Russia's Nuclear-Powered Cruise Missie

The claim is that it can fly indefinitely.   I am very skeptical.   If it is heating gas of some sort to produce propulsion, it will run out of reaction mass.  The only alternative is that it is warming air enough to get thrust.  I know enough chemistry and physics to find it implausible that a reactor can heat atmospheric gasses enough to get dramatic propulsion.  That would require an enormous amount of heat in contact with incoming air.  Is there something that I am missing?