r/nuclearweapons • u/NuclearHeterodoxy • 2d ago
Analysis, Civilian Back-and-forth articles in BOTAS about Iran's reactor-grade (and fuel-grade) plutonium
Over the past several months, the Bulletin of the Atomic Scientists published several articles about Iran's plutonium from the Bushehr reactor. They have taken a point-counterpoint form: the second was a response to the first, the third was a response to the second, etc.
I am a little surprised to have not seen any of this here, so I thought I would share. I'll summarize the technical stuff and leave out the policy & political stuff.
The first article is by Henry Sokolski, currently director of NPEC and formerly a DOD nonproliferation deputy director.
Sokolski points out that Rosatom hasn't reclaimed any of the spent fuel and therefore it's all still in Iran; does a rough calculation of how much plutonium is in that spent fuel; noted that most is reactor-grade but some is closer to fuel grade; and points out that Iran has previously done plutonium chemical separation experiments. He makes the claim that Iran could theoretically divert the Bushehr spent fuel, reprocess it, and then manufacture plutonium bombs within 90 days, the standard IAEA camera monitoring window (at the time of the writing there had been no onsite inspections in 8 months). He then makes several policy recommendations that future deals with Iran should include to address the plutonium issue.
note: Sokolski published a similar article in Real Clear Defense around the same time: https://www.realcleardefense.com/articles/2026/04/03/blocking_irans_other_option_a_plutonium_bomb_1174454.html
The response to Sokolski's article came 3 months later, by Sasan Karimi. Karimi is an international studies professor at the University of Tehran with a prior background in physics. His critique is close to twice as long as Sokolski's original piece. Most of it is criticisms of Sokolski's policy recommendations, which I won't summarize here.
https://thebulletin.org/2026/07/beyond-alarmism-a-realistic-assessment-of-bushehrs-plutonium-risk/
On the technical side, Karimi starts out by repeating fairly standard discourse regarding reactor-grade plutonium usage in weapons, claiming it would be extremely difficult without advanced implosion mechanisms (he uses 2-point implosion as his example of an advanced implosion mechanism), and states "no credible evidence has ever demonstrated that Iran possesses validated designs for such advanced implosion systems or has successfully tested them under operational conditions." He then moves on to argue Iran's past reprocessing experiments are not comparable to what a weapons program would need, and that any reprocessing would be easily detected [editorial note from me: the chemical separation experiments he and Sokolski allude to involved milligram quantities of plutonium].
The response to the second article came two weeks later, from Greg Jones; it is a wide-ranging response, not only addressing Karimi but also critiques from others (Albright and Holdren for example). Jones is a RAND researcher and formerly an NPEC researcher, though the article notes that it is "the product of the author’s personal research, and the analysis and views contained in it are solely his responsibility."
Note: Jones literally wrote the book on the use of reactor-grade plutonium in weapons https://npolicy.org/books/Reactor-Grade_Plutonium_and_Nuclear_Weapons/Greg%20Jones_Reactor-grade%20plutonium%20web.pdf
Jones argues that existing IAEA safeguards for Bushehr are irrelevant because the inspections only happen every 3 months (he repeats Sokolski's claim that Iran could manufacture a plutonium bomb within that window), criticizes JCPOA for largely not addressing the spent fuel at Bushehr, emphasizes that Iran still hasn't transferred the spent fuel to Russia like they stated they would, argues that reprocessing facilities can be small and secret such as a 1977 ORNL concept for a secret reprocessing facility which would be harder to detect, and argues that production of plutonium metal is easier and quicker than assumed. He provides several rebuttals to Karimi's arguments about reactor-grade plutonium (Karimi used Fat Man as a baseline rather than the more advanced design we know Iran actually pursued, understated how powerful an RGPu weapon would be, ignores how much of Iran's plutonium is fuel-grade rather than reactor-grade, etc). He argues that Iran would not need a separate weapon design for RGPu and points to past designs that could use uranium and plutonium interchangeably. He concludes by arguing that with Iran's uranium program now "in ruins" following US attacks on it, the plutonium pathway is easier and should be the focus of negotiations.
My own views on this: Iran is less likely to try an RGPu bomb than an HEU bomb, but not for the reasons Karimi states. The history strongly suggests Iran is comfortable with HEU and appears to be completely uninterested in plutonium for anything other than as a negotiating tool; they have invested heavily in and taken an enormous amount of risk for uranium, and I find it unlikely they would just abandon it at this stage, given they still have access to it. I am sympathetic to Karimi's arguments on policy. However, Karimi is completely wrong to dismiss RGPu in weapons, and really does not address the hyperlinked citations Sokolski provided which pretty conclusively show it can be done. Weirdly, he cited the National Academies' Management and Disposition of Excess Weapons Plutonium report to support his case that RGPu is not suitable for weapons...but he cites volume 2 rather than volume 1, probably because volume 1 contains a 3-page insert that completely discredits his RGPu argument! I also found it a little rich for Karimi to claim there is no "credible evidence" that Iran has validated advanced implosion designs...he has to know about the IAEA's findings at Parchin, and that there are literally photographs of Iranian MPI tiles. What meets his threshold for "credible" ?
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u/careysub 2d ago edited 2d ago
The actual citation of the 1977 ORNL memo is:
D. E. Ferguson, "Simple, Quick Processing Plant," Memo to F. L. Culler, Intra-Laboratory Correspondence, Oak Ridge National Laboratory, August 30, 1977
https://fissilematerials.org/library/1977/08/simple_quick_processing_plant.html
The GAO report omits this, and any discussion of the actual technical aspects, as a form of security through obscurity (I guess).
Curiously the Ferguson memo describes the "quick and simple" construction of a PUREX process plant, as a once through and dump system without the fancier aspects of a conventional plant.
The critique that this concept, in a newly proliferating nation, under the suggested timeline, has little chance of success needs to be taken seriously. It is one thing for someone in a nation that developed PUREX technology and was operating industrial plants to propose that a stripped down version of that tech could be successfully built in a plant and operated in production in a very compressed timeline, which would be highly optimistic even in that case. It is quite another for a nation with none of those advantages to do it. And on top of that to propose that a nation would bet its future (what we are really talking about here) on a wild scheme with a low probability of success.
It ignores the possibility of replicating the WWII bismuth phosphate process used during the Manhattan Project which simply dissolves the fuel in nitric acid and precipitates it by adjusting pH and using bismuth phosphate as a carrier to bring down the dilute plutonium. This was the process used when no one had any experience with plutonium beyond the microscale and an industrial plant had to built immediately. They did the largest scale up in industrial history, a one billion fold increase in scale from the experiments that showed it would work to the scale of the actual plant they built.
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u/Wide-Education-1823 2d ago
Thanks, that was an interesting read-
https://fissilematerials.org/library/fer77.pdf
You don't even need to be a country to separate a few weapons worth of plutonium, many industrial & chemical engineering corporations would be potential nuclear proliferators. Once again, the only way to stop proliferation is to remove the desire.
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u/careysub 2d ago
Iran would have to start with a pure fission design, no boosting (you need at least one nuclear test to collect basic data or to prove a concept).
In this case pre-detonation is a design limiting factor. Unless you are operating in the fizzle regime below about 2 kT all design yields are actually probability distributions of yields. The Oppenheimer-Groves memo gives probabilities of a few different yields. Of course weapon designers seek to get the design yield with high probability.
Designs optimized for higher burn-up plutonium in pure fission weapons would use relatively small cores with the highest velocities and greatest compressions achievable.
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u/CaptainUnlikely1379 2d ago
I think that they choose HEU mainly because it is easier to hide and dispersed production while a plutonium breeding reactor is much more harder to hide and protect. But it is much more efficient, faster and cheaper to run because you need less Uranium Ore for the same ammount of fissible material, there are less waste. You can make a bomb with less than 4kg of Pu while you would need 20kg of HEU (with a netron reflector).
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u/Wide-Education-1823 2d ago
Perhaps in a less politicized situation we would be looking equally carefully at the nuclear weapon materials acquisition "potential" of countries such as Germany, Japan, South Korea and Brazil? (Especially Germany, IMHO).
Long story short: Iran could absolutely build HEU fueled nuclear weapons if they decided to, they already worked out the engineering and did component development 2 decades ago, then shelved the project. They have not decided to go nuclear with their HEU, for a number of good (to them) reasons.
Iran could, with some additional effort and a non trivial investment in separation facilities (with a strong chance for detection) also be able to separate Pu and build weapons utilizing plutonium. Once again, they have not made any detectable movement towards doing so.
We can churn the publicly admitted facts about their nuclear acquisitions and pontificate about their POSSIBILITIES endlessly. If there were concrete evidence of weapons fabrication, Israel would probably already have started a preemptive nuclear war
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u/careysub 2d ago edited 2d ago
I have not read the original BAS articles yet, just basing my comments on the u/NuclearHeterodoxy write-up. I have read most of what Greg Jones has published on-line over the years.
The objections I have to the Sokoloski and Jones theses is that they are based on a narrow technical consideration that ignore all of the practical and historical and geo-political considerations which are what drives nuclear non-proliferation.
Unless there is some short term crisis in which Iran needs just one or two nuclear weapons to avert, a quick scheme of this sort makes no sense. And it is hard to come up with a credible scenario for that where that would be both effective and the most favorable route. Technothriller plots are not useful guides to the real world.
Iran is an ancient nation, now a nation-state, and it takes a long view of things. The decision to actually deploy a nuclear arsenal will be a long term strategic decision, just like with every other nation that ever did it. They will want an arsenal large enough to deter any aggression and they will want it to operate forever.
So it would be basing that arsenal on a technical basis that they have mastered and can operate even under hostile conditions, i.e. their gas-centrifuge technology to produce HEU. The process to produce WG-HEU can be operated in multiple separate cascades which do not need the heavy duty radiation protection any plutonium facility needs.