In response to a question about fusion reactors, Joel Cannon wrote, in part,
" This shielding whatever it is will be highly radioactive after it is
finished. The half life of the shielding radioactivity will be less than
that of plutonium but still significant (I believe we are talking hundreds
of years)."
If memory serves me correctly, some of the materials used in the pole pieces
contain Nb and, upon neutron activation, produce isotopes with half lives
longer than "hundreds of years."
Wayne then responded, again in part, "If fusion yeilds waste products that
only have a half life of a few hundred years, that is not bad at all! The
main issue with fission reactors is that the waste products have to be
stored for hundreds
> of thousands of years. That's approaching geologic time scales. There
> are
> no truly "safe" places to put the waste."
>
I beg to differ. Most of the fission and activation products in used fuel
and reactor components have relatively short half lives. A relatively small
number, including some Pu isotopes, I-129, and Tc-99 have half lives in the
order of 100,000 years. Yes, they have to be disposed of and, at this
stage, the international consensus is that geological disposal is the
prefered option. It does not matter all that much what host rock is
selected, be it tuff (US), salt (US, Germany), clay (Belgium, France,
Hungary) or granite (Canada, Sweden, Finland, Korea, China). The approach
is to use "defence in depth and I will use the Canadian concept as an
example, although most national programs use a similar approach. The highly
insoluble ceramic fuel (UO2) encapsulated in zirconium steel fuel sheaths is
further encapsulated in titanium alloy, or copper containers. These
containers are in turn surrounded by a swelling clay/sand mixture that will
expand when contacted by water and disposed off in granitic rock at a depth
of 500 - 1000 m.
There is sufficient evidence from experimental program and natural analog
studies that this is acceptably safe. I use the word "acceptably" because
nothing is "truly safe." Airplanes are not "truly safe," yet most of us
accept the risk of flying because the benefit is greater. As for natural
analogs, I can mention the natural reactors at Oklo, Gabon, the high-grade
uranium deposit in Cigar Lake, Saskatchewan, that has resisted dissolution
over the last billion years (sorry, YECs). Another analog is the copper
canon from a Swedish warship that sank soon after launching off the coast of
Sweden and that, upon retrieving from brackish water and clay some 300 years
later, showed very little corrosion.
Compare the care, attention, and money dedicated to the disposal of nuclear
fuel waste with the lack of attention is disposing of fly ash from
coal-fired power stations. Compare it to the way we casually toss out old
smoke detectors that contains Am-241, or Coleman lantern mantles that
contains ThO2.
I've spent the last twenty or so years researching nuclear waste disposal.
It's not a trivial matter, but disposal is not all that difficult and it is
possible to do so safely.
I think the worst thing to do is to leave the waste as a legacy for our
children to deal with. We've already used up the most accessible resources
as it is and we are leaving the next generation not only depleted resources,
but the trash as well. I don't think that this is a responsible way of
doing things.
Transmutation, IMHO, is another pipe dream. For starters, it will taken an
enormous amount of energy (some think that the energy needed to transmutate
the waste will generate more waste than it will transmute, so this would be
a non-win situation). In the second place, not all the waste would be
transmuted because, as the waste is transmuted, there are progressively
fewer targets to hit and, so, the problem would remain.
Wayne, I'm with you in the hope that God will provide. On the other hand, I
don't think we've always been good stewards of what He has given us.
Chuck Vandergraaf
Pinawa, MB
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