Where is Iran's uranium? Truce highlights mystery over stockpile

Jonathan Tirone, Bloomberg News on Jun 24, 2025

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U.S. President Donald Trump’s declaration of a ceasefire between Israel and Iran may curb the exchange of missile fire, but the biggest mystery of the war remains unsolved: the location of Tehran’s near-bomb-grade uranium.

The International Atomic Energy Agency acknowledged just five days into the conflict its inspectors had lost track of Iran’s 409 kilograms (902 pounds) of highly-enriched uranium — enough for 10 nuclear warheads should Supreme Leader Ayatollah Ali Khamenei opt to pursue weaponization.

The stockpile can be stored in 16 cylinders measuring 36-inches (91.4 centimeters) in height, according to estimates published by U.S. regulators, or about the size of a large scuba-diving tank. Each one would weigh about 25 kilos — light enough to be carried to a secret location on foot or in the back of a small vehicle.

Even if Israel and the U.S. have effectively destroyed Iran’s enrichment infrastructure for the foreseeable future — and the evidence to date is far from clear — the risk is the uranium already at near-weapons grade could be hidden away indefinitely.

IAEA Director General Rafael Mariano Grossi said he’s still optimistic that a durable ceasefire could pave the way to a reopening of talks on Iran’s nuclear program and the return of inspectors.

“There needs to be a cessation of hostilities for the necessary safety and security conditions to prevail so that Iran can let IAEA teams into the sites to assess the situation,” Grossi told an emergency session of the board of the United Nations watchdog on Monday.

The unknown location of Iran’s nuclear fuel underlines the high-risk nature of Israel’s decision to take military action against the Islamic Republic almost two weeks ago, a call made after five rounds of U.S.-Iran talks failed to yield an agreement.

Before the attacks, IAEA monitors kept meticulous track of Iran’s declared uranium inventory, inspecting more than one site a day to ensure the material was accounted for and not being diverted for use in weapons.

But the June 13 Israeli strikes prompted Iran to relocate the material to an undeclared facility — even before the U.S. joined in with more advanced bombing technology last weekend. While Grossi has demanded the Islamic Republic inform his inspectors of the new location, there’s no guarantee they’ll be granted access, whether or not the ceasefire holds.

The Iranian parliament’s National Security and Foreign Policy Commission this week approved the outlines of a bill that would require the government to suspend its cooperation with the IAEA. That would mean a halt to all engagement with the atomic watchdog “until the security of the country’s nuclear facilities is guaranteed,” according to Mizan, Iran’s legal news agency.

Iranian leaders have criticized the IAEA for failing to stand up for its rights under the nuclear Non-Proliferation Treaty — a bedrock international agreement struck a half century ago to prevent the spread of atomic weapons. It gave signatories like Iran access to nuclear technologies on the condition they did not seek to make weapons.

Because much of that tech is dual use — with applications in civilian or military lines of work — the treaty empowers the IAEA with ensuring nuclear material is used appropriately.

Tehran’s IAEA envoy, Reza Najafi, said Monday that the integrity of the accord had been dealt an “irreparable blow” by the Israel and U.S. decision to bomb Iran’s nuclear sites rather than persist with talks over a diplomatic solution.

“The existing NPT framework has been rendered ineffective,” Najafi told reporters.

Even if the legal and political relationship between Iran and agency inspectors hadn’t deteriorated as a result of the military action — though it has — the attacks on nuclear sites have made monitoring far more difficult. The Fordow, Isfahan and Natanz sites — all targeted relentlessly by Israeli and U.S. bombers over the past 12 days — are strewn with localized chemical and radiological contamination, likely rendering key verification tools ineffective.

And the stockpile of high enriched uranium is still missing.

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—With assistance from Arsalan Shahla.