In the 1950s, the US went a bit crazy about the whole atomic age. Of course, there were the hundreds of above ground weapons tests, and that sort of thing. But other applications for nuclear power were envisioned as well. For instance, the Army saw small nuclear reactors as a means of prime power generation for remote bases.
One possibility seen was actually using a nuclear reactor to power an airplane. At first, that sounds a bit nutty. But what is the output of a nuclear reactor? Heat, or, if you will, thermal energy. If you take a look at a jet engine, what is the purpose of jet fuel, other than to provide thermal energy? If the heat from a nuclear reactor could be used in place of the heat of jet fuel, theoretically, you could design a plane with essentially unlimited range.
But before the Air Force could begin to design a nuclear powered airplane, they had to learn what it would be like to actually operate a nuclear reactor in flight. And so, they contracted with Convair, maker of the B-36, to design a test reactor, and to fly a series of tests to investigate shielding, operation, and handling procedures.
In the event, the improvement in jet engines, the weight, shielding and handling issues of a reactor, and the widespread acceptance of aerial refueling showed the Air Force that nuclear propulsion was an aviation dead end. Still, it was, if a somewhat futile effort, a certainly interesting one.