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nearly everyone in the world is part of some community whether large or small
and all of these communities have similar needs
they need light they need heat
they need air conditioning people can't function very well when
it's too hot or too cold
they need food to be grown or provided distributed and stored safely
they need waste products to be collected removed and processed
people in the community need to be able to get from one place to another
as quickly as possible
and a supply of energy is the basis for all of these activities
energy in the form of electricity provides light and air conditioning
energy in the form of heat keeps us warm and energy in chemical form
provides fertilizer drives farm machinery and transportation
now i spent 10 years at NASA
and in the beginning of my time there in 2000 i was very interested in communities
but this is the kind of community i was thinking of
a lunar community it had all of the same needs as a community on earth would have
but it had some very unique constraints
and we had to think about how we would provide energy for this very unique community
there's no coal on the moon there's no petroleum
there's no natural gas there's no atmosphere
there's no wind either
and solar power has a real problem: the moon orbits the earth once a month
for two weeks the sun goes down and your solar panels don't make any energy
you want to try to store enough energy in batteries for two weeks
it just simply isn't practical
so nuclear energy was really the only choice
now back in 2000 i really didn't know too much about nuclear power
so i started trying to learn almost all of the nuclear power
we use on earth today uses water as the basic coolant
that has had some advantages but it has a lot of disadvantages
if you want to generate electricity
you have to get the water a lot hotter than you normally can
at normal pressure water will boil at 100 degrees celsius
this isn't nearly hot enough to generate electricity effectively
so water-cooled reactors have to run at much higher pressures
than atmospheric pressure
some water-cooled reactors run at over 70 atmospheres of pressure
and others have to run at as much as 150 atmospheres of pressure
there's no getting around this it is simply what you have to do
if you want to generate electricity using a water-cooled reactor
and this means that you have to build a water-cooled reactor as a pressure vessel
with steel walls over 20 centimeters thick if that sounds heavy that's because it is
things get a lot worse if you have an accident where you lose pressure inside the reactor
if you have liquid water at 300 degrees celsius and suddenly you depressurize it
it doesn't stay liquid for very long it flashes into steam
so water-cooled reactors are built inside of big thick concrete buildings
called containment buildings
which are meant to hold all of the steam that would come out of the reactor
if you had an accident where you lost pressure
steam takes up about 1000 times more volume than liquid water
so the containment building ends up being very large relative to the size of the reactor
another bad thing happens if you lose pressure and your water flashes to steam
if you don't get emergency coolant to the fuel in the reactor it can overheat and melt
now the reactors we have today use uranium oxide as a fuel
it's a ceramic material similar in performance to that of the ceramics that
we use to make coffee cups or cookware or the bricks we use to line fireplaces
they are chemically stable but they're not very good at transferring heat
if you lose pressure you lose your water
and soon your fueld will melt down and release the radioactive fission products within it
making solid nuclear fuel is a complicated and expensive process
and we extract less than 1% of the energy from the nuclear fuel
before it can no longer remain in the reactor
water cooled reactors have another additional challenge
they need to be near large bodies of water where the steam they generate
can be cooled and condensed otherwise they can't generate electrical power
now there's no lakes or rivers on the moon so if all this makes it sound like water-cooled reactors
aren't such a good fit for a lunar community i would tend to agree with you
you see i had the good fortune to learn about a different form of nuclear power
that doesn't have all these problems for a very simple reason: it's not based on water cooling
and it doesn't use solid fuel surprisingly it's based on salt
one day i was at a friend's office at work and i noticed this book on his shelf
fluid fueled reactors and i was interested and asked if i could borrow it
i learned about research in the United States back in the 1950s into a kind of
nuclear reactor that wasn't based on solid fuel or water cooling it didn't have the problems
of the water-cooled reactor and the reason why was pretty neat
it used a mixture of fluoride salts as a nuclear fuel
specifically the fluorides of lithium, beryllium, uranium and thorium
fluorides are remarkably chemically stable
they do not react with air and water you have to heat them to 400 degrees celsius
to get them to melt but that's actually perfect
for trying to generate power in a nuclear reactor
here's the real magic: they don't have to operate at high pressure
and that makes the biggest difference of all
this means that they don't have to be in heavy thick steel pressure vessels
they don't have to use water for coolant and there's nothing in the reactor
that's going to make a big change in density like water
so the containment building around the reactor
can be much smaller and close fitting unlike the solid fuels that can melt down
if you stop cooling them these liquid fluoride fuels are already melted
at a much, much lower temperature
in normal operation you have a little plug here at the bottom of the reactor vessel
this plug is made out of
a piece of frozen salt that you've kept frozen
by blowing cool gas over the outside of the pipe
if there's an emergency and you lose all the power to your nuclear power plant
the little blower stops blowing
the frozen plug melts and the liquid fluoride fuel inside the reactor
drains out of the vessel
through the line into another tank called a drain tank
inside the drain tank it's all configured to maximize the transfer of heat
so as to keep the salt passively cooled as its heat load drops over time
in water-cooled reactors you generally have to provide power to the plant
to keep the water circulating to prevent a meltdown as we saw in japan
but in this reactor if you lose the power to the reactor it shut itself down
all by itself without human intervention
and puts itself in a safe and controlled configuration
now this was sounding pretty good to me i was getting excited about the potential
of using a liquid fluoride reactor to power a lunar community
but then i learned about thorium and the story got even better
thorium is a naturally occurring nuclear fuel that is 4 times more common in the Earth's
crust than uranium it can be used in liquid fluoride thorium reactors
to produce electrical energy heat and other valuable products
it's so energy dense that you can hold a lifetime supply of thorium energy
in the palm of your hand
thorium is also common on the moon and easy to find
here's a map of where the lunar thorium is located
thorium has an electromagnetic signature that makes it easy to find
even from a spacecraft
with the energy generated from a liquid fluoride thorium reactor we could recycle all of the air
water and waste products within the lunar community in fact doing so
would be an absolute requirement for success
we can grow the crops needed to feed the members of the community even during the two-week
lunar night using light and power from the reactor
it seemed like the liquid fluoride thorium reactor or LFTR could be the power source that could make
the self sustainable lunar colony a reality but i had a simple question
if it was such a great thing for a community on the moon
why not a community on the earth? a community of the future
self-sustaining and energy independent
the same energy generation and recycling techniques
that could have a powerful impact on surviving on the moon
could also have a powerful impact on surviving on the Earth
right now we're burning fossil fuels because they're easy to find and because we can
unfortunately they're making some parts of our planet look like the moon
using fossil fuels and entangles us in conflict in unstable regions of the world
and costs money and lives
things could be very different if we were using thorium
you see in a LFTR we can use thorium about 200 times more efficiently
than we're using uranium now because the LFTR is capable
of almost completely releasing the energy in thorium
this reduces the waste generated over uranium by factors of hundreds
and by factors of millions over fossil fuels
we're still going to be liquid fuels for vehicles and machinery
but we could generate these liquid fuels from the carbon dioxide in the atmosphere
and from water much like nature does we can generate hydrogen by splitting water
and combining it with carbon harvested from CO2 in the atmosphere
making fuels like methanol ammonia and
dimethyl ether which could be a direct replacement for diesel fuels
imagine carbon neutral gasoline and diesel sustainable and self produced
do we have enough thorium? yes we do
in fact in the United States we have over 3200 metric tons of thorium
that was stockpiled 50 years ago and is currently buried in a shallow trench in Nevada
this thorium if used in LFTRs
could produce almost as much energy as the United States uses in 3 years
and thorium is not a rare substance either there are many sites like this one in Idaho
when area the size of a football field would produce enough thorium each year
to power the entire world
using the LFTR technology we could move away from expensive and difficult aspects
of current water-cooled solid fuel uranium nuclear power
we wouldn't need large high pressure reactors and big containment buildings that they go in
we wouldn't need large low efficiency steam turbines
we wouldn't need to have as much long distance power transmission infrastructure
because thorium is a very portable energy source that can be located near to where it is needed
a liquid fluoride thorium reactor would be a compact facility
very energy efficient and safe that would produce the energy we need day and night
and without respect to weather conditions
in 2007 we used 5 billion tons of coal 31 billion barrels of oil
and 5 trillion cubic meters of natural gas
along with 65,000 tons of uranium to produce the world's energy
with LFTR we could do the same thing with 7,000 tons of thorium
that could be mined at a single site if all this sounds interesting to you
i invite you to visit our web site where a growing enthusiastic community
of thorium advocates is working to tell the world
about how we can realize the clean safe and sustainable energy future
based on the energies of thorium thank you very much


【TEDx】TEDxYYC - Kirk Sorensen - Thorium

2602 タグ追加 保存
阿多賓 2014 年 3 月 7 日 に公開
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