Iran has informed the IAEA of a multi-stage process involving the production of uranium metal for the purpose of making reactor fuel rods. The US condemned the plan as “provocative.”
Iran plans to send 20% enriched uranium oxide to a plant in Esfahan, where it will be converted to uranium tetrafluoride, and subsequently to uranium metal, which will be formed into fuel rods.
20% enriched uranium fuel rods are used at the Tehran Research Reactor (TRR) in Iran, the nation’s primary source of nuclear isotopes for medical use. Despite the US objecting to the fuel production, the US built the TRR in the first place, in 1967.
The TRR was not meant to last 50+ years as it has, but has remained a necessary option for Iran, as it was meant to be replaced by a heavy water reactor, and the US objected to the design. There is work internationally to design an alternative version, though this is advancing much more slowly than anticipated.
The chemical compound in which the 20% material is first obtained is UF6 or uranium hexafluoride. Apparently it is sufficiently stable that it is impossible to chemically extract two fluorine atoms to make the tetrafluoride.
My hunch is that the oxide is the safest form for storage.