By Laura Zuckerman
(Reuters) - Government scientists have not been able to replicate a chemical reaction suspected of causing a radiation leak at a U.S. nuclear waste dump in New Mexico, complicating efforts to understand what went wrong, a U.S. Energy Department official said Friday.
The Waste Isolation Pilot Plant, where drums of radioactive refuse from nuclear weapons sites and laboratories are buried in salt caverns 2,100 feet (640 meters) underground, has been shut down since Feb. 14 when at least one drum ruptured.
The mishap near the town of Carlsbad exposed 22 workers at the facility with low levels of radiation and ranked as its worst accident and one of the few blemishes on its safety record since it opened in 1999. The facility is the nation’s only underground repository for so-called transuranic waste.
Shipments from U.S. nuclear labs of tools, rags and other debris contaminated with radioisotopes such as plutonium are on hold indefinitely as scientists probe the accident.
Investigators have said a chemical reaction between nitrate salts and organic kitty litter used as an absorbent generated sufficient heat to melt seals on at least one drum of contaminated sludge, which had originally come from the Los Alamos National Laboratory near Santa Fe.
But experiments conducted by scientists from Los Alamos and other U.S. nuclear labs have failed to reproduce the chemical reaction, and hundreds of drums of similarly packaged nuclear waste are still intact, said Energy Department spokeswoman Lindsey Geisler.
“There’s still a lot we don’t know,” she said.
Managers of the Waste Isolation Pilot Plant have said it may take as long as three years for the facility to be fully operational, complicating disposal of containers of transuranic waste stored above ground at nuclear research complexes such as Los Alamos and Idaho National Laboratory.
Officials at Los Alamos last month notified New Mexico they would not be able to meet a June 30 deadline to remove drums of waste stored on a mesa where they could be threatened by wildfires.
Idaho National Laboratory faces a 2018 deadline to remove drums and boxes of transuranic waste sent to the eastern Idaho desert for storage from a defunct federal nuclear weapons-making plant outside Denver.
Geisler said the Energy Department was reviewing disposal options but she could not provide details.
(Reporting by Laura Zuckerman in Salmon, Idaho, Editing by Alex Dobuzinskis and Ken Wills)