Officials at the Idaho National Laboratory said Wednesday that they had confirmed that at least two workers suffered internal exposure to plutonium and 14 others may have been exposed in an accident at the facility Tuesday afternoon.
A lung scan showed a decay product of plutonium embedded in the two workers' tissue. Other workers had confirmed contamination of their skin, which could indicate internal exposure. Four of the workers were treated with drugs to flush their systems of radioactive material.
So far, health officials at the lab said they could not determine the doses that any of the workers received.
Lab officials said they could not rule out that 16 workers had been exposed in an area known as the zero power physics reactor at the site, located 38 miles from Idaho Falls. On Tuesday, the lab said 17 workers had potentially been exposed.
Plutonium emits alpha radiation that does not penetrate the body from the outside, but inhaling it can cause long-term exposure that can increase the risk of cancer.
The Energy Department is investigating the incident. Deputy Lab Director David Hill acknowledged that some type of safety breakdown had occurred, for which the lab would have to take responsibility.
The accident occurred as workers were preparing to ship plutonium fuel to Nevada. Lab officials said they believe stainless steel cladding around the plutonium may have failed during the last three decades and allowed the fuel to oxidize into a powder that dispersed in the room.
Officials said a worker removed a fuel plate from a container and found it wrapped in plastic. Senior lab officials authorized the worker by telephone to remove the plastic. Grains of material fell away, indicating some type of failure had occurred and the room was evacuated.
Arjun Makhijani, president of the Institute for Energy and Environmental Research in Takoma Park, Md., said a warning about using plastic to wrap radioactive materials was issued by the Defense Nuclear Facilities Safety Board in 1994, noting it could cause the emission of hydrogen gas from the plastic. The gas could have explained the failure of the steel cladding, Makhijani said.
But the Idaho reactor is part of the Energy Department's civilian nuclear reactor program, not the defense portion of its mission, and whether the safety board's findings were widely shared is unknown.
Hill said he considers any exposure extremely serious, but did not want to compare it to other accidents in the Energy Department lab system. Makhijani called a single accident exposing 16 people "extremely rare" and said it most likely will point to a serious lapse in safety.
-- Ralph Vartabedian
Photo: The Idaho National Laboratory. Credit: Idaho National Laboratory