Iran’s nuclear stockpile: The issue at the heart of US-Iran negotiations

The material weighs less than a small family car. Yet the fate of roughly 440kg of highly enriched uranium may determine whether the United States and Iran can turn a fragile ceasefire into a broader diplomatic agreement.

Weeks of negotiations have brought Washington and Tehran closer to a possible framework that could extend the ceasefire, reopen the Strait of Hormuz and launch a new phase of talks. But one issue continues to overshadow almost every other discussion: what happens to Iran’s stockpile of highly enriched uranium. According to international inspectors, the material could potentially be sufficient for around 10 nuclear weapons if further enriched, making it one of the most sensitive issues on the negotiating table.

US President Donald Trump has repeatedly insisted that Iran must surrender what he has called its “nuclear dust”, while Iranian officials maintain that the country has the right to pursue a civilian nuclear programme. With both sides still divided, the uranium stockpile has become one of the most consequential sticking points in the negotiations. CNN has reported that even if a broader ceasefire framework is agreed, the future of Iran’s enriched uranium is likely to remain the focus of subsequent talks.

Iran possesses a large stockpile of enriched uranium, including approximately 440kg enriched to 60 per cent purity — a level far beyond what is generally required for civilian nuclear energy programmes.

International Atomic Energy Agency (IAEA) estimates indicate that, if further enriched to weapons-grade levels, this stockpile could theoretically be enough for around 10 nuclear weapons.

Iran also holds about 184kg of uranium enriched to 20 per cent purity, as well as a much larger stockpile of lower-enriched uranium. According to CNN, some experts argue that even these lower-grade reserves may need to be addressed because Iran has already demonstrated the ability to enrich uranium rapidly using advanced centrifuges.

The concern is not merely the quantity of uranium Iran possesses, but how close it already is to weapons-grade material.

Natural uranium contains less than one per cent uranium-235, the fissile isotope used in nuclear reactors and weapons. Through enrichment, that concentration is increased. Weapons-grade uranium is generally considered to be about 90 per cent pure.

According to nuclear experts cited by CNN, once uranium has reached 60 per cent purity, the remaining technical journey to weapons-grade levels becomes significantly shorter.

Eric Brewer, a former US intelligence and counterproliferation official now with the Nuclear Threat Initiative, told CNN that further enrichment could take only “days to weeks” if Iran retains an operational enrichment facility.

That is why many non-proliferation experts view the 60 per cent stockpile as the most urgent concern in the negotiations.

Iran enriches uranium by converting it into uranium hexafluoride gas and feeding it through cascades of centrifuges at facilities including Natanz, Fordow and Isfahan.

The centrifuges gradually increase the concentration of uranium-235. According to CNN, most of Iran’s highly enriched uranium is believed to remain in gas form, allowing it to be further processed if the necessary facilities are available.

Yes.

The United States and Israel carried out major strikes against Iran’s nuclear facilities in June 2025 during what the Pentagon called Operation Midnight Hammer. The attacks targeted key sites including Natanz, Fordow and Isfahan.

However, according to CNN, US intelligence assessments concluded that much of the highly enriched uranium stockpile was likely buried rather than destroyed. While facilities suffered significant damage, the fate of all the material remains uncertain.

That uncertainty has complicated diplomatic efforts. Iran restricted international inspections after the strikes, leaving questions about the precise location and condition of some of the uranium.

The Trump administration has laid down three major conditions for any agreement.

Treasury Secretary Scott Bessent has said Iran must surrender its highly enriched uranium, abandon any pursuit of a nuclear weapon and restore free navigation through the Strait of Hormuz.

Trump has repeatedly argued that Iran should either transfer the material to another country for disposal or destroy it under international supervision. He has also warned that military options could return if diplomacy fails.

According to CNN, some US experts believe any agreement that allows Iran to retain highly enriched uranium would leave open the possibility of future weapons development.

Experts have identified two principal options.

The first is removal.

According to CNN, Russia previously accepted enriched uranium under the 2015 nuclear agreement and could potentially do so again. The United States also possesses specialised capabilities to stabilise, package and transport nuclear material.

The second option is known as “downblending”.

This involves mixing highly enriched uranium with lower-grade uranium to reduce its concentration to levels unsuitable for weapons use. The process could potentially take place inside Iran under international monitoring.

Both options would require extensive inspection and verification mechanisms.

Even if Iran cooperates fully, experts say verification may be difficult.

One concern is that some material may have been moved before the 2025 strikes or may no longer be fully accounted for. CNN quoted Brewer as warning that inspectors may never be able to establish with complete certainty what happened to every kilogram of enriched uranium.

That challenge explains why the uranium question remains central to the negotiations.

A ceasefire may be within reach. Shipping through the Strait of Hormuz may resume. Sanctions relief could eventually enter the discussion.

But the issue that continues to loom over the negotiations is the future of Iran’s enriched uranium stockpile — and whether both sides can agree on how to secure, remove or neutralise it.

- with inputs from CNN, AFP, IANS