The promise right after WWII, was that nuclear power was so fantastic, that it was too cheap to meter, clean and green.
There would be atomic powered airplanes, cars, submarines, ships, and more. Nuclear bombs would be used to dig lakes, canals and other things, in an ATOMS FOR PEACE campaign.
Of course, these things did not work out, because it turned out that the promises were based on lies. Harry Truman did not trust the military with this power either, so he created the civilian controlled Atomic Energy Commission, which eventually closed and was disbanded due to the absolutely corrupting influence of the nuclear and military industry.
The Aircraft Nuclear Propulsion program researched and developed two main systems of nuclear powered jet engines. The Direct Air Cycle program was the first of these. Developed by General Electric, this facet of the program was based in Evendale, Ohio.
The Direct Air Cycle program was popular because it was simple, reliable and suitable and the engines were able to start quickly. It worked by letting compressed air run through the reactor of a conventional jet engine where it could be heated before being exhausted through the turbine. The X-39 engine was produced by this program and it proved to be highly successful with several upgrades made to the system at later stages.
The final HTRE-3 would have most likely been used to power the X-6 nuclear propulsion aircraft if the project hadn't been scrapped.
The major issue was how to protect the crew from the deadly radiation, so the idea was to use older crew, and base the aircraft on only uninhabited islands.
Radiation shielding was experimented with. The experimenters combined water jackets and lead shielding to separate the crew from the nuclear reactor.
The problem still remained, what to do if the plane crashed? The plan was that each nuclear powered bomber would carry a crew of Marines, who in case of a crash, would parachute out of the plane BEFORE it crashed, and seal off the area from curious onlookers. The nuclear powered plane weighed about 80 tons.
The other problem that was never solved was the amount of radiation coming out of the plane's engine, due to the direct heating of the air from the hot, radioactive material inside the reactor. GE developed this engine.
The problem of radiation coming out of the bomber anywhere it went, created the need for an indirect heating system. An indirect heating system would reduce the radioactivity entering the air from the nuclear reactor. Pratt and Whitney worked on the indirect atomic energy system for planes, but never perfected it, despite years of research.
President Eisenhower ordered a stop to the flying nuclear bomber research program. Then the Soviets announced that they had perfected a nuclear powered plane, so he restarted the program due to public pressure. This Soviet announcement turned out to be fake news propoganda.
The Soviets eventually did build a direct cycle radiation powered plane, which passed dirty, contaminated radioactive materials into the air, where ever it flew.
They solved the weight problem by taking out the shielding and making the reactor hotter, so it would produce more power, but also more radiation.
The plane was also poorly shielded, so the crew was exposed to pretty large doses of radiation. About 40 test flights were conducted. Most of the crew of this experiment died from radiation poisoning. Radiation was spread over a large area, due to nothing more than the plane flying overhead.
When President Kennedy came into office, he found out that the Republicans and the military industrial complex had been pushing a lie on the American public for years. They had said that the Soviets were way ahead in terms of bombers, missiles and technology. This was a lie. Through aerial spying, Kennedy found out that the Soviets only had a few missiles, a few bombers and no superior technology.
The exposure of this lie led to the nuclear disarmament treaties, because there really was no race in terms of weapons building. The US had been wasting a huge amount of money on a useless build up of weapons that would never be used.
Convair NB-36H Peacemaker and WS125 Nuclear-Powered Aircraft; via @AGreenRoad