Iran has announced plans to begin operating a second set of uranium centrifuges in the coming days. Spinning at supersonic speeds, the centrifuges can produce fuel for nuclear power plants, or (more likely, in the case of Iran), nuclear bombs.
A statement from the official Iranian news agency states that Tehran has already begun "dry testing" a second set of 164 centrifuges, and will begin injecting UF-6 gas into the devices in the coming days. Gas insertion represents the next, critical step in using the centrifuges to produce nuclear fuel. Iran began operating its first set of centrifuges in April, producing a tiny amount of enriched uranium.
Tehran's decision to open a second centrifuge array is clearly an act of defiance--but does it indicate substantial progress toward producing a nuclear bomb? As we noted six months ago, using the centrifuges to produce enriched uranium is an important technological step, but Iran still faces critical hurdles in operating enough centrifuges to produce required quantities of nuclear fuel--and at the purity required for use in a weapon. Two cascades (with a total of 328 centrifuges) leaves Iran on the slow track for weapons development. To produce a bomb over the short term (say, the next year or 18 months), Tehran would need as many as 54,000 of the older centrifuges, or at least 12-13,000 of the larger P-2 models. Iran supposedly gained access to P-2 technology through Pakistan's infamous A.Q. Kahn nuclear proliferation ring. At this point, we don't know what type of centrifuges are being used in the Iranian cascades.
We're also unsure about the quality of enriched uranium now being produced. Fuel for nuclear power plants is typically low-grade stuff (around 5%--within Iran's current technical capabilities). On the other hand, the level required for weapons-grade material is much, much higher, and (so far) there's no definitive word on whether Tehran has crossed that threshhold. It's also worth noting that these capabilities are based, in part, on "official" Iranian claims. There is continued concern that Tehran may also be operating a covert nuclear program, housed in undisclosed research complexes and military facilities. A covert program might be much further along the weapons development track, operating larger centrifuge arrays, and producing enriched uranium at much higher purity levels.
If the "official" cascade reports are accurate, Iran is probably four years--or more--away from having the bomb, possibly longer. But, if Tehran is also operating a parallel, covert track, the timetable for nuclear weapons may be much shorter. If I had to venture a guess, I'd say that Iran probably has some semblance of a covert program, a hedge against potential sanctions and/or military action by the west. We'll stand by our assessment of six months ago: the window of opportunity for heading off Iran's nuclear program is closing, and closing rapidly.