Nuclear Fusion question

From: Iain Strachan (
Date: Mon Sep 04 2000 - 12:28:01 EDT

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    On Tue, 03 Sep 2002 15:44:13 John Burgeson wrote:
    >Glenn -- you have a lot of data on how the oil supply is running out.
    >Do you (or anyone) have any ideas on when Nuclear Fusion will replace it?

    I used to work for the UK Atomic Energy Authority Culham laboratory,
    which was the main lab for research on Nuclear Fusion, and the host
    site for the European JET experiment.

    It appears that Fusion is a very long-term prospect, and though I've
    not worked there for over 10 years, I think it's still very much a
    moving goal-post.

    In the '50s an experimental reactor called ZETA was built at Harwell
    (the sister lab of Culham), and early experiments led scientists to
    believe that they had actually achieved sustained Nuclear Fusion, and
    that it was only a short while before it could be realised as a
    useful power source. As it turned out, what they had observed was
    not due to Nuclear Fusion, but due to impurities in the plasma.

    The JET experiment finally achieved sustained Nuclear Fusion in the
    90's with a D-T fusion reaction. The original plan was for there to
    be a successor project NET, somewhere else in Europe (JET stood for
    Joint European Torus, and NET stood for Next European Torus).
    However, that has never materialised, and as a consequence JET's
    lifetime has been extended to well beyond the project end date. The
    original reactor shell was only designed to be able to run a limited
    number of Fusion shots (with radioactive products from the D-T
    fusions), before it would have to be dismantled. Since the lack of a
    successor project meant extending the project, the use of the
    facility is confined to H plasmas, without Fusion, to better
    understand the problems involved in containing a high energy hot

    However, that is only a subset of the problems that have to be
    solved. The next obvious problem is how to power the magnetic
    containment coils. The JET coils consumed a vast amount of energy
    (requiring a sub-station from the local Power Station to avoid
    dropping the power from the grid). There would be no way to get even
    break-even in the energy produced. (And that was not the intention
    of the experiment). A commercial fusion power plant would have to
    use Superconducting coils. Another problem is the choice of a
    suitable material for the vacuum vessel. As it stands, the JET
    vacuum vessel has a limited lifetime, during which it gets intensely
    radioactive from the neutron radiation given off from the DT
    reaction. A power plant would have to use a material that didn't get
    excessively radioactive when bombarded with neutrons. And finally,
    there is the problem of breeding of the Tritium necessary for the
    reaction (A D-D fusion is not practicable, because the temperatures!
      etc are even higher). This would be done by breeding from Lithium,
    which would have to be embedded somehow in the vacuum vessel, and
    recycled etc.

    So, there are a host of technology problems above and beyond the
    sustaining of the nuclear reaction. When asked how long it will
    take, I think people usually say 50 years to a demo power station.
    But they've been saying the same for 20 years.

    Possibly there's someone else on the list more up-to-date than me on
    what happens next?


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