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