Iran’s formal notification on Monday to the IAEA that it is going to start producing 20 percent enriched uranium in order to supply its research reactor that produces medical isotopes, means that it will be taking a major stride towards producing weapons-grade fuel.
The Washington Post reports:
…enriching uranium under the guise of medical needs will get Tehran much closer to possessing weapons-grade material. Iran insists it has no interest in nuclear weapons. But Albright said 70 percent of the work toward reaching weapons-grade uranium took place when Iran enriched uranium gas to 3.5 percent. Enriching it further to the 19.75 percent needed for the reactor is an additional “15 to 20 percent of the way there.”
Once the uranium is enriched above 20 percent, it is considered highly enriched uranium. The uranium would need to be enriched further, to 60 percent and then to 90 percent, before it could be used for a weapon. “The last two steps are not that big a deal,” Albright said. They could be accomplished, he said, at a relatively small facility within months.
Jeffrey Lewis provides a more detailed explanation of why 20 percent HEU is much closer to 90 percent than 3.5 percent LEU is to 20 percent.