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112-410: The liquid fluoride thorium reactor ( LFTR ; often pronounced lifter ) is a type of molten salt reactor . LFTRs use the thorium fuel cycle with a fluoride -based molten (liquid) salt for fuel. In a typical design, the liquid is pumped between a critical core and an external heat exchanger where the heat is transferred to a nonradioactive secondary salt. The secondary salt then transfers its heat to

224-404: A nuclear power plant using a thorium fuel cycle in a breeder reactor . Increased research into Generation IV reactor designs renewed interest in the 21st century with multiple nations starting projects. As of June 2023, China has been operating its TMSR-LF1 thorium unit. MSRs eliminate the nuclear meltdown scenario present in water-cooled reactors because the fuel mixture is kept in

336-434: A steam turbine or closed-cycle gas turbine . Molten-salt-fueled reactors (MSRs) supply the nuclear fuel mixed into a molten salt. They should not be confused with designs that use a molten salt for cooling only (fluoride high-temperature reactors) and still have a solid fuel. Molten salt reactors, as a class, include both burners and breeders in fast or thermal spectra, using fluoride or chloride salt-based fuels and

448-414: A LFTR. The working gas can be helium, nitrogen, or carbon dioxide. The low-pressure warm gas is cooled in an ambient cooler. The low-pressure cold gas is compressed to the high-pressure of the system. The high-pressure working gas is expanded in a turbine to produce power. Often the turbine and the compressor are mechanically connected through a single shaft. High pressure Brayton cycles are expected to have

560-600: A blanket around the core, or contained in special fuel rods . Since plutonium-238 , plutonium-240 and plutonium-242 are fertile, accumulation of these and other nonfissile isotopes is less of a problem than in thermal reactors , which cannot burn them efficiently. Breeder reactors using thermal-spectrum neutrons are only practical if the thorium fuel cycle is used, as uranium-233 fissions far more reliably with thermal neutrons than plutonium-239. A subcritical reactor —regardless of neutron spectrum— can also "breed" fissile nuclides from fertile material, allowing in principle

672-403: A closed fuel cycle—as opposed to the once-through fuel currently used in conventional nuclear power generators. MSRs exploit a negative temperature coefficient of reactivity and a large allowable temperature rise to prevent criticality accidents . For designs with the fuel in the salt, the salt thermally expands immediately with power excursions. In conventional reactors the negative reactivity

784-511: A company that initially intends to develop 20–50 MW LFTR small modular reactor designs to power military bases; Sorensen noted that it is easier to promote novel military designs than civilian power station designs in the context of the modern US nuclear regulatory and political environment. An independent technology assessment coordinated with EPRI and Southern Company represents the most detailed information so far publicly available about Flibe Energy's proposed LFTR design. Copenhagen Atomics

896-710: A complex interleaving of core and blanket tubes was necessary to achieve a high power level with acceptably low power density. ORNL chose not to pursue the two-fluid design, and no examples of the two-fluid reactor were ever constructed. However, more recent research has questioned the need for ORNL's complex interleaving graphite tubing, suggesting a simple elongated tube-in-shell reactor that would allow high power output without complex tubing, accommodate thermal expansion, and permit tube replacement. Additionally, graphite can be replaced with high molybdenum alloys, which are used in fusion experiments and have greater tolerance to neutron damage. A two fluid reactor that has thorium in

1008-487: A continued chain reaction. Examples of fissile fuels are U-233, U-235 and Pu-239. The second type of fuel is called fertile . Examples of fertile fuel are Th-232 (mined thorium) and U-238 (mined uranium). In order to become fissile these nuclides must first absorb a neutron that's been produced in the process of fission, to become Th-233 and U-239 respectively. After two sequential beta decays , they transmute into fissile isotopes U-233 and Pu-239 respectively. This process

1120-430: A cost of 2.85 cents per kilowatt hour. The IThEMS consortium planned to first build a much smaller MiniFUJI 10 MWe reactor of the same design once it had secured an additional $ 300 million in funding, but IThEMS closed in 2011 after it was unable to secure adequate funding. A new company, Thorium Tech Solution (TTS), was founded in 2011 by Kazuo Furukawa, the chief scientist from IThEMS, and Masaaki Furukawa. TTS acquired

1232-414: A fissile material by irradiation in a reactor include: Artificial isotopes formed in the reactor which can be converted into fissile material by one neutron capture include: Some other actinides need more than one neutron capture before arriving at an isotope which is both fissile and long-lived enough to probably be able to capture another neutron and fission instead of decaying. Since these require

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1344-691: A helium-cooled VHTR operating in similar conditions; passive safety systems and better retention of fission products in the event of an accident. Reactors containing molten thorium salt, called liquid fluoride thorium reactors (LFTR), would tap the thorium fuel cycle . Private companies from Japan, Russia, Australia and the United States, and the Chinese government, have expressed interest in developing this technology. Advocates estimate that five hundred metric tons of thorium could supply U.S. energy needs for one year. The U.S. Geological Survey estimates that

1456-409: A large variety of fuel compositions due to its on-line fuel control and flexible fuel processing. The standard MSFR would be a 3000 MWth reactor that has a total fuel salt volume of 18 m with a mean fuel temperature of 750 °C. The core's shape is a compact cylinder with a height to diameter ratio of 1 where liquid fluoride fuel salt flows from the bottom to the top. The return circulation of

1568-474: A moderator (usually graphite) to slow the neutrons down and moderate temperature. They can accept a variety of fuels (low-enriched uranium, thorium, depleted uranium , waste products) and coolants (fluoride, chloride, lithium, beryllium, mixed). Fuel cycle can be either closed or once-through. They can be monolithic or modular, large or small. The reactor can adopt a loop, modular or integral configuration. Variations include: The molten-salt fast reactor (MSFR)

1680-477: A molten state. The fuel mixture is designed to drain without pumping from the core to a containment vessel in emergency scenarios, where the fuel solidifies, quenching the reaction. In addition, hydrogen evolution does not occur. This eliminates the risk of hydrogen explosions (as in the Fukushima nuclear disaster ). They operate at or close to atmospheric pressure , rather than the 75–150 times atmospheric pressure of

1792-470: A neutron to become Cl , then degrades by beta decay to S . Lithium must be in the form of purified Li , because Li effectively captures neutrons and produces tritium . Even if pure Li is used, salts containing lithium cause significant tritium production, comparable with heavy water reactors. Reactor salts are usually close to eutectic mixtures to reduce their melting point. A low melting point simplifies melting

1904-473: A one and a half or two fluid LFTR is whether a more complicated reprocessing or a more demanding structural barrier will be easier to solve. An LFTR with a high operating temperature of 700 degrees Celsius can operate at a thermal efficiency in converting heat to electricity of 45%. This is higher than today's light water reactors (LWRs) that are at 32–36% thermal to electrical efficiency. In addition to electricity generation , concentrated thermal energy from

2016-636: A peak temperature of 860 °C. It produced 100 MWh over nine days in 1954. This experiment used Inconel 600 alloy for the metal structure and piping. An MSR was operated at the Critical Experiments Facility of the Oak Ridge National Laboratory in 1957. It was part of the circulating-fuel reactor program of the Pratt & Whitney Aircraft Company (PWAC). This was called Pratt and Whitney Aircraft Reactor-1 (PWAR-1). The experiment

2128-421: A pump. The working fluid is usually water. A Rankine power conversion system coupled to a LFTR could take advantage of increased steam temperature to improve its thermal efficiency . The subcritical Rankine steam cycle is currently used in commercial power plants, with the newest plants utilizing the higher temperature, higher pressure, supercritical Rankine steam cycles. The work of ORNL from the 1960s and 1970s on

2240-576: A range of fissile or fertile consumables. LFTRs are defined by the use of fluoride fuel salts and the breeding of thorium into uranium-233 in the thermal neutron spectrum. The LFTR concept was first investigated at the Oak Ridge National Laboratory Molten-Salt Reactor Experiment in the 1960s, though the MSRE did not use thorium. The LFTR has recently been the subject of a renewed interest worldwide. Japan, China,

2352-413: A slow-decaying isotope between them which facilitates neutron absorption by Cl . Chlorides permit fast breeder reactors to be constructed. Much less research has been done on reactor designs using chloride salts. Chlorine, unlike fluorine, must be purified to isolate the heavier stable isotope, Cl , thus reducing production of sulfur tetrachloride that occurs when Cl absorbs

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2464-402: A small reactor prototype comparable to the MSRE. The two-fluid design is mechanically more complicated than the "single fluid" reactor design. 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 neutrons and slowly converts its thorium to protactinium-233 . Protactinium-233 can be left in

2576-514: A smaller generator footprint compared to lower pressure Rankine cycles. A Brayton cycle heat engine can operate at lower pressure with wider diameter piping. The world's first commercial Brayton cycle solar power module (100 kW) was built and demonstrated in Israel's Arava Desert in 2009. The LFTR needs a mechanism to remove the fission products from the fuel. Fission products left in the reactor absorb neutrons and thus reduce neutron economy . This

2688-528: A total of 3 or 4 thermal neutrons to eventually fission, and a thermal neutron fission generates only about 2 to 3 neutrons, these nuclides represent a net loss of neutrons. A subcritical reactor operating in the thermal neutron spectrum would have to adjust the strength of the external neutron source in accordance with the build-up or consumption of such materials. In a fast reactor , those nuclides may require fewer neutrons to achieve fission, as well as producing more neutrons when they do fission. However, there

2800-536: A typical light-water reactor (LWR). This reduces the need and cost for reactor pressure vessels . The gaseous fission products ( Xe and Kr ) have little solubility in the fuel salt, and can be safely captured as they bubble out of the fuel, rather than increasing the pressure inside the fuel tubes , as happens in conventional reactors. MSRs can be refueled while operating (essentially online- nuclear reprocessing ) while conventional reactors shut down for refueling (notable exceptions include pressure tube reactors like

2912-423: A valuable radiolabel dye for marking cancerous cells in medical scans). The more noble metals ( Pd , Ru , Ag , Mo , Nb , Sb , Tc ) do not form fluorides in the normal salt, but instead fine colloidal metallic particles. They can plate out on metal surfaces like the heat exchanger, or preferably on high surface area filters which are easier to replace. Still, there is some uncertainty where they end up, as

3024-412: Is a Danish molten salt technology company developing mass manufacturable 100MWth molten salt reactors . The Copenhagen Atomics Waste Burner is a single-fluid, heavy water moderated, fluoride-based, thermal spectrum and autonomously controlled molten-salt reactor. This is designed to fit inside of a leak-tight, 40-foot, stainless steel shipping container. The heavy water moderator is thermally insulated from

3136-470: Is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a mixture of molten salt with a fissile material. Two research MSRs operated in the United States in the mid-20th century. The 1950s Aircraft Reactor Experiment (ARE) was primarily motivated by the technology's compact size, while the 1960s Molten-Salt Reactor Experiment (MSRE) aimed to demonstrate

3248-607: Is a proposed design with the fuel dissolved in a fluoride salt coolant. The MSFR is one of the two variants of MSRs selected by the Generation IV International Forum (GIF) for further development, the other being the FHR or AHTR. The MSFR is based on a fast neutron spectrum and is believed to be a long-term substitute to solid-fueled fast reactors. They have been studied for almost a decade, mainly by calculations and determination of basic physical and chemical properties in

3360-576: Is also a proposed Generation IV molten-salt reactor variant regarded promising for the long-term future. The FHR/AHTR reactor uses a solid-fuel system along with a molten fluoride salt as coolant. One version of the Very-high-temperature reactor (VHTR) under study was the liquid-salt very-high-temperature reactor (LS-VHTR). It uses liquid salt as a coolant in the primary loop, rather than a single helium loop. It relies on " TRISO " fuel dispersed in graphite. Early AHTR research focused on graphite in

3472-525: Is also purified, first by fluorination to remove uranium, then vacuum distillation to remove and reuse the carrier salts. The still bottoms left after the distillation are the fission products waste of a LFTR. The advantages of separating the core and blanket fluid include: One weakness of the two-fluid design is the necessity of periodically replacing the core-blanket barrier due to fast neutron damage. ORNL chose graphite for its barrier material because of its low neutron absorption , compatibility with

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3584-437: Is also the chance of (n,2n) or even (n,3n) "knockout" reactions (an incident fast neutron hits a nucleus and more than one neutron leaves) with fast neutrons which are not possible with thermal neutrons. A fast-neutron reactor , meaning one with little or no neutron moderator and hence utilising fast neutrons , can be configured as a breeder reactor , producing more fissile material than it consumes, using fertile material in

3696-493: Is attractive to use pyroprocessing , high temperature methods working directly with the hot molten salt. Pyroprocessing does not use radiation sensitive solvents and is not easily disturbed by decay heat. It can be used on highly radioactive fuel directly from the reactor. Having the chemical separation on site, close to the reactor avoids transport and keeps the total inventory of the fuel cycle low. Ideally everything except new fuel (thorium) and waste (fission products) stays inside

3808-412: Is called a break-even breeder or isobreeder. A LFTR is usually designed as a breeder reactor: thorium goes in, fissile products come out. Reactors that use the uranium-plutonium fuel cycle require fast reactors to sustain breeding, because only with fast moving neutrons does the fission process provide more than 2 neutrons per fission. With thorium, it is possible to breed using a thermal reactor . This

3920-401: Is called breeding. All reactors breed some fuel this way, but today's solid fueled thermal reactors don't breed enough new fuel from the fertile to make up for the amount of fissile they consume. This is because today's reactors use the mined uranium-plutonium cycle in a moderated neutron spectrum. Such a fuel cycle, using slowed down neutrons, gives back less than 2 new neutrons from fissioning

4032-670: Is delayed since the heat from the fuel must be transferred to the moderator. An additional method is to place a separate, passively cooled container below the reactor. Fuel drains into the container during malfunctions or maintenance, which stops the reaction. The temperatures of some designs are high enough to produce process heat, which led them to be included on the GEN-IV roadmap. MSRs offer many potential advantages over light water reactors: MSRs can be cooled in various ways, including using molten salts. Molten-salt-cooled solid-fuel reactors are variously called "molten-salt reactor system" in

4144-409: Is especially important in the thorium fuel cycle with few spare neutrons and a thermal neutron spectrum, where absorption is strong. The minimum requirement is to recover the valuable fissile material from used fuel. Removal of fission products is similar to reprocessing of solid fuel elements; by chemical or physical means, the valuable fissile fuel is separated from the waste fission products. Ideally

4256-435: Is held for about 2 days until almost all Xe-135 and other short lived isotopes have decayed. Most of the gas can then be recycled. After an additional hold up of several months, radioactivity is low enough to separate the gas at low temperatures into helium (for reuse), xenon (for sale) and krypton, which needs storage (e.g. in compressed form) for an extended time (several decades) to wait for the decay of Kr-85 . For cleaning

4368-452: Is no longer a problem. This results in a breeder reactor with a fast neutron spectrum that operates in the Thorium fuel cycle. MSFRs contain relatively small initial inventories of U . MSFRs run on liquid fuel with no solid matter inside the core. This leads to the possibility of reaching specific power that is much higher than reactors using solid fuel. The heat produced goes directly into

4480-543: Is not absorbed but instead knocks a neutron out of the nucleus), generate U . Because U has a short half-life and its decay chain contains hard gamma emitters, it makes the isotopic mix of uranium less attractive for bomb-making. This benefit would come with the added expense of a larger fissile inventory or a 2-fluid design with a large quantity of blanket salt. The necessary fuel salt reprocessing technology has been demonstrated, but only at laboratory scale. A prerequisite to full-scale commercial reactor design

4592-541: Is not created in the core (as is present in boiling water reactors ), and no large, expensive steel pressure vessel (as required for pressurized water reactors ). Since it can operate at high temperatures, the conversion of the heat to electricity can use an efficient, lightweight Brayton cycle gas turbine. Much of the current research on FHRs is focused on small, compact heat exchangers that reduce molten salt volumes and associated costs. Molten salts can be highly corrosive and corrosivity increases with temperature. For

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4704-461: Is specified, this must be done quite often (for example, every 10 days) to be effective. For a 1 GW, 1-fluid plant this means about 10% of the fuel or about 15 t of fuel salt need to go through reprocessing every day. This is only feasible if the costs are much lower than current costs for reprocessing solid fuel. Newer designs usually avoid the Pa removal and send less salt to reprocessing, which reduces

4816-455: Is the R&;D to engineer an economically competitive fuel salt cleaning system. Reprocessing refers to the chemical separation of fissionable uranium and plutonium from spent fuel. Such recovery could increase the risk of nuclear proliferation . In the United States the regulatory regime has varied dramatically across administrations. A systematic literature review from 2020 concludes that there

4928-418: Is the lead-cooled, salt-fueled reactor. MSR research started with the U.S. Aircraft Reactor Experiment (ARE) in support of the U.S. Aircraft Nuclear Propulsion program. ARE was a 2.5 MW th nuclear reactor experiment designed to attain a high energy density for use as an engine in a nuclear-powered bomber. The project included experiments, including high temperature and engine tests collectively called

5040-434: Is triggered and achieved by redundant and reliable devices such as detection and opening technology. During operation, the fuel salt circulation speed can be adjusted by controlling the power of the pumps in each sector. The intermediate fluid circulation speed can be adjusted by controlling the power of the intermediate circuit pumps. The temperature of the intermediate fluid in the intermediate exchangers can be managed through

5152-449: Is very limited information on economics and finance of MSRs, with low quality of the information and that cost estimations are uncertain. In the specific case of the stable salt reactor (SSR) where the radioactive fuel is contained as a molten salt within fuel pins and the primary circuit is not radioactive, operating costs are likely to be lower. While many design variants have been proposed, there are three main categories regarding

5264-518: Is well established in enrichment. The higher valence fluorides are quite corrosive at high temperatures and require more resistant materials than Hastelloy . One suggestion in the MSBR program at ORNL was using solidified salt as a protective layer. At the MSRE reactor fluorine volatility was used to remove uranium from the fuel salt. Also for use with solid fuel elements fluorine volatility is quite well developed and tested. Another simple method, tested during

5376-502: The TMSR-LF1 . China plans to follow up the experiment with a 373MW version by 2030. 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

5488-499: The atmosphere , and locate them at a space facility at the Earth–Moon L1 Lagrangian point where manufacture of fissile material would occur, eliminating the safety risk of transport of fissile materials from Earth. While uranium and thorium are present on the moon , they seem to be in more limited supply than on earth, especially near the surface. If in situ resource utilization is desired to fuel nuclear power plants on

5600-408: The corrosivity of hot salts and the changing chemical composition of the salt as it is transmuted by the neutron flux . MSRs, especially those with fuel in the molten salt, offer lower operating pressures, and higher temperatures. In this respect an MSR is more similar to a liquid metal cooled reactor than to a conventional light water cooled reactor. MSR designs are often breeding reactors with

5712-532: 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 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

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5824-463: The "single fluid" and "two fluid" thorium thermal breeder molten salt reactors. The one-fluid design includes a large reactor vessel filled with fluoride salt containing thorium and uranium. Graphite rods immersed in the salt function as a moderator and to guide the flow of salt. In the ORNL MSBR (molten salt breeder reactor) design a reduced amount of graphite near the edge of the reactor core would make

5936-497: The European Union and Russian Federation. A MSFR is regarded sustainable because there are no fuel shortages. Operation of a MSFR does in theory not generate or require large amounts of transuranic (TRU) elements . When steady state is achieved in a MSFR, there is no longer a need for uranium enrichment facilities. MSFRs may be breeder reactors . They operate without a moderator in the core such as graphite, so graphite life-span

6048-572: The FUJI design and some related patents. 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. An expected intermediate outcome of

6160-542: The Generation IV proposal, molten-salt converter reactors (MSCR), advanced high-temperature reactors (AHTRs), or fluoride high-temperature reactors (FHR, preferred DOE designation). FHRs cannot reprocess fuel easily and have fuel rods that need to be fabricated and validated, requiring up to twenty years from project inception. FHR retains the safety and cost advantages of a low-pressure, high-temperature coolant, also shared by liquid metal cooled reactors . Notably, steam

6272-631: The Heat Transfer Reactor Experiments: HTRE-1, HTRE-2 and HTRE-3 at the National Reactor Test Station (now Idaho National Laboratory ) as well as an experimental high-temperature molten-salt reactor at Oak Ridge National Laboratory – the ARE. ARE used molten fluoride salt NaF/ZrF 4 /UF 4 (53-41-6  mol% ) as fuel, moderated by beryllium oxide (BeO). Liquid sodium was a secondary coolant. The experiment had

6384-459: The MSBR assumed the use of a standard supercritical steam turbine with an efficiency of 44%, and had done considerable design work on developing molten fluoride salt – steam generators. The Brayton cycle generator has a much smaller footprint than the Rankine cycle, lower cost and higher thermal efficiency, but requires higher operating temperatures. It is therefore particularly suitable for use with

6496-474: The MSRE only provided a relatively short operating experience and independent laboratory experiments are difficult. Gases like Xe and Kr come out easily with a sparge of helium. In addition, some of the "noble" metals are removed as an aerosol . The quick removal of Xe-135 is particularly important, as it is a very strong neutron poison and makes reactor control more difficult if unremoved; this also improves neutron economy. The gas (mainly He, Xe and Kr)

6608-531: The MSRE program, is high temperature vacuum distillation. The lower boiling point fluorides like uranium tetrafluoride and the LiF and BeF carrier salt can be removed by distillation. Under vacuum the temperature can be lower than the ambient pressure boiling point. So a temperature of about 1000 °C is sufficient to recover most of the FLiBe carrier salt. However, while possible in principle, separation of thorium fluoride from

6720-493: The Molten-Salt Reactor Experiment (MSRE). MSRE was a 7.4 MW th test reactor simulating the neutronic "kernel" of a type of epithermal thorium molten salt breeder reactor called the liquid fluoride thorium reactor (LFTR). The large (expensive) breeding blanket of thorium salt was omitted in favor of neutron measurements. Fertile material Naturally occurring fertile materials that can be converted into

6832-538: The Shanghai Institute of Applied Physics. An expansion of staffing has increased to 700 as of 2015. As of 2016, their plan is for a 10MW pilot LFTR is expected to be made operational in 2025, with a 100MW version set to follow in 2035. At the end of August 2021, the Shanghai Institute of Applied Physics (SINAP) completed the construction of a 2MW (thermal) experimental thorium molten salt reactor in Wuwei, Gansu , known as

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6944-484: The TMSR research program is to build a 2 MW pebble bed fluoride salt cooled research reactor in 2015, and a 2 MW molten salt fueled research reactor in 2017. This would be followed by a 10 MW demonstrator reactor and a 100 MW pilot reactors. The project is spearheaded by Jiang Mianheng , with a start-up budget of $ 350 million, and has already recruited 140 PhD scientists, working full-time on thorium molten salt reactor research at

7056-464: The UK and private US, Czech, Canadian and Australian companies have expressed the intent to develop, and commercialize the technology. LFTRs differ from other power reactors in almost every aspect: they use thorium that is turned into uranium, instead of using uranium directly; they are refueled by pumping without shutdown. Their liquid salt coolant allows higher operating temperature and much lower pressure in

7168-475: The bismuth alloy in a separate step, e.g. by contact to a LiCl melt. However this method is far less developed. A similar method may also be possible with other liquid metals like aluminum. Thorium-fueled molten salt reactors offer many potential advantages compared to conventional solid uranium fueled light water reactors: LFTRs are quite unlike today's operating commercial power reactors. These differences create design difficulties and trade-offs: The FUJI MSR

7280-414: The blanket region where neutron flux is lower, so that it slowly decays to U-233 fissile fuel, rather than capture neutrons. This bred fissile U-233 can be recovered by injecting additional fluorine to create uranium hexafluoride, a gas which can be captured as it comes out of solution. Once reduced again to uranium tetrafluoride, a solid, it can be mixed into the core salt medium to fission. The core's salt

7392-427: The bred plutonium. Since 1 neutron is required to sustain the fission reaction, this leaves a budget of less than 1 neutron per fission to breed new fuel. In addition, the materials in the core such as metals, moderators and fission products absorb some neutrons, leaving too few neutrons to breed enough fuel to continue operating the reactor. As a consequence they must add new fissile fuel periodically and swap out some of

7504-476: The consumption of very low grade actinides (e.g. Spent MOX fuel whose plutonium-240 content is too high for use in current critical thermal reactors) without the need for highly enriched material as used in a fast breeder reactor . Proposed applications for fertile material includes a space-based facility for the manufacture of fissile material for spacecraft nuclear propulsion . The facility would notionally transport fertile materials from Earth, safely through

7616-437: The core. The added disadvantage of keeping the fluids separate using a barrier remains, but with thorium present in the fuel salt there are fewer neutrons that must pass through this barrier into the blanket fluid. This results in less damage to the barrier. Any leak in the barrier would also be of lower consequence, as the processing system must already deal with thorium in the core. The main design question when deciding between

7728-401: The deposition of solid particles in reactor operation. Sulfur must be removed because of its corrosive attack on nickel-based alloys at operational temperature. Structural metals such as chromium, nickel, and iron must be removed for corrosion control. A water content reduction purification stage using HF and helium sweep gas was specified to run at 400 °C. Oxide and sulfur contamination in

7840-437: The design to prevent its release into the environment. Many other salts can cause plumbing corrosion, especially if the reactor is hot enough to make highly reactive hydrogen. To date, most research has focused on FLiBe, because lithium and beryllium are reasonably effective moderators and form a eutectic salt mixture with a lower melting point than each of the constituent salts. Beryllium also performs neutron doubling, improving

7952-400: The even higher boiling point lanthanide fluorides would require very high temperatures and new materials. The chemical separation for the 2-fluid designs, using uranium as a fissile fuel can work with these two relatively simple processes: Uranium from the blanket salt can be removed by fluorine volatility, and transferred to the core salt. To remove the fissile products from the core salt, first

8064-422: The fertile and fissile fuel together, so breeding and splitting occurs in the same place. Alternatively, fissile and fertile can be separated. The latter is known as core-and-blanket, because a fissile core produces the heat and neutrons while a separate blanket does all the breeding. Oak Ridge investigated both ways to make a breeder for their molten salt breeder reactor. Because the fuel is liquid, they are called

8176-400: The fertile fuel (thorium or U-238) and other fuel components (e.g. carrier salt or fuel cladding in solid fuels) can also be reused for new fuel. However, for economic reasons they may also end up in the waste. On site processing is planned to work continuously, cleaning a small fraction of the salt every day and sending it back to the reactor. There is no need to make the fuel salt very clean;

8288-476: The form of graphite rods that would be inserted in hexagonal moderating graphite blocks, but current studies focus primarily on pebble-type fuel. The LS-VHTR can work at very high temperatures (the boiling point of most molten salt candidates is >1400 °C); low-pressure cooling that can be used to match hydrogen production facility conditions (most thermochemical cycles require temperatures in excess of 750 °C); better electric conversion efficiency than

8400-405: The fuel salt is sometimes called a "one and a half fluid" reactor, or 1.5 fluid reactor. This is a hybrid, with some of the advantages and disadvantages of both 1 fluid and 2 fluid reactors. Like the 1 fluid reactor, it has thorium in the fuel salt, which complicates the fuel processing. And yet, like the 2 fluid reactor, it can use a highly effective separate blanket to absorb neutrons that leak from

8512-526: The fuel salt. In a converter configuration fuel processing requirement was simplified to reduce plant cost. The trade-off was the requirement of periodic uranium refueling. The MSRE was a core region only prototype reactor. The MSRE provided valuable long-term operating experience. According to estimates of Japanese scientists, a single fluid LFTR program could be achieved through a relatively modest investment of roughly 300–400 million dollars over 5–10 years to fund research to fill minor technical gaps and build

8624-440: The fuel salt. Usually the fuel salt temperature can be brought down by 100 °C using a 3% proportion of bubbles. MSFRs have two draining modes, controlled routine draining and emergency draining. During controlled routine draining, fuel salt is transferred to actively cooled storage tanks. The fuel temperature can be lowered before draining, this may slow down the process. This type of draining could be done every 1 to 5 years when

8736-472: The heat transfer fluid. In the MSFR, a small amount of molten salt is set aside to be processed for fission product removal and then returned to the reactor. This gives MSFRs the capability of reprocessing the fuel without stopping the reactor. This is very different compared to solid-fueled reactors because they have separate facilities to produce the solid fuel and process spent nuclear fuel. The MSFR can operate using

8848-490: The heavy water CANDU or the Atucha-class PHWRs, light water cooled graphite moderated RBMK , and British-built gas-cooled reactors such as Magnox , AGR ). MSR operating temperatures are around 700 °C (1,292 °F), significantly higher than traditional LWRs at around 300 °C (572 °F). This increases electricity-generation efficiency and process-heat opportunities. Relevant design challenges include

8960-457: The high-temperature LFTR can be used as high-grade industrial process heat for many uses, such as ammonia production with the Haber process or thermal Hydrogen production by water splitting, eliminating the efficiency loss of first converting to electricity. The Rankine cycle is the most basic thermodynamic power cycle. The simplest cycle consists of a steam generator , a turbine, a condenser, and

9072-428: The intermediate product protactinium Pa would be removed from the reactor and allowed to decay into highly pure U , an attractive bomb-making material. More modern designs propose to use a lower specific power or a separate thorium breeding blanket. This dilutes the protactinium to such an extent that few protactinium atoms absorb a second neutron or, via a (n, 2n) reaction (in which an incident neutron

9184-460: The inventory of fission products, control corrosion and improve neutron economy by removing fission products with high neutron absorption cross-section, especially xenon . This makes the MSR particularly suited to the neutron-poor thorium fuel cycle . Online fuel processing can introduce risks of fuel processing accidents, which can trigger release of radio isotopes . In some thorium breeding scenarios,

9296-717: The laboratory, and with only a few elements. There is still more research and development needed to improve separation and make reprocessing more economically viable. Uranium and some other elements can be removed from the salt by a process called fluorine volatility: A sparge of fluorine removes volatile high- valence fluorides as a gas. This is mainly uranium hexafluoride , containing the uranium-233 fuel, but also neptunium hexafluoride , technetium hexafluoride and selenium hexafluoride , as well as fluorides of some other fission products (e.g. iodine, molybdenum and tellurium). The volatile fluorides can be further separated by adsorption and distillation. Handling uranium hexafluoride

9408-523: The largest-known U.S. thorium deposit, the Lemhi Pass district on the Montana - Idaho border, contains thorium reserves of 64,000 metric tons. Traditionally, these reactors were known as molten salt breeder reactors (MSBRs) or thorium molten-salt reactors (TMSRs), but the name LFTR was promoted as a rebrand in the early 2000s by Kirk Sorensen. The stable salt reactor is a relatively recent concept which holds

9520-409: The molten salt fuel statically in traditional LWR fuel pins. Pumping of the fuel salt, and all the corrosion/deposition/maintenance/containment issues arising from circulating a highly radioactive, hot and chemically complex fluid, are no longer required. The fuel pins are immersed in a separate, non-fissionable fluoride salt which acts as primary coolant. A prototypical example of a dual fluid reactor

9632-424: The molten salts, high temperature resistance, and sufficient strength and integrity to separate the fuel and blanket salts. The effect of neutron radiation on graphite is to slowly shrink and then swell it, causing an increase in porosity and a deterioration in physical properties. Graphite pipes would change length, and may crack and leak. Another weakness of the two-fluid design is its complex plumbing. ORNL thought

9744-693: The most use in liquid sodium fast breeder reactors and CANDU 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 . At ORNL, two prototype molten salt reactors were successfully designed, constructed and operated. These were the Aircraft Reactor Experiment in 1954 and Molten-Salt Reactor Experiment from 1965 to 1969. Both test reactors used liquid fluoride fuel salts. The MSRE notably demonstrated fueling with U-233 and U-235 during separate test runs. Weinberg

9856-451: The neutron economy. This process occurs when the beryllium nucleus emits two neutrons after absorbing a single neutron. For the fuel carrying salts, generally 1% or 2% (by mole ) of UF 4 is added. Thorium and plutonium fluorides have also been used. Techniques for preparing and handling molten salt were first developed at ORNL. The purpose of salt purification is to eliminate oxides, sulfur and metal impurities. Oxides could result in

9968-424: The old fuel to make room for the new fuel. In a reactor that breeds at least as much new fuel as it consumes, it is not necessary to add new fissile fuel. Only new fertile fuel is added, which breeds to fissile inside the reactor. In addition the fission products need to be removed. This type of reactor is called a breeder reactor . If it breeds just as much new fissile from fertile to keep operating indefinitely, it

10080-429: The outer region under-moderated, and increased the capture of neutrons there by the thorium. With this arrangement, most of the neutrons were generated at some distance from the reactor boundary, and reduced the neutron leakage to an acceptable level. Still, a single fluid design needs a considerable size to permit breeding. In a breeder configuration, extensive fuel processing was specified to remove fission products from

10192-460: The plant. One potential advantage of a liquid fuel is that it not only facilitates separating fission-products from the fuel, but also isolating individual fission products from one another, which is lucrative for isotopes that are scarce and in high-demand for various industrial (radiation sources for testing welds via radiography), agricultural (sterilizing produce via irradiation), and medical uses ( Molybdenum-99 which decays into Technetium-99m ,

10304-671: The primary cooling loop, a material is needed that can withstand corrosion at high temperatures and intense radiation . Experiments show that Hastelloy-N and similar alloys are suited to these tasks at operating temperatures up to about 700 °C. However, operating experience is limited. Still higher operating temperatures are desirable—at 850 °C (1,560 °F) thermochemical production of hydrogen becomes possible. Materials for this temperature range have not been validated, though carbon composites, molybdenum alloys (e.g. TZM), carbides , and refractory metal based or ODS alloys might be feasible. The salt mixtures are chosen to make

10416-406: The primary cooling loop. These distinctive characteristics give rise to many potential advantages, as well as design challenges. By 1946, eight years after the discovery of nuclear fission , three fissile isotopes had been publicly identified for use as nuclear fuel : Th-232, U-235 and U-238 are primordial nuclides , having existed in their current form for over 4.5 billion years , predating

10528-419: The purpose is to keep the concentration of fission products and other impurities (e.g. oxygen) low enough. The concentrations of some of the rare earth elements must be especially kept low, as they have a large absorption cross section. Some other elements with a small cross section like Cs or Zr may accumulate over years of operation before they are removed. As the fuel of a LFTR is a molten salt mixture, it

10640-720: The reactor safer and more practical. Fluorine has only one stable isotope ( F ), and does not easily become radioactive under neutron bombardment. Compared to chlorine and other halides, fluorine also absorbs fewer neutrons and slows (" moderates ") neutrons better. Low- valence fluorides boil at high temperatures, though many pentafluorides and hexafluorides boil at low temperatures. They must be very hot before they break down into their constituent elements. Such molten salts are "chemically stable" when maintained well below their boiling points. Fluoride salts dissolve poorly in water, and do not form burnable hydrogen. Chlorine has two stable isotopes ( Cl and Cl ), as well as

10752-451: The reactor. With a half-life of 27 days, 2 months of storage would assure that 75% of the Pa decays to U fuel. The protactinium removal step is not required per se for a LFTR. Alternate solutions are operating at a lower power density and thus a larger fissile inventory (for 1 or 1.5 fluid) or a larger blanket (for 2 fluid). Also a harder neutron spectrum helps to achieve acceptable breeding without protactinium isolation. If Pa separation

10864-429: The removal of the lanthanides is the contact with molten bismuth . In a redox -reaction some metals can be transferred to the bismuth melt in exchange for lithium added to the bismuth melt. At low lithium concentrations U, Pu and Pa move to the bismuth melt. At more reducing conditions (more lithium in the bismuth melt) the lanthanides and thorium transfer to the bismuth melt too. The fission products are then removed from

10976-422: The required size and costs for the chemical separation. It also avoids proliferation concerns due to high purity U-233 that might be available from the decay of the chemical separated Pa. Separation is more difficult if the fission products are mixed with thorium, because thorium, plutonium and the lanthanides (rare earth elements) are chemically similar. One process suggested for both separation of protactinium and

11088-536: The role of molten salt: The use of molten salt as fuel and as coolant are independent design choices – the original circulating-fuel-salt MSRE and the more recent static-fuel-salt SSR use salt as fuel and salt as coolant; the DFR uses salt as fuel but metal as coolant; and the FHR has solid fuel but salt as coolant. MSRs can be burners or breeders. They can be fast or thermal or epithermal . Thermal reactors typically employ

11200-638: The salt and continuously drained and cooled to below 50 °C (122 °F). A molten lithium-7 deuteroxide (7LiOD) moderator version is also being researched. The reactor utilizes the thorium fuel cycle using separated plutonium from spent nuclear fuel as the initial fissile load for the first generation of reactors, eventually transitioning to a thorium breeder. Copenhagen Atomics is actively developing and testing valves, pumps, heat exchangers, measurement systems, salt chemistry and purification systems, and control systems and software for molten salt applications. Molten salt reactor A molten-salt reactor ( MSR )

11312-451: The salt at startup and reduces the risk of the salt freezing as it is cooled in the heat exchanger. Due to the high " redox window" of fused fluoride salts, the redox potential of the fused salt system can be changed. Fluorine-lithium-beryllium (" FLiBe ") can be used with beryllium additions to lower the redox potential and nearly eliminate corrosion. However, since beryllium is extremely toxic, special precautions must be engineered into

11424-475: The salt mixture several methods of chemical separation were proposed. Compared to classical PUREX reprocessing, pyroprocessing can be more compact and produce less secondary waste. The pyroprocesses of the LFTR salt already starts with a suitable liquid form, so it may be less expensive than using solid oxide fuels. However, because no complete molten salt reprocessing plant has been built, all testing has been limited to

11536-418: The salt mixtures were removed using gas sparging of HF / H 2 mixture, with the salt heated to 600 °C. Structural metal contamination in the salt mixtures were removed using hydrogen gas sparging, at 700 °C. Solid ammonium hydrofluoride was proposed as a safer alternative for oxide removal. The possibility of online processing can be an MSR advantage. Continuous processing would reduce

11648-464: The salt, from top to bottom, is broken up into 16 groups of pumps and heat exchangers located around the core. The fuel salt takes approximately 3 to 4 seconds to complete a full cycle. At any given time during operation, half of the total fuel salt volume is in the core and the rest is in the external fuel circuit (salt collectors, salt-bubble separators, fuel heat exchangers, pumps, salt injectors and pipes). MSFRs contain an emergency draining system that

11760-420: The sectors are replaced. Emergency draining is done when an irregularity occurs during operation. The fuel salt can be drained directly into the emergency draining tank either by active devices or by passive means. The draining must be fast to limit the fuel salt heating in a loss of heat removal event. The fluoride salt-cooled high-temperature reactor (FHR), also called advanced high temperature reactor (AHTR),

11872-452: The uranium is removed via fluorine volatility. Then the carrier salt can be recovered by high temperature distillation. The fluorides with a high boiling point, including the lanthanides stay behind as waste. The early Oak Ridge's chemistry designs were not concerned with proliferation and aimed for fast breeding. They planned to separate and store protactinium-233 , so it could decay to uranium-233 without being destroyed by neutron capture in

11984-420: The use of a double bypass. This allows the temperature of the intermediate fluid at the conversion exchanger inlet to be held constant while its temperature is increased in a controlled way at the inlet of the intermediate exchangers. The temperature of the core can be adjusted by varying the proportion of bubbles injected in the core since it reduces the salt density. As a result, it reduces the mean temperature of

12096-572: 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 Experiment. 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. An industry group presented updated plans about FUJI MSR in July 2010. They projected

12208-498: Was proven to work in the Shippingport Atomic Power Station , whose final fuel load bred slightly more fissile from thorium than it consumed, despite being a fairly standard light water reactor . Thermal reactors require less of the expensive fissile fuel to start, but are more sensitive to fission products left in the core. There are two ways to configure a breeder reactor to do the required breeding. One can place

12320-474: Was removed from his post and the MSR program closed down in the early 1970s, after which research stagnated in the United States. Today, the ARE and the MSRE remain the only molten salt reactors ever operated. In a nuclear power reactor , there are two types of fuel. The first is fissile material, which splits when hit by neutrons , releasing a large amount of energy and also releasing two or three new neutrons. These can split more fissile material, resulting in

12432-427: Was run for a few weeks and at essentially zero power, although it reached criticality. The operating temperature was held constant at approximately 675 °C (1,250 °F). The PWAR-1 used NaF/ZrF 4 /UF 4 as the primary fuel and coolant. It was one of three critical MSRs ever built. Oak Ridge National Laboratory (ORNL) took the lead in researching MSRs through the 1960s. Much of their work culminated with

12544-432: Was surprisingly hard to find, so in 2006 Sorensen started "energyfromthorium.com", a document repository, forum, and blog to promote this technology. In 2006, Sorensen coined the liquid fluoride thorium reactor and LFTR nomenclature to describe a subset of molten salt reactor designs based on liquid fluoride-salt fuels with breeding of thorium into uranium-233 in the thermal spectrum. In 2011, Sorensen founded Flibe Energy,

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