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Problems with Nuclear Fusion

  1. Feb 24, 2013 #1
    Nuclear power plant which use of fission process have been made but why not fusion power plants, what affect its feasibility ??
     
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  3. Feb 24, 2013 #2

    Simon Bridge

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    This is an active area of research.
    So far, nobody has been able to produce a controlled fusion reaction that outputs the same (or more) energy than it uses. A quick google will show you lots of things that have been and are being tried.
     
  4. Feb 24, 2013 #3
    It is thought to require millions of degrees for several seconds.
     
  5. Feb 24, 2013 #4

    Astronuc

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    The fusion process has yet to be perfected.

    There are various efforts ongoing, particular the international program, ITER, near Cadarache.
    www.iter.org - ITER is under construction in southern France adjacent to the CEA Cadarache Research Centre, located in the commune of Saint-Paul-lez-Durance.

    http://www.ccfe.ac.uk/ - Abingdon, Oxfordshire, UK

    http://www.pppl.gov/ - Princeton, NJ, US

    https://fusion.gat.com/global/Home - General Atomic, CA, US

    and others

    Most experimental systems have been exploring ways to heat and stabilize the plasma. Along the way, they have also discovered the challenges of confining plasmas long enough to sustain a fusion reaction.

    Other attempts have been made with inertial confinement, which currently looks pretty dismal. https://lasers.llnl.gov/
     
  6. Feb 24, 2013 #5

    Simon Bridge

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    Muon catalyzed fusion does not require such high temperatures - it's use for power generation keeps coming up but afaik nobody has made much headway. The trouble there is that muons don't last and they cost a lot to make.
     
  7. Feb 24, 2013 #6
    but these r only 4 experimental purpose and can't be used for energy production ( googled some stuff ).....anyway thanks for the help.
     
  8. Feb 24, 2013 #7

    Astronuc

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    Yes - they are ongoing research programs. The objective has been, and still is, to develop fusion to the point where it is commercially viable. That objective has proved elusive over the last 6 decades. If it was so simple, we'd have commercial fusion plants.

    Sustained confinement of fusion plasmas has not yet been achieved such that fusion is ready for commercial application. The research has however been moving in that direction, albeit rather slowly. The objective of ITER is to approach the minimum conditions for sustainable fusion, however, it could very well fall short of commercial viability.
     
  9. Feb 24, 2013 #8
    i understood that it requires about 10 million K to initiate a fusion reaction but since the energy output is not high as the input it would not initiate further reactions......so what is meant uncontrollable reaction

    To explain my doubt-
    Suppose energy input for fusion= x
    and energy output = y
    and as I have found on google x>y, as technology developed till now allows
    hence the output from one reaction would not b sufficient to initiate another reaction since required energy will be x but energy available will be y only

    so there is no need of controlling it unlike fission reactors where moderators are used to slow down neutrons...isn't it
     
  10. Feb 24, 2013 #9
    so after these all experiments have been done, is there any chance to use the same technology to make commercially viable plants in near future
     
  11. Feb 24, 2013 #10

    Astronuc

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    If ITER is successful, then perhaps there is a chance - depending on how successful the experiment is.
     
  12. Feb 24, 2013 #11

    Simon Bridge

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    The question asked was "why not fusion plants" and these examples show you why not.
    I'm making a (somewhat glib) reference to thermonuclear weapons. This approach to getting a fusion reaction works but is not feasible for power generation for, hopefully, obvious reasons.

    Anyway - you don't have to have a chain reaction for the a thing to be uncontrollable.
    Women and cats spring to mind...
     
  13. Feb 24, 2013 #12

    mheslep

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    ... muons cost a lot of energy to make, relative to the energy resulting from the fusion process.
     
  14. Feb 24, 2013 #13
    Joint European Torus
    http://en.wikipedia.org/wiki/Joint_European_Torus
    "Lifetime of the plasma: 5–30 s"
    This is more than enough. For ITER this parameter should be even longer.
    The problem more in the achievable temperature. As density is also enough but reactivity of plasma is still low due to low temperature achieved.

    ITER has projected Plasma Internal Energy about 520 MJ and total Heating Power about 70 MW. Neglecting energy losses they need 520 / 70 = 7.4 sec for increasing internal energy till required value.
    More power will turn TOKAMAK out from stability area. That is a real problem.

    Also neutral beam injection NBI is technically inconvenient for practical reactors way as assumes the direct connection of gas filled "neutralizer" with vacuum camera (reactor vessel).
    http://www-users.york.ac.uk/~bd512//teaching/media/mcf_lecture_08.pdf See Figure on page 19
     
  15. Feb 24, 2013 #14

    Astronuc

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    30 s does not a commercially viable reactor make. Try 30 days, then 30 months, and even 30 years with a capacity of greater than 0.90, and preferably greater than 0.95.
     
  16. Feb 24, 2013 #15
    TOKAMAKs always (from the beginning till now) was thought as pulse machines. Recall that current required there for creation of poloidal field is an induced current and therefore is a pulse current.
    But now modern TOKAMAKs start driving current by conventional for them induction mode and then current is driven by neutral particles beam (the so called "beam driven current").
    This allows prolongation of pulse (desired goal in 70s of last century was about 1 s, Lawson criterion (double product) was counted as IIRC 1.5E20 sec/m3 and this parameter has been achieved) and also allows running in so called “H-mode” (high confinement mode discovered in IIRC 1986 in German TOKAMAK.
    ITER is indented for longer pulse then 30 sec - approximately 1000 sec. But in either way machine is indented to run "pulse by pulse" or "shot by shot".
    As result pulse neutrons flux bombard lithium blanket with releasing more energy from "n+Li6" reaction from where coolant takes that energy for running e.g. then steam turbines in nonstop mode.
     
  17. Feb 25, 2013 #16

    Simon Bridge

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    Just in case someone thought I meant the dollar cost? Fair enough.

    I didn't want to write too much in case nobody was interested. Considering the rest of the thread - it seems nobody is :) I suppose readers should also be aware that the experimental break-even point is just where energy in matches energy out ... a power reactor needs to do better if it is to provide it's own operating power, and a commercially viable reactor even better since it has to make a profit.

    I was more interested in pointing to an example of low-temp fusion that wasn't junk science.

    Fusion does not have to involve very high temperatures but:
    1. the high temperature projects look like they have more promise these days
    2. there is a lot of junk and pseudo-science around low-temp fusion ideas to trap the unwary investor.
     
  18. Feb 25, 2013 #17
    Not all fusion research is for power. More than a few fusion dollars go into weapons research. For example it is the main mission of NIF fusion lab in America. I wonder what percentage of the total fusion budget is split this way.
     
  19. Feb 25, 2013 #18
    Power generation is much significant challenge than task of improvement (and not creation) of weapons that never be used and huge inventory of which is already in existence.
    Simply, low energy efficiency of today's lasers (not more than 1%) defines impossibility for NIF program to enter in power generation sector. Simply you should pump into the laser 100 J for pulse energy 1 J that goes to the thermonuclear target (hohlraum) which at Q=5 gives you fusion energy 5 J which then should be converted into the electricity with 50-60% of efficiency. So, in the best case spending 100 J you gain 2.5-3 J.
    We need go two ways for laser inertial fusion:
    1. To improve efficiency of laser at least on order of magnitude
    2. To improve Q factor of hohlraum on 1, 2 and better 3 orders of magnitude.
    Both these ways have some difficulties and at today's level of technology have very limited opportunities of further improvement.
    But people involved in NIF say that they can simulate the weapon. And they've got financing from the DOD in excess of DOE. I think that only this is the reason why NIF is considered as weapon program.
     
  20. Feb 26, 2013 #19

    Simon Bridge

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    There are lots of reasons to study fusion besides energy production and weapons development - but I bet those are the big payers.
     
  21. Feb 26, 2013 #20
    I doubt on "a lot".
    There is one reasonable at least for me reason why NIF is considered as weapon program – less promising for power generation approach found some financing from the DOD.
    And there are many other examples of financing of useless things by Governmental organizations.

    Can you mention one more reason of usage fusion except power generation or weapon?
    Space traveling? Actual?

    We live in the end of oil era, when risk of big nuclear conflicts are neglectable with increasing risks of asymmetric conflicts in which technology advanced countries fight with outdated combatants and therefore only power generation is significant for us today.
    Because of it DOE and similar other organizations are the best payers. And not for example NASA and DOD.
    DOE pays billions, DOD millions, while NASA thousands.
    That is only priorities issue.
     
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