SALMON, Idaho At least six workers were contaminated by low-level plutonium radiation and 11 others were exposed on Tuesday at a U.S. nuclear research lab in Idaho, but the public was not at risk, the government said.
The mishap at the Idaho National Laboratory occurred inside a deactivated reactor housed in a facility used for remotely handling, processing and examining spent nuclear fuel, radioactive waste and other irradiated materials, the lab said in a series of statements.
The so-called Materials and Fuels Complex is located near the edge of the U.S. Energy Department's sprawling 890-square-mile laboratory site in the high desert in eastern Idaho about 38 miles from the city of Idaho Falls.
But lab bulletins on the mishap, believed to be the most serious accident at the site in at least four years, said there was no evidence of a release of radiation outside the facility, and "there is no risk to the public or environment."
A total of 17 technicians, all employees of lab contractor Battelle Energy Alliance, were working inside the decommissioned research reactor when "a container was opened for normal, scheduled work, resulting in low-level worker exposure to plutonium," the lab said.
There were no immediate details from the lab on the precise cause or nature of the radiation release, such as whether it resulted from an equipment malfunction or human error.
Lab spokesman Earl Johnson said the exposed workers were engaged in an activity and were in an area that required no special protective shielding.
"We certainly didn't expect this to happen," he said, adding that radiation-control technicians monitoring the area detected the low-level release.
The contamination was confined to the room where it was detected, and the room was evacuated and sealed. Workers elsewhere in the reactor building were also evacuated as a precaution, officials said.
FULL EXTENT OF EXPOSURE TO BE DETERMINED
The exposed workers underwent initial decontamination procedures at the complex before they were taken to a medical facility elsewhere on lab grounds for further evaluation, the lab said.
Six of those exposed initially tested positive for low levels of contamination detected on their skin and clothing, Johnson said. All 17 were undergoing full-body scans to determine how much of a radiation dose they may have received, the lab said.
The workers were offered treatments designed to speed their bodies' elimination of any contaminants ingested or inhaled, including intravenous fluids with calcium or zinc to bind radioactive particles before expelling them from the body.
Details about the condition of the workers were not immediately available and the lab said it may be weeks before the full extent of exposure and contamination is known. The effects of radiation worsen the longer radioactive material remains in the body.
"If it is trapped -- for example in the lungs -- it has the potential to lead to damage to the body's cells," the lab said.
Johnson said the "zero power physics reactor" where the accident occurred was decommissioned in 1992 and had been used to study and test technology for space and commercial nuclear reactors. The plutonium at issue in the accident was contained in leftover reactor fuel, he said.
Some 6,000 employees and contractors work at the Idaho National Laboratory, the Energy Department's leading facility for nuclear reactor technology. It opened in 1949 as a national reactor testing station.
According to lab records, Tuesday's incident appeared to be the most serious accident at the lab since June 2007, when a worker was treated for minor burns and smoke inhalation from a small laboratory fire, though no radiation release was reported in connection with that mishap.
It was too early to say how serious Tuesday's accident was compared to previous mishaps "since we don't yet know what the consequences of the accident will be," said Liz Woodruff, head of a private, nonprofit nuclear watchdog group in Idaho called the Snake River Alliance.
But she said: "These are a lot of workers."
According to lab officials, the worst accident at the laboratory occurred in 1961, when three workers were killed in a reactor explosion there.
(Reporting by Laura Zuckerman; Writing by Steve Gorman; Editing by Cynthia Johnston and Jerry Norton)