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The past twelve months have not been good for Iran. Domestically, the country still roils from the electoral chicanery of the previous August. Internationally, the United Nations has placed fresh sanctions on the regime for failing to comply with its resolutions. Economically, it seems recession has hit the nation, though it is hard to be certain — the government has ceased releasing numbers entirely.

According to the latest report by the International Atomic Energy Agency (IAEA), the year was also unkind to Iran’s uranium enrichment program. Contrary to plans, Iran’s number of installed centrifuges has risen only slightly, from 8,308 to 8,856, and, more importantly, the Iranians have failed to maintain their number of operating centrifuges, which has actually fallen from 4,592 to 3,772.

A happy consequence of this turn of events is that there is more time for diplomacy. Last October, I wrongly predicted that the United States would be faced with something like a do-or-die decision on the Iranian nuclear program by this time this year — now there is a second chance to deter Iran through the intelligent application of carrots and sticks.

This is a lucky break, and one which both hawks and doves should celebrate. However, this brief respite from Iran’s inexorable march toward nuclear weapons should not give us the false hope that inaction is a tolerable policy. If diplomacy is to work, it must work quickly. While Iran may not have advanced its enrichment facilities over the past year, it does appear to have advanced its technical know-how in centrifuge operations. Last August the Iranians were eking out roughly 0.7 separative work units (SWU) per centrifuge per year — today they are closer to 1.08 SWU/centrifuge-year. It remains to be seen whether this improvement in productivity is a statistical fluke or a genuine improvement in technical know-how, but for the moment, despite the decline in numbers of operating centrifuges, Iran’s total operational capacity has increased by roughly 40 percent.

Besides the rising productivity of Iran’s centrifuges, there is also the problem of their recent foray into higher isotopic enrichment levels. In the past six months, Iran has enriched 22kg of uranium hexafluoride (UF6) to a 19.7 percent concentration of U-235— under IAEA limits, but closer to weapons grade.

More simply put, time has never been on our side. Iran never needed to accelerate or expand its program; a year of operation is a year closer to their goal. At the start of August, 2009, Iran had 1,508kg of 3.5-percent-enriched UF6. As of August 6th of this year, it has nearly doubled its stockpile of enriched material to 2,803kg of 3.5-percent-enriched UF6.

To be of practical use in a bomb, the Iranians will need to enrich their uranium much more, to roughly 90 percent U-235. It is uncertain how much of this highly enriched uranium (HEU) will be needed for a nuclear device. Without any neutron reflection, a critical mass of 90 percent HEU is 54kg, and the first American device that used uranium, Little Boy, used 64kg. With neutron reflection, the critical mass is roughly 15kg. 20kg might prove sufficient for an effective first-generation weapon — officially, the IAEA considers 25kg to be a significant quantity.

If we suppose a slightly conservative scenario of 28kg per device, Iran, using only its existing stockpile of enriched uranium and the centrifuges currently operating at its Natanz site (which produce about 4,100 SWU/year), could obtain a bomb’s worth of HEU in less than three months, and two bombs’ worth in a little more than seven months.

It is fair to say that this is less than a “breakout” capacity — the mullahs may be uncomfortably close to the bomb, but three months is a long time to react to IAEA inspectors being tossed out of a country, and a single, untested device is hardly a solid nuclear deterrent.

Nonetheless, a breakout capacity is on the horizon. Here are four scenarios, along with back-of-the-envelope calculations as to where they put the Iranians at the start of March, 2011.

Scenario A: Iran continues its current operations as is — it does not bring more centrifuges online, and does not enrich beyond 3.5 percent in significant quantity. Scenario B: Iran slowly brings the remainder of its installed centrifuges online and operates them at current productivity levels, but does not enrich beyond 3.5 percent in significant quantity. Scenario C: Iran fails to bring more of its installed centrifuges online, but enriches its stockpile from 3.5 percent to 19.7 percent. Scenario D: Iran brings the remainder of its installed centrifuges online and shifts its enrichment from 3.5 percent to 19.7 percent.

Scenario A leaves Iran 10 weeks from acquiring one bomb’s worth of material, and 14-15 months from acquiring three bombs’ worth. Scenario B leaves it four weeks from one bomb, and five months from three bombs. Scenario C leaves it 2.5 weeks from one bomb, and 14-15 months from three bombs. Scenario D leaves it one week from one bomb, and four months from three bombs.

Kissinger once said, “A statesman’s duty is to bridge the gap between his nation’s experience and his vision.” There is yet hope for diplomacy. But should it fail, we will have short time before a hard decision must be made. If our president is a true statesman, he will begin preparing his nation for that decision today.