Joshua PollackConsensus Emerges on Iran's Centrifuges

An announcement. (Sound of a fork tapping a glass.) Ladies and gentlemen — may I have your attention?

Ladies and gentlemen, although there were no armistice talks, the SWU Wars have ended in a truce. The experts have reached a consensus, roughly speaking, about the actual separative power of Iran’s IR-1 gas centrifuges — the devices enriching uranium at the Natanz Fuel Enrichment Plant (FEP) and Pilot Fuel Enrichment Plant (PFEP). (The latter facility has been in the news lately.)

It looks like this:

Perhaps you’d like more explanation than that?

Faithful readers will recall that this subject has been covered here previously (see: Estimating SWU with Expert Opinion, December 6, 2009, and IR-1 Estimates Revisited, January 18, 2010). The discussions summarized therein involved some disagreements — strong ones, at times.

But now, way down in Section 10 of a new ISIS paper dated February 11, 2010, Iran’s Gas Centrifuge Program: Taking Stock, David Albright and Christina Walrond conclude that “the average separative capacity” of an individual IR-1 at the FEP in Natanz is between 0.5 and 1.0 kg SWU/yr.

As a result, the experts’ estimates, depicted in the figure above, now largely overlap.

(There’s no significance to how high or low each estimate is placed in the histogram — that’s purely an aesthetic choice.)

In effect, we’ve just seen a slow-motion, public version of a “behavioral” approach to expert consensus: the question is argued until the participants converge, or as much as they’re willing. This is probably not the ideal approach, as there is evidence that a purely mathematical combination of initial estimates produces a better result. On the other hand, what happened is what happened. And, despite my original take, it seems better not to try to aggregate numbers when none of the experts has stated the level of confidence surrounding their estimates (e.g., 90%, 95%, or 99%). With that caveat, though, there’s no reason not to draw a picture like the one above.

So here are the estimates that are represented visually above.

Author(s) Data source(s) kg SWU/yr Date
Persbo Cascades operating between 27 and 36% of total capacity (based on 2.2 kg SWU/yr. nominal) 0.59 to 0.79 2/27/09
Wisconsin Project IAEA reports 0.5 11/16/09
Oelrich & Barzashka (FAS) IAEA reports 0.44 to 0.88 (0.88 is highly unlikely) 12/1/09
Kemp IAEA reports 0.6 to 0.9 12/1/09
Albright & Walrond (ISIS) Multiple sources 0.5 to 1.0 2/11/10

A final caveat: Consensus is in the eye of the beholder, and not everyone involved in this debate would necessarily agree that it has concluded, or concluded appropriately. (See also the view of Ivan Oelrich and Ivanka Barzashka of FAS.) I could certainly imagine ways to do this better.

But for now, it will do. On to the IR-3 and IR-4, should they ever go beyond testing:

Interviewer: “P2 centrifuges?”

Ali-Akbar Salehi: “P3, P4, Allah willing. We will announce this in two months’ time.”

Interviewer: “Iran is currently enriching uranium using P1 centrifuges, but it announced that it began experimenting with P2. Has Iran actually begun enriching uranium using the P2 centrifuges?”

Ali-Akbar Salehi: “Not yet. But Allah willing, in two months, we will experiment with P3 and P4, and after that, we will announce the steps we will take.”

So far, at least, the new machines are just spin jobs…

Update | Feb. 17. The latest from Iranian President Ahmadinejad:

We’ve tested the new generation of our centrifuges whose capacity is five times that of the current centrifuges. We’ll run them in the near future in order to supply fuel to our power plants and reactors. We keep our 20% production until our needs are met. The IAEA inspectors are well aware of our work.


  1. Binyamin

    Is it true that the Urenco version 6 machines being installed in their new facility in New Mexico are 250 kg. SWU/yr.? Some comparisons to other countries capabilities from you experts would be useful to us amateurs in putting this info into a useful context. Just a thought.

  2. Josh (History)

    I hadn’t seen that figure before. It’s conceivable; USEC claims that its new AC100 is designed to produce 350 kg SWU/yr./machine.

    All of this is cutting-edge; I don’t believe machines with triple-digit SWU have gone into regular operation anywhere just yet. The middle double digits was the standard set by URENCO machines in the 1990s.

    What’s in use at the Natanz FEP is modified 1970s-vintage URENCO technology.

  3. mark hibbs

    Urenco machines at 250 SWU/yr? Nope. Not even close.

  4. Josh (History)

    Googling around a bit, there are numbers out there, but their origins are hazy.

    This item gives a figure of 80 kg SWU/yr. for URENCO’s TC-21. A few years ago, Alexander Glaser had a figure of 100 SWU. He gave the same figure more recently.

    A couple of years later, Robert Eby of USEC put the TC-21 at “less than 100” SWU. Of course, he was talking smack about a competitor. Thompson and Forden put it at “approximately 100” SWU. A nice, round number.

  5. Binyamin

    So Mark, what’s the right number? I ask because, aren’t the technical facts relevant to answering a larger question: how far is a Third World country like Iran from First World WMD capability? And, by extension, how far are other TW nations (e.g. Argentine, Brazil, Egypt etc.) from such capabilities. The problem with this site is you are drowning in technical trees and failing to see the policy forest.

  6. Murray Anderson (History)

    The LES plant in New Mexico uses TC-12 centrifuges, according to various sources, including this:
    That’s probably a 40 SWU centrifuge.

  7. Ben S (History)

    This PDF is a little out of date. But it has really useful info on this stuff.

  8. Binyamin

    That’s to all for the hot links. Its an education.
    My conclusion? Iran is a decade away from modern centrifuge capability. If this stuff were easy, everybody would have nukes.

  9. Josh (History)

    Alas, if it were only so simple. No country requires cutting-edge commercial technology to produce fissile material for nuclear weapons. Indeed, the same type of machine (P-1, aka IR-1) sufficed for the Pakistanis.

  10. Iranian

    We don’t use the word “Allah” in our daily conversations because it’s Arabic; we use our own Farsi word for it; next time I would appreciate if you could just use the word God when translations are made from Farsi to English.

    Thank You

  11. mark hibbs

    Folks: It would be fair to describe TC-21 as “about 100 SWU/yr” and its commercial predecessor TC-12 to be about a third of that, maybe just a little more, but no more than 40 SWU/yr. The decisions to set up the Urenco plants in the US and in France were made before TC-21 was ready for commercialization at the time of construction. My understanding is that the initial machines will be TC-12s, and then they will go on (I know this was the plan for the French plant) to progress to TC-21s. There are NO plans at Urenco to build a machine with a throughput of 250 SWU/yr—about that I am quite confident.

  12. nick (History)

    I found two errors in Albright’s report, I hope another pair of eyes could check it. Firstly, his notion of efficiency for the Zippe centrifuges is wrong; the numbers simply don’t add up. With Zippe efficiency of 30% at SWU of .94 Kg/yr(max), we get effective SWU of .28 Kg/year and not .56. It seems he is using (1-efficiency) which is not correct. Also as for the Fordo assessment, (b) he claims that assuming Fordo has the same SWU per year as FEP right now, which is 2500 Kg per year, in two years it will have enough for 25 Kilo bomb. So now he claims it takes 5 tons of LEU to produce one bomb? USG and the media claim Iran, already has enough for one bomb (@1800Kg) of size 25 Kilo.

  13. Yale Simkin (History)


    The maximum possible separative capacity on paper of the SSZ-100 is calculated as 1.88 kg swu/yr.

    The actual separative efficiency of the design maxs at 40%-50% of that value.

    This means that the maximum separative capacity in the real world of the SSZ-100 is between 1.88 × 0.4 and 1.88 × 0.5 or
    between 0.75-0.94 kg SWU/yr.

    While actual running a SSZ-100, Zippe was able to achieve in the real world, not the max efficiency of 40-50%, but only 30%.

    So, 1.88 kgSWU/yr(theoretical max) x 30%(empirical efficiency) yields the 0.56 kgSWU/yr(actual)

  14. Yale Simkin (History)

    Albright is using 16 – 30 kg of 90% HEU for a first-generation bomb (you can go w.a.a.a.a.y less than that.)

    That covers designs with cores ranging from 15 – 25 kg HEU and includes (recoverable) process-lost HEU.

    Starting from natural Uranium, that requires:
    2500 SWU (at 0.5 tails) to get 16 kg HEU (using 7 tons of natural-U)
    4600 SWU to get the 30kg HEU (using 12 tons of natural-U).

    Starting from 3.5% LEU, you need only:
    975 SWU to get 16 kg HEU (using 1/2 ton of LEU)
    1830 SWU to yield 30 kg HEU (using just under a ton of LEU)

    So, using Albright’s 2500 kg SWU/yr and natural Uranium, you get one 15kg bomb/yr or a bit under 2 years to get a 25kg bomb core.

    Using LEU, you get a bomb in a bit under 5 months to 9 months.

    As an aside, if you plumb the cascades to shove out a bomb quickly, and you set the tails high, you can cut these numbers in half.

    Lastly, if Iran started with LEU at 20% and 0.5% tails, you get a bomb every 5-6 weeks.

  15. Bahram Chubin (History)

    To “Iranian”: I take it that
    “Allah willing,” is the translation for “Enshallah,” which does have the morpheme “allah” in it. Except that it is a somewhat secular word in Persian, to the point that even an atheist might use it. It’s probably best translated as “God-willing” or, less desirably, as “hopefully”; but “Allah willing” is not a bad translation.

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