Comment by spauldo

Depends what you're trying to protect yourself from.

Reinforced concrete is great if they're just shelling you. Sure, all the outdoor infrastructure will be toast but your reactor probably won't get damaged. It'll take a bit to get back on the grid but you don't need to rebuild the plant.

Bunker busters, on the other hand, eat reinforced concrete for breakfast. A pinpoint strike into each reactor hall and you're down for good.

The former is cheaper, less risky for the attacker, and hurts you bad enough for most military purposes, so the latter isn't really worth worrying about unless you're Iran or North Korea.