Hello? Power plants make lousy weapons manufacturing sites.
They are not the same kinds of machines at all. They also don't produce the same kinds and amounts of fissible materials.
A bomb can be produced in a lab. Electricity takes an industrial facility. Reactor core analysis actually can detect whether there is anything missing, though not where it went. But since the byproducts of a power reactor are not useful for bombmaking, hey, why not consider it?
To get the kind of materials needed for a bomb, all the Iranians have to do is skip across their northern border and find a willing seller on the black market. Interdiction will not keep them from that. International agreements might. People are less likely to destroy something they have a stake in. Like, oh, the world.