Iran’s nuclear stockpile — a key part of negotiations to end the war and a focus of Trump’s — explained

By Davis Winkie, CNN

(CNN) — What happens to Iran’s enriched uranium stockpile, including the 970 pounds that it has highly concentrated to near-weapons grade, is one of the primary sticking points as the US and Iran have trudged through weeks of negotiations to potentially end the Iran war.

President Donald Trump has insisted that Iran must hand over what he calls its “nuclear dust.” Iranian officials have repeatedly said that the country has a right to a non-weapons nuclear program.

But what is in Iran’s stockpile, and what does it mean for Iran’s ability to build a nuclear weapon?

With the right equipment, the highly enriched uranium that Iran has could reach weapons-grade purity within weeks or even days, according to nuclear experts. And it’s enough for 10 nuclear weapons, international inspectors say.

Iran and the US are reportedly close to an agreement to formalize a ceasefire and open the Strait of Hormuz. But the question of what happens to the uranium would remain unsettled and a key part of subsequent negotiations, according to CNN’s reporting.

Those talks would likely focus on the nearly 1000 pounds of uranium purified to 60%.

“The US shouldn’t take a deal that doesn’t include removing the [highly enriched uranium],” said Eric Brewer, a nuclear materials expert for the Nuclear Threat Initiative (NTI) nonprofit who previously oversaw counterproliferation at the National Security Council during Trump’s first administration and led Iran intelligence analysis for the Defense Intelligence Agency.

Building a nuclear weapon requires a significant amount of radioactive heavy elements, or what experts call fissile material. One such radioactive isotope, uranium-235, occurs in nature, but it makes up less than one percent of raw uranium ore that’s mined.

Enrichment concentrates the uranium-235 from raw ore and prepares it for conversion into weapons-usable fissile material. Iran enriched its uranium by converting it into a gas — uranium hexafluoride — and spinning it in a series of centrifuge machines in underground plants primarily at the country’s Natanz, Fordow and Isfahan nuclear complexes.

Iran’s near-half ton of 60% enriched uranium (and its estimated 405.9 pounds of 20% U-235) is believed to remain in gas form, as it was at the time of the International Atomic Energy Agency’s last verification in June 2025. Iran shut out international nuclear inspectors the following month in the wake of joint US-Israel airstrikes on its facilities.

Further enrichment to 90% purity, considered the threshold for weapons-grade uranium, would “only take days to weeks” if Iran has an operational enrichment facility, Brewer said.

The June 2025 strikes on Iran’s nuclear facilities, what the Pentagon termed Operation Midnight Hammer, was assessed by US intelligence to have buried much of Iran’s highly enriched uranium stockpile at Isfahan, but didn’t destroy it, despite administration statements that Iran’s nuclear program was “obliterated.”

Earlier this month Trump threatened “to go in” with force and retrieve the uranium should negotiations fail. CNN reported in March that military planners had reviewed options for such an effort at the Isfahan complex, assessing that it could require hundreds if not thousands of troops and risk a high number of casualties. In addition to bringing in specialized forces and equipment to handle the material itself, creating a security perimeter to allow those troops to work would mean a large footprint.

Nuclear experts are also skeptical that a US military operation could even locate and verify all the uranium, much less safely and completely remove it. Doing such a removal under hostile conditions would be unprecedented.

“We don’t know where Iran could have dispersed some of this [uranium] material ahead of the strikes,” said Brewer.

It’s unclear if Iran currently has the capability of turning its 60% uranium gas into metal as needed to produce a nuclear warhead, but before the 2025 strikes it did have the right kinds of facilities, Brewer said.

It’s also not clear how quickly the Iranian regime could resume and complete weaponization work, which includes fashioning the bomb’s core and developing the explosives required to detonate it. When China completed its uranium enrichment in 1964, it only required “three to five weeks to convert [the gas to metal] … and assemble an atomic bomb,” Harvard physicist and China nuclear expert Hui Zhang wrote for the Bulletin of the Atomic Scientists last year.

Scott Roecker, who served as head of the National Nuclear Security Administration’s Office of Nuclear Material Removal and now oversees the NTI’s nuclear materials security program, told CNN that removing even Iran’s low-enriched uranium including more than 13,000 pounds of 5% enriched material may be necessary to prevent future nuclear weapons work.

That’s because Iran has developed the skills and experience to produce advanced centrifuges that can quickly and efficiently enrich the uranium further.

While Iran has insisted that it has not been pursuing a nuclear weapon, Roecker said its highly enriched stockpile is telling.

“There’s no plausible civilian purpose for that material,” he said, adding that the “main focus” of US negotiations should be getting rid of it.

There are two primary options for removing or otherwise neutralizing Iran’s stockpile, according to Roecker and Brewer.

A first common step between them likely would be converting from uranium gas to an “inherently more stable” powder form, Roecker said, making transport significantly safer.

In the case of a peaceful removal led by the US, the Department of Energy’s National Nuclear Security Administration has a mobile uranium facility that can deploy from its home at Oak Ridge National Laboratory, in Tennessee, to anywhere in the world and “stabilize, package, and remove nuclear materials,” according to an agency fact sheet. That process would likely take weeks.

Russia is also capable of accepting enriched uranium, as it did under the 2015 Iran nuclear deal, Roecker noted.

A second option, known as “downblending,” could occur on Iranian soil. Downblending would involve diluting highly enriched uranium with low-purity uranium to reduce its U-235 concentration.

The key to any successful removal, regardless of the method, is the ability for the US and the international community to monitor and verify the process.

Brewer said that verification will be challenging even if Iran fully cooperates.

“You run the risk of … Iran saying, ‘We can’t account for that 100 kilograms [of uranium] because it actually blew up in the strikes,’ and you’re never going to know if that’s true or not, right?” Brewer said.

Davis Winkie’s work at CNN is supported by a partnership between Outrider Foundation and Journalism Funding Partners (JFP). CNN retains full editorial control of the reporting.

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CNN’s Natasha Bertrand, Zachary Cohen, Haley Britzky, Kevin Liptak and Alayna Treene contributed to this report.