I've done some checking, and apparently, they are using nuclear power in space, but not through fission. They only use the energy generated by the radiation.
As for the idiocy in thinking a NUCLEAR REACTOR would be placed anywhere near your house, well, that just speaks for itself. For those of you who think radiation is oh so dangerous, then I suggest you kill yourselves right now, because at this very moment, you are being bombarded with it from space, and naturally, from our friend (although it really shouldn't be at this point, considering the hell we've put it through), the Earth.
The S4 Reactor is the safest thing around (it's less dangerous than driving, and in terms of nuclear power, it's very safe). Like I think people have mentioned before, the only real danger is the sodium, which has a tendency of burning. Li-6 is not a very harmful substance - your daily intake of sugar and chemicals is far more deadly.