Why Iran’s 60 per cent enriched uranium is non-negotiable

The three main sticking points in a US-Iran peace deal are Iran’s untraceable 440.9 kg of 60 per cent highly enriched uranium (HEU), the period of suspension of nuclear enrichment and the control of the Strait of Hormuz.

The HEU is the biggest stumbling block. Iran has repeatedly stressed that the enriched uranium is non-negotiable.

Where is Iran’s Highly Enriched Uranium

According to the IAEA, Iran’s enriched uranium stock a day before Israel’s attack on June 13, 2025, was 9,874.9 kg, of which 9,040.5 kg was uranium hexafluoride (UF6). The UF6 stockpile included 440.9 kg of 60 per cent HEU.

Donald Trump believes that the HEU is buried in the rubble of the damaged Natanz Uranium Enrichment Complex and the Fordow Fuel Enrichment Plant (FFEP). However, two days before the June 2025 US bombing, IRGC’s former commander Mohsen Rezaei said that the enriched uranium had already been moved to secure locations.

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Even a Pentagon intelligence assessment and a Defence Intelligence Agency report indicated the same. In fact, two Israeli officials told The New York Times that intelligence suggested Iran had moved equipment and a part of the stockpile from Fordow.

According to the IAEA, around 50 per cent of the HEU stored in a tunnel complex at the Isfahan Nuclear Technology Centre (INTC) remains there. In the June bombing, the facility was targeted by 30 UBM-109 Tomahawks, not GBU-57 bunker busters. The remaining 240 kg of the stockpile was split between the Natanz and Fordow facilities before the bombing.

Now, the French newspaper Le Monde and a team of visual investigators, including the Bulletin of the Atomic Scientists, have visually and technically analysed a previously unreported satellite image dated June 9, 2025, of a large truck loaded with containers at INTC.

The analysis suggested that the HEU was around 540 kg, not 440.9 kg, and the stockpile was moved to INTC, not distributed, much before the bombing.

In the image, taken from one of the two Airbus Pléiades Neo satellites, a flatbed or lowbed truck loaded with 18 blue containers, either cylindrical or cubical, is seen parked facing the tunnel entrance. A smaller truck, parked behind the flatbed truck—which isn’t fully loaded—apparently has a yellow crane that probably unloaded the containers.

Uranium Enrichment Process and Levels

Uranium oxide consists mostly of 0.7 per cent uranium-235 (U-235)—essential for nukes—and 99.3 per cent uranium-238 (U-238) isotopes. U-235 must be enriched to increase its concentration into a form usable in nukes.

Uranium can be enriched in three ways: Gas centrifuge (used by Iran), laser enrichment and gaseous diffusion.

In the gas centrifuge method, a reaction between uranium and hydrofluoric acid creates UF6 gas. A centrifuge spins the gas at high speed. The heavier U-238 atoms move towards its walls while the U-235 atoms stay at the centre. Every time the gas is spun, the concentration of U-235 increases. When the process is repeated thousands of times inside centrifuges chained in long cascades, the gas created is highly enriched in U-235.

Low-enriched uranium (LEU) contains less than 20 per cent U-235, high-assay LEU has 5-19.75 per cent and HEU has more than 20 per cent U-235, which can be used to build a nuke.

Iran Doesn’t Need 90 Per Cent HEU to Build a Nuke

A purity of 60 per cent isn’t required for civil nuclear power generation—that was the reason for the West’s alarm.

The bigger concern is that Iran could enrich the 60 per cent HEU to 90 per cent in a week. Uranium enriched up to 93 per cent is the ideal purity to build a nuke. In March 2025, the IAEA reported that Iran could produce 90 per cent HEU within a week.

Per the IAEA, 25 kg of weapon-grade uranium (WGU) is needed per nuke.

Analysis of the IAEA’s May 2025 ‘Iran Verification and Monitoring Report’ by the Institute for Science and International Security on June 9 showed that Iran could enrich 60 per cent of its HEU to 233 kg of WGU at FFEP, making 9 nukes.

Countless news reports, the IAEA, analyses by scientists and experts and concerns expressed by the West for years have highlighted how Iran can quickly enrich 60 per cent HEU to 90 per cent.

Iran doesn’t need 90 per cent HEU to make a bomb—60 per cent is enough.

This is the reason Iran doesn’t want to surrender or transfer the stockpile and the US is desperate for it.

According to the IAEA’s Safeguards Glossary 2022, “significant quantity” (SQ) is the “approximate amount of nuclear material for which the possibility of manufacturing a nuclear explosive device cannot be excluded”.

“Direct use material”—uranium enriched to 20 per cent or more—is defined as “nuclear material that can be used for the manufacture of nuclear explosive devices without transmutation or further enrichment”.

The math is simple.

The IAEA’s SQ is 25 kg of 90 per cent HEU for an implosion weapon. If it’s 60 per cent HEU, the SQ should be 41.7 kg of total uranium, explains Edwin Lyman, the director of Nuclear Power Safety with the Union of Concerned Scientists’ Climate and Energy programme.

The higher the level of enrichment, the smaller the amount of HEU needed to make a smaller, lighter and easier-to-deliver nuke.

The Nuclear Threat Initiative (NTI), a Washington, D.C.-based nonprofit, nonpartisan organisation, explains by visualising both the mass and diameter of a bare spherical critical mass of enriched uranium (in a weapon design using a reflector) for various levels of enrichment.

Critical mass is the minimum amount of fissile material (like U-235 or Plutonium-239) required to maintain a self-sustaining nuclear chain reaction.

Uranium has almost the same density as gold and occupies much less volume for its weight than another metal like iron would.

The mass and size required to build a nuclear weapon vary according to the level of enrichment.

Around 3,600 kg of 5 per cent LEU will be a bare spherical critical mass of 70 cm diameter; 143 kg of 19.75 per cent LEU will be a 24 cm ball; 36 kg of 45 per cent HEU will be a 19 cm volleyball; and 12 kg of 93 per cent HEU will be a 10.5 cm apple.

Last June, the US struck the two enrichment plants at Natanz (one was destroyed), the one deep inside a mountain at Fordow and the massive nuclear fuel cycle complex at Isfahan. Per the IAEA, the underground plants at Natanz and Fordow were badly damaged.

Iran’s nuclear programme isn’t “obliterated”, as claimed by Trump. In fact, Iran can restart enrichment within months, the IAEA said last June.

However, WGU isn’t enough to build a nuke.

Weaponisation, a time-consuming process, is the main part. Iran would need to convert WGU into metallic components, integrate them and mount the weapon on a missile for an underground test—all thus under extreme secrecy. It could take months or a year.

At best, Iran can make a crude nuclear bomb using the 60 per cent HEU under an accelerated programme without producing warheads for ballistic missiles.

Though such a nuclear device would have a larger and heavier core and require more high explosives to compress the core and other structures to increase fission reactions, Iran would become the 10th nuclear power.

(The writer is a freelance journalist with more than two decades of experience and comments primarily on foreign affairs. He tweets as @FightTheBigots. Views expressed in the above piece are personal and solely those of the writer. They do not necessarily reflect Firstpost’s views.)