Still, the report suggested a narrowing window as Iran positions itself to increase enrichment.
Iran now has more than 10,000 centrifuges enriching uranium at its main plant at Natanz, 225 kilometers (140 miles) southeast of Tehran, making low-level material. Additionally it has about 800 machines turning out 20 percent enriched uranium at Fordo, a bunkered structure fortified against an air attack near the holy city of Qom, as well as about 2,000 more installed but not yet running.
Uranium enriched to 20 percent can be turned into weapons-grade material much more quickly than low-enriched uranium. If the centrifuges at Fordo, which are now idle, also start operating and are used to make 20 percent material, Iran — using its total enrichment output of low and higher grade uranium — could produce enough weapons-grade uranium for a warhead within three or four weeks, said the summary.
Olli Heinonen, who stepped down as the IAEA's deputy director general in charge of the Iran file in 2010, said the Institute for Science and International Security report contains "good and technically sound estimates."
He said Fordo will nearly double its production capacity of 20 percent enriched uranium to up to 30 kilograms (more than 60 pounds) a month, if and when all the machines there are operating.