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UF6 Cylinders

Iran is reported to have produced some 400 kilograms of uranium enriched to 60% in the isotope U-235, enough with further enrichment to “weapon grade” (~90%) for up to 10 nuclear weapons. A big question now: what has happened to that stockpile since the beginning of the Israeli bombardment? 

Here’s background on the form of the uranium and how it is stored and transported. 

Uranium hexafluoride (UF6) is the gas used in centrifuge uranium enrichment. It sublimes at 56.5°C (134°F) under atmospheric pressure. It can be liquefied and solidified for storage and transport. 

UF6 is stored and transported in steel cylinders designed to contain the corrosive and radioactive UF6. Large 48Y cylinders are used for natural (0.7% U-235) and depleted UF6 and smaller 30B cylinders (photo) for low enriched UF6.

High enriched uranium (20% or more U-235) hexafluoride is stored and transported in specialized cylinders, which are designed to prevent “criticality.” 

IAEA inspectors routinely verify the amount and enrichment of uranium in UF6 cylinders at enrichment facilities (photo of enrichment verification).
 

Iran was producing 20% and 60% uranium at Natanz and at Fordo. And some of the stockpile was said to be stored at Isfahan. At Natanz, the above ground part of the enrichment facilities, producing 60%, was destroyed in the first Israeli attack. Some UF6 cylinders may have been torn open, releasing some UF6 to the atmosphere. The IAEA has reported that radiation levels near the Natanz facility have not changed. At Isfahan, several facilities were destroyed or damaged in the first attack. Some UF6 cylinders may have been destroyed and some UF6 released to the atmosphere. The underground Fordo was not attacked; 60% uranium was being produced there, and the stockpile was not affected. 

As Israeli bombardment continues, and with a possible MOAB attack on Fordo (and possibly on Natanz), and with IAEA inspectors gone, the Iranians have had time to take action to protect the UF6 cylinders, probably by moving them to safer locations. Israel is no doubt using its on-the-ground agents to try to determine where the UF6 cylinders are. 

And that’s where this key factor stands today - the amount and whereabouts of Iran’s 60% and 20% UF6 cylinder stockpile. If Iran retains enough of that stockpile, it has the possibility to “break out” along with withdrawing from the NPT. A number of non-Iranian commentators believe that would be the proper strategic decision for Iran, especially if President Trump takes the U.S. to war with Iran, at the side of Israel.

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