According to Lockheed Martin, the L-225 design was thecompany’s second attempt at a bomber powered by a small nuclear reactor.
Ultimately, neither the US nor the USSR actually built anoperational nuclear-powered aircraft. It was probably too expensive and muchtoo dangerous–given that if one these machines crashed, it would likelycontaminate a very wide area–which is bad. But it was probably mostly the costissues and numerous technical challenges that drove the US and USSR to abandondevelopment of these things.
Apparently, a nuclear-powered aircraft’s engines–other thanthe reactor–would have probably looked a lot like a regular jet. That isexcept that there would be no combustion chamber; instead there would be a heatexchanger where molten salt would be used to heat compressed air for theturbine section. Apparently, something like this was tested in 1954 and ranabout 1000 hours.
If I recall correctly, there was a Convair NB-36H that wasactually built and flown over Texas with an operating nuclear reactor onboardbetween 1955 and 1957, but it was never actually powered by the reactor. TheSoviets did something similar with a Tupolev Tu-95 Bear.