Apparently, you can produce prodigious amounts of plutonium this way. You can attenuate the reaction using graphite, or heavy water. Except with heavy water, the uranium interacts with the deuterium and thru a couple of short half-life isotopes, becomes plutonium. Plutonium is so highly reactive it is dangerous to design a gun-type bomb because of pre-ignition. A link describing the process: www.fas.org/nuke/intro/nuke/plutonium.htm Iran is basically telling the west to stick it.
So you're saying they can blow themselves up to smithereens? If so, it should save us a lot of money.