Video - The Convair WS 125 atomic powered bomber.

Wikipedia | A nuclear aircraft is an aircraft powered by nuclear energy. Research into them was pursued during the Cold War by the United States and the Soviet Union as they would presumably allow a country to keep nuclear bombers in the air for extremely long periods of time, a useful tactic for nuclear deterrence. Neither country created any nuclear aircraft in production numbers. One design problem, never adequately solved, was the need for heavy shielding to protect the crew from radiation sickness. Since the advent of ICBMs in the 60s the tactical advantage of such aircraft was greatly diminished and respective projects were cancelled. Because the technology was inherently dangerous it was not considered in non-military contexts.

Unmanned missiles have been designed to use nuclear thermal rockets, but such designs were considered too dangerous for crews to fly.