The 275 canisters produced in fiscal 2012 at the Defense Waste Processing Facility represent the highest yearly number since the facility opened in March 1996, according to Savannah River Remediation, the site’s liquid waste contractor.

The material, left over from Cold War nuclear weapons programs, is stored in 49 underground tanks at the site, two of which were closed in the past year.

The tanks contain sludge with a consistency similar to peanut butter and a caustic material that turns to salt. Although the salt material accounts for much of the volume, the peanut-butter-like sludge is the most radioactive and more dangerous.

That high-level material is “vitrified” in glass and sealed inside steel canisters. At the beginning of 2012, about 3,339 canisters were in storage at SRS, with an eventual goal of producing 7,557 canisters as the remaining waste is processed.

The completed canisters remain stored at SRS. The government’s Yucca Mountain repository in Nevada was long considered a destination for that material, but the Obama administration canceled that project.

The salt solution from the waste tanks is sent to the site’s saltstone production and disposal facility, which processed nearly 1.3 million gallons of decontaminated salt solution during 2012 and disposed of the waste on-site in concrete vaults.

Two more underground tanks are scheduled to close in 2013.