Iran’s nuclear breakout window narrows


March 9, 2022

Based on a recent International Atomic Energy Agency’s (IAEA) Iran Verification and Monitoring Report of March 3, 2022 [1], and subsequent Institute for Science and International Security (ISIS) analysis [2], Iran is continuing to advance its nuclear capabilities, hide nuclear research facilities, and thwart international inspections.

Here are ten things you need to know about the nuclear capacity of the Islamic Republic of Iran in order to offer cogent analysis of Iran’s compliance with the existing Joint Comprehensive Plan of Action (JCPOA) and/or ongoing negotiations by the U.S. to adapt that agreement before joining it once again as a participating party.

  1. It takes about 25 kg of weapons-grade uranium (generally uranium enriched to contain 90 percent U-235, the fissile isotope) to make an atomic bomb.


  1. Iran has already accumulated uranium hexafluoride (UF6) –as of 19 February 2022 at least 49.1 kg of UF6 containing 33.2 kg of 60 percent enriched uranium and some 20 percent enriched uranium) that it can quickly feed into centrifuge cascades to produce weapons-grade uranium. Iran has estimated total stockpile of just over 180 kg of 20 percent enriched uranium in UF6 and other chemical forms


  1. With 33.2 kg of 60 percent enriched uranium and its known/declared centrifuge capacity, Iran could produce enough weapons-grade uranium for one atomic weapon within a period estimated to as fast as two to three weeks. Within three to six weeks Iran could produce enough weapons-grade uranium to fuel two bombs.


  1. Although previous Iranian efforts to produce an atomic weapon (e.g., the Amad plan led by Mohsen Fakhrizadeh, see footnote [3] below) focused on the use of weapons-grade uranium, Iran’s concealment of its prior programs, facilities, and hindrance of inspections leaves open the possibility that it may have explored the development of cruder weapons capable of using 60 percent enriched uranium. Iran needs only an additional 8 kg of 60 percent enriched uranium (HEU) to make a crude nuclear weapon not requiring additional centrifuge passes. ISIS estimates that Iran could produce 54 kg of HEU annually. At Iran’s current pace, it will have sufficient HEU to make a crude bomb by summer (2022).


  1. Prior declarations and inspections show an ongoing effort by Iran, including multi-step enrichment experiments – to upgrade its uranium enhancement capacity.


  1. Iran’s stockpiling of enriched uranium, including the production of near 5 percent and 2 percent enriched uranium, has accelerated. Since the last IAEA report. Iran’s 20 percent enriched uranium stock increased by from 113.8 kg to 182.1 kg, and the near 60 percent enriched uranium (HEU) stock increased by 15.5 kg to 33.2 kg.


  1. Since February 2021, Iran has denied the IAEA the ability to inspect and/or monitor known/declared Iranian nuclear research facilities (including Esfahan or Karaj sites). Gaps also exist in both monitoring and Iran’s accounting for the number and use of centrifuges at other facilities including the Natanz Fuel Enrichment Plant and Fordow Fuel Enrichment Plant


  1. According to ISIS, “the IAEA also reports that it cannot verify Iran’s JCPOA commitments related to prohibited nuclear weapons development activities.”


  1. Although Iran has sent 23.3 kg of it HEU to its Fuel Plate Fabrication Plant (FPFP) in Isfahan, according to ISIS, “it is expected that only a tiny fraction will be converted into targets. As such, the production of targets will not remove the proliferation and breakout risks posed by Iran’s stockpile of HEU. This step should be viewed as a cynical attempt by Iran to place a civilian mask on an inherently military material and lay a precedent for future production of HEU.”


  1. As it had warned in December 2021, in early February 2021, Iran began producing uranium metal (see background information below) from both 20 percent enriched uranium and 60 percent enriched uranium for by the Tehran Research Reactor (TRR). This an open violation of its JCPOA commitments. In an article published in Science on 15 July 2021 (“Iran’s plans for research reactor fuel imperil revival of nuclear deal”), Andrea Stricker, a nonproliferation analyst at the nonprofit Foundation for Defense of Democracies countered Iran’s claim that it was using the metal to produce medical isotopes. “Iran is pursuing a strategy of brinkmanship,” said Stricker, “It is using civil-use justifications as a pretext to brazenly advance its nuclear weapons–related knowledge.”







[3] Despite continual Iranian denials that it ever pursued nuclear weapons, in a 2015 report by the IAEA titled “Final Assessment on Past and Present Outstanding Issues regarding Iran’s Nuclear Programme,” IAEA scientists concluded that “a range of activities relevant to the development of a nuclear explosive device were conducted in Iran prior to the end of 2003 as a coordinated effort, and some activities took place after 2003…”




Background for non-scientists


Uranium, atomic number 92 on the Periodic Table is the heaviest naturally occurring element on Earth. The uranium nucleus contains 92 protons but a variable number of neutrons to create uranium-238, uranium-235, and uranium-234 isotopes of uranium.  About 0.72 percent of natural uranium is U-235 All uranium isotope are radioactive as they decay, but only U-235 is capable of fission (a spitting of the nucleus) when it absorbs a neutron. This splitting releases tremendous energy


Uranium ore treated to form uranium oxide (“yellowcake”) and then combined over a series of steps with anhydrous hydrogen fluoride and fluorine gas to form uranium hexafluoride (UF6). Uranium hexafluoride can exist as a gas used in further enhancement or as a liquid or solid for storage and shipping. Uranium hexafluoride does not react with atmospheric gases (oxygen, nitrogen, carbon dioxide, etc.) but is reacts with water and water vapor in the air to form hydrogen fluoride (a corrosive) and uranyl fluoride (UO2F2).


During gaseous diffusion, uranium hexafluoride (UF6) gas passes through hundreds of fine porous filters that help separate the faster moving U-234 and U-235 atoms from the heavier and slower moving U-238 isotopes. Accordingly, two output streams — one enriched in U-235 and the other depleted in U-235 are observed. With further processing of the enriched uranium the percentage of U-235 increases.


To be used as nuclear fuel the uranium must be enriched 3 to 5 percent. Highly Enriched Uranium is 60 percent U-235 and weapons grade-uranium is 90-plus percent U-235


Centrifuges produce a force much stronger than the normal gravitational force. The spinning of gaseous uranium hexafluoride (UF6) creates a sight separation of heavier U-238 and relatively lighter U-235 atoms. By drawing off the U-235 enriched region and repeating the process thousands of times through a chain or cascade of high-speed centrifuges that spin about 100,000 rpm, one obtains increasing purified or enhanced U-235. Adding calcium to the enriched U-235 creates a salt and a pure uranium metal for fuel rods or if enriched to weapons grade U-235, nuclear weapons.



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