So I’ve watched Oppenheimer and a recurring theme in the movie was how tedious task it was to get fission material (demonstrated as filling a large fish bowl by marbles). All they manage to collect in two year period was just enough for two bombs. but fast forward few years US have a complete arsenal of bombs to flat the earth. I understand they must’ve innovated a method and the exact method maybe classified, what i’m interested in is knowing what was the obstacle(s) for this and rough idea of how they might’ve overcome it.
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Natural uranium is almost completely U-238, less than 1% is fissile U-235. Enrichment for weapons grade needs to be almost 90% U-235. That’s a challenge. Next you need massive energy intensive processes and the correct chemistry to exploit to get good separation. One way now is to go through “yellowcake” from ore processing, to UO2 to UF4 to UF6 which then can go into the centrifugal separation unit. You only get a tiny amount back of high purity U-235. Which then needs converted back to UO2 or metal. “Depleted” uraniums is about 99.5% U-238 (natural is roughly 99.3% U-238). Basically it just takes a lot of work to get everything online and dialed in. Once you’re up and running okay, but until then it’s a lot to get established. UF6 is also highly corrosive (reacts quickly with moisture to give off hydrofluoric acid), so you need adequate safety and process controls in place. Many groups at National labs are not authorized to use / study UF6 despite how important it is in the purification process. Anywho it’s a pain in the ass, you’re isolating only a tiny amount of fissile material from the large amount of starting material and takes a while to get any new process online and producing at scale.
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