Lately, there has been considerable discussion about the risk of an Iranian breakout. The argument is that Iran could use its stockpile of 1.1 metric tonnes of low enriched uranium hexafluoride gas as feedstock for an effort bringing the enrichment up to about 93 per cent. Some readers may have noted my comment in GSN where I said that: "at the moment, I'm not very concerned".
My reasoning is very simple. A break-out at this stage would be very risky for the Iranian government. The amassed low-enriched material is about right for one uranium-based weapon, but in order to get that processed into weapons-grade, Iran would need to reconfigure the cascade and run the material through the facility again. Then, the weapons grade material would need to be converted into uranium metal, which is then shaped into a metal pit. This pit has to be put into a physics package, which then has to be inserted into a suitable delivery vehicle.
How long will that process take? Well, estimates vary, but the reconfiguration and processing phase is likely to last a minimum of two months. Add another four to five months to convert the material, shape the pit, and construct the physics package, and we're up to half a year. Even if the Iranians have done their weaponization homework, they'll have to move from theory to practice for the first time. There will be material production losses, and they might have project delays. After all, they only have enough material for one weapon. It is literally a one-shot deal.
Now, if you put yourself into the mind of an Iranian leader getting briefed by his technicians on this, would you give the go-ahead? Six months is a long time in international politics, and the West's response is likely to be swift and possibly violent. Would you not want a comfortable margin before you kick out inspectors? I would, so I crunched the numbers on what the situation might look like by this time next year.
Even if the Iranians are only converting imported U3O8, they have a large stockpile of natural uranium hexafluoride gas. By this time next year, they could have a stockpile of 420.02 metric tonnes of gas. If there is no input of domestically produced U3O8 (as implied by an ISIS report) this would have completely depleted their stocks of imported South African U3O8.
Out of the stockpile, 35.06 metric tonnes would be transferred to Natanz for processing (leaving a sizable stockpile of 384.97 metric tonnes of natural uranium hexafluoride gas in the balance). This figure is based on the assumption that unit A26 will operate with 984 centrifuges for two months, 2,460 centrifuges for four months, and 2,592 centrifuges for six months. I assume no further progress on the other cascades. In addition, I assume that the Iranians hook up new centrifuges instantly. I do admit that there are clear limitations in my assumptions, which makes this somewhat of a "worst case scenario".
Over the year, the 35.06 tonne shipment would be enriched to 3.49 per cent U235. If the cascades are running at 100 per cent, and operating around the clock, unit A24 would have produced 2,140 kilograms of low-enriched gas by 31 January 2010. By comparison, unit A26 would lag somewhat, but will still be able to produce about 1,880 kilograms, bringing the total stockpile of LEUF6 up to about 5,030 kilograms.
The situation becomes interesting if the centrifuges were reconfigured in January 2010. The two cascades could produce a maximum of 168.4 kilograms of uranium hexafluoride gas enriched to 93 per cent U235 by late september 2010. This translates into a production of roughly 21.5 kilograms of weapons grade material per month. The total quantity could be machined into at least 6 nuclear weapons.
The cascades would need to be substantially reconfigured, as follows:
Unit A24 and A26 reconfiguration
As indicated by the figure, the new cascade would comprise 177 stages. Stages 1 to 47 would be stripping stages, and stages 48 to 177 would be enriching stages. This is, of course, a radically different configuration than if the cascade were enriching low-enriched uranium.
Recall that this is a worst case scenario, which assumes that Iran stops under-feeding its centrifuges and moves to maximum production. And note that even in early 2010, Iran would still need several months to complete its breakout, during which it may well be intensively bombed. So this is by no means an easy task.
If Iran really wants to acquire a nuclear weapon, the best strategy would be to bypass safeguards altogether and to build a clandestine enrichment facility. This would likely require the construction of a clandestine conversion facility as well, but that is a subject for another post.
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