QNRs are a totally new nuclear technology developed in the 1990s that use neither fission or fusion of atoms.  Instead, if you bombard the QNR fuel with X-rays from a standard hospital-type X-ray machine, the fuel gives off a stream of gamma rays that is 50 times more powerful and can directly heat a stream of air to push the aircraft forward.  Thus you're leveraging your available input power by a factor of fifty via a gizmo that produces no radioactive exhaust and can be throttled by controlling the X-ray generator.  Turn off the X-rays, you turn off the QNR.  Pretty neat if it works.  Not everybody believes it has, does or will. Regardless, Los Alamos and Sandia nuclear engineers in New Mexico have been instructed to discourage public discussion of QNRs even as the Department of Defense has put the machine on its Militarily Critical Technologies List to put it on the fast track for future funding.

The QNR fuel of choice is hafnium-178 (actually its metastable nuclear isomer, currently obtained by bombarding sub-hafnium elements with protons, neutrons and alpha particles), which has a half-life of only 30 years or so and isn't particularly dangerous - OK, OK, compared to plutonium in a conventional fission nuclear reactor.  No need to worry about a crash of a QNR Global Hawk; the crash site would clean itself up of any spilled radioactive material in a century or so! With a golfball-sized chunk of Hf-178m estimated as having the energy of ten kilotons of conventional explosives (half a Hiroshima), this technology is also a potential contender for a breakthrough Moon/Mars propulsion system.  Or a superbomb.  Or not.