[evgen]

You should really check out the safety features of RTGs. As one example, in 1970 the lunar module from the failed Apollo 13 mission (which had an RTG with a plutonium dioxide core) was burnt up over Fiji and dropped into the Tonga trench in the Pacific. The heat and stress of this event was far beyond anything that would happen during the launch of a spacecraft. The area where the RTG ended up is still tested for an increase in background radiation and to date nothing has shown up that would indicate that the containment vessel has leaked.

[Tuna-Fish]

But we are not talking about RTG:s here, we are talking about real reactors.

... Which are potentially even safer, because the fuel is not terribly radioactive until it has actually been in the reactor. Ship it up in parts, assemble when safely in orbit.