Today’s The letter from Iran to the IAEA is indeed a worrying development. As Jeffrey points out, our worst fears have been realized. Iran has – using the fact that IAEA inspectors cannot venture beyond declared strategic points – constructed a new enrichment facility. National technical means combined with human intelligence, however, seems to have averted the worst outcome, the establishment of a parallel fuel cycle.

However, two serious questions remain:

First, the unclassified US talking points state that the facility would be capable of producing about a weapons worth of material per year. A 3,000 centrifuge facility using Iran’s antiquated IR-1 centrifuges would be able to produce about one and a half weapons worth of high enriched uranium per year (39 kilograms with tails set to 0.4 per cent and 34 kilograms with tails set to 0.3 per cent). If equipped with more advanced centrifuges, the facility becomes quite lethal. The last generation of SNOR designs, for instance, if installed in Qom, could easily produce up to 80 kilograms worth of weapons grade uranium per year. The centrifuges would require little room, about 30 meters square, and draw very little power.

In practice, the facility would probably have three product areas: one for low enrichment, one for intermediate enrichment, and one for enrichment up to weapons grade. In a later briefing, US White House officials said the size of a facility would be about right “for a bomb or two a year”. They also said that the facility was “very heavily protected, very heavily disguised”.

Second, the facility would need to be supplied between 18 and 40 metric tons of natural uranium hexafluoride gas per year. An attempt to divert this from Esfahan, Iran’s only declared conversion facility, would entail a diversion of about seven to 16 per cent of its total capacity. I don’t have to do MUF calculations on that. A diversion that big would, with an extremely high probability, be detected by the IAEA. Indeed, I almost dare to say that detection is assured. This means that Iran would need to set up a clandestine conversion facility somewhere in order to bypass safeguards. There is nothing in the US speaking notes on that. But it seems like that the US intelligence community is keeping an eye on this.

Finally, we are definitely looking at a safeguards violation. It’s worth recalling that Iran did upgrade its subsidiary arrangements to oblige them to report facilities to the IAEA when they were at the design stage. They did this in 2003. They unilaterally pulled out of this arrangement in 2007. As James Acton correctly points out, the arrangement entered into force through simple exchange of letters. As in any contract, the principle pacta sunt servanda prevails (just put that term in Google).

A state can no more pull out of a contract than you can get out of, say, a mobile phone contract before it expires. It takes two parties to terminate an agreement. And the IAEA never accepted Iran’s withdrawal.

Not that it matters. It would seem like construction started at some time before March 2007. That is, at a time when even Iran itself considered itself bound by Code 3.1.

This is going to be very difficult to explain away, even by Iran’s highly talented spin-doctors.