BOISE, Idaho - Decades-old plutonium powder that escaped its damaged shell is the main suspect behind a serious incident at the Idaho National Laboratory that exposed 16 workers to potentially harmful radiation.
U.S. Department of Energy officials and private contractors said Wednesday they're closely monitoring two workers at the lab in the eastern Idaho desert who had radioactive material in their lungs.
The 16 employees underwent "initial decontamination" and went home following the incident Tuesday, but they've returned to the lab's medical facilities for additional monitoring and treatment.
They are being offered IV treatments with calcium or zinc, which speeds the elimination of plutonium from the body.
Lab health director Sharon Dossett says none of the exposed workers are exhibiting outward symptoms of radiological exposure, so far.
Still, according to lab officials, it may be weeks before the extent of the workers' exposure is known. The health impacts of exposure vary depending on the type of plutonium.
If the plutonium is released quickly, it's unlikely to cause harm. If it's trapped in places like the lungs, however, it can lead to cell damage, the lab said.
Deputy lab director David Hill suspects stainless steel cladding that surrounded plutonium fuel from the 1970s was damaged, beginning a slow-but-steady process of plutonium oxidation that led to the exposure.
The laboratory has designed and constructed 52 reactors since its founding in 1949 in the desert west of Idaho Falls.
There's still active research at the facility, but hundreds of workers are also cleaning up radioactive waste that's left over from more than 60 years of activities, including at the Zero Power Physics Reactor.
The employees were working inside the reactor Tuesday afternoon when the container holding plutonium was opened. Investigators were at the site trying to determine what went wrong.
There was no evidence that radiation was released outside the facility, and there was no risk to the public or the environment, the laboratory said in a statement.
Before the Zero Power Physics Reactor was decommissioned in 1992, researchers used it to build and test nuclear reactors more cheaply than constructing an entire power plant.
Last year, cleanup workers had finished removing millions of pounds of steel and other materials that made up the reactor core, but its shell remains along with plutonium fuel that once powered the reactor.