A Department of Energy plan to reclassify some of the country's radioactive waste to lesser threat levels in order to save time and money is angering environmental groups and raising questions among experts.

Last week, the Energy Department put into place its new interpretation for high-level radioactive waste, saying that the updated definition will allow the agency to more easily move less hazardous waste from old nuclear weapons facilities where it has languished without a permanent disposal solution.

The agency's previous classification efforts managed hazardous waste based on how it was produced instead of its radioactivity. For example, the use of uranium fuel in a nuclear reactor produces high-level radioactive waste. Classifications for the waste determine disposal methods, which can vary in things like how deeply such material is buried in the ground or how thick the protective material in which it is encased.

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The Energy Department said its past approach cost billions of dollars and led to decades of delays.

"Recognizing this failure, this Administration is proposing a responsible, results-driven solution that will finally open potential avenues for the safe treatment and removal of the lower level waste currently housed in three states," the Energy Department's Undersecretary for Science Paul Dabbar said.

By changing the process to allow for some high-level radioactive waste to be categorized as low-level, the agency said it will be able to start moving waste that has been trapped in Energy Department facilities in Washington state, South Carolina and Idaho.

Management of high-level radioactive waste has effectively been at a standstill as Nevada's Yucca Mountain, which houses a deep geological repository storage facility, awaits proper licensing.

Yucca Mountain has suffered from "technical and political disagreement" for decades, says Rod Ewing, a professor in nuclear security at Stanford University.

"There's an understandable pressure to do something with at least some of the waste," Ewing says.

Under the proposal, waste newly deemed less harmful that is currently housed at Hanford Nuclear Reservation in Washington state, the Savannah River Plant in South Carolina and the Idaho National Laboratory could be removed for disposal.

But the Natural Resources Defense Council says reclassifying the waste is akin to the Energy Department giving itself the authority to declare victory and abandon cleanup at these sites.

"The Trump administration is moving to fundamentally alter more than 50 years of national consensus on how the most toxic and radioactive waste in the world is managed and ultimately disposed of," Geoff Fettus, a senior attorney at the environmental group, said in a statement. "No matter what they call it, this waste needs a permanent, well-protected disposal option to guard it for generations to come."

Washington Gov. Jay Inslee said he would not stop state efforts to clean up the Hanford site to a higher standard and challenged the legality of the federal change.

"By taking this action, the administration seeks to cut out state input and move towards disposal options of their choosing, including those already deemed to be unsafe by their own assessments and in violation of the existing legally binding agreement," he said. "We will consider all options to stop this reckless and dangerous action."

Experts agreed that reclassification is a valid issue for the Energy Department to examine but had questions about the agency's process.

"In principle, it does make sense to try to tie these definitions more closely to hazards," says Edwin Lyman, a senior scientist at the Union of Concerned Scientists. However, the agency "would have to do a much more rigorous job defining their methodology," he says.

Determining the class of radioactive waste involves assessments that can be "highly controversial," Ewing says.

The assessment process can allow for some leeway, which "opens the door for monkey business," Lyman says.

The Energy Department paired its announcement with a notice that the agency is starting an environmental impact analysis for an alternative disposal method for low-level radioactive waste at the Savannah River Site.

Tom Clements, the director of non-profit public interest group Savannah River Site Watch, pushed back against the agency's move.