The Callaway nuclear plant is expected to remain shut down for several days while Ameren Missouri workers perform tests and repair damage from a small fire Friday night.
The blaze was caused by an electrical arc along the main power conduit from the power-generating turbine leading to electrical distribution power lines, a plant engineer said Monday.
Cleveland Reasoner, vice president of engineering at the Callaway Energy Center, said the small fire, reported at 11:49 p.m. Friday, at no time caused a threat to the public.
No one was injured in the blaze, which was brought under control in a few minutes by the plant's fire brigade.
Reasoner said the arc occurred just outside the turbine building along a large metal bar that conducts electricity generated by the plant's turbine to electric power lines. He said the bar has a huge electrical charge pushing all electricity generated from the plant.
The arc or spark from the large metal bar jumped up to the metal ductwork, and traveled along the ductwork inside the turbine building, causing a fire when insulation along the ductwork ignited.
The arc flash from the short-circuit tripped the plant's main circuit breaker, which stopped the flow of all electricity from the plant. This in turn caused an automatic shutdown of the nuclear reactor as a safety precaution.
"We will be out of service for several days at least in order to disassemble and repair the equipment," Reasoner said.
While out of service, the energy the nuclear plant produces will be replaced by other Ameren Missouri energy centers.
Two inspectors of the U.S. Nuclear Regulator Commission (NRC) are stationed permanently at the plant and will conduct an investigation to determine what caused the the electrical arc.
The fire caused the plant to shut down as part of multiple safety layers required by the NRC. Those regulations require the plant to declare an "unusual event."
The term "unusual event" was established by the NRC to describe a relatively minor occurrence at a nuclear plant that could reduce the overall level of safety. During such an event, no public action is advised or necessary.