No radiation leaked during the fire on a Finish nuclear station on Thursday. All the workers are safe but reactor was shut down.
The small fire, on a turbine bearing, was "quickly put out with a hand-held extinguisher," said Reijo Sundell, director of operations at the Olkiluoto plant.
"The fire was very small, on an area of about a 1 square centimeter (0.16 square inches), but we shut down the reactor immediately to be on the safe side," Sundell said. "A fire is always exceptional, and we want to find out the cause of the incident."
"It posed no danger to anyone," he said, adding that the shutdown likely would last a few hours.
Olkiluoto, situated 250 kilometers (155 miles) northwest of Helsinki, has two 860-megawatt reactors. It is also the construction site of the country's fifth nuclear plant - a 1,600-megwatt reactor - expected to be online by 2011.