They'd be transportable if you have a nuclear submarine, cruiser or aircraft carrier to move them about. :) Oh, or in an ice breaker, the Russians have several of those.
We've had small nuclear power plants almost from the beginning. Naval nuclear plants. You could mount the most recent designs on barges, then tow them into place. For inland areas you'd need to prepare a "pond" off of a navigable river.
We've had the ability to do it since at least the early 1960s. Of course the enviro-wackos would have a whole herd of cows over the notion. Since they continue to be in the cat-bird seat, it's not going to happen any time soon. Probably not in my lifetime..baring significant, and probably "unsettling" change. We can only hope.