Edward Sproat, head of the department's civilian nuclear waste program, said the 77,000-ton limit Congress put on the capacity of the proposed Yucca waste dump will fall far short of what will be needed and has to be expanded, or another dump built elsewhere in the country.
The future of the Yucca Mountain project is anything but certain.
President-elect Obama has said he doesn't believe the desert site 90 miles northwest of Las Vegas is suitable for keeping highly radioactive used reactor fuel up to a million years and believes other options should be explored.
Senate Majority Leader Harry Reid, D-Nev., has vowed to block the project.
Sproat, addressing a conference on nuclear waste, said the Energy Department will send a report to Congress in the coming weeks maintaining that the Yucca site will need to be expanded. He said within two years the amount of waste produced by the country's 104 nuclear power plants plus defense waste will exceed 77,000 tons. Yucca Mountain is not projected to be opened before 2020 at the earliest.
"We've done enough testing around the site to know that we can make it bigger," Sproat told reporters. But he said Congress will have to remove the capacity limit now in place.
If the limit is not removed, said Sproat, the report will urge Congress to give the department authority to begin looking for and evaluating a second nuclear waste repository elsewhere in the country. The law currently prohibits any such search, said Sproat.
The Nuclear Regulatory Commission must issue a license to build the underground waste dump at Yucca Mountain, a ridge of volcanic rock in the Nevada desert not far from where the government exploded numerous nuclear bombs during the Cold War era. The NRC has four years to make a decision.
Sproat acknowledged that the next president could withdraw the license application now before the NRC. But he said that would throw "the whole process... into a lot of confusion and uncertainty" since Congress also has prohibited the government from considering any place other than the Nevada site.
An alternative could be a temporary above-ground repository, possibly on a federal site.
Sproat said the report, which has been completed, will say either expand Yucca Mountain, begin the process of finding a second repository, or "don't do anything and let this whole thing just sit for another 10 to 20 years and see what happens." He said the department would prefer the go-ahead for a larger Yucca site.
"We do think there is room for additional storage at Yucca. How much, we're not clear on," said Sproat.
Allison Macfarlane, a geologist and associate professor for environmental science and policy at George Mason University who has studied the Yucca Mountain area, said there are clear limits to Yucca expansion because of nearby earthquake fault lines and potential volcanic activity.
"There are geological constraints on Yucca Mountain. It is not an endless sink for nuclear waste," said Macfarlane at the conference sponsored by the Center for Strategic and International Studies.