Iran has not moved closer to making nuclear weapons

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Dr. T. Douglas Reilly

Much has been reported recently regarding Iran exceeding the JCPOA limit of 300 kg of 3.67% enriched uranium, and the announcement that it will begin enriching to higher levels by Sunday. These higher levels are still below the 20% limit that the IAEA defines as the boundary between low- and high-enriched uranium; LEU/HEU.

The 300 kg of 3.67% enriched uranium contains 11 kg of 235U, i.e. the fissile isotope of uranium. The IAEA defines a Significant Quantity (SQ) of HEU to be 25 kg; the SQ for plutonium is 8 kg. These limits are chosen to be roughly the amount of nuclear material necessary to built one nuclear explosive. Such explosives can be made with lower amounts of U or Pu; but these are what IAEA safeguards have accepted.

It is absolutely impossible to make a nuclear explosive from 3.67% U. The critical mass of 20% enriched U is roughly 400 kg (900 lbs); it is very impractical to make a weapon with a core weighing 400 kg.

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