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This report estimates how soon Iran could fuel a nuclear weapon. With its thousands of gas centrifuges, Iran now has the ability to enrich uranium to a grade suitable for use in nuclear reactors or to a higher grade suitable for use in nuclear warheads. The data below, which are based on reports from the International Atomic Energy Agency, describe Iran’s uranium stockpile, its centrifuges, and the rate at which its nuclear capacity is growing. [a] These data reflect Iran’s suspension of some enrichment work beginning on January 20, 2014, in line with an interim nuclear accord Iran struck with the United States and its partners in the P5+1 group of countries.
- By using the approximately 9,000 first-generation centrifuges operating at its Natanz Fuel Enrichment Plant, Iran could theoretically produce enough weapon-grade uranium to fuel a single nuclear warhead in about 1.7 months.
- Iran's more advanced IR-2m centrifuges, about 1,000 of which are installed at Natanz, would allow Iran to produce weapon-grade uranium more quickly.
- Iran's stockpile of low-enriched uranium is now sufficient, after further enrichment, to fuel approximately eight nuclear warheads.
- Because Russia has a ten-year contract to fuel Iran’s only power reactor at Bushehr, Iran has no present need for enriched uranium to generate civilian nuclear energy.
- Before using uranium in a warhead, it must be enriched to weapon-grade (90 percent or more U-235) and processed into a metallic shape sufficient to explode in a chain reaction. Iran is producing low enriched uranium gas (about 3.5 percent U-235) but Iran has suspended the production of higher enriched uranium gas (about 20 percent U-235).
Bomb potential of Iran's low-enriched uranium
- Total amount of uranium hexafluoride (UF6) enriched to approximately 3.5 percent U-235 produced as of May 2014:
11,977 kg [b]
- Amount of this material ready for further enrichment (i.e., stored in gaseous form) as of May 2014:
8,475 kg [c]
- Amount theoretically needed to produce a bomb's worth of weapon-grade uranium metal:
1,053 kg [d]
- Number of first-generation implosion bombs this 8,475 kilograms could fuel, if further enriched:
- Time needed to convert this uranium to one bomb's worth of finished uranium metal enriched to 90 percent U-235:
3 - 12 months [f]
- Date by which Iran's uranium stockpile probably was sufficient to fuel one first-generation implosion bomb, if further enriched:
February 2009 [g]
- Approximate number of first generation IR-1 centrifuges being fed with UF6 at the Natanz Fuel Enrichment Plant, as of the last reported visit by IAEA inspectors:
- Number of months theoretically needed for these 9,000 centrifuges operating at their present capacity to produce enough enriched uranium for one bomb:
Civilian need for this uranium
- Approximate amount of low-enriched uranium needed annually to fuel Iran’s sole civilian power reactor at Bushehr:
21 metric tons [j]
- Percent of this uranium Russia will supply under a fuel contract covering the next ten years:
- Amount of uranium Iran will need to fuel other power reactors during the next five years:
0 kg [l]
Bomb potential of Iran's higher enriched uranium
- Total amount of uranium hexafluoride (UF6) enriched to approximately 20 percent U-235 produced as of January 2014:
447.8 kg [m]
- Amount of this material ready for further enrichment (i.e., stored in gaseous form) as of May 2014:
38.4 kg [n]
- Amount theoretically needed to produce a bomb’s worth of weapon-grade uranium metal:
140 kg [o]
- Average monthly production rate of this material before the January 20, 2014 suspension:
14.8 kg [p]
- Total number of IR-1 centrifuges installed at Fordow:
- Number of months theoretically needed for these centrifuges to raise the enrichment of a bomb's worth of 20 percent enriched UF6 to weapon-grade :
Growth of enrichment capacity at the Natanz Fuel Enrichment Plant
Date of IAEA Inventory
IR-1 Centrifuges Being Fed with UF6
Other IR-1 Centrifuges Installed
|17 Feb 2007||0||656|
|13 May 2007||1,312||820|
|19 Aug 2007||1,968||656|
|3 Nov 2007||2,952||0|
|12 Dec 2007||2,952||?|
|7 May 2008||3,280||2,624|
|30 Aug 2008||3,772||2,132|
|7 Nov 2008||3,772||2,132|
|1 Feb 2009||3,936||1,968|
|1 Jun 2009||4,920||2,296|
|12 Aug 2009||4,592||3,716|
|2 Nov 2009||3,936||4,920|
|31 Jan 2010||3,772||4,838|
|24 May 2010||3,936||4,592|
|28 Aug 2010||3,772||5,084|
|5 Nov 2010||4,816||3,610|
|16 Nov 2010||0||~ 8,426|
|22 Nov 2010||~4,592||~3,834|
|20 Feb 2011||~5,184||~2,816|
|14 May 2011||~5,860||~2,140|
|28 Aug 2011||~5,860||~2,140|
|2 Nov 2011||~6,208||~1,792|
|19 Feb 2012||8,808||348|
|19 May 2012||8,818||512|
|21 Aug 2012||9,156||270|
|10 Nov 2012||9,156||1,258|
|19 Feb 2013||~8,990||~3,680|
|15 May 2013||~8,990||~4,565|
|24 Aug 2013||9,156||6,260|
|9 Nov 2013||~8,800||~6,620|
|10 Feb 2014||~9,000||~6,420|
|14 May 2014||~9,000||~6,420|
Date of IAEA Inventory
IR-2m Centrifuges Being Fed with UF6
IR-2m Centrifuges Installed
19 Feb 2013
15 May 2013
24 Aug 2013
9 Nov 2013
|10 Feb 2014||0||1,008|
|14 May 2014||0||1,008|
- On January 20, 2014, the IAEA verified that Iran was implementing the restrictions on its nuclear program set forth in the “Joint Plan of Action,” an interim accord between Iran and the P5+1 group of countries (Britain, China, France, Germany, Russia, and the United States). These restrictions include a suspension in the production of 20 percent enriched uranium, a freeze on manufacturing, installing, and operating additional centrifuges, and a commitment to either downblend or convert part of its 20 percent enriched uranium stockpile.
- The centrifuges Iran had been using for the production of 20 percent enriched uranium (328 IR-1 centrifuges at the Natanz pilot plant and 696 IR-1 centrifuges at the Fordow plant) were repurposed beginning on January 20 for the production of 3.5 percent enriched uranium. The cascades at these plants are no longer interconnected.
- This assessment assumes that Iran would use 16 kg of weapon-grade uranium (~90 percent U-235) in the finished core of each nuclear weapon. Sixteen kilograms are assumed to be sufficient for an implosion bomb. This was the amount called for in the implosion device Saddam Hussein was trying to perfect in the 1980’s, and the design for such a device 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.[s] If Iran chose to use an amount smaller than 16 kg, the time required to make 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 weapon-grade 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 required.
- Uncertainties about the number of centrifuges that Iran is operating make it difficult to draw a conclusion about the performance of individual machines. An increase or decrease in the production rate could be attributed to the fact that more machines were operating when IAEA inspectors were not present at the plant, rather than because the machines were operating more efficiently.
- Following start-up, centrifuge cascades must be operated for a time without product withdrawal. This process is called passivation.
[a] The following estimates are based on information in quarterly reports by the International Atomic Energy Agency (IAEA), which is responsible for nuclear inspections in Iran. These quarterly reports are available here: http://www.iranwatch.org/authoring-agency/iaea-report.
[b] According to the IAEA, Iran had an inventory of 10,357 kg of low-enriched UF6 as of November 5, 2013, based on production from the beginning of operations in February 2007. Iran produced a further 1,620 kg of this material through May 2014, for a total stockpile of 11,977 kg. According to the IAEA, Iran continues to produce low-enriched UF6 at a rate similar to that indicated in the Agency’s February 2014 report. At that time, and based on recent production numbers, Iran was estimated to be producing an average of 7.9 kg of low-enriched UF6 each day.
[c] Prior to the interim nuclear accord, Iran had used some of its stockpiled low-enriched UF6 (~3,400 kg) for the production of 20% enriched uranium gas. Under the accord, this production has been suspended and Iran is either downblending the 20% material to low-enriched UF6 or converting it to oxide form. Iran is also using centrifuges that had been producing 20% enriched uranium gas for the production of low-enriched UF6. As a result of these activities, Iran had approximately 8,457 kg of low-enriched UF6 as of May 2014, according to the IAEA.
[d] This is assuming uranium tails of 1% U-235, a feed assay of 3.5% U-235, a product assay of 90% U-235, a 20% loss of material during processing, and that 16 kg of finished uranium metal enriched to 90% are needed for a bomb. See the Separative Work Unit (SWU) calculator published by URENCO, a European uranium enrichment consortium: web.archive.org/web/20021226100607/www.urenco.de/trennarbeit/swucal_e.html.
[e] If 1,053 kg of low-enriched uranium are required to produce a bomb’s worth of weapon-grade uranium (see note d), the 8,475 kg of low-enriched uranium in Iran’s stockpile as of May 2014 might be sufficient to fuel about eight first-generation implosion bombs.
[f] The IAEA estimates the conversion time for low-enriched uranium to weapon-grade uranium metal to be approximately 3-12 months (www-pub.iaea.org/MTCD/publications/PDF/nvs-3-cd/PDF/NVS3_prn.pdf).
[g] According to the IAEA, Iran had produced about 1,010 kg of low-enriched UF6 by late January 2009. Given the average daily production rate of this material at the time, Iran's stockpile probably contained the requisite 1,053 kg by the following month.
[i] According to production data at the Natanz Fuel Enrichment Plant, Iran's IR-1 centrifuges have achieved an average annual output of about .78 Separative Work Units, or SWUs, per machine. A SWU is a standard measure of the effort required to increase the concentration of the fissionable U-235 isotope within natural uranium. Based on the assumptions set forth above (see note d), Iran would need approximately 955 SWUs to bring 1,053 kg of low-enriched UF6 to weapon grade. If each of Iran’s 9,000 centrifuges produces an average of .78 SWUs per year, their total output over one year would be 7,045 SWUs, or 587 SWUs per month. Thus, it would take about 1.7 months to produce 955 SWUs.
[j] A typical 1,000 MWe pressurized light water reactor of the type Iran is operating at Bushehr requires about 21 tons of low-enriched uranium fuel each year. See the nuclear fuel cycle simulation system published by the IAEA (http://infcis.iaea.org/NFCSS/NFCSSMain.asp?RightP=Calculation&EPage=2&Refresh=0&ReactorType=1).
[k] Russia and Iran signed a nuclear fuel agreement in late February 2005. Under the agreement, Russia committed to supplying fuel for Bushehr for ten years and Iran committed to returning the spent fuel to Russia.
[l] Only plans for a 360 MW nuclear power plant at Darkhovin so far has been declared to the IAEA. The status of this reactor is unclear but it is not expected to come online before at least 2018. In addition, Iran has initiated a plan to identify “candidate areas” for the construction of new nuclear power plants, according to the IAEA. Sixteen “preferred candidate areas” had been identified by February 2014, but no construction had begun in these areas.
[m] Until January 20, 2014, Iran had been producing 20% enriched UF6 at both its Natanz pilot plant and its Fordow enrichment plant, allegedly for the purpose of fueling the Tehran Research Reactor. This production was suspended as part of a November 2013 interim accord with the P5+1. According to the IAEA, Iran had produced 447.8 kg of this material through January 20, 2014 (201.9 kg at the Natanz and 245.9 kg at Fordow).
[n] According to the IAEA, 38.4 kg of Iran’s 20% enriched uranium stockpile remained in gaseous form as of May 2014; 303.2 kg had been converted to uranium oxidel; and 106.2 kg had been downblended to 3.5% enriched UF6.
[o] This is assuming uranium tails of 1% U-235, a feed assay of 19.75% U-235, a product assay of 90% U-235, a 20% loss of material during processing, and that 16 kg of finished uranium metal enriched to 90% are needed for a bomb core. See the SWU calculator published by URENCO, a European uranium enrichment consortium: web.archive.org/web/20021226100607/www.urenco.de/trennarbeit/swucal_e.html. Media reports, citing Israeli sources, estimate that Iran would need about 240 kg of this 20 percent enriched uranium gas to fuel one weapon.
[p] Iran verifiably suspended the production of 20% enriched uranium on January 20, 2014, in line with an interim nuclear accord reached with the P5+1. Until then, this production took place at two locations, the Natanz pilot plant and the Fordow plant. Between September 16, 2012 and August 16, 2013, Iran estimates that it produced 48.7 kg of 20% enriched UF6 at the Natanz pilot plant, for an average monthly production rate of 4.8 kg. Between November 18, 2012 and August 16, 2013, Iran produced 93.5 kg of 20% enriched UF6 at the Fordow plant, for an average monthly production rate of just over 10 kg.
[r] Based on the assumptions set forth above (see note d), Iran would need approximately 292 SWUs to bring 140 kg of 20% enriched UF6 to weapon grade. If each of the 2,710 IR-1 centrifuges installed at the Fordow enrichment plant were to achieve the same average production rate as those at the main enrichment plant at Natanz (.78 SWU per machine), then it would take less than two months to achieve 292 SWUs at the Fordow plant. See the SWU calculator published by URENCO, a European uranium enrichment consortium: web.archive.org/web/20021226100607/www.urenco.de/trennarbeit/swucal_e.html.
[s] Thomas B. Cochran and Christopher E. Paine, “The Amount of Plutonium and Highly Enriched Uranium Needed for Pure Fission Nuclear Weapons,” (Washington, DC: Natural Resources Defense Council, revised April 13, 1995).