Iran Can Keep Its 440 kg of 60% Uranium, but Only Diluted to 3.6%

On May 28, 2026, United States and Iranian negotiators reached a tentative agreement to extend the ceasefire in the three-month war by sixty days and to open a new round of talks on Iran’s nuclear program. According to a US official familiar with the discussions, the first item on that agenda is the disposition of Iran’s highly enriched uranium. The International Atomic Energy Agency places that inventory at 440.9 kilograms enriched to 60 percent, which it describes as a short technical step from the 90 percent associated with weapons.

Reporting on the draft memorandum indicates that the parties will discuss how to dispose of the material, a phrase that analysts have read as including the option of down-blending the uranium to a lower enrichment level and retaining it inside Iran. As of this writing, President Trump has not endorsed the framework, and Vice President Vance has identified the stockpile and the future of enrichment as the issues still in flux.

The negotiation reduces to a single technical question. What should be done with 440.9 kilograms of 60 percent uranium so that Iran retains what it describes as a peaceful program while the international community removes the weapons risk that this particular material represents.

Two stated positions have framed the dispute for the past year. Washington has insisted on zero enrichment and the removal of the existing stockpile. Tehran has maintained that it holds a right to enrich under the Non-Proliferation Treaty and has rejected limits on that right. Between these positions sits a third option that is technically established, historically tested, and consistent with both sides’ declared goals: dilution of the stockpile to reactor grade under international verification.

What 60 percent enrichment means

Natural uranium contains about 0.7 percent of the fissile isotope uranium-235. Enrichment is the industrial process of raising that fraction. Fuel for commercial power reactors typically requires between 3 and 5 percent, and the 2015 nuclear agreement capped Iran at 3.67 percent. Material enriched to 20 percent or above is classified as highly enriched uranium. The concern attached to the 60 percent stockpile is that most of the separative work required to reach weapons grade has already been performed.

The effort needed to move from 60 to 90 percent is small relative to the effort already invested in reaching 60 percent from natural uranium, which is why the Agency characterizes the present material as close to weapons usable. By common reference, roughly 42 kilograms of 90 percent uranium is sufficient for a single device, so the existing quantity, if further enriched, would correspond to several weapons’ worth of material. I have addressed the strategic implications of this inventory in a previous analysis.

Down-blending is an established procedure

Dilution, technically termed down-blending, is the reverse of enrichment and is considerably simpler to perform. The high-assay material, which Iran stores in the form of uranium hexafluoride gas, is blended with natural or depleted uranium that is poorer in uranium-235, lowering the average concentration of the mixture to the desired level. The process requires no enrichment cascade and consumes little of the separative work that enrichment demands.

Of particular relevance to the current dispute, the material is not exported. It is converted from a stock of near weapons-relevant uranium into reactor-grade fuel without direct military application, while remaining physically in Iranian possession.

The historical precedent is substantial

Down-blending of weapons-relevant uranium has been carried out before, at a scale far larger than the Iranian stockpile. Between 1993 and 2013, the United States and Russia conducted the program known as Megatons to Megawatts, under which Russia down-blended 500 metric tons of weapons-grade uranium, derived from approximately 20,000 dismantled warheads, into low-enriched uranium sold to the United States as commercial reactor fuel. That fuel supplied close to a tenth of US electricity for years. The program shows that uranium enriched well beyond 60 percent can be reduced to civilian fuel reliably and under verification.

Iran has performed the procedure on its own material. Under the 2015 agreement, it reduced its enriched uranium stockpile from roughly 10,000 kilograms to 300, capped enrichment at 3.67 percent, dismantled more than 13,000 centrifuges, and shipped the large majority of its enriched uranium to Russia. The technical capacity and the diplomatic precedent already exist within Iran’s own recent record.

Verification is the operative condition

The value of dilution depends entirely on independent observation. For the procedure to reduce proliferation risk rather than merely appear to, it must be conducted under the inspection of the IAEA and within a framework that the United States can confirm.

Megatons to Megawatts operated under a transparency regime administered by the US Department of Energy that allowed each government to verify the disposition of the material at every stage. Dilution conducted without monitoring would leave the international community unable to distinguish material that had been genuinely reduced from material that had been relocated or concealed.

This condition is also the principal obstacle at present. Iran suspended the Agency’s access to its declared facilities in early 2026, removing monitoring cameras and seals. A verified dilution cannot proceed in the absence of inspectors. The restoration of IAEA access is therefore a precondition for the very option that the current talks are reported to be considering.

Dilution compared with destruction

The alternative to a negotiated reduction is the continued attempt to eliminate the material and the capacity by force. Assessments of the military strikes conducted in 2025 and 2026 place the resulting delay to Iran’s program at one to two years, and the most detailed recent analysis extends that estimate to roughly two and a half years at most, absent external assistance. Strikes do not remove the technical knowledge held by Iranian scientists, and the enriched stockpile itself is believed to have survived in deep storage.

Re-enrichment of reactor-grade fuel back toward 60 percent would require functioning enrichment infrastructure and a considerably longer period than the final step from 60 to 90 percent, and under an inspection regime it would be detectable from its earliest stage. A military setback is finite and recoverable, whereas verified dilution combined with continued monitoring constrains the proliferation risk for as long as the monitoring is maintained.

The material retains civilian value

Down-blending does not consume or waste the stockpile. It converts near weapons-relevant uranium into commercial reactor fuel that keeps real economic value. The Megatons to Megawatts program was carried out as a commercial transaction worth billions of dollars, and the fuel it produced supplied close to a tenth of United States electricity for roughly fifteen years. The Iranian inventory is far smaller, yet the principle is identical.

The 440.9 kilograms, once diluted, would yield on the order of eight to nine metric tons of reactor-grade fuel, corresponding to roughly 2.5 billion kilowatt-hours of electricity. The practical use of that fuel would depend on fabrication and on Iran’s reactor capacity, which remains limited, but the material would stay an asset rather than be destroyed or surrendered.

The incentive extends beyond the fuel. Under the framework now being negotiated, the disposition of the enriched uranium is tied to sanctions relief, the release of frozen Iranian assets, and the lifting of restrictions in the Strait of Hormuz. Dilution is the technical measure that would allow Iran to retain its material while unlocking the economic terms of an agreement and supporting the country’s recovery from the war. The option can be placed on the record regardless of whether the current government is prepared to accept it.

Conclusion

The technical record establishes that Iran’s 440.9 kilograms of 60 percent uranium can be rendered free of direct military relevance without being removed from Iranian territory. The procedure is well understood, has been carried out at far greater scale by other states, and has already been applied to Iran’s own stockpile within the past decade. The requirement that separates a meaningful reduction from a symbolic one is verification, which in turn requires the return of the inspectors that Iran removed earlier this year.

The disposition of the stockpile is, by the negotiators’ own account, the first matter to be addressed in the sixty-day window now opening. Whether a measure this technically straightforward, and this consistent with Iran’s stated commitment to a peaceful program, is adopted will indicate more clearly than any declaration of intent what that program is finally intended to produce.