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While international concern about Iran's nuclear programme is generally focused on its uranium enrichment programme, Iran is also proceeding down a separate potential path to a nuclear weapon: the plutonium route. All nuclear-armed countries have pursued both paths. Speaking at an IISS discussion meeting on 11 September, Dr Ephraim Asculai, Senior Research Fellow at the Institute for National Security Studies in Tel Aviv, said if Iran continues on the plutonium path, it could probably produce a plutonium nuclear device by the end of 2016.  

The key facility for Iran's potential plutonium path is the heavy water-moderated research reactor at Arak, which, though delayed, is scheduled to start up sometime next year. Asculai noted that 46 countries have research reactors, which are used for training, research and production of radioisotopes for medical, industrial and other civil purposes. But only four of these countries – Canada, India, France and Algeria – use heavy water reactors for isotope production. Most others use light water-moderated reactors that are easier to operate. And most countries simply purchase medical isotopes from the international market. (During the Q&A session, IISS Non-Proliferation and Disarmament Programme director Mark Fitzpatrick, who was chairing the session, noted that although such isotopes had been in short supply, the CEO of one isotope manufacturer told him that he had offered Iran a guaranteed supply which would mean that Iran would not need itself to operate reactors for this purpose but the offer was not taken up.)

A key feature of Arak is that it runs on natural uranium fuel, comprised of mainly 99.3% U238 isotope and 0.7% U235 isotope. Plutonium is produced by the irradiation of the U238 isotope, so the higher the percentage of this isotope, the more plutonium is produced. The other key feature of Arak is its size: 40MWt. Fitzpatrick noted that this is larger than necessary for isotope production and is the approximate size of the natural-uranium-fuelled reactors that India and North Korea used to produce weapons-grade plutonium. With North Korea's help, Syria had also begun to construct a plutonium-production reactor of about that size (before it was destroyed in September 2007).

Due to concern over the proliferation potential, the United Nations Security Council in 2006 mandated that Iran suspend construction of the Arak reactor and (any) reprocessing activity. For weapons purposes, the plutonium must be separated from the rest of the spent fuel through a relatively straightforward chemical separation operation called reprocessing. Iran carried out reprocessing experiments between 1988 and 1992, but does not today have a reprocessing capability.

If Arak were used to maximise plutonium production, the International Atomic Energy Agency (IAEA) would be tipped off by the operational schedule of the reactor. In general, the lower the burn-up time, the higher the quality of the plutonium. In particular, the percentage of Plutonium240 isotopes must be kept below 6%. Irradiating natural uranium for three months produces plutonium with a PU240 content of 2%. But there is trade-off between quality and quantity. Running Arak for only three months would not produce enough plutonium for a weapon. To produce 8kg of plutonium, which is the amount needed when a plutonium weapon is made for the first time, the fuel should be irradiated for eight months.

Before reprocessing can begin, the spent fuel must be cooled for 6–12 months. Reprocessing time depends on the size of the facility; Asculai judged that if Iran were to take this route, it would probably build a moderately sized plant that would reprocess plutonium at about the same rate that the spent fuel was produced. Each batch might take six months.

Reprocessing plants are large buildings with thick walls, construction of which could be detectable from overhead satellites unless they are built underground. While in operation, reprocessing plants emit detectable gases, but the IAEA needs an Additional Protocol to be in place for it to have the access and tools to detect such emissions.

Asculai did not estimate the time to build a reprocessing plant (a US laboratory estimated a simple plant could be built in 4-6 months), but he said the construction time does not factor into his timeline calculation because it could be undertaken in tandem with other steps. 'By the time they need it, they would have it,' Asculai assumed. Adding up the other steps produces his estimate of the end of 2016 for a plutonium-based device. He noted that the difference between a device and a bomb is that the latter requires a means of delivery, a subject not touched upon in his presentation.

In May, Iran told the IAEA it planned to begin pre-commissioning Arak in the fourth quarter of 2013 using dummy fuel assemblies and regular water, and that commissioning using real fuel assemblies and heavy water would begin in the first quarter of 2014, with start-up planned for the third quarter of 2014. In August, however, Iran informed the IAEA that this schedule was not achievable. One reason is probably that Iran has had problems producing the fuel assemblies. Asculai said the fuel assemblies were based on a Russian design that was not ideally suited for Arak.

The plan to use dummy rods and regular water to test Arak is very strange, Asculai said, noting that he had no information that this has been done before elsewhere. After such testing, the facility would have to be thoroughly dried before it could be operated normally, because heavy water has to be 99.75% pure. The contamination from even a small amount of regular water would make it unusable. Asculai, therefore, could not eliminate the suspicion that the pre-commissioning plan is a ruse, and that real rods and heavy water would be used from the start. This would be in violation of Iran's pledge to provide six months' notice to the IAEA of introducing fuel, but it could be a way for Iran to render the reactor invulnerable.

There is an international norm against bombing operating reactors, Asculai explained, because of the radiation that would be released into the environment as a result. Once Arak starts up, it is protected by this norm.  

As an aside, Asculai compared Arak with Syria's miniature Neutron Source Reactor near Damascus, which has a rating of 30kWt (more than 1,000 times smaller than Arak).  If it were for any reason bombed, the resulting radioactive danger would not spread beyond the immediate building.

Rapporteur: Mark Fitzpatrick

A physicist, Dr Ephraim Asculai worked at the Israel Atomic Energy Commission (IAEC) for over 40 years. In 1986, he worked at the IAEA in Vienna on radiation protection. In 1992, Dr Asculai returned to Israel and became heavily involved in the deliberations leading to the conclusion of the Comprehensive Test-Ban Treaty (CTBT). During a sabbatical at the Institute for Science and International Security in Washington, DC he authored Verification Revisited: The Nuclear Case. In 2002, he joined the Jaffee Center for Strategic Studies (now incorporated into the INSS). He has since published several papers on WMD non-proliferation in general, and Middle East issues in particular.

This meeting was chaired by Mark Fitzpatrick, Director, Non-Proliferation and Disarmament Programme at the IISS. It took place in the Lee Kuan Yew Conference Room at Arundel House,13–15 Arundel Street, Temple Place, London WC2R 3DX.

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Event details

Discussion Meeting
Dr Ephraim Asculai
Senior Research Fellow, Institute for National Security Studies (INSS)
Arundel House, London
Wednesday 11 September 2013