United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-25: Supplement 1: Loss of Vital AC Power With Subsequent Reactor Coolant System Heat-Up

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                               March 11, 1991


Information Notice No. 90-25, SUPPLEMENT 1:  LOSS OF VITAL AC POWER WITH 
                                                 SUBSEQUENT REACTOR COOLANT 
                                                 SYSTEM HEAT-UP


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose:

This information notice supplement is intended to give addressees additional 
information regarding switchyard administrative control as reported in 
NUREG-1410, "Loss of Vital AC Power and The Residual Heat Removal System 
During Mid-Loop Operations at Vogtle Unit 1 on March 20, 1990," dated June 
1990.  Specifically, this supplement provides the licensee's findings and 
corrective actions pertaining to NUREG-1410, Finding 10.2, regarding the 
adequacy of switchyard administrative control.  Two previous events at other 
plants that bear a similarity to the Vogtle incident are summarized.  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 supplement to the 
information notice do not constitute NRC requirements; therefore, no 
specific action or written response is required.

Description of Circumstances:

On March 20, 1990, a truck driver accompanied by a security escort entered 
the protected area with the site's fuel-and-lubricants truck at Vogtle.  The 
driver was scheduled to refuel air compressors and welding machines located 
around the site during the Unit 1 outage.  The truck was driven into the 
Unit 1 switchyard to fuel a welding machine.  Upon determining that the 
welding machine did not need fuel, the driver backed the truck (rear view 
blocked) into a support pole for a 230-kV feeder line causing a 
phase-to-ground electrical fault and the loss of vital ac power. 

The damage caused by the truck could have been more severe if electrical 
arcing had ignited the fuel on the truck.  Additional damage that could have 
resulted from a fire or explosion would have further complicated recovery 
from the incident.



9103050397 
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                                                  IN 90-25, Supplement 1 
                                                  March 11, 1991 
                                                  Page 2 of 3 


Discussion:

This event was caused by inadequate procedures and supervision oversight 
regarding access to the 230 kV switchyard.  The findings for NUREG-1410 were 
as follows:  The licensee for Vogtle did not have (1) restrictions or access 
controls prohibiting vehicles or equipment from entering and remaining 
inside the switchyard except that they be there on official business, and 
(2) specific restrictions to control combustibles and other hazardous 
materials within the switchyard.  

Vogtle plant procedures require that "non-designated" vehicles (vehicles not 
designated solely for use in protected areas) be escorted by a security 
officer to ensure that they are used only by authorized persons and only for 
authorized purposes.  The security officer performed his duties as required 
by procedures and was seated in the cab of the fuel-and-lubricants truck 
when the driver backed the truck into a support column for the 230-kV feeder 
line.  However, procedures did not ensure that a ground guide (flagman) was 
provided.  The licensee revised the training to emphasize that security 
officers have authority and responsibility to assist vehicle operators in 
such a way as to ensure that vehicles operate safely.  Specifically, 
security escorts will ensure that a flagman provides assistance when large 
vehicles are maneuvered inside the protected area.  As a result of the 
March 20, 1990, event, the licensee disciplined the truck driver for 
inattention and a lack of alertness in backing the truck when his visibility 
was impaired.  The licensee issued a management directive to all site 
employees on the control and operation of vehicles and revised 
administrative procedures to incorporate this directive.  To avoid 
unnecessary equipment and vehicle traffic in the switchyard, outage area 
coordinators have been instructed to stage welding machines and other 
materials outside the switchyard on the east and west ends of the turbine 
building.  This change will eliminate the need for a fuel-and-lubricants 
truck to enter the switchyard.  The licensee revised maintenance procedures 
to restrict staging of equipment in the switchyard.  The licensee installed 
barriers with signs stating the requirement for authorization from the unit 
shift supervisor for vehicle access to the switchyard.  The licensee also 
revised plant procedures to control hazardous materials and transient 
combustibles in the switchyard and other sensitive plant areas.

At Vogtle, human error caused the loss of offsite power during a refueling 
outage, typically a time when (1) the electrical distribution system is most 
vulnerable to a single fault causing a loss of power when other equipment is 
out of service for maintenance, and (2) more site activities are taking 
place that can cause such a fault (e.g., operation of heavy equipment, more 
vehicles onsite, and construction activities).  Therefore, particularly 
during plant outages, activities and hazardous materials in switchyards and 
protected areas need to be controlled properly to prevent an incident 
similar to the Vogtle event.

The incident at Vogtle led to a loss of power to the only transformer 
supplying offsite power to the Unit 1 safety buses.  The only available 
emergency diesel generator then started and tripped, cutting off all power 
to the safety buses.  In two previous events at other plants, discussed in 
NUREG 1410, the initiators 
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                                                  IN 90-25, Supplement 1 
                                                  March 11, 1991 
                                                  Page 3 of 3 


(human errors associated with maintenance activities) of the events closely 
resembled the cause of the Vogtle incident: 

     (1)  Workmen on the roof of the emergency diesel generator building 
          lowered an extension cord and accidentally allowed it to touch a 
          transmission line connected to the only transformer supplying 
          offsite power to the plant.  During this event, the only available 
          diesel generator started and energized one safety bus.

     (2)  Workmen in the low voltage switchyard inadvertently grounded a 
          transmission line to the only transformer supplying offsite power 
          to the plant when they raised a metal pole.  During the event, the 
          only available emergency diesel generator started and energized 
          one safety bus. 

This information notice supplement requires no specific action or written 
response.  If you have any questions about the information in this notice, 
please contact the technical contact listed below or the appropriate NRR 
project manager. 




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


Technical Contact:  Frank J. Witt, NRR
                    (301) 492-0767


Attachment:  List of Recently Issued NRC Information Notices
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