This timetable estimates how soon Iran could enrich enough uranium to fuel a small nuclear arsenal. It assumes Iran would try to build an arsenal of five warheads of the implosion type – the goal Iran set for itself when it began to work on nuclear weapons decades ago. With its thousands of gas centrifuges, some operating and some in storage, Iran can enrich uranium to a grade suitable for nuclear reactor fuel or to a higher grade suitable for nuclear weapons. On January 5, 2020, Iran announced that it would no longer observe any limit (such as that set by the nuclear accord of 2015) on the use of its centrifuges, or on the possession of uranium they enrich. Since then, Iran has expanded its stockpile of enriched uranium, increased the enrichment level of that stockpile, and brought more advanced centrifuges into operation.

The analysis below reflects the status of Iran’s enrichment program as of October 26, 2024, the date of the latest estimates provided by the International Atomic Energy Agency (IAEA). Because Iran has reduced its cooperation with the Agency, the Agency is no longer able to precisely verify Iran's stockpile of enriched uranium at any one time. The Agency can verify uranium product that has been removed from the enrichment process, but it must rely on information provided by Iran to account for the amount that remains in-process. Because the in-process uranium represents a fraction of the total stockpile that is later verified, the estimates are suitable for use as a baseline measurement of how much enriched uranium Iran possesses. The analysis below is based on those estimates.

Summary

Iran’s nuclear program has reached the point at which, within about one week, Iran might be able to enrich enough uranium for five fission weapons. For that uranium to pose a nuclear weapon threat, however, it would have to be processed further, and the other components of a successful weapon would have to be ready to receive the processed uranium. Weaponization activities could take anywhere from several months to a year or more, although the timeframe is uncertain.^[1] Some of these activities could be done in parallel with the fissile material production and could take place on a laboratory scale, which would make them difficult to detect.

Iran's ability to enrich uranium quickly has improved with its progress in the testing and deployment of more powerful centrifuge models. Centrifuge performance is measured in separative work units (SWU), which indicates the work required to increase the concentration of the fissionable U-235 isotope. Iran has installed several cascades of these models in production lines where they have steadily increased both the size and enrichment level of Iran's uranium stockpile.

This progress increases the risk of secret sites – permitting them to be smaller and easier to hide. Iran has used such sites to carry out illicit activity in the past and they continue to pose the greatest nuclear weapon risk. That risk has increased further because of Iran’s decisions to limit inspections by the IAEA. Since February 2021, Iran has denied IAEA access to recorded data from centrifuge production plants and in June 2022 forced the IAEA to remove monitoring equipment altogether from such plants as well as from uranium enrichment and uranium concentrate (yellowcake) production facilities. Although a few cameras were re-installed at centrifuge production plants in May 2023, the Agency still cannot access the recordings. Iran has also refused to cooperate with the Agency’s investigation of uranium particles found at two undeclared sites. The overall effect has caused the IAEA to lose knowledge of essential elements of Iran’s program.

Nuclear Weapon Potential of Iran's Centrifuges and Enriched Uranium

As of October 2024, Iran was operating 36 cascades of IR-1 centrifuges as well as 30 cascades of more powerful centrifuges (15 IR-2m cascades, 12 IR-4 cascades, and three IR-6 cascades) at the Natanz Fuel Enrichment Plant (FEP). In addition, Iran was operating six cascades of IR-1 centrifuges and two cascades of IR-6 centrifuges at the Fordow Fuel Enrichment Plant (FFEP) and nearly a thousand centrifuges at the Natanz pilot plant, notably the IR-4 and IR-6. Iran also had several thousand IR-1 centrifuges in storage at Natanz and continues to test other more powerful centrifuge models in smaller numbers at the Natanz pilot plant. Some of these models are adding to Iran’s enriched uranium stockpile. By deploying them in larger numbers, Iran would be able to produce nuclear weapon fuel more quickly.

Iran's centrifuges have not produced uranium usually defined as weapon-grade, which is uranium enriched to 90% in the isotope U-235.^[2] All of Iran’s production has been at lower grades. Thus, the lower-grade uranium would have to be enriched further to reach at least 90%. The estimates below assume that, in a dash to make weapons, Iran would rely on its centrifuges operating in production mode at FEP, including IR-1, IR-2m, IR-4, and IR-6 centrifuges, and would use its accumulated stockpile of enriched uranium^[3] to produce nuclear weapon fuel. Iran's enriched uranium stockpile already contains sufficient uranium enriched to 60% U-235 to fuel at least five nuclear warheads with further enrichment.^[4] The estimates also assume that the IR-1 centrifuges currently operating will perform at the same rate they have in the past and that the IR-2m, IR-4, and IR-6 centrifuges would perform at a rate below their estimated nominal output.^[5]

These estimates are the minimum theoretical times it would take Iran’s known operating centrifuges at FEP, running continuously at their proved or estimated capacity, to accomplish the required amount of work. The time actually needed in practice would be greater, for instance if Iran elected not to use all of its centrifuges. The time estimate for five bombs can be expected to continue to fall, as Iran brings more centrifuges into production mode and if it further raises the enrichment level of its uranium stockpile.

It is important to consider that the enriched uranium produced would be in a gaseous compound, uranium hexafluoride (UF6). It would take additional time to convert the uranium in the gas to metallic form, and then to cast and machine the metal into weapon components. According to the IAEA, Iran began work on uranium metal production in early 2021. The uranium metal, however, would only be a threat if Iran had already perfected all the other parts needed for a working weapon, such as the high explosives and firing circuit, and had made sure the parts would work together to achieve a nuclear explosion. There is ample evidence in the public domain that Iran has tried to achieve that goal (see Weaponization below), but no conclusive evidence that it has succeeded. 

The Risk of Secret Sites

Intelligence agencies have long been unanimous in one prediction: If Iran makes nuclear weapons, it would do so at secret sites. The reasons are clear. If, in a dash to make weapons, Iran were to divert known (and therefore inspected) sites, material, or equipment to weapon making, it would risk detection before success, would violate the Nuclear Nonproliferation Treaty (NPT) and would make itself an international pariah. It would also invite an attack on the very sites, material, and equipment it diverted. No country has ever chosen to make an illicit diversion and dash to weapons, probably for the reasons just stated. 

The data below reveal that as Iran develops more powerful centrifuges, it could use ever smaller sites to enrich weapon quantities of uranium. And the smaller the site, the more difficult it will be to detect. For example, operating at 80% of its nominal capacity of 5 SWU, Iran’s IR-2m centrifuge, of which Iran has over 6,000 installed, could enrich the same amount of uranium as the IR-1 centrifuge in approximately one-fifth the space. Iran’s enrichment plant at Fordow, which was publicly exposed in 2009, was built clandestinely by Iran to house about 3,000 centrifuges. For this reason, the estimates below use 3,000 centrifuges as the possible size of a secret enrichment plant. 

These centrifuges would require only about 32,000 square feet, equal to approximately twice the size of the ice surface of a professional hockey rink.^[14] Alternatively, Iran could decide to split these 3,000 IR-2m centrifuges equally among three smaller sites of approximately 11,000 square feet each. That would decrease the size of each site and therefore the likelihood of detection. Each site would be about two-thirds the size of the ice surface of a professional hockey rink.^[15]

If Iran instead filled the facility or facilities with 3,000 IR-6 centrifuges rather than IR-2m centrifuges, it could make a secret dash more quickly. According to Iran, the IR-6 produces about 10 SWU per year, about twice as much as the IR-2m and ten times as much as the IR-1. At Fordow, Iran temporarily used two cascades of IR-6 machines enriching natural uranium to produce the 5% feed for the IR-1 centrifuges enriching up to 20% U-235.^[16] To produce enough feed for this configuration, each IR-6 machine would have to produce at least 6.6 SWU.^[17]

Again, these IR-6 centrifuges would require approximately the same space as the model IR-2m centrifuges above, or approximately twice the size of the ice surface of a professional hockey rink. The space requirements above reveal that as Iran develops more efficient centrifuges, it could rely on ever smaller sites to enrich weapon quantities of uranium.

The Status of Weaponization Efforts

The analysis above assumes that Iran would use 16 kg of highly enriched uranium metal (about 90% U-235) in the finished core of each nuclear weapon. Sixteen kilograms are assumed to be sufficient for an implosion weapon. This was the amount called for in a design for such a device that has circulated on the nuclear black market, to which Iran has had access.

Some experts believe that Iran could use less material, assuming Iran would accept a lower yield for each weapon. According to these experts, Iran could use as few as seven kilograms of this material if Iran’s weapon developers possessed a “medium” level of skill, and if Iran were satisfied with an explosive yield slightly less than that of the bomb dropped on Hiroshima, Japan.^[21] If Iran chose to use an amount smaller than 16 kg, the time required to make the fuel for each weapon would be less than estimated here. Or, in the amount of time estimated here, Iran could make a greater number of weapons. Iran could decide not to use such a smaller amount of uranium if Iran wanted to have more confidence that its weapons would work, or if it wanted to reduce the size of its weapons by reducing the amount of high explosive.

According to an investigation by the IAEA into "possible military dimensions" of Iran's nuclear program, Iran had a coordinated nuclear weapon program between 1999 and 2003. Specifically, the IAEA found that Iran developed several components of a nuclear weapon and undertook related research and testing. The investigation revealed Iran's efforts in the following areas:

• computer modeling of implosion, compression, and nuclear yield;
• high explosive tests simulating a nuclear explosion using non-nuclear material in order to see whether an implosion device would work;
• the construction of at least one containment vessel at a military site, in which to conduct such high explosive tests;
• studies on detonation of high explosive charges, in order to ensure uniform compression in an implosion device, including at least one large scale experiment in 2003, and experimental research after 2003;
• support from a foreign expert in developing a detonation system suitable for nuclear weapons and a diagnostic system needed to monitor the detonation experiments;
• manufacture of a neutron initiator, which is placed in the core of an implosion device and, when compressed, generates neutrons to start a nuclear chain reaction, along with validation studies on the initiator design from 2006 onward;
• the development of exploding bridgewire detonators (EBWs) used in simultaneous detonation, which are needed to initiate an implosive shock wave in fission weapons;
• the development of high voltage firing equipment that would enable detonation in the air, above a target, in a fashion only making sense for a nuclear payload;
• testing of high voltage firing equipment to ensure that it could fire EBWs over the long distance needed for nuclear weapon testing, when a device might be located down a deep shaft; and
• a program to integrate a new spherical payload onto Iran’s Shahab-3 missile, enabling the missile to accommodate the detonation package described above.

Information obtained by Israeli intelligence and revealed in April 2018 indicates that Iran sought to preserve this program after 2003 by dividing its nuclear program between covert and overt activities and retaining an expert team to continue work on weaponization. This "atomic archive" includes blueprints, spreadsheets, charts, photos, and videos – apparently official Iranian documents – that provide additional detail about Iran's efforts to develop a working nuclear weapon that could be delivered on a ballistic missile. In mid-2024, the U.S. intelligence community dropped its longstanding assertion that “Iran is not currently undertaking the key nuclear weapons-development activities necessary to produce a testable nuclear device.”

Iran's Violations of Nuclear Accord

Following the U.S. withdrawal from the 2015 nuclear accord in May 2018, Iranian leaders threatened to stop implementing some of Iran’s commitments under the accord. Approximately one year later Iran began doing so. The table below summarizes the steps Iran has taken since July 2019.