In 1954, the Army Nuclear Power Program (ANPP) was formed as a joint program between the Atomic Energy Commission and the Department of Defense (DOD). One focus area for the ANPP were micro-reactors, something that the United States is pursuing once again. As we learned how to effectively harness nuclear energy, the DOD was pursuing many different uses for the newfound power supply (e.g. nuclear overland trains, battlefield power and fuel conversions, nuclear aircraft)
W. Sterling Cole was a House Representative (New York) from 1935 to 1957. On June 22, 1955, he sent a letter to the Speaker of the House of Representatives, Sam Rayburn making his case for a 25,000 kW nuclear reactor for Capitol Hill. He was the leading member of the Joint Congressional Committee on atomic energy. Discussions with the Capitol Architect were already completed.
In December 1957 Cole became the Director-General of the International Atomic Energy Agency. On March 15, 1987, cole passed away from cancer at the age of 82.
We likely will not ever know if there is a reactor in Capitol Hill or beneath the Pentagon. However, the letter above tells you that the United States was thinking about nuclear power for all uses, heating, electrical generation, and others.