Republican lawmakers in the U.S. Senate are demanding the Obama administration provide scientific and legal evidence to support its decision not to store nuclear waste at the long-planned Yucca Mountain depository in Nevada.

U.S. Energy Secretary Steven Chu testified at a congressional hearing in March that Yucca Mountain was no longer an option for holding radioactive waste from nuclear power plants and weapons complex sites around the country, repeating the position of President Barack Obama.

Republican senators want to know why Chu is against Yucca Mountain, given dozens of studies that show disposing of nuclear waste deep underground is the safest approach and the government has already spent billions of dollars to get the site ready.

Given this history, President Obama's memoranda that science will guide public policy and his commitment to an unprecedented level of openness, we find it difficult to reconcile your statement that Yucca Mountain is 'not an option' made after only six weeks in office, the lawmakers said in a letter to Chu on Wednesday.

Have you discovered, in a few short weeks, research that discredits the scientific work that supports Yucca Mountain, they asked.

The lawmakers said they want a better understanding of Chu's decision making, including the list of scientists who briefed him on the technical and scientific aspects of Yucca as a storage site.

Instead of Yucca, Chu has said the department will establish a blue ribbon panel to develop a comprehensive plan this year to handle the disposal of radioactive wastes.

The department will also consider solidifying liquid radioactive waste that is currently held at 121 locations across the nation, as the government works to develop a permanent solution, Chu has said.

The nuclear industry claims utilities would be reluctant to build more reactors if there is not a central depository to store spent nuclear fuel.

The Nuclear Regulatory Commission has received 17 applications to build 26 new U.S. nuclear reactors and could get five more applications for seven reactors by the end of next year. Each new reactor is expected to cost $6 billion to $8 billion, including financing costs.

The NRC expects electricity will likely be generated by the next new nuclear power reactor in 2016.

(Reporting by Tom Doggett; Editing by David Gregorio)