Fire broke out Friday at the world's second-largest fast-breeder nuclear reactor, in Russia's Ural Mountains, but officials said that radiation levels are normal and that there were no injuries.
Smoke poured from the Beloyarsk reactor, 25 miles north of Yekaterinburg, but firefighters eventually put out the blaze, the Interfax news agency said, quoting the regional civil defense unit.
Russia's nuclear plants, now funded by some government aid but mostly by consumers, face a money shortage that often means they take shortcuts in safety measures, environmentalists and nuclear officials charge.
Last year, the government recorded about 20,000 violations of safety rules. Many were blamed on the shortfall in revenue since Russia began market reforms in 1992.
The fire Friday at the Beloyarsk reactor was caused by leaking liquid sodium, said Hans-Friedrich Meyer, a spokesman for the International Atomic Energy Agency.
Liquid sodium is used as a cooling agent to transfer heat away from the reactor and to generate steam for the turbines. It burns easily when it comes in contact with water.
A preliminary evaluation put the accident between zero and one on the International Nuclear Events Scale, meaning "no influence on the environment," Meyer said.