Confusion over whether Iran really needed just “two weeks to four weeks” to build a nuclear weapon, as President Donald Trump suggested Monday, hangs over the ongoing US-Israeli war against the Persian Gulf nation. Nuclear experts call this claim unlikely — but the confusion may stem from some basic nuclear 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 the Middlebury Institute of International Studies. His comments echoed those of other experts after the start of the war, as well as statements by International Atomic Energy Agency (IAEA) chief Rafael Grossi at the time and in 2025 and last year’s “threat assessment” report by US intelligence agencies.
According to an IAEA estimate, as of June 2025, Iran had 441 kilograms of 60 percent enriched uranium, where the percentage refers to the proportion of the isotope uranium 235 (U 235) found in the material. It would be enough for 10 nuclear weapons if the material could be further enriched to a full 90 percent weapons-grade concentration, according to the IAEA. The additional enrichment would take a few weeks in a fully functioning Iranian nuclear complex, perhaps explaining the timeline of Trump’s declaration.
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However, that step alone does not equal a bomb. And Iran’s main enrichment capability was “completely and totally wiped out”, according to Trump himself in June, after the US bombed three underground Iranian facilities. The administration’s special envoy for the Middle East, Steve Witkoff, nevertheless claimed on March 3, after the start of the current war, that Iran had the ability to make 11 nuclear bombs. Trump administration officials reportedly failed to include nuclear technical experts on their negotiating teams with Iran before the war, adding to the uncertainty. If Iran had truly rebuilt those facilities, it could have led — over months, not weeks — to the nation’s resumption of uranium enrichment, Lewis says. “But this is all ‘if’, ‘maybe’ and ‘later,'” he adds.
Enrichment
First, it is not easy to enrich uranium, says former Los Alamos National Laboratory chemist Cheryl Rofer. It begins with the extraction of uranium ore, which is then filtered and dried to make “yellowcake” uranium oxide concentrate. Yellowcake is only about 0.7 percent U 235, where a standard nuclear bomb typically requires uranium metal that is 90 percent enriched. To get there, technicians must chemically convert the yellowcake into uranium hexafluoride gas (a molecule containing one uranium atom and six fluorides) and feed it into centrifuges. Spinned at 50,000 to 100,000 revolutions per minute, molecules containing the slightly lighter U 235 separate from those of the heavier, and much more common, uranium isotope U 238. The U 235 stream then moves through cascades of multiple centrifuges that spin to first further concentrate the rich stream (called 20 percent). uranium) and then to 60 percent concentration. “It takes many stages to separate the two isotopes,” says Rofer.
Since the first Trump administration pulled out of the international agreement with Iran to halt enrichment in 2018, Iran had stopped at the intermediate stage of 60 percent enrichment in its uranium production and had not progressed to the 90 percent required for bombs. “Iran’s decision was intended to send a political message: ‘We have gone as far as we can go 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 entrances to tunnels at its Isfahan nuclear complex in February, concluding that the uranium monitors were likely to remain in February. containers of uranium hexafluoride gas, or in disarray there after the bombing of the site in June 2025.
To be as close as Trump claimed to having a conventional nuclear weapon, Iran would have needed to secure and enrich that gas to 90 percent in centrifuges, extract and chemically separate it back into solid uranium, shape it into balls of uranium metal (a task that is “not easy,” Rofer says) and then construct 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, but it is not clear for what purpose.
“It’s not impossible to imagine that Iran had maneuvered itself into a ‘breakout situation,'” consistent with Trump’s claims of an imminent weapon, said nuclear historian Alex Wellerstein of the Stevens Institute of Technology. “But it’s also entirely possible that they haven’t.” Big claims require big evidence, especially when lives are at stake.”
Pickup
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 obtain Iran’s stockpiles of enriched uranium in a commando operation. Secretary of State Marco Rubio is said to have discussed the alternative at a closed congressional briefing on Tuesday, according to Axios. “We haven’t gone after it. We wouldn’t do it now. Maybe we will later,” Trump said last week.
Safely retrieving these uranium canisters—which likely take the form of dozens of 25- to 50-pound canisters filled with pressurized uranium hexafluoride gas—would be very challenging under wartime conditions. To start, we need military control to bring in bulldozers, ground and air transport for the canisters, as well as the ability to deal with any challenges in locating and moving the material from inside places like the mountain in Isfahan to the outside, says nuclear proliferation expert Miles Pomper of the James Martin Center for Nonproliferation Studies. Another difficulty would be determining whether the team had really recovered all the uranium, he says, given that the lack of safeguards in recent months means the “chain of custody” has essentially been broken.
Aside from the military challenges, a command team would also have to worry about damaged canisters flying around spewing corrosive, radioactive gas and about improperly storing them leading to a nuclear “critical event” — an uncontrolled nuclear fission chain reaction, Rofer says. It would not lead to an explosion “but a blue flash and many released neutrons”, fatal to anyone nearby, she adds. “You can’t just send a bunch of guys with a truck to throw stuff in the back and drive off.”
In 1994, US forces removed 600 kilograms of highly enriched uranium from Kazakhstan that was left over from the Soviet Union in “Project Sapphire”. With Kazakhstan’s cooperation, the material traveled on three C-5 cargo planes, an effort that took a team of specialists, including Rofer, nearly a month of 12-hour days from October to November 1994 to complete. “The Soviets didn’t keep good records, and it was everywhere,” says Rofer.
The best outcome now would be the resumption of peaceful IAEA monitoring of Iran’s enrichment capabilities, says Pomper. If the war in Iran leads to concern that the uranium is falling into “dangerous hands”, however, the possibility of a recovery mission may become more urgent, he says. Israeli news reports claim that the Mossad intelligence service has some knowledge of the uranium’s security, which could ensure alarms over its movement.
Still, most experts see a pick-up raid on Iran as “pretty awesome,” Wellerstein says. “It will certainly require more thought and planning than the Iran war has shown so far.”
Editor’s Note (3/11/26): This story is in development and may be updated.
