Let's say that you have a commercially/privately-operated jet aircraft. It's not something that's going to be used by a single pilot, or someone making mail runs, or a bush pilot; it's more of the type of thing that would be run by a commercial airline, or a UPS-style delivery company. You will see why.
Now, unlike most jet aircraft, this one runs on a nuclear jet engine; specifically, a fission model, and one of the indirect air cycle variety, in which the reactor is not exposed to the inside of the engine but instead heats it via a series of fluid loops (likely liquid metal or sodium).
Advantages to this include:
time aloft is no longer limited by fuel supply; instead, it is limited by crew endurance
an absence of greenhouse gas emissions
the reactor can be used to provide electricity for the rest of the aircraft
a vehicle with this type of propulsion can operate in zero-oxygen atmospheres, as it does not rely on a hydrocarbon-oxygen combustion reaction
However, this model of aircraft is commercially owned and operated. That means that, instead of it being some kind of experimental vehicle piloted only by test pilots, there are going to be thousands of the things, and they're not going to be exclusively flying over test ranges anymore.
Given that this aircraft runs on a fission engine, which is radioactive if breached, as well as that it runs on fuel that is probably quite valuable to any hijacker, what safety features or operational standards would it require in order to become commercially-viable?