United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-96: Electrical Shock Fatalities at Nuclear Power Plants

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                December 14, 1988

                                   POWER PLANTS 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to events 
involving fatalities from electrical shock that have occurred at nuclear 
reactor facilities.  In addition to causing tragic personnel loss, some of 
these events have had significant nuclear safety implications because of the 
loss or potential loss of safety-related equipment.  It is expected that 
recipients will review the information for applicability to their facilities 
and consider actions, as appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances:

At Wolf Creek on September 13, 1988, an electrician, who was attempting to add 
new wires to a 3/4-inch conduit containing 480-volt energized circuits, was 
electrocuted.  The electrician had difficulty inserting a nonconducting snake 
through the conduit fire seals.  Some of the energized wires in the conduit 
were damaged during either a previous modification or attempts to remove the 
fire seals.  The electrician disconnected the conduit from a junction box in 
order to remove the fire seals. At this point, the ungrounded conduit 
apparently came in contact with the damaged energized wires, becoming 
energized itself.  The electrician, who was standing on some piping holding 
the conduit, provided the missing ground and was electrocuted.

An electrocution occurred under similar circumstances at Quad Cities Unit 1, 
on July 16, 1971.  An electrician was pulling a new conductor into position in 
the high pressure coolant injection (HPCI) room, and for some reason the cable 
became energized, causing the death of the electrician.

At Wolf Creek, on October 14, 1987, an electrical technician, who was cleaning 
the potential transformer cubicles on the 'B' train emergency safety features 
switchgear, came in contact with a 4160-volt energized line and was electro-
cuted.  Miscommunication regarding the equipment that was to be deenergized, 

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failure to follow work procedures requiring voltage checks on supposedly 
deenergized equipment, and the defeating of safety features built into the 
potential transformer drawers all contributed to the cause of this tragedy.

Wolf Creek has two redundant 4160-volt safety features busses (NB01 and NB02, 
shown in Figure 1), each fed from separate transformers.  Each of these trans-
formers also feeds an alternate crossover line to the other bus to permit 
powering this opposite bus in case the normal power source for the bus fails. 
In order to permit the "B" train switchgear to be cleaned, inspected and 
tested, a shift supervisor prepared a clearance to deenergize the switchgear.  
In doing this, he left the normal transformer (XNB02) for the "B" train 
switchgear energized.  He reasoned that this transformer should be left ener-
gized to provide redundant power to the "A" train via the alternate line, and 
he believed that he had the concurrence of the Electrical Department for this 
configuration.  The electrical supervisor with whom he discussed this matter, 
however, believed that the shift supervisor was referring to the fact that the 
alternate line to the "B" side from the "A" side transformer (XNB01) was to be 
left energized, as this line could not be deenergized without shutting down 
the "A" bus also. Thus the incoming lines from both transformers to the "B" 
train switchgear remained energized, but the electricians believed that the 
line from the "B" side transformer had been deactivated. 

This misunderstanding would have been discovered if the workmen had followed 
the maintenance procedure for this work, which required that all of the sta-
tionary disconnects in each cubicle be checked using high voltage gloves and a 
voltage tester to ensure that no voltage was present.  In this case, the 
day-shift electricians who were doing this part of the procedure only checked 
a few of the disconnects.

The night shift was working by the time the electricians got to the cleaning 
of the potential transformer drawers.  These drawers are arranged such that 
when they are pulled out the exposed part of the drawer is deenergized, 
regardless of the electrical status of the rest of the switchgear.  However, 
the electrical technician, who was doing the cleaning, and his supervising 
electrician decided to pull the tops off the potential transformer cubicles in 
order to facilitate the work.

While the electrical technician was working on the potential transformer on 
the switchgear (NB0209) for the line from the normal "B" train transformer, he 
came in contact with an energized potential transformer stub and was 
electrocuted.  The breaker (PA0201) in the line feeding the "B" side 
transformer apparently tripped immediately after the energized stub was 
contacted.  However, the victim was in contact with the cabinet (NB0212) for 
the energized line from the "A" side transformer.  His sleeve, ignited by 
arcing current, was on fire. This apparently led other electricians in the 
area who responded to the emergency to believe that the victim was still in 
contact with energized equipment.  Using belts and hoses, the electricians 
tried unsuccessfully to remove the victim.  At this point, the Halon fire 
protection system in the switchgear room was initiated by the fire, forcing 
the electricians out of the room temporarily.
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                                                            Page 3 of 4 

The electricians in the switchgear area relayed incorrect information to the 
control room that a man was hung up on the breaker (NB0212) for the still-
energized alternate line from the "A" side transformer.  In their haste to 
free the victim, the operators opened the breaker (NB0112) downstream from the 
point at which the alternate line to the "B" bus (NB02) leaves the line from 
the 'A' side transformer (XNB01).  Consequently, this action deenergized the 
"A" bus (NB01), but not the alternate line to the B" bus.  This action caused 
the "A" side diesel generator (NE01) to start, repowering the "A" bus.  
However, when the control room personnel were informed that the alternate line 
to the "B" side was still energized, they disconnected all power sources, 
including the running diesel for both busses by opening breakers 13-48 and 
NB0111.  As a result, all of the emergency safety systems, including the 
operating residual heat removal system, were deactivated.

After the victim had been removed, the operators tried to repower the "A" bus 
(NB01) by closing the breaker (NB0111) to the still running diesel but discov-
ered that the diesel generator controls had to be reset in the diesel 
generator room first.  The "A" bus was then repowered from its normal 
transformer (XNB01).  The residual heat removal system was out of service for 
17 minutes during this event.  However, the core was only partially loaded 
with fuel at the time, and the reactor coolant temperature rise was 
negligible.  The Wolf Creek staff have since provided a modification to the 
diesel controls to permit them to be reset from the control room after the 
diesel power has been interrupted from the control room.

This Wolf Creek event also has a similar precedent.  An electrical worker was 
electrocuted at the San Onofre Nuclear Power Plant on November 22, 1980 when 
he came in contact with a 4-kv line while he was cleaning breaker cubicles.


Working on or around live circuits is common practice at nuclear power plants. 
As these events show, this practice can not only be very hazardous to person-
nel, but because of the need to take extraordinary actions during emergency 
situations, it can have a serious impact on reactor safety as well.  Licensees 
are encouraged to review their maintenance practices to ensure that the 
following considerations are applied to electrical maintenance activities:

1.   Equipment clearance procedures assure that work on live circuits is 
     undertaken only when absolutely necessary and that when this is the case, 
     proper consideration is given to the potential for electrical shock and 
     the loss of safety-related equipment. 
2.   Procedures for pulling new cables or wires past energized wires include 
     provisions to prevent damage to the existing wires, prohibitions against 
     the ungrounding of conduits and junction boxes containing live wires, and 
     provisions to isolate the electrical workers from the energized wires.
3.   Clearance procedures assure that when work on or around energized equip-
     ment is necessary, the operators and everyone involved with the actual 
     work clearly understand exactly which equipment is out of service and 
     which equipment is to be left energized.
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                                                            Page 4 of 4 

4.   Maintenance supervision ensures that everyone working on electrical 
     equipment is aware of the importance of following safety procedures, such 
     as those that require checking for voltage on contacts that are expected 
     to be deenergized.  This safety procedure is particularly important when 
     more than one crew is involved in the work.

5.   Maintenance safety procedures include warnings against defeating protec-
     tive features designed to deenergize equipment when it is serviced. 
No specific action or written response is required by this information notice.  
If you have any questions about this matter, please contact one of the techni-
cal contacts listed below or the Regional Administrator of the appropriate 
regional office.

                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical Contacts:  R. Vickrey, RIV
                    (817) 860-8239

                     Donald C. Kirkpatrick, NRR
                     (301) 492-1152

1.  Figure 1, Electrical One-Line Diagram
2.  List of Recently Issued NRC Information Notices
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                                                            IN 88-96 
                                                            December 14, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-95          Inadequate Procurement        12/8/88        All holders of OLs
               Requirements Imposed by                      or CPs for nuclear
               Licensees on Vendors                         power reactors. 

88-94          Potentially Undersized        12/2/88        All holders of OLs
               Valve Actuators                              or CPs for nuclear
                                                            power reactors. 

88-93          Teletherapy Events            12/2/88        All NRC medical 

88-92          Potential for Spent Fuel      11/22/88       All holders of OLs
               Pool Draindown                               or CPs for nuclear
                                                            power reactors. 

88-91          Improper Administration       11/22/88       All holders of OLs
               and Control of                               or CPs for nuclear
               Psychological Tests                          power reactors and
                                                            all fuel cycle 
                                                            facility licensees 
                                                            who possess, use, 
                                                            import, export, or 
                                                            transport formula 
                                                            quantities of 
                                                            strategic special 
                                                            nuclear material. 

88-90          Unauthorized Removal of       11/22/88       All NRC licensees 
               Industrial Nuclear Gauges                    authorized to 
                                                            possess, use, 
                                                            manufacture, or 
                                                            industrial nuclear 

88-89          Degradation of Kapton         11/21/88       All holders of OLs 
               Electrical Insulation                        or CPs for nuclear
                                                            power reactors. 

88-88          Degradation of Westinghouse   11/16/88       All holders of OLs
               ARD Relays                                   or CPs for nuclear
                                                            power reactors. 
OL = Operating License
CP = Construction Permit
Page Last Reviewed/Updated Friday, May 22, 2015