I was also wondering about this. How exactly are they powering it with a nuclear source? Nuclear power comes in two forms, (as far as I know). A) Steam B) Peltier Seebeck effect (often used in space probes). Neither of which is useful here. Though I did hear of theoretical spacecraft that used timed mini nuclear explosions behind the ship to propel it forward, but by mini, it was still on a much larger scale than an average missile.