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An expert on nuclear weapons explains the very basics of Iran’s nuclear program

Iranian President Hassan Rouhani.
Iranian President Hassan Rouhani.
Andrew Burton/Getty Images

It's crunch time for Iran's nuclear program. By November 24, the United States, Iran, and the five other parties to the talks (Russia, China, the UK, France, and Germany) are supposed to have an agreement. In theory, this agreement would freeze Iran's progress towards being able to build a nuclear weapon while simultaneously lifting international sanctions on the pariah state.

Whether there will be an actual deal by the deadline is totally unclear. That's because the main sticking points in negotiations are extremely difficult to resolve. And they're also very hard for a layman to understand: discussions of Iran's nuclear program are often steeped in technical jargon, making it hard to understand the progress (or lack thereof) in the talks, much less the actual mechanics of how the nuclear program works.

To clarify these points, I got in touch with Jacques Hymans, an associate professor of international relations at the University of Southern California. Hymans is an expert on nuclear proliferation — how and why countries acquire nuclear weapons. I asked him to walk through the basics of Iran's nuclear program, giving a clear guide to the essential technical aspects of Iran's nuclear program and an explanation of why the United States and international community are so worried about them. What follows is a transcript of our conversation, edited for length and clarity.

Zack Beauchamp: Let's say I wanted to build a nuclear bomb. What do I need?

Jacques Hymans: If you want to build a bomb, you need to get the fuel for the bomb — otherwise known as the "fissile material." There are two basic types of fuel: highly enriched uranium and plutonium.

You get highly enriched uranium by separating uranium-235 from the uranium you dig out of the ground. It's a very difficult technical process: you have to separate the less than one percent that's u-235, which can be used in a bomb, from the 99 percent of "regular" uranium that can't be.

The other potential pathway is through plutonium, a man-made element. The only way that you can make it is by burning uranium in the reactor, so in both cases you need the uranium.

ZB: So is Iran developing highly enriched uranium or plutonium, and why is the US concerned about it?

JH: In the Iranian case, they've focused most of their attention and progress in the highly enriched uranium direction rather than plutonium direction, though there's a little bit of plutonium work. So Iranian uranium enrichment is the most difficult point in the negotiations over Iran's nuclear program.

By now, they have approximately 10,000 centrifuges in operation, which turn very quickly connected to each other. They're the things that separate u-235 from the rest. Those 10,000 centrifuges give Iran the potential to get a very high amount of u-235 sufficient to produce the fixings, or fuel, for a bomb in perhaps a few months time.

Natanz IAEA inspectors (Kazem Ghane/AFP/Getty Images)

International inspectors and Iranian scientists disconnect connections between twin centrifuge cascades in Natanz, one of Iran's two major enrichment plants. (Kazem Ghane/AFP/Getty Images)

The Americans are interested in reducing the number of Iranian centrifuges, if not eliminating them, so they can be assured that Iran can't use that method to quickly break out of their commitment not to build a nuclear weapon under the Non-Proliferation Treaty (NPT).

The Iranians are resisting destroying or dismantling this huge enrichment production line that they've put a lot of time and money into. That's the most important sticking point, though there are other areas of disagreement.

ZB: What are the other areas of disagreement?

JH: The other one that appears to be have been most difficult so far is the issue of what the Iranians may have done in the direction of nuclear weapons before. In order to build a bomb, you don't just need highly enriched uranium. You also need to have a working device that can use the fuel, which is not child's play.

There's an important question about how close Iran may be to a working bomb, which relates to how far they've gotten in those other technical areas in building the device. The Iranians have flat-out denied that they've ever done any work on nuclear weapons, but there's a lot of suspicion that that's not true.

So there's a desire on the part of the other parties at the table [the US, the UK, Russia, China, France, and Germany — called the P5+1] to find out what they've done in the past. And if the Iranians have built anything, there's a desire to neutralize it to the extent possible.

ZB: This all seems to hinge on questions of monitoring. How do the US and the rest of the negotiating countries verify that Iran has stopped spinning centrifuges or wasn't producing the technical work on the bomb you were just describing?

JH: The answer is different depending on which of the pieces you're talking about. In terms of the centrifuges, those are pretty big factories. And we know where at least two of them are [in Fordow, near the city of Qom, and in Natanz].

As far as verifying what's happening in those factories, it's a pretty routine procedure. The International Atomic Energy Agency [IAEA] inspectors come regularly to verify what's been happening in those factories, so we have a good degree of certainty that we know what they've been making and what additional centrifuge cascades they've been setting up.

Since the interim agreement was put in place [in November 2013], inspectors have verified that the Iranians actually have been keeping to their commitment not to enrich any more uranium up to the more dangerous 20 percent [level of enrichment that is necessary to make] u-235 level [uranium, which is research-grade]. Ninety percent [enrichment] is necessary for the bomb, but you only need 3-5 percent enrichment for a nuclear power plant (except for a research plant Iran claims it needs 20 percent for). Anyway, they haven't been making more 20 percent, and they downblended quite a bit of the stockpile, so they have less of that highly enriched uranium than when we started that process.

But all of that is a routine operation for the international inspectors. There's a question, however, about the possibility of other factories that the Iranians have built or might have built in the future that we haven't learned about. There's precedent for worrying about this: both of Iran's enrichment facilities were discovered by leaks to the international community. So there's some reason to worry that there could be some operation that's going on that isn't known about, and so can't be inspected in the routine way.

ZB: If Iran might be doing secret work, how can a deal ever guarantee it won't build a bomb?

JH: That's one of the issues that's on the table in the ongoing negotiations. Basically, the question is whether international inspectors could tell the Iranians that they wish to visit some site somewhere that the Iranians haven't acknowledged holds nuclear activities.

The Iranians, of course, don't want this to become a kind of endless search. They're very leery about getting into a dynamic where, rather than clearing up the issue by providing documents, the provision of such documents is simply used as opening shots for Americans and others to demand more documents in an endless loop that ends with a lot of embarrassment on the Iranian side and no progress on sanctions. That's not unlike what happened in Iraq [under Saddam].

So the scope of inspections is a difficult sticking point.

ZB: You mentioned last year's interim deal with Iran, known as the Joint Plan of Action (JPOA). What did it do, and why is it insufficient to serve as a final deal?

JH: It's very difficult to argue the interim deal hasn't been a success. You had a program [in Iran] that was enriching pretty large amounts of uranium up to the 20 percent level. What you do when you go from 3-5 percent [enriched] uranium that's used in commercial power to 20 [percent enriched uranium] is you cut the time that it would take you to get to 90 percent [enriched uranium], the bomb-grade uranium, in half. The more 20 percent uranium Iran has, the closer they are to being able to move quickly to get the fuel for a bomb.

The deal stopped that enrichment up to 20 percent, at least as far as the facilities we know about. In fact, it actually rolled it back by a considerable amount. So this agreement has clearly been a positive step from the US national interest perspective.

kerry zarif iran nuclear

US Secretary of State John Kerry (R) and Iranian Foreign Minister Javad Zarif (L) shake hands as Omani Minister Responsible for Foreign Affairs Yussef bin Alawi (2nd R) and former EU top diplomat Catherine Ashton watch. (Nicholas Kamm/AFP/Getty Images)

However, it's left in place the basic centrifuge cascades that the Iranians would be able to use to build up their stockpile of enriched uranium once again. They have been enriching up to the low [3-5 percent level] but not the high [20 percent] level. As long as they have those centrifuges sitting there, the deal is really walking on thin ice.

A permanent deal that reduces the number of centrifuges, and not simply the amount of highly enriched uranium, is the one that everybody on the US side of the fence wants to see happen.

ZB: Besides enriched uranium, centrifuges, and inspections, what else about Iran's nuclear program is a sticking point in negotiations?

JH: There are other kinds of nuclear facilities they have. There's a regular power reactor at Bushehr they bought from the Russians. And there's a experimental reactor that a lot of people view as their bid to try to pursue the plutonium pathway — the Arak reactor.

The Arak reactor is something the Iranians have been building that's too small to be useful for electric power, unlike the Bushehr reactor. The Arak reactor would be very useful for making plutonium, which would produce another proliferation headache. That's not up and running, and the negotiators in Geneva may have found a way to solve the Arak problem — changing the innards of the reactor to reduce its plutonium production level. [Note from Zack: Recent reports suggest the consensus over that solution has broken down.]

ZB: How much time is there to resolve all of this?

JH: The standard story is what I gave you initially — the idea that the fissile material is the most important thing and, once you have that, you're basically there. So if their centrifuges are just left as is, they could get that fissile material rapidly. Say, in a few months.

That is assuming, however, that they are a crack scientific operation. But the history of nuclear proliferation in general, and certainly the history in Iran, suggests that this isn't the case. States trying to build nuclear bombs often have sub-par scientific establishments. Libya, for example, was able to buy the whole nuclear catalog from [rogue Pakistani scientist] A.Q. Khan, but they couldn't figure out what to do with it.

netanyahu iran bomb diagram

Israeli Prime Minister Benjamin Netanyahu diagrams Iran's progress towards a nuclear bomb at the 2012 UN General Assembly. (Don Emmert/AFP/Getty Images)

Iran is also a good example. The current Iranian regime's nuclear program (there was also a program under the Shah) started in the mid-1980s. In 1992, [current Israeli Prime Minister] Benjamin Netanyahu predicted that Iran would be ready to have the bomb in three to five years. He based that estimate on the standard thinking about the technical requirements for getting nuclear weapons. Now, Iran is kind of in the position to do that. But it's 20 years later!

So we need to be a little bit cautious when people throw around dates, particularly the most scary estimates about an Iranian bomb within six months. Those are assuming a level of organizational and professional efficiency they've never demonstrated until now. Doves and hawks both, for their own reasons, start from the premise that Iran is just a whisker away from having the bomb. Whereas it seems to me that actually there's more cushion there than people usually believe.

Correction: Hymans said that the amount of u-235 that naturally occurs is two percent; it's less than one. He also incorrectly stated the number of years Benjamin Netanyahu estimated Iran needed to get a bomb in 1992; the correct number was three to five years, not two to three. We regret the errors.