All other power sources, except maybe hydro, are almost perfectly safe. They're a lot more damaging to people's health and the environment, yes, but that is a different thing from danger.
I wrote "in the long term" for a reason, by the way. I'd prefer to get rid of coal before nuclear despite the danger.
Why isn't nuclear the backup? "90% renewable, 10% nuclear" sounds politically-viable; it's still "moving away from nuclear."