Prof. Ted Postol: 440kg: The Clock on Iran's Nuclear Potential

Added: 2026-05-18

[00:00:00]basically before the Americans uh the June uh 2025 attack on uh on Iran, the Iranians were producing 400 over 400 centrifuges per month. We know that because it was under monitoring from uh the International Atomic Energy Agency.

[00:00:26]That's a lot of centrifuges.

[00:00:28]And um we don't know what amount of that manufacturing capacity is underground in tunnels. Now presumably parts of it were destroyed in this massive attack that occurred but that doesn't mean it was all destroyed. And given the situation and the Iranians uh the Iranian sensitivity to the uh extreme uh um uh aggressiveness of the United States and Israel, uh it's very hard for me to believe. I don't know, but it's very hard for me to if I I just, you know, I just put myself in the Iranians position.

[00:01:20]Incidentally, if you're ever really doing serious policy work, that's the only way to understand the other side so that you can negotiate with them sensibly. And I sit there and I say, I'm advising the Ayatollah, any Ayatollah, not just the last one. Um, and I'm a technical person and the ITL asks me, uh, what should we do? Well, I'd say, well, we we should certainly move some of our manufacturing facilities to locations where the Americans can't get it. These are these tunnels, which are very essentially impossible for practical purposes to destroy.

[00:02:03]And uh we don't have to have it all there, but we should make sure that we have what we need to continue enrichment should we need to. It's just prudent. It's not, you know, and it's very hard for me to believe that the Iranians haven't done this. I'm I'm not trying to uh ascribe immoral behavior to them.

[00:02:27]This is an existential threat they're facing.

[00:02:30]Why would you do otherwise when you're facing adversaries who literally want to destroy your civilization?

[00:02:39]You know, you you you have no choice but to do prudent things like this. So, for example, I think it's plausible I again, I don't know. It's plausible to assume that the um Iranians uh can produce 100 or even 200 centrifuges per month even now and that they may have a significant number of centrifuges already in place in tunnels somewhere.

[00:03:13]Whether they're all set up in centrifuges, maybe they are, maybe they're not. We don't know.

[00:03:20]But to assume that they have no capability is really uh the ultimate in stupidity. It's the ultimate in stupidity.

[00:03:30]Let me uh why don't we take a look at slide number six because I want to make a few points. Yeah, >> we won't have a chance to go through a lot of it, but this is this shows you the curve of the critical mass uh versus percentage of enrichment. So if you look at the uh the x axis on let's look at the left curve.

[00:04:05]If you look at the x-axis on the lex curve, you see it goes from zero to 100%.

[00:04:12]And you see a red line at roughly 90%.

[00:04:16]And you see a curve uh at the um at the bottom um you see a red line. You you see red line starting at the 90% and going upward and intersecting a curve at about 14 kilograms.

[00:04:39]That is about that's the critical mass you need to build a nuclear weapon if you surround the weapon with what's called a reflector. I'll describe what I mean by that shortly.

[00:04:52]When people say the Iranians can build 10 or 11 nuclear weapons by quickly enriching the 60% enriched uranium uranium hexaflloride they have they are talking about 25 kilogram critical masses.

[00:05:12]So that's the last if you look uh you can I think you should be able to read it. You see a red line at the top of of the group of solid lines below. That's the 25 kilogram point.

[00:05:29]So you can see that if you design a weapon with either a uranium and I'll I'll describe what I mean by that or burillium reflector, you could need much less uranium to build a nuclear weapon.

[00:05:49]So uh let's take a look at slide 10.

[00:05:55]This is a notional This is a a notional discussion.

[00:06:01]Slide 10. You got it. There you go. This is a notional diagram of a nuclear weapon called gun assembled nuclear weapon where um this looks nothing like the bomb that was designed and dropped on Hiroshima.

[00:06:21]This is a more modern design.

[00:06:24]It's uh you have a a sphere of of enriched uranium with a significant uh um hole in it.

[00:06:38]And in that hole, uh, you could have more uranium 235, which you would shove in using explosives to drive plugs of U235 into the center, resulting in a sphere of a certain critical mass.

[00:06:58]All right. So um so this is a reasonable design for a um uh you know uh a second second generation. By second generation I mean unsophisticated uh atomic bomb using uranium 235.

[00:07:19]Uh it's uh easily implemented.

[00:07:25]You don't need to test this as a nuclear test because the only thing you need to test is the assembly mechanism which you can do with depleted uranium. Make sure it all works as you expect it to. And then all you do is substitute uh enriched uranium, the weapons grade uranium for the depleted uranium and the system will certainly work. So this is a weapon you don't need to test. Let's look at slide 11.

[00:07:56]Let's put some numbers on this.

[00:08:00]Well, if we look to the left, the leftmost uh the grided the circles, the spheres that are gr red uh uh gritted circles show you rough diameter of a critical mass of uh uranium to get a nuclear detonation. if you have nothing surrounding it. In other words, it the the neutrons leak out and you just need more and more uranium to make up for the new. So you need 55 kilograms to um um to um build a nuclear weapon uh with 20 kilograms of um of uranium of enriched uranium.

[00:08:59]You would have to surround it with about 10 cm. So you see the diameter is maybe 25 cm but there's 10 cm on either side of uranium 238.

[00:09:15]Uranium 238 mainly performs the function of um reflecting neutrons back in. It also performs the function of putting a very large mass around the enriched uranium core which means that when the core goes nuclear and starts pushing outward the mass will delay the rapid expansion outward and thereby lead to a higher yield nuclear weapon.

[00:09:49]So now the weight of the uranium reflector is large.

[00:09:54]So if I take the reflector and and the and the core together, the whole thing weighs 350 kg.

[00:10:04]But if everything else I need weighs another 150 kg, this whole thing can weigh 500 kg.

[00:10:13]So, uh, that that's enough to, um, be carried by any of the standard long range missiles that Iran is now using to attack Israel.

[00:10:27]So when you uh look at the most recent edition of the U Bulletin of the Atomic Scientists, another one of my favorite uh inaccurate information societies, um you'll you'll see this little video they put out and at the end of it a guy named Steve Federer uh who should know better because he's actually technical technically trained and he's uh was in the science advisor 's office. He's there telling people wrongly wrongly that uh an Iranian nuclear weapon would be much too big and cumbersome and heavy to fly on on an Iranian ballistic missile. Bulocks.

[00:11:12]That's not true. And uh if maybe the bulletin wants to come out with a design analysis that shows why this is wrong, I'd be really interested. But I don't think they have the technical capabilities in the organization. even though they claim to be experts. So this is a real problem. Now why is it a real problem? Why am I always so uh you know focused on these organizations? Because they misinform people.

[00:11:40]And and it's important to understand that the Iranians are not far away from this capability if they choose to do it.

[00:11:52]Because if you think they are far away from it, then you will have a policy that does not assume that you have a critical need to negotiate with them. So this is not just Tosal having a vendetta against the bulletin, which incidentally I do. I don't I don't like this organization. I it's a group of people who misrepresent themselves as experts and uh and and they don't do their homework. They could do their homework, but they don't. So, it's inexcusable, but they're driving policy decisions because lots of people assume they know what they're talking about. After all, they say they're experts. So, the Albert Einsteins and Openheimers are no longer part of the bulletin. The bulletin has degenerated into a social club and there not many technical people there. And the technical people there have limited knowledge and they're lazy. So, that's important. That's why I keep going back to this. You need accurate information in order to formulate policies that make sense. And if you have accurate information on this particular issue, you will know that it's absolutely imperative to quickly make it possible for the Iranians to negotiate with you.

[00:13:10]It's not it's not the Iranians. They're happy to negotiate, as I've tried to explain.

[00:13:16]They have every reason to negotiate. But if you're so screwed up that you can't even figure out how to, you know, put them in a position where they think they can negotiate with you, then you got a real problem. Now, on the right side, there's the 14.1 kilogram core.

[00:13:34]And uh so that's um uh that's um uh also surrounded by 10 cm of in this case burillium. Burillium is an extremely lightweight material and it operates as a um as a neutron reflector.

[00:13:57]So the advantage of it is the weapon you would build would have an overall weight the components would would have an overall weight of 40 or 50 kilograms rather than 350.

[00:14:10]Uh but uh this would probably give you a somewhat lower yield explosion because the tamper the the reflector also operates as a massive shield that prevents the the the uninhibited uh expansion of the core when it goes nuclear. And this is a very light core.

[00:14:35]So it doesn't have the mass that the uranium reflector has. So again if I were the technical advisor to you uh to uh Ayatollah Nema uh I would uh I would advise you I'd say well well uh you know we have the we have the capacity to carry 500 600 700 kg on a longrange missile. So that's not an issue. The weapon size will not be very different. Its weight will be different.

[00:15:08]Let's use the uranium reflected core.

[00:15:11]First of all, it's easier to work with than burillium. And also, um, uh, we'll probably get a higher yield weapon because the these weapons are these weapons can yield between five and 15 kilotons without implosion. Implosion gives you more density in the uranium, but it's a complicated scheme and an implosion mechanism is much we have to test that.

[00:15:40]We we we can't just use it against the Israelis without testing. So if we want a simple device that we just have without ever testing, but have it, the the the uranium reflected weapon is fine. It will do the job for us. So my guess is we're looking at uranium uh uranium reflected weapons. That's you know that that's what the um the um uh the Iranians are have in the background.

[00:16:15]So I'm not saying they they're doing it yet, but All right. So what does all this mean? [clears throat] Let's go to slide 23.

[00:16:26]See, I'm skipping over an enormous amount.

[00:16:30]Um, we have this um, let's go to slide 21 very quickly.

[00:16:39]This shows you what I had described earlier that as you each uh, amount of work I do removes a fixed amount of uranium 238.

[00:16:54]it you can think of it as separative work units in this case. And so when we get to the right side and we have 50% enriched uh uranium hexafflloride to enrich to 100% takes much less effort than to enrich to 50% because the enrich to 50% took eight steps, seven or eight steps. um whereas one step gets me to 100% from the 50%. So, so we have this accelerating capability.

[00:17:31]So, when we have 60% enriched uranium hex hexafflloride, let's go to slide 23.

[00:17:37]Now, we would need 5,500 uh kilograms [snorts] separated work units per year to get 25 kg of 90% enriched uranium.

[00:17:54]But if we have um um a small maybe 38 kilograms of 60% enriched uranium hexaporide I um I can get 25 kilograms of enriched uh 90% enriched uranium uh with with about 120 separative work units and given a cascade of maybe 350 centrifuges which the Iranians have demonstrated. We know that they can do this. The I IAEA reported this. It's one and a half weeks of work. you know, if if it's all set up to get that enrichment, that's that gives us uh and since they're 44, if you look at the next step down, they're 440 kg of uh 60% enriched uranium and we need 38 kg to have 25 kg for a bomb means we have roughly 11 bombs worth of um of uranium uh in the 60% enriched uranium.

[00:19:08]However, what if we only need 14.1 kg of enriched uranium? Because we're building bombs with 10 cm depleted uranium reflectors like I just described.

[00:19:28]Technology for doing that is no harder.

[00:19:31]not harder at all to fabricate such a bomb relative to um you know the 25 kilogram bomb. It's a heavier bomb, but we know we can carry it on a ballistic missile.

[00:19:47]So if if we only need uh 68 uh uh we only need 68 separated work units uh to to take the a smaller amount uh 21 we have 21 kilograms now 60% enriched uranium 21 kg gives us 14 kilograms of 90% enriched uranium then we have um we only need 68 swoo separated work units.

[00:20:20]We That's about five or six days to get the 14.1 kilograms of 90% enriched uranium for a bomb.

[00:20:30]Notice also that since we only need um um uh actually this number here is wrong. Uh the number below there is 14.1 in the second in the last equation on the bottom. That's wrong. I put it together this morning. Um that should be 440 kg over 21 kilograms.

[00:20:57]So we're really talking about 20 20 or 22 or 23 bombs that I can build with the currently available 60% uranium. So the the current wisdom is these guys could build 10 bombs, [clears throat] but in fact that's not correct. They can build 20 bombs if they're willing to have a heavier bomb. And and the 20 uh the 10 bomb number comes from a number that was bureaucratically arrived at when people were talking about uranium enrichment.

[00:21:36]You know, they were trying to set standards for the non-prololiferation treaty. And after a lot of uh hemming and hawing and bureaucratic infighting, they arrived at a standard that 25 kg of highlyenriched uranium would constitute a potential bomb. But in fact, it's 14 or 15 kg.

[00:21:57]And um if you were Steve Federer, you should know that and you should understand that the bomb you would design would also be able to be carried by a um um you know a a ballistic missile that already exists and is operating.

[00:22:17]So, does this mean we we the Americans and the Israelis must redouble and redouble again our efforts to destroy Iran? No. What it means is we have to do everything we can. It's in our interest to do what the Iranians also want to do. give them a negotiated position that allows them to guarantee their security while at the same time uh gives us uh confidence that they're not an active nuclear weapons state. They're they may be a potential nuclear weapon state, but they're not active. They know what's in their best interest. They're not going to go further unless we give them the reason to go further. So this is an argument not for going after the Iranians more aggressively. This is an argument for being very serious about negotiating.

[00:23:18]And uh I can't understand why so many people are trying to downplay this threat. I'm not trying to overstate it. I'm I'm talking the technical reality. somebody can show if Steve Federer wants to put invite him on. Let him explain why I'm wrong. Have the bulletin on. Let them let them do it. Let's let's hear their argument. But um by lulling people into the sense that there's no problem here is is crazy because it not only shows a lack of understanding of the technical realities, it shows a lack of understanding and respect for the politics of Iran. Because these people are not crazy. They're not a bunch of crazy uh Osama bin Laden's.

[00:24:12]They're a bunch of very deeply thinking, well-informed, highly educated people who know what's in their security interest and they understand that not having a nuclear weapon is in their interest. So, give them a chance, negotiate with them. Anyway, so that's that's the point of this number. But we're talking about many more nuclear weapons, all of them deliverable by ballistic missiles in a short period of time.

[00:24:39]I'm not talking about if you want to uh produce, you know, if this situation were to persist, let's say it persists for four or five years, which could well happen, and the Iranians choose to uh enrich um natural uranium, they could produce a bomb per year from natural uranium in addition to the stuff the the 20 nuclear weapons that can produce from the 60% enriched uranium in weeks.

[00:25:14]So these this country has a lot of firepower, a lot of firepower and they don't want to use it.

[00:25:25]So work out a deal.

[00:25:28]You know, they're happy to be inspected as long as it's reasonable and you're not trying to destroy their ability to defend themselves.

[00:25:38]If if you want to take an Israeli statement, the Israelis like to say we have the right to defend ourselves.

[00:25:45]Well, so do the Iranians.

[00:25:47]You know, this idea that they they have the the Israelis have the right to defend themselves by killing and massacring all the people around them while all the Iranians want us to be left alone in order to defend to defend themselves.

[00:26:02]I mean, it's so ridiculous. It's hard to believe. And this is because of the incredible uh uh shortsightedness of western people and and also the complete lack of serious discussion from the community that sees itself as the arms control community. the community that sees itself as the community that is um um negotiating uh a more a safer world. So why isn't the bulletin of the atomic scientists producing analysis like this and saying look these politically these guys want to negotiate here's here's the evidence we have lots of evidence that they wanted they they went into this agreement the JCPOA so we know they want to negotiate if we listen to their analysis people who were involved in the negotiations they give you the argument that I just gave not my argument it's an argument they came up. I I I came I mean I I would like I said if I looked at the situation the way Muhammad Zarif looked at it you know yeah sure um uh I come up with the same answer because the constraints are the same and if you're using logic you come up with the same solution. So there's no argument here from the Iranian point of view that they want to negotiate.

[00:27:37]But the West is not making it possible.

[00:27:40]So why isn't the bulletin explaining to people why the incentive should be emphasized to negotiate?

[00:27:48]Instead, they're putting out nonsense about the Iranians can't do this. After all, we know that, you know, they they I don't mean to be insulting. They ride on cabbles, you know.

[00:28:00]>> [laughter] >> It's just it's just so pathetic. It really is pathetic. And there is an underlying racism here.

[00:28:08]There is an underlying I have argued this for many years. It's like um uh you know uh there was a debate in the United States around the 2000 2010.

[00:28:21]It was so was so ridiculous that it's shameful. But I should bring it up because it show it exposes ignorance and racism. It was a a debate uh about deterrence, you know, deterrence.

[00:28:38]Could other could what could what are other countries um uh rational enough to be deterred like we would be?

[00:28:49]I mean, I mean, if you go on a farm and go near a cow that's just had calves, you would understand deterrence.

[00:28:59]A female cow who's just had calves will will deter you from going near her calves. I mean, what are you talking about? The underlying racism in that argument is extraordinary.

[00:29:16]And this was a conversation that was going on at the top of American uh government and people with straight faces were making it and nobody said do you understand that that's racist [laughter] I mean you know it's hard to believe and and this is the kind of uh narrowness of intellect that we see in the Certainly in the American mind, the Israeli mind is distorted in a different way, but distorted no doubt. And uh and unless you recognize the you the rationality and humanity of your potential adversary, you're you're always going to do the wrong thing.

[00:30:09]Because if you're dealing with someone irrational, there's no way to stop them. if they have the resources and the Iranians have the resources, but the irrational players in this case are the Israelis.

[00:30:24]I don't know what these guys are capable of. I just don't know what they're capable of. I mean, I have friends in Israel. I, you know, I know I I wouldn't say I know Israel Israel well now because I can't imagine the Israel I knew from 10 or 20 years ago. I can't I know the soldiers. I know many of these people. I these people would never never shoot a child, you know, uh, as a sniper. Never. This is routinely going on there. Something has changed in a horrifying way and the society has descended into some kind of horrifying uh, semi well not semi-fascist state and this is really problematic.

[00:31:11]So >> anyway so I didn't get a chance to talk about centrifuges my all my work >> we're going to continue these talks that and that's >> but but the point I want to make here is that we are talking about a country that has extraordinarily sophisticated technical capabilities and extraordinary rationality in its policy. policy making and you know when you go to war it's a terrible thing you destroy things but they have fought this war with unbelievable skill they have shown that they know what they're doing in the way they fought the war they they've really effectively defeated and if the war starts again which I think it will I hope I'm wrong uh they're going to put Israel and the United States both in a much worse military situation. The game is over from the point of view of the military the weight of of the military defeat. It's going to get worse, not better uh for United States and and and Israel. And you know, we're going to have that the fleet, the American naval forces standing off, you know, thousand kilometers or 600 kilometers off the straight of Hormuz helpless. So we can f bomb to some extent the Iranian structures on on on on the surface. We can't do anything to their military. There was a report I just saw.

[00:32:55]I don't know how accurate it is, but I believe it. I think it's that 75% of the launchers that the CIA uh just issued a report that 75% of the launchers are still operating in Iran almost. In fact, it sounds to me a little high.

[00:33:14]I mean, a little low, I'm sorry, a little low because I don't know where we could have destroy how we could have destroyed all these launchers. I mean I you it's so hard to find these things and you're only over the country a short interval of time and you know you just don't have the capacity to do it. So uh so the CIA you know they destroyed it all you know earlier and there's nothing left now now there's a CIA report that leaks says 75% of the launches are still there. So you're not talking about a country We don't have 75% of our strike capability anymore. We've [laughter] used up all our, you know, our cruise missiles. We're, you know, uh, all of our standoff missiles, almost all of our air defense missiles.

[00:34:07]Who's in a worse situation?

[00:34:10]It's amazing.

[00:34:12]and still having a reasonable approach to diplomacy is not on the uh on the drawing board.

[00:34:23]And and and the organizations that's supposed to be explaining to people [clears throat] why what a rational policy alternative would be are out there saying, "Oh, don't worry. They can't build a bomb because it'll be too big to to fly on a missile. Don't worry about those guys, you know. They can't do it.

[00:34:47]Well, they can do it and they don't want to do it. That's the other important thing. They can do it and they don't want to do it. So, give them a chance.

[00:34:56]Use diplomacy. That's the point of this discussion here now.

[00:35:00]>> Yeah. Exactly. Exactly.

[00:35:03]Thank you so much, Dad, for being with us today. [laughter] Great pleasure as always. Well, call the bulletin and ask them why they're not arguing for that policy. Write them [laughter] if you if you can get a if you can get an address for them. They're all so hard to reach. I took me a little while to get people's email addresses.

[00:35:22]If you want, just write me a note. I'll send them to you.

[00:35:25]>> I'll send you the the CEO's address. Uh, you know, she's as she said in my discussion with her, she's she's very busy. So, she didn't have a chance to read anything that I sent her. So, I'm not busy, of course, but she's busy.

[00:35:40]Important person. So, um, too busy to know what you're talking about. That's what the bottom line was.

[00:35:48]>> Yeah.

[00:35:48]>> I'm here to tell you I'm an expert, give you advice, and by the way, I I I just have no interest in understanding what sound advice would be.

[00:36:01]>> So, I produced these nonsense like they just produced in their most recent edition. Go look at the video.

[00:36:08]>> Yeah.

[00:36:08]>> And complain.