The Nuclear Regulatory Commission says six workers at a Wyoming uranium mine inhaled the radioactive element while cleaning up a spill inside a building.
The federal agency alleges the workers' urine afterward tested positive for uranium.
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The spill and cleanup of 1,500 pounds of yellowcake happened just over a year ago at the remote Lost Creek uranium mine in southern Wyoming. Yellowcake is a precursor of enriched uranium.
The regulatory commission issued a violation notice Nov. 14 against mine owner Ur-Energy (YOU'-are Energy) for failing to issue a permit to clean up the spill.
Ur-Energy President Wayne Heili said Friday the workers' exposures were nowhere near their annual dose limits, and they had no ill effects.
He says mine officials didn't stop to complete paperwork before cleaning up the spill.