In 2007 , there were 104 ( 69 pressurized water reactors , 35 boiling water reactors ) commercial nuclear generating units licensed to operate in the United States , producing approximately 20 % of the country 's electrical energy needs . In absolute terms , the United States is the world 's largest supplier of commercial nuclear power . However , the development of nuclear power in the United States has been stymied ever since the Three Mile Island nuclear accident in 1979 . Future development of nuclear power in the U.S. was to be enabled by the Energy Policy Act of 2005 and co-ordinated by the Nuclear Power 2010 Program , but many license applications filed with the Nuclear Regulatory Commission for proposed new reactors have been suspended or cancelled
Three Mile Island nuclear accident
Three Mile Island accident
Nuclear energy policy by country