A conventional strike on Iran's nuclear facilities will not produced any sort of nuclear explosion, unless the Israelis use a nuclear bomb themselves. . The facilities will be heavily guarded and deep underground, though we see from the assassination of the Hezbollah leader, enough penetrating bombs can overcome the best concrete fortification. They'll also have more effective anti-aircraft arms than Lebanon, which doesn't seem to have any.

The most likely strike if done, will be on the centrifuges that enrich the Uranium 235 and on the laboratories, and human infrastructure, power facilities etc. which will be easier to attack. If breached, there will be some sort of a radiation problem in the immediate locality. There will also be storage facilities for uranium hexafluoride which is the gaseous form of uranium used in the centrifuges and yellow cake uranium oxide as the raw material derived from the ore. A heavy bombardment could effectively put the programme to a nuclear weapon, if indeed that is what Iran is doing, and I think it is, back by a number of years. The centrifuges are by far the most expensive and difficult to replace items in any enrichment process. And Iran is on a sanction regime too.