Smith_Richard_2012
Copyright © 2012 by Richard Smith. Published by the Mars Society with permission.
LIQUID FLUORINE THORIUM REACTORS ON MARS
Richard W. Smith
[email protected]
ABSTRACT
Liquid salt fluorine thorium nuclear reactors are a little known form of nuclear power that are uniquely
suitable for use in early Mars colonization. Molten Salt Reactors based on the Thorium fuel cycle are
500 times more efficient than traditional nuclear power (per tonne of ore mined), produce a 1,000 times
less, long-term, nuclear wastes and are unsuitable for nuclear bomb proliferation. This paper focuses on
the advantages of this technology for use on Mars.
The paper will discuss the basics of nuclear power (assuming you have a basic knowledge of nuclear
chemistry and how nuclear reactors work). Liquid fluorine thorium reactors will be compared with
traditional pressurized light water reactors. The thorium nuclear projects active in several countries
including India, Japan, China, Australia and Czech Republic will be noted. Additionally the paper will
describe the low-level thorium deposits found by the 2001 Mars Odyssey mission via remote sensing
with its Gamma-Ray Spectrometer.
KEYWORDS: Thorium, LFTR, Molten Salt, Odyssey, Power on Mars, Liquid Fluorine Thorium
Reactor, and Nuclear Waste.
INTRODUCTION
Iron and Nickel are the elements with the highest nuclear binding energies. You can get energy from
joining smaller into atoms closer to Fe and Ni (fusion) or breaking apart huge elements so that the
fragments are closer in size to them (fission). Normal nuclear reactors use fission.
The number of protons in the nucleus determines what element an atom is. (For example, anything
with exactly 6 protons is a Carbon atom.) However the number of neutrons may vary. If a Carbon
atom has 6 protons and 6 neutrons then it is Carbon 12, if there are 6 p and 7 n then you have Carbon
13. If there are 6 p and 8 n then you have Carbon 14. These variations are called isotopes and the
number of protons plus neutrons is called the mass number.
Note that with small atoms, the number of protons and neutrons are approximately equal. However,
the protons all have a positive charge and will try to push the nucleus of an atom apart. Neutrons and
protons exchange virtual particles called 'gluons' which hold nuclei together with the strong nuclear
force. As the cumulative positive charge increases in the core of an atom, more neutrons are needed to
hold it together. (If you search for a table of isotopes, you can see how stable elements need more
neutrons as the mass number gets larger.)
When a very large element fissions into smaller fragments (called fission products) the results are
neutron rich. Fissions will throw out some neutrons at once and the fission products will typically
undergo a beta decay or two, where neutrons turn into protons shooting out a beta particle (an electron)
and an anti-electron neutrino.
Radiation can be neutrons, beta particles (electrons), alpha particles (a Helium 4 nucleus with 2 protons
and 2 neutrons), or gamma radiation (which is electromagnetic waves like heat, light, or radio waves).
However, gamma particles are much more dangerous, being in the hard x-ray or gamma ray spectrum.
Note that while it is easy to shield against alpha and beta radiation, gamma rays are dangerous and very
hard to shield against. Also note that neutron bombardment can make normal matter radioactive,
usually for a short time. Some atoms are unstable and will break down releasing radioactivity.
Which is more dangerous?
-- a kg of substance that has a half life of a billion years, or
-- a kg of substance that has a half life of 1 day?
(Assume both give off the same amount of radioactivity and both immediately form a stable atom.)
Many people would say that the longer lived element is more dangerous. After all it is radioactive for
billions of years! However, the kg of substance with a half life of one day is far more dangerous. It
will break down at a furious pace and you would quickly pick up a lethal dose of radiation if you were
near it. The kg of the element with a billion year half life is barely radioactive. Your body has time to
repair the damage and you could walk around with this substance for years with likely no ill effect.
Substances with short half lives are wildly dangerous for a short time, but breakdown into stable
elements quickly. Thus, time will soon make these safe. Extremely long lived isotopes are barely
radioactive and relatively safe. It is elements with a medium duration half life that are most
troublesome: they are radioactive enough to be dangerous, and last long enough to be dangerous for a
long time.
TRADITIONAL NUCLEAR POWER
At a high level, the core of a nuclear power plant gets hot. This heat is moved to some place where we
can extract useful work from it (typically by boiling water and turning a steam turbine). After burning
the fuel for several months, the fuel rods are removed from the reactor and become nuclear waste. We
will look at this in more detail below.
When an atom fissions, it typically shoots out a neutron or two or three. These neutrons come out at a
very high velocity – about 0.2% of the speed of light. These are called 'fast' neutrons. If the neutron is
not absorbed it ricochets off of other atoms and slows down. When it is moving about as fast as the
other atoms are jiggling about (because of the local temperature) it is called a 'slow' or 'thermal'
neutron.
Usually in a nuclear reactor we want thermal (slow) neutrons so we must put in some substance that
can slow them down without absorbing them. This is called the moderator.
A reactor produces heat as the fuel fissions. Even after it is turned off, there is a significant amount of
fission products in it which will also release heat (a lot of it). Thus, even after the reactor is shut down,
we must handle the heat of fission products. The fission product heat is very high for some hours after
the reactor is shut down and then gradually reduces making it easier and easier as time goes by to
handle this waste heat.
Contrast this with a coal burning plant, where once you stop adding fuel it will completely cool down
in an hour or so.
So in a power plant, we need to have the nuclear fuel near a moderator and have some sort of cooling
system.
The fuel cycle
Uranium comes in two main natural isotopes: U 238 (common) and U 235 (very rare). Uranium 235
makes up only 0.7% of natural uranium. Unfortunately, Uranium 238 is barely radioactive and quite
stable – we need the rare stuff.
Uranium 235 is about 5 times more common than Gold or Platinum. Further, it is very, very difficult
to separate it from the U 238. Thus it is significantly more expensive than Platinum. The nuclear fuel
used by most reactors today is like burning gold. It is so energy rich (nuclear reactions are about one
million times more energy dense than chemical reactions) that we can actually make money 'burning' it
up.
After we have our very expensive fuel, we put it into a reactor and 'burn' it. (When we say, 'burn' we
mean 'transmute it into another element' but it is quicker to say 'burn'. Note that this is not really
burning, since burning is combining an element with an oxidizer – normally which of these we mean is
clear from context.) Note that we do not 'burn' pure U 235, it it mixed with a large amount of U 238 so
that the U 235 is only 3 or 4% total. This is called enriched uranium. (Uranium for atom bombs must
be very highly enriched where U 235 makes up around 85% (weapons grade) of the total.)
However, nuclear reactors only 'burn' 0.5% of our fuel. This is a terrible efficiency. In the USA, the
spent fuel is all treated as nuclear waste. In other countries such as Japan, Russia, and France the fuel
is reprocessed to regain the 99.5% of this very valuable fuel to try to 'burn' it again.
Why does the USA not reprocess its nuclear waste to remove the Uranium 235 (and the Plutonium 239)
and burn it again? The reason is that it is more expensive to reprocess the waste than to use new U
235.
To reprocess the waste we have to turn it into some sort of liquid (usually by dissolving it in a powerful
acid), and do chemical processing to separate out the Uranium. Then we have to isotopically remove a
bit of the U 238, which is tricky. Finally, we have to turn it back into solids and make fuel rods out of
it. This material is far more radioactive than natural uranium which adds to the expense.
As a side note, those who claim that we will soon run out of U 235 are wrong. They ignore the fact
that there are many likely areas where we have not yet checked for Uranium ore; they ignore the
massive amounts of U 235 that are stored in the nuclear wastes; they ignore the fact that the oceans
contain 50,000 times more Uranium than can be found in solid ores. (The Uranium dissolved in sea
water can be pulled out using chemical filters which collect Uranium and Vanadium.)
If the Uranium 238 absorbs a neutron, it will transform into Plutonium 239. If Plutonium is hit by a
fast neutron it will fission, releasing about 3 neutrons. Thus U 238 is not fissile (it will not fission if hit
by a neutron) but it is fertile (it will transform into something that is fissile). If Plutonium 239 is hit by
a thermal neutron, it will likely simply absorb it, which is not what we want. (A nuclear reactor
depends on fissions to produce heat and create additional neutrons needed to continue the reaction.)
Those that would like to build Plutonium breeder reactors (which make more fuel than they 'burn') need
lots of fast neutrons. The fast breeder reactors that have been build use liquid sodium as a coolant,
because water is a moderator, and they don't want the neutrons slowed down. However, sodium is a
very dangerous metal. Liquid sodium will burn or explode if it touches air or water. A few molten
sodium fast breeder reactors have had dangerous fires and have been closed down. After billions of
dollars have been spent on them, we still do not have a profitable commercial fast breeder. (I am not
saying they are impossible – I do think they are dangerous and that a better fuel cycle is available.)
So to summarize, we can breed U 238 (the common form of Uranium) into Pu 239 in a fast breeder
reactor. This is good (we make more fuel) but it creates Pu which is bad. Pu is bad because it is quite
toxic, radioactive with a 24,200 year half life (which is short enough to be dangerous and long enough
to last for a long time) and because it can be used to make atom bombs.
Finally Uranium / Plutonium reactors create a fair amount of long term nuclear wastes. Plutonium
(24,200 years), Americium (432 years) and Californium (898 years) are all radioisotopes which fall in
that unhappy middle ground where their half lives are short enough to be quite dangerous and long
enough to last a long time. Thus, this fuel cycle builds up significant amounts of long term wastes
which should be kept out of the environment for several tens of thousands of years.
Efficiency of nuclear power plants and safety
In thermodynamics, a heat engine takes something hot and extracts useful work by lowering the
temperature. The exhaust heat is a constant – if a nearby river is at a cool 10 C, then that is the best
you can do for the low temperature. To make a power plant more efficient we must make it hotter.
Some nuclear reactors are called boiling water reactors. These are safe and have little plumbing.
However, they use water as both a moderator and a coolant. The water boils and the steam is used to
turn a turbine to make power at about 20 to 25% efficiency.
If we could get the temperature of the reactor higher, we could get more electricity out. Pressurized
Light Water Reactors (PLWR), use a thick steel pressure vessel around the reactor to allow the water to
go up to around 300 C with out boiling. These reactors are about 33% efficient.
Most coal burning plants are around 31% efficient. (They burn hot enough to be better, up to 47%, but
this takes exotic materials and expensive high tech. Few people bother with the expense when building
coal plants.)
Natural gas power plants burn very hot. They typically are at 56% efficiency. However, as demand
soars for gas, and the easy gas is depleted, it is expected that natural gas prices will rise further.
If we could get nuclear power plants to be ~400 C hotter, we could use more efficient turbine cycles
and improve a nuclear power plant's efficiency to 50 or 60%.
A Pressurized Light Water Reactor (PLWR) has costs associated with its improvement in efficiency
over boiling water reactors. The reactor cores require stainless steel cast 20 cm or more thick. This is
expensive and currently only one company in the world (in Japan) can build these. Further, if a tiny
crack appears, the super heated water will flash to steam, expanding in volume more than 1,000 times.
To guard against steam explosions, such reactors need a huge containment building.
There is a problem with using water as a moderator / coolant. If it gets too hot, it will split into
Hydrogen and Oxygen. This can cause a Hydrogen explosion (which is what broke open the reactor at
Fukushima).
To summarize, traditional nuclear power plants are wildly inefficient. They 'burn' fuel that is more
expensive than platinum, use up less than 0.5% of it and work at too low a temperature to efficiently
convert the heat into electricity.
Pressurizing the water allows better efficiencies in electrical conversion but risks steam explosions.
Finally, using water allows the possibility of Hydrogen explosions if the water gets too hot.
We will now look at Thorium based reactors.
LIQUID FLUORIDE THORIUM REACTORS
A long forgotten type of power plant is making a comeback in the last couple years. This is the molten
salt Liquid Fluoride Thorium Reactor (LFTR).
Thorium has only one natural isotope, Th 232, which is not fissile. However, it is fertile. If it absorbs
a neutron, it turns into Th 233, which quickly decays into Protactinium 233 then into Uranium 233.
Uranium 233 is wonderfully fissile and will fission 92% of the time if hit by a thermal neutron. (The
8% of the time that it does not fission it will absorb neutrons until it reaches U 235 where it is 85%
likely to fission from a thermal neutron.)
When U 233 fissions, it releases 2 or 3 neutrons, which can breed more Thorium into U 233 and split
another U 233. (The extra neutron which is occasionally generated is used to make up the inevitable
neutron losses that occur in the reactor.)
Note that the neutrons that are freed from the fissioning U 233 are fast neutrons and have to be slowed
down with a moderator to thermal speeds.
In a LFLR (lifter) the thorium is reacted with Fluorine to make the salt ThF4. This is mixed with other
Fluorine salts (usually Lithium Fluoride LiF and Berillium Fluoride BeF2) which give it the desired
moderating and temperature properties.
These salts are extremely stable. They have an amazingly wide temperature range (from 300 C to
1,300 C depending on the exact mixture); the salts have a low vapor pressure, they are stable at 1
atmosphere pressure, they do not react if air or water touch them. Finally, they are stable under
tremendous heat and neutron bombardment. Fluorine has the most powerful bond in chemistry and its
salts are extraordinarily stable.
The idea is that these Fluorine Thorium salts are melted and bombarded with neutrons. The Thorium
blanket absorbs neutrons and soon decays into Uranium 233. This is still a Fluorine salt and sent to the
core of the reactor. There the U 233 fissions, creating more fissions and breeding more U 233 fuel
from the Thorium blanket.
There is a critical advantage to having the fuel as a liquid. Chemical processes work on fluids (liquids
and gases). Bubbling Fluorine gas thru the Thorium salts (with newly bred U 233 in it) will add two
Fluorine atoms, to the U 233. Uranium will form hexafluoride gases, Thorium will not. Thus the U
233 will become a gas, and will be easily separated from the Thorium. This ability to chemically
separate the new fuel or waste products, while the reactor is running, is a key advantage over reactors
where the fuel and waste products are solids locked behind metal cladding in fuel rods.
There is another advantage to using liquid fuels. A troublesome fission product is Xenon which is a
bad neutron poison. That is, it greedily absorbs neutrons which we need for our reactor to run. The gas
damages the solid fuel and makes the reactor less efficient and less predictable. Being a gas it is trivial
to remove the Xe from the liquid fuel, making the reactor safer and more efficient.
Reactors remain quite hot after they are shut down because of the fission products that they produce.
(Most of these are radioactive with short half lives. After they decay to stable elements they are no
longer hot.) Many of these fission products are valuable. These include platinum group metals like
gold and platinum, rare earth elements including Neodymium and Gadolinium (used in super magnets
and modern electronics), medical radioisotopes, radioisotopes for space probes, etc. When the reactor
has a liquid core it is much cheaper to periodically clean it out compared to solid fuel reactors. With
liquid cores, we can use straightforward chemical processing and recover the fission products. A
LFTR might produce hundred of millions of dollars worth of electricity during its life span and only a
couple hundred thousand dollars of fission products, but it is an extra bonus and reduces the volume of
nuclear wastes generated.
Let us say that a reactor “burns” fuel faster as it gets warmer. This makes it even hotter and it warms
up even more, etc. This is called a 'positive temperature coefficient'. It is very dangerous and no
reactor in the USA is allowed to be designed where it can ever have this situation come up.
(In Chernobyl the reactor briefly reached a positive temperature coefficient and blew up. It lacked a
containment vessel around the core and a reactor containment building to contain the steam explosion.
It blew off its metal roof and allowed radioactivity to be released into the environment.)
If we have a reactor where when it gets cooler, the reaction speeds up, then this is a 'negative
temperature coefficient'. This is safe, and much of the effort of reactor design is intended so that in all
situations, the reactor always has a negative temperature coefficient. Liquid fuel reactors have very
strong negative temperature coefficients.
For example, we draw a lot of heat out of the reactor (say by making electricity with it), then the fluid
cools down. As the fluid cools, then it contracts and more fuel will fit into the reactor speeding up the
reaction.
If, later, it gets too hot, then the fluid expands and less fuel will fit into the reactor core. Thus, the
reaction is slowed and the reactor cools. If we extract less electricity, it generates less power! This
means that a LFTR is 'load following'. It will automatically, without any control rods, adjust its
reaction rate to follow the demand placed on it by the power grid.
This greatly simplifies the reactor and makes it safer. First, it is safer because it is less complex and
there is less equipment to go wrong. Second, most major nuclear disasters have happened because of
operator error and this reactor uses simple physics to control the reactor.
There is another safety feature associated with this form of reactor. A small fan blows cool air on a
pipe under the reactor. Fluorine salts which touch this cool pipe freeze, plugging the pipe. If there is a
complete loss of power (or the reactor gets too hot somehow), the freeze plug melts and the entire
reactor drains into emergency dump tanks which are too small to allow a nuclear reaction and are
designed to passively pull the heat away from the fluid. Thus, the safety system only requires gravity
to shut down the reactor.
To put it another way, no active safety systems (requiring power and human intervention) are needed.
The reactor automatically safes itself if effort is not made to keep it going.
When these reactors were being tested in Oak Ridge National Laboratories in the 1950's and '60's the
reactor was run 24 hours a day. But no one wanted to work weekends, so they turned off the fan each
Friday night and let the reactor drain into the dump tanks. When they came in on Monday, they heated
up the salt, pumped it back into the reactor and continued. Thus, this safety feature has been tested
hundreds of times.
A LFTR uses a two fluid system. (One fluid is the fissile U 233 salt, the other is the blanket of fertile
Thorium. The two are separated by a graphite moderator.) A one fluid system mixes both fluids
together. A two fluid system has slightly more complex plumbing than a single fluid system, but it
allows easier chemical processing of the fission products and more efficient burn-up of Th 232.
Proliferation Issues
Thorium 232 can produce U 233 which is fissile. However, the US Army tried to build a bomb with U
233 and found it was very dangerous and hard to work with. First, it is more radioactive than U 235.
Second, it soon decays into elements which are a very hard gamma ray source. This makes it easy to
detect from space or the ground, the gamma rays are deadly dangerous to anyone trying to build a
bomb, the gamma rays damage electronic equipment that triggers the bomb and make the conventional
explosive needed to compress the fissile core of the bomb less stable.
The Uranium 233 bred from Thorium is far more dangerous and harder to build a bomb with than U
235 and Pu 239.
Now a LFTR makes a tiny amount of Plutonium but the Plutonium it creates is Pu 238, which instead
of having a half life of 24,200 years, has a half life of only 90 years. This makes it far too radioactive
to make it easy to form into atom bombs. (Its decay products also create dangerous gamma rays that
are easy to spot from space.)
(Pu 238 is used on NASA space probes to power radioisotope generators on probes to the outer solar
system. The USA has gone thru all of its Pu 238, has bought Russia's entire supply and is now
canceling deep solar system probes because the world lacks Pu 238. If we had LFTR's we could cook
up more and sell them to NASA allowing us to continue creating these sorts of missions.)
No one has EVER built an atom bomb out of nuclear wastes and it would be even harder from those
from a LFTR since they are kept in the reactor core as a liquid, and they are much harder to work with
than those formed from traditional solid fuel reactors.
If additional safety is wanted, liquid Fluoride U 238 could be dumped into the reactor if some bad guy
was trying to steal this highly radioactive liquid. This is called “denaturing”. But in my opinion this is
a needless complexity. States which have wanted to build atom bombs simply buy Uranium on the
open world market and isotopically separate out the U 235. This is simpler and safer than dealing with
the far more radioactive, low-purity reactor wastes.
Nuclear waste issue
Sylvan David, et al, wrote a paper in Europhysics News 32(2), page 25, which describes the radioactive
wastes produced by LFTR's. They found that both LFTR's and traditional solid fuel power plants
produced the same amount of fission products (which makes sense since fissioning is the whole point
of fission reactors). However, the LFTR made 1,000 times less long term transuranic wastes (ones that
you should store for thousands of years). In about 800 years the LFTR's long term wastes are 10,000
times less than those produced by Uranium / Plutonium reactors.
It is easy to see why. When in the reactor, Th 232 must absorb 7 neutrons before it can reach elements
heavier than U 238. U 238 only needs one. Further, Th 232 can fission at U 233 (92%), and at U 235
(85%) whereas the traditional reactors get only one, lower probability attempt, at Pu 239 (65%).
As for the fission products, almost all of them have very short half lives. (The exception is
Technetium, which it produced in tiny amounts.) Within 300 years, the fission products + a LFTR's
long term wastes decay to a level that is LOWER than natural Uranium ore. (In fact, variations of
LFTR's can be built to 'burn up' nuclear wastes from traditional reactors. These reactors are the only
ones ever invented that will reduce the amount of nuclear waste in the world.)
It is far more reasonable to assume that we can keep wastes safely out of the biosphere for 300 years
than tens or hundreds of thousands of years.
There is another reason why LFTR's produce less wastes. We mine vast quantities of Uranium ore and
(very expensively) concentrate the U 235. Then we only 'burn up' 0.5% of the U 235 before
designating the whole fuel rod as waste. In a Thorium reactor, we can add fuel while the reactor is
running as we slowly remove the fission products. Virtually 100% of the thorium is 'burnt' (a tiny
amount is turned into transuranic wastes without 'burning').
The Cost of Building and Operating LFTR’s
LFTR's will be far cheaper to build and run because:
-- The fuel is cheaper. Thorium is 3 to 4 times more abundant than U 238 and ~800 hundred times
more common than the rare, radioactive U 235. Vast amounts of Th are purified in mining of Rare
Earth Elements, and many tonnes are in already crushed rock tailings from Uranium mines. The USA
has 3,216 tonnes of Th 232 buried under 12 feet of dirt at a Nevada test site, which is enough to run a
Thorium program in the US for decades.
-- A ping pong ball sized mass of Thorium is equal to the energy content of 6,300 barrels of oil or 1470
tonnes of bituminous coal. The mining costs for this amount of Thorium are trivial compared to coal
mining or modern oil extraction.
-- LFTR's do not require very expensive isotopic separation for its fuel.
-- The reactors do not need huge expensive containment buildings capable of withstanding a steam
explosion. (They are also safe from Hydrogen – Oxygen explosions.)
-- They do not need a heavy pressurized reactor core. LFTR's run at air pressure.
-- LFTR's run hotter than regular Pressurized Light Water Reactors. This allows them to use an
efficient Brayton closed cycle gas turbine that can produce electricity at 50 to 60% efficiency.
Additionally, if desired, the waste heat could be set at a high enough temperature to desalinate seawater
for those cities where retreating glaciers are threating water supplies.
-- LFTR's can be made a lot smaller. Smaller (potentially mass produced), LFTR's require less start-up
capital and less time to build. This means less interest is paid before the reactor is operational and
starting to pay back its loan.
-- LFTR's become more profitable if the price of electricity goes up. Natural gas prices are rising as
demand soars and traditional gas wells produce less. Coal requires oil to run the mining machinery.
Additionally, in 2006, 40% of the price of coal (at the power plant) was spent on oil, to run the diesel
locomotives, hauling the coal to the plant. When oil prices soar, the price of coal will likewise shoot
up.
-- LFTR's are proliferation safe and require less expensive storage of nuclear wastes. This reduces the
operating costs of the reactors.
Challenges to LFTR’s and why so long forgotten?
LFTR's have numerous advantages over regular nuclear reactors, so why were they forgotten?
In Oak Ridge National Labs they tested molten salt reactors from 1958 to '69. For over 4 years (from
early '65 to late '69) they ran the Molten Salt Reactor Experiment breeding Thorium. (They used a
single fluid design.) This 8 MWatt reactor was a huge success and bred more fuel that in consumed.
The Oak Ridge director, Alvin Weinberg expected that a full scale test plant would be build and then
commercial power plants would follow.
But the whole program was shut down. Why?
The standard answer is that the Thorium fuel cycle didn't produce any weapons grade material. But
there was a bit more going on than that.
-- First, Nixon was a Republican and at that time California was a swing state. Nixon promised
California a $2 billion for a liquid sodium based fast breeder reactor. Once this money was slated,
those who would benefit were not welcoming to anything that would threaten that fuel cycle.
-- The traditional nuclear power industry gained no benefit from the Thorium fuel cycle. It would only
make their large investments uncompetitive.
-- The US military had a huge amount of influence on the civilian nuclear program. They had far more
experience with U 235 and Pu 239 and understood those metals. Also they were very short of weapons
grade material and were looking for power plants to make Pu for them.
-- The USA had experience with Pressurized Light Water Reactors from nuclear subs. It would cost
more to pursue two different lines of technology.
Thus the USA made a critical error and shut down a superior technology.
The report that recommended shutting down Th reactors glossed over all of their advantages and
mentioned 3 technical problems. (Two of these problems were fixed before the report went to press.)
The third was the problem of the graphite moderator swelling under neutron bombardment.
At the time, the reactor core had hundreds of small holes drilled through a huge block of graphite. A
slight swelling had a major effect on the rate of flow. (This is why the final reactor was a single fluid
design.) However, today we have found that a tube-within-a-tube geometry (with the U 233 inside,
followed by the graphite and surrounded by the fertile thorium) works better, and is not so strongly
affected by slight changes in the graphite volume. Also, modern materials such as carbon – carbon,
fullerines or carbon composites may work better than simple carbon. In a worse case scenario, the
graphite tube could be replaced every 5 to 8 years or so.
LIQUID FLUORIDE THORIUM REACTORS ON MARS
Thorium has a very long half life (over 14 billion years), so it decays very, very slowly. However,
some elements on its decay chain will produce gamma rays at a precise frequency. The Mars Odyssey
Orbiter watched for this frequency and discovered low levels of Th 232 all over Mars. However, there
were areas with 8 times that concentration in the northern basin where people believe that the ancient
Borealis Ocean used to be.
Thorium is only very slightly soluble in water. If water flowed into the norther ocean for a very long
time, it would result in the observed build-up in that area. The Mars Odyssey can only see minerals in
the top half meter or so of the soil, so any thick layers of dust or sand dunes would hide this signal.
These northern deposits are poor quality compared to Earth ores, but are easily high enough quality to
give us an energy profit if we mine them. However, it is very likely, given Mars' volcanic history, that
better Thorium ores exist on the planet.
Thorium runs at a higher temperature than Pressurized Light Water Reactors (PLWR), so there will be
more process heat for chemical factories that need heat to build their products. A LFTR will give
MUCH more process heat than a geothermal heat power plant.
Given Thorium's many advantages over traditional nuclear power (more than 500 times more efficient
per amount of material mined, smaller lighter reactors, far less nuclear waste, short lived nuclear waste,
etc.), I believe that it is the logical form of nuclear power to be deployed by early colonists.
I will work with the Mars Foundation Project to figure out the smallest amount of mass that needs to be
sent to Mars to allow a LFTR to be built. The smaller the Martian industrial capacity the more mass
that might be sent. What would be needed...
-- Mining and Prospecting. (Thorium is very easy to find.)
-- Chemical processing to reduce rocks (to get the metallic Th) and create acids, etc. to free the fluorine
from rocks.
-- Steel production facilities.
-- Local made Sorel cement and a constructionindustry.
-- High tech materials (e.g. radiation resistant hastelloy N alloys).
If we are willing to accept lower efficiencies and shorter lifetimes for the reactors, we may be able to
substitute more traditional building materials for high tech materials.
We assume no R&D would be needed as LFTR's are being build on the Earth now.
The point is that the more of the above list that the Martian colonists can do on their own, the less mass
which would be needed to be sent from Earth.
CURRENT THORIUM REACTOR PROJECTS ON EARTH
•
India has the largest Th reserves on the planet and they have been working on reactors using the
Thorium fuel cycle for several years. However, they are using solid fuel which loses most of
the operational advantages of a LFTR.
•
France is spending money on studying chlorine based LFTR's which are designed to “burn up”
nuclear wastes from their other nuke plants. This is part of their 4th generation reactor studies.
•
Australia has huge Thorium reserves. They have partnered with the Czech Republic to build a
LFTR (not sure if money has been spent yet). The Czech Republic has a long history with coal
burning plants and has had some nuclear power plants for several years. They have promised to
reduce their carbon footprint and are looking to increase the amount of nuclear power
generated.
•
The UK has a powerful, bi-partisan Thorium movement but it seems to be at the study phase
currently.
•
Norway is looking to have a particle accelerator smash neutrons into Th 232 in order to breed
fuel.
•
The Netherlands (design studies only).
•
South Africa (a company wants to build these and is working on getting needed permits).
•
Canada and Chile. In 2012 on April 23, the Canadian Firm “Thorium Power Canada” bought a
Chilean firm. The Chilean firm already had all permits from Chile and the USA to build a
LFTR and the Canadian firm is providing funding. They are building a small 10 MWatt
(electric) plant which will provide power and desalination.
•
In January 2011, at the Chinese Academy of Science Conference they announced that they
would build LFTR's. Their program is headed by Jiang Mianheng who has political pull – he is
the son of former Chinese president Jiang Zemin. Jiang Mianheng is the vice president of the
Chinese Academy of Sciences. He lead a delegation of scientists on two visits to Oak Ridge
Labs to learn about the US molten salt program. He has a $400 M budget and 200 personnel
working on LFTR's. He expects to have two reactors finished by 2015.
•
US firms want to build LFTR's for power or to 'burn up' nuclear waste. They are so hamstrung
by regulations and licensing, that all of them say, “LFTR's will be built elsewhere first”. If
Peak Oil hits hard, I believe that the US will be buying these reactors from others.
CONCLUSION
Mars industries and cities will need abundant power and heat to quickly grow, and a LFTR is far safer
and more compact than traditional power plants. They also require less than 1/500th mining to gain
their fuel, which makes them uniquely suitable for a Martian colony.
REFERENCES
Videos on YouTube: (Search for...)?
-- “Google Tech Talk Aim High”
-- “Google Tech Talk Save U233”
-- “LFTR in 16 minutes”
-- “Google Tech Talk Is Nuclear Waste Really Waste”
-- energyfromthorium Blog and Forums.
-- Liquid Fluorine Thorium Reactors on Wikipedia
-- The Book “Super Fuel: Thorium the Green Energy Source for the Future” by R. Martin
-- The Book “Thorium: Energy Cheaper than Coal” by Robert Hargraves