Fire broke out at around 8:40 p.m. on the first floor of a maintenance facility of an experimental fast-breeder reactor. Firefighters were mobilized and the fire was contained around 10:25 p.m., no one was hurt and the possibility of a radioactive leak or fire spreading to the reactor has been ruled out. A vinyl sheet used to cover the tank work site was damaged. The maintenance facility is a square concrete structure. It accommodates maintenance equipment to clean pumps used in the reactor. Two hours before the fire, personnel at the facility had been cleaning equipment used in the reactor. A sodium cleansing tank inside the building is believed to be the source of the fire (spontaneous ignition of Na in air).