ML20044H526

LER 93-007-00:on 930430,unplanned Emergency Generator Start & Rt Signal Occurred.Caused by Inadequate Attention to Detail,Labeling of Fuse Drawers,Caution Signs & Training. Labeling & Caution Signs upgraded.W/930601 Ltr

ML20044H526
Person / Time
Site:	Fort Calhoun
Issue date:	06/01/1993
From:	Gates W, Lindquist S OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-007, LER-93-7, LIC-93-0064, LIC-93-64, NUDOCS 9306090154
Download: ML20044H526 (6)

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Omaha Public Power District P.O. Box 399 Hwy.75 - North of Ft. Calhoun Fort Calhoun, NE 680230399 l 402/636-2000 June 1, 1993 LIC-93-0064  ;

U. S. Nuclear Regulatory Commission Attn: Document Control Desk i Mail Station P1-137 Washington, DC 20555

Reference:

Docket No. 50-285 Gentlemen:

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Subject:

Licensee Event Report 93-007 for the Fort Calhoun Station Please find attached Licensee Event Report 93-007 dated June 1, 1993. This report is being submitted pursuant to 10 CFR 50.73(a)(2)(iv). If you should have any questions, please cor. tact me. i Sincerely, iv f) bb W. G. Gates Vice President WGG/jrg Attachment c: J. L. Milhoan, NRC Regional Administrator, Region IV S. D. Bloom, NRC Project Manager R. P. Mullikin, NRC Senior Resident Inspector INP0 Records Center

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Fort Calhoun Station Unit No. 1 05000285 10F 5 Tmm s Unplanned Emergency Diesel Generator Start and Reactor Trip Signal ~

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UCENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER pwude Area Coco)

Scott A. Lindquist, Shift Technical Advisor (402) 533-6829 COMPLETE ONE UNE FOR EACH COMPONENT FAILURE oESCRIBED IN THIS REPORT (13)

CAusE SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENr MANUFACTUFER PRD TO l

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ABSTRACT (Umit to 1400 spaces, i.e., approximately 15 single-Spaced typewritten lines) (16)

On April 30, 1993 at approximately 1019 CDT, with the Fort Calhoun Station in Hot Shutdown (Mode 3), a non-licensed operator was performing an independent verification of the return-to-service positions of equipment which had previously been taken.out of service for maintenance. While intending to verify the installation of potential transformer fuses for Transformer T1A-1, the individual pulled the drawer with the .

potential transformer fuses for 4160V Bus 1A1. This resulted in a Bus 1Al low voltage l alarm, an automatic start of Emergency Diesel Generator DG-1 and load shedding of '

Bus 1A1 (including tripping of Reactor Coolant Pump RC-3A). Actual voltage on Bus 1Al remained normal. The tripping of RC-3A resulted in a subsequent Low Reactor Coolant Flow reactor trip signal.

The causes of the event were determined to be inadequate attention to detail, inadequate labeling of the fuse drawers, inadequate caution signs and inadequate training.

Corrective actions will include upgrading of labeling and caution signs for 4160V cubicles and training for operators on potential transformer fuses.

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NUMBER NUMBER l Fort Calhoun Station Unit No. 1 05000285 2 OF 5 l 93 -- 007 -- 00 i

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BACKGROUND l

The Fort Calhoun Station (FCS) 4160V electrical distribution system includes four I separate 4160V buses. Unit Auxiliary Buses 1A1 and 1A2 feed large auxiliary loads j directly at 4160V. House Service Buses 1A3 and 1A4 feed the remainder of the 4160V  ;

components as well as supplying power to all 480V plant loads through 4160/480V '

transformers. Engineered safeguards loads are powered via Buses 1A3 and 1A4, either directly or through 480V load centers. Buses 1A3 and 1A4 may each be supplied from an emergency diesel generator.

The 4160V electrical distribution system is equipped with an undervoltage relay protection scheme which is designed to ensure that adequate voltage exists on station buses to permit safe reactor shutdown and maintain the reactor in a safe shutdown condition under all grid conditions. Indication of a loss of voltage initiates a load shed signal which opens breakers on the affected bus to prevent overloading an incoming supply and initiates an automatic start of the associated emergency diesel generator.

The Reactor Protective System (RPS) monitors certain critical plant operating parameters and compares them to predetermined setpoints. If one or more of the monitored parameters reaches its setpoint on two of the four channels, the RPS will initiate a ,

reactor trip. There are twelve different reactor trips that can be initiated from the  !

RPS. The trip unit of interest for this event is the Low Reactor Coolant Flow reactor l trip. l The low flow trip provides protection against departure from nucleate boiling should ,

coolant flow suddenly decrease significantly. The trip setpoint is 95% of nominal core flow. Shutdown or loss of one or more reactor coolant pumps will initiate a Low Reactor Coolant Flow RPS signal.

EVENT DESCRIPTION On the morning of April 30, 1993, with FCS in Hot Shutdown (Mode 3) for a short duration planned outage, a non-licensed operator was directed to perform an independent verification of the return-to-service positions of equipment which had previously been taken out of service for maintenance. The maintenance had involved a synchronizing potential transformer in the 345kV system. Earlier that day, potential transformer fuses had been reinstalled by an electrician.

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After reviewing the tag sheet, the operator performing the independent verification began by verifying the return-to-service position of the feeder breaker to Bus 1A1. He then intended to locate and verify the installation of the potential transformer fuses for Transformer T1A-1. He began by looking for fuses in the Dus 1Al feeder breaker cubicle (Cubicle 1Al-7). Next, as he closed the Cubicle 1Al-7 door, he noticed a sign on the adjacent cubicle (Cubicle 1Al-6) which read, " Pulling PT Fuses Will De-Energize Bus 1Al". The operator then opened the door to Cubicle 1Al-6, which houses the potential transformer fuses for Bus 1Al rather than the potential transformer fuses for Transformer T1A-1. The operator was under the mistaken impression that this cubicle might contain the fuses that he was trying to locate.  :

1 Inside Cubicle 1Al-6, the operator noticed a drawer which he knew to contain fuses. l There was also an additional caution sign which indicated that pulling fuses would de-energize the bus. The operator overlooked a small label on the outside of the drawer which identified the fuses in the drawer. The operator pulled the drawer out to look for fuse labels and saw no labels inside the drawer. The drawer was then shut. A low .

voltage alarm was received in the Control Room for Bus 1Al at this time, which cleared )

shortly thereafter. l The operator then returned to the IA1 feeder breaker cubicle (Cubicle 1Al-7) to re-verify that it did not contain any fuses. He then went back to Cubicle 1Al-6 to re-examine it. Approximately twenty seconds after initially pullir.g the drawer, he pulled the drawer again. This time the drawer was pulled out long enough to initiate load shedding of Bus 1A1 in addition to the low voltage alarm in the Control Room. (There is i a two second time delay prior to initiation of load shedding.) The indication of low voltage on Bus 1Al resulted in an automatic start of Emergency Diesel Generator DG-1, and initiated load shedding which tripped Reactor Coolant Pump RC-3A and Circulating Water Pump CW-1A (which are both powered from Bus 1A1). Actual voltage remained normal on the bus. The tripping of RC-3A resulted in a subsequent Low Reactor Coolant Flow reactor trip signal at 1019 CDT.

Following the reactor trip signal, Emergency Operating Procedures E0P-00, " Standard Post Trip Actions," and E0P-01, " Reactor Trip Recovery," were completed and plant systems were returned to their normal alignment.

The NRC was notified of this event on April 30, 1993 at 1323 CDT pursuant to 10CFR50.72(b)(2)(ii). This report is being submitted pursuant to 10CFR50.73(a)(2)(iv).

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'l The affect of this event on plant safety was minimal. Engineered safety features i functioned as designed in response to the event. Actual voltage remained normal on J

, Bus 1A1 in spite of the low voltage alarm, load shedding and diesel generator start. .i

! Also, Bus 1A1 does not supply power to engineered safeguards loads.

I The plant was in Hot Shutdown with all control rods fully inserted at the time of this event. Therefore, while the tripping of Pump RC-3A resulted in a low Reactor Coolant i Flow RPS signal, the plant was in a condition in which the RPS low flow trip is not required (i.e., Technical Specifications allow this trip to be bypassed below 1.0 E-4%

power). ,

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l CONCLUSIONS

, A Human Performance Evaluation System review identified the following causes as l contributing to this event. ,

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.A . Inadequate Attention to Detail - The operator was attempting to verify the installation of potential transformer fuses for Transformer T1A-1, but was not in the correct cubicle. The potential transformer fuses for Transformer T1A-1 are located in Cubicle 1Al-8 which was labeled " Potential XFMR and Ground Fault Locator Compartment Transformer TIA-1 Secondary". The operator pulled the drawer in Cubicle 1Al-6 which was labeled " Potential XFMR Compartment' 4160 VAC Bus 1Al". The tag sheet for the fuses to be verified had correctly listed the location of the fuses as Cubicle 1Al-8.

B. Inadequate Labeling of the Fuse Drawers - These fuses are not labeled l adequately. The small label was overlooked by the operator.

C. Inadequate Caution Signs - The operator was misled by the caution sign hanging L on the outside of the cubicle door which stated " Pulling P. T. Fuses Will De-Energize Bus IAl". The operator believed that pulling the fuses from the drawer, rather than pulling the drawer, would de-energize the bus.

D. Inadequate Training - Operations personnel are not currently trained on the location or operation of potential transformer fuses, although per Standing Order 0-20, they may be required to perform the independent verification of these components.

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'TtxT p ,no,. .n.c. aoi,.a. u mon.i oe Nac rorm asea 3 cit 3 CORRECTIVE ACTIONS The following corrective actions have been or will be completed:

1. The operator was counseled on the need for attention to detail and was involved in the preparation of a video tape to be used for training on the event. (See Corrective Action 4.) ,

2. The labeling of electrical equipment located inside 4160V cubicles will be <

inspected during the 1993 Refueling-Outage to identify specific. labeling changes needed to more clearly identify the equipment contained within the cubicle. Ap3ropriate labels will then be procured and installed no later than the end of t1e following refueling outage.

3. The caution signs on the outside of 4160V cubicles containing potential transformer fuses have been upgraded to clarify that pulling the fuse drawer rather than pulling the fuse will cause a trip of-the associated component (s).

4. Training will be provided to operators on the location and operation of potential transformer fuses which they may be required to verify. Training will also be provided on this event, emphasizing the need for attention to detail. This action will be completed by September 10, 1993.

PREVIOUS SIMILAR EVENTS LER 87-009 reported a loss of off-site power during a refueling shutdown, due to inadvertently pulling the wrong potential transformer fuses.

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