Russia’s Burevestnik is a supersonic nuclear warhead-equipped cruise missile, powered by a nuclear reactor cooled with sodium or similar metals. The coolant then runs through a kind of radiator. Atmospheric air entering the radiator through the front of the missile is then superheated by the hot radiator and directed out the back of the missile at very, very high speed, providing thrust.
The missile is launched by a conventional solid-fueled rocket motor that accelerates to a high enough velocity for the ram jet to work. Then the rocket motor falls away, and the reactor begins to operate. The missile is 39 feet long when launched, and can fly until the reactor runs out of fuel, hits its target or (unlikely) is intercepted and shot down. It can fly for a long time at high speeds before striking a target.
The idea of this kind of missile system dates to at least the time of the old 1960s’ U.S. Bomarc nuclear-powered cruise missile, which was similarly powered but never deployed, due to material difficulties. Burevestnik appears to have solved the technical challenges. On background discussion, a leading U.S. physicist noted that any leakage of radioactive isotopes, like xenon, would be instantly picked up by U.S. capabilities. No such leakage was noted during the test flight of Burevestnik.
