Sen. James Inhofe, R-Okla., posed the question in a letter sent to Chu on Wednesday. It was signed by 16 other Republican senators.

Among the signers was Sen. John McCain of Arizona, who has said he is preparing amendments that would rebate billions of dollars from a repository construction fund back to consumers if Obama scraps the Yucca site.

The letter and McCain's planned legislation are parts of a resistance effort by nuclear power supporters who have expressed chagrin over Obama's energy policies. The administration has indicated that funding for the Yucca project would be cut to a level just high enough to keep it breathing while a blue ribbon panel is convened to come up with alternatives.

Matt Dempsey, Inhofe's communications director, said the letter was meant to underscore that Obama's nuclear waste policy was being driven by politics, disregarding research that has been completed and ongoing evaluations being conducted by the Nuclear Regulatory Commission.

An Energy Department spokeswoman said the senators will get a response to their letter.

"But Secretary Chu has made clear that nuclear energy needs to be part of America's energy mix and he is committed to finding a safe, responsible solution to our nuclear waste needs," Stephanie Mueller said.

A spokesman for Harry Reid, D-Nev., a Yucca Mountain critic who advises Obama on nuclear waste, said the letter was an act of desperation by Yucca Mountain supporters.

"Everyone knows the dump is not going to be built, and this is another last ditch effort," Reid spokesman Jon Summers said. Reid also questions why Republican budget hawks concerned with federal spending want to continue sending money to the project, Summers said.

Reid and other repository critics contend that years of research have turned up flaws in the mountain 100 miles northwest of Las Vegas that will endanger public health over time. They argue that the government has acted to work around the problems rather than acknowledge the site is unsuitable.

They also argue that transporting radioactive spent fuel to Nevada carries undue risks, a point that has been debated by government and nuclear industry experts.

In their letter, the Republican senators asked Chu to explain his conclusion that Yucca Mountain "is not an option," whether it was backed by specific research, and who advised him on the matter.

They asked whether he consulted with the Navy, whose used nuclear fuel has been planned for disposal at Yucca Mountain, and with governors of states that are holding military waste also awaiting disposal.

Contact Stephens Washington Bureau Chief Steve Tetreault at stetreault@stephensmedia.com or 202-783-1760.