By Laura Zuckerman
Feb 27 (Reuters) - Dozens more workers at a nuclear waste site in New Mexico will be tested for contamination after 13 employees were found to have inhaled radioactive particles from an accidental radiation release this month, managers said on Thursday.
An air-monitoring system at the underground Waste Isolation Pilot Project tripped an alarm on Feb. 14 indicating high levels of radiation in the ancient salt formation in southeastern New Mexico near Carlsbad where radioactive waste is stored.
It was the first such mishap at the facility since it opened in 1999 to store so-called transuranic waste shipped from U.S. nuclear laboratories and weapons sites. The items include discarded machinery and clothing contaminated with plutonium or other radioisotopes heavier than uranium.
Particles emitted from the decay of those elements can harm humans if ingested or inhaled and the effects of radiation worsen the longer radioactive material remains in the body.
No workers were below ground when the release occurred and 139 employees working above ground at the Department of Energy complex were told to shelter in place. They were released the next day after testing of their skin and clothing showed no contamination.
But results released on Wednesday from preliminary testing of biological samples lifted from the workers showed that 13 of them had been contaminated with manmade radioisotopes like americium-241, which is associated with nuclear weapons making.
The findings prompted Energy Department officials and the contractor that runs the repository, Nuclear Waste Partnership LLC, to expand testing to include more employees working above ground at the site on the morning after the accident.
They were not advised at the time to wear protective clothing or self-contained breathing equipment, plant managers said.
"We are requesting biological samples to determine if they were also affected," Nuclear Waste Partnership President and Project Manager Farok Sharif told a news conference on Thursday.
Sharif declined to say how much of a radiation dose the workers who tested positive for exposure may have received, citing privacy. But he said experts had recommended against a chemical therapy designed to rid the body of radioactive materials because "exposure numbers are so low."
Testing of additional workers and further testing of those with known exposure is under way, and it will be weeks before the full extent of exposure is known, he said.
Monitoring of air in and around the facility has shown elevated radiation but no threat to human health or the environment, he said.
Managers said a possible cause of the accident was the breach of drums containing radioactive materials in a waste-disposal area below ground. It was not known how the breach occurred and when operations at the plant might resume.
The facility in the Chihuahuan Desert normally receives up to 6,000 cubic meters of nuclear waste a year and employs more than 800 government workers and contractors. (Editing by Cynthia Johnston and Cynthia Osterman)