We can't swap tiles we can't see though, sorry.
Once the reactor is off, Sanitation should be fine to target N15 with their ability. If you turn off the reactor on action 1, they can do it on action 2, or any other action besides 1. This will remove the radiation there in the reactor.
This situation isn't as bad as it sounds. Once the reactor is off, the radiation goes away. It's waaay for away from people right now, like 3-4 turns at least.