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This table estimates how soon Iran could fuel a nuclear weapon. With its thousands of gas centrifuges, and its growing stockpile of enriched uranium, Iran now has the ability to make fuel for nuclear reactors or, by enriching the uranium further, for nuclear warheads. The data below, which is 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.
- By using the approximately 8,800 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.
- The more advanced centrifuges being 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 six nuclear warheads.
These estimates, and those below, account for the fact that Iran has been converting some of its low-enriched uranium gas (about 3.5 percent in the isotope U-235) to medium-enriched uranium gas (about 20 percent U-235), and that Iran has converted about 52 percent of the medium-enriched uranium gas into fuel assemblies for a research reactor. 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.
As Iran deploys more centrifuges, and increases its stockpile of enriched uranium, it will consolidate its status as a "virtual" nuclear weapon state. Iran's progress towards this status is estimated below [a]. These estimates are based upon the theoretical performance of Iran's existing centrifuges and upon how these centrifuges appear to have performed in the past:
Bomb potential of Iran's low-enriched uranium stockpile
- Amount of uranium hexafluoride (UF6) enriched to approximately 3.5 percent U-235 produced as of November 5, 2013:
10,357 kg [b]
- Amount of this material stored in gaseous form as of November 2013:
7,154.3 kg [c]
- Average daily production rate of this low-enriched UF6 at the Natanz Fuel Enrichment Plant:
7.7 kg [d]
- Amount of this low-enriched UF6 needed to produce a bomb's worth of weapon-grade uranium metal:
1,053 kg [e]
- Number of separative work units (SWUs) needed to accomplish the above [f]:
- Number of first-generation implosion bombs this low-enriched uranium stored in gaseous form could fuel, if further enriched:
- Time needed to convert this low-enriched uranium to one bomb's worth of finished uranium metal enriched to 90 percent U-235:
3 - 12 months [i]
- Date by which Iran's low-enriched uranium stockpile probably was sufficient to fuel one first-generation implosion bomb, if further enriched:
February 2009 [j]
- 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:
- Average number of SWUs each centrifuge appears to be producing:
- Number of months theoretically needed for these 8,800 centrifuges operating at such a capacity to produce the 955 SWUs theoretically needed to produce weapon-grade fuel for one bomb:
- Approximate total number of IR-1 centrifuges installed at the Natanz Fuel Enrichment Plant:
Bomb potential of Iran's medium-enriched uranium stockpile
- Amount of medium-enriched uranium hexafluoride (UF6) gas (approximately 20 percent U-235) produced as of November 2013:
410.4 kg [o]
- Amount of this material stored in gaseous forms as of November 2013:
196 kg [p]
- Amount of this material converted to uranium oxide for use in fuel plates, as of November 2013:
213.54 kg [p]
- Amount of this 20 percent enriched UF6 theoretically needed to produce a bomb’s worth of weapon-grade uranium metal:
140 kg [q]
- Average monthly production rate of this 20 percent enriched UF6 at the Natanz pilot plant:
4.8 kg [r]
- Number of first generation IR-1 centrifuges being fed with UF6 at the Natanz pilot plant as of the last reported visit by IAEA inspectors:
- Average monthly production rate of this 20 percent enriched UF6 at the Fordow plant since the last IAEA report:
10 kg [t]
- Number of first generation IR-1 centrifuges being fed with this UF6 at the Fordow fuel enrichment plant as of the last reported visit by IAEA inspectors:
- Total number of IR-1 centrifuges installed at Fordow:
- Number of SWUs needed to accomplish the enrichment of a bomb's worth of this 20 percent enriched UF6 to weapon-grade:
- Number of months theoretically needed for the 2,710 IR-1 centrifuges currently installed at Fordow to accomplish the above:
Increasing 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|
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
- 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.[y] 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 7,451 kg of low-enriched UF6 as of October 21, 2012, based on production from the beginning of operations in February 2007. Iran produced a further 2,906 kg of this material through August 10, 2013, for a total stockpile of 10,357 kg.
[c] According to the IAEA, Iran has used some of its stockpiled low-enriched UF6 (~2,880 kg) for the production of 20% enriched uranium gas. Therefore, Iran had approximately 7,154.3 kg of low-enriched UF6 left as of mid-August, 2013.
(e) 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 SWU calculator published by URENCO, a European uranium enrichment consortium: web.archive.org/web/20021226100607/www.urenco.de/trennarbeit/swucal_e.html.
(f) The Separative Work Unit is the standard measure of the effort required to increase the concentration of the fissionable U-235 isotope. See www.urenco.com/Content/89/Glossary.aspx.
(g) Based on the assumptions set forth above (see note e), Iran would need approximately 955 SWUs to bring 1,053 kg of low-enriched UF6 to weapon grade. See the SWU calculator published by URENCO, a European uranium enrichment consortium: web.archive.org/web/20021226100607/www.urenco.de/trennarbeit/swucal_e.html.
(h) If 1,053 kg of low-enriched uranium are required to produce a bomb’s worth of weapon-grade uranium (see note e), the 7,154.3 kg of low-enriched uranium in Iran’s stockpile as of November 2013 might be sufficient to fuel about six first-generation implosion bombs. This number takes into account the conversion of almost one third of Iran’s low-enriched UF6 stockpile to 20% enriched uranium gas
(i) 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).
(j) 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.
(l) Iran's IR-1 centrifuge is estimated to have an annual enrichment capacity of about 2 SWU. Iran, however, has been achieving a lower ouput. For instance, between October 2012 and August 2013, during which time Iran is estimated to have been operating an average of 9,000 centrifuges, 2,253 kg of low-enriched UF6 were produced. Assuming a product assay of 3.5% U-235 and tails of .4% U-235, this amounts to about 5,538 SWUs (6,818 SWUs over one year), or about .76 SWU per machine.
(m) If each of Iran’s 8,800 centrifuges produces an average of .76 SWUs per year, their total output over one year would be 6,688 SWUs, or 557 SWUs per month. Thus, it would take 1.7 months to produce 955 SWUs.
(n) According to the IAEA, as of November 2013, a total of 15,420 centrifuges (90 cascades) had been fully installed in Production Hall A of the Natanz Fuel Enrichment Plant. As of that date, preparatory installation work had been completed for a further 36 centrifuge cascades. The cascades contain first-generation IR-1 centrifuges of either 164 or 174 machines each. An avearge of 170 machines per cascade has been used to estimate the total number of centrifuges.
(o) Iran is 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. According to the IAEA, Iran has produced an estimated 410.4 kg of this material through November 2013. The IAEA has verified that Iran produced 129.1 kg of this material between February 9, 2010 and September 15, 2012 at Natanz. Since then, Iran has produced an estimated 48.7 kg of 20% enriched UF6 at Natanz. The IAEA has also verified that Iran produced 101.2 kg of 20% enriched UF6 at the Fordow plant between December 11, 2011 (when production began) and November 17, 2012. Iran estimates that it produced a further 93.5 kg at Fordow through August 16, 2013.
(q) 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.
(u) Since mid-December 2011, Iran has been enriching uranium in two interconnected cascades of 174 centrifuges each (348 machines) at the Fordow plant. Iran began enriching uranium in two additional cascades of 174 centrifuges each in late January 2012.
(w) Based on the assumptions set forth above (see note q), Iran would need approximately 292 SWUs to bring 140 kg of 20% enriched UF6 to weapon grade. See the SWU calculator published by URENCO, a European uranium enrichment consortium: web.archive.org/web/20021226100607/www.urenco.de/trennarbeit/swucal_e.html.
(x) If 292 SWUs are needed to bring a bomb’s worth of 20% enriched UF6 to weapon-grade, and if the 2,710 IR-1 centrifuges installed at Iran’s Fordow enrichment plant were to achieve the same average production rate as those in the main enrichment plant at Natanz (.76 SWU per machine), then it would take less than two months to achieve 292 SWUs at the Fordow plant.
(y) 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).