Why Iran's Low-Enriched Uranium Stockpile May Be the Most Dangerous Number in the Nuclear Talks

By the time negotiators sit down to finalize any nuclear agreement with Iran, they will have spent months arguing about approximately 440 kilograms of uranium enriched to 60 percent purity. That number, roughly the weight of a grand piano, has dominated diplomatic discourse, intelligence assessments, and media coverage since the June 2025 strikes. It is, undeniably, the most acute proliferation risk on the table.

But veteran Israeli military analyst Ron Ben-Yishai, speaking on Galei Yisrael this week, redirected attention to a number that has received far less scrutiny: the roughly 11 tons of low-enriched uranium that Iran has accumulated since the collapse of the 2015 nuclear deal. His warning was pointed. While the world fixates on the 60-percent stockpile, he said, this vastly larger reservoir of lower-grade material could be enriched to weapons-grade levels within months, and almost nobody is talking about it.

He is correct. And the implications are serious.

How We Got Here

Under the original Joint Comprehensive Plan of Action, Iran was permitted to hold only 300 kilograms of uranium enriched to no more than 3.67 percent. The logic was straightforward: restricting both the quantity and the enrichment level of Iran's stockpile ensured that even if Tehran broke its commitments, it would need at least a year to produce enough weapons-grade material for a single device. That one-year "breakout time" was the deal's central security guarantee.

After President Trump withdrew the United States from the JCPOA in 2018, Iran rebuilt its stockpile from near-zero to some 11 tons of enriched uranium. That material spans a range of enrichment levels, from 2 percent to the 60-percent stockpile that commands all the headlines. By the time of the June 2025 strikes, Iran's breakout time had collapsed from over a year under the deal to one week or less.

The strikes damaged significant portions of Iran's enrichment infrastructure. An early Pentagon assessment found that U.S. and Israeli strikes damaged Iran's nuclear facilities but "did not destroy the core components of the country's nuclear program and likely only set it back by months." Critically, the IAEA itself stated that Fordow "is expected to have suffered very significant damage," but independent satellite analysis found the deep bunker only partially compromised, with tunnel entrances backfilled and core areas of uncertain status. Iran terminated all IAEA access on February 28, 2026, disabling surveillance cameras and removing seals from all declared facilities, creating the most significant verification blackout in the agency's history with Iran.

In short: we do not know with certainty what survived, what was moved before the strikes, or what Iran is doing now.

The 11-Ton Problem

The diplomatic conversation has converged almost entirely on the 60-percent stockpile as the central bargaining chip. Nuclear experts at the Nuclear Threat Initiative have said the U.S. "shouldn't take a deal that doesn't include removing the highly enriched uranium," and that further enrichment to 90 percent would take "only days to weeks" if Iran has an operational enrichment facility.

That is true. But it frames the problem too narrowly.

Low-enriched uranium, typically enriched to between 2 and 5 percent, is not inert. It represents enormous stored "enrichment work," the cumulative energy and centrifuge-hours already invested in separating U-235 from natural uranium. The physics of enrichment is not linear: approximately 60 to 70 percent of the work required to produce weapons-grade uranium is performed in the initial stages of enrichment, from natural levels to roughly 4 percent. A country that holds 11 tons of low-enriched material has already done the heavy lifting. Pushing it to 20 percent, then to 60 percent, then to 90 percent involves progressively less additional work, using fewer centrifuges and less time at each stage.

This is precisely Ben-Yishai's concern. Even if every kilogram of 60-percent uranium were removed, destroyed, or verifiably diluted, Iran would retain a vast reservoir of lower-grade material that could be re-enriched to weapons grade in a matter of months, given functional centrifuges and a decision to proceed.

Andrea Stricker of the Foundation for Defense of Democracies has warned that retaining any of the lower-enriched material "would give them the ability to go higher to weapons grade at a time of their choosing," describing it as a potential "poison pill" in any agreement.

The Deal Being Discussed

The framework that has emerged from current negotiations, described variously as the Islamabad Declaration and the leaked Yedioth Ahronoth terms, focuses heavily on the 60-percent stockpile as the primary deliverable. Under the current structure, Iran's approximately 440 kilograms of uranium enriched to 60 percent would remain in Tehran's possession throughout a 60-day follow-on negotiation period, with no named verification mechanism or inspection protocol.

What happens to the 11 tons of lower-grade material appears, based on available reporting, to be substantially unresolved. Iranian Foreign Minister Abbas Araghchi has offered to "downblend" the 60-percent stockpile to lower purities, which Iran has characterized as a major concession. But downblending highly enriched material into low-enriched material does not eliminate the proliferation risk. It redistributes it, adding to the very reservoir Ben-Yishai is worried about.

Iran has been explicit that retaining enrichment capability is a red line. The U.S. has proposed a framework that would prohibit enrichment on Iranian soil, advocating instead for a regional consortium model in which civilian enrichment would take place in neighboring countries. Iran has acknowledged the proposal but criticized it as unbalanced.

If Iran retains even a modest number of functioning centrifuges and a large low-enriched stockpile, the breakout calculation does not fundamentally change. The centrifuges need not be sophisticated. The timeline would stretch from days to months, but months is not the strategic reassurance that a deal should be providing.

The Verification Black Hole

Compounding everything is the verification crisis. Experts have noted that even if Iran fully cooperates with removal or dilution processes, verification will be challenging. As one analyst put it, Iran could claim material was destroyed in the strikes and "you're never going to know if that's true or not."

The IAEA's loss of continuity of knowledge, which began in 2022 when Iran disabled monitoring cameras, means that inspectors cannot provide an authoritative baseline for what existed before the strikes, let alone what exists now. Any deal that does not include immediate, unconditional, and comprehensive IAEA access is being negotiated in the dark.

What a Real Solution Looks Like

Ben-Yishai's warning points toward a conclusion that arms control experts have reached through a different route: any agreement that focuses only on the headline stockpile of 60-percent uranium while leaving the broader low-enriched reservoir unaddressed is structurally incomplete.

A genuinely durable arrangement would need to address the disposition of all enriched material above natural uranium levels, not just the highest-grade portion. It would require Iran to either ship the material out of the country entirely, as it did with roughly 98 percent of its stockpile under the original JCPOA, or subject it to destruction or permanent dilution under verified international supervision. It would need to constrain centrifuge numbers and capability to extend breakout timelines meaningfully, not merely symbolically. And it would require the restoration of full IAEA access, including the Additional Protocol's right to inspect suspected undeclared sites.

None of that is simple. All of it is necessary.

The 440 kilograms of 60-percent uranium is the nuclear file's most photogenic problem. But as Ben-Yishai understands, the 11 tons sitting behind it is the one that could quietly survive any deal and leave the underlying threat exactly where it began.