Bit of an aside: Nuclear plant security should not be comparable to fossil fuel plant security, it should be much much tighter.

Yes agreed, given the risks of meltdown or the theft of radioactive material I would think security should be much more important.

Radiation alone provides security. The plant diagram already has two fences with coresponding checkpoints. One needs to stop potential looters, so basically checkpoits with a guard each and a patrol vehicle with a team of two. Make it armed guards if you're in the US where everyone and their grandmother owns not one but several firearms. That plus the usual access cards and CCTV. This isn't a military nuclear weapons lab, it's a civilian power facility.

I'd still feel safer with the number of armed guards being nearer the 'nuclear weapons lab' end of the scale than the 'power facility' end.