There is nothing preventing you from flying over powerplants. It's just not a good idea. No reason to draw any attention to you if you don't need to. There is a coal powerplant that we use as a VFR reporting point and I will fly a mile or two north or south of it for this reason. There is also a nuclear plant that is directly under a cross country route that I like sending my students on for their first solo x-c. When doing the flight dual, I make it a point to tell them to go a bit to the south and have never had a problem.
I believe that when the "color-coded fear guide" goes to orange some nuke plants get a TFR. I could be wrong, but there's never a reason to fly over them. Take a couple minutes and deviate off course a bit.