UPDATE 3/10 7a: The U.S. Department of Energy says new air testing in the nation's only underground nuclear repository shows no detectable radioactive contamination from a leak last month.
Officials at the Waste Isolation Pilot Plant near Carlsbad said Sunday that instruments used to measure air quality and radioactivity were sent underground Friday and Saturday in the first step to resuming operations at the plant.
They say initial results indicate no contamination in the air or on the measuring equipment.
Federal officials say four more employees have tested positive for low levels of contamination, adding to the 13 tested immediately after the leak.
Authorities say none should suffer health effects.
WIPP officials say they may send personnel into the mine next week.
Sensors alerted officials to a release of radiation on Feb. 14.
Officials at the nation's only underground nuclear waste dump in southern New Mexico sent in a probe Friday after a radiation leak in mid-February exposed workers and caused the facility to shut down.
The leak was detected thousands of feet underground at the Waste Isolation Pilot Plant near Carlsbad where the nation stores waste from nuclear weapons production.
The facility’s filtration system kicked on to prevent radiation from being released aboveground. But within days, elevated levels in the air were detected a half-mile away.
The Department of Energy's Joe Franco says researchers calculated where the particles might have gone.
“We sent a team out there,” Franco said, “in protective equipment to go take some samples along the main path routes that were identified.” He says tests on plant and soil samples found no contamination.
“Yes, it's very small amounts,” nuclear watchdog Don Hancock of the Southwest Research and Information Center said, “but there is continuing radioactivity in the underground that can come out, even through the filter system.” Hancock says he wants to know exactly how many employees were exposed and why some weren’t told about the leak before they arrived to work their shifts at the facility.
Researchers say nearby radiation readings are far below safety levels set by the Environmental Protection Agency. Thirteen workers tested positive for exposure, but plant officials say a second round of tests show these workers are unlikely to get sick.
Sending a probe to explore the underground plant should allow officials to determine when it’s safe to send down crews to find out what caused the leak and when the plant can re-open.