Two Pacific Northwest National Laboratory employees inhaled small amounts of radioactive tritium while doing work in the Hanford 300 Area last month.
The incident was reported in a recently released weekly report by the Defense Nuclear Facilities Safety Board.
The workers' radiological exposure was less than 5 millirem, providing about the same radiation exposure as a cross-country airline flight, said PNNL spokesman Greg Koller. It also was only a fraction of PNNL's annual limit for workplace radiation exposure of 500 millirem per year.
Three staff members were working with tritium in a fume hood in the Radiochemical Processing Laboratory just north of Richland as part of a PNNL program supporting work to produce tritium for the nation's nuclear weapons program.
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Tritium inadvertently spread outside the fume hood, including along the routes to radiological trash disposal.
"Contamination levels on the floor immediately adjacent to the fume hood were well above the threshold for a High Contamination Area," according to the defense board staff report.
Two workers found contamination on their skin and personal clothing and had positive nasal smears, according to the report. The third worker had contamination on his clothing only.
The results of urinalyses, plus smear samples from noses, exposed skin and shoes, showed the workers were contaminated with minor amounts of tritium and that the exposures presented no adverse health effects, Koller said.
PNNL decontaminated the area and the workers were cleared to return to work.
The event is still under investigation and it's too soon to say if any changes will be made to laboratory procedures, Koller said.