Energy Department officials have said they plan to negotiate "incentives" for utilities to accept the "transportation, aging and disposal," or TAD, containers that could be adapted for shipping highly radioactive spent fuel and eventually burying it in the repository planned for 100 miles northwest of Las Vegas.

"The utilities see the political environment, and they are like, what if I go two years and load TADs and then all of a sudden Yucca Mountain is not going to happen?" Cummings said. "I will have a TAD that is Yucca Mountain-approved, but there is no Yucca Mountain to send it to."

Cummings, who is Holtec's manager of DOE programs, made the comments following a presentation to the Advisory Committee on Nuclear Waste and Materials, a panel that advises the Nuclear Regulatory Commission on Yucca Mountain technical matters.

"Incentives from DOE will dictate whether TADs are implemented," Cummings said in his presentation.

Getting nuclear power companies to accept the TAD canisters illustrates yet another challenge facing the Department of Energy as it pushes to license a Yucca Mountain repository. The DOE, on its Web site, maintains the TADs will be "simpler, safer and more cost-effective," but it has yet to persuade the utilities to buy into them.

Cummings said the most significant concern among utilities is that the TADs would be smaller than the containers they now use for on-site nuclear waste storage. More casks would need to be loaded, more time would be needed to load more casks, and "more casks mean more cost."

Utilities "want to see real progress being made," Cummings said. "I think DOE is getting there, but there is still some concern among utilities."

About 7,500 canisters would be needed to fill Yucca Mountain to its 70,000 metric ton capacity, DOE officials have said. 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, and weigh 54.25 tons fully loaded.

"The TADs will certainly work," DOE spokesman Allen Benson said.

As for whether a repository will be open to accept them, "we are on schedule to submit a license application to the NRC which includes the TADs," he said. The DOE has set a June 30, 2008, application goal.

Holtec is one of four companies working on TAD designs for the Department of Energy.

The New Jersey-based firm is trying to interest DOE and the Nuclear Regulatory Commission on a design that would allow nuclear waste awaiting final burial at Yucca Mountain to be stored temporarily in below-surface boreholes rather than on more conventional above-ground pads.

Cummings said such a layout would better shield waste canisters from earthquakes and from airplane or missile crashes, and would require less space at the site.

"We brought that to DOE and said we think it would be good for the repository site from a technical basis," he said. The DOE has yet to comment.

When Cummings began talking about politics surrounding Yucca Mountain and the opposition from Senate Majority Leader Harry Reid, D-Nev., the committee chairman, Michael T. Ryan, cut him off.

"I want to remind you this is a technical committee," Ryan said. "Move along."