The 2015 accord limiting Iran’s nuclear program in exchange for sanctions relief was designed to slow Iran’s nuclear program to the extent that, if it were to ditch the agreement, it would have needed a year to produce enough fissile material to fuel a nuclear weapon. That so-called breakout time had been estimated at a few months before the deal went into effect. Following the US withdrawal in 2018 under then-President Donald Trump, Iran has gradually accelerated its own violations of the agreement. Now, it’s thought to need only weeks to produce a bomb’s worth of the necessary enriched uranium. Iran would still have to master the process of weaponizing the fuel before it would have an operable nuclear device that could hit a remote target.
In exchange for the lifting of economic sanctions imposed because of suspicions around its nuclear program, Iran agreed that for 15 years it would not enrich uranium beyond 3.7% - the concentration of the fissile isotope uranium-235 needed for nuclear power plants. Iran also pledged to limit its enriched-uranium stockpile to 300 kilograms (661 pounds), or about 3% of the amount it held before the deal was struck. But starting a year after the US left the accord and reimposed sanctions, which denied Iran the economic benefits the deal promised, Tehran began to ramp its program back up. Iran has accumulated enough enriched uranium to construct several bombs should its leaders choose to purify the heavy metal to the 90% level typically used in weapons. Moreover, it has not only returned to enriching to 20% but has for the first time gone to 60%, a level of purity the International Atomic Energy Agency says is technically indistinguishable from weapons-grade fuel. Inspectors reported in May that Iran had accumulated 43 kilograms of uranium enriched to 60%, a rise of 30% over the previous three months.