Officials acknowledge they are in uncharted territory in responding to something that has never happened since the Waste Isolation Pilot Plant opened in 1999. The site is important to US efforts to clean up decades of Cold War-era waste, and administrators are eager to resume operations once they are convinced it's safe to do so.
The first major step in finding out what caused the radiation release happened over the weekend as crews - covered from head to toe in special blue protective suits and booties slowly lowered a bundle of air and gas monitoring machines into the repository's air intake system and its salt shaft.
Enclosed mostly in plastic and sealed with tape, the battery-powered monitors fed about an hour's worth of information about the air in the shafts to another machine that logged the data. The monitors detected no radioactive contamination.
Radiation levels in the underground corridors and waste storage areas are unknown, plant spokesman Donavan Mager said.
Once plans for entering the repository are finalized, Mager said crews will practice doing dry runs first. They will also be outfitted in protective gear.