Iran and uranium enrichment

Iran’s threat to enrich uranium for nuclear weapons is an empty threat at best. Based on what I have seen Iran’s stocks of UF4 gas is too contaminated with Moly and other heavy metals to be converted to UF6. Why does a little Moly hurt? Because during the conversion to UF4 to UF6 the Moly (and other metals) will react with the fluorine gas, and become solid. This will clog the pipes and valves and slow the conversion. If they do manage to keep the pipes from clogging then the tiny particles will destroy to centrifuges used to enrich the U235. If the gas centrifuges are destroyed not only would it be a financial and environmental disaster. Sure Iran would lose a lot of uranium but uranium is cheap, they are careful since the centrifuges are difficult to replace.
Now why don’t they purify their uranium, since it is fairly easy to do? The way you get rid of Moly and other metals that are more reactive than U, is thermal decomposition, which basically takes UF4 and decomposes it to U and F2 X 2. Then the U is distilled off leaving the impurities behind and the fluorine gas separated before it can recombine with the U. Well this is easy to do on a small scale, perhaps even a couple of kgs, but Iran needs to refine tons of U. Fluorine is nasty nasty stuff, (F is so electronegative that it can under certain circumstances bond with the noble gases), so working with it on a large-scale requires very special technologies. Only a few countries have these technologies and most aren’t willing to share them.
I am not saying Iran isn’t a nuclear threat. They could refine enough U235 to feed a fission reactor. After several years of reprocessing spent fuel rods Iran might have enough Pu to build nuclear weapons. However, it is hard to reprocess spent fuel, and it is even harder to do it and avoid detection. I personally don’t think Israel would take Iran’s nuclear ambitions lightly and if Iran did begin to reprocess, Israel would make it very hard.
Basically Iran enriching because they want something and they know that someone will eventually buy them off to stop. Then during the down time Iran’s nuclear scientists will analyze what they learned so they will do better next time. They will also acquire more technology so next time they can get further. If they could make a bomb they wouldn’t be talking so much, they would make and test a bomb since a mushroom cloud speaks volumes. Most semi-nuclear nations follow this pattern, the politicians what attention, the nuclear scientists want lab time, so they fire the program back up, the scientists get as far as they can, then shutdown once progress slows and they get a nice chunk of change to show for it. Nuclear research is a profitable investment; nuclear research money not only gets them the advancements in the technology, it also pays dividends in humanitarian aid money to stop, and warns the world country X is to be feared.