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Future fusion vs future fission

  1. Nov 14, 2011 #1

    Ryan_m_b

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    This question was borne out of a discussion with a friend. We were talking about meeting future energy demands and we both think a predominantly nuclear approach supplemented by renewables and energy saver (i.e. cavity insulation for all houses) technologies would be desirable. When the conversation came to implementing fusion reactors if they prove viable we stumbled upon the fact that speculative generation IV nuclear fission reactors have about the same estimated time frame for development and implementation and offer great advantages. Which begs the question; presuming that projects like ITER/DEMO succeed in generating commercial fusion will there be that much of a competitive advantage over generation IV reactors? Neither of us are experts and so couldn't judge whether or not our answers would have made sense.
     
    Last edited: Nov 14, 2011
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  3. Nov 14, 2011 #2

    mathman

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    In the long run fusion is preferable. The main reasons are the problems relating to waste disposal and accidents (Fukushima), which are serious problems for fission.

    However for the last 50 years or so fusion has always been 10 years away.
     
  4. Nov 14, 2011 #3

    Drakkith

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    As Mathman said, the main things are safety. Fusion reactors cannot go critical in any way like fission reactors can. There is also very little contamination compared to fission if there is an accident, and long term waste is greatly reduced. So I wouldn't say there much of a COMPETATIVE advantage in terms of cost and time, but in safety it is much better.
     
  5. Nov 15, 2011 #4

    Ryan_m_b

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    Good points guys, I'd thought of the meltdown and waste advantages but had heard that the likelihood and level of both these things could be significantly less in gen IV reactors. Whilst that's still not better on paper than fusion I wondered which one would be more economically viable when/if they both arrive.
     
  6. Nov 15, 2011 #5

    mathman

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    Since no one has developed a working fusion reactor, addressing economic questions is a long way off.
     
  7. Nov 15, 2011 #6
    in the long run we'll all be dead. Right now, we have fission and fossil.
     
  8. Nov 15, 2011 #7

    Drakkith

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    And that contributes to the thread how?
     
  9. Nov 15, 2011 #8

    Ryan_m_b

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    Speak for yourself :tongue: some of us are still young enough to be asked for ID

    EDIT: Also; +1 to what Drakkith said
     
  10. Nov 18, 2011 #9

    cmb

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    'Slow' fission reactors appear likely to have a relatively short 'lifetime'. OK, beyond our graves perhaps, but only just. For fission power to be useful for the next 10,000 years we'd need 'fast' fission reactors. Some attempts have been made to make these commercially viable, but too many political machinations have seen the back of those come and go.

    One such venture, Superphénix, well-demonstrates some of the political issues of running a reactor that produces weapons-grade plutonium as an intermediate product! (Yes, don't forget the issue of proliferation - probably a bigger issue than disposal, just at the moment.)

    An excellent article that covers some of this is available at IEEE; http://spectrum.ieee.org/energy/nuclear/nuclear-wasteland/0 . Well worth a read!

    Beyond 10,000 years, I'd say [just an opinion] we either have fusion power, or what we know as industralised societies will break down and fail, and the necessary 'critical-mass' of industrial infrastructure will never be recovered again. Perhaps we might get to that point earlier, anyway! (Especially if we don't get fast breeder reactors up and running in the next 100 years.)
     
  11. Nov 18, 2011 #10
    The obvious answer is that policy would swing in the direction of fusion. Look at the money government has invested in solar power over the years. It's nowhere near cost effective in most areas but the appeal is undeniable. If fusion reactors could actually be built, activists and politicians would insure their integration. Assuming they were prohibitively expensive at first, I'm guessing a working fusion reactor would cause the DOE and other agencies around the world to start pouring funding that way.
     
  12. Nov 19, 2011 #11

    Morbius

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    Just because a reactor is a fast reactor does NOT mean that it is a proliferation problem.

    Argonne's Integral Fast Reactor (IFR) is a fast reactor and as Dr. Till explains in the Frontline interview below, it is impossible to make weapons from IFR waste:

    http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/till.html

    Q: Now, what about the issue of proliferation, the issue of making plutonium available to terrorists?

    A: The object in the IFR demonstration was to invent, if you like, a process that did not allow separations of pure plutonium that would be necessary for weapons. In order to recycle, you need some kind of a chemical process. And the chemical process that was invented here at Argonne used quite different principles than present processes do. It allows the separation of that group of things that are useful, but not one from the other, so that you cannot separate plutonium purely from uranium and the other things. You can separate uranium, plutonium, and the other useful things from the fission products. So it does exactly what you want it to do. It gives you the new fuel, and it separates off the waste product, but it doesn't allow careful distinguishing between the materials that are useful, such that you could use one or another of those materials for weapons.

    Q: So it would be very difficult to handle for weapons, would it?

    A: It's impossible to handle for weapons, as it stands.

    It's highly radioactive. It's highly heat producing. It has all of the characteristics that make it extremely, well, make it impossible for someone to make a weapon.


    Greg
     
  13. Nov 20, 2011 #12

    cmb

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    Thanks, but I did not say it did. Please do read what I wrote, and don't read more than I wrote.

    All I said was that i) there are political issues running a reactor that makes weapons-grade plutonimum, and ii) a reminder to mention the proliferation issue. Do you contest one or both of these? I posited no exclusion that alternative designs could not be constructed.

    Hat-tip to you for posting a follow up expanding the point on new designs.

    The issues of (ii) are what prompted the IAEA to come into being, after all, and needs to be raised in respect of this thread's topic. My purpose of linking to the excellent IEEE article was so that people can read a good piece on the issues for themselves.
     
    Last edited: Nov 20, 2011
  14. Nov 20, 2011 #13

    Morbius

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    cmb,

    Yes - the whole idea of reactors as proliferation opportunities is way overblown by the anti-nukes. The AEC ran a nuclear test in 1962 with some low-burnup spent fuel from the
    UK, and said that although a bomb could be made from "reactor grade" fuel, the only way to
    do so is using techniques that nascent bomb-designers wouldn't know.

    The AEC used low burnup fuel from the UK at a time when reactor burnups were about
    25,000 Mw-Days/metric tonne. The DOE declassified this fact in the late '70s when reactor discharge burnups were about 40,000 Mw-Days/metric tonne.

    Currently, reactors can get 55,000 to 60,000 Mw-Days per metric tonne burn-ups. The higher the burn-up, the greater the percentage of undesirable Pu-240 and Pu-242 in the fuel that can cause a nuclear device to fail.

    About 4 decades ago, it was an "iffy" proposition with fuel that was less than 25,000 Mw-Days /metric tonne. Today's burnups are more than twice that; so the issue of spent reactor fuel being a proliferation opportunity is really a "red herring".

    Greg
     
  15. Nov 20, 2011 #14

    cmb

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    ? So do I understand your 'yes' above to mean you do contest my points!?

    That you are contesting that the issue of the proliferation of nuclear fission material is a political issue!?!? :eek:

    I am sure that on your planet, you have overcome these hurdles to make nuclear power common-place! But I can assure you that here on earth the simpleton humans do put politics square in the frame when considering nuclear energy!!
     
  16. Nov 21, 2011 #15

    Morbius

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    It's really not a political question, but a scientific one. The question is whether having a nuclear power reactor and access to the waste therefrom helps a country to get nuclear weapons. The answer to that is no.

    The country could build a "production reactor", and run it with a low-burnup cycle - that is to stop the reactor frequently to refuel. That certainly can be done; because that is how the USA obtained its "weapons-grade" plutonium from specially built "production reactors" at Hanford, Washington and Savannah River, South Carolina.

    However, if a nation attempts to do that; we would have irrefutable proof that they are attempting to build nuclear weapons in violation of the Nuclear NonProliferation Treaty.

    The problem is whether a nation can develop nuclear weapons clandestinely by hiding the plutonium making operation by making it look like commercial nuclear power; and thereby avoid the crippling sanctions that would ensue if their true motives came to light.

    That I do NOT believe is possible.

    Greg
     
  17. Nov 22, 2011 #16

    cmb

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    I think you have read my initial reply out of context of the original question.

    My point being that if we had fusion or advanced fission then neither would win-out in a fair head-to-head technological competition, because politics would be used (righty or wrongly) by those with respective interests in each.

    I was claiming the above by the example of fast breeder reactors. I mean, just look at the reality! - fast breeders are a 'known' science, we know they can be made to work. We know we could have on-line fast breeder electrons surging through the world's electrical grids within a few years if the technology was allowed to evolve. Yet there is no funding for those to develop the technology to commercial viability, instead there is a vast budget to fusion instead which, even by the existing timetable of ITER and DEMO, will be 50 years before we see fusion-energy driven electrons on the grid....

    ... and, yet, do we need more [fossil-fuel-free] power now, or in 50 years? So which technology should be funded more urgently?

    So my point is that, wrt OP's question, 'competetive advantage' between fission v fusion is clearly not the deciding factor today, and we can only guess about when/whether it will ever be in the future.
     
  18. Nov 27, 2011 #17
    Sadly, I don't believe any more that fusion in a tokamak is clean. Far less seducing then.

    It's not only the worry of fast neutrons activating the torus' walls.

    You have an ugly story, not well known to the public, but which tokamak developers are very aware of. Fusion reactors will have to breed their own tritium, which needs a neutron multiplier. The only practical way (at present, it looks like the only way at all) uses lithium as a tritium source and lead as a neutron multiplier, and alas, fast neutrons impinging lead create radioisotopes.

    I tried to evaluate the activity produced by very few reactions, and found it to be close to the activity uranium fission produces for the same heat output.

    I didn't find very long-lived waste like Pu, but by hand estimates I could only check half a dozen reaction rates among the most obvious ones. If checking successive spallations and neutron absorptions, including the less abundant products, expect to find long-lived waste as well.

    This does not apply to other fusion methods whose more extreme conditions enable reactions without tritium.
     
  19. Nov 27, 2011 #18

    Drakkith

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    Yes, it is known that fusion via D-T in a Tokamak produces radioactive waste. However a fusion reactor is still FAR safer than a fission one. There is literally zero chance of a meltdown or other catastrophe on a similar scale. There is no chance of proliferation and waste disposal doesn't have to plan ahead on the order of thousands of years like fission.

    Fission reactors are generally seen as much cleaner and safer than fossil fuel plants, and if fusion is even better than fission, then it is a very attractive power source if we can get it to work.
     
  20. Nov 27, 2011 #19
    By you maybe, but this doesn't mean "generally"!
    And not everyone is willing to accept the "nuke or hydrocarbon" story. Geothermy, thermal solar, wind... all are usable and nearly cheap as of now.
    Uranium is a fossil energy.

    As for long-lived radioactive waste at fusion reactors, I'm confident there will be, and enough to be a worry. Just simulate it properly, you'll certainly find some.

    And for proliferation: plenty of tritum in it!
     
  21. Nov 27, 2011 #20

    Drakkith

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    While I'm sure it's arguable, as everything is, I have never heard or seen differently from anyone who knows much about nuclear power. It is *usually* people who have little knowledge of nuclear power that have problems with it. At least in my limited experience.

    All of those have their own problems to deal with, both in use and in manufacturing. And uranium is not a fossil energy to my knowledge.

    Of course there will be enough to be a worry. Just not the same as we worry about current nuclear waste. Also, there is not enough tritium inside the reactor at one time to do anything with and, as far as I know, it will not be stored anywhere, instead it being burnt soon after production. And even then, tritium by itself is useless. You can't make a thermonuclear warhead with just tritium-deuterium alone, you need a regular nuke to provide the required compression and energy.
     
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