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Combine fusion reactors with fission reactors

  1. Jan 28, 2009 #1
    I have long wondered if you could combine fusion reactors with fission reactors. After all fusion produces large numbers of neutrons which can drive fission reactions. Then I saw this:


    So will this work? Is a combination of PWR and these things likely to get a fuel cycle as efficient as the fast breeders? Can it burn the sterile plutonium? Could it burn thorium?
  2. jcsd
  3. Jan 28, 2009 #2


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    Re: Fusion/Fission

    D+T fusion produces fast neutrons (14.1 MeV), so there has been thought about using U-238 blankets to produce Pu-239, as well has heat. The blankets could be cooled by Li, and the heat transferred to a conventional steam Rankine cycle.
  4. Jan 28, 2009 #3
    Re: Fusion/Fission

    ppnl - I don't think this particular design is intended to produce power - it's just waste disposal, transmuting minor actinides and some fission products with fast neutrons from D-T fusion.

    But the concept of fusion-fission hybrid power reactors is sound. A closely related idea is an accelerator-driven subcritical reactor, which uses a spallation neutron source (proton accelerator aimed at a heavy metal target to produce neutrons) providing fast neturons to "drive" a fission reactor that is otherwise in a subcritical state. (This also goes by the name "energy amplifier", because the fission reactor produces more than enough energy to power the accelerator that drives it). The point is, the neutron spectrum is very hard (because of the spallation neutrons), so you get efficient transmutation like in a fast reactor, or better.


    There's a review paper by the NEA:

    Accelerator-driven Systems (ADS) and Fast Reactors (FR) in Advanced Nuclear Fuel Cycles

    I suppose a fusion-fission hybrid would be similar to an ADS, with fusion providing fast neutrons to drive a subcritical mass of fissile isotopes. I don't know about the relative advantages of the three different methods (ADS, FR, fusion-fission), but fusion has hotter neutron spectra than all fast fission reactors, so it's probably more efficient at transmuting the minor actinides.
    Last edited: Jan 28, 2009
  5. Jan 29, 2009 #4
    Re: Fusion/Fission

    But if you burn up all the left over uranium and plutonium how can you avoid producing energy? It seems no different than a fast breeder in fuel requirements and even seems to allow a wider range of possible fuels. But breeder reactors have a history of problems and may take a very long time to bring to market. I have no doubt that they can work and if nothing better is found the should be built. But would the fusion/fission system be less complex and easier to bring to market? And can it burn thorium directly?

    The problem with accelerator driven reactors is that they use a great deal of energy to produce the fast neutrons. I'm basically viewing the fusion/fission reactor as a more efficient way to produce those neutrons.

    Also this could be a gateway technology for developing a full fusion reactor. Many of the problems you have to solve are the same. You just don't have to solve them completely all at once before you have a working reactor.

    And you have the advantage that you can sell them to the public as waste incinerators initially.
  6. Jan 29, 2009 #5


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    Re: Fusion/Fission


    You are correct - if you burn up the left over uranium and plutonium - you will get energy.

    As far as breeder reactors; Argonne's Integral Fast Reactor is an interesting design that actually
    made it to the prototype stage before it was cancelled in 1994:


    Another fusion / fission hybrid idea is Lawrence Livermore's LIFE project:



    Dr. Gregory Greenman
  7. Jan 30, 2009 #6
    Re: Fusion/Fission

    Yes I really like the IFR but it has political baggage that may make it hard to bring to market. I was wondering if Fusion/fission could be ready to go in a shorter time for less. And how would the reprocessing procedure compare to IFR? If there is no time or complexity savings with fussion/fission then I say full speed ahead with IFR.

    We need to stop burning coal by the cubic mile and at the same time we need to get as many plug in hybrids on the grid as possible. I just can't see wind power as anything but a minor player. Solar has more potential because it has output during peak demand. But it still isn't on demand power. Nuclear is the only technology that has any chance of delivering the power we need any time soon. We can either use it or we can turn out the lights and starve in the dark.
  8. Jan 31, 2009 #7


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    Re: Fusion/Fission


    The IFR uses metal fuel so that the reprocessing step is actually a metalurgical process rather than a
    chemical separation. Specifically, the IFR reprocessing step consists of "halide slagging" and electrorefining.
    The whole idea was to make the reprocessing step as simple as possible so that reprocessing can be done
    on site. Many potential nuclear utilities would balk if they had to operate a chemical reprocessing plant.
    The metalurgical reprocessing was meant to be simpler for the operator.

    As far as nuclear being the only technology; you are echoing the words of Dr. Patrick Moore:


    Nuclear energy is the only non-greenhouse gas-emitting power source that can effectively
    replace fossil fuels and satisfy global demand.”

    —Dr. Patrick Moore, PhD

    as well as the Directors of the Dept. of Energy's national labs including our new
    Secretary of Energy Dr. Steven Chu:


    Dr. Gregory Greenman
  9. Feb 1, 2009 #8
    Re: Fusion/Fission

    Yes I understand that. But wouldn't you use a version of the same process to prepare nuclear waste for burn up in a fusion/fission device? But a fusion/fission device never has to be close to a critical mass because it is driven by fusion neutrons. Maybe you could make it even simpler.

    I said it first! It was clear to me from the beginning that nuclear power is the only hope for freeing us from fossil fuels. And there are sufficient geopolitical reasons for doing this without even considering global warming. The fact is we could have got a very good start on this for far less than the cost of the Iraq war.

    The Obama seems to have picked a very good science team. I hope he listens to them. And if he does I hope others listen to him.
  10. Feb 1, 2009 #9


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    Re: Fusion/Fission


    Yes - Obama has made a very good pick in Dr. Steven Chu as Secretary of Energy.

    On the other hand, he has also picked Carol Browner to be his "energy czar". Browner was the
    EPA Administrator during the Clinton Administration and is anti-nuclear.

    President Obama has said that he likes people with strong opinions - and it just may be
    President Obama's "style" to pick a pro-nuclear Secretary of Energy and an anti-nuclear
    "energy czar" - and let them "duke it out"; with Mr. Obama making the final decision.

    If that's the case; then I hope President Obama makes the decision in favor of nuclear power
    for the good of the USA. After all; the two protagonists are NOT equally matched - Dr. Chu
    is a scientist and a Nobel Prize winner and Browner is a lawyer.

    We'll have to wait and see what type of decision our new President makes.

    Dr. Gregory Greenman
  11. Feb 2, 2009 #10
    Re: Fusion/Fission

    Fusion hybrid machines could become reality very soon. By making the power output very small the materials problems are drastically reduced and the equipment needed is all available now (with improvements to industrial service levels). Being rich in neutron production even small machines can do useful work including destruction of fission wastes and breeding fuel for fission reactors.
    I refer you to our paper, R. Galvao et al, IAEA Fusion Conference, October 2008, Geneva, for technical details. The paper also shows why fuel breeding is NECESSARY by 2035 or so to maintain any rapid growth of fission power. PM me for a copy of this and to go on my mailing list for other web papers. The paper is by an international team from Brazil, China, Russia, and UK. China is very enthusiastic about this and plans for 1500 fission reactors by 2050 are under discussion.
    We hope this sort of work will emerge as major part of the solution to our energy and climate change problems.

    Last edited by a moderator: Mar 12, 2009
  12. Mar 12, 2009 #11
    Re: Fusion/Fission

    how do they propose to create the fusion reactions???
  13. Mar 12, 2009 #12
    Re: Fusion/Fission

    The Fusion cores we propose are based on the Spherical Tokamak with a strong toroidal magnetic field around 3.5Tesla and a toroidal plasma current of about 4MAamps in a vessel with a major radius of 2-2.5m. This is mainstream magnetic fusion but with a much more tightly wound magnetic field than the huge ITER class machines. Neutral beam heating at 150keV is adequate to support a fusing 10keV plasma and is available off the shelf. This contains higher pressure plasma and also helps stabilise microinstabilities. This performance - MAST @Culham and NSTX@Princeton - is adequate to produce 20-50MW of Fusion power, not much for electricity production, but the neutrons can then be put to work. The fusion neutron flux to the first wall is around 0.25MW/m^2 and gives a decent lifetime against neutron damage for current steels.
    A pre-cursor to the IAEA paper is my paper on Fission and Fusion hosted by General Atomics at http://gt-mhr.ga.com, on a link at the foot of this page. This lays out the argument as to why Fusion is now Necessary for a big nuclear program.
    I also recommend to you a new book by David Mackay on Sustainable Energy without the hot air. It is weak on nuclear and useless on Fusion but an outstanding compendium of all the formulae and analysis you need to see how all other contributors to our energy future will really perform. Try Amazon.

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