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View Diary: Energy from the Moon (165 comments)

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  •  I cannot recall where I heard this, (none)
    perhaps on a program on Air America Radio, but some study concludes that there is no net energy gain from mined uranium until at least 8 years after the uranium has been in use in a nuclear reactor, by reason of the costs in fossil fuels to mine and transport it, and to produce the power plants.
    •  Sort of (none)
      You are correct that it takes ~8 years of reactor operation to recover the energy it took to build the plant and refine the fuel. But it takes similar amounts of time for other types of power plant.

      This difference is part of why power companies are so keen to manage demand, offering incentives to get people to co-gen or to install demand side management (which allows the utility to shut off high consumption devices like heaters and air conditioners on a rotating basis). This allows them to avoid the huge up-front capital investment in new plant as long as possible.

      I don't have figures on natural gas plants and coal plants, but it would not surprise me to hear that it was only slightly less than the time for nuclear plants.

      Yes, the gas centrifuge process used to cull out the rarer fissionable isotope of uranium takes a great deal of power (imagine the amount of heat it takes to vaporize uranium). I am not an expert on this subject, but I believe that this has been done with both hydro-power and plants powered by fast breeder reactors and run by the US gov't. If it had been done any other way, it would not have been economically feasible. This is mere hearsay on my part. As I said, I am not a nuclear engineer (but my brother is an ex-Navy Nuc and he knows a great deal about this stuff - I tend to parrot him a lot).

      For what it is worth, my favorite renewable source, solar photovoltaics, take anywhere from 9-15 years to payback their energy cost to manufacture, depending on the type of PV material and panel. Thin films at the low end, mono-crystalline silicon at the high end.

      Every energy production technology has a "payback time."

      TANSTAAFL.

      [-7.13, -8.41 http://www.politicalcompass.org/]

      by evilpenguin on Fri Nov 11, 2005 at 11:30:50 AM PST

      [ Parent ]

      •  Um, yikes? (none)
        So, with a 9-15 year period just to break even on an energy basis (let alone cost), why do you favor PV so much?  It seems like a weak (if any) payoff on energy and a poor payoff on investment money.

        I have heard PV cells degrade pretty badly as well, so that I wonder how practical it is to expect most non-utility run PV systems to really be fully functional after such a long time - I'll wager most cells sold to consumers NEVER pay off the energy that went into making them.

        That said, I've heard rumors of newer PV materials that could really improve the situation.

        Still ... I'd put more hope in improving wind technology, tidal/current water systems, or researching solar-thermal systems as long term payoffs.

      •  gas centrifuges and power requirements (none)

        The old way of enriching uranium, by gaseous diffusion, does require enormous amounts of power.

        Gas centrifuges do need significant power, but it is far less.   And for reactors you need only enrich a moderate amount, much less than for nuclear weaponry.

        The fact that uranium has such a high energy density versus fossil fuels means that it's worth quite a bit of energy to do so.

        Exploration for uranium has been far less rigorous than for fossil fuels.   And there's always reprocessing, and breeders.

        Though probably superior is the thorium cycle and there's lots more thorium.

        Anwyay, worrying about the fuel for nuclear fission should not be significant: it is not a problem for tens of centuries.

        We have to worry about climate change and peak oil in 1.5 generations.  Look the climate projections for 2200 or 2300.  They're horrifying.

        Nuclear power is NOT a competitor to wind power, tidal or solar, or any of those other good things.   It is properly viewed as a competitor to coal.

        We needs nukes and wind and biofuels. As much as possible, as soon as possible.

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