Yes, I get very annoyed at glib Lunar He3 mining stories. We don't know if or when He3 fusion reactors will be technically and economically feasible, regardless of the price of He3. It certainly will be several decades AT LEAST. And there are many unknowns about lunar He3 mining.
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Originally Posted by TinFoilHat
In order to understand the economic rational for mining He3, we have to look at what makes it a desireable fusion fuel. For economic feasability we have to look not just at He3 but compare it to alternative power sources. Deteurium-Tritium fusion is the easiest form of fusion we are likely to use as a power source. It occurs at a temperature lower than any other fusion, releases a lot of energy per reaction, and we will never run out of fuel for it. The downside is that much of the reaction energy is released in the form of fast neutrons. Converting fast neutrons into electricity is inefficient, and the reactor walls will suffer neutron embrittlement and need periodic replacement, generating a steady stream of highly radioactive waste.
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Well, there is plenty of deuterium. Tritium must be produced by transmutation of Lithium 6 with neutrons. A "Lithium blanket" is another feature that supposedly would be present in a working D-T reactor, but is still largely undeveloped. Incidentally tritium will decay to He3, so if a lot of tritium is produced, it could be a source for some He3-D reactors.
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He3 fusionis more difficult to achieve, taking about twice the temperature,and releasing less energy per reaction. On the plus side the reaction is nearly aneutronic (the He3-D reaction releases no neutrons, but some D-D reactions will also occur, releasing some fairly low-energy neutrons) and the energy released can be converted into electricity at higher efficiency.
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Yes, let's be clear that we aren't even close to a commercially useful fusion reactor or ANY sort. Also, while the reaction would be low on neutrons, it is by no means "radiation free." I expect the strong anti-nukes would not be satisfied. While there would be great design advantages, there would still be reactor erosion issues due to the extremely hot plasma.
The tougher requirements for D-He3 fusion would probably add decades to the time it could be feasible.
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So, the question is, is extracting He3 from the moon cheaper and easier than dealing with the radioactive waste products from the D-T reactors?
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Or what about technology we have today? That is, conventional fission reactors. I'd like to see more work done in refining fission technology - my preference would be to move to passively safe high burnup reactors. THAT we can do. One of the sad things about the cutoff in U.S. commercial nuclear development is that current reactors are largely unchanged from '60s designs. Not that they are bad, but there is room for improvement.
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And by the time we can afford to build this kind of system, we may have better options for energy. Hydrogen-Boron fusion looks to be very hard to achieve, but is also clean and uses fuel that we have here on earth in effectively unlimited quantities.
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I agree on the time scale issue - it just doesn't make sense to be talking about something as unproven as He3 fusion today, and time will change the rules. On H-B11 fusion: This is a LOT harder to achieve. In a magnetic confinement system there would likely be huge bremsstrahlung losses. It is also a relatively low energy reaction, so breakeven would be very difficult. It would likely take an absolutely huge reactor (possibly a single reactor that could produce a good fraction of current total power production) or a novel design.
My hunch is that, if He3 does become important, we'll get it from Uranus. It has a lower escape velocity than Jupiter, Saturn, or Neptune and there is a lot of helium in the atmosphere.