Iran's Nuclear Timetable
Updated June 4, 2010
Iran’s bank of rapidly spinning centrifuges has produced a growing stockpile of low-enriched uranium, able to fuel nuclear reactors, but able also to fuel nuclear weapons if further enriched. Enrichment raises the concentration of the uranium isotope U-235, which fissions in first-generation nuclear weapons.
Based on the amount of low-enriched uranium Iran has stockpiled, and the amount it is believed to be producing each month, the Wisconsin Project estimates that by December 2008, Iran had accumulated enough U-235 to fuel one bomb quickly. The Project further estimates that by the end of 2009, Iran had enough U-235 to fuel a second bomb. "Quickly," in this context, means two to three months -- about the time it would take Iran to raise the level of U-235 in its uranium stockpile from 3.5 percent to over 90 percent, if Iran were to use every means at its disposal and did not encounter technical difficulties.
As Iran increases its stockpile of low-enriched uranium, it will consolidate its status as a "virtual" nuclear weapon state.
Iran's progress towards this status as of June 1, 2010 is estimateda below. 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:
- Amount of U-235 contained in Iran’s stockpile of low-enriched uranium:
60.3 kg b
- Amount of this U-235 produced each month:
2.8 kg c
- Date by which Iran probably had stockpiled the above:
December 2008 f
- Number of additional months needed to convert this low-enriched uranium to weapon-grade g:
Two to three h
- Date by which Iran probably had enough U-235 to fuel a second bomb:
December 2009 i
Additional estimates: Moving from reactor-grade to weapon-grade uranium
- Amount of uranium hexafluoride (UF6) enriched to 3.5 percent U-235 now on hand:
2,550 kg j
- Average daily production rate of this low-enriched UF6:
3.97 kg k
- Amount of this low-enriched UF6 needed to produce a bomb’s worth of weapon-grade UF6:
914 kg l
- 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:
3,936 o
- Average number of SWUs each centrifuge now appears to be producing per year:
.92 p
- Total number of centrifuges installed at Natanz as of the last reported visit by IAEA inspectors:
8,528 q
- Number of SWUs these 8,528 centrifuges are assumed to be capable of producing per year:
8,600 r
- Number of months needed for these 8,528 centrifuges operating at such a capacity to produce 840 SWUs:
1.2 s
Comments:
- If Iran were to export 1,200 kg of its low-enriched uranium stockpile to Turkey, as set forth in an agreement Iran signed with Turkey and Brazil on May 17, Iran would be left with approximately 1,350 kg of this material. 1,350 kg of uranium enriched to 3.5 percent contains 32 kg of U-235, which is more than sufficient to fuel a first generation implosion bomb (see note e). And as the agreement does not appear to require Iran to suspend enrichment, Iran’s stockpile of low-enriched UF6 would continue to grow. In about four months, at current production rates, Iran’s stockpile of low-enriched UF6 would contain enough U-235 for two bombs.
- Iran has not increased the number of centrifuges enriching uranium at Natanz; the number appears to have remained at just under 4,000 machines since November 2009. Iran had nearly three operational units (of about 3,000 machines each) at the plant as of late May 2010, though it was enriching uranium in less than half of those machines at that time.
- Iran’s monthly production rate of low-enriched uranium seems to have increased in recent months, though Iran still appears to be operating its centrifuges below their estimated capacity. However, uncertainties about the number of centrifuges that Iran is operating make it difficult to draw a conclusion about machine performance. An increase 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.
- Under the current inspection arrangement, the IAEA verifies Iran's estimate of low-enriched UF6 production once a year, when a physical inventory verification is carried out. The results of the Agency’s most recent inventory, completed in December 2009, largely confirm the estimates reported by Iran. Between November 2008, the date of the last inventory, and November 1, 2009, Iran estimated its production of low-enriched UF6 to be 924 kg. The Agency’s inventory concluded that Iran had produced 969 kg of this material between November 2008 and November 22, 2009. It should be noted that the results of the previous inventory revealed that Iran had underestimated by about one third the amount of low enriched UF6 actually produced.
Additional information: Number of centrifuges deployed over time
| Date of IAEA inventory | Centrifuges being fed with UF6 | Other centrifuges (installed or being installed) |
|---|---|---|
2/17/2007 |
0 |
656 |
5/13/2007 |
1,312 |
820 |
8/19/2007 |
1,968 |
656 |
11/3/2007 |
2,952 |
0 |
12/12/2007 |
2,952 |
? |
5/7/2008 |
3,280 |
2,624 |
8/30/2008 |
3,772 |
2,132 |
11/7/2008 |
3,772 |
2,132 |
2/1/2009 |
3,936 |
1,968 |
6/1/2009 |
4,920 |
2.296 |
8/12/2009 |
4,592 |
3,716 |
11/2/2009 |
3,936 |
4,920 |
1/31/2010 |
3,772 |
4,838 |
5/24/2010 |
3,936 |
4,592 |
ENDNOTES
(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.
(b) According to the IAEA, Iran had produced a total of 1,808 kg of low-enriched UF6 as of November 22, 2009. Since then, Iran has produced approximately 742 kg of this material for a total of 2,550 kg (see note j) (http://www.iranwatch.org/international/IAEA/iaea-iranreport-053110.pdf). Of that amount, 1,723 kg is uranium; 1,723 kg of uranium enriched to 3.5% contains 60.3 kg of U-235.
(c) Iran is estimated to produce about 3.97 kg of low-enriched UF6 each day (see note k), for an average monthly production rate of 120 kg, 81 kg of which is uranium; enriched to 3.5%, this 81 kg contains 2.8 kg of U-235.
(d) 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. The critical mass of a sphere of U-235 metal is only 15 kg with a Beryllium reflector. See Gunter Hildenbrand, Nuclear energy, nuclear exports and the proliferation of nuclear weapons, AIF Conference on International Commerce and Safeguards for Civil Nuclear Power, March 1977. For a schematic diagram of an implosion bomb, see: www.wisconsinproject.org/bomb-facts/images/nw-1.jpg.
(e) Because of losses during the enrichment and weaponization processes, Iran would need about 914 kg (see note l) of UF6 enriched to 3.5% U-235, of which about 618 kg would be uranium, in order to achieve 16 kg of weapon-grade uranium. 618 kg of uranium enriched to 3.5% U-235 contains 21.6 kg of U-235. 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) Assuming 19.9 kg of U-235 on hand as of November 17, 2008, a requirement of 21.6 kg for a first bomb, and a production rate, at the time, of 1.6 kg of U-235 each month, Iran would have had enough in December 2008.
(g) Once enriched to weapon-grade, this material would still need to be converted from gas to metal and then machined into a form suitable for a bomb.
(h) 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). However, if it would take approximately 840 SWUs to produce 16 kg of U-235 from a stockpile of 3.5% enriched uranium (see note n), and if Iran is capable of producing 8,300 SWUs per year (see note s), then a conversion time at the lower end of this range is probable. Therefore, Iran could have weapon-grade UF6 within 2-3 months, even assuming a delay in processing.
(i) Assuming 41.7 kg of U-235 on hand as of November 1, 2009, a requirement of 21.6 kg for a first bomb, and a production rate, at the time, of 2 kg of U-235 each month, Iran would have accumulated the requisite 21.6 kg for a second bomb by the end of December 2009.
(j) According to the IAEA, Iran had an inventory of 1,808 kg of low-enriched UF6 as of November 22, 2009, based on production from the beginning of operations in February 2007. Iran has estimated that it produced 619 kg of this material from November 23, 2009 through May 1, 2010. This gave Iran a total of about 2,427 kg of low-enriched UF6 by May 1. Assuming a daily production rate of 3.97 kg (see note k) since then, Iran produced a further 123 kg of low-enriched UF6, bringing its total stockpile to 2,550 kg (http://www.iranwatch.org/international/IAEA/iaea-iranreport-053110.pdf).
(k) Iran estimates that it produced 362 kg of low-enriched UF6 over 91 days, from January 30, 2010 to May 1, for an average daily production rate of 3.97 kg.
(l) This is assuming uranium tails of 1% U-235, a feed assay of 3.5% U-235, a product assay of 93% U-235, a 5% loss of material during bomb manufacture, and that 16 kg of this product 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.
(m) 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.
(n) Based on the assumptions set forth above (see footnote l), Iran would need approximately 840 SWUs to bring 914 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.
(o) According to the IAEA, as of late May 2010 Iran was operating an 18 cascade unit (A24) of 2,952 machines and six cascades (984 machines) in a second unit (A26) at the Natanz Fuel Enrichment Plant (http://www.iranwatch.org/international/IAEA/iaea-iranreport-053110.pdf).
(p) Iran is operating its IR-1 centrifuges at below their estimated capacity. For instance, between January and May 2010, during which Iran is estimated to have been operating between 3,772 and 3,936 machines, an estimated 362 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 890 SWU over 3 months (3,560 SUW over one year), or about .92 SWU per machine.
(q) According to the IAEA, as of late May 2010 Iran was operating an 18 cascade unit (A24) of 2,952 machines and six cascades (984 machines) in a second unit (A26); 12 cascades at unit A26 (1,968 centrifuges) and 16 cascades (2,624 machines) at unit A28 were installed (http://www.iranwatch.org/international/IAEA/iaea-iranreport-053110.pdf).
(r) Iran’s IR-1 centrifuge is widely estimated to have an annual enrichment capacity of about two SWUs. Iran, however, has been achieving a lower output (see note p). If Iran were to increase the efficiency of its centrifuges to one SWU per machine, the machines at the Natanz Fuel Enrichment Plant would produce about 8,600 SWUs per
(s) If 840 SWUs are needed to bring a bomb’s worth of Iran’s stockpiled low-enriched UF6 to weapon-grade, and if Iran’s centrifuges were to produce approximately 8,600 SWUs per year, or 716 SWUs per month, then it would probably take less than two months to achieve 840 SWUs.