Not really. The emissions, if they keep their eyes on them, would be pretty safe. And if it blows up in outer space, well, it ain't gonna do any harm.

The only problem is having it on the Space Shuttle during Exit/re-entry. What if it blows up then? Dirty Bomb high in the sky, anyone?

It's like Russian Subs, but different. They have their own Nuclear Reactors. Easier than carting around a load of fuel...and if it goes critical and blows a hole in the side, well, it sinks to the bottom of the sea and nobody gets hurt.