Information Notice No. 92-13: Inadequate Control Over Vehicular Traffic at Nuclear Power Plant Sites
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 18, 1992
NRC INFORMATION NOTICE 92-13: INADEQUATE CONTROL OVER VEHICULAR TRAFFIC
AT NUCLEAR POWER PLANT SITES
All holders of operating licenses or construction permits for nuclear power
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to continuing problems resulting from the failure
of some licensees to maintain adequate control over vehicular traffic at
their plants. These licensees failed to follow established administrative
procedures related to the use of self-propelled cranes. Their failures
resulted in unnecessary challenges to safety systems and threatened the
health and safety of plant personnel. 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 are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
Diablo Canyon Unit 1: On March 7, 1991, during a refueling outage, the
Diablo Canyon Nuclear Power Plant, Unit 1, experienced a total loss of
offsite power (LOOP). The event was caused when an electrical flashover
occurred between a 500 kV transmission line and the boom of a mobile crane.
The boom was positioned approximately three feet from the transmission line.
At the time of the event, power to plant loads was being supplied from
offsite by back-feeding through the main output transformer from the 500 kV
switchyard. Two standby startup transformers, the normal sources of offsite
power to the plant, had been removed from service for scheduled maintenance.
The flashover caused protective relaying to actuate to isolate the faulted
line and, as a result, offsite power to plant loads was interrupted.
All three emergency diesel generators started and loaded successfully.
Operation of the residual heat removal system was restored within about 1
minute. The temperature of the core did not increase. No radiological
release resulted. The fault did not affect Diablo Canyon, Unit 2, which was
operating at full power.
Palo Verde Unit 3: On November 15, 1991, while the Palo Verde Nuclear
Generating Station, Unit 3, was shutdown in hot standby, the boom of a
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crane made contact with one of two 13.8 kV offsite power feeder lines
located in the plant's protected area. The crane was being used to replace
the "A" phase bushing on the main output transformer. The original bushing
had been damaged by lightning a day earlier. Prior to final installation
and after high voltage testing had been completed, the bushing was returned
to its shipping cask. The crane operator shut down the crane motor and
engaged one of several braking devices on the crane boom. The crane
operator then exited the crane cab to discuss replacement procedures with
other maintenance personnel.
A wind gust caused the boom of the crane to rotate and contact one of the
phases of the 13.8 kV feeder. The feeder was transmitting power from the
startup transformer to various vital and non-vital loads in the "A" train.
The electrical fault current which was generated was not of sufficient
magnitude to cause protective devices to actuate because the crane had not
been grounded as required by plant procedure. Therefore, the feeder
remained energized and the fault current initiated small asphalt fires in
the areas where the crane's front outrigger pads made ground contact. The
rear outrigger pads were not extended.
The maintenance foreman (the foreman) contacted the shift supervisor and
incorrectly identified the "B" train feeder as being faulted. The shift
supervisor opened the supply circuit breaker for the "B" train feeder before
the foreman could correct his misstatement. Electrical power was
interrupted to non-vital loads, including two of four reactor coolant pumps
(RCPs). Power to vital train "B" loads was momentarily interrupted but was
reestablished following the successful start and loading of the train "B"
emergency diesel generator (EDG).
The correct "A" feeder was subsequently deenergized, resulting in the start
and loading of the "A" EDG and causing the loss of power to the remaining
two operating RCPs. The reactor was cooled by natural circulation for about
28 minutes until a reactor coolant pump was started. A notification of an
unusual event was made by the licensee based on a fire located in the
protected area lasting longer than 10 minutes. The event resulted in no
personnel injuries and no release of radioactive material.
Fermi Unit 2: On December 12, 1991, an event involving a self-propelled
crane occurred at the Enrico Fermi Atomic Power Plant, Unit 2. The Fermi
Unit was in cold shutdown in preparation for replacing a main output
transformer. The crane, with its boom extended, attempted to turn onto a
roadway that is outside the protected area but inside the owner controlled
area at the plant. While the crane spotter was directing traffic, the crane
operator proceeded to turn onto the roadway. A lifting strap, which was
dangling from the end of the crane boom made momentary contact with one
phase of a 120 kV transmission line which was providing offsite power to the
plant. The circuit breaker for the line immediately opened and reclosed,
interrupting and reestablishing the power supply in a matter of cycles. No
When the operator stopped the crane, the crane came to rest with the end of
the boom extended above the transmission line and with the transmission line
passing between the boom and lifting strap. The operator then backed up the
crane. A second contact occurred between the transmission line and the
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strap. The circuit breaker again opened and reclosed rapidly so that no
actual LOOP occurred. The crane operator then informed his supervisor of
the event. No personnel injuries or equipment damage resulted. No
challenge to plant safety systems occurred.
Information Notice 90-25, Supplement 1, "Loss of Vital AC Power with
Subsequent Reactor Coolant System Heat-up," informed licensees of problems
that can occur when vehicular traffic is not properly controlled near safety
systems or systems important to safety. A significant operating event
occurred at the Alvin W. Vogtle Generating Plant (Vogtle) on March 20, 1990.
An NRC incident investigation team described the circumstances of the event
in detail in NUREG-1410 titled, "Loss of Offsite AC Power and the Residual
Heat Removal System During Mid-Loop Operations at Vogtle Unit 1 on March 20,
1990." The Vogtle Unit 1 event was initiated when a fuel and lubricants
truck, conducting routine operations in the switchyard, backed into a
support column for a 230 kV feeder which was supplying offsite power to the
Unit. Ensuing events led to the total loss of vital ac power at the plant
and operation in natural circulation while the reactor coolant system was
drained down to mid-loop.
One of the lessons learned from the Vogtle incident was the need for
licensees to develop appropriate programs for controlling vehicular traffic
at their sites. Although the events at the Diablo Canyon, Palo Verde, and
Fermi plants were of less safety significance than the Vogtle event, they
demonstrate that problems associated with inadequate control of vehicles
continue to occur.
This information notice 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 Office of Nuclear
Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contact: N. Fields, NRR
Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015