4 ms·

The half life of U-235 is 700 million years.

• Retric 5y ago
  Yes, and obvious if you are predicting out 2.5 million years that’s important. Though U238 is more plentiful and has a half life of 4.468 billion years. So, if the reactor needs a fixed amount of U235 that’s an issue but if you change the designs it’s less of a problem. Really, it’s just more complicated than I wanted to get into.
  • titzer 5y ago
    > if you are predicting out 2.5 million years that’s important I believe the stated claim is that there is enough fuel for 100,000 years, which is about 7000x smaller than the half-life of U-235. Even then, 2.5 million years with a 700 million year half-life is absolutely negligible. It's exponential decay, not linear, so you won't even get a 1% reduction. > U238 is more plentiful It's not radioactive enough; you need to subject it to a neutron flux to get something fissile, e.g. P239 through exposure in a reactor (https://www.britannica.com/technology/uranium-processing/Conversion-to-plutonium https://www.britannica.com/technology/uranium-processing/Con...), which incidentally is what breeder reactors are designed to do. If we're talking breeder reactors, then we have several orders of magnitude more energy available to us than the above calculations.
    • Retric 5y ago
      > million years that was a typo it should have been billion. “It is impossible for humans to extract enough uranium to lower the overall seawater concentrations of uranium over the next billion years, even if nuclear provided 100% of our energy and our species lasted a billion years.” At which point decay rates do matter.
      • deleted 5y ago
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