Ask HN: Nuclear Cruise Missile Fuel

The recent civilian video showing the very large shock wave from the recent Russian offshore military explosion, as evidenced by condensation behind the shock wave front, indicates either a low-power nuclear detonation or massive chemical explosion. Since the fission reaction rate for normal density plutonium is too low to achieve nuclear explosive yield, plutonium must be imploded to give sufficient density for nuclear detonation. Presumably the nuclear cruise missile motors would not have been built with implosive shells of high explosives, which seems to indicate that the nuclear motor fuel was uranium-235. Does this reasoning seem correct?