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.
Explore further: Radiation leak detected at New Mexico nuclear plant