IRAN’S NUKESEntering Dangerous, Uncharted Waters: Iran’s 60% Highly Enriched Uranium

By David Albright and Sarah Burkhard

As soon as mid-to-late April, Iran is expected to reach a new dangerous, destabilizing threshold, having enough highly enriched uranium (HEU) to fashion a nuclear explosive, about 40-42 kilograms (kg) of 60 percent enriched uranium (uranium mass).¹ With this quantity, an enrichment level of 60 percent suffices to create a relatively compact nuclear explosive; further enrichment to 80 or 90 percent is not needed. According to the International Atomic Energy Agency (IAEA), 41.7 kg of 60 percent enriched uranium (uranium mass) is a significant quantity, which the IAEA defines as the “approximate amount of nuclear material for which the possibility of manufacturing a nuclear explosive cannot be excluded.”²

A common fallacy is Iran would require 90 percent HEU, more commonly called weapon-grade uranium, to build nuclear explosives. Although Iran’s nuclear weapons designs have focused on 90 percent HEU and likely prefer that enrichment, modifying them for 60 percent HEU would be straightforward and well within Iran’s capabilities.³ Historically, the term highly enriched uranium was developed in the nuclear weapon states to distinguish between enriched uranium able to fuel a practical nuclear weapon versus enriched uranium, labeled low enriched uranium, unable to do so. Their cutoff is at 20 percent enriched uranium. At the least, a device made from 60 percent HEU would be suitable for underground nuclear testing or delivery by a crude delivery system such as an aircraft, shipping container, or truck, sufficient to establish Iran as a nuclear power.

Moreover, Iran could further enrich its stock of 60 percent enriched uranium quickly to weapon-grade uranium, where this threshold quantity would be enough to produce about 25 kilograms, enough for a nuclear weapon and close to the IAEA-defined significant quantity. The delay caused by further enrichment would be measured in days if Iran used a significant part of its enrichment capacity and weeks if Iran operates just two production-scale cascades of advanced centrifuges.

Avoiding this uncharted threshold is a priority. To that end, Iran’s recent move to chemically convert some of its HEU into an oxide form would suggest positive news, but it is not a remedy and does not prevent other dangerous situations. This new development does not reduce breakout timelines, may disguise preparation to make HEU metal, and creates other dangerous precedents. Moreover, Iran’s actions stand in sharp conflict with today’s international norms to avoid civilian HEU.