Iran was nowhere close to a nuclear bomb, experts say

Confusion over whether Iran really only needed “two to four weeks” to build a nuclear weapon, as President Donald Trump suggested Monday, looms over the ongoing war between the United States and Israel against the Persian Gulf country. Nuclear experts consider this claim improbable, but the confusion may arise from some fundamental principles of atomic chemistry.

“There was no evidence that Iran was close to a nuclear weapon,” says Jeffrey Lewis of the James Martin Center for Nonproliferation Studies at Middlebury’s Institute of International Studies. His comment echoes those of other experts after the war began, as well as statements by the head of the International Atomic Energy Agency (IAEA) then and in 2025, as well as last year’s “threat assessment” report by US intelligence agencies.

According to an IAEA estimate, as of June 2025, Iran possessed 441 kilograms of uranium enriched to 60%, the percentage referring to the share of the isotope uranium 235 (U 235) found in the material. That would be enough to make 10 nuclear weapons if the material could be enriched to weapons-grade concentrations of 90 percent, according to the IAEA. This additional enrichment would take a few weeks at a fully operational Iranian nuclear complex, which perhaps explains the timing of Trump’s statement.

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However, this step alone is not a bomb. And Iran’s key enrichment capabilities were “completely and totally wiped out,” according to Trump himself in June, after the United States bombed three Iranian underground facilities. The US administration’s special envoy to the Middle East, Steve Witkoff, nevertheless asserted on March 3, after the start of the current war, that Iran had the capacity to manufacture 11 nuclear bombs. Trump administration officials reportedly did not include nuclear technical experts on their Iran negotiating teams before the war, adding to the uncertainty. If Iran had actually rebuilt these facilities, it could have led – within months, not weeks – to the country’s resumption of uranium enrichment, Lewis says. “But all that is just ‘if’, ‘maybe’ and ‘later’,” he adds.

Enrichment

For starters, uranium enrichment isn’t simple, says Cheryl Rofer, a former chemist at Los Alamos National Laboratory. It begins with the extraction of uranium ore, which is then filtered and dried to produce a “yellowcake” uranium oxide concentrate. Yellowcake contains only about 0.7 percent U-235, whereas a standard atomic bomb typically requires uranium metal enriched to 90 percent. To achieve this, technicians must chemically convert yellowcake into uranium hexafluoride gas (a molecule containing one uranium atom and six fluorides) and feed it into centrifuges. Spinned at a speed of 50,000 to 100,000 revolutions per minute, molecules containing the slightly lighter U 235 separate from those containing the heavier and much more common uranium isotope U 238. The stream of U 235 then travels through cascades of additional centrifuges swirling to further concentrate the stream, first to 20 percent enrichment (called highly enriched uranium), then to 60 percent concentration. “It takes several steps to separate the two isotopes,” explains Rofer.

Since the first Trump administration withdrew from the international agreement with Iran to stop enrichment in 2018, Iran has stopped at the intermediate stage of 60% enrichment in its uranium production and has not reached the 90% required for bombs. “Iran’s decision was intended to send a political message: ‘We have gone as far as possible in response to provocations without producing weapons-grade uranium,'” noted Robert E. Kelley of the Stockholm International Peace Research Institute in 2021. Iran had buried the tunnel entrances to its Isfahan nuclear complex in February, leading observers to conclude that the uranium remained stored, probably in uranium hexafluoride canisters, or in disarray after June. Bombing of the site in 2025.

To come as close as Trump claimed to possessing a conventional nuclear weapon, Iran would have had to secure and enrich this gas to 90 percent in centrifuges, extract and chemically separate it into solid uranium, shape it into spheres of uranium metal (a task that is “not simple,” Rofer says), and then build explosive devices around them. A handful of smaller bombs could be made from the material at its current concentration of 60 percent, according to physicist Edwin Lyman of the Union of Concerned Scientists.

“It’s not impossible to imagine that Iran found itself in a breakout situation,” consistent with Trump’s claims of an imminent weapon, says nuclear historian Alex Wellerstein of the Stevens Institute of Technology. “But it’s also quite possible that they didn’t. Big allegations require big evidence, especially when lives are at stake.”

Recovery

Lawmakers such as Democratic Sen. Chris Coons of Delaware, as well as news reports, have raised the possibility that the United States or Israel could somehow recover Iran’s enriched uranium reserves in a commando operation. Secretary of State Marco Rubio reportedly discussed this option during a closed-door congressional briefing on Tuesday, according to Axios. “We didn’t pursue it. We wouldn’t do it now. Maybe we will later,” Trump said last week.

Safely recovering these uranium canisters – which likely take the form of dozens of 25- to 50-pound containers filled with pressurized uranium hexafluoride – would be very difficult under wartime conditions. To begin, we would need military control to bring in bulldozers, ground and air transportation for the canisters, and the ability to meet all the challenges of locating and moving material from inside places like Isfahan Mountain to the outside, says Miles Pomper, a nuclear proliferation expert at the James Martin Center for Nonproliferation Studies. Another difficulty would be determining whether the team actually recovered all the uranium, he says, given that the lack of safeguards in recent months means that “the chain of custody” has essentially been broken.

Leaving aside military challenges, a team of commandos would also have to worry about damaged containers flying around and spewing corrosive and radioactive gases and their improper storage leading to a nuclear “criticality event” — a chain reaction of uncontrolled nuclear fission, Rofer says. This would not cause an explosion “but a blue flash and a lot of neutrons released”, fatal for everyone nearby, she adds. “You can’t just send a bunch of guys with a truck to throw the stuff in the back and drive away.”

In 1994, U.S. forces removed 600 kilograms of highly enriched uranium from the Soviet Union from Kazakhstan as part of “Project Sapphire.” With Kazakhstan’s cooperation, the material traveled aboard three C-5 cargo planes, an effort that took a team of specialists nearly a month of 12-hour days from October to November 1994. “The Soviets didn’t keep good records, and it was everywhere,” Rofer says.

The best outcome now would be the IAEA’s resumption of peaceful monitoring of Iran’s enrichment capabilities, Pomper says. If the war in Iran raises concerns about uranium falling into “dangerous hands,” the possibility of a recovery mission could become more urgent, he says. Israeli media say Mossad intelligence has some knowledge of the security of uranium, which could raise alarms about its movement.

Still, most experts consider a recovery raid in Iran “pretty fantastic,” Wellerstein says. “This would certainly require more foresight and planning than the Iranian war has demonstrated thus far. »

Editor’s Note (3/11/26): This story is currently developing and may be updated.