IDAHO FALLS — U.S. Department of Energy researchers are investigating the cause and complications of a November accident that exposed 16 workers at the Idaho National Laboratory to radiation.

On Nov. 8, workers in the Materials and Fuels Complex were exposed to a fuel plate containing plutonium. At least one worker inhaled plutonium when co-workers opened a small container and cut through a plastic sheet, exposing the plate.

INL Spokeswoman Misty Benjamin said all 16 employees are back at work and undergoing consistent monitoring.

Energy Department investigators spent about a month on site, but are now back in Washington, D.C., preparing a report that is due next month, The Post Register reported.

Benjamin did not disclose details about the strength and location of the dose each worker received during the incident. But she said so far, none of the workers have experienced any severe health problems as a result of the exposure

The lone employee who tested positive for radioactive material in the lungs had breathed in Americium-241, an isotope commonly found in nuclear waste.

At the time of the exposure, workers were recovering the fuel so it could be shipped to a U.S. Department of Energy facility in an undisclosed state. They had on lab coats and gloves but not respiratory gear.

Lab officials suspect the stainless steel cladding that surrounded the plutonium was damaged years ago, beginning a slow-but-steady process of plutonium oxidation that led to the exposure. When workers opened an aluminum box that housed the fuel plates and cut away plastic wrapping, they noticed several grains of powder that escaped.