When the United States and Israel launched military operations against Iran on February 28, President Donald Trump stated that one of the primary goals was stopping Iran from developing a nuclear weapon. That objective has drawn fresh attention to Iran’s uranium stockpile and the technical process used to transform this naturally occurring element into material capable of sustaining a nuclear reaction — a procedure known as enrichment.
Several of Iran’s key nuclear facilities were struck by U.S. and Israeli forces last summer and again during the most recent conflict. Iran’s leadership continues to maintain that its nuclear program exists solely for peaceful purposes. However, prior to the start of the war, the International Atomic Energy Agency reported that Iran held a supply of enriched uranium that was only a short technical step away from weapons-grade material. The IAEA and Western nations say Iran operated an organized nuclear weapons program until 2003.
So what exactly is uranium enrichment, and why does it matter?
Uranium occurs naturally in slightly different forms. One version, called U-235, is the most effective at powering nuclear reactions. It is less stable than the more common form, making it easier to split apart and release the energy required for generating electricity or building a weapon. The catch is that U-235 makes up less than one percent of all uranium found in nature.
To increase the concentration of U-235, scientists must remove its more stable counterpart, U-238, through the enrichment process.
The most widely used method involves spinning uranium in gas form inside a centrifuge. Because U-235 is lighter than U-238, the two separate during spinning. This is carried out in multiple stages using many centrifuges working together to gradually increase the concentration of U-235.
Nuclear security specialist Sébastien Philippe at the University of Wisconsin-Madison explained that the early stages of enrichment are the most labor-intensive because there is so much more U-238 present. As the process continues, it becomes progressively easier. Depending on the size of the facility, the technology in use, and the desired enrichment level, the entire process can take anywhere from a few days to several months or even years.
Uranium enriched to around 5% is sufficient to power a standard electricity-generating nuclear reactor. Reactors used for scientific research operate on uranium enriched up to 20%. According to the Center for Arms Control and Non-Proliferation, anything enriched to 20% or higher is classified as “highly enriched” uranium, while material enriched above 90% is considered weapons-grade — though some highly enriched uranium is used for research and medical applications.
The IAEA estimates that Iran currently holds approximately 972 pounds, or 441 kilograms, of uranium enriched to 60% purity. Philippe noted that a basic nuclear weapon could potentially be constructed using uranium at that enrichment level, and that further enriching it to the 90% threshold needed for a missile-ready bomb is a relatively straightforward step.
IAEA Director General Rafael Grossi told the Associated Press last year that Iran’s existing stockpile could theoretically be used to build as many as 10 nuclear bombs if the country chose to weaponize its program — though he emphasized that this does not mean Iran currently possesses such weapons.
Once uranium has been enriched, it undergoes additional processing before being converted back into solid form, pressed into pellets, and loaded into sealed metal fuel rods for use in a nuclear reactor. Alternatively, enriched uranium can be shaped into the core of a nuclear weapon — a highly complex process that involves significant engineering challenges, including making the warhead small and light enough to be mounted on a missile.
More than 100 countries, including both the United States and Iran, are signatories to the Treaty on the Non-Proliferation of Nuclear Weapons, which first took effect in 1970 and has been updated periodically since. Under the agreement, nations without nuclear weapons commit to using nuclear materials only for peaceful purposes, while those that already possess nuclear weapons agree to work toward disarmament. The IAEA conducts regular on-site inspections to verify compliance.
Iran was found to be in violation of the treaty in the early 2000s because of a covert nuclear weapons program. It was again found out of compliance in June 2025, this time for failing to provide what the IAEA called “technically credible” explanations for uranium particles discovered by inspectors at several locations in Iran that had not been officially declared.
According to a confidential IAEA report circulated to member states and reviewed by the Associated Press in February, Iran has not permitted inspectors access to the nuclear facilities that were bombed by Israel and the United States during a 12-day conflict in June 2025. The report noted that the agency “cannot verify whether Iran has suspended all enrichment-related activities,” or determine the size of Iran’s uranium stockpile at the affected sites.
