The Iran Deal Explained

The Iran Deal Explained

A comprehensive guide to the nuclear agreement with Iran—and why it’s a major advance for global nuclear security.

E3/EU+3 and Iranian representatives announce the deal, July 14 (European External Action Service)

One month ago in Vienna, the United States and five other countries (China, France, Germany, Russia, and the UK) along with a representative of the European Union, collectively known as the E3/EU+3, signed a nuclear agreement with Iran. The deal was immediately hailed as historic by both its supporters and its detractors. Yet very few of its supporters—or its detractors—know what the Joint Comprehensive Plan of Action (JCPOA) signed in Vienna actually says. In this note, I seek to do my part to help change that. (I do not discuss the removal of sanctions or the questions of what Iran might or might not do with the increased resources that removal of sanctions will provide.)

The Plan of Action very effectively shuts off all of Iran’s paths to a nuclear weapon for fifteen years and provides other safeguards against Iran’s pursuit of nuclear weapons indefinitely. Even in a worst-case scenario—where Iran kicks out all international inspectors and races for a bomb—for at least ten to fifteen years, the breakout time for one nuclear weapon would be roughly one year. Most significantly, the Plan of Action decisively shuts down the plutonium pathway for fifteen years, and in all likelihood much longer.

Below, I explain these conclusions.


Four pathways to nuclear weapons

The Plan of Action addresses four routes to nuclear weapons that Iran could take. It could produce weapons-grade uranium at its Natanz facility; it could produce weapons-grade uranium at its underground Fordow facility; it could generate plutonium at its (still not completed) Arak heavy-water reactor, or conceivably at another reactor; or it could produce plutonium or weapons-grade uranium clandestinely. Any nuclear weapon must contain either weapons-grade uranium or plutonium.


Some Background on Enrichment

Natural uranium is comprised of 0.7 percent of the isotope U-235 and 99.3 percent of the isotope U-238. A nuclear weapon nominally requires uranium enriched in U-235 to 90 percent. (Uranium enriched to over 20 percent U-235 is designated as highly enriched uranium and could allow a fast explosive chain reaction in a very large critical mass; but practically, a bomb requires much more enrichment, as noted.)

Since the isotopes are chemically identical, enrichment is difficult. It is done mostly today by centrifuges, rapidly rotating cylinders which separate the two isotopes, U-235 and U-238, slightly. If enough centrifuges are connected together in a so-called cascade, the desired enrichment can be achieved.

Enrichment is measured in something called separative work units (SWUs). Roughly speaking, it takes about 200 SWUs to produce one kilogram of weapons-grade uranium if you start with natural uranium as feed. The International Atomic Energy Agency (IAEA) denotes 28 kilograms of weapons-grade uranium (of which 25 kilograms are U-235) as a “significant quantity”—the amount needed for a nuclear weapon. In fact, for a sophisticated implosion weapon, fifteen kilograms might be a better estimate—but for a country to develop such a weapon without testing would be a huge gamble. For a simpler, so-called gun-type design, such as the one the United States used in the Hiroshima bomb, 50–60 kilograms would be necessary. But let us assume 28 kilograms. If one started not with natural uranium, but instead with low-enriched uranium (3 to 20 percent U-235) such as Iran has already produced, the number of SWUs needed to produce weapons-grade uranium would be less. If the feed were 20 percent U-235, over 90 percent of the separative work needed to produce weapons-grade uranium would already have been done.


1. Natanz

Today, Iran has about 16,000 IR-1 centrifuges installed at Natanz, with roughly 9,000 centrifuges spinning and the others on standby. The centrifuges are the first generation machines, each of which have an enrichment capacity of somewhat less than 1 SWU/year. They currently produce low-enriched uranium, but like all centrifuges, the cascade can be reconfigured to produce weapons-grade uranium. The Plan of Action calls for Iran, for the next ten years, to keep no more than 5,060 IR-1s spinning at Natanz and to store the other 11,000 (roughly) under continuous monitoring by the IAEA. For fifteen years, Iran will carry out all its uranium enrichment–related activities, including R&D, exclusively at the Natanz facility, and keep its level of uranium enrichment to less than 3.67 percent.

For the next fifteen years, the Plan of Action also requires Iran to reduce its current stockpile of low-enriched uranium, mostly in the form of hexafluoride gas (though some in solid, oxide form), from about 12,000 kilograms to 300 kilograms of 3.67 percent U-235. Iran will be required to get rid of any uranium oxide enriched to between 5 percent and 20 percent that is not turned into fuel for the Tehran Research Reactor. The excess low-enriched uranium will be eliminated either by sending it out of the country or by down-blending it to natural uranium (that is, mixing it with depleted uranium), a process which can be done in a matter of weeks.

If, then, after the Plan of Action is implemented, Iran suddenly decides to go rogue and build a bomb, it will have to start from scratch—using natural uranium instead of the low-enriched uranium it now has—and with fewer than 5,060 centrifuges. It could of course take the other centrifuges out of storage, but this would be immediately observed by the IAEA, and it would take Iran considerable time to connect up into workable cascades. With 5,060 centrifuges and natural uranium as feed, it would take Iran about one year to produce one bomb’s worth of weapons-grade uranium.

All in all, the plan represents a significant step in preventing Iran from acquiring a nuclear weapon. Only a year and a half ago, at the time of the Lausanne Interim Agreement (implemented in January 2014) that froze Iran’s nuclear program and required Iran to eliminate much of its 20 percent U-235, Iran had a breakout time of a few weeks. It is about two months today.


2. Fordow

At present, Iran has about 3,000 IR-1 centrifuges at Fordow, and about 1,000 more advanced IR-2 centrifuges. Before the Interim Agreement, Iran was producing 20 percent U-235 at Fordow, but since the Agreement, only 700 IR-1s have been spinning.

Under the Plan of Action, Iran will convert its Fordow facility into a nuclear physics and technology center. Slightly over 1,000 centrifuges will remain. Roughly one-third of the centrifuges will spin without uranium and be reconfigured for stable isotope production. The other two-thirds will remain idle under continuous IAEA monitoring. All other centrifuges and enrichment-related infrastructure will be removed and stored under IAEA monitoring.

For fifteen years, Iran will not conduct any uranium enrichment or any uranium enrichment related R&D and will have no nuclear material at the Fordow facility.

However, for the next ten years, Iran will be permitted limited enrichment R&D, including on small numbers of advanced centrifuges, at other sites. For fifteen years, all testing of centrifuges with uranium will be done only at Natanz. Computer modeling and simulations will be permitted at universities and other sites.


3. Plutonium: The Arak Heavy-Water Reactor

Plutonium, the other nuclear weapon material, is produced in a reactor through neutron capture by a U-238 nucleus. For use in a bomb, the plutonium contained in the spent fuel from the reactor has to be separated from the highly radioactive fission products also contained in the spent fuel in a reprocessing plant under heavy shielding. The spent fuel is typically discharged from the reactor after a year or more of reactor operation.

At the time of the Interim Agreement, Iran had a research reactor under construction—the Arak reactor—which was designed to use heavy water and natural uranium as fuel.1 Work on the reactor was largely suspended after the Interim Agreement. Under the Plan of Action, Iran undertakes to rebuild the Arak heavy-water reactor based on a conceptual design agreed upon with Iran’s negotiating partners and formulated to minimize the production of plutonium. The new design will use low-enriched uranium as fuel instead of natural uranium, and its power will be limited to 20 thermal megawatts. In low-enriched uranium, there is less U-238 and thus less chance for plutonium production. With the old design (using natural uranium as fuel, and with a planned power output of 40 thermal megawatts), Arak could produce about 9 kilograms of plutonium per year, enough for one or two nuclear weapons. The new design will produce about 1 kilogram of plutonium per year. Moreover, for the lifetime of the reactor, Iran undertakes to ship all spent fuel from the redesigned reactor (containing the plutonium) out of the country. In short, no plutonium that could be used to develop a nuclear weapon will stay in Iran.

Iran also for fifteen years undertakes not to build any other heavy-water reactor or accumulate more heavy water. All heavy water beyond what is needed for the redesigned reactor will be sent out of the country. More generally, Iran agrees that it will not for fifteen years, and “does not intend thereafter,” to engage in any spent fuel reprocessing or spent fuel reprocessing R&D activities.

In addition to regulating the potential materials a nuclear weapon, the Plan of Action covers various activities that could contribute to the design and development of a bomb. This includes, for example, designing, developing, acquiring, or using computer models to simulate nuclear explosive devices or designing, developing, or using multi-point explosive detonation systems suitable for a nuclear explosive device. Under the plan, Iran agrees not to pursue any such activities, for an indefinite period. Iran also undertakes not to pursue plutonium or uranium metallurgy for fifteen years, activities that could aid in the construction of a nuclear weapon.

Furthermore, the Plan of Action commits Iran to explain past weapons-related activities. Along with the Plan of Action signed on July 14, 2015, Iran and the IAEA signed a “Roadmap for Clarification of Past and Present Outstanding Issues.” This agreement sets a timetable to resolve all outstanding issues in the IAEA’s investigation of Iran’s past and present nuclear weaponization activities. The Plan of Action specifies that all steps in the Roadmap must be taken before there is major sanctions relief.


4. The Clandestine Route: Transparency and Verification

Could Iran nevertheless, if it were determined, clandestinely develop a nuclear weapon in a facility hidden from IAEA inspectors? Here, again, the barriers imposed under last month’s agreement make it very unlikely. Along with the Joint Plan of Action, Iran has undertaken to adopt the Additional Protocol to the Comprehensive IAEA Safeguards Agreement. Iran, as a party to the Nonproliferation Treaty, is already committed to the Comprehensive Safeguards Agreement, but not the Additional Protocol. This protocol allows the IAEA to take soil and air samples and other measures to look for undeclared forbidden nuclear-related activities. Adherence to the protocol is of unlimited duration.

In addition, the IAEA will monitor all uranium mining and ore concentration for twenty-five years, and all centrifuge rotors and related production or acquisition for twenty years. Also, the Plan of Action establishes a “Procurement Working Group” to oversee the import of all equipment and material that could be used for nuclear purposes. If the IAEA or U.S. or another country’s intelligence services discover the import of items that should have been declared by Iran but were not, this would be sufficient evidence to allow the IAEA to conduct further investigations.

The Plan of Action also sets up a mechanism for authorizing the IAEA to undertake “challenge inspections” at any facility in Iran, including military facilities, if the IAEA has concerns regarding undeclared nuclear activities at the site. The IAEA must first request Iran’s access to a site of suspicion. If the IAEA and Iran are unable, within fourteen days of the IAEA’s original request, to reach satisfactory arrangements to verify that no undeclared nuclear activities are taking place, a Joint Commission set up under the Plan of Action will consider the issue, and by a vote of five or more of its eight members will advise on means for the IAEA to go forward. This consultation by the Joint Commission will not last longer than seven days, and Iran will have a further three days to implement the steps asked for.

Altogether, there could be a twenty-four-day delay between the first IAEA request to visit a suspicious site and the actual visit. In that intervening time, the United States would have the ability to monitor the suspicious site from satellites. Of course, activities inside buildings could not be seen. But come the actual visit, it would be very hard for Iran to conceal evidence of any work done during that period. The U.S. technical team working on the Plan of Action reportedly examined in detail what kinds of activities could be erased in the twenty-four-day period, and found that it would be extremely difficult to erase all indication of activity, especially if such activity involved radioactive isotopes. Modern detection technology is remarkably effective at detecting minute traces of nuclear material even years after nuclear activities take place.

What does this all add up to? Given the continuous monitoring by the IAEA of all declared sites, and of all declared uranium mining and centrifuge production, and with the Additional Protocol giving the IAEA the means to look for undeclared activities, it would appear difficult for Iran to build and operate a clandestine site, either producing weapons-grade uranium or plutonium, on any significant scale. Were Iran producing weapons-grade uranium or plutonium at a clandestine site, even a possible twenty-four-day delay it would likely not be able to erase all the evidence. It’s possible that activities not involving uranium and plutonium, such as work on bomb design, could be erased in the twenty-four-day period; but such activities would not bring Iran close to a nuclear weapon capability without concurrent work on amassing the weapons-grade uranium or plutonium essential for a bomb and performing implosion tests with uranium.


What happens after ten, fifteen, twenty-five years?

After ten years, Iran will be able to begin to replace the IR-1 by more advanced machines. However, between ten and fifteen years, it would do so by not increasing significantly the overall SWU capacity of the centrifuges. For fifteen years, it will still be limited to 300 kilograms of low-enriched uranium, and thus, for that time, a breakout would still take considerable time.

After fifteen years, as long as Iran is in good standing under the Nonproliferation Treaty, it would be able to increase its enrichment capacity by adding more, and more advanced, centrifuges.

To pursue a clandestine route, Iran would have to evade IAEA safeguards on uranium mining, set for twenty-five years, and centrifuge production, set for twenty years. Iran’s commitment to the Nonproliferation Treaty and IAEA safeguards, including the Additional Protocol, is of indefinite duration. Also of indefinite duration is Iran’s commitment not to engage in weapons activities.


What happens if the U.S. rejects the Plan of Action?

Congress has until September 17 to approve or reject the nuclear agreement. President Obama has vowed to veto any disapproval resolution, but it is possible that such a resolution could garner enough votes to overcome Obama’s veto, blocking his administration from lifting U.S. sanctions on Iran and essentially crippling the deal. What then?

Even if the Plan of Action is not implemented, Iran would still be bound by the Nonproliferation Treaty and IAEA safeguards, but would not be bound by the Additional Protocol or the special verification measures on uranium mining and centrifuge production called for in the Plan of Action. Clandestine activities would be harder to discover than would be the case under the Plan of Action.

Without the agreement, Iran would be able to resume activities suspended at the time of the Interim Agreement of January 2014. It could keep and then increase its stockpile of low-enriched uranium and bring to operation all its current stockpile of 19,000 centrifuges. It could also expand the number of centrifuges both at Natanz and Fordow, an eventuality made vivid by the fact that in the year before the Interim Agreement, when all international sanctions were in place, Iran was still able to install several thousand new centrifuges. It could also resume, at Fordow, enrichment of uranium to 20 percent, an activity halted after the Interim Agreement. With some stock of 20 percent uranium-235, Iran’s breakout time for one nuclear weapon would quickly revert to a few weeks or so, and the breakout time to several nuclear weapons would also become progressively shorter.

Perhaps more worryingly still, Iran could move to complete the Arak reactor with its original design, capable of producing enough plutonium for one to two nuclear weapons per year.

Overall, under the Plan of Action, Iran commits to unprecedented constraints on its civilian nuclear program and unprecedented transparency measures that effectively cut off its pathways to nuclear weapons for fifteen years. After that time, the breakout time could shrink if Iran expands its civilian nuclear power program, although Iran will still be bound by the Nonproliferation Treaty, all its safeguards requirements, and by significant commitments it made in the Plan of Action. If Congress derails the deal, it will throw away a historic advance in global nuclear security.

Harold Feiveson just retired as Senior Research Scientist at the Princeton University Program on Science and Global Security, which he had co-directed for 30 years. He is co-author of Unmaking the Bomb: A Fissile Material Approach to Nuclear Disarmament and Nonproliferation, published by MIT Press in 2014.

1. In any reactor, the neutrons released by fission have to be slowed and this is done by a so-called moderator. In most reactors, the moderator is either water or graphite. But ordinary (“light”) water cannot be used as a moderator if natural uranium is used as the fuel. For natural uranium fuel, “heavy water”—combining deuterium, rather than regular hydrogen, and oxygen—must be employed.

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