Even on military flights, regular manned aircraft need to stop regularly so the crew can rest, bathe and unwind. But an unmanned drone can keep flying until it runs low on fuel, so the U.S. military drew up plans for nuclear powered drones that could stay airborne for months at a time.
The catch 22 is that while a manned aircraft can stay airborne for extended periods using mid-air refueling, this requires a skilled team on the plane making true long tern endurance impossible.
Working in collaboration with Sandia National Labs, Northrup Grumman drew up plans for a drone powered by a helium-cooled nuclear reactor, giving both vastly extended endurance and a big upgrade to the onboard juice to power all of that nifty spy gear.
While the existence of this long-established program was just recently revealed, it turns out that political conditions have placed it on the back burner for now. The technology could undoubtedly have been made to work, but the consequences of a nuclear drone crash was just too much of a political risk to take. If a nuke drone crashed over enemy territory, that country would undoubtedly claim that the U.S. had exploded a dirty bomb over their state. Then add to that the problem of all that technology falling into the wrong hands, and it was decided that the risks were simply too high.
This means that for now drones will continue to fly using the very fuel produced by some of the countries they are being flown over. How ironic.