Liquid fluoride thorium reactor

"LFTR" redirects here. For the American indie rock band "LFTR PLLR", see Lifter Puller.

Liquid FLiBe salt

The liquid fluoride thorium reactor (acronym LFTR; spoken as lifter) is a thermal breeder reactor which uses the thorium fuel cycle in a fluoride-based molten (liquid) salt fuel to achieve high operating temperatures at atmospheric pressure.

The LFTR is a type of thorium molten salt reactor (TMSR). Molten-salt-fueled reactors (MSFRs) such as LFTR, where the nuclear fuel itself is in the form of liquid molten salt mixture, should not be confused with only molten-salt-cooled but solid-fueled reactors.

This technology was first investigated at the Oak Ridge National Laboratory Molten-Salt Reactor Experiment in the 1960s. It has been recently investigated by Japan, China, the UK, and private US and Australian interests. Flibe Energy aims to develop a small modular reactor version using liquid FLiBe salt.

Background

Thorium is relatively abundant in the earth's crust

Tiny crystals of Thorite, a thorium mineral, under magnification

Molten Salt Reactor at Oak Ridge

By 1946, only eight years after the discovery of nuclear fission, three fissile isotopes had been publicly identified for use as nuclear fuel:

• Uranium-235, which is already fissile, but occurs as <1% of natural uranium
• Plutonium-239, which can be bred from non-fissile Uranium-238 (>99% of natural uranium)
• Uranium-233, which can be bred from non-fissile Thorium-232 (~100% of natural thorium; about four times more common than uranium)

Th-232, U-235 and U-238 are primordial nuclides, having existed in their current form for over 4.5 billion years, predating the formation of the Earth; they were forged in the cores of dying stars through the r-process and scattered across the galaxy by supernovas. Their radioactive decay produces about half of the earth's internal heat.

For technical (outlined in a section below) and historical reasons, the three are each associated with different reactor types. U-235 is the world's primary nuclear fuel and is usually used in light water reactors. U-238/Pu-239 has found the most use in liquid sodium fast breeder reactors. Th-232/U-233 is best suited to molten salt reactors (MSR).

Alvin M. Weinberg pioneered the use of the MSR at Oak Ridge National Laboratory. The Aircraft Reactor Experiment in 1954 and Molten-Salt Reactor Experiment from 1965 to 1969 both used liquid fluoride salts; the latter notably demonstrated the use of U-233 as a fuel source. Unfortunately for MSR research, Weinberg was fired and the MSR program closed down in the early 1970s, after which research stagnated in the United States.

The following reasons are cited as responsible for the program cancellation in January 1973:

1. The political and technical support for the program in the United States was too thin geographically. Within the United States, only in Oak Ridge, Tennessee, was the technology really understood and appreciated.

2. The MSR program was in competition with the fast breeder program at the time, which got an early start and had copious government development funds being spent in many parts of the United States. When the MSR development program had progressed far enough to justify a greatly expanded program leading to commercial development, the AEC could not justify the diversion of substantial funds from the LMFBR to a competing program.

Two versus Single fluid

Two concepts were investigated at Oak Ridge, the "two fluid" and "single fluid" thorium thermal breeder molten salt reactors:

Two Fluid Reactor

The "two fluid" reactor has a high-neutron-density core that burns uranium-233 from the thorium fuel cycle. A separate blanket of thorium salt absorbs the neutrons and eventually is transmuted to ²³³U fuel.

The advantage of the two-fluid design is a simplified chemical system to process the salts. In particular, protactinium-233 is separated from the thorium blanket in a two step process that uses bismuth and fluorination. Protactinium 233 has a 27 day half-life, and decays to the needed fuel, U233. So 10 months after the Protactinium is chemically separated from the salt, it is 99.9% U233. The kernel's salt is also purified, first by fluorination to remove uranium, then vacuum distillation to remove and reuse light-atomic-weight carrier salts. The still bottoms left after the distillation are the fission products of the waste.

The design weakness of the two-fluid design was its complex plumbing. The design used brittle graphite pipes to hold the fuel salt. The pipes separated the fuel salt and breeding salt, so they were essential. The problem is that graphite expands under intense neutron bombardment. So, graphite pipes would change length, crack and become very leaky. Graphite was the only known substance that combined the needed properties: It is not dissolved by the salt, it must survive the neutron bombardment, it must not absorb a lot of neutrons, it must survive at very high temperatures, and it must be tough enough not to crack. Zirconium alloys would work, except they dissolve in the salt. In modern research, copper-reinforced graphite fiber cloth seems theoretically suitable, but no physical tests have been done. At the time, no solution was known, so this type of reactor was never constructed.

The recovery of high-purity Uranium 233 has been raised as a potential nuclear proliferation concern. Most LFTR advocates thus prefer a design with no Pa separation and a breeding ratio ~1.0, not presenting the risk of U-233 separation and ensuring that any U-233 is contaminated with U-232 whose decay chain emits 2 MeV gamma rays too hazardous for weapons workers.

Single Fluid Reactor

The "single fluid" reactor was mechanically much simpler, and was actually prototyped (as the MSRE, above.) It was a large tank filled with salt. The moderator was graphite rods immersed in the salt. The engineers discovered that by carefully sculpting the moderator rods (to get neutron densities similar to a core and blanket), and modifying the fuel reprocessing chemistry, both thorium and uranium salts could coexist in a simpler, less expensive yet efficient "one fluid" reactor. The MSRE provided valuable long-term operating experience.

The disadvantage was that the reprocessing chemistry was much more complex. No simple combination of distillation and fluorination (simple, proven methods) could separate the fission products (the nuclear ashes) from the fuels.

The power reactor design produced by Weinberg's research group was similar to the MSRE. This was because the MSRE was designed to test the design of the risky, hot, high-neutron-density "kernel" part of the two fluid "kernel and blanket" thorium breeder (see above).

Advantages

Thorium-fueled molten salt reactor offers many potential advantages:

Safety

• LFTRs can be designed to be inherently safe: They can have passive nuclear safety, strong negative temperature coefficient of reactivity and operate at atmospheric pressures. (i.e., since the core is not pressurized, it cannot explode)
• MSFRs can include a freeze plug at the bottom that has to be actively cooled, usually by a small electric fan. If the cooling fails, say because of a power failure, the fan stops, the plug melts, and the fuel drains to a subcritical easily cooled storage facility. This not only stops the reactor, also the storage tank can more easily shed the decay heat from the short-lived radioactive decay of irradiated nuclear fuels.
• LFTRs can dramatically reduce the long-term radiotoxicity of their reactor wastes. Light water reactors with Uranium fuel have fuel that is 80 to 97% U238. These reactors normally transmute some U238 to Pu239, a toxic transuranic isotope. Plutonium 239 has a half life of 24,000 years, and is the most common transuranic in spent nuclear fuel from light water reactors. Transuranics like Pu239 cause the perception that reactor wastes are an eternal problem. In contrast, the LFTR uses the Thorium fuel cycle, which transmutes Thorium to U233. U233 has two chances to fission in a LFTR. First as U233 (95% fission) and then again as it transmutes to U235 (98%). The fraction of fuel reaching Neptunium 237, the most likely transuranic element, is therefore less than 0.1%. A related advantage is that the LFTR's fuel is relatively pure U233 (perhaps with 1% U232). When these two features are combined, a Thorium fuel cycle reduces the production of transuranic wastes by more than a thousand-fold compared to a conventional once-through uranium-fueled light-water reactor. The LFTR does still produce radioactive fission products in its waste, but they don't last very long - the radiotoxicity of these fission products is dominated by Cesium 137 and Strontium 90. The longer half-life is Cesium: 30.17 years. So, after 30.17 years, decay reduces the radioactivity by a half. Ten half-lives will reduce the radioactivity to two raised to a power of ten, a factor of 1,024. Fission products at that point, in 301.7 years, are less radioactive than natural uranium. Burial in rock or clay is reasonable and safe by that time, because we've always lived with uranium in rock.
• Since the LFTR fuel is liquid, relatively small, simple equipment can continuously remove transmutation products. This immensely simplifies the reactor's behavior, i.e. it is more predictable, thus more easily controlled and safer than a conventional LWR reactor.
• Fluoride combines ionically with almost any transmutation product. This is an MSFR's first level of containment. Fluoride is especially good at holding biologically active "salt loving" wastes such as Cesium 137.
• If there is an accident beyond the design basis for the multiple levels of containment, fluorides do not easily enter the biome. The salts do not burn, explode, or chemically degrade in air or water. The fluoride salts of radioactive actinides and fission products are generally not soluble in water or air.
• The reactor is easy to control at all times. Xenon-135, an important neutron absorber makes solid fueled reactors difficult to control. In a molten fueled reactor, it can be removed at a predictable place, where the fuel is coolest, the pump bowl. In solid-fuel reactors, it remains in the fuel and interferes with reactor control.
• A LFTR operates at or above 650C, well above the 250C Wigner annealing temperature of graphite. This prevents Wigner energy from forming in the graphite moderator. The continual annealing bleeds it off. A sudden release of Wigner energy is thus not possible. Therefore, a Windscale-style graphite-incited fire cannot be caused by the graphite's nonexistent Wigner energy.
• The LFTR resists diversion of its fuel to nuclear weapons. There are two ways: First, the Thorium breeds by converting first to Protactinium, which then decays to U233. If the Protactinium remains in the reactor, small amounts of U232 are also produced. U232 has a decay chain product (Thallium 208) that emits powerful, dangerous gamma rays. These are not a problem inside a reactor, but in a bomb, they complicate bomb manufacture, harm electronics and reveal the bomb's location. On another track, a LFTR doesn't make much spare fuel. It produces at most 9% more fuel than it burns each year, and it's even easier to design a reactor that makes 1% more fuel. With this kind of reactor, building bombs quickly will take power plants out of operation, and this is an easy indication of national intentions.

Economy and efficiency

Comparison of annual fuel requirements and waste products of a 1GW uranium-fueled LWR and 1GW Thorium-fueled LFTR power plant

• A LFTR breeds thorium into uranium-233 fuel. The Earth's crust contains about three times as much Thorium as U238, or 400 times as much as U235 - thorium is about as abundant as lead. It is a byproduct of rare-earth mining, and is normally discarded as waste. Thorium currently (2011) costs only US$ 30/kg. In contrast, the price of Uranium has risen above $100/kg, not including costs for enrichment and fuel fabrication. Using LFTRs, there is enough affordable thorium to satisfy the Earth's energy needs for hundreds of thousands of years. Besides thorium, LFTRs have used all three fuels (U235, U233 and U239). LFTRs have higher neutron fluxes and burnup, and so can utilize spent nuclear fuel.
• Conventional reactors consume less than one percent of their uranium fuel, leaving the rest as waste. LFTR consumes 99% of its thorium fuel. The improved fuel efficiency means that 1 tonne of natural thorium in a LFTR produces as much energy as 35 t of enriched uranium in conventional reactors (requiring 250 t of natural uranium), or 4 166 000 tonnes of black coal in a coal power plant.
• Since all natural thorium can be used as a fuel, and the fuel is in the form of a molten salt instead of solid fuel rods, expensive fuel enrichment and solid fuel rods' validation procedures and fabricating processes are not needed. This greatly decreases LFTR fuel costs.
• LFTR's are cleaner: as a fully recycling system, the discharge wastes from a LFTR are predominately fission products, most of which have relatively short half lives compared to longer-lived actinide wastes. This results in a significant reduction in the needed waste containment period in a geologic repository (300 years vs. tens of thousands of years)
• The LFTR can "burn" problematic radioactive waste with transuranic elements from traditional solid-fuel nuclear reactors, thus solving the High level waste problem by turning the liability into an asset
• LFTRs scale well: Small, 2–8 MW(thermal) or 1–3 MW(electric) versions are possible, enabling submarine or aircraft use
• LFTRs have liquid fuels, and therefore there is no need to take apart the reactor just to refuel it. LFTRs can thus refuel without causing a power outage.
• A LFTR can react to load changes in less than 60 seconds (unlike "traditional" solid-fuel nuclear power plants), thus it can satisfy both base load and peak load power demands.
• The LFTR has very high temperatures. So, it is possible to use very efficient Brayton cycle generating turbines. The thermal efficiency from the high temperature operation reduces fuel use, wastes and the cost of auxiliary equipment (major capital expenses) by 50% or more.
• Since the core is not pressurized, it does not need the most expensive item in a light water reactor, a high-pressure reactor vessel for the core. Instead, there is a low-pressure vessel and pipes (for molten salt) constructed of relatively thin materials. Although the metal is an exotic nickel alloy that resists heat and corrosion, Hastelloy-N, the amount needed is relatively small and the thin metal is less expensive to form and weld.
• By using liquid salt as the coolant instead of pressurized water a containment structure only slightly bigger than the reactor vessel can be used. Light water reactors use pressurized water which flashes to steam and expands a thousandfold in the case of a leak, necessitating a containment building a thousandfold bigger in volume than the reactor vessel. This gives the LFTR a substantial theoretical advantage in terms of smaller size and lower construction cost.
• It can be air-cooled, which is critical for use in many regions where water is scarce
• Fission products of a LFTR include stable rare elements such as rhodium, ruthenium, palladium, xenon, neodymium, molybdenum, zirconium and cesium, which are relied heavily on in modern electronics and industrial processes. Medically valuable isotopes such as bismuth-213 and technetium-99m useful for radiotherapy, as well as radionuclides used in powering radioisotope thermoelectric generators are also among the LFTR fission products. Compared to solid fuel oxide waste of traditional nuclear reactors contaminated by transuranic elements, these can be relatively easily extracted from the LFTR waste.

Kirk Sorensen expects that with these advantages, LFTR technology will produce energy significantly cheaper than coal; he comments that this would make moot both carbon pricing schemes and more expensive alternative energy solutions In remarks prepared for the Low-Carbon Energy Summit on 20 October 2011, Sorensen stated that "The most important thing that we can do to fight climate change is to replace coal as our primary source of electricity" and advocated the LFTR as an "even less expensive" replacement. The ultimate goal is to "provide electricity for less cost than any other competing solution" which Sorensen thinks will "eventually get to 1 cent per kilowatt hour using this technology"

Ease of reprocessing

A molten salt reactor's fuel can be continuously reprocessed with a small adjacent chemical plant. Weinberg's groups at Oak Ridge National Laboratory found that a very small reprocessing facility can service a large 1 GW power plant: All the salt has to be reprocessed, but only every ten days. The reactor's total inventory of expensive, poisonous radioactive materials is therefore much smaller than in a conventional light-water-reactor's fuel cycle, which has to store spent fuel rod assemblies. Also, everything except fuel and waste stays inside the plant. The reprocessing cycle is:

• A sparge of fluorine removes volatile high-valence fluorides as gas, including uranium hexafluoride containing the uranium-233 fuel as well as other isotopes of uranium; neptunium hexafluoride; technetium hexafluoride and selenium hexafluoride containing the long-lived fission products technetium-99 and selenium-79, as well as fluorides of various strongly radioactive short-lived fission products such as iodine-131, ⁹⁹molybdenum, and ¹³²tellurium. See fluoride volatility for boiling points. The volatile fluorides are condensed from the sparge fluorine, reduced back to less volatile lower-valence fluorides, and returned to the reactor.
• A molten bismuth column separates protactinium from the fuel salt, to return it to the reactor before the high temperature distillation of the salts (see below). Some portion is transmuted to U232 in the reactor, but this helps make the U233 harder to use in nuclear weapons. Oak Ridge's chemistry designs were not concerned with proliferation. They planned to separate and store protactinium-233, so it could decay to very pure uranium-233 without being destroyed by neutron capture in the reactor. With a half-life of 27 days, ten months of storage would assure that 99.9% of the ²³³Pa decays to ²³³U fuel, while any ²³¹Pa remains in the bismuth.
• The remaining fuel salt is then distilled at increased temperature and lowered pressure. The distillate is condensed and returned to the reactor.
  • The light carrier salts beryllium fluoride and lithium fluoride form the bulk of the salt; individually at atmospheric pressure they evaporate at 1169 °C and 1676 °C, while the 2:1 FLiBe mixture with proportions Li₂BeF₄ evaporates at 1430 °C. Boiling points under vacuum are lower.
  • Cesium fluoride, containing the most radioactive medium-lived fission product cesium-137, boils at 1251 °C under standard conditions, and will evaporate with the carrier salt fluorides.
  • Thorium(IV) fluoride evaporates at temperatures about 1680 °C or less under vacuum.
  • Lanthanide trifluorides and alkaline earth fluorides have boiling points higher than 2200 °C under standard conditions, and would remain after thorium fluoride evaporates; the lanthanides include the worst long-term neutron poisons, while strontium fluoride contains the other major medium-lived fission product strontium-90. These still bottoms would be the nuclear waste of the LFTR.

The amount of waste involved is about 800 kg per gigawatt-year generated (1.5 grams/minute for a 1 GW reactor), so the equipment is very small. Salts of long-lived transuranic metals go back into the reactor as fuel. With salt distillation, an MSFR can burn plutonium, or even fluorinated nuclear waste from light water reactors.

• Theoretically, a "two-fluid" reactor design could separate the fertile thorium from the fissile fuel salts. This would eliminate the technologically challenging separation of thorium fluoride (boiling point 1680 °C) and lanthanide fission product fluorides via high-temperature distillation, at the cost of a more complex reactor. Oak Ridge researchers abandoned two-fluid designs because no good pipe materials were known to operate in the high-temperature, high-neutron, corrosive environment of a MSR core.

Disadvantages

• The proposed salt mixture FLiBe, contains large amounts of beryllium, a poisonous element. The salt in the primary and secondary cooling loops must be isolated from workers and the environment to protect them from beryllium poisoning.
• FLiBe also has lithium salts, which can be psychoactive drugs. These also must be isolated from workers and the environment.
• Hot fluoride salts naturally produce hydrofluoric acid in contact with water. When cool, fluoride salts are nearly insoluble in water. Although HF generation would be taken into consideration in the reactor's design and shutdown/decommission processes, this hazard needs to be addressed in emergency situations that damage all five levels of the reactor's containment while the salt is hot.
• As with any nuclear reactor, there are the expected needs to contain the radioactive core, which is dangerous to life and health.
• There is also a need to manage the waste, which is still very radioactive, even though it is hazardous for a shorter period.

Design challenges

• Only a few MSRs have actually been built; those experimental reactors having been constructed more than 40 years ago. This leads some technologists to say that it is difficult to critically assess the concept.
• High neutron fluxes and temperatures in a compact MSR core can change the shape of a graphite moderator element, causing it initially to shrink, then expand. The 1960 two-fluid design had an estimated graphite replacement period of four years. Eliminating graphite from sealed piping was a major incentive to switch to a single-fluid design. Most MSR designs do not use graphite as a structural material, and arrange for it to be easy to replace. At least one design used graphite balls floating in salt, which could be removed and inspected continuously without shutting down the reactor. Reducing the power density of the reactor design increases graphite lifetime.
• Corrosion is significant if the reactor is exposed to any isotope of hydrogen, which forms corrosive, chemically reactive, radioactive hydrogen fluoride (HF) gas. The high neutron density in the core rapidly transmutes lithium-6 to tritium, a radioactive isotope of hydrogen, which is nearly identical, chemically speaking. In hot fluoride salts, the tritium forms tritium fluoride. Because of this, if a MSR design uses a lithium salt, it uses the lithium-7 isotope to prevent tritium formation. In the MSRE, Tritium formation was prevented by the removal of lithium-6 from the fuel salt via isotopic enrichment. Since lithium-7 is at least 16% heavier than lithium-6, and is the most common isotope of lithium, the lithium-6 is comparatively easy and inexpensive to extract from naturally occurring lithium. Vacuum distillation of lithium achieves efficiencies of up to 8% per stage and only requires heating of raw lithium in a vacuum chamber. The aforementioned method worked in preventing hydrogen corrosion in the MSRE. Practical MSRs also operate the salt under a blanket of dry inert gas, usually helium.
• The reactor makes small amounts of Tellurium as a fission product. In the MSRE, this caused small amounts of corrosion at the grain boundaries of the special Nickel alloy, Hastelloy-N used for the reactor. Metallurgical studies showed that adding 1 to 2% Niobium to the Hastelloy-N alloy was found to offer improved resistance to corrosion by Tellurium. One additional strategy against corrosion was to keep the fuel salt slightly reducing by maintaining the ratio of UF₄/UF₃ to less than 60.
• If the Fluoride fuel salts are stored in solid form over many decades, radiation can cause the release of corrosive Fluorine gas, and Uranium hexafluoride. The salts should be defueled and wastes removed before extended shutdowns. Fluoride containing wastes could go through a vitrification process to be encased in borosilicate glass suitable for long-term disposal.
• Developing a large Helium or critical carbon dioxide turbine is needed for the highest efficiency designs. Since prototypes of large machinery are expensive, in excess of several hundred million dollars each, it could cost several billion dollars to construct the needed prototypes and finish the design. This exact problem caused the failure of Romawa's gas-cooled pebble bed reactor program in S. Africa.^{[citation needed]}

Recent developments

The Fuji MSR

The FUJI MSR was a design for a 100 to 200 MWe molten-salt-fueled thorium fuel cycle thermal breeder reactor, using technology similar to the Oak Ridge National Laboratory Reactor. It was being developed by a consortium including members from Japan, the United States, and Russia. As a breeder reactor, it converts thorium into nuclear fuels. As a thermal-spectrum reactor, its neutron regulation is inherently safe. Like all molten salt reactors, its core is chemically inert, under low pressures to prevent explosions and toxic releases. It would likely take 20 years to develop a full size reactor but the project seems to lack funding.

Chinese Thorium MSR project

The People’s Republic of China has initiated a research and development project in thorium molten-salt reactor technology. It was formally announced at the Chinese Academy of Sciences (CAS) annual conference in January 2011. Its ultimate target is to investigate and develop a thorium based molten salt nuclear system in about 20 years.

Flibe Energy

Main article: Flibe Energy

Kirk Sorensen, former NASA scientist and Chief Nuclear Technologist at Teledyne Brown Engineering, has been a long time promoter of thorium fuel cycle and particularly liquid fluoride thorium reactors. He first researched thorium reactors while working at NASA, while evaluating power plant designs suitable for lunar colonies. Material about this fuel cycle was surprisingly hard to find, so in 2006 Sorensen started "energyfromthorium.com", a document repository, forum, and blog to promote this technology. In 2011, Sorensen founded Flibe Energy, a company aimed to develop 20-50 MW LFTR reactor designs to power military bases. (it is easier to approve novel military designs than civilian power station designs in today's US nuclear regulatory environment).

Small modular design

Kirk Sorensen of Flibe Energy, presenting at the 2011 Thorium Energy Conference, described how various factors influence design for small modular reactors.

Neutron temperature requirements matter on two fronts. Primarily is fuel choice:

• U-235 and Th-232/U-233 work most efficiently with thermal spectrum neutrons (<1 eV)
• U-238/Pu-239 requires fast spectrum neutrons (>100,000 eV) to sustain breeding

Second is the amount of fissile material needed in the reactor. Fast spectrum neutrons deal with a much smaller nuclear cross section, meaning that for any given distance, they are less likely to be absorbed by a fissile or breedable nucleus than thermal spectrum neutrons. This drives up the minimum fissile inventory for a given power level.

Operating Temperature has two basic ranges. "Moderate" is defined as 250-350 C, and is comparable to conventional Light Water Reactor and fossil plant temperature ranges. "High" is defined as 700-1000 C, which provides greater efficiency due to the higher temperature gradient with ambient, but provides challenges for material selection.

Operating Pressure can be anywhere between "Atmospheric" and "High" pressure (15.5 MPa (153 atm) for a Pressurized water reactor is considered high). These ranges are related to coolant type.

Here are four examples among the proposed small modular reactor designs, one for each temperature/pressure combination:

• Water: Moderate Temperature, High Pressure (e.g. B&W mPower, NuScale, Westinghouse, IRIS, KLT-40)
• Gas: High Temperature, High Pressure (e.g. Pebble bed modular reactor, Gas turbine modular helium reactor, Energy Multiplier Module)
• Liquid Metal: Moderate Temperature, Atmospheric Pressure (e.g. Hyperion, Toshiba 4S, GE PRISM)
• Molten salt reactor: High Temperature, Atmospheric Pressure (e.g. LFTR)

Various conclusions about the three fuels and possible reactor types are then drawn:

Higher temperature reactors can operate at higher thermal efficiency (e.g. with Brayton cycle turbines), which is desirable. High turbine pressure is a safety concern, as the proposed turbines - using Supercritical carbon dioxide - would need to operate at over 20 MPa (195 atm). The safety concern is more industrial than radiological, however, as turbine systems are generally not built close enough to their heat generators to be a risk to them.

The main drawback of U-235 is its scarcity. Even so, most currently operating reactors use it in water-cooled reactors. Gas-based concepts (e.g. PBMR, VHTR, GT-MHR) are also feasible.

The liquid metal coolants used are poor neutron moderators, thus such systems strongly favor U-238/Pu-239 usage; adding moderators to enable use with U-235 or Th-232/U-233 would be "feasible but unattractive". Conversely, water is a good moderator and this rules out exclusive plutonium breeding in such systems. Gas-cooled systems with U-238/Pu-239 (Gas Cooled Fast Breeder Reactor (GCFR) and EM2 concepts) are described as feasible but with difficult fuel processing, while molten salt systems with U-238/Pu-239 (e.g. MSFR) are only "somewhat feasible."

Sorensen notes that while Th-232/U-233 was used in a water-cooled reactor at the Shippingport Atomic Power Station and a gas-cooled reactor at the Fort St. Vrain Generating Station, thorium dioxide fuel is "very difficult to process," making Th-232/U-233 unattractive for all systems except liquid salt, e.g. where thorium and uranium fluorides are used instead.

In Sorenson's opinion, the LFTR design combines the desirable characteristics of abundant fuel supply, high operating temperature, atmospheric operating pressure and simple fuel processing.

The Weinberg Foundation

The Weinberg Foundation is a British non-profit organisation founded in 2011 dedicated to promotion and development of a liquid fluoride thorium reactor. It was formally launched at the House of Lords on 8 September 2011.

See also

• Generation IV reactor
• Small modular reactor
• Molten salt reactor
• Thorium fuel cycle

Proponents

• James Hansen
• Kirk Sorensen
• Stephen Tindale
• Bryony Worthington

Further reading

• Dr. Robert Hargraves (2009). Aim High!: Thorium energy cheaper than from coal solves more than just global warming. BookSurge Publishing. ISBN 1439225389. 

Available here in pdf

External links

• EnergyFromThorium.com - Blog / Website about LFTR with ORNL molten salt reactor program reports, research papers repository and discussion forum
• Thorium Energy Alliance - advocacy and educational organisation dedicated to thorium energy
• International Thorium Energy Organisation
• ThoriumMSR.com - a comprehensive website and blog about thorium molten salt reactor technology
• Weinberg Foundation website
• Flibe Energy company website
• Thorium and LFTR Top Ten Attributes (a talking points memorandum by Flibe Energy)

Videos:

• Google TechTalks – Liquid Fluoride Thorium Reactor: What Fusion Wanted To Be by Dr. Joe Bonometti NASA / Naval Post Graduate School
• Kirk Sorensen discuss "Thorium" at TEDxYYC 2011
• "Thorium Remix 2011" - a video describing the thorium fuel cycle and LFTR
• An overview of the proposed LFTR power plant design by Thorium Energy Alliance
• Motherboard TV: The Thorium Dream documentary
• Potential of Thorium Fueled Molten Salt Reactors - presentation by Dr. David LeBlanc at TEAC3 Conference
• Dr. Robert Hargraves: Aim High! - Thorium Energy Cheaper Than From Coal presented at TEAC3 Conference
• James Kennedy - "U.S. Heavy Rare Earth Cooperative, the Global Economics of Thorium Energy" presented at TEAC3 Conference
• Google TechTalks – The Thorium Molten-Salt Reactor: Why Didn't This Happen - A presentation examining the history of thorium molten salt reactor development at Oak Ridge and political climate and reasons responsible for the cancellation of the program

Media articles:

• The Telegraph: Obama could kill fossil fuels overnight with a nuclear dash for thorium
• The Telegraph: Safe nuclear does exist, and China is leading the way with thorium
• C&EN News: Reintroducing Thorium
• Mechanical Engineering: Too Good to Leave on the Shelf
• Russia Today: Scientists hail metal thorium as alternative source of energy
• American Scientist: Liquid Fluoride Thorium Reactors
• Forbes: Is Thorium the Biggest Energy Breakthrough Since Fire? Possibly.
• Wired: Uranium Is So Last Century — Enter Thorium, the New Green Nuke
• The Guardian: Why thorium nuclear power shouldn't be written off
• The Guardian: China enters race to develop nuclear energy from thorium
• CNN: Thorium: World's greatest energy breakthrough?
• COSMOS: New age nuclear
• The Week: Could thorium make nuclear power safe?
• The Independent: Is thorium the answer to our energy crisis?
• Popsci: Development of Tiny Thorium Reactors Could Wean the World Off Oil In Just Five Years
• Financial Times: New life for forgotten fuel
• Australian Mining: Australian and Czech consortium announce thorium joint venture
• Huffington Post: LFTR: A Long-Term Energy Solution?

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