[Fyron]

If you're out of the bLast radius too...

The bLast radius of a Nuke is so large because the bLasted chunks of uranium/plutonium/etc. moving at incredible cause fission in all of the molecules around the detonation point that they run into, which then cause more fission and so on. There is less and less of it as you move away, but the chain reaction is what makes it so large. In space, the explosion would be very small in comparison. Not less deadly at the bLast point though, just a much smaller area of effect.