 KW in preparation for a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> PMT run. While group isolations occurred and functioned as designed, ongoing outage activities were not affected.  :

The 4160 VAC 1G Bus was de-energized for approximately ten minutes. f Initially, Spent Fuel Fool cooling was lost due to the loss of flow "

instrumentation, causing the filter-demineralizer outlet valves to .;

close. An operator was immediately dispatched to open the bypass valve  ;

around the filter-demineralizers. It is estimated that Spent Fuel Fool l cooling flow was restored in approximately five minutes. The effect of  :

the flow interruption on Spent Fuel Pool temperature was negligible. At  ;

3:56 pm, the 1GS breaker lockout relay was reset and the 1GE breaker  !

automatically closed, repowering the 1G Bus. Normal breaker lineup was i restored at 4:01 pm.

1 F. Eafety Imnlications The activities associated with installation of the overvoltage relays i that caused the loss of the 4160 VAC 1G Bus would only have been ~;

performed during Cold Shutdown. Therefore, for this type of activity,  ;

shutdown conditions would be the worst case initial plant conditions.

G. Corrective Action The work was stopped and a change to the DC was made and approved to ,

move the step de-energizing the lockout circuit ahead of the step for  ;

overvoltage relay installation. Work was -started.and both divisions l of overvoltage relay installations were completed without further l incident.

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.This event will be reviewed with all design engineering personnel to emphasize the need for conservative decision making during development ,

of DC installation instructions.

i H. Similar Events- .j None l

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