Even if that were true, which as far as I can tell it isn't (both Soviet and US nuclear aircraft programs were canceled before any powered prototypes were made)

Even if that were true, which as far as I can tell it isn't (both Soviet and US nuclear aircraft programs were canceled before any powered prototypes were made), aircraft at least are not meant to crash. All cruise missiles crash. Deliberately pulverizing a fueled-up nuclear reactor is not a nice thing to do. In fact, according to Wikipedia, the risk of crashing and making a mess was a factor in the cancellation of both programs.