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Natural uranium is 0.7% U-235, and enrichments of 80%+ are needed for U-based weapons (like Little Boy). The enrichment process used during the Manhattan proje

by _n_b_ 6y ago

Natural uranium is 0.7% U-235, and enrichments of 80%+ are needed for U-based weapons (like Little Boy). The enrichment process used during the Manhattan project (electromagnetic and then gaseous) not perfectly efficient, and there are losses during conversion, but assuming 100% efficiency that means just Little Boy required 8 tons of raw U. If you add up all the work going on, all the experiments, all the piles (reactors) off consuming uranium, this figure doesn’t seem too surprising to me.

bbarnett 6y ago
From the article: Mines in the US and Canada were considered a “good” prospect if they could yield ore with 0.03% uranium. At Shinkolobwe, ores typically yielded 65% uranium. The waste pile of rock deemed too poor quality to bother processing, known as tailings, contained 20% uranium.
- ivann 6y ago
  Those are the yields of uranium in the ore. The 80%+ needed is the quantity of the Uranium-235 isotope.
- sandworm101 6y ago
  If it were 65% uranium, the mine itself would be a massive nuclear reactor. (A situation that did happen elsewhere in prehistory.) It would heat up and into a red-hot cauldron. 65% is the richness of the ore not the percentage of uranium in the rock overall.
  - timothevs 6y ago
    Quite interesting, do you have an article, or a paper about the prehistoric episode you mentioned? I’m genuinely curious.
    - intotheabyss 6y ago
      The only naturally occurring nuclear fission reactor was found to be in Oklo, Gabon in Central Africa and was thought to be active about 1.5 billion years ago. https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...
    - kenned3 6y ago
      This provides much better coverage: https://blogs.scientificamerican.com/guest-blog/natures-nuclear-reactors-the-2-billion-year-old-natural-fission-reactors-in-gabon-western-africa/ https://blogs.scientificamerican.com/guest-blog/natures-nucl...
  - kenned3 6y ago
    This is NOT the case, even if the mine was 100% Uranium this would not happen, at least not today. As someone else pointed out, the world did have a natural reactor, Oklo, Gabon 1.5 billion years ago. When Uranium is refined, they are enriching the U235 vs U238. The ratio is too low today to sustain any natural reactors, but 1.5 billion years ago this wasnt the case.
    - sandworm101 6y ago
      Not the case on day-1, but an open pit of 65% uranium isn't a typical lab experiment. Add some rain, some evaporation, some oxygen, countless other micro effects, and after a while you will get localized concentrations of U235. Then things start to get interesting as the fertile U238 is changed into other things. I'm not saying that that actually happened, just that a hypothetical multi-kiloton pile of 65% natural uranium isn't a neutral pile of sand.
      - credit_guy 6y ago
        Evaporation, oxygen and any number of other effects won't change the ratio of U235 and U238. Those isotopes are chemically identical. The only way they are different is by their different atomic mass, i.e. their gravitational effects. And since the atomic mass is different by only about 1%, even the gravitational effects are almost identical. So U235 constitutes between 0.71% and 0.72% of the Uranium everywhere in the world.
      - kenned3 6y ago
        Exactly as the other guy posted. U235 doesnt do anything "interesting" until you get it to around 3%. Due to somewhat obvious reasons (not a lot of net-new uranium being formed, and the half life is fairly stable), the Uranium concentration is pretty uniform around the world and is something like: uranium-235 0.720% uranium-238 99.275% uranium-234 0.006% Evaporation and other factors wont change this, it hasnt changed this ratio in the muti-billion years Uranium has been on earth. What does change this is the half life of U235. U235 wont naturally 'accumulate', it doesnt move around in rock to form higher concentrations, it is generally 0.720 everywhere. The natural reactor ran becaues back then there was simply more U235 (half life 700 million years) vs the half life of U238 (4.5 billion years) No Hypothetical examples needed. Open pit mines wont do anything 'interesting' unless you can either go back in time, or reverse the U235 Decay and then add water and you will probably get something like what took place at Gabon.

by _n_b_ 6y ago

bbarnett 6y ago

From the article: Mines in the US and Canada were considered a “good” prospect if they could yield ore with 0.03% uranium. At Shinkolobwe, ores typically yielded 65% uranium. The waste pile of rock deemed too poor quality to bother processing, known as tailings, contained 20% uranium.

ivann 6y ago
Those are the yields of uranium in the ore. The 80%+ needed is the quantity of the Uranium-235 isotope.
sandworm101 6y ago
If it were 65% uranium, the mine itself would be a massive nuclear reactor. (A situation that did happen elsewhere in prehistory.) It would heat up and into a red-hot cauldron. 65% is the richness of the ore not the percentage of uranium in the rock overall.
- timothevs 6y ago
  Quite interesting, do you have an article, or a paper about the prehistoric episode you mentioned? I’m genuinely curious.
  - intotheabyss 6y ago
    The only naturally occurring nuclear fission reactor was found to be in Oklo, Gabon in Central Africa and was thought to be active about 1.5 billion years ago. https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...
  - kenned3 6y ago
    This provides much better coverage: https://blogs.scientificamerican.com/guest-blog/natures-nuclear-reactors-the-2-billion-year-old-natural-fission-reactors-in-gabon-western-africa/ https://blogs.scientificamerican.com/guest-blog/natures-nucl...
- kenned3 6y ago
  This is NOT the case, even if the mine was 100% Uranium this would not happen, at least not today. As someone else pointed out, the world did have a natural reactor, Oklo, Gabon 1.5 billion years ago. When Uranium is refined, they are enriching the U235 vs U238. The ratio is too low today to sustain any natural reactors, but 1.5 billion years ago this wasnt the case.
  - sandworm101 6y ago
    Not the case on day-1, but an open pit of 65% uranium isn't a typical lab experiment. Add some rain, some evaporation, some oxygen, countless other micro effects, and after a while you will get localized concentrations of U235. Then things start to get interesting as the fertile U238 is changed into other things. I'm not saying that that actually happened, just that a hypothetical multi-kiloton pile of 65% natural uranium isn't a neutral pile of sand.
    - credit_guy 6y ago
      Evaporation, oxygen and any number of other effects won't change the ratio of U235 and U238. Those isotopes are chemically identical. The only way they are different is by their different atomic mass, i.e. their gravitational effects. And since the atomic mass is different by only about 1%, even the gravitational effects are almost identical. So U235 constitutes between 0.71% and 0.72% of the Uranium everywhere in the world.
    - kenned3 6y ago
      Exactly as the other guy posted. U235 doesnt do anything "interesting" until you get it to around 3%. Due to somewhat obvious reasons (not a lot of net-new uranium being formed, and the half life is fairly stable), the Uranium concentration is pretty uniform around the world and is something like: uranium-235 0.720% uranium-238 99.275% uranium-234 0.006% Evaporation and other factors wont change this, it hasnt changed this ratio in the muti-billion years Uranium has been on earth. What does change this is the half life of U235. U235 wont naturally 'accumulate', it doesnt move around in rock to form higher concentrations, it is generally 0.720 everywhere. The natural reactor ran becaues back then there was simply more U235 (half life 700 million years) vs the half life of U238 (4.5 billion years) No Hypothetical examples needed. Open pit mines wont do anything 'interesting' unless you can either go back in time, or reverse the U235 Decay and then add water and you will probably get something like what took place at Gabon.