From: johncobb@ut-emx.cc.utexas.edu (John W. Cobb)
Newsgroups: sci.physics
Subject: Re: Fusion reactor disasters --- impossible
Date: 6 Apr 92 16:03:49 GMT
Reply-To: johncobb@ut-emx.cc.utexas.edu (John W. Cobb)
Distribution: na
Organization: The University of Texas at Austin

In article <FRANL.92Apr3132432@draco.centerline.com>,
franl@centerline.com (Fran Litterio) writes:
|>In article <69672@ut-emx.uucp> johncobb@ut-emx.cc.utexas.edu (John W.
Cobb) writes:
|>
|>> Moreover, you don't have
|>> nasty by products like radioactive cesium and iodine that would come from
|>> a leak. You may have some tritium and some induced radioactivity from
|>> structural components, but again, the total inventory is much smaller.
|>
|>Isn't liquid lithium forseen as the medium used to absorb the
|>neutrons speeding away from the fusion reaction?  The
|>(themodynamically) hot lithium would heat pressurized water that would
|>eventually drive steam turbines to make electricity.  Over time the
|>lithium becomes radioactive and needs to be replaced.  Being a liquid
|>would actually make it harder to manage the storage of waste over many
|>decades (in general, liquids leak, evaporate, corrode containers, etc.
|>more easilly than do solids).
|>--
|>franl@centerline.com   || Fran Litterio                               
|>uunet!centerline!franl || CenterLine Software R&D                     
|>617-498-3255           || 10 Fawcett St, Cambridge, MA, USA 02138-1110
                   
Fran, you're right on target. However, the analysis should be done in a
comparative manner. The amount of induced radioactivity from a fusion
plant, even if it used a liquid lithium blanket will be much smaller. This
is because it is induced radioactivity. With fission you have both. When you
split the Uranium, you will inevitably end up with fission by products
that will include long lived isotopes that can be readily metabolized.
With Fission you also have induced radioactivity in the strucutral
materials, the moderators, etc. However, this induced radioactivity is
much lower than the high level waste in the fission by-products. With
fusion you will only have the induced radioactivity, but not the high level
reaction by-products. So comparatively, fusion is cleaner. But make no
mistake, I wouldn't want to be in the next room when the vacuum is
breached.

I was responding to a question about radiation hazards, and I said, and
still say that a fusion plant will not have an accident scenario like a
fission meltdown --- That is a catastrophic release of MegaCurie doses.
Once on a tour of the Supercondudting Cyclotron at Mighigan State,
someone asked about hazardous working conditions because the cyclotron
and the offices were in the same building. The scientist giving the tour
noted that 2 people had been killed in the construction --- because they
had touched capacitor banks that were not fully discharged. The radiation
risks were much smaller than mundane risks which were discounted. In that
same sense, I would be scared of the liquid lithium, not so much because
of its induced radioactivity, but because of its chemical activity. 
Sometime try taking a pinch of lithium in metallic form and dropping it
in a bowl of water. Be warned to stand back and only use a small pinch.
Now most blanket scenarios (I believe) talk in terms of lithium salts
for breeding which are more stable, but at the temperatures were are
talking about, radiation would be the last of my worries if I was close
to a liquid lithium leak. Of course, it would be fair to ask about other
energy generation dangers such as how many workers have died from steam
scalding at coal and oil plants and how many will die from falling off of
roofs where solar power was being installed. These seem small, but they
might be, numerically more devastating.

finally, there should be only a little worry about long term storage for
two reasons. 1) all activity is induced thus smaller in general 2) most
radioactive components will be chemically seperated out to use as future
fuel. This is the reason to use lithium --- in order to breed tritium.

One last remark, there are scenarios and fuel cycles that would obviate
the need for a lithium blanket, in fact that is what I work on.

John W. Cobb
jwc@fusion.ph.utexas.edu