Ho aperto in passato in questo ed in altri ng alcuni thread sui reattori MSR
(altrimenti noti come LFTR, liquid fluoride thorium reactor), una tecnologia
nucleare
veramente potente ed innovativa (di cui sono un grosso sostenitore),
concepita e realizzata a partire dagli anni ' 50 dai due Nobel per la fisica
Wigner e Weinberg, e di cui credo ben poco purtroppo si conosca
E' stato di recente pubblicato un video di presentazione su google tech :
http://www.youtube.com/watch?v=VgKfS74hVvQ
L' autore ha anche un proprio sito, dove possono essere visionate le slides
del video ed altro materiale annesso
http://rethinkingnuclearpower.googlepages.com/aimhigh
Per chi non avesse seguito o ricordasse i miei post precendenti incollo un
paio di link :
Prima di tutto un paio di vecchi video sempre di google tech, ma pi�
specifici del precedente
http://www.youtube.com/watch?v=AHs2Ugxo7-8
http://www.youtube.com/watch?v=8F0tUDJ35So&feature=related
1)
http://www.theoildrum.com/node/5002
"....Our nuclear technology still has faults:
a.. it uses only a fraction of the energy in the uranium we mine,
b.. it leaves much more waste than is necessary, and
c.. it presents proliferation hazards that could be avoided.
We should do better, and we can.
The USA has developed technologies to address all of these problems, and
then mothballed them. The failure to develop our capabilities was not
technical, but political, and came mostly from within your own party. This
is another luxury we can no longer afford. These should go back on the
front burner as soon as humanly possible.
The neglected technologies are:
a.. The molten-salt reactor (MSR)
b.. The Integral Fast Reactor (IFR)
These two technologies have several very valuable properties in common:
1.. They reprocess their fuel at the reactor site.
2.. Because of the on-site reprocessing, there is no storage of spent
fuel.
3.. Also because of this, the volume of waste is minuscule; the waste from
a reactor's entire lifetime can be stored on-site and not removed until
decommissioning.
4.. They can use roughly 100 times as much of the raw fuel material as
today's reactors.
A ton of raw nuclear fuel (uranium or thorium) can make approximately one
gigawatt-year of electric power in an MSR or IFR. The total electric power
needs of the USA could be satisfied by less than 500 tons per year of
either, and a great deal of this could come from material already mined or
even designated as "waste". Because of these properties, the MSR and IFR
are potential solutions to both the USA's energy difficulties and the
nuclear waste problem.
The Molten-Salt Reactor (MSR)
The Molten-Salt Reactor was originally developed for nuclear aircraft, but
it was later tested as an alternative to water-cooled reactors. An
experimental reactor at Oak Ridge National Laboratory was tested using three
different fuels: enriched uranium-235, plutonium and uranium-233 (bred from
thorium). It ran well on all of them. The final run was intended to gather
data to evaluate the feasibility of a thorium-uranium fuel cycle, and was
apparently successful.
Molten-salt reactors have a number of advantages over today's water-cooled
technology:
1.. They cannot suffer a meltdown, because the fuel is already molten. If
the cooling systems are shut off, the reactors shut down through their
essential physics; they are inherently safe.
2.. They cannot explode, because they run well below the boiling point of
the salts and require no pressure vessels. This also makes their components
relatively lightweight and easy to manufacture.
3.. They can run at relatively high temperatures, which increases their
efficiency and makes the heat usable for many industrial purposes.
4.. They can remove fission wastes continuously, so there is never a
danger from "afterheat" when a reactor is shut down.
5.. The extracted wastes are relatively pure rather than containing large
amounts of unused fuel, so their bulk is comparatively tiny. The wastes can
be made ready for permanent disposal right at the reactor site. Fuel cannot
be diverted for weapons because it never leaves the reactor building.
6.. They can be started up with plutonium from spent nuclear fuel or
reclaimed weapons material, and can destroy this fuel while breeding new
fuel from thorium.
7.. The physics of breeding thorium to uranium creates uranium-232 as well
as uranium-233, which is not a difficulty for power production but makes the
material unsuitable for use in weapons. Even more so than light-water
reactors, molten-salt thorium breeders do not pose a risk of nuclear weapons
proliferation.
According to recent news, the USA has approximately 900,000 tons of
high-grade thorium reserves. This is approximately 2000 years of supplies
at current rates of electric consumption, or hundreds of years if thorium
was substituted for all fossil fuel. Lower-grade thorium resources include
coal ash.
In addition to reactors using molten fluoride salts, it appears to be
possible to make fast-breeder reactors using molten chloride salts. This
has not yet been tested, but it probably should be.
.....
The Consequences of Breeders
Between the two technologies of the MSR and IFR, the USA's entire inventory
of spent nuclear fuel (43,000 tons of uranium as of 2002), depleted uranium
(roughly 6 times as much) and thorium (900,000 tons of reserves) become
available as domestic fuel reserves. The entire electric demand of the USA
could be met with roughly 500 tons per year of this; the entire energy needs
of the USA would take perhaps 1500 tons. We could export both clean,
no-carbon power generators and the fuel to run them. If we are looking to
save the world from climate change, we have to grab these opportunities with
both hands... "
2)
http://thoriumenergy.blogspot.com/2009/04/kloosterman-on-tmsrlftr-technology.html
the MSR in combination with the thorium fuel cycle has many advantages:
- Fluoride inorganic salts are used as a carrier for the fuel and as a
coolant. They are among the most stable of chemical compounds and have
proven stable under reactor operating conditions. They have a high
solubility for actinides, very low vapor pressure, and good heat transfer
properties. Furthermore, they do not react with air or water, and are inert
to some commonly used structural materials.
- Soluble fission products can be removed on-line in a chemical processing
plant, while non-soluble fission products and the noble metals can be
extracted from the salt by helium bubbling. This enhances the neutron
economy. Together with the large number of neutrons liberated in U-233
fission events, new fissile material can be bred from abundantly available
thorium.
- There are no mechanical valves in the salt circuit. Flow is blocked by
plugs of frozen salt cooled by electrical fans. If the salt heats up to
levels above design values or if the power supply fails, the plugs will melt
and the salt will be drained into storage drums cooled by natural convection
(see the Figure).
- A fast excursion of the fuel temperature will lead to salt expansion
providing instantaneous negative reactivity feedback, which will slow down
or completely stop the fission process. Although heating of the graphite
moderator will generally introduce positive reactivity, this process is much
slower and can easily be controlled. Furthermore, a fuel salt temperature
too high will always lead to drainage of the fuel into passively cooled
storage tanks.
- The primary and secondary circuits are operated under ambient pressure,
which is considered a very important safety feature.
- The thorium fuel cycle produces much less long-lived nuclear waste.
Compared with the standard once-through fuel cycle in a Light Water Reactor
(LWR), a thorium fueled MSR produces 4,000 times less neptunium, plutonium,
americium and curium. Plutonium production is reduced even with a factor of
10,000.
- Among all nuclear reactors, the MSR is most suited to utilize the thorium
cycle. Neutron capture by Th-232 produces Pa-233, which decays with a half
life of 27 days to U-233. To avoid Pa-233 capturing an extra neutron, which
would produce the non-fissile U-234, part of it can easily be stored in a
hold-up tank to let it decay to U-233. This enhances the breeding process,
which makes the MSR, in combination with its excellent neutron economy, the
most attractive reactor for using thorium.
3)
http://www.theoildrum.com/node/4971
" ...Famed Climate Scientist James Hanson, recently spoke of thorium's great
promise in material that he submitted to President Elect Obama:The
Liquid-Fluoride Thorium Reactor (LFTR) is a thorium reactor concept that
uses a chemically-stable fluoride salt for the medium in which nuclear
reactions take place. This fuel form yields flexibility of operation and
eliminates the need to fabricate fuel elements. This feature solves most
concerns that have prevented thorium from being used in solid-fueled
reactors. The fluid fuel in LFTR is also easy to process and to separate
useful fission products, both stable and radioactive. LFTR also has the
potential to destroy existing nuclear waste.(The) LFTR(s) operate at low
pressure and high temperatures, unlike today's LWRs. Operation at low
pressures alleviates much of the accident risk with LWR. Higher temperatures
enable more of the reactor heat to be converted to electricity (50% in LFTR
vs 35% in LWR). (The) LFTR (has) the potential to be air-cooled and to use
waste heat for desalinating water.LFTR(s) are 100-300 times more fuel
efficient than LWRs. In addition to solving the nuclear waste problem, they
can operate for several centuries using only uranium and thorium that has
already been mined. Thus they eliminate the criticism that mining for
nuclear fuel will use fossil fuels and add to the greenhouse effect.The
Obama campaign, properly in my opinion, opposed the Yucca Mountain nuclear
repository. Indeed, there is a far more effective way to use the 500 a pound - perhaps 1500. The
price of coal has been somewhat depressed by the economic down turn. Last
year coal sold on the spot market for as much as 6000. How long would 3 billion tons last the
United States? If all of the energy used in the United States were derived
from thorium for the next two million years, there would be still several
hundred thousand years of thorium left that could be recovered for the
equivalent of $3000 a pound in January 2009 dollars..."
Received on Tue Jun 02 2009 - 14:36:49 CEST