James ActonSafeguards in Iran. And Elsewhere.

Partial schematic of Iran’s planned fuel cycle, once facilities currently under construction have been completed.

I was travelling on Friday and got back to the internet to observe the aftermath of the s*!t storm over material accountancy in Iran.

The story that seems to be emerging is that Iran understated the quantity of low enriched UF6 it produced because of a genuine error in calculation, as reported by various sources including Mark Hibbs (in the comments to Jeffrey’s post and, I assume, elsewhere) and Global Security Newswire. Presumably, during its annual physical inventory verification (PIV), the IAEA found an anomaly and worked with Iran to discover it was an error rather than anything more suspicious.

What is the significance of the IAEA’s phrase about “measurement uncertainties normally associated with enrichment plants of a similar throughput”?
In its report the IAEA repeated its standard comment that the results of the PIV were “within the measurement uncertainties normally associated with enrichment plants of a similar throughput.” This raises an interesting question: What uncertainty would be expected in performing a physical inventory at the Fuel Enrichment Plant (FEP)?

The typical measurement errors associated with weighing canisters, sampling UF6 and measuring enrichment levels are actually very small. They are all given in a favourite of mine—the gloriously wonkish International Target Values 2000.

I don’t have the time now to do a calculation to work out what measurement uncertainty would be expected for the FEP as it currently stands but, a couple of years ago, I did this calculation assuming the facility was fully fitted out with 50,000 centrifuges and producing 30 tU/yr of 3.5% enriched LEU. It’s in a study I did for VERTIC with the memorable title, The use of voluntary safeguards to build trust in states’ nuclear programmes: The case of Iran. Incidentally, in Appendix I, this paper contains a moderately technical summary of the principles of nuclear materials accountancy—if you’re interested.

Anyway, I calculated the measurement uncertainty for a PIV in the FEP when completed would probably be just a few kg of uranium (depending on the exact type of measurement techniques used). This is consistent with the expected values given by the IAEA in its Safeguards Glossary (table III, p. 53). So, the measurement error for the FEP today, which has just 4,000 centrifuges (or thereabouts), would be considerably smaller (no, it’s not a linear relationship).

What this means is that the IAEA’s comment that the results of the PIV were “within the measurement uncertainties normally associated with enrichment plants of a similar throughput” almost certainly refers to situation after the error in Iran’s calculations was spotted. The 209 kg discrepancy that sparked the controversy is way, way outside the typical measurement uncertainty.

Why did Iran not spot the error itself?
This is a question that I have been asking myself. I would have expected Iran to have checked its calculations by actually measuring UF6 masses and enrichment levels. I mean you’d do that if you ran an enrichment plant, wouldn’t you?

Certainly, this is standard practice in the one enrichment facility I have seen up close and personal. All UF6 cylinders were continually weighed. After each one was full it was heated (to “homogenize” the material) and a sample taken so its enrichment level could be ascertained by mass spectrometry. With these practices an error of 1 kg—let alone 209 kg—would be spotted pretty quickly.

The fact that Iran failed to spot its own error suggests that it isn’t doing any of this standard housekeeping. And, I think, this gives us a glimpse into a programme that in its rush to get started and churn out LEU has forsaken normal operating practices.

It ties in with the fact that Iran has stated its maximum enrichment level is higher than the IAEA measured, and also with a story I heard from one of the first inspectors to go to the conversion facility at Esfahan once it had started operating. This person said that the Iranian technicians were very keen to learn basic safety techniques from the inspectors, including how to deal with UF6 leaks. Health and safety has not been a major concern for the Iranian nuclear programme either.

To be clear: none of this sloppiness is illegal—it’s just bad practice. And, it makes the IAEA’s job harder.

Tightening safeguards?
The measurement uncertainty discussed above matters because it sets the size of a diversion that the IAEA could confidently detect. In my paper I calculated that, with 95% probability, the IAEA could detect a diversion of about 5 kg from the FEP when it is fully kitted out. This is 15 times smaller than the 75 kg target value for LEU. Bear in mind that IAEA safeguards are designed for much larger facilities than Natanz so it’s not surprising the IAEA could detect such a small diversion. So, I am very confident in the IAEA’s ability to detect the diversion of one significant quantity of LEU from Natanz.

However, I am much less confident in the IAEA’s ability to detect a diversion in a timely manner (or to detect a clandestine facility—but that’s a different story). Specifically, the IAEA aims to detect the diversion of LEU within one year.

Currently a PIV at Natanz (when the IAEA measures a pre-determined fraction of all the nuclear material at the facility so it can accurately estimate the total inventory) is conducted once a year—the standard practice in most (if not all) facilities under IAEA safeguards. Given the time taken to process the results of this inspection, it means that a diversion occurring just after a PIV might not be detected for 13 or 14 months.

I say “might” because containment and surveillance is in place and that might detect a diversion even before the PIV comes around. Similarly, the IAEA conducts interim inspections in many facilities, normally to verify material flows into or out of the facility but sometimes to conduct interim inventories (albeit in a less rigorous manner than during a PIV). If such inspections occur at Natanz they would increase the probability of detecting a diversion within a year. (Note: These are different from the short-notice randomly-occurring inspections in the cascade hall that are definitely happening and occur about once a month).

In any event, given what we know (or rather don’t know) about the safeguards approach for Natanz, I think there are legitimate questions about whether detection in Iran would be timely. Others have made this point too—including David Albright. But, to be fair, this is not just an Iranian problem. It is true in bulk handling facilities in other states as well.

It would not be hard to fix, if funds were available. Performing a PIV twice a year or increasing the frequency of interim inspections would be useful in helping the Agency meets its current timeliness detection goal or even a more ambitious one. And, in an ideal world, I argued in my paper that this is exactly what the IAEA should do.

But, here’s the rub. Any change to the IAEA’s verification approach could only be effected with Iran’s permission. The safeguards approach for Natanz (contained in the co-called facility attachment) took about a year to negotiate. And, reading between the lines of the IAEA’s reports, it was a painful process. I find it almost impossible to imagine Iran agreeing to the IAEA performing a PIV more often or conducting more frequent interim inspections.

And, again, to be fair, this is not just an Iranian issue. At a fundamental level, the main problem with IAEA safeguards is not the accuracy of measuring techniques or the frequency of inspections—but severe limits on the Agency’s legal authority. I have no doubt that intransigence on negotiating or renegotiating a facility attachment is an issue in many other states too. The situation in Iran just throws this problem into sharper relief.


  1. Arnold Evans (History)

    These problems are all artifacts of the political decision taken by the United States on Israel’s behalf that the IAEA should be used as one tool to prevent any regional state from having domestic enrichment or reprocessing – which would make that state “nuclear capable” in the eyes of US/Israeli strategists, even if in full compliance with all actual NPT obligations.

    There is no reason an IAEA-examined facility should not already have easy access to best practice safety standards without technicians having to ask inspectors for advice.

    Iran has also said that they’ll sign anything the West wants in terms of inspections as long as it retains internationally accepted domestic enrichment. They’ll go back to implementing the Additional Protocols, which they implemented until the referral to the security council, and if you want PIVs more often, why not?

    The problem is not Iranian technological ineptness, it is not Iranian intransigence, it is not inadequate safeguards regimes. The problem is that the US is trying to prevent Iranian domestic enrichment in contradiction to the clearly expressed terms of the NPT.

    And is there really a legitimate question of whether Iran could divert a weapon’s worth of uranium before it was detected? Really?

    Are you saying it’s plausible that Iran could take all of the LEU it has now and put it somewhere unmonitored without anyone noticing in a timely fashion? Really?

    If we’re talking about less than a weapon’s worth, why would Iran divert it if that would be discovered after an “untimely” period of one year?

    This way-beyond-worst-case thinking about Iran’s nuclear program is tied more to strategic considerations – Israeli strategic considerations – shared by the US foreign policy community and the US non-proliferation community than it is to any technical safeguards issue.

    Lastly, the yearly PIV is what was negotiated. The US non-proliferation community just exudes bad faith when it comes to agreements. What happened to the US’ obligation to begin negotiations toward full nuclear disarmament?

  2. Major Lemon (History)

    “Health and safety has not been a major concern for the Iranian nuclear programme either.” Excuse me! I hear they recently bought a consignment of “DANGER – CATASTROPHIC NUCLEAR MELTDOWN IN PROGRESS – KEEP OUT!” vinyl signs in Farsi. Either they have been tightening up on safety or they are trying to impress the world they are ready for any eventuality. Heck, it’s only peaceful nuclear power after all.

  3. Andreas Persbo

    I got the health and safety aspect confirmed by an Iranian associated with the nuclear programme quite recently. They want to learn more, much more, about that.

  4. Mark

    I just want to re-emphasize the definition of an SQ of LEU according to the IAEA: 75 kg of U-235.

    According to the IAEA report, as of the end of January Iran has produced ~ 839 + 171 = 1010 kg of LEUF6. At 3.49% enriched, this is ~ 23.8 kg of U-235. (1010 kg UF6 * 0.676 U/UF6 * 0.0349 U-235/U)

    So for Iran to divert an SQ of LEU, it would have to divert more than three times the total amount of LEU it has produced so far at the FEP. I’m pretty sure the IAEA’s containment and surveillance methods would catch this in a timely manner.

    Not that diverting lesser amounts isn’t significant, just that is doesn’t meet the IAEA’s definition of a “Significant Quantity”.

  5. Yale Simkin (History)

    The old IAEA SQ definition is simply irresponsible.

    Since (much)less then 15kg of 90% U235 is needed to build a bomb, the 75kg U235 LEU standard is crazy.
    As Cochran and Paine and pointed out years ago:

    The IAEA’s official “SQ” values also form the basis for public, media, and policy making assessments of the bomb-making potential of nations or terrorist groups seeking to acquire nuclear weapons. Unfortunately,… the IAEA persists in using SQ values that are outdated, technically erroneous, and even dangerous…

    Iran’s roughly 1150 kg of LEU, if run thru their centrifuges with a tails assay of 1.66%, will produce 16.5kg of 90% U235 (the rest is in the tails).
    Losing 10% in conversion and machining, the 15kg remainder is enough to produce 1 basic bomb, or 2 or more somewhat more sophisticated warheads.

    This is physics and engineering, not agency rule-making.

    Using Iran’s current array of centrifuges and stated performance, there is a breakout time, from LEU to metal, of 2 to 3 months.

    As they buildout the remaining 10’s of thousands of centrifuges over the coming months, the breakout time falls to days.

    With a clandestine diversion rather than overt breakout, the breakout time depends on the size of clandestine array and the quantities that they are comfortable redirecting.

  6. b (History)

    A bit of lunatic discussion here.

    Missing the real percentage of the enrichment Iran has done – the sole reason for the differences of Iranian estimates and the IAEA physical accounting – is nothing serious.

    The IAEA observes every gram of U going in and out of Natanz – an enrichment level difference at Natanz of 3 or 5% is irrelevant as long as the result stays there.

    The idea that one potential bomb, would that be from 15 or 75 kilogram of highly enriched U (which Iran does not have nor seems to strive for), would be a game changer is ludicrous.

    Anyone who thinks strategically would want to test a weapon before – potentially – using it.

    So what would a one bomb-capacity really give you but a test followed with much trouble with no possible way to defend against that as all the U was used for the test?

    Why use such capacity at all? Is there any successful use of nukes documented since multiple powers have achieve nuke status?

    Iranian officials say they see no real use for a nuke. Why not agree with that analysis?

    What would YOU do, in an Iranian decider role with nukes? Kill your own 60++ million people?

    For what purpose?

  7. Mark


    I agree with you that smaller quantities are significant. The IAEA clearly agrees, also (e.g., the fuss they raised with South Korea over sub-gram quantities of plutonium).

    My point was addressing the question in the original post: can the IAEA meet its timeliness goals in detecting diversion of an SQ of LEU at Natanz within 1 year. How long would it take the IAEA to detect if Iran produced triple the amount of LEUF6 it has so far produced at the FEP and then diverted all of it? Much shorter than one year, I believe.

    I was clarifying the use of the IAEA definitions, not addressing the adequacy of those definitions and timeliness goals for effective safeguards. Don’t strawman me.

  8. hass (History)

    IAEA spokesman Melissa Fleming corrected the record set so askew by all the hyped media coverage just yesterday:

    “The (IAEA) has no reason at all to believe that the estimates of LEU produced in the (Natanz) facility were an intentional error by Iran. They are inherent in the early commissioning phases of such a facility when it is not known in advance how it will perform in practice,” said IAEA spokeswoman Melissa Fleming…

    “No nuclear material could have been removed from the facility without the agency’s knowledge since the facility is subject to video surveillance and the nuclear material has been kept under seal.”

  9. James Acton (History)

    Hass: Quite. Which is why I used the words “genuine error in calculation” to described what happened.

  10. Yale Simkin (History)


    Please understand I was nor trying to “strawman” you. Nothing was further from my mind. I was not speaking directly to the point you were making (with which I don’t disagree). I was simply “enriching” the discussion by amplifying your comment:
    Not that diverting lesser amounts isn’t significant, just that is doesn’t meet the IAEA’s definition of a “Significant Quantity”.

    Hope this clears any misunderstanding.


  11. kme

    Yale: When I do the calculation starting from 1150 kg of 3.49% LEUF6 to a product/tails assay of 90%/1.66% I get 14.32 kg of U235 in the product (and 12.49 kg in the tails). The product totals 15.93 kg of U.

    I don’t think this materially changes your argument, though.

  12. Yale Simkin (History)


    The figure I stated was for the quantity of 90% U235 HEU such as would be used in a bomb. Your figure is for the U235 contained in the HEU, not the HEU itself.

    After adjusting for the apples and oranges, the figures are the same. The minor residual difference is based on rounding I did (because I was too lazy to look back at my original numbers). My calculated HEU values were actually based on using LEU (hex) from the IAEA inspection report of 1010 kg (as of 1/31/09) and adding 173 kg I estimated that Iran produced by 2/20/09.

    Using the actual and derived 1,183 kg LEU (hex) gives my 16.5 kg HEU with 90% U235 content (or 14.45 kg of pure U235).

    The whole treatment (and production assumptions) are found in an earlier thread here

    But, as you say, the exact numbers don’t affect the argument. 15 kilograms of HEU is not a magic number. Bombs can be made much, much more or much, much less (altho using very much more or very much less is real tricky)

  13. hass (History)

    Acton: The point is that if the facility is subject to 24 hour monitoring, then even the once year PIV is sufficient safeguard on the LEU.

  14. hass (History)

    Incidentally, the Iranians were supposed to receive safety assistance under the terms of the IAEA’s Technical Cooperation Program —- which was terminated under US pressure

  15. kme

    Yale: Ah, I see. Putting in 1183kg I get 16.39 kg of 90% HEU containing 14.73 kg of U235 (my understanding is that the enrichment percentages are by molar quantities, not mass).

    Does anyone know if the LEU product is being converted back to oxide?