"Some of us thought certain ways and others thought other ways, and we didn't make a whole lot of progress. It is a pretty contentious issue," said Allison Macfarlane, an associate professor of environmental science at George Mason University who believes the Nevada site may not be fitting.

"We just recognized the facts, which were that the project has continued to miss its schedule," said Paul Genoa, policy development director for the Nuclear Energy Institute, which favors the site.

The group members agreed that a deep underground geologic repository was the best option for long-term nuclear waste disposal, and that Finland appears on track to build the first.

The Scandinavian nation, which has four operating reactors and is building two others, is excavating a repository on Olkiluoto, an island off its west coast.

As for Yucca Mountain, the group noted the project could end up 20 years behind schedule. Under the latest Energy Department "best achievable" timeline, the repository could begin receiving waste in 2017, although DOE officials concede that 2020 or 2021 is more likely.

Even at that, the report said, more legal challenges may be likely from the state of Nevada and environmental groups that oppose the site.

Experts confirmed that the legal capacity of a Yucca repository will be smaller than the amount of spent fuel expected to be produced from currently operating reactors. They did not opine whether the Nevada site capacity should be expanded.