Does Iran have nuclear material? Does Iran have nuclear waste? If so, it has a nuclear dirty bomb.
Take radioactive waste like bits of metal, warp around an explosive and detonate in the air above a block.... Chunks of radioactive material impregnates the buildings and forces you to tear the buildings down so to remove the radioactive material.
There for if you have any nuclear program, you have nuclear weapon.
I guess one area of nuclear to investigate might be the security of fissionable material since the dissolution of the USSR. How much is not accounted for, who has it, what type of security is undertaken to protect it.
I'm not sure where you're getting that number. The last time I checked, the IAEA couldn't give a definitive answer, since Iran wasn't letting them into all of their enrichment centers and the like. [link] "Iran is not providing the necessary cooperation, including by not implementing its Additional Protocol, the Agency is unable to provide credible assurance about the absence of undeclared nuclear material and activities in Iran, and therefore to conclude that all nuclear material in Iran is in peaceful activities."
Either way Iran is surely aware of how stupidly suicidal it would be to develop a nuclear program with the aim of throwing a few warheads and then get destroyed by a nation that's willing to annihilate the entire planet over an egotistical belief they are the chosen people if they were threatened with complete destruction.