A Hitch in Iran's Nuclear Plans?

Iran's supply of low-enriched uranium -- the potential feedstock for nuclear bombs -- appears to have certain "impurities" that "could cause centrifuges to fail" if the Iranians try to boost it to weapons grade.  Iran may have had no alternative but to seek foreign help in enrichment because its own centrifuges wouldn't work. "It's especially cheeky for Iran to try to leverage as a concession their willingness to receive international cooperation in supplying nuclear fuel," noted George Perkovich, the director of the nonproliferation program at the Carnegie Endowment for International Peace.