DOE officials say aging pads are an element of a "thermal loading" strategy to manage the intense heat generated by decaying nuclear fuel as it would be placed in Yucca Mountain.

But the above-ground activities at the site have drawn protests from Nevada officials who say the amount of nuclear waste the government plans to keep above ground constitutes illegal onsite storage.

In a presentation Tuesday, Christopher Kouts, waste management director for Yucca Mountain, told members of a Nuclear Regulatory Commission advisory board that DOE is computer-modeling the aging pads and operations of industrial waste-handling facilities at the site 100 miles northwest of Las Vegas.

Kouts also announced the Energy Department has crossed a threshold in creating all-purpose waste canisters for the Yucca program.

DOE has finalized specifications for the canisters, which would be used to ship waste assemblies, store them at the site, and bury them underground, Kouts said. About 7,500 canisters would be needed to fill Yucca Mountain to its 77,000 ton capacity.

The containers are nicknamed "TAD" canisters, an acronym for "transport, aging, disposal." They would be constructed of borated stainless steel, would be between 15.5 feet and 17.5 feet long with a diameter of 66.5 inches. They would weigh 54.25 tons fully loaded.

"We did quite a bit of homework, and hopefully we've developed a specification that will meet our needs," Kouts said.

DOE officials plan to invite vendors to design canisters to the specifications and then proceed to fabrication. Kouts said the canisters may be available by 2012.

About 90 percent of nuclear waste would arrive at Yucca in TADs, Kouts said. Damaged waste and other special materials would be handled separately.

Once DOE ramps up Yucca operations, it expects to receive close to 350 canisters annually at the site, while emplacing 200 to 250 canisters in the repository, according to calculations Kouts presented to the NRC Advisory Committee on Nuclear Waste.

The difference, Kouts said, would be steered to aging pads or utilized in processing facilities onsite. Each canister would contain eight to nine tons of nuclear waste, according to DOE spokesman Allen Benson.

The state of Nevada in December filed a petition with the Nuclear Regulatory Commission challenging the DOE "thermal loading" strategy and asking that the amount of waste allowed at the Yucca site be limited to no more than 5,000 tons.

State officials maintain the amount of waste DOE envisions onsite amounts to "interim storage" that Congress outlawed at the Yucca site.

Bob Loux, director of the Nevada Agency for Nuclear Projects, said Tuesday the state awaits a response from NRC.

"Assuming they deny that, we would go to District Court and claim this is an illegal facility," Loux said.

The Associated Press contributed to this story