|Aug2-07, 01:17 PM||#1|
Reusability of Radioactive Waste?
I was doing a little research, and found out that 95% of fission radioactive waste is High Level Waste. Of course this waste is very dangerous, but it emits so much energy in radiation, can't we harness it in, say, a radioisotope thermoelectric generator and hook it up to the power grid?
I have heard arguments that the really radioactive stuff have short half-lives, and so disappears pretty quick. Also, i've heard that a lot of the waste is only moderately radioactive, not radioactive enough to generate much electricity, but bad enough to endanger life.
Obviously I am not a nuclear physicist, and the idea is so obvious they would have done it already were it feasible. But I can't see any problem here.
|Aug2-07, 04:26 PM||#2|
I don't know where you did your research - but 95% of the waste is NOT High Level Waste.
About 95% of the spent reactor fuel is Uranium-238; that is no more radioactive than the
day it was dug out of the ground. From the British Parliament, House of Commons report:
Spent fuel is about 95 per cent U-238 but it also contains U-235 that has not fissioned,
plutonium and fission products, which are highly radioactive.
Uranium-238 has a half life of 4.5 Billion years. The longer the half-life the weaker the
radioactivity - the decay rate. U-238 has a half-life of 4.5 Billion years because it decays
so slowly - hence it is not very radioactive. In fact, U-238 is almost stable. [ A stable
element would have an infinite half-life.]
No - the high level waste is the fission products; the remnants of the Uranium-235 which
is the fuel [ not the U-238 ]. The fresh fuel has only about 3% U-235; so the spent fuel
is about 3% high level waste by mass.
It's the anti-nukes that keep going around saying that the major component of nuclear
waste is high level and that if we reprocess it - then that will create even more waste
than before. [ They want to stop reprocessing - and "constipate" the nuclear fuel
cycle which is what they did in the USA.]
In actuality; if you reprocess the waste - you can separate out the 95% that is U-238
which does NOT require Herculean efforts to store. If you separate out the 3-5% of the
waste that really does need to be isolated - then you've reduced the amount of waste
by a factor of at least 20.
You are correct that the really radioactive waste decays away quite rapidly. We really
don't need to store waste for millions of years or whatever the "scare story" du jour
states. Some isotopes like Plutonium-239 which has a half-life of 24,000 years is
present in the waste stream. But it doesn't have to be - if you reprocess - you send
the Pu-239 back to the reactor as fuel so that you don't have a 24,000 year half-life
That U-238 is of no concern. First the radiation from U-238 is "alpha" radiation - which
won't even penetrate the dead layer of skin - so you could put it in your hand. Alpha
radiation won't penetrate a sheet of paper.
In fact, U-238 is used all the time in airliners as ballast.
Dr. Gregory Greenman
|Aug3-07, 02:29 PM||#3|
(a) spent nuclear reactor fuel, not intended for reprocessing or research, or
(b) the highly radioactive liquid, whose radioactivity consists mainly of fission products, with some actinides also present, that are generated during chemical reprocessing of irradiated nuclear fuel (aqueous waste from the first solvent extraction cycle and those waste streams combined with it), or
(c) any other waste with a radioactivity level comparable to clause (a) or (b); (« déchet radioactif de haute activité »)
Under that definition, all spent fuel (used fuel is a better term, as it is not really spent) is High Level Waste.
As far as your question is concerned, the heat produced from radioactive decay of elements within the spent fuel bundles is probably not enough to produce electricity in a cost effective manner on a sustained basis.
|Aug5-07, 09:55 AM||#4|
Reusability of Radioactive Waste?
I think one needs to distinguish between spent fuel and the fission products which are the actual 'waste products'. In a once-through fuel cycle, the spent fuel is treated as HLW, in addition to being SNM.
As Morbius indicated, spent fuel can be reprocessed whereby the U (238, 235) and Pu are separated and recycled into new fuel.
These days, U-enrichment is usually in the range of 4-4.95% in commercial LWR fuel. Depending on exposure, spent fuel may have about ~1% of U-235 remaining with about 2-3% Pu, which originiates from the conversion of U-238 by neutron absorption.
|Aug6-07, 08:47 AM||#5|
thanks for all the input, I guess I should find more reliable sources.
It looks like we'll (USA) be going in the nuclear direction soon anyway, but there's another thread for that debate.
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