Iran says it is enriching only to power reactors and for scientific and medical purposes. But because of its nuclear secrecy, many countries fear that Iran may break out from its present production that is below the weapons-grade threshold and start enriching to levels of over 90 percent, used to arm nuclear weapons.
Tehran now has more than 10,000 centrifuges enriching uranium at its main plant at Natanz, 225 kilometers (140 miles) southeast of Tehran, to fuel grade at below 4 percent. Its separate Fordo facility, southwest of Tehran, has close to 3,000 centrifuges — most of them active and producing material enriched to 20 percent, which can be turned into weapons-grade uranium much more quickly.
Iran has depended on domestically made and breakdown-prone IR-1 centrifuges whose design is decades old at both locations up to now, but started testing more sophisticated prototypes in the summer of 2010.
David Albright, whose Washington-based Institute for Science and International Technology serves as a resource for some U.S. government branches, estimated in a 2011 report that 1,000 of the advanced machines "would be equivalent to about 4,000-5,000 IR-1 centrifuges" in production speed.