Stored solar energy is how one can think about all types of fossil fuels. Plants convert solar radiation (light) energy into chemical energy through photosynthesis. Layers of plant matter build up and, throughout millions of years, it converts into coal, oil, and natural gas.

It is noteworthy to point out that in 2011, 474 exaJoules of energy was used by the first world, or about 2 billion people – depending on how one defines the first world. This is equivalent to 449 quadrillion BTUs, representING all forms of energy combined (coal, oil, gas, nuclear, hydro, etc.). This is roughly equivalent to 15 billion tons of coal. If we wish to bring the other 5 billion people up to a first world standard of living, we would need to increase this energy production rate by three to five times, ignoring any advances in efficiency. If we wish to increase the standard of living beyond that of where the first world is today, bringing the energy per capita for everybody on the earth to twice that of the present level in the United States, we might need 10 times this rate of energy production. Achieving this with fossil fuels would be challenging to say the least. Even if one does not believe in climate change, consuming fossil fuels at 10 times the present rate should, at least, make one rethink that position.

Often considered the ultimate in renewable energy is solar energy. However, the world’s energy requirements are huge. If we wanted to meet all of the world’s energy needs with solar power alone, we would need a solar array that was a square, 280 miles on a side, an area approaching twice the size of the state of Ohio. Wind energy might help (wind is another form of solar energy), but it is doubtful solar energy will supply more than a small percentage of our energy needs for quite some time. Still, advances in solar cell technologies, and wind turbines, may result in solar energy being competitive with fossil fuels someday.

Let us aim high and ask: How can we raise the standard of living (more specifically, energy per capita) for everybody on planet Earth to U.S. levels, and increase that level by a factor of two? Also, let us achieve this without greenhouse gas emissions. To achieve this, we will almost certainly require a source that is very energy dense and available at a low cost.

Nuclear energy has one very significant advantage over all forms of fossil fuels (as well as all other forms of energy). Theoretically, nuclear energy has an energy density that exceeds that of fossil fuels by a factor of one million. The ramifications of this are enormous and cannot be overstated. If you want to have energy in abundance you need to give nuclear energy a serious look. Present day nuclear power plants consume (or burn) an isotope of Uranium, U-235. Only 0.7% of natural Uranium is U-235. The other 99.3% of Uranium is U-238. Conversion of U-238 to Plutonium-239 is through a process called breeding, where Plutonium-239 can then burn as fuel. There have been significant efforts during the past 60 years to build reactors that breed and burn Pu-239 (Liquid Metal Fast Breeder Reactors) but these have met with limited success. However, another element exists that can be bread into a consumable fuel. That element is Thorium, which can be bread into Uranium-233, also consumable nuclear fuel.

Back in the 1950s and 60s there was a significant effort to develop reactors to consume and breed U-233 from thorium. This occurred at Oak Ridge National Labs under the direction of the lab’s director, Alvin Weinberg (en.wikipedia.org/wiki/Alvin_M._Weinberg). Interestingly, Weinberg is the patent holder of the light water reactor (LWR), the predominant type of nuclear power reactor used in the world today. At the dawn of the nuclear era, nearly all nuclear scientists and engineers, including Weinberg, considered nuclear power based on the consumption of U-235 as a stopgap measure. The real promise of nuclear power was to be with breeder reactors. Here, arguably, history took a wrong turn. Two methods of breeding nuclear fuel exist: Method 1 – The breeding of Pu-239 from U-238 and Method 2 – The breeding of U-233 from Th-232. Pursuit of Method 2 was not to the degree it merited. The reason’s Method 1 was more vigorously pursued ahead of Method 2 were partially technical but mostly political (whitehousetapes.net/transcript/nixon/004-027). However, despite receiving only a tiny fraction of the funding of Method 1, the work done at Oak Ridge demonstrated the feasibility of breeding U-233 from Thorium as well as burning U-233 in Molten Salts. These molten salts serve as a carrier fluid for both Thorium and Uranium. The resulting design has been coined the Liquid Fluoride Thorium Reactor or LFTR. Below is a simplified LFTR diagram.

In a LFTR, fission takes place in a liquid core. Fission generates heat that ultimately finds use to do some useful work (e.g. drive a turbine to make electricity). Surrounding the core is a blanket of liquid carrying Thorium. Neutrons from fission pass from the core to the blanket for absorption by the Thorium. This transforms the Thorium to Uranium-233. After chemical removal of the Uranium-233 from the blanket, it goes into the core as new fuel. Next is the chemical removal of the fission products from the core. The process is self-sustaining, requiring only Thorium as input.

A LFTR was never build at ORNL. However, they did build and operate the Molten Salt Reactor Experiment (MRSE) for four years (en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment) from 1965 through 1969. This reactor generated 7.5 Megawatts of heat, allowing the scientists to determine the design parameters and work through system issues to arrive at a design that allows for the burning nuclear fuel in molten salts. The MSRE worked out nearly all key issues needed to build a LFTR.
The MSRE demonstrated:

1. The burning of both U-235 as well as U-233 in a carrier salt of LiF-BeF2-ZrF4-UF4
2. Operation at high temperature (650°C) at full power for more than one year
3. Operation at atmospheric pressure
4. That carrier salts were impervious to radiation damage
5. The carrier salt chemistry and metals metallurgy to eliminate corrosion
6. An efficient method of on-line refueling
7. Largely validated predictions

The MSRE did not:

1. Have a blanket to breed U-233 from Thorium (therefore, it was not a complete LFTR)
2. Have the size of a utility class power plant, (this was the next step before funding ceased)
3. Have a power conversion system to generate electricity

Conventional Nuclear Power suffers from two key issues: spent nuclear fuel or nuclear waste and costs of plant construction. Significant mitigation of both of these issues is with a LFTR.

Owing to the LFTRs liquid core, fuel stays in the core until consumption. This increases the fuel efficiency enormously, by a factor of 30 or more. So, there is much less production of waste. Moreover, because there is U-233 and almost no U-238 in the core, a LFTR produces almost no transuranics, which are the reason for the long storage (300,000-year storage and Yucca Mountain). The result is that compared to conventional nuclear energy, a LFTR produces less than 1% of the waste, and that waste needs to be stored for a much shorter period (300 years).

Conventional nuclear power plant costs are driven by safety issues along with the fact that water is used in the reactor to cool the core and transfer heat out to do useful work. For water to function efficiently as a medium to carry heat to a turbine, it needs to be much hotter than the 100°C where water normally boils. Accomplishment of this is by running the reactor under pressure – up to 140 atmospheres of pressure. This means the reactor is inside a pressure vessel at pressures up to 2,000psi. If for some reason pressure was lost, (e.g., a pipe break), the water would flash to steam and cooling of the reactor core would all but cease. Fission would stop, but the decay heat (heat generated from residual radioactivity from the fission products) would continue. If we do not get water on the core to cool it, the core will soon melt and release the fission products. This is what happened at Fukushima. Guarding against this event drives the design of the reactor and drives up the cost enormously. We have a thick steel walled pressure vessel, placed inside a thick walled reinforced concrete containment building with about 1,000 times the internal volume of the reactor pressure vessel (to contain the steam), and we have a variety of pumps and backup systems to get water on the core if things go wrong. All built to reactor grade specifications. Contrast this to a LFTR. Because LFTRs use molten salts that remain liquid at high temperatures and at atmospheric pressures, LFTRs have no need for a pressure vessel. LFTRs have no water that can flash to steam and thus no need for the large reinforced concrete containment building. If you need to shut down a LFTR, you drain the liquid core into a series of drain tanks underground, configured to dissipate the decay heat passively. There is no need for high-pressure backup pumping systems to keep the core cool in the event of an emergency. This significantly simplifies the total system design and lowers the capital cost. In fact, the liquid core of a LFTR allows for compact designs that can be built in a modular fashion in a factory, significantly driving down costs further.

LFTRs have some significant advantages compare to today’s nuclear power. The most significant of these stem from the liquid core running at atmospheric pressure.

These advantages are:

1. No water under pressure, therefore no pressure vessel, reducing cost
2. No large reinforced concrete containment building is required, reducing cost
3. Can be built in a factory, reducing costs
4. Because the core can be drained, LFTRs exhibit an enormous level of passive safety
5. Can be refueled without shut down
6. Exhibit 100% fuel burn up and generates almost no long lived radioactive waste
7. Configurations of LFTRs can consume the long lived radioactive elements in our present stockpiles of nuclear waste
8. Allow for the extraction of molybdenum-99 for medical purposes. Eliminating a supply shortage issue (ncbi.nlm.nih.gov/pubmed/21512666)
9. Allows for the extraction (in large quantities) of other radioactive isotopes for medical purposes
10. Can operate at high temperature, allowing the use of waste heat to desalinate seawater; higher temperatures can make for economical generation of synthetic fuels, (could use CO₂ from the atmosphere, thus making synthetic fuels carbon neutral)

Thorium exists in high concentrations in a number of locations on earth, often found in high concentrations with rare earth elements (REEs). Because present policy requires treating thorium as low-level nuclear waste, very little REE mining occurs within the United States (thoriumenergyalliance.com/downloads/TEAC4%20presentations/Kennedy_TEAC4.pdf).

Since 100% of Thorium in the earth’s crust is Th-232 you can use all natural Thorium as fuel. The earth’s crust has nearly four times as much Thorium as Uranium. In fact, small amounts of thorium are present in all rocks, soil, water, plants, and animals. Soil contains an average of about six parts of thorium per million parts of soil. That may not sound like much, but recall that the energy density of Thorium is over 1 million times greater than that of any fossil fuel. That means there is roughly the energy of four barrels of oil (in the form of thorium) in a cubic foot of dirt, everywhere – including the dirt in your backyard. Therefore, if the population of the earth was to consume energy at 10 times our present rate, we could power the world for one year on 10 billion tons of dirt. The world presently consumes more than half this quantity of coal alone in a single year. Since we are talking about common dirt, we could supply the world with energy (at 10 times our present rate) for millions of years. Additionally, thorium exists in a number of locations around the world, including the United States, at much greater concentrations than six parts per million. To learn more visit energyfromthorium.com/lftradsrisks.html.

All images courtesy of U.S. Department of Energy and Oak Ridge National Laboratory, Advanced SMR Technology Symposium Small Modular Reactors, 2011

Yesterday I wrote a bit on the nuclear “waste” issue that is facing our country. I keep putting nuclear “waste” in quotes not in an attempt to be cheeky, but rather as a recognition that most people see this issue fairly differently than I do. They see nuclear “waste” as just that, a waste, whereas I see it as an under-appreciated opportunity.

So it was with great delight that I opened my emails this morning and saw one from a friend at the Oak Ridge National Lab talking about a recently released report titled “Fast Spectrum Molten Salt Reactor Options“. Now I’ll readily admit that a title like that probably isn’t going to cause many people to reshuffle their vacation reading list, but let me tell you a little bit about why I think you should care about what’s in that paper. In short, it describes some very compelling technology to not only solve the nuclear “waste” problem but how to turn it into a financial opportunity.

In the United States and over all the world, our nuclear reactors today are based on using uranium very inefficiently. We only consume a small fraction of the energy content in the uranium (less than 1%) before we remove it and throw it away. We don’t do this because we’re stupid or evil, we do it because it’s very difficult to get the vast majority of the energy out of the uranium. My nuclear engineering friends will probably cringe when they hear me say this, but it’s because most of the uranium doesn’t “burn good”. Only a little bit “burns good” and that’s the part we “burn”.

Building nuclear reactors that “burn” the rest of the uranium is hard, because we have to build a totally different kind of reactor from the kinds we have today. These reactors use “fast” neutrons instead of “slow” neutrons in the reactor. All of our reactors today use “slow” neutrons, and again, there’s some very good reasons for that. We’re not using “slow” neutrons because it’s a bad idea–in fact, using “slow” neutrons solves a lot of problems.

But when it comes to getting uranium to “burn good”, you have to get into using “fast” neutrons and dealing with the challenges that go along with doing that. And that’s why this paper is so interesting–it describes a way to build reactors that use fast neutrons but are much simpler and safer than other ideas we’ve had on how to build reactors that use fast neutrons.

The most basic difference is that the Oak Ridge paper suggests using liquid nuclear fuels instead of solid nuclear fuels. That solves a lot of problems right from the outset. Liquid fuels are mixed up in big batches, by remote control, with very simple procedures. Solid fuels also have to be mixed up in big batches by remote control but then have to be fabricated into shapes, typically pellets or spheres. Getting the fabrication just right is a major cost and technical challenge. That’s just not a problem for liquid fuels.

Another big difference is how you move the heat generated by nuclear fission out of the reactor. In the standard ideas for a “fast” neutron reactor, liquid sodium metal coolant has been used to transfer the heat generated in the solid rods from the inside of the reactor to the outside. Liquid sodium is very good at absorbing heat–as engineers would say, it’s very “thermally conductive“, but it’s not very good at holding a lot of heat–as an engineer would say, it doesn’t have a lot of “thermal capacity“. So you tend to need a lot of sodium to move the heat from the inside of the reactor to the outside.

Sodium metal has another big problem. It’s super-reactive and burns on contact with air or water, so you have to keep all this sodium away from the two most common things on our planet. If you watch the video I linked, you should know that this was a small piece of metallic sodium. These sodium-cooled fast reactors have hundreds of tonnes of the stuff, in a heat exchanger with guess what? High pressure water. No kidding.

The material used for the fuel in the Oak Ridge report is different. It’s asalt, which means it’s in a class of materials that are the most stable and non-reactive known to man. And since the fuel is a liquid, it is its own vehicle for moving that heat from the inside of the core to the outside. It doesn’t react with air and water. These salts aren’t as good as sodium at moving heat (thermal conductivity) but they hold a lot more heat than sodium (thermal capacity). This means that they have the potential to be more compact and less expensive.

So again, why should you care about these little engineering facts? Because you’ve got a personal $83 share in the $25 billion waste fund that has been collected over the last 30 years to deal with nuclear “waste”, and this liquid-salt-based nuclear reactor could be the means to dealing with that waste in a way that will make money rather than consume it.

More on that to come…

Appears in Print As: Thinking Nuclear? Think Thorium

Thorium-based reactors could be more efficient and create less waste than today’s uranium-based generating plants.

Authored by: Kirk Sorensen Nuclear-engineering graduate student Univ. of Tennessee Madison, Ala.Edited by Stephen J. Mraz stephen [dot] mraz [at] penton [dot] comResources: Energy from Thorium,energyfromthorium.comThorium Energy Alliance,www.thoriumenergyalliance.com

From the early 1950s to the mid-1970s, an active R&D program at Oak Ridge National Laboratory in Tenn. came up with a promising way to use thorium for making large amounts of energy cleanly and safely. It was based on a revolutionary kind of nuclear reactor that uses liquid rather than solid fuel. Liquid fuel has significant theoretical advantages in operation, control, and processing over solid fuel, but a basic question had to be answered: “Will it work?”

To that end, Oak Ridge engineers built four liquid-fueled reactors. Two used water-based liquids, and two were based on liquid fluoride salts. The water-based reactors had to operate at high pressures to generate the temperatures needed for economical power generation. They could also dissolve uranium compounds, but not those containing thorium, which made fuel reprocessing as complicated for the water-based rectors as it is for solid-fueled versions.

The fluoride reactors had neither of these drawbacks. They could operate at high temperature without pressurization. They could also dissolve both uranium and thorium in their fluoride-salt mixtures, and the mixtures were impervious to radiation damage due to their ionic bonds. Therefore, Oak Ridge engineers opted to concentrate on the technically superior liquid-fluoride-salt approach in future R&D.

In the late 1960s, however, the director of Oak Ridge National Lab, Alvin Weinberg, was fired by the U.S. Atomic Energy Commission for his advocacy for this type of reactor and his efforts to enhance the safety of conventional light-water reactors, a design he had patented. With Weinberg’s departure, the AEC squashed research in liquid-fluoride reactors in favor of liquid-sodium-metal-cooled fast breeder reactors, which were based on converting conventional uranium to plutonium. Technical overlap between the two programs was almost nonexistent, so after cancellation, research into liquid-thorium reactors faded away.

Interest in thorium reactors has undergone a significant resurgence in the last few years. Despite the lack of funding, individual efforts continue to advance the technology. This “open-source” effort has been greatly aided by the Internet and the vast amount of research done by government scientists and engineers.

Thorium basics
Thorium is a naturally occurring, mildly radioactive element. To use it in reactors, thorium must absorb neutrons, a process that eventually converts it to an artificial isotope of uranium, uranium-233. U-233 is fissile, and when it absorbs a neutron it generally fissions, releasing two or three neutrons plus a million times more heat (energy) than burning an equivalent mass of fossil fuel. It takes two neutrons to release energy from thorium and U-233 can supply them, which means it is theoretically possible to sustain energy release from thorium indefinitely. This is the basis of a thorium reactor.

Another approach to thorium Thorium as a nuclear fuel has been proposed for a variety of different nuclear reactors. One approach is to use solid thorium-oxide fuel rods in existing water-cooled nuclear reactors. This was demonstrated in the Shippingport nuclear reactor in the late 1970s and is currently advocated by a company called Lightbridge, McLean, Va. (www.ltbridge.com). Used in conventional reactors, thorium increases fuel performance by allowing longer fuel burn up, but the gains are nowhere near the improvement possible in LFTRs. That’s because the thorium fuel would have to be reprocessed to extract more of its energy, and reprocessing thorium oxide fuel is substantially more difficult than reprocessing uranium oxide fuel, a procedure that is not currently cost effective.

Recent efforts focuses on a concept called the Liquid-Fluoride Thorium Reactor (LFTR, pronounced “lifter”). In a LFTR, the reactor vessel contains two types of liquid-fluoride salts. One, the fuel salt, holds the fissile fuel (U-233) that sustains the nuclear reaction. The other, the blanket salt, has enough thorium to absorb about half of the neutrons from fission and produce more U-233.

The blanket salt also shields the reactor vessel from neutron damage and gamma-ray irradiation. As thorium in the blanket converts to U-233, it is physically transferred to the fuel salt, where it fissions, releasing neutrons and heat. Heat moves to a coolant salt outside the core, then to the working fluid of a closed-cycle gas-turbine engine to generate electricity. Waste heat can be rejected to either air or water, depending on the availability of cooling water. Waste heat could also be used to, for example, desalinate seawater, letting it profitably produce potable water.

How it works
There are some key requirements for the fuel and blanket salts. They must:

• be chemically stable
• be impervious to radiation
• have little appetite for neutron absorption
• be able to dissolve significant amounts of uranium, thorium, and fission products
• have minimal melting temperatures
• have high heat capacities.

Fortunately, chemists long ago identified a mix of lithium and beryllium fluoride salts that fits the bill. One main ingredient is lithium fluoride (LiF), which is highly enriched in lithium-7. This isotope makes up 90% of natural lithium and has almost no propensity to absorb neutrons. The other ingredient is beryllium difluoride (BeF₂). It is toxic and must be used carefully, but is well understood by beryllium manufacturers. (This mix, lithium fluoride and beryllium fluoride (LiF-BeF₂) is sometimes called “FLiBe.”)

Uranium tetrafluoride (UF₄) is dissolved in the FLiBe fuel salt, while thorium tetrafluoride (ThF₄) is dissolved in the blanket salt. Both mixtures have a volumetric heat capacity comparable to that of water (or four times that of liquid sodium and 2,000 times that of helium). This means reactors can be smaller than conventional ones with the same power output.

The coolant salt could be a variety of different mixtures, but the leading candidate is currently a mix of lithium fluoride, sodium fluoride, and potassium fluoride (LiF-NaF-KF), sometimes called “FLiNaK”. Coolant salt pumped through the primary heat exchanger pulls heat out of the fuel salt, then gives up that heat to a gaseous working fluid in the gas heaters.

The closed-cycle gas turbine could be based on a variety of different pure gases or gas mixtures. It differs from other gas turbines proposed for nuclear reactors because the gas in the turbine never directly cools the nuclear fuel itself. This is referred to as an indirect rather than a direct gas-turbine cycle, which has been proposed for pebble-bed and gas-cooled solid-fueled reactors.

Indirect gas turbines have several advantages over direct versions. For example, the gas never has to withstand the damaging neutronic environment of the reactor. Contamination concerns, which bedeviled nuclear-gas-turbine efforts such as pebble-bed reactors, are also nearly eliminated by keeping the gas away from the reactor fuel. Indirect turbines also let the core operate at ambient pressure even though the gas loop is at high pressure. The coolant salt that separates the gas and fuel salt prevents pressurization of the fuel salt in case of a gas leak into the coolant by blowing out check valves, thus preventing core pressurization.

The gas-turbine approach for LFTR could use nitrogen as a working fluid, which is essentially identical to air for design purposes. This would let engineers apply their vast knowledge of open-cycle, air-based gas turbines, saving time and money.

In the closed-cycle gas-turbine approach, the gas must be heated and cooled externally. Heating comes from the reactor’s coolant salt. Cooling, on the other hand, will come from using either air or water as a heat sink. If air is used, the gas-to-gas heat exchangers will be large, but the reactor will not need local cooling water. This would let LFTRs be built in arid regions and other locations traditionally not able to handle nuclear plants because of scarce water supplies.

If water cools the gas in the turbine, the heat exchangers (and capital costs) will be much smaller. And using seawater as a coolant opens further possibilities. Currently, power plants using steam for power conversion must reject heat through the plant’s condenser isothermally (at a constant temperature). So to improve efficiency at these plants, condensation is done at pressures far below atmospheric pressure and at extremely low densities. This leads to large equipment, large capital costs, and the need for lots of cooling water.

A LFTR’s gas cooling, on the other hand, rejects heat from about 100°C down to about 30°. In properly built heat exchangers, the waste heat could be used to distill seawater into fresh water. Multiple-stage distillation at different pressures would even let this waste heat be “reused” several times to get even more fresh water. Thus LFTR plants in coastal regions could send both electricity and fresh water to local consumers.

Burning it all up
The temperatures at which LFTRs operate (700 to 800°C) let their power-conversion system hit efficiency levels of nearly 50%, compared to only 35% for conventional nuclear plants. And the efficiency at which a LFTR converts thorium into heat lets utilities get 200 to 300 times more useful energy of out of a kilogram of thorium than they can from a kilogram of uranium.

Current uranium-fueled reactors can only extract a small amount of uranium’s potential energy before it becomes too badly damaged from radiation and depleted of fissile content. Currently, technicians remove the spent and damaged uranium and it is stored until eventual disposal. The fuel could be reprocessed using conventional methods such as plutonium-uranium extraction (Purex) to remove fissile material and refabricate new fuel elements. But these techniques are expensive and only improve the energy payoff by a few more percent. To access all the energy in uranium fuel requires a fast breeder reactor, which costs significantly more than a conventional uranium reactor. Thus utilities have powerful incentives to use fresh uranium, extracting only a small amount of energy before throwing it away.

LFTRs, on the other hand, can profitably extract essentially all of thorium’s energy without complicated reprocessing or excessive capital costs. This is because the fuel type and reactor configuration would be specifically chosen to simplify fuel processing. As uranium-233 fuel forms in the LFTR’s blanket, it can be removed easily by sparging with fluorine gas in an external fluorination column. This converts the uranium tetrafluoride (UF₄) in solution into gaseous uranium hexafluoride (UF₆). UF₆ percolates out of the blanket and is directed to the fuel salt, where it is reduced back to UF₄ by hydrogen gas in a reduction column. The HF created during reduction is electrolytically split back into H₂and F₂ to provide reactants for the process all over again.

Within the fuel salt, gaseous fission products such as xenon are released during fission that can “poison” the fission process and make changing power settings quite difficult. All high-power civilian reactors have to fight xenon poisoning during power level changes, and grid blackouts are especially troublesome. If a conventional nuclear reactor is shut down for more than a few hours because of a blackout, it has to remain shut down for about a day to let the xenon decay sufficiently before it can be restarted.

In LFTRs, xenon comes out of solution as the fuel salt is pumped, letting it be removed effortlessly and disposed of properly. This lets the reactor respond quickly and effectively to changes in power settings and changes in the power grid.

LFTRs also address the problem of fission products building up. The LiF-BeF₂-UF₄ fuel salt accumulates fission products which need to be removed every year or so. This could be done by removing the valuable uranium-233 from the salt by fluorination, as was mentioned previously, leaving a “bare” salt of FLiBe and fission products. Then in a high-temperature distillation still, the LiF and BeF₂ are volatilized and separated from the remaining fission products. LiF, BeF₂, and UF₄ are then recombined to reform the fuel salt which is reintroduced into the reactor. The remaining fission products contain valuable stable minerals such as neodymium, lanthanum, and praseodymium which can be separated and used commercially.

And one of LFTR’s major benefits is that because it completely “uses up” the thorium, there is relatively little nuclear waste.

The fuel choices, reactor configuration, and power conversion system of LFTR have all been chosen to make efficient energy from thorium a reality. It will take research, substantial development effort, and national will to achieve this goal, but the payoff will be immense. A world powered by thorium safely for many tens of thousands of years is the goal of those working to realize the potential of thorium.

There’s thorium in them thar hills Thorium is more common in the Earth’s crust than tin, tungsten, mercury, or silver, not to mention uranium. Out of a cubic meter of average crust, there is the equivalent of about 40 gm or four sugar cubes of thorium. This is enough thorium to provide enough electricity to fully support one person for about 10 to 15 years if completely fissioned to release its energy.Our current regulatory environment requires that mined thorium be considered “waste” and disposed of at great expense. In fact, the U.S. has buried 3,200 metric tonnes of refined thorium nitrate in the Nevada desert due to the lack of demand.It’s estimated that there are 160,000 tons of thorium that could be dug out of the U.S. And it’s easy to find the element on other planets such as Mars. In fact, our Moon has as much as the Earth. To make matters even simpler, the increased demand for rare-earth elements such as neodymium and samarium will lead to large amounts of available thorium in the near future because it is commonly found alongside these elements.

• By Richard Martin
• Email Author
• December 21, 2009 |
• 10:00 am |
• Categories: Wired Jan 2010

Photo: Thomas Hannich

The thick hardbound volume was sitting on a shelf in a colleague’s office when Kirk Sorensen spotted it. A rookie NASA engineer at the Marshall Space Flight Center, Sorensen was researching nuclear-powered propulsion, and the book’s title — Fluid Fuel Reactors — jumped out at him. He picked it up and thumbed through it. Hours later, he was still reading, enchanted by the ideas but struggling with the arcane writing. “I took it home that night, but I didn’t understand all the nuclear terminology,” Sorensen says. He pored over it in the coming months, ultimately deciding that he held in his hands the key to the world’s energy future.

Published in 1958 under the auspices of the Atomic Energy Commission as part of its Atoms for Peace program, Fluid Fuel Reactors is a book only an engineer could love: a dense, 978-page account of research conducted at Oak Ridge National Lab, most of it under former director Alvin Weinberg. What caught Sorensen’s eye was the description of Weinberg’s experiments producing nuclear power with an element called thorium.

At the time, in 2000, Sorensen was just 25, engaged to be married and thrilled to be employed at his first serious job as a real aerospace engineer. A devout Mormon with a linebacker’s build and a marine’s crew cut, Sorensen made an unlikely iconoclast. But the book inspired him to pursue an intense study of nuclear energy over the next few years, during which he became convinced that thorium could solve the nuclear power industry’s most intractable problems. After it has been used as fuel for power plants, the element leaves behind minuscule amounts of waste. And that waste needs to be stored for only a few hundred years, not a few hundred thousand like other nuclear byproducts. Because it’s so plentiful in nature, it’s virtually inexhaustible. It’s also one of only a few substances that acts as a thermal breeder, in theory creating enough new fuel as it breaks down to sustain a high-temperature chain reaction indefinitely. And it would be virtually impossible for the byproducts of a thorium reactor to be used by terrorists or anyone else to make nuclear weapons.

Weinberg and his men proved the efficacy of thorium reactors in hundreds of tests at Oak Ridge from the ’50s through the early ’70s. But thorium hit a dead end. Locked in a struggle with a nuclear- armed Soviet Union, the US government in the ’60s chose to build uranium-fueled reactors — in part because they produce plutonium that can be refined into weapons-grade material. The course of the nuclear industry was set for the next four decades, and thorium power became one of the great what-if technologies of the 20th century.

Today, however, Sorensen spearheads a cadre of outsiders dedicated to sparking a thorium revival. When he’s not at his day job as an aerospace engineer at Marshall Space Flight Center in Huntsville, Alabama — or wrapping up the master’s in nuclear engineering he is soon to earn from the University of Tennessee — he runs a popular blog called Energy From Thorium. A community of engineers, amateur nuclear power geeks, and researchers has gathered around the site’s forum, ardently discussing the future of thorium. The site even links to PDFs of the Oak Ridge archives, which Sorensen helped get scanned. Energy From Thorium has become a sort of open source project aimed at resurrecting long-lost energy technology using modern techniques.

And the online upstarts aren’t alone. Industry players are looking into thorium, and governments from Dubai to Beijing are funding research. India is betting heavily on the element.

The concept of nuclear power without waste or proliferation has obvious political appeal in the US, as well. The threat of climate change has created an urgent demand for carbon-free electricity, and the 52,000 tons of spent, toxic material that has piled up around the country makes traditional nuclear power less attractive. President Obama and his energy secretary, Steven Chu, have expressed general support for a nuclear renaissance. Utilities are investigating several next-gen alternatives, including scaled-down conventional plants and “pebble bed” reactors, in which the nuclear fuel is inserted into small graphite balls in a way that reduces the risk of meltdown.

Those technologies are still based on uranium, however, and will be beset by the same problems that have dogged the nuclear industry since the 1960s. It is only thorium, Sorensen and his band of revolutionaries argue, that can move the country toward a new era of safe, clean, affordable energy.

Named for the Norse god of thunder, thorium is a lustrous silvery-white metal. It’s only slightly radioactive; you could carry a lump of it in your pocket without harm. On the periodic table of elements, it’s found in the bottom row, along with other dense, radioactive substances — including uranium and plutonium — known as actinides.

Actinides are dense because their nuclei contain large numbers of neutrons and protons. But it’s the strange behavior of those nuclei that has long made actinides the stuff of wonder. At intervals that can vary from every millisecond to every hundred thousand years, actinides spin off particles and decay into more stable elements. And if you pack together enough of certain actinide atoms, their nuclei will erupt in a powerful release of energy.

To understand the magic and terror of those two processes working in concert, think of a game of pool played in 3-D. The nucleus of the atom is a group of balls, or particles, racked at the center. Shoot the cue ball — a stray neutron — and the cluster breaks apart, or fissions. Now imagine the same game played with trillions of racked nuclei. Balls propelled by the first collision crash into nearby clusters, which fly apart, their stray neutrons colliding with yet more clusters. Voilè0: a nuclear chain reaction.

Actinides are the only materials that split apart this way, and if the collisions are uncontrolled, you unleash hell: a nuclear explosion. But if you can control the conditions in which these reactions happen — by both controlling the number of stray neutrons and regulating the temperature, as is done in the core of a nuclear reactor — you get useful energy. Racks of these nuclei crash together, creating a hot glowing pile of radioactive material. If you pump water past the material, the water turns to steam, which can spin a turbine to make electricity.

Uranium is currently the actinide of choice for the industry, used (sometimes with a little plutonium) in 100 percent of the world’s commercial reactors. But it’s a problematic fuel. In most reactors, sustaining a chain reaction requires extremely rare uranium-235, which must be purified, or enriched, from far more common U-238. The reactors also leave behind plutonium-239, itself radioactive (and useful to technologically sophisticated organizations bent on making bombs). And conventional uranium-fueled reactors require lots of engineering, including neutron-absorbing control rods to damp the reaction and gargantuan pressurized vessels to move water through the reactor core. If something goes kerflooey, the surrounding countryside gets blanketed with radioactivity (think Chernobyl). Even if things go well, toxic waste is left over.

When he took over as head of Oak Ridge in 1955, Alvin Weinberg realized that thorium by itself could start to solve these problems. It’s abundant — the US has at least 175,000 tons of the stuff — and doesn’t require costly processing. It is also extraordinarily efficient as a nuclear fuel. As it decays in a reactor core, its byproducts produce more neutrons per collision than conventional fuel. The more neutrons per collision, the more energy generated, the less total fuel consumed, and the less radioactive nastiness left behind.

Even better, Weinberg realized that you could use thorium in an entirely new kind of reactor, one that would have zero risk of meltdown. The design is based on the lab’s finding that thorium dissolves in hot liquid fluoride salts. This fission soup is poured into tubes in the core of the reactor, where the nuclear chain reaction — the billiard balls colliding — happens. The system makes the reactor self-regulating: When the soup gets too hot it expands and flows out of the tubes — slowing fission and eliminating the possibility of another Chernobyl. Any actinide can work in this method, but thorium is particularly well suited because it is so efficient at the high temperatures at which fission occurs in the soup.

In 1965, Weinberg and his team built a working reactor, one that suspended the byproducts of thorium in a molten salt bath, and he spent the rest of his 18-year tenure trying to make thorium the heart of the nation’s atomic power effort. He failed. Uranium reactors had already been established, and Hyman Rickover, de facto head of the US nuclear program, wanted the plutonium from uranium-powered nuclear plants to make bombs. Increasingly shunted aside, Weinberg was finally forced out in 1973.

That proved to be “the most pivotal year in energy history,” according to the US Energy Information Administration. It was the year the Arab states cut off oil supplies to the West, setting in motion the petroleum-fueled conflicts that roil the world to this day. The same year, the US nuclear industry signed contracts to build a record 41 nuke plants, all of which used uranium. And 1973 was the year that thorium R&D faded away — and with it the realistic prospect for a golden nuclear age when electricity would be too cheap to meter and clean, safe nuclear plants would dot the green countryside.

The core of this hypothetical nuclear reactor is a cluster of tubes filled with a fluoride thorium solution. 1// compressor, 2// turbine, 3// 1,000 megawatt generator, 4// heat exchanger, 5// containment vessel, 6// reactor core.
Illustration: Martin Woodtli

When Sorensen and his pals began delving into this history, they discovered not only an alternative fuel but also the design for the alternative reactor. Using that template, the Energy From Thorium team helped produce a design for a new liquid fluoride thorium reactor, or LFTR (pronounced “lifter”), which, according to estimates by Sorensen and others, would be some 50 percent more efficient than today’s light-water uranium reactors. If the US reactor fleet could be converted to LFTRs overnight, existing thorium reserves would power the US for a thousand years.

Overseas, the nuclear power establishment is getting the message. In France, which already generates more than 75 percent of its electricity from nuclear power, the Laboratoire de Physique Subatomique et de Cosmologie has been building models of variations of Weinberg’s design for molten salt reactors to see if they can be made to work efficiently. The real action, though, is in India and China, both of which need to satisfy an immense and growing demand for electricity. The world’s largest source of thorium, India, doesn’t have any commercial thorium reactors yet. But it has announced plans to increase its nuclear power capacity: Nuclear energy now accounts for 9 percent of India’s total energy; the government expects that by 2050 it will be 25 percent, with thorium generating a large part of that. China plans to build dozens of nuclear reactors in the coming decade, and it hosted a major thorium conference last October. The People’s Republic recently ordered mineral refiners to reserve the thorium they produce so it can be used to generate nuclear power.

In the United States, the LFTR concept is gaining momentum, if more slowly. Sorensen and others promote it regularly at energy conferences. Renowned climatologist James Hansen specifically cited thorium as a potential fuel source in an “Open Letter to Obama” after the election. And legislators are acting, too. At least three thorium-related bills are making their way through the Capitol, including the Senate’s Thorium Energy Independence and Security Act, cosponsored by Orrin Hatch of Utah and Harry Reid of Nevada, which would provide $250 million for research at the Department of Energy. “I don’t know of anything more beneficial to the country, as far as environmentally sound power, than nuclear energy powered by thorium,” Hatch says. (Both senators have long opposed nuclear waste dumps in their home states.)

Unfortunately, $250 million won’t solve the problem. The best available estimates for building even one molten salt reactor run much higher than that. And there will need to be lots of startup capital if thorium is to become financially efficient enough to persuade nuclear power executives to scrap an installed base of conventional reactors. “What we have now works pretty well,” says John Rowe, CEO of Exelon, a power company that owns the country’s largest portfolio of nuclear reactors, “and it will for the foreseeable future.”

Critics point out that thorium’s biggest advantage — its high efficiency — actually presents challenges. Since the reaction is sustained for a very long time, the fuel needs special containers that are extremely durable and can stand up to corrosive salts. The combination of certain kinds of corrosion-resistant alloys and graphite could meet these requirements. But such a system has yet to be proven over decades.

And LFTRs face more than engineering problems; they’ve also got serious perception problems. To some nuclear engineers, a LFTR is a little … unsettling. It’s a chaotic system without any of the closely monitored control rods and cooling towers on which the nuclear industry stakes its claim to safety. A conventional reactor, on the other hand, is as tightly engineered as a jet fighter. And more important, Americans have come to regard anything that’s in any way nuclear with profound skepticism.

So, if US utilities are unlikely to embrace a new generation of thorium reactors, a more viable strategy would be to put thorium into existing nuclear plants. In fact, work in that direction is starting to happen — thanks to a US company operating in Russia.

Located outside Moscow, the Kurchatov Institute is known as the Los Alamos of Russia. Much of the work on the Soviet nuclear arsenal took place here. In the late ’80s, as the Soviet economy buckled, Kurchatov scientists found themselves wearing mittens to work in unheated laboratories. Then, in the mid-’90s, a savior appeared: a Virginia company called Thorium Power.

• Uranium-Fueled Light-Water Reactor
• Fuel Uranium fuel rods
• Fuel input per gigawatt output250 tons raw uranium
• Annual fuel cost for 1-GW reactor $50-60 million
• Coolant Water
• Proliferation potential Medium
• Footprint 200,000-300,000 square feet, surrounded by a low-density population zone

• Seed-and-Blanket Reactor
• Fuel Thorium oxide and uranium oxide rods
• Fuel input per gigawatt output4.6 tons raw thorium, 177 tons raw uranium
• Annual fuel cost for 1-GW reactor $50-60 million
• Coolant Water
• Proliferation potential None
• Footprint 200,000-300,000 square feet, surrounded by a low-density population zone

• Liquid Fluoride Thorium Reactor
• Fuel Thorium and uranium fluoride solution
• Fuel input per gigawatt output1 ton raw thorium
• Annual fuel cost for 1-GW reactor $10,000 (estimated)
• Coolant Self-regulating
• Proliferation potential None
• Footprint 2,000-3,000 square feet, with no need for a buffer zone

Founded by another Alvin — American nuclear physicist Alvin Radkowsky — Thorium Power, since renamed Lightbridge, is attempting to commercialize technology that will replace uranium with thorium in conventional reactors. From 1950 to 1972, Radkowsky headed the team that designed reactors to power Navy ships and submarines, and in 1977 Westinghouse opened a reactor he had drawn up — with a uranium thorium core. The reactor ran efficiently for five years until the experiment was ended. Radkowsky formed his company in 1992 with millions of dollars from the Initiative for Proliferation Prevention Program, essentially a federal make-work effort to keep those chilly former Soviet weapons scientists from joining another team.

The reactor design that Lightbridge created is known as seed-and-blanket. Its core consists of a seed of enriched uranium rods surrounded by a blanket of rods made of thorium oxide mixed with uranium oxide. This yields a safer, longer-lived reaction than uranium rods alone. It also produces less waste, and the little bit it does leave behind is unsuitable for use in weapons.

CEO Seth Grae thinks it’s better business to convert existing reactors than it is to build new ones. “We’re just trying to replace leaded fuel with unleaded,” he says. “You don’t have to replace engines or build new gas stations.” Grae is speaking from Abu Dhabi, where he has multimillion-dollar contracts to advise the United Arab Emirates on its plans for nuclear power. In August 2009, Lightbridge signed a deal with the French firm Areva, the world’s largest nuclear power producer, to investigate alternative nuclear fuel assemblies.

Until developing the consulting side of its business, Lightbridge struggled to build a convincing business model. Now, Grae says, the company has enough revenue to commercialize its seed-and-blanket system. It needs approval from the US Nuclear Regulatory Commission — which could be difficult given that the design was originally developed and tested in Russian reactors. Then there’s the nontrivial matter of winning over American nuclear utilities. Seed-and-blanket doesn’t just have to work — it has to deliver a significant economic edge.

For Sorensen, putting thorium into a conventional reactor is a half measure, like putting biofuel in a Hummer. But he acknowledges that the seed-and-blanket design has potential to get the country on its way to a greener, safer nuclear future. “The real enemy is coal,” he says. “I want to fight it with LFTRs — which are like machine guns — instead of with light-water reactors, which are like bayonets. But when the enemy is spilling into the trench, you affix bayonets and go to work.” The thorium battalion is small, but — as nuclear physics demonstrates — tiny forces can yield powerful effects.

Richard Martin (rmartin [at] newwest [dot] net), editor of VON, wrote about the Large Hadron Collider in issue 12.04.

• check CO2 and global warming,
• cut deadly air pollution,
• provide inexhaustible energy
• increase human prosperity

Our world is beset by global warming, pollution, resource conflicts, and energy poverty. Millions die from coal plant emissions. We war over mideast oil. Food supplies from sea and land are threatened. Developing nations’ growth exacerbates the crises.

Few nations will adopt carbon taxes or energy policies against their economic self-interests to reduce global CO2 emissions. Energy cheaper than coal will dissuade all nations from burning coal. Innovative thorium energy uses economic persuasion to end the pollution, to provide energy and prosperity to impoverished peoples, and to create energy security for all people for all time.

A market-based environmental solution

We can solve our global energy and environmental crises straightforwardly – through technology innovation and free-market economics. We need a disruptive technology – energy cheaper than coal. If we offer to sell to all the world the capability to produce energy that cheaply, all the world will stop burning coal. It’s as simple as that. Rely on the economic self-interest of 7 billion people in 250 nations to choose cheaper, nonpolluting energy.

Energy is about 7% of the economy. We, and especially developing nations, can not afford to pay much more for energy. Many environmentalists advocate replacing fossil fuel energy with wind and solar energy sources, blind to the fact that these are 3-4 times more costly! Global economic prosperity requires lower energy costs, not higher costs from taxes or mandated costly wind and solar sources. THORIUM: energy cheaper than coal advocates lowering costs for clean energy – a market-based environmental solution.

Chapters

1 Introduction: an introduction to world crises related to energy and the environment, and the potential for good solutions.

2 Energy and civilization: the relationship between energy, life, and human civilization, easy energy science, life’s dependence on energy flows, civilization’s progress with the energy of the Industrial Revolution, and the 21st century crises of global warming and energy consumption.

 3 An unsustainable world: global warming and its terrifying implications for water, agriculture, food, and civilization; depletion of economical petroleum reserves, deadly air pollution from burning coal, increased competition for natural resources from a growing population, and the solution of new energy technology, cheaper than coal.

4 Energy sources: the character and cost of current and principal emerging energy sources: coal, oil, natural gas, hydropower, solar, wind, biomass, and nuclear.

5 Liquid fluoride thorium reactor (LFTR): the history and technology of liquid fuel nuclear reactors, the Oak Ridge demonstration molten salt reactors, thorium, LFTR, the denatured molten salt reactor (DMSR), builders, and possible contenders for energy cheaper than coal.

 6 Safety: the safety of molten salt reactors, comparisons to alternative energy sources, radiation risks, waste, weapons, and fear.

 7 A sustainable world: environmental benefits of thorium energy cheaper than coal: reduced CO2 emissions, reduced petroleum consumption, synthetic fuels for vehicles, hydrogen power, water conservation, desalination.

8 Energy policy: current confused policies; failure to reduce CO2 emissions, subsidies, recommendations, leadership.

Recommendations

“This book presents a lucid explanation of the workings of thorium-based reactors. It is must reading for anyone interested in our energy future.”
Leon Cooper, Brown University physicist and 1972 Nobel laureate for superconductivity

“As our energy future is essential I can strongly recommend the book for everybody interested in this most significant topic.”

George Olah, 1994 Nobel laureate for carbon chemistry

“Hargraves’ book contains a wealth of information that I’ve never seen anywhere. Very informative and insightful.”

Steve Kirsch, San Jose entrepreneur and philanthropist

“The book describes mankind’s hope for a sustainable and prosperous future: high-temperature thorium-based reactors. The writing is clear and factual, and the book will helpful to anyone interested in energy choices.”

     Meredith Angwin, Director of Energy Education for the Ethan Allen Institute

“A terrific book-length description of the need for energy solutions for this century, leading the reader to the advantages of thorium fissioning in a fluid of of molten salt. He explains the technical basis for how such a power plant works and why it can be cheaper than making power from coal — the dominant fuel for power plants today. This book will be a valuable aid for the many people who will take this demonstrated technology of the 1960s at the Oak Ridge National Laboratory in Tennessee through the rebirth phase and into deployment in this century possibly to dominate the power plants by the later part of the 21st century. Another book about why the molten salt reactor development option was abruptly stopped in early 1970s, even though its demonstration was successful and the use of thorium held great promise is Super Fuel by Richard Martin (2012). For background the reader is referred to The First Nuclear Era by Alvin Weinberg (1994).”
     Ralph Moir, retired Lawrence Livermore Laboratory physicist, expert in fusion and molten salt reactors