By Laura Zuckerman
March 5 (Reuters) - Workers who initially tested positive for radiation exposure after an accidental release at a nuclear waste site in New Mexico are unlikely to experience any ill health effects, site managers said on Wednesday.
Early tests of workers - who were above ground at the facility when unsafe levels of radiation were detected last month in an underground salt formation where nuclear waste is stored - showed 13 had inhaled radioactive elements at low levels, officials at the U.S. Department of Energy facility said.
But further testing of the 13 workers have shown no further signs of contamination by radioisotopes such as plutonium, and they are thus unlikely to experience any health effects, managers at the facility said on Wednesday.
"Follow-up testing of employees who were exposed to airborne radioactive material during the February 14 radiation release at the Waste Isolation Pilot Plant shows exposure levels were extremely low and the employees are unlikely to experience any health effects as a result," managers said in a statement.
Samples have been sent to the federal Centers for Disease Control for validation, and testing continues for dozens of additional employees who worked above ground at the complex in the Chihuahuan Desert the day after the accident, said Farok Sharif, president of Nuclear Waste Partnership, the contractor that runs the repository.
The radiation release half a mile underground set off alarms on air monitors and automatically triggered a ventilation system designed to filter 99.97 percent of airborne radioactive particles and prevent them from escaping above ground. No workers were below ground when the accident happened.
Testing of air in and around the facility in the days after the mishap revealed elevated radiation levels but none that were considered harmful to human health or the environment, officials said.
It was the first such mishap since the site opened in 1999 to store so-called transuranic waste from U.S. nuclear laboratories and weapons sites. The items include equipment and clothing contaminated with plutonium or other radioisotopes heavier than uranium. Particles emitted from the decay of those elements can harm humans if inhaled or ingested.
Joe Franco, manager of the Energy Department office in Carlsbad that oversees the repository, said in a statement that ongoing air and environmental monitoring "is showing no significant off-site contamination."
Shipments to the site were suspended after Feb. 5, when a truck hauling salt in the underground formation caught fire for reasons still not determined. Radiation levels many times higher than those considered safe were detected more than a week later in a separate salt chamber where drums of waste are entombed.
No one has been underground since the leak was detected and it was unclear when the facility would resume operations. Plans are under way to send monitoring devices below ground to test air quality in advance of dispatching investigators, Franco said.
The leak may have been caused by falling slabs of salt that created a breach of a drum or drums containing waste, officials have said. (Editing by Cynthia Johnston and Ken Wills)