A Clean Source of Energy That Will Be Available Forever
Thorium, discovered in 1828, is abundant in the earth and has been used since in industrial processes. Not only that, thorium just might underlie the future of a plentiful and widespread prosperity on earth, make wars over scarce fossil fuels obsolete, eliminate the release of choking and poisonous pollutants into the atmosphere and make the debate over global warming and climate change a moot point.
The reason uranium won out over thorium at the dawn of the Atomic Age was its ability to undergo fission and provide material for atomic weapons. Thorium was safer, cleaner and more abundant than uranium, but because nuclear weapons could not be built from it, it was relegated to a footnote in atomic energy journals for the past half century.
Like a Phoenix, Thorium Rising
The only way to leave fossil fuels in the ground, estimated at today’s market rates as having a value of over $40 trillion, is to find a source or sources of fuel that will undercut fossil fuel prices, making them uneconomical. The recent boom in fracking, not without its own environmental issues, has put a temporary damper on the use of coal in the United States but this is not the case in other parts of the world where coal is being used In large amounts, causing millions of deaths a year.
In “Thorium Energy Cheaper than Coal”, author Robert Hargraves compares coal, solar, wind, biofuels and other energy resources to “Liquid Fluoride Thorium Reactors.”
New Nuclear Technology Safer Than Fossil Fuels?
According to Kirk Sorensen, a former NASA engineer and president of Flibe Energy of Huntsville, Alabama, US utilities preparing to replace more than 30 nuclear reactors should consider the “liquid fluoride thorium reactor” (LFTR) or “lifter”, which is considered to be more efficient and safer. Sorensen, who coined the term “liquid fluoride thorium reactor”, believes the nuclear industry is thwarting the development of this technology to protect its turf while at the same time conceding its advantages.
Following is a video of Sorensen talking about thorium reactors:
US Competitor Are “All In” On Thorium
While all of US nuclear plants run on uranium, countries including India and Japan are beginning to adopt thorium as the fuel of choice for nuclear power plants of the future due to their efficiency and safety.
Flibe Energy Overview of the Florium Fuel Cycle
For a technical discussion about the differences between using uranium versus thorium for nuclear fuel, we turn to Flibe Energy and their detailed overview of the florium fuel cycle, in its entirety.
According to Flibe Energy, “in today’s approach to generating nuclear energy, we mine uranium oxide ore out of the ground and chemically convert it to a fluoride salt—first uranium tetrafluoride and then uranium hexafluoride. The reason for this is so that the uranium can be enriched.
But at the end of the process the uranium fluoride salt must be converted back to an oxide form and this is chemically unfavorable. Then the oxide powder is sintered into pellets which are loaded into rods which are formed into assemblies. It is these assemblies that are loaded into the reactor, irradiated to produce electricity, and then removed and disposed.
A liquid-fluoride reactor has the potential to dramatically simplify several of the steps in the nuclear fuel chain. Because the reactor uses fuel in the fluoride form, there is no need to convert uranium hexafluoride back to oxide and to form it into pellets, rods, and assemblies. The uranium hexafluoride can be reduced to uranium tetrafluoride as it is loaded into the reactor and used in that form to produce electrical energy. By using the nuclear fuel in fluoride form we not only simplify the fuel cycle but we make recycling of the fuel far more straightforward.
Although liquid-fluoride reactor technology can enable us to use uranium fuel with greater efficiency than we do today, we believe that the long-term viability of nuclear energy will come about when we are able to use nuclear fuels with far greater efficiency than we can today.
Only a small fraction of natural uranium is fissile. Most of the uranium and all of the thorium is fertile, meaning that it can be converted into fissile fuel inside a nuclear reactor.
Both thorium and uranium-238 require two neutrons to release their energies. One neutron converts them into a fissile form and the other neutron actually causes the fission. Thorium absorbs a neutron and becomes uranium-233, which will fission when struck by another neutron.
Uranium-238 absorbs a neutron and becomes plutonium-239, which will also fission.
But there is an important difference between these two options. The fission of uranium-233, when one accounts for non-fission absorptions, will produce 2.3 neutrons. This is enough to continue the conversion of more thorium to uranium-233 fuel, even when accounting for various losses. But the fission of plutonium-239 will produce less than two neutrons. It is not sustainable in today’s thermal-spectrum reactors.
The only way to sustainably use uranium-238 and plutonium is to go to fast-spectrum reactors, which intentionally attempt to keep neutrons at as high a velocity as possible. In these reactors, non-productive neutron absorption in plutonium is suppressed and plutonium fission will produce more than two neutrons, enabling sustained consumption of uranium.
The fundamental disadvantage of fast reactors is that the probability of neutron reactions, typically represented by a cross-sectional area, is much lower when the reactions are caused by fast neutrons than by slowed-down, thermal neutrons.
This picture depicts the “size” of a plutonium-239 nucleus to a thermal neutron on the left. The blue region represents the probability that the nucleus will fission and the red area represents the probability that the plutonium will simply absorb the neutron. As you can see, plutonium-239 will absorb thermal neutrons roughly one out of three times. On the right, to the same scale, you can see the size of the cross-sections of plutonium-239 for fast neutrons. They are much, much smaller; so much so that it requires hundreds of plutonium atoms to achieve the same probability of fission as a single plutonium atom to a thermal neutron. The implication of this difference is that fast reactors require much larger inventories of fissile fuel for a given power rating.
When we compare and contrast the performance of uranium-233, which comes from thorium, and plutonium-239, which comes from uranium, we can see that uranium-233 has a much greater probability of fission and less probability of non-productive absorption. This is the reason why we are so excited about the use of the thorium fuel cycle in thermal-spectrum reactors.The central advantage of thorium as a nuclear fuel is its unique ability to be sustainably consumed in a thermal spectrum reactor.
Thus nature presents us with three nuclear options. We can continue to do what we do today, which is to use the tiny sliver of fissile uranium that occurs naturally, or we can build fast spectrum reactors with large fissile inventories that can consume most of the uranium, or we can build thermal-spectrum reactors using the thorium fuel cycle that have low fissile inventories.”
The foregoing overview of the florium fuel cycle was provide, courtesy of Flibe Energy. For more details, visit the company’s website.
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References and related content:
- Thorium WoW
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- Kirk Sorensen: Thorium, an alternative nuclear fuel | Talk Video | TED.com