One of the things to keep in mind is that there is nothing magically
dangerous about "transuranics". By any reasonable measure: per unit
mass, volume, or atom, there are plenty of things much more dangerous on
either a chemical or a radiological basis (and that's leaving out the
vastly more dangerous possibilities in the bacteriological and viral
categories). The claim that "Plutonium is the most dangerous substance
in the world" has been thoroughly exploded.
-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of George Stanford
Sent: Tuesday, December 02, 2008 6:08 PM
To: radsafe at radlab.nl
Subject: RE: [ RadSafe ] Fast neutron reactors
Jaro:
The goal, which I am told is achievable, is to have less than
1% of the transuranics reach the waste stream.
Per GWe-yr, there is roughly one tonne of waste that leaves a
fast-reactor plant (e.g., IFR or S-PRISM) . Annual output of
transuranics would therefore be 10 kg or less per GWe-yr (there's an
economic tradeoff).
In the spent fuel from current (thermal) reactors, there's
about 240 kg of transuranics per gWe-yr, currently destined for Yucca
Mountain.. If instead it were to be used for input to fast-reactors, a
1% loss would mean that 2.4 kg of transuranics per GWe-yr of
thermal-reactor power would be in the waste stream, mixed with a tonne
of fission products.
I'm sorry the Scientific American article did not make this
clearer.
Regarding the long-term hazard of nuclear waste, essential
perspective is in Bernie Cohen's article, to be found at
<http://www.phyast.pitt.edu/~blc/pra-ppr.pdf>. Bottom line: Yucca
Mountain would be just fine, especially with a major reduction in
transuranic content.
Molten salt for the secondary loop sounds good to me (but
that's not my field).
Cheers,
-- George Stanford
Reactor physicist, retired.
<~~>++<~~>++<~~>++<~~>++<~~>++<~~>++<~~>
At 03:10 PM 11/30/2008, Jaro wrote:
The Sci. Am. article includes these statements :
<quote>
Because the fast-reactor waste would contain no significant quantity of
long-lived transuranics, its radiation would decay to the level of the
ore from which it came in several hundred years, rather than tens of
thousands.
.....
Tailored waste forms that would only have to remain intact for 500
years, after which material would no longer be hazardous.
<end quote>
Yet it is difficult to get any numbers on the actual amount of TRUs
(including Pu) that would end up in the waste stream.
The only clue we get is this :
<quote>
....the pyroprocess collects virtually all the transuranic elements
(including the plutonium), with considerable carryover of uranium and
fission products.
Only a very small portion of the transuranic component ends up in the
final waste stream...
<end quote>
The problem is that since this is a U-Pu cycle, large amounts of Pu
(many
tons) would pass through the pyroprocess, so that even a small level of
inefficiency could result in significant amounts of Pu (+ other TRUs) in
the waste -- possibly not sufficiently low to support the claim that the
"material would no longer be hazardous" after 500 years.
Has anyone seen some figures on pyroprocess Pu-TRU extraction efficacy ?
(Thnx)
(By contrast, a fuel cycle based on U-Th has about two orders of
magnitude less Pu to begin with, so the amount that ends up in the waste
is correspondingly less also, assuming similar extraction efficacy....)
PS. as for the statement that "Engineers do not consider sodium's
flammability to be a major problem," it is interesting to note that
recent fast reactor design studies include the possibility of changing
the secondary heat transfer circuit sodium -- which passes through the
water boiler -- with molten salt : The latter carries no risk of
violent chemical reaction with water or steam....
Jaro
^^^^^^^^^^^^^^^^^^^^^
-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl]On
Behalf Of Rainer.Facius at dlr.de
Sent: Saturday, November 29, 2008 1:00 PM
To: sjd at swcp.com; radsafe at radlab.nl
Subject: AW: [ RadSafe ] Fast neutron reactors
Steven,
I forward a paper and a commentary by George Stanford (and colleagues)
which can answer your question authoritatively, much more so than I can.
>From the paper the following quote gives the gist of the argument.
"Fast reactors can extract more energy from nuclear fuel than thermal
reactors do because their rapidly moving (higher energy) neutrons cause
atomic fissions more efficiently than the slow thermal neutrons do. This
effectiveness stems from two phenomena. At slower speeds, many more
neutrons are absorbed in nonfission reactions and are lost. Second, the
higher energy of a fast neutron makes it much more likely that a fertile
heavy metal atom like uranium 238 will fission when struck. Because of
this fact, not only are uranium 235 and plutonium 239 likely to fission
in a fast reactor, but an appreciable fraction of the heavier
transuranic atoms will do so as well.
"
>From the commentary the following quote summarizes the consequence:
"Yes, reprocessing spent nuclear fuel in fast reactors can indeed solve
the 'waste problem'. It will allow more than 99% of the energy in
uranium to be used -- unlike today's reactors, which utilize less than
1%."
Kind regards, Rainer
Dr. Rainer Facius
German Aerospace Center
Institute of Aerospace Medicine
Linder Hoehe
51147 Koeln
GERMANY
Voice: +49 2203 601 3147 or 3150
FAX: +49 2203 61970
________________________________
Von: radsafe-bounces at radlab.nl im Auftrag von Steven Dapra
Gesendet: Sa 29.11.2008 17:28
An: radsafe at radlab.nl
Betreff: [ RadSafe ] Fast neutron reactors
Nov. 29
According to a book review in "Health Physics News" (Nov. 2008;
p.
9, col. 3), fast neutron reactors will minimize waste and make better
use of uranium resources. How will such reactors reduce rad waste and
use uranium more efficiently?
Steven Dapra
sjd at swcp.com
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