It is not B-747. It is the C-5 Galaxy, the largest aircraft ever in the U.S. arsenal - civilian or military.
That kind of launch is never done, except for X-15s, because NERVA, or any other nuclear thermal rockets has never been proved successful. Outside of nuclear thermal rockets, there is no other propulsion known to yield enough velocity.
No, not because of the quantity of fuel, but because nuclear thermal rockets - which the NERVA is - yields much higher exhaust velocity than solid- or liquid-propellant rockets.
As for radioactivity, the nuclear reactor in NERVA is clos