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How much of a proliferation threat is Iran’s uranium enrichment?

A uranium metal ‘button’. Iran’s production of 20 per cent-enriched uranium metal has caused concern, but appears to be for conversion to uranium silicide reactor fuel.
A uranium metal ‘button’. Iran’s production of 20 per cent-enriched uranium metal has caused concern, but appears to be for conversion to uranium silicide reactor fuel.

Iran’s atomic energy agency announced last week that it had produced 55 kilograms of 20 per cent-enriched uranium in barely four months. This marked rapid progress towards the ‘at least 120 kilograms of enriched uranium with a 20-percent purity level (sic) each year’ ordered by the Iranian Parliament in December 2020 as part of its Strategic Action Plan to Lift Sanctions and Protect Iranian Nation’s Interests.

Iran’s production of 20 per cent-enriched uranium metal is a clear and deliberate step away from compliance with the terms of the troubled 2015 Iran nuclear deal. The Joint Comprehensive Plan of Action (JCPOA), as the nuclear deal is formally known, is intended to prevent Iran from developing a nuclear weapons programme. However, while any breach of the deal’s terms is a cause for concern, Iran’s production of 20 per cent-enriched uranium does not necessarily bring it closer to producing a nuclear weapon. In fact it diverts resources away from any weapons programme.

The Iran nuclear deal

Last week’s announcement came as the remaining signatories—China, France, Germany, Russia, the United Kingdom and the European Union—are in talks aimed at saving the deal and, in particular, facilitating the United States’ re-entry to the deal. The Trump Administration withdrew the USA from the JCPOA in May 2018, reimposing sanctions on Iran that had been lifted as part of the deal; a move whose legality has been called into question. Joe Biden has repeatedly promised the USA would re-enter the JCPOA, ‘if Tehran returns to compliance’.

Since the US withdrawal, Iran and the remaining signatories have attempted to keep the deal alive. However, although insisting on their full reversibility should sanctions be lifted, Iran has breached a number of the terms, first in small ways, later becoming greater deviations.

Highly enriched uranium production

December’s Strategic Action Plan to Lift Sanctions was the latest step in this campaign. It commanded the Atomic Energy Organization of Iran (AEOI) to carry out several activities that breach the JCPOA’s terms. The instructions to produce 20 per cent-enriched uranium, and to ‘inaugurate the metallic uranium factory in Isfahan’ have attracted the most attention.

Under the terms of the JCPOA, Iran agreed not to isotopically enrich uranium beyond 3.67 per cent. Thus, the decision to produce and store 20 per cent-enriched uranium has been cited as a move towards Iran developing a stockpile of weapons-grade uranium. Sources have pointed out that enriching natural uranium up to 20 per cent is much more difficult and time-consuming than enriching it from 20 per cent to 90 per cent—the level of enrichment needed for a nuclear weapon.

However, with the technology Iran has, it can only enrich uranium in the form of uranium hexafluoride (UF6) gas. While 20 per cent-enriched UF6 gas can relatively easily be enriched to weapons grade, reducing it to metallic form at this stage represents a step away from that goal—even if it is fairly straightforward to reverse. This suggests that further enrichment of this uranium is not Iran’s technical goal.

So what is that goal? Twenty per cent-enriched uranium metal is not useful for weapons, or for any of the other multitude of military and civilian uses of uranium, such as armour-piercing bullets or shielding. However, in February this year the International Atomic Energy Agency (IAEA) confirmed that Iran had notified it in December 2020 of plans to start R&D at Isfahan on producing advanced uranium silicide (U3Si2) research reactor fuel using 20 per cent-enriched uranium metal. Indeed, Iran claimed in January to have notified the IAEA of plans to produce this advanced fuel in 2018.

Iran wants this advanced fuel for the Tehran Research Reactor, which is used for producing medical isotopes and basic scientific research, not weapons. Iran has been limited to a dated process of producing 20 per cent-enriched U3O8 powder for reactor fuel. Under the terms of the JCPOA, advanced reactor fuel is to be made available to Iran at ‘international market prices’.

Once enriched uranium has been compounded into uranium silicide fuel, it is impossible to separate it out again without significant investment of time and money. And if it has been irradiated in a reactor, it is useless for weapon production without a reprocessing programme, which Iran does not have. Thus, 120 kg of uranium converted to silicide fuel is 120 kg of uranium that is, practically speaking, unavailable to a hypothetical weapons programme. The same can be said of the centrifuge capacity dedicated to producing the 20 per cent-enriched metal for conversion into fuel.

Uranium metal production: a risk in itself?

Some saw the decision to inaugurate the metallic uranium facility at Isfahan as a disturbing development. In fact, the uranium conversion facility at Isfahan been publicly described in 2005. And uranium metal is nothing new to Iran. The IAEA carried out measurements in 2003 and 2011 of Iranian uranium metal in Iran that was known to be under IAEA seals since 2003. This was produced in Iran even prior to 2003 and was known to the US government. Iranian conversion experiments have been known to the IAEA since 1995. In 2011 the IAEA also asked Iran to explain experiments involving uranium deuteride. Uranium deuteride is made by reacting deuterium with uranium metal. Furthermore, in the fuel-production process, the uranium is in metal form only as an intermediate product in the manufacturing of fuel for the TRR.

Nevertheless, it has been argued that any production of uranium metal would give Iran experience that could be applied to nuclear weapons production. This overlooks not only Iran’s past work with uranium metal, but also the fact that Iran already has plenty of experience in producing it.

Iran informed the IAEA that it had converted about 0.4 tons of uranium tetrafluoride (UF4) into uranium metal in 2000. On the Isfahan site there is also a zirconium metal plant scaled to produce tons of zirconium and hafnium metals. Zirconium can be reduced to metal using a process similar to the one for reducing uranium metal from UF4 declared to the IAEA. All this suggests that Iran already has the know-how to produce uranium metal on an industrial scale, and has nothing new to learn about uranium metallurgical reduction by making small amounts of research reactor fuel.

There is one interesting caveat. If Iran stopped its weapons programme in 2003, as most believe, metal production knowledge may have been lost. This is consistent with Israel finding Iran’s weapons documents in a dusty archive and indications that old equipment had been put into storage. If Iran put its knowledge into a static archive it may be the clearest sign yet that Iran stopped its weapons programme years ago.

The instruction to produce 20 per cent-enriched uranium and inaugurate the Isfahan plant is certainly another move away from technical compliance with the JCPOA—and will most likely need to be reversed if the USA is to re-enter the deal. However, there is good reason to believe that it is about producing research reactor fuel for civilian purposes, not a step towards producing a nuclear weapon.


Robert E. Kelley is a Distinguished Associate Fellow at SIPRI.