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Radioactive Waste as a Power Source?

  1. May 29, 2009 #1

    Roo

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    Dear all,

    When I was a nipper, my favourite TV show was 'Space 1999' - anyone remember that? Anyway, I think the main reason why I liked it (aside from Barbara Bain and Catherine Schell) was because a lot of the technology portrayed had a sense of realism to it, which in the 70's didn't seem an impossible feat for 30 years or so in the future.

    One of the few things that has stayed in my mind from that TV show throughout the past 30 years or so is the power generation system - in that it was fed from radioactive waste deposited in large and sealed sub-surface housings away from the base. I'm not a nuclear engineer and only have a basic understanding of it, but my question to you is whether this is actually possible and could it in fact be realised as a potential source of power for an installation, space or otherwise?

    Roo
     
  2. jcsd
  3. May 29, 2009 #2

    mgb_phys

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    More efficient to just reprocess the waste and use it in a regular reactor like other countries do.
     
  4. May 29, 2009 #3

    Morbius

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    Roo,

    Compared to using nuclear fission there is very little energy to be had from the decay energy of
    spent fuel or "nuclear waste". As soon as you shut a reactor down, the "decay power" of the
    waste is about 7% of what the reactor was outputting before it was shutdown - and the decay
    power falls off rapidly from there.

    You need to supply a small amount of cooling to the cooling pools of nuclear power plants to
    dissipate the heat from the decay power of spent fuel - but it really isn't a viable energy source.

    As mgb_phys points out; the best thing to do with the waste is to reprocess it, and recycle it back
    into a reactor so that more energy can be derived from nuclear fission.

    Dr. Gregory Greenman
    Physicist
     
  5. May 29, 2009 #4

    Roo

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    Thanks for the answers so far gents.

    But could I ask, irrepective of them and more out of general curiosity now, could nuclear 'waste' still power an installation if the level of waste was large enough?

    Roo
     
  6. May 29, 2009 #5

    mgb_phys

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    Sure, but would you rather have 600Mw from a reactor or a few KW from lukewarm water in a cooling pond.
    You could power your car with the heat of your coffee cup and a Stirling engine but you aren't going to go as fast.
     
  7. May 29, 2009 #6

    Morbius

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    Roo,

    Yes - but why would you want to have a bunch of nuclear waste when you could have a reactor that was
    1/1000-th the size.

    Additionally, you don't have a throttle on the energy output of the waste as you do on a reactor. You
    would have to have a pile of nuclear waste big enough so that the energy output meets your peak
    energy demand. When you are not at peak demand - you would need to dump the excess heat energy
    somewhere.

    A reactor can be throttled - you can run the reactor power up and down as needed to meet the demand.

    So why would you want to have a pile of waste - a reactor is a much better idea.

    Dr. Gregory Greenman
    Physicist
     
  8. May 29, 2009 #7

    Astronuc

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    Adding to Morbius's comment, fission produces on the order of 200 MeV per fission, whereas beta+gamma decay produces on the order of 1 MeV (actually keV to ~2 MeV), so one would need about 200 times the number of fission product (waste) atoms to produce the same energy. If it's power however, one has to look at the decay rates compared to fission rates, and that may mean another signficant factor in mass.

    A large reactor core (for a 1 GWe unit) is about 100 tonne. So the equivalent energy in waste would require something like 20000 tonne, which is a lot of volume. It doesn't work well on a large scale.

    As Morbius indicated, radioactivity is not something that one can turn off. It goes like the sun, although over time, the radioactive atoms decrease exponentially with the decay process.
     
  9. May 29, 2009 #8
  10. May 30, 2009 #9

    Astronuc

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    Radioisotopic thermal generators (RTGs) are rather compact, and the half-life of Pu-238 is 87.7 y which is a good decay rate for a multiyear mission.

    Pu-238 is not considered a waste product, since it has use as a thermal source in RTG's.
     
  11. Jun 3, 2009 #10

    Roo

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    Thanks for all the answers gents.

    I have to add that this thread was purely out of interest. I know that a modern system is much the obvious choice - I just wanted to know whether the 'idea' was possible at all, even if highly un-necessary!

    Thanks - my childhood visions are still safe then.

    Roo.
     
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