Jeffrey LewisIran & the Bomb 1: How Close Is Iran?

This is first part in a three part series on Iran’s nuclear capabilities that I am writing at the urging of Noah Shachtman from DefenseTech.

When some moron like Charles Krauthammer claims Iran is now just “months” away from a bomb, you can pretty much ignore him: He has no idea what he is talking about.

Overall, Iran is probably a little less than a decade away from developing a nuclear weapon. The key question here is how long it will take Iran to enrich a few tens of kilograms of uranium to more than 90 percent U-235.

Dafna Linzer reported that the US Intelligence Community does not believe that Iran could do so before “early to mid next decade”—a revision of previous assessments that Iran would “have the ability to produce nuclear weapons early in the next decade.”

Why so long? The answer is that Iran still has to build, install and operate its centrifuges to enrich uranium.

David Albright and Corey Hinderstein at the Institute for Science and International Security (ISIS) released an estimate that breaks down the steps for Iran to make fissile material for a bomb, along with a nifty satellite image (at right) of Iran’s Fuel Enrichment Plant (FEP) at Natanz.

Most references to Iran being “months” away from a bomb are really statements about how close Iran will be once it completes the FEP—something, as you will soon see, that will take a few years.


But, first a little digression …

Iran plans to house about 50,000 centrifues in the Fuel Enrichment Plant (FEP) at Natanz in order to produce low enriched uranium for a notional civil nuclear power program. The output of a centrifuge is measured in “seperative work units”—a measure of the amount of work required to enrich a given amount (product) uranium. In math:

Separative work per unit of product = V(XP) – V (XW) – F/P *[V(XF) – V(XW)]

V(S) = (2*S – 100) * LOG (S/(100-S)]

F/P = (XP- XW)/(XF-XW), where

XF = feed assay (W/O)
XP = product assay (W/O)
XW = tails assay (W/O)
V = separation potential
S = XF, XP, or XW
F/P = feed to product ratio

URENCO understood that most of us find math a quaint endeavor in the age of the calculator, so they posted a sweet SWU calculator on their website. Now, you too can caclulate how much SWU is required to produce 25 kg of HEU (a few thousand depending on some technical factors).

Each of Iran’s centrifuges has an output between 2-3 SWU/year. Iran plans a that the full scale FEP at Natanz will house 50,000 centrifuges, giving the plant a capacity of 150,000 SWU/year—enough for annual reloads of LEU for the Bushehr reactor or, if configured differently, 25-30 nuclear weapons worth of HEU per year. (More on Natanz)

Of course, those are Iran’s plans. Iran probably only has about 700 centrifuges, as well as components for another 1,000 or so.


So, the real question, however, is how quickly Iran could assemble and operate 1,500 centrifuges in a crash program to make enough HEU for one bomb (say 15-20 kg).

Albright and Hinderstein have created a notional timeline for such a program:

  • Assemble 1,300-1,600 centrifuges. Assuming Iran starts assembling centrifuges at a rate of 70-100/month, Iran will have enough centrifuges in 6-9 months.
  • Combine centrifuges into cascades, install control equipment, building feed and withdrawal systems, and test the Fuel Enrichment Plant. 1 year
  • Enrich enough HEU for a nuclear weapon. 1 year
  • Weaponize the HEU. A “few” months.

Total time to the bomb—about three years.

David and Corey state that this timeline is a worst case estimate that assumes Iran encounters no significant problems along the way:

This result reflects a worst case assessment, and thus is highly uncertain. Though some analysts at the IAEA believe that Iran could assemble centrifuges quicker, other analysts, including those in the US intelligence community, appear to believe that a date of 2009 would be overly optimistic. They believe that Iran is likely to encounter technical difficulties that would significantly delay bringing a centrifuge plant into operation. Factors causing delay include Iran having trouble making so many centrifuges in that time period or it taking longer than expected to overcome difficulties in operating the cascades or building a centrifuge plant.

The interesting question is what technical problems the US IC expects Iran to encounter. The thing about a crash program is that things, well, crash. In another paper, Albright and Hinderstein note some of the potential problems:

Iran might not be able to meet such a schedule for bringing a centrifuge plant into operation. The suspension of manufacturing and operating centrifuges could be reestablished, or Iran might have trouble making so many centrifuges. In addition, Iran does not appear to have accumulated enough experience to operate a cascade of centrifuges reliably. Iran had assembled 164 centrifuges into a cascade just before the suspension, but it did not acquire sufficient experience in operating the cascade to be certain it would perform adequately. Centrifuges can crash during operation, causing other centrifuges in the cascade to fail—in essence, destroying the entire cascade. Thus, Iran might need a year or more of additional experience in operating test cascades before building and operating a plant able to make HEU for nuclear weapons.

Yes, centrifuges spinning at supersonic speeds can crash. Especially if you don’t get the lead out.


Well, not really lead—but molybdenum hexafluoride (MoF6) (Folks in the 18th century thought molybdenum was lead—hence the name derived from molybdos, or lead in Greek).

I’ve previously emphasized one technical problem—the inability of Iran to make relatively pure uranium hexafluoride (“hex”) to be fed into centrifuges for enrichment. (See Got Gas? Iran Stinks at Making UF6, Aug 13, 2005)

Before introducing UF6 into a centrifuge cascade, the Iranians must rid the gas of impurities like MoF6 or the impurities will plug cascade piping, crashing Iran’s centrifuges.

Richard Stone in this week’s Science Magazine further documents the problems that Iran is having purifying hex at its Uranium Conversion Facility (UCF) near Esfahan:

Creating purified UF6, which can be fed as a gas into centrifuges for isotope separation, would be a much bigger one. According to an official at the U.S. State Department, Iran has struggled to convert UF4 into UF6, a dangerous process involving highly toxic and corrosive fluorine gas. The official also claims that Iranian UF4 is tainted with large amounts of molybdenum and other heavy metals. These oxyfluoride impurities in UF6 “might condense” and thereby “risk blockages” of valves and piping, an IAEA specialist told Science.

Iran’s bad at making hex in part because the Clinton Administration convinced the Chinese to stop building the UCF—a major nonproliferation victory that Stone mentions. Stone cites an interview that Dr Mohammad Saeidi, AEOI deputy for planning and international affairs, discussing the deleterious impact of the Chinese cut-off. (See: Sticks and Stones: China, Iran and the UCF, Sep 05, 2005 . Contains the full-text of the interview, in the event you’re interested.)

Stone also mentions a series of stories by Mark Hibbs detailing Iran’s difficulty in using pulse columns to purify uranium. (Iran’s UF6 Is Crap, Sep 28, 2005 and Chinese mixer-settlers at UCF, Oct 20, 2005).

How long will it take Iran to get it’s act together on hex? Hibbs reported a wide variety of estimates among intelligence services:

Intelligence analysts do not agree on how long it will take Iran to solve current process chemical problems at its restarted Uranium Conversion Facility (UCF) at Isfahan.

These difficulties have thus far prevented Iran from producing uncontaminated uranium hexafluoride (UF6) feedstock for its gas centrifuge enrichment program. Last month, as Iran prepared to operate the plant, Vienna officials said that Iran would require “at least several months” to address its problems (NF, 15 Aug., 1).

According to Israeli government analysts now examining related technical issues, it may take Iran two or three months to begin producing pure UF6. According to U.K. government experts, however, Iran may need about 18 months to do that.

But government analysts do agree on one point: The higher the enrichment level sought by Iran from its gas centrifuges, the more critical it will be for Iran to first eliminate technical problems associated with producing pure UF6.


Iran still faces a number of technical challenges before it can start churning out fissile material. Those challenges are going to years to solve.

Parts 2 and 3 will discuss whether Iran could mate a warhead to a missile and prospects for a strike against Iran’s nuclear facilities.


  1. James (History)

    And all of this predicting timelines ignores the fact that once the enrichment passes a certain point, it will be instantly known that Iran is accumulating material for a bomb. Assuming they remain under the inspections regime mandated by the NPT, we will have a minimum of three months to bomb all the sites into oblivion. I don’t see a crisis here.

    The Iranians themselves have proposed a more intensive inspections scheme than that mandated by the NPT. They could withdraw from the treaty, of course, once they have built the plant, but there would still be those three months to deal with them militarily.

    Bottom line: no matter what they are building, even if we have reason to suspect a bomb, it’s far better to have them in the system than outside it.

  2. Ferdinand

    Is it reasonable to conclude from that last quote that the more time Iran invests in trying to produce pure UF6 the more suspicious the rest of the world should be of their intentions?

  3. Mark

    I agree with James’ assessment and I’m not worried, but just as Devil’s advocate… If Iran continues their current program and avoids international action for another 6 months, they could have the kinks worked out at the PFEP and 90 tons of pure, low-enriched UO2 stored at Bushehr. Then they’d be in a much better position for a quick “crash program”, if they withdraw from the NPT and run a small cascade at a hidden, protected site. The low-enriched feed could be made weapons-grade in a quarter of the time of starting with natural uranium, and there wouldn’t be any of those purity issues like with the stuff coming out of the UCF.

    Of course, for Iran to betray Russia like that would be the quickest path to DPRK-like isolation, which wouldn’t do anybody any good.

    (And for all I know, Russia might have considered this and is planning to dope the Bushehr fuel with some contaminants that wouldn’t affect its use in the reactor but could wreck a centrifuge cascade.)

  4. J.R. (History)

    Love the article, but the math section would be easier to read with a few [SUB]script tags.

    I can’t wait for Parts II and III!

  5. mark gubrud (History)

    “We can always bomb Iran later” is unconvincing. Probably we can, but maybe they’ll heap the dirt higher and buy more air defense in the meantime. More importantly, the political context has to be correct. Iran breaking out of IAEA safeguards wouldn’t be enough; people would say, “Wait, let’s give them time to reconsider.” Maybe the Clintons would be back in the White House. Maybe the EU3 would have cashed out of the game and Russia wouldn’t be so accomodating, either. “Strike while the iron is hot.”

    The election of Ahmadinejad, collapse of the EU3 talks, and some favorable developments on Iraq have handed Bush a get out of jail free card, and the Israeli succession crisis lights the fuse at the other end; it’s a three-ended fuse if you add in Iranian bullheadedness. The demonization of Ahmadinejad, greatly aided by his own pronouncements, is coming along fine. My mediaometer clearly indicates we are in the beginning stages of another war buildup. Next stop: the Security Council. Which must, of course, “fail” so that Bush can invoke “self-defense” – but we’ve all seen this movie before. It’s the politics, stupid. Whether and when the US and/or Israel attacks Iran has little to do with nuclear technology considerations at this point.

  6. Haninah

    My two cents on the Israel front: at the risk of being the moron who tried to predict history and ended up with egg on his face, I think Sharon was unlikely to go unilateral and bring out the F-16Is any time soon, and Olmert is even less likely now.
    For one thing, there have been moments in Israeli history where a show of military bravado was likely to help a leader going into an election; this is not one of those. Olmert’s strategy is to run as the successor of the man who brought the conflict down to its current “manageable” simmer, and his image would not be particularly helped by a sudden massive military operation, even though most of the voters would believe him if he said it was necessary.
    Second, there are many types of common sense Israeli leaders typically lack; one aphorism they’re generally pretty good at, though, is that once you’ve pulled off a neat trick, it won’t work a second time. Public pressure aside, I’m sure this super-media-image-obssessed Kadima clique is at least as aware of the difficulties of pulling off another Osirak as anyone else.

  7. mediageek

    Ok, probably a dumb question, but what’s to keep Iran from simply buying fissile material?

    If everyone’s watching the centerfuges for the magic point where they go from being something to produce peaceful nuclear energy to the stuff you shove into the nose cone of an ICBM, it wouldn’t be terribly bright of them to actually attempt to go through with that plan, right?

  8. j house (History)

    this all assumes Iran will only obtain bomb-grade uranium indigenously in the next 10 years.With oil at $60+ a barrel and NPK starved for cash, they may get there sooner

  9. mgd

    No Mediageek it’s not a dumb question. It’s THE question. North Korea has already supplied Iran with missile tech, why not through in a little fissionable as well? What’s scary is that the author of the article is smart enough to come up with those equations but too obtuse to see the obvious.

  10. Richard (History)

    Wouldn’t a dirty bomb suffice in Iran? The Al Qaeda connection by Paul Williams talks about how Al Qaeda obatained nukes already from Russia’s blackmarket.

  11. David Keppel (History)

    Bomb a Future Purchase?

    Those with worst case scenarios posit an Iranian purchase of highly enriched uranium. If so, how will bombing their fledgling ability to enrich uranium slow the program?

    Given the confusion—apparently even among those privy to “secret” information—any US/Israeli attack would have to be sweeping, and aim at degrading the entire Iranian military infrastructure, including its “conventional” retaliatory capability. Advocates of war need to be honest about the costs of such an attack.

  12. Arrigo (History)

    For those talking about Iran acquiring fissionable material directly from DPRK: surely this means that the DPRK has both enriched U235 and Pu239 lines wheras most information appears to point to the latter.

    If this is the case then why purchase U235 in the first place intstead of PU239 for which a far smaller quantity is required for a pretty boom?

    Conversely, if they purchased enriched U235 from DPRK then either the DPRK is swimming in it (and given the amount of time and delicate equipment required allow me to be skeptical) or they have sacrificed substantial amounts to seed what? A ridiculously small cascade? In the Manhattan Project the seeding of the cascades was done with Lawrence’s U235 from the calutrons and that wasn’t exactly in kilo quantities and then it went into huge cascades.

    My questions, as an obviously naive European, are as follows:

    1) why is GWB trying to build up a case for war in Iran? What is the benefit to himself given that at the end of this term he can’t seek re-election? Or is there a cunning plan (cf. Baldrick in Blackadder) to place the next Bush in the dynasty at the White House?

    2) Although I am not advocating appeasement, would it not be a good idea to tread carefully given that Iran’s internal politics is obviously in turmoil? Doesn’t lending credence and weight to the Iranian “agents provocateurs” actually give a longer lifeline to the wrong faction? Would it not be a rather radical step to endorse an entirely civilian programme under NPT protocols and verification?

  13. Bobby A. (History)

    Great Article! Thanks for the Info!

  14. mgd


    I’ll agree that you’re an obviously naive European.

    1. Where is GWB building up a case for war?? And even if he was, why must it necessarily be self-serving? Maybe he’s just actually concerned about an apocalyptic regime who wants to wipe Israel off the face of the earth acquiring nukes. It doesn’t appear that the EU is too keen on it either. BTW why on earth would you think that another war would help him get re-elected anyway? Quite the opposite.

    2. You are essentially advocating appeasement. Time is of the essence here. Ahmadineja can pussy-foot around just enough to give him time to finish off the Tehran Project. Sort of like allowing Hitler to re-arm
    after WWI.

  15. merton

    If Europe convincingly proclaimed solidarity with the USA in economic pressure, then military force if necessary…then perhaps neither would ever have to be used.

    The lack of resolve is what will allow this to play out in the worst fashion.

  16. Papa Ray (History)

    We are not talking conventional threat here, so the typical military/administration planning here can’t be the old “plan to your enemies capabilities”.

    With an Islamic state that has made over 80 billion dollars just in the last year on its oil sales, with a somewhat loony President and Mullahs that no one really knows much about, except that they advocate destroying Israel and the United States…

    The President of the United States and his Military has to plan a little differently.

    They must plan according to their enemies intentions as well.

    Knowing that there is fuel available from somewhere that they may have had for years and been able to refine. Knowing that there is the small chance that the final product has been already purchased either ready to make a bomb or already made into a bomb.

    When the outcome of not guessing right or guessing wrong can result in thousands if not millions of dead or a complete shutdown of electricity and electronics in a large part the United States…

    President Bush must make a very hard decision. But knowing that his concern and responsibility are to the American People, I have no doubt that if he does err it will be on the side of the safety of the American People and the United States of America.

    Papa Ray
    West Texas

  17. Greg (History)

    Is this the same intelligence community that told us Saddam was dripping with weapons of mass destruction?

    Since Frank Church neutered our human intelligence capabilities long ago, I’m not willing to bet my family and nation on satellite photos and a CIA motivated more to topple their Commander-In-Chief than deal with threats.

  18. Baldy (History)

    Wouldn’t it be a “shame” if they came so close, and were bombed out of business? Would it not make sense to at least receive some mat’l from abroad, as a protection from the US etc, until they could achieve it themselves? There is an understandable fear that bombing once “online” would spread fallout… This way, they just need enough for a bomb or two, as insurance against attack.

  19. ant (History)

    A military solution seems precarious to me – cutting off another major supplier of oil to the US when supply is barely keeping up with demand would certainly be a shock to the economy. The markets are already jittery over Iranian threats to cut off supplies. So it seems, at least in this respect, Iran is holding the cards.

  20. ehud

    Ant, are you serious? If Iran launches even one nuclear warhead at the US, the cost of oil will be irrelevant. It’s hard to drive a car when you’re dead, “jittery markets” nonwithstanding.

  21. Henry Bowman (History)

    I intend to post a few more comments after reading Parts II & III, but you really do not help your argument with ad hominem attacks. Your opening statement (calling Charles Krauthammer a “moron”) is not only useless to your argument, it is ridiculous, as Krauthammer is in fact a very sharp guy. That doesn’t mean he’s well-informed on this topic, of course. Calling him a moron makes one wonder if you are a bit over the top yourself.

  22. Jeffrey Lewis (History)

    That’s the aesthetic here.

    I write plenty of boring, staid stuff at work where I’d never dream of calling anyone, even Krauthammer, a moron.

    As a colleague says, “Blogging is like hockey. It’s supposed to be rough.”

  23. Baldy (History)

    Does anyone get the feeling it’s all too easy? That Iran almost seems to be asking for regime change? What do we NOT know? What WMD may they have that we don’t know about? Or what cells are in place in which capitals that are ready to strike? We (the Civilized world) are missing something.

  24. ant (History)

    Gotta reply. Yeah, I am serious. Read part 2. Iran isn’t going to be hitting the US any time soon – at least not with a missle. Other options ARE more worrisome, but the quesion comes down to WHY is Iran seeking the bomb. Are they looking to use them offensively? Or do they, instead, see them as a defensive tool and as a device to threaten their neighbors? I certainly need to do more reading on the subject, but it’s an important question.

    Economic warfare is a reality and the Iranian threat to cut off their own oil as well as hinder access from other states is a serious one. Additionally, a military strike on Iran has ramifications throughout the region and may lead to a backlash just as devastating (though more dispersed) as a nuclear strike. It’s impossible to know what course of action is the best, but military strikes aren’t as clear cut a decision as they seem. There are consequences and they could be dire – for both Iran and the West.

    The fact that we’re even having this discussion betrays a massive foreign policy failure. Perhaps it wasn’t avoidable but it seems to me that we’ve come to a lose-lose situation and there is no easy way out of it.

  25. quellish

    “If this is the case then why purchase U235 in the first place intstead of PU239 for which a far smaller quantity is required for a pretty boom?”

    Composite levitated core. Using both means you need much less of each. And the DPRK has production lines for both U235 and Pu.

  26. dan (History)


    There’s no mystery. Cast your mind back to the Katrina and Rita double whammy for the oil industry and the desperation with which the EU/US acted to get the oil price back down below $70 per barrel. IIRC there were supposed to be substantive discussions of the Iran dossier at the IAEA in their meetings in both October and November; these discussions were postponed on both occasions as there were large hurricanes threatening the GoM at the time, and there was considerable anxiety that oil prices would breach that magic number again – obviously adding further geopolitical risk premiums wouldn’t have helped.

    I suspect that Karl Rove has done his homework and knows that sustained pump prices above $3 per gallon are politically toxic in an election year.

    In short,what we have is a very well telegraphed market signal that constitutes a pause for thought for the Bush administration, $70 per barrel oil.

  27. mgd

    I’m glad to see others have defended Krauthammer. I was surprised to see that comment myself. The guy is sharp as a tack.

    Yes, I think it’s too easy. There is some talk that Iran is warcrying so that the US will keep troops in Iraq and keep the Sunni resistance quelled. Iran wants its Shia friends in power.

  28. Hassi (History)

    Course, there is absolutely no evidence whatsoever that Iran has a nuclear weapons program—this is just speculation about what Iran “could do”—and any country could do the same.

  29. Drew (History)

    What is the difference in your timelines if one assumes that Iran builds/has P-2 type centrifuges vice P-1? What do we know about their possession of P-2s beyond plans for them?

  30. nemo

    Didn’t hear much about that other term of the equation, Russia.

    I guess that nothing can be done now by just one country, things are way too complicated for unilateral action.

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