The Associated Press

OAK RIDGE, Tenn. — Uranium chips at the Y-12 nuclear weapons plant spontaneously caught fire Thursday and the small blaze was quickly extinguished, officials said.

No workers were injured or contaminated by radiation and no damage was done to the building, said Bill Wilburn, spokesman for BWXT Y-12, the managing contractor for the Department of Energy facility. The building, where about 150 people work, was evacuated.

"The fire occurred as workers were transferring uranium chips from one container to another and the chips were exposed to air," Wilburn said.

Employees extinguished the fire with powdered graphite before the plant's fire department arrived. An investigation was under way.

The Y-12 plant makes parts from highly enriched uranium for every warhead in the U.S. nuclear arsenal. It also is the country's primary storehouse for bomb-grade uranium.

Fires occur periodically at the plant. One happened Dec. 15 when a "alcohol-moistened cloth ignited during a spark-producing task to separate parts," according to the Defense Nuclear Facilities Safety Board.

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Bob Alvarez, a former DOE adviser, released a report last year saying there had been at least 23 fires and explosions involving nuclear and non-nuclear materials at Y-12 since 1992.