BOISE, Idaho (AP) -- A total of four barrels containing radioactive sludge at an eastern Idaho nuclear site were found to have ruptured, officials said Wednesday, after initially saying earlier this month that one barrel was leaking.
Officials said there were no injuries and no threat to the public, and workers in protective gear have installed a closed-circuit video camera to monitor the situation.
Erik Simpson, a spokesman for U.S. Department of Energy contractor Fluor Idaho, said it appears all four 55-gallon (208-liter) barrels ruptured the same day they had been packed. An alarm on April 11 alerted officials that one barrel ruptured at the 890-square-mile (2,305-square-kilometer) federal site that includes the Idaho National Laboratory.
Simpson said three Idaho National Laboratory firefighters that entered the earthen-floored structure on April 11 to extinguish a smoldering barrel reported other possible breaches, and crews outside heard some of the barrels rupture.
A three-person crew last week entered the structure and confirmed the additional ruptures, Fluor Idaho said.
Simpson said the ruptured barrels contained material sent in other barrels to Idaho in the 1960s. He said those 1960s barrels likely contained fluids and solvents from nuclear weapons production at the Rocky Flats Plant near Denver. He said it's possible the barrels might have originated elsewhere and been shipped to Denver before eventually being sent to Idaho.
The barrels were initially buried in unlined pits in Idaho, but were unearthed as part of a cleanup process at the site. Simpson said a high-tech examination of the unopened barrels found they had unopened containers, and were moved to the earthen-floor structure that's 380 feet (116 meters) long and 165 feet (50 meters) wide.
He said the barrels were emptied, the contents examined, and then repackaged in new barrels on April 11. At least one and possibly all of those newly-packed barrels ruptured later that same day, he said.
He said the facility had successfully processed about 9,500 barrels before the ruptures occurred.
"This had not happened before, and we want to get to the bottom of why this waste was reactive," he said. "We're using a very deliberative process to get to the reason of why this happened."
Whatever was in the barrels reacted in such a way to increase pressure inside the barrels to the point of causing the ruptures. Simpson said there are no immediate theories, but everything from the contents to the process of repackaging will be examined.
The barrels were eventually going to be shipped to the Waste Isolation Pilot Plant near Carlsbad, New Mexico, but hadn't yet gone through a certification process to allow that to occur, Simpson said.
At the underground repository in 2014, a barrel of radioactive waste ruptured after being inappropriately packed at Los Alamos National Laboratory. The waste had been mixed with organic cat litter to absorb moisture, resulting in a chemical reaction.
The incident resulted in a radiation release that forced the closure of the repository for nearly three years and prompted an expensive recovery effort and a major policy overhaul for handling Cold War-era waste.
Simpson said shipments of waste from Idaho that has gone through the certification process have resumed, with loads of about 16 barrels heading to New Mexico four to six times a week.
The sprawling Idaho site in high-desert sagebrush steppe sits atop the giant Eastern Snake Plain Aquifer that's used by cities for drinking water and farmers for irrigation.
The site has been used for nuclear waste disposal and storage beginning in the 1950s. The federal government has been cleaning it up following court battles and several agreements with Idaho in the 1990s amid concerns by state officials that Idaho was becoming the nation's nuclear waste dump.
The Energy Department has already missed several deadlines under those agreements involving moving nuclear waste out of Idaho and has paid about $3.5 million in fines.
Idaho Attorney General Lawrence Wasden on Wednesday declined to comment.