Iran’s enrichment effort continues to move forward as their scientists and technicians continue their relentless pursuit of ever higher enrichment levels, and ever more effective centrifuges. At least that’s the official story, eagerly broadcast by Iranian officials.

Few have probably missed the 23 June claim by Mr. Ali Akbar Salehi, the head of the Atomic Energy Organization of Iran, that Iran has produced 17 kilograms of 19.75 per cent enriched uranium hexafluoride gas. He also said that his outfit can produce as much as five kilograms a month. ISIS has pointed out that Mr. Salehi’s statement does not square neatly with the IAEA’s latest report on Iran.

The report suggests that the product flow rate between 9 February and 7 April has been precisely 100 grams a day (according to the IAEA logs, the Iranians withdrew 5.7 kilograms after 57 days). If Mr. Salehi’s production claim is true, the flow rate for the period 9 February to 23 June has in fact been about 127 grams a day.

If you think that most of the 11.3 remaining kilograms of uranium hexafluoride gas was produced after 7 April, the product flow rate of the facility jumped from 100 to about 147 g/day. That is [still] a remarkable increase in productivity.

Mr. Salehi does say the cascade can produce that much. He’s claiming that Natanz can gear up to around 164.5 grams a day. This, to me, sounds optimistic.

If the P-1 machines were running at their theoretical limits, one 164 machine cascade should not be able to achieve a higher product flow rate than about 112 g/day. This is assuming 2.2 SWU/machine, an average feed enrichment of 3.5 wt %, and a tails enrichment of 0.2 wt %. Increasing the tails to, say, 0.5 wt % could pump up the flow rate to about 155 g/day, which still falls short of Mr. Salehi’s statement, and well short of 200 grams a day.

Indeed, on a single cascade, the tails would need to be set to 0.6 wt %, all other variables being equal, to achieve the stated capacity. In other words, the cascade would have close to natural uranium in its tails, flowing out at 934 g/day. I leave to others to judge whether this is an economical way to run an enrichment plant.

This leaves the alternative that Iran has put both cascades into action. Having two cascades of P-1 centrifuges, again at peak performance, will increase the flow rate to 224 g/day, assuming a 0.2 wt % tails setting. Mr. Salehi’s estimate of 164.5 g/day makes sense in that context. However, the latest Agency report reveal that as of 24 May, the second cascade was not put into operation. Even if it were put on-stream the following day, it is unlikely that the two interconnected cascades can have brought the balance up to 17 kilograms.

It should be said in closing that diversion risks are tiny when material balances are this small, provided the IAEA is allowed to apply safeguards as it considers right. Rumblings from senior Iranian officials that Iran may in fact reduce its cooperation with the IAEA are therefore unfortunate. How Iran intends to draw down on cooperation is also fundamentally unclear, since they presently seem to cooperating at the bare minimum.

Update: A friend of the wonk has pointed out that increasing the feed rate would result in reduced enrichment. So if Iran would have bumped up the feed rate, it would in fact dilute the product quite a bit. That’s something to ponder indeed.

Update 2: Thank you Ataune for spotting a calculation error. 11.3 kg / 77 days is 146.8 grams per day. The post has been revised accordingly.

Update 3: Thanks for all comments, both on and off-line. The general thrust is that although SWU calculations – on which this post is based – can be useful, a cascade calculation will yield better results. In fact, the tails are most likely LEU and not DU as posted here. When I get back from Wilton Park, I’ll revise the post to in light of all comments. This is a truly remarkable readership – none mentioned none forgotten.