Ryan Stolt
ENGR 2392-D02
08/03/2018
Liquid Fluoride Thorium Reactors
Abstract
In the realm of power production, there are a few major players constantly competing for
prominence around the globe. Coal, natural gas, nuclear, and renewables such as hydro, solar,
and wind are the leading power producers. Each form of power production comes with their own
unique sets of positives and negatives. It is no secret that the leading power producer, coal, is not
the best option with regards to the safety and welfare of the public due to the harmful byproducts
it releases into the atmosphere. As engineers, we are ethically obligated to strive towards a much
safer and cleaner option for power production.
Nuclear energy in its current form results in the lowest number of deaths per unit of
energy produced when compared to the other leading power producers. This is not to say that
nuclear energy in its current form is perfect. Although, we have the opportunity to continue to
work towards much safer and cleaner forms of nuclear power. The Liquid Fluoride Thorium
Reactor, a specific type of Molten Salt Reactor, is much safer and cleaner than any nuclear
power plant operating today. This paper will elaborate on the science behind this type of reactor,
the benefits and drawbacks of this technology, and the ethical theories and moral obligations that
are attached to it. This paper scratches the surface of the enormously complex science behind the
reactor and political and regulatory realities attached to the implementation of the reactor, but it
will become clear that the utilization of this technology can and should be the future of power
production. [1]
LFTR Background
There are currently 99 operating Nuclear Reactor Power Plants in the United States. 65
are Pressurized Water Reactors (PWR) and the remaining 34 are Boiling Water Reactors (BWR).
Both of these reactors were designed in the 1950’s and operate using a form of solid Uranium as
fuel. [2]
The Liquid Fluoride Thorium Reactor, (LFTR), is a Molten Salt Reactor, (MSR). This
type of nuclear reactor uses this liquid fluoride thorium mixture as fuel and coolant. The
thorium-232 isotopes will absorb a neutron, fission, and release more neutrons. Criticality is
achieved when this process is self-sustaining. As the fuel fissions, it releases heat which is
absorbed by the surrounding molten salt. This now ‘hot’ molten salt is carried away to heat
exchangers, which is used to power a turbine and ultimately, produce power in the form of
electricity. [3]
The Oak Ridge National Laboratory is responsible for the vast majority of research on the
MSR, with the first reactor, MSRE, going critical in 1965 and running for four years. This
reactor had a power rating of 7.4 MW and used a liquid fluoride salt as coolant. From 1970 to
1976, Oak Ridge National Lab proposed a Molten Salt Breeder Reactor. A Breeder Reactor is a
reactor that produces fissile material at a greater rate than the rate in which the fuel is consumed.
Around this time, funding fizzled out for the MSR’s research due to the countries favor in the
Fast Breeder Reactors (FBR). This happened for political and technical reasons during this time
period. [4]
The Liquid Fluoride Thorium Reactor is intended to create usable power in the form of
electricity like any other power producing system, but the appeal in the LFTR comes from how
clean and safely this energy can be produced. It is no secret as to how harmful coal power plant
byproducts are, with air pollution strictly from these coal plants prematurely ending the lives of
up to 52,000 people each year in the United States. As engineers, we are ethically obligated to
strive for a much safer form of energy production, even if it doesn’t seem economically
beneficial in the short term. [1] [5]
Nuclear Reactors in their current form produce about 11% of the world’s electricity and
20% of the Unites States’ electricity annually, but only cause 0.07 deaths per terawatt-hour of
energy produced, compared to the leading energy provider coal’s 57 deaths per terawatt-hour.
Even though nuclear energy has resulted in the lowest number of deaths per unit of energy
produced compared to all other forms of energy production, it is still viewed as unsafe in the
eyes of the public due to the few major nuclear incidents in the past few decades. This includes
the infamous Chernobyl disaster in 1986, the meltdown at Three Mile Island, and more recently,
the meltdown resulting from a tsunami at Fukushima Daiichi in 2011. [6] [1]
As engineers, we are obligated to do our absolute best to design and build these power
plants to be impervious to these incidents in the past and possible future ones. The LFTR would
by far be the safest Nuclear Reactor ever built. The LFTR operates at low pressures compared to
the current reactors which operate at extremely high pressures to keep the water or (coolant)
from boiling. The incident at Fukushima was a result of a high pressure explosion, causing the
meltdown of all 3 reactor cores. The LFTR would also have a constantly cooled freeze plug, so
when an incident occurred causing power failure, the plug would no longer be cooled, would
melt, and allow the fuel of the reactor to pass into a subcritical cooled storage container. This
design would result in a fail-safe that would easily handle any sort of power outage. [2] [5]
Another major concern from the public nuclear waste in the form of spent nuclear fuel.
Our current reactors use a form of low-enriched uranium as fuel. The uranium used in our
reactors is 5% U-235, and 95% U-238. Uranium-238 will transmute in a reactor into
plutonium-239, which has a half-life of 24,000 years. For good reason, people do not like the
idea of storing waste in the ground that will continue to be radioactive for such a long period of
time, even if it is safely stored in specialized casks. LFTR’s are different in the fact that they use
the thorium fuel cycle, a substance 4 times as abundant as natural Uranium. This cycle results in
thorium-232 being transmuted into uranium-233, which has a 90% chance of fissioning. If it
does not fission, it will then be transmuted into uranium-235 which has an 80% chance of
fissioning. This process allows the recycling of spent fuel into usable fuel in a LFTR. These
reactors result in 20 time less transuranic waste when compared to our conventional PWR and
BWRs used today. The waste that the LFTR produces also has a significantly lower half-life than
plutonium-239. The thorium fuel cycle produces cesium-137 and strontium-90 as fission
products, having half-lives of 30.2 years and 28.8 years respectively. After just 300 years, the
spent fuel will be as radioactive as the natural radiation you get from every-day living, posing no
threat to human health. [7] [8]
The thought of an ill-intentioned country producing weapons-grade radioactive material
is a scary thought. The byproducts of our uranium-fuel reactors produce plutonium-239, the
same material used in the “Fat-Man” bomb dropped on Nagasaki at the end of World War 2.
This is believed to be one of the main reasons why these reactors were favored in the 70’s by
Nixon, as our nuclear weapons arsenal increased during the cold-war. The idea of a nuclear
power plant producing this kind of material is something that is to be avoided and controlled at
all costs to reduce nuclear proliferation around the globe. Thankfully, the thorium fuel cycle
doesn’t produce plutonium-239, it produces plutonium-238, an isotope that cannot be used for
fission-bombs due to its high temperature and the abundance of neutrons spontaneously emitted.
The LFTR fuel can also be transmuted into thallium-208, a high energy gamma-ray emitter
which is easily identifiable and can harm potential electronic components used in a bomb. The
use of thorium as fuel would reduce the need for uranium as fuel in our current reactors. This
would remove the need for uranium enrichment, the same process used to convert natural
uranium into weapons-grade uranium. [9] [10]
There are disadvantages to the actual constructing and start-up of LFTR. The main one
being that the field of research has become almost stagnant after being defunded in the 1970’s.
The 99 nuclear reactors we have today in the United States are not capable of handling molten
salts. This means that these LFTR reactors would have to built from scratch, resulting in start-up
costs much larger than that of the pre-existing BWR or PWR. If the world ran on simply ‘doing
the right thing’ instead of using the most economically lucrative option, the LFTR would be well
researched and in construction and operation. This is obviously not the case, and has to be
financially viable for proper funding. The LFTR design has unique parts and equipment that are
not currently available like they are for the PWR and BWRs. [10] [11]
A material issue that arises is the corrosiveness of the molten salts used throughout the
reactor. The previously mentioned MSRE in the 1970’s used Hastelloy-N as the material that is
in direct contact with the salts. This produced small amounts of corrosion at the grain boundary.
If not improved upon, this corrosion could cause serious long term problems to the reactor
materials, causing performance issues. [4]
In terms of the economic feasibility of the LFTR reactor, the decommissioning costs is
believed to be much higher than that of a typical reactor used today. It cost around $130 million
to decommission and clean the MSRE. This was due to the unexpected effects of the cold fuel
salt storage. The current LFTR designs have dealt with this problem, understanding that the spent
fuel must be stored above about 100 C to keep it from cooling and evolving into hazardous
material. [12]
Communities, and the public as a whole would benefit from the LFTRs because due to
the safety it provides when compared to current nuclear reactors, and especially when compared
to the silently deadly coal and natural gas power plants. Even with the overwhelming benefits
that come with the LFTR, it is not easy to simply build the reactor. The reactor start-up
complexities involve economics, politics, regulatory commissions, and investors.
Critical Analysis
It is obvious that the implementation of the LFTR would benefit the general public. It is
simply a safer and cleaner way of producing power when compared to any other type of power
production facility. The world’s energy demands are only going to increase in the coming years,
so it seems clear that finding the safest and cleanest form of power production is paramount for
our long term goals. In terms of reliability, the LFTR does not rely on the everchanging variables
in unity with renewables like wind for wind turbines and sunlight for solar power plants. The
nature of a nuclear power plant makes it an extremely reliable producer of power.
The major concern regarding the problem with the LFTR is that the regulatory
commission agencies revolving around nuclear power plants have been built from the ground up
specifically for the types of reactors we have today. There would have to be major changes and
additions to the regulatory agencies, which in addition to expensive startup costs, makes the
LFTR design an economically and logistically unappealing option. Again, this is not an ideal
world that operates on good intentions, money is required to make things happen. In its current
form, the LFTR just isn’t an economically attractive option when compared to many other forms
of power production. [13]
The implementation of clean energy production falls most in line with the ethical theory
of utilitarianism. Utilitarianism, in short, is the idea of making decisions that will result in the
best benefits to the largest possible number of people. The thing that makes utilitarianism
difficult to utilize when making decisions is when money is involved. Utilitarianism requires the
decision maker to take an unbiased look at a situation, something very difficult for people to do,
and to treat each and every affected individual with the same amount of significance. One of the
biggest hurdles facing the production of LFTRs is that in the short term, it is logistically difficult
to regulate and financially unappealing to invest in. To take an utilitarianism approach would
require the organizations or groups providing the funding to not think of how much of a return
they could receive when compared to a more harmful alternative power production plant.
Instead, they would have to think of the large number of people that it would positively affect in
the long term. To act in a way as to produce the greatest good for the largest number of people,
nothing quite does that like directly saving lives from providing a much cleaner and safer form of
power production when compared to the prominent forms of power production used today. If the
people in positions to make progress of the construction and operation of the LFTR would take a
more utilitarianistic approach, they could put aside their short sighted financial and logistical
goals and provide the support needed to get the LFTR on track to become the leading power
producer. [13] [14]
In regards to the NSPE Code of Ethics, the element that most accurately aligns with clean
power production that the LFTR would provide, is the first statement under the fundamental
canons. Engineers shall “hold paramount the safety, health, and welfare of the public”.
Something as prominent, ever-growing, and consistent as power production should be as safe as
possible to the general public. When it is a known fact that our leading power production
facilities like coal and natural gas result in significant shortening or loss of human life, engineers
are ethically obligated to fix this problem. To continue to fund and support these power
production facilities in the name of convenience and profit is to accept the casualties that come
with it. [15]
In the code of ethics, under the ‘Professional Obligations’ article, in section 2 it states
that “Engineers shall at all times strive to serve the public interest”. More specifically, it also
states that “Engineers are encouraged to adhere to the principles of sustainable development in
order to protect the environment for future generations”. This specific statement explains what
the LFTR is about when compared to our current nuclear reactors. Even though nuclear power is
much safer than other forms of power production, the burying of long lived radioactive waste
and the few nuclear incidents that have occurred are unacceptable. The LFTR would bring safe
and clean energy to the public, without harming the environment. [15]
Conclusion
As the NSPE code of ethics states, it is most important that we “hold paramount the
safety, health, and welfare of the public”. To continue to use forms of power production that are
harmful and dangerous to the public is to ignore the first and foremost fundamental canon of the
code of ethics. The LFTR addresses and solves the 2 major public concerns with nuclear power.
First, the radioactive waste will change from our current reactor’s 24,000 year half-life to the
LFTR’s 30 year half-life. Secondly, the possibility of a meltdown, releasing harmful radiation
into the surrounding, is minimized with the design of a secondary tank that will collect the fuel
and coolant if there is a power loss. [15] [7]
The most compelling argument against the implementation of the LFTR is that is not
regulatorily or economically easy to achieve. There are other financially safer options that the
government funds for research, and the reality is that there would have to design improvements
to address some of the functionality concerns of the LFTR before it received an adequate level of
funding. The problem with this is that without funding, it is studied and researched in a
conceptual manner only. These needed improvements come from trial and error, something
impossible to do until the actual construction and operation of the reactor occurs. [12]
I believe that nuclear power is the future of power production. It will have to be studied
and refined for decades or even centuries before it is perfected, but it is our safest bet for safe and
clean energy. The LFTR design is one of many reactor designs that are striving for increased
performance and safety and deserves the proper funding it once received to continue to move
forward. As engineers, we are obligated to supply the public with the safest form of power
production available. I believe that nuclear power, and more specifically the LFTR, can lead us
in the right direction to solve this power production problem.
References
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[12] Crocker, Brittany. “Contaminated Molten Salt Reactor Experiment May Be Entombed in
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