RE: Fusion Reactors

From: Iain Strachan (iain.strachan2@ntlworld.com)
Date: Sat Sep 07 2002 - 12:18:17 EDT

  • Next message: george murphy: "Re: Fusion Reactors"

    Glenn wrote:

      In 1% of the world's deuterium, there is 500,000 times=20
    more energy than is contained in all the worlds fossil fuels that will =
    ever=20
    be burned. Given what I know about world oil production, I would prefer =
    to=20
    spend our money on something that will make a difference--fusion, not =
    wind=20
    energy or a Mother Jones contraption.=20

    This is true and shows the immense potential for fusion, but you omit to =
    mention that Tritium
    is also needed for a nuclear fusion reactor, as I pointed out in another =
    post to the group.

    The problem is that the temperatures required for a sustained D-D fusion =
    reaction are far
    too high.

    Tritium does not occur naturally and has to be "bred" from Lithium =
    (something like Li + neutron ->
    Helium 3 + Tritium + neutron). I have a colleague who worked on the NET =
    design team, who is
    of the opinion that this is an immense problem, over and above the =
    problems of containing a
    high temperature plasma for long enough. (Toroidal plasmas are subject =
    to Magneto-Hydrodynamic
    instabilities, and requre complex systems of feedback coils to keep them =
    stable).

    Various breeding schemes have been explored, but none, I think, have =
    been finalised. Additional problems exist in that Tritium is extremely =
    nasty stuff, with a half life of 12.8 years.

    Another common misconception (I think) is the idea that fusion is a =
    "clean" source of energy because there are no radioactive fission =
    products to dispose of. But as my colleague from NET pointed out, =
    although the public perception is that the fission products (i.e =
    high-level waste) is the real problem, in fact the real problem is the =
    huge amounts of low-level waste that still have to be disposed of. For =
    example, the JET experiment is encased in 2.8 m concrete walls, to =
    contain the neutron radiation. A gap in that wall would have caused an =
    instantly lethal dose of neutron radiation on the site perimeter fence =
    during a fusion shot. Hence, eventually the concrete will have to be =
    disposed of, and the amount of such waste is comparable with a fission =
    reactor. I'm all in favour of fusion, but don't get any ideas that it's =
    a clean source of energy.

    It's my feeling that scientists continually underestimate the difficulty =
    of solution of the problems that
    are considered subsidiary to the main target (i.e. to get sustained =
    fusion). This syndrome occurred
    with the Prototype Fast Reactor (PFR) at Dounreay. As I recall, there =
    was absolutely nothing wrong
    with the basic physics, and the reactor core worked perfectly. It was =
    at this stage that the beaurocrats
    in the funding bodies decided that since they'd cracked it, that funding =
    would be cut. As a result corners
    were cut in the conventional design of the cooling systems, and they =
    never worked reliably. The problem
    being that a fast reactor requires liquid sodium as the primary coolant, =
    and water as the secondary. =20
    If water hits liquid sodium it's major bad news. As I recall it was the =
    welds in the secondary heat exchangers
    that caused problems, and this was down to cutting corners in the =
    design. People ended up getting PhDs studying
    the weld problems in the secondary heat exchangers!

    I say all this to reinforce the case; one must put proper funds into it =
    at the moment. Current experiments are just aimed at getting the fusion =
    working (I understand that TFTR at Princeton has now overtaken JET in =
    length of fusion shot). But it takes so long for all the other =
    technology problems to get solved that we must act now. I doubt if it =
    will happen; the cost of experiments is so high, that it requires =
    international collaboration big time. The NET experiment never =
    materialized, because Europe isn't big enough to put in all the funds =
    required. There is talk of ITER, which is a collaboration of several =
    countries (something like Europe, Russia, America, Japan). The problem =
    is that for such long term projects, there is never the political will =
    when governments are short term.

    Iain.

    (Excuse the post from a different email from the one that I'm subscribed =
    to. I set up the Eudora mail account for posting to public forums but =
    have found that there are delays of over 48 hours on incoming mail. I =
    shall in due course change over to a hotmail account).



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