Not to mention that the idea is that these are "secret" bunkers. If you start laying rebar and pouring concrete over top of them, you are kinda shouting out, "HEY, THERE'S A SECRET UNDERGROUND BUNKER HERE". kinda defeats the purpose of putting it underground in the first place. If I was Iran, I'd do my nuclear testing in a nice safe place. Turkey. After all, the US isn't going to start bombing Turkey anytime soon.