![Molten Salt Reactor](https://upload.wikimedia.org/wikipedia/commons/0/08/Molten_Salt_Reactor.svg)
A molten salt reactor (MSR) is a class of
nuclear fission reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from n ...
in which the primary
nuclear reactor coolant
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the Environment (systems), environment.
Frequently, a chain of two coolant loops are used b ...
and/or the fuel is a
molten salt
Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.[< ...]
mixture. Only two MSRs have ever operated, both research reactors in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
. The 1950's
Aircraft Reactor Experiment
The Aircraft Reactor Experiment (ARE) was an experimental nuclear reactor designed to test the feasibility of fluid-fuel, high-temperature, high-power-density reactors for the propulsion of supersonic aircraft. It operated between November 8-12, ...
was primarily motivated by the compact size that the technique offers, while the 1960's
Molten-Salt Reactor Experiment
The Molten-Salt Reactor Experiment (MSRE) was an experimental molten salt reactor research reactor at the Oak Ridge National Laboratory (ORNL). This technology was researched through the 1960s, the reactor was constructed by 1964, it went critica ...
aimed to prove the concept of a
nuclear power plant
A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a electric generator, generato ...
which implements a
thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...
in a
breeder reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mate ...
. Increased research into
Generation IV reactor
Generation IV reactors (Gen IV) are six nuclear reactor designs recognized by the Generation IV International Forum. The designs target improved safety, sustainability, efficiency, and cost.
The most developed Gen IV reactor design is the sodium ...
designs began to renew interest in the technology, with multiple nations having projects, and , China is on the verge of starting its
TMSR-LF1 thorium MSR.
MSRs are considered safer than conventional reactors because they operate with fuel already in a molten state, and in some designs in the event of an emergency, the fuel mixture is designed to drain from the core to a containment vessel where it will solidify in fuel drain tanks. This prevents the uncontrolled
nuclear meltdown
A nuclear meltdown (core meltdown, core melt accident, meltdown or partial core melt) is a severe nuclear reactor accident that results in core damage from overheating. The term ''nuclear meltdown'' is not officially defined by the Internation ...
and associated hydrogen explosions (as in the
Fukushima nuclear disaster
The was a nuclear accident in 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. The proximate cause of the disaster was the 2011 Tōhoku earthquake and tsunami, which occurred on the afternoon of 11 March 2011 and ...
) that are a risk in conventional (solid-fuel) reactors. They operate at or close to
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
, rather than the 75-150 times atmospheric pressure of a typical
light-water reactor
The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reacto ...
(LWR), hence reducing the need for large, expensive
reactor pressure vessel
A reactor pressure vessel (RPV) in a nuclear power plant is the pressure vessel containing the nuclear reactor coolant, core shroud, and the reactor core.
Classification of nuclear power reactors
Russian Soviet era RBMK reactors have each fuel a ...
s used in LWRs. Another advantage of MSRs is that the gaseous fission products (
Xe and
Kr) do not have much solubility in the fuel salt, and can be safely captured as they bubble out of the molten fuel, rather than increasing the pressure inside the
fuel tubes over the life of the fuel, as happens in conventional solid-fuelled reactors. MSR's can also be refueled while operating (essentially online-
nuclear reprocessing
Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...
) while conventional reactors must be shut down for refueling (Pressure tube heavy water reactors like the
CANDU
The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...
or the Atucha-class PHWRs, and British-built Gas-cooled Reactors (
Magnox
Magnox is a type of nuclear power/production reactor that was designed to run on natural uranium with graphite as the moderator and carbon dioxide gas as the heat exchange coolant. It belongs to the wider class of gas-cooled reactors. The n ...
,
AGR) being notable exceptions).
A further key characteristic of MSRs is operating temperatures of around , significantly higher than traditional LWRs at around , providing greater
electricity-generation efficiency, the possibility of grid-storage facilities, economical hydrogen production, and, in some cases, process-heat opportunities. Relevant design challenges include the
corrosivity
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engin ...
of hot salts and the changing chemical composition of the salt as it is
transmuted by the
neutron flux
The neutron flux, φ, is a scalar quantity used in nuclear physics and nuclear reactor physics. It is the total length travelled by all free neutrons per unit time and volume. Equivalently, it can be defined as the number of neutrons travelling ...
in the
reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place and the heat is generated. Typically, the fuel will be low-enriched uranium contained in thousands of indiv ...
.
MSRs offer multiple advantages over conventional nuclear power plants, although for historical reasons they have not been deployed.
Properties
MSRs, especially those with molten salt fuel, differ considerably from conventional reactors. Reactor core pressure can be low and the temperature much higher. In this respect an MSR is more similar to a
liquid metal cooled reactor
A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal cooled reactors were first adapted for nuclear submarine use and have been s ...
than to a conventional light water cooled reactor. MSRs are often planned as breeding reactors with a closed fuel cycle—as opposed to the once-through fuel currently used in U.S. nuclear reactors.
Safety concepts rely on a negative
temperature coefficient of reactivity Fuel temperature coefficient of reactivity is the change in reactivity of the nuclear fuel per degree change in the fuel temperature. The coefficient quantifies the amount of neutrons that the nuclear fuel (such as uranium-238) absorbs from the fi ...
and a large possible temperature rise to limit reactivity excursions. As an additional method for shutdown, a separate, passively cooled container below the reactor can be included. In case of problems, and for regular maintenance, the fuel is drained from the reactor. This stops the nuclear reaction and acts as a second cooling system. Neutron-producing accelerators have been proposed for some super-safe subcritical experimental designs.
The temperatures of some proposed designs are high enough to produce process heat for hydrogen production or other chemical reactions. Because of this, they are included in the GEN-IV roadmap for further study.
Advantages
MSRs offer many potential advantages over current light water reactors:
*As in all low-pressure reactor designs, passive decay heat removal is achieved in MSRs. In some designs, the fuel and the coolant are the same fluid, so a loss of coolant removes the reactor's fuel, similar to how loss of coolant also removes the moderator in LWRs. Unlike steam, fluoride salts dissolve poorly in water, and do not form burnable hydrogen. Unlike steel and solid uranium oxide, molten salts are not damaged by the core's neutron bombardment, though the reactor vessel still is.
*A low-pressure MSR lacks a boiling water reactor's (BWR) high-pressure radioactive steam and therefore do not experience leaks of radioactive steam and cooling water, and the expensive containment, steel core vessel, piping and safety equipment needed to contain radioactive steam. However, most MSR designs require radioactive fission product-containing fluid in direct contact with pumps and heat exchangers.
*MSRs may make closed
nuclear fuel cycle
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the ''front end'', which are the preparation of the fuel, steps in the ''service period'' in w ...
s cheaper because they can operate with slow neutrons. If fully implemented, any reactor that closes the nuclear fuel cycle reduces environmental impacts: Chemical separation turns long-lived actinides back into reactor fuel. The discharged wastes are mostly fission products (nuclear ashes) with shorter half-lives. This reduces the needed geologic containment to 300 years rather than the tens of thousands of years needed by a light-water reactor's spent nuclear fuel. It also permits the use of alternate nuclear fuels, such as thorium.
*The fuel's liquid phase might be
pyroprocessed to separate fission products (nuclear ashes) from actinide fuels. This may have advantages over conventional reprocessing, though much development is still needed.
*Fuel rod fabrication is not required (replaced with fuel salt synthesis).
*Some designs are compatible with the fast neutron spectrum, which can "burn" problematic transuranic elements like Pu240, Pu241 and up (reactor grade plutonium) from traditional light-water nuclear reactors.
*An MSR can react to load changes in under 60 seconds (unlike "traditional" solid-fuel nuclear power plants that suffer from
xenon poisoning).
*Molten salt reactors can run at high temperatures, yielding high thermal efficiency. This reduces size, expense, and environmental impacts.
*MSRs can offer a high "specific power," that is high power at a low mass as demonstrated by ARE.
*A possibly good neutron economy makes the MSR attractive for the neutron-poor
thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...
Disadvantages
*In circulating-fuel-salt designs, radionuclides dissolved in fuel come in contact with major equipment such as pumps and heat exchangers, likely requiring fully remote and possibly expensive maintenance.
*Some MSRs require onsite chemical processing to manage core mixture and remove fission products.
*Required regulatory changes to deal with radically different design features
*Some MSR designs rely on nickel-based alloys to hold the molten salt. Alloys based on nickel and iron are prone to embrittlement under high neutron flux.
*Corrosion risk. Molten salts require careful management of their redox state to handle corrosion risks. This is particularly challenging for circulating-fuel-salt designs, in which a complex mix of fissile/fertile isotopes and their transmutation/fission/decay products is being circulated through the reactor. Static fuel salt designs profit from modularising the problem: the fuel salt is contained within fuel pins whose regular replacement, primarily due to neutron irradiation damage, is part of the operating concept; while the coolant salt has a simpler chemical composition and, under appropriate redox state management, does not pose a corrosion risk either to the fuel pins or to the reactor vessel. (Regarding redox state management, see the descriptions for the
stable salt reactor's fuel and
coolant
A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosio ...
salts). The MSRs developed at ORNL in the 60's were only safe to operate for a few years, and operated at only about . Potential corrosion risks include dissolution of chromium by liquid fluoride thorium salts at greater than , hence endangering stainless steel components. Neutron radiation can also transmute other common alloying agents such as Co and Ni, shortening lifespan. If using lithium salts (e.g. FLiBe), it is preferable, if expensive, to use to reduce tritium generation (tritium can permeate stainless steels, cause embrittlement, and escape into the environment). ORNL developed Hastelloy N to help address these issues, and there is an effort to certify other structural steels for use in reactors (316H, 800H, inco 617).
*Some MSR designs might be modified to make a
breeder reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mate ...
able to produce weapons-grade nuclear material.
*The MSRE and aircraft nuclear reactors used enrichment levels so high that they approach the levels of nuclear weapons. These levels would be illegal in most modern regulatory regimes for power plants. Most modern designs avoid this issue.
*Neutron damage to solid moderator materials can limit the core lifetime of an MSR that uses moderated thermal neutrons. For example, the MSRE was designed so that its graphite moderator sticks had very loose tolerances, so neutron damage could change their size without damage. "Two fluid" MSR designs are unable to use graphite piping because graphite changes size when it is bombarded with neutrons, and graphite pipes would crack and leak.
MSR using fast neutrons cannot use graphite anyway to avoid moderation.
*Thermal MSRs have lower breeding ratios than fast-neutron breeders, though their doubling time may be shorter.
Coolant
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 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 reactor
A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal cooled reactors were first adapted for nuclear submarine use and have been s ...
s. Notably, steam is not created in the core (as is present in BWRs), and no large, expensive steel pressure vessel (as required for PWRs). Since it can operate at high temperatures, the conversion of the heat to electricity can use an efficient, lightweight
Brayton cycle
The Brayton cycle is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. The original Brayton engines used a piston compressor and piston expander, but modern gas tur ...
gas turbine.
Much of the current research on FHRs is focused on small, compact
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
s that reduce molten salt volumes and associated costs.
Molten salts can be highly corrosive and corrosivity increases with temperature. For the primary cooling loop, a material is needed that can withstand
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
at high temperatures and intense
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
. 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
thermochemical production of
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
becomes possible. Materials for this temperature range have not been validated, though
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
composites,
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
alloys (e.g. TZM),
carbide
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
Interstitial / Metallic carbides
The carbides of the ...
s, and refractory metal based or
ODS alloys Oxide dispersion strengthened alloys (ODS) are alloys that consist of a metal matrix with small oxide particles dispersed within it. They have high heat resistance, strength, and ductility. Alloys of nickel are the most common but includes iron alum ...
might be feasible.
A workaround suggested by a private researcher is to use the new beta-titanium Au alloys as this would also allow extreme temperature operation as well as increasing the safety margin.
Fused salt selection
![FLiBe](https://upload.wikimedia.org/wikipedia/commons/d/d4/FLiBe.png)
The salt mixtures are chosen to make the reactor safer and more practical.
Fluorine
Fluorine has only one stable isotope (), and does not easily become radioactive under neutron bombardment. Compared to chlorine and other halides, fluorine also absorbs fewer neutrons and slows ("
moderates
Moderate is an ideological category which designates a rejection of radical or extreme views, especially in regard to politics and religion. A moderate is considered someone occupying any mainstream position avoiding extreme views. In American ...
") 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
Chlorine has two stable isotopes ( and ), as well as a slow-decaying isotope between them which facilitates neutron absorption by .
Chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
s permit fast
breeder reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mate ...
s 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, , thus reducing production of
sulfur tetrachloride
Sulfur tetrachloride is an inorganic compound with chemical formula SCl4. It has only been obtained as an unstable pale yellow solid. The corresponding SF4 is a stable, useful reagent.
Preparation and structure
It is obtained by treating sulfur d ...
that occurs when absorbs a neutron to become , then degrades by
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
to .
Lithium
Lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
must be in the form of purified , because effectively captures neutrons and produces
tritium
Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
. Even if pure
7Li is used, salts containing lithium cause significant tritium production, comparable with heavy water reactors.
Mixtures
Reactor salts are usually close to
eutectic mixtures to reduce their melting point. A low melting point simplifies melting 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
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...
window" of fused fluoride salts, the
redox potential
Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
of the fused salt system can be changed. Fluorine-lithium-beryllium ("
FLiBe
FLiBe is a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). It is both a nuclear reactor coolant and solvent for fertile or fissile material. It served both purposes in the Molten-Salt Reactor Experiment ...
") can be used with
beryllium
Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
additions to lower the redox potential and nearly eliminate corrosion. However, since beryllium is extremely toxic, special precautions must be engineered into 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 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
Mole (or Molé) may refer to:
Animals
* Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America
* Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpida ...
) of UF
4 is added. Thorium and plutonium fluorides have also been used.
Fused salt purification
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 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 metal 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 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.
Fused salt processing
The possibility of online processing can be an MSR advantage. Continuous processing would reduce the inventory of fission products, control corrosion and improve neutron economy by removing fission products with high neutron absorption cross-section, especially
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
. This makes the MSR particularly suited to the neutron-poor
thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...
. Online fuel processing can introduce risks of fuel processing accidents,
which can trigger release of
radio isotopes.
In some thorium breeding scenarios, the intermediate product
protactinium
Protactinium (formerly protoactinium) is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds ...
would be removed from the reactor and allowed to decay into highly pure , 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 is not absorbed but instead knocks a neutron out of the nucleus), generate . Because has a short half-life and its decay chain contains hard
gamma
Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter re ...
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 is the R&D to engineer an economically competitive fuel salt cleaning system.
Fuel reprocessing
![Changing composition molten salt reactor-en](https://upload.wikimedia.org/wikipedia/commons/0/02/Changing_composition_molten_salt_reactor-en.svg)
Reprocessing refers to the chemical separation of fissionable uranium and plutonium from spent fuel.
Such recovery could increase the risk of
nuclear proliferation
Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as " Nuclear Weapon States" by the Treaty on the Non-Proliferation of Nuclear Wea ...
. In the United States the regulatory regime has varied dramatically across administrations.
Costs and economics
A systematic literature review from 2020 concludes that there 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.
Types of molten salt reactors
While many design variants have been proposed, there are three main categories regarding 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.
Designs
MSRs can be burners or breeders. They can be
fast or
thermal
A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
or
epithermal
Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
. Thermal reactors typically employ 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
Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium with a lower content of the fissile isotope than natural uranium.: "Depleted uranium possesses only 60% of the radioactivity of natural uranium, hav ...
, 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:
Molten salt fast reactor
The
molten salt fast reactor
Melting, or Enthalpy of fusion, fusion, is a physical process that results in the phase transition of a chemical substance, substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the appli ...
(MSFR) 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.
[''Molten Salt Reactors.](_blank)
WNA, update May 2021 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 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 reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mate ...
s. They operate without a moderator in the core such as graphite, so graphite life-span 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
233U. 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 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 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
3 with a mean fuel temperature of 750
oC. 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 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 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 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 the fuel salt. Usually the fuel salt temperature can be brought down by 100
oC 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 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.
Fluoride salt-cooled high-temperature reactor
The
fluoride salt-cooled high-temperature reactor (FHR), also called advanced high temperature reactor (AHTR), 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
A high-temperature gas-cooled reactor (HTGR), is a nuclear reactor that uses a graphite moderator with a once-through uranium fuel cycle. The HTGR is a type of high-temperature reactor (HTR) that can conceptually have an outlet temperature of ...
(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
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoin ...
" fuel dispersed in graphite. Early AHTR research focused on graphite in 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
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
production facility conditions (most
thermochemical cycle Thermochemical cycles combine solely heat sources (''thermo'') with ''chemical'' reactions to split water into its hydrogen and oxygen components. The term ''cycle'' is used because aside of water, hydrogen and oxygen, the chemical compounds used in ...
s require temperatures in excess of 750 °C); better electric conversion efficiency than a helium-cooled VHTR operating in similar conditions;
passive safety
Automotive safety is the study and practice of design, construction, equipment and regulation to minimize the occurrence and consequences of traffic collisions involving motor vehicles. Road traffic safety more broadly includes roadway design ...
systems and better retention of fission products in the event of an accident.
Liquid fluoride thorium reactor
Reactors containing molten thorium salt, called liquid fluoride thorium reactors (LFTR), would tap the
thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...
. Private companies from Japan, Russia, Australia and the United States, and the Chinese government, have expressed interest in developing this technology.
[Evans-Pritchard, Ambrose (6 January 2013]
China blazes trail for 'clean' nuclear power from thorium
The Daily Telegraph
''The Daily Telegraph'', known online and elsewhere as ''The Telegraph'', is a national British daily broadsheet newspaper published in London by Telegraph Media Group and distributed across the United Kingdom and internationally.
It was fo ...
, UK. Accessed 18 March 2013[Barton, Charles (March 2008]
Interview with Ralph Moir
at Energy From Thorium blog
at NextBigFuture blog, 23 May 2011
Advocates estimate that five hundred metric tons of thorium could supply U.S. energy needs for one year.
The
U.S. Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and ...
estimates that the largest-known U.S. thorium deposit, the
Lemhi Pass
Lemhi Pass is a high mountain pass in the Beaverhead Mountains, part of the Bitterroot Range in the Rocky Mountains and within Salmon-Challis National Forest. The pass lies on the Montana-Idaho border on the continental divide, at an elevation o ...
district on the
Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
-
Idaho
Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...
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.
Stable salt reactor
The stable salt reactor is a relatively recent concept which holds 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.
Dual-fluid molten salt reactors
A prototypical example of a
dual fluid reactor
The Dual Fluid Reactor is a reactor concept of the Canadian company Dual Fluid Energy Inc. combining the advantages of the molten salt reactor with those of the liquid metal cooled reactor, it is supposed to reach the criteria for reactors of the ...
is the lead-cooled, salt-fueled reactor.
History
1950s
Aircraft Reactor Experiment, US
![ARE Building](https://upload.wikimedia.org/wikipedia/commons/a/a1/ARE_Building.JPG)
MSR research started with the U.S. Aircraft Reactor Experiment (ARE) in support of the U.S.
Aircraft Nuclear Propulsion
The Aircraft Nuclear Propulsion (ANP) program and the preceding Nuclear Energy for the Propulsion of Aircraft (NEPA) project worked to develop a nuclear propulsion system for aircraft. The United States Army Air Forces initiated Project NEPA on ...
program. ARE was a 2.5
MWth nuclear reactor experiment designed to attain a high
energy density
In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or .
Often only the ''useful'' or extract ...
for use as an engine in a nuclear-powered bomber.
The project included experiments, including high temperature and engine tests collectively called the Heat Transfer Reactor Experiments: HTRE-1, HTRE-2 and HTRE-3 at the National Reactor Test Station (now
Idaho National Laboratory
Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...
) 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%
In chemistry, the mole fraction or molar fraction (''xi'' or ) is defined as unit of the amount of a constituent (expressed in moles), ''ni'', divided by the total amount of all constituents in a mixture (also expressed in moles), ''n''tot. This ex ...
) as fuel, moderated by
beryllium oxide
Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and exceeds that of m ...
(BeO). Liquid sodium was a secondary coolant.
The experiment had a peak temperature of 860 °C. It produced 100 MWh over nine days in 1954. This experiment used
Inconel
Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys.
Inconel alloys are oxidation-corrosion-resistant materials well suited for service in extreme environments subjected t ...
600 alloy for the metal structure and piping.
[Rosenthal, Murry]
An Account of Oak Ridge National Laboratory's Thirteen Nuclear Reactors, ORNL/TM-2009/181
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
Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military aviat ...
Aircraft Company (PWAC). This was called Pratt and Whitney Aircraft Reactor-1 (PWAR-1). The experiment was run for a few weeks and at essentially zero power, although it reached criticality. The operating temperature was held constant at approximately . The PWAR-1 used NaF-ZrF
4-UF
4 as the primary fuel and coolant. It was one of three critical MSRs ever built.
1960s and 1970s
MSRE at Oak Ridge, US
Oak Ridge National Laboratory
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
(ORNL) took the lead in researching MSRs through the 1960s. Much of their work culminated with 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
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 ...
(LFTR). The large (expensive) breeding blanket of thorium salt was omitted in favor of neutron measurements.
MSRE's piping, core vat and structural components were made from
Hastelloy
Haynes International, Inc., headquartered in Kokomo, Indiana, is one of the largest producers of corrosion-resistant and high-temperature alloys. In addition to Kokomo, Haynes has manufacturing facilities in Arcadia, Louisiana, and Mountain Home, ...
-N, moderated by
pyrolytic graphite
Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets as a result of imperfections in its production.
Pyrolytic carbon is man-made and is thought not to be found in nature.Ratner, Buddy D. ...
. It went critical in 1965 and ran for four years. Its fuel was LiF-BeF
2-ZrF
4-UF
4 (65-29-5-1)
mol%
In chemistry, the mole fraction or molar fraction (''xi'' or ) is defined as unit of the amount of a constituent (expressed in moles), ''ni'', divided by the total amount of all constituents in a mixture (also expressed in moles), ''n''tot. This ex ...
. The graphite core moderated it. Its secondary coolant was
FLiBe
FLiBe is a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). It is both a nuclear reactor coolant and solvent for fertile or fissile material. It served both purposes in the Molten-Salt Reactor Experiment ...
(2LiF-BeF
2). It reached temperatures as high as and achieved the equivalent of about 1.5 years of full power operation.
Theoretical designs at Oak Ridge, US
=Molten salt breeder reactor
=
From 1970 to 1976 ORNL researched during the 1970–1976 a molten salt breeder reactor (MSBR) design. Fuel was to be LiF-BeF
2-ThF
4-UF
4 (72-16-12-0.4)
mol%
In chemistry, the mole fraction or molar fraction (''xi'' or ) is defined as unit of the amount of a constituent (expressed in moles), ''ni'', divided by the total amount of all constituents in a mixture (also expressed in moles), ''n''tot. This ex ...
with graphite moderator. The secondary coolant was to be NaF-NaBF
4. Its peak
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
was to be .
[Section 5.3, WASH 1097]
Energy From Thorium's Document Repository "The Use of Thorium in Nuclear Power Reactors"
ORNL.gov It would follow a 4-year replacement schedule. The MSR program closed down in the early 1970s in favor of the
liquid metal fast-breeder reactor (LMFBR),
after which research stagnated in the United States.
, ARE and MSRE remained the only molten-salt reactors ever operated.
The MSBR project received funding from 1968 to 1976 of (in dollars) $.
Officially, the program was cancelled because:
* The political and technical support for the program in the United States was too thin geographically. Within the United States the technology was well understood only in Oak Ridge.
* 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 with contracts that benefited many parts of the country. When the MSR development program had progressed far enough to justify an expanded program leading to commercial development, the
United States Atomic Energy Commission
The United States Atomic Energy Commission (AEC) was an agency of the United States government established after World War II by U.S. Congress to foster and control the peacetime development of atomic science and technology. President H ...
(AEC) could not justify the diversion of substantial funds from the
LMFBR
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mater ...
to a competing program.
=Denatured molten salt reactor
=
The denatured molten salt reactor (DMSR) was an Oak Ridge theoretical design that was never built.
Engel et al 1980 said the project "examine[ the conceptual feasibility of a molten-salt power reactor fueled with denatured uranium-235 (i.e. with low-enriched uranium) and operated with a minimum of chemical processing." The main design priority was proliferation resistance.
Although the DMSR can theoretically be fueled partially by thorium or plutonium, fueling solely with low enriched uranium (LEU) helps maximize proliferation resistance.
Other goals of the DMSR were to minimize research and development and to maximize feasibility. The Generation IV international Forum (GIF) includes "salt processing" as a technology gap for molten salt reactors.
The DMSR design theoretically requires minimal chemical processing because it is a burner rather than a breeder.
United Kingdom
The UK's Atomic Energy Research Establishment (AERE) was developing an alternative MSR design across its National Laboratories at Harwell, Oxfordshire, Harwell, Culham Science Centre, Culham, Risley, Warrington, Risley and Winfrith. AERE opted to focus on a
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
-cooled 2.5 GWe Molten Salt Fast Reactor (MSFR) concept using a
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
.
They also researched helium gas as a coolant.
The UK MSFR would have been fuelled by
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
, a fuel considered to be 'free' by the program's research scientists, because of the UK's plutonium stockpile.
Despite their different designs, ORNL and AERE maintained contact during this period with information exchange and expert visits. Theoretical work on the concept was conducted between 1964 and 1966, while experimental work was ongoing between 1968 and 1973. The program received annual government funding of around £100,000–£200,000 (equivalent to £2m–£3m in 2005). This funding came to an end in 1974, partly due to the success of the
Prototype Fast Reactor at Dounreay which was considered a priority for funding as it went critical in the same year.
Soviet Union
In the USSR, a molten-salt reactor research program was started in the second half of the 1970s at the
Kurchatov Institute
The Kurchatov Institute (russian: Национальный исследовательский центр «Курчатовский Институт», 'National Research Centre "Kurchatov Institute) is Russia's leading research and developmen ...
. It included theoretical and experimental studies, particularly the investigation of mechanical, corrosion and radiation properties of the molten salt container materials. The main findings supported the conclusion that no physical nor technological obstacles prevented the practical implementation of MSRs.
Twenty-first century
MSR interest resumed in the new millennium due to continuing delays in
fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whi ...
and other
nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
programs and increasing demand for energy sources that would incur minimal greenhouse gas (GHG) emissions.
Commercial/national/international projects
Canada
Terrestrial Energy
Terrestrial Energy is a Canadian nuclear technology company working on Generation IV nuclear technology
Nuclear technology is technology that involves the nuclear reactions of atomic nuclei. Among the notable nuclear technologies are nuclear ...
, a Canadian-based company, is developing a DMSR design called the
Integral Molten Salt Reactor
The Integral Molten Salt Reactor (IMSR) is a nuclear power plant design targeted at developing a commercial product for the small modular reactor (SMR) market. It employs molten salt reactor technology which is being developed by the Canadian comp ...
(IMSR). The IMSR is designed to be deployable as a
small modular reactor
Small modular reactors (SMRs) are a proposed class of nuclear fission reactors, smaller than conventional nuclear reactors, which can be built in one location (such as a factory), then shipped, commissioned, and operated at a separate site. The ...
(SMR). Their design currently undergoing licensing is 400MW thermal (190MW electrical). With high operating temperatures, the IMSR has applications in industrial heat markets as well as traditional power markets. The main design features include neutron moderation from graphite, fueling with low-enriched uranium and a compact and replaceable Core-unit. Decay heat is removed passively using nitrogen (with air as an emergency alternative). The latter feature permits the operational simplicity necessary for industrial deployment.
Terrestrial completed the first phase of a prelicensing review by the
Canadian Nuclear Safety Commission
The Canadian Nuclear Safety Commission (CNSC; french: Commission Canadienne de sûreté nucléaire) is the federal regulator of nuclear power and materials in Canada.
Mandate and history
Canadian Nuclear Safety Commission was established under t ...
in 2017, which provided a regulatory opinion that the design features are generally safe enough to eventually obtain a license to construct the reactor.
China
China initiated a thorium research project in January 2011, and spent about 3 billion yuan (US$500 million) on it by 2021.
A 100 MW demonstrator of the solid fuel version (TMSR-SF), based on
pebble bed technology, was planned to be ready by 2024. A 10 MW pilot and a larger demonstrator of the liquid fuel (TMSR-LF) variant were targeted for 2024 and 2035, respectively. China then accelerated its program to build two 12 MW reactors underground at
Wuwei research facilities by 2020,
beginning with the 2 megawatt
TMSR-LF1 prototype. The project sought to test new corrosion-resistant materials.
In 2017,
ANSTO
The Australian Nuclear Science and Technology Organisation (ANSTO) is a statutory body of the Australian government, formed in 1987 to replace the Australian Atomic Energy Commission. Its head office and main facilities are in southern outs ...
/Shanghai Institute Of Applied Physics announced the creation of a NiMo-SiC alloy for use in MSRs.
In 2021, China stated that Wuwei prototype operation could start power generation from thorium in September,
with a prototype providing energy for around 1,000 homes. It is the world's first nuclear molten salt reactor after the Oak Ridge project.
The 100 MW successor was expected to be 3 meters tall and 2.5 meters wide, capable of providing energy to 100,000 homes.
Further work on commercial reactors was announced with the target completion date of 2030. Chinese government plans to realize similar reactors in deserts and plains of western China as well as up to 30 in countries involved in China's "
Belt and Road
The Belt and Road Initiative (BRI, or B&R), formerly known as One Belt One Road ( zh, link=no, 一带一路) or OBOR for short, is a global infrastructure development strategy adopted by the Chinese government in 2013 to invest in nearly 150 ...
" initiative.
In 2022, Shanghai Institute of Applied Physics (SINAP) was given approval by the Ministry of Ecology and Environment to commission an experimental thorium-powered MSR.
Denmark
Copenhagen Atomics
Copenhagen Atomics is a Danish molten salt technology company developing mass manufacturable molten salt reactors. The company is pursuing small modular, molten fuel salt, thorium fuel cycle, thermal spectrum, breeder reactors using separa ...
is a Danish molten salt technology company developing mass manufacturable 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 the salt and continuously drained and cooled to below . 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.
Seaborg Technologies
Seaborg Technologies is a private Danish startup. It is developing small molten salt reactors.
Founded in 2015 and based in Copenhagen, Denmark, Seaborg emerged as a small team of physicists, chemists, and engineers with educational roots at the ...
is developing the core for a compact molten salt reactor (CMSR). The CMSR is a high temperature, single salt, thermal MSR designed to go critical on commercially available
low enriched uranium
Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238 ...
. The CMSR design is modular, and uses proprietary NaOH moderator.
The reactor core is estimated to be replaced every 12 years. During operation, the fuel will not be replaced and will burn for the entire 12-year reactor lifetime. The first version of the Seaborg core is planned to produce 250 MW
th power and 100 MW
e power. As a power plant, the CMSR will be able to deliver electricity, clean water and heating/cooling to around 200,000 households.
France
The
CNRS
The French National Centre for Scientific Research (french: link=no, Centre national de la recherche scientifique, CNRS) is the French state research organisation and is the largest fundamental science agency in Europe.
In 2016, it employed 31,637 ...
project EVOL (Evaluation and viability of liquid fuel fast reactor system) project, with the objective of proposing a design of the molten salt fast reactor (MSFR), released its final report in 2014. Various MSR projects like FHR, MOSART, MSFR, and TMSR have common research and development themes.
The EVOL project will be continued by the EU-funded Safety Assessment of the Molten Salt Fast Reactor (SAMOFAR) project, in which several European research institutes and universities collaborate.
Germany
The German Institute for Solid State Nuclear Physics in Berlin has proposed the
dual fluid reactor
The Dual Fluid Reactor is a reactor concept of the Canadian company Dual Fluid Energy Inc. combining the advantages of the molten salt reactor with those of the liquid metal cooled reactor, it is supposed to reach the criteria for reactors of the ...
as a concept for a fast breeder lead-cooled MSR. The original MSR concept used the fluid salt to provide the fission materials and also to remove the heat. Thus it had problems with the needed flow speed. Using 2 different fluids in separate circles solves the problem.
India
In 2015, Indian researchers published a MSR design, as an alternative path to thorium-based reactors, according to
India's three-stage nuclear power programme
India's three-stage nuclear power programme was formulated by Homi Bhabha, the well-known physicist, in the 1950s to secure the country's long term energy independence, through the use of uranium and thorium reserves found in the monazite sa ...
.
Indonesia
Thorcon is developing the
TMSR-500 molten salt reactor for the Indonesian market.
National Research and Innovation Agency
The National Research and Innovation Agency ( id, Badan Riset dan Inovasi Nasional, BRIN) is a cabinet-level government agency formed by the Indonesian government in 2019. Originally a new agency attached to the Ministry of Research and Technolo ...
, through its
Research Organization for Nuclear Energy
The Research Organization for Nuclear Energy ( id, Organisasi Riset Tenaga Nuklir, ORTN) is one of Research Organizations under the umbrella of the National Research and Innovation Agency (, BRIN). It was founded on 1 September 2021. The organizat ...
announced its renewal of interest on MSR reactor research on 29 March 2022 and planned to study and develop MSR for
thorium-fueled nuclear reactors.
[World Nuclear New]
(26 Jan 2022) Empresarios Agrupados contracted for first ThorCon reactor
Japan
The
Fuji Molten Salt Reactor
The FUJI molten salt reactor is a proposed molten-salt-fueled thorium fuel cycle thermal reactor, thermal breeder reactor, using technology similar to the Oak Ridge National Laboratory's Molten Salt Reactor Experiment – liquid fluoride thorium re ...
is a 100 to 200
MWe LFTR, using technology similar to the Oak Ridge project. A consortium including members from Japan, the U.S. and Russia are developing the project. The project would likely take 20 years to develop a full size reactor, but the project seems to lack funding.
Russia
In 2020, Rosatom announced plans to build a 10 MW
th FLiBe
FLiBe is a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). It is both a nuclear reactor coolant and solvent for fertile or fissile material. It served both purposes in the Molten-Salt Reactor Experiment ...
burner
Burner may refer to:
* Gas burner, coal burner or oil burner, a mechanical device that burns a gas or liquid fuel in a controlled manner
** Laboratory gas burners:
*** Bunsen burner
*** Meker–Fisher burner
*** Teclu burner
** Hot-air balloon de ...
MSR. It would be fueled by
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
from reprocessed
VVER
The water-water energetic reactor (WWER), or VVER (from russian: водо-водяной энергетический реактор; transliterates as ; ''water-water power reactor'') is a series of pressurized water reactor designs originally de ...
spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor an ...
and fluorides of
minor actinides
The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkeli ...
. It is expected to launch in 2031 at
Mining and Chemical Combine
The Mining and Chemical Combine was established in 1950 to produce plutonium for weapons. It is in the closed city Zheleznogorsk, Krasnoyarsk Krai. The company is currently part of the Rosatom group.
The site had three underground nuclear reacto ...
.
United Kingdom
The Alvin Weinberg Foundation
The Alvin Weinberg Foundation was a registered UK charity, operating under the name Weinberg Next Nuclear, that campaigned for research and development into next-generation nuclear energy. In particular, it advocated advancement of Liquid Fluor ...
is a British non-profit organization founded in 2011, dedicated to raising awareness about the potential of thorium energy and LFTR. It was formally launched at the
House of Lords
The House of Lords, also known as the House of Peers, is the Bicameralism, upper house of the Parliament of the United Kingdom. Membership is by Life peer, appointment, Hereditary peer, heredity or Lords Spiritual, official function. Like the ...
on 8 September 2011. It is named after American nuclear physicist
Alvin M. Weinberg
Alvin Martin Weinberg (; April 20, 1915 – October 18, 2006) was an American nuclear physicist who was the administrator at Oak Ridge National Laboratory (ORNL) during and after the Manhattan Project. He came to Oak Ridge, Tennessee, in 1945 ...
, who pioneered thorium MSR research.
The stable salt reactor, designed by Moltex Energy, was selected as the most suitable of six MSR designs for UK implementation in a 2015 study commissioned by the UK's innovation agency,
Innovate UK
Innovate UK is the United Kingdom's innovation agency, which provides money and support to organisations to make new products and services. It is a non-departmental public body operating at arm's length from the Government as part of the United ...
. UK government support has been weak, but Moltex has obtained support from New Brunswick Power for the development of a pilot plant in Point Lepreau, Canada, and financial backing from IDOM (an international engineering firm) and is currently engaged in the Canadian Vendor Design Review process.
United States
Idaho National Laboratory
Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...
designed a molten-salt-cooled, molten-salt-fuelled reactor with a prospective output of 1000
MWe.
[
]
Kirk Sorensen, former
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
scientist and chief nuclear technologist at
Teledyne Brown Engineering
Teledyne Technologies Incorporated is an American industrial conglomerate. It was founded in 1960, as Teledyne, Inc., by Henry Singleton and George Kozmetsky.
From August 1996 to November 1999, Teledyne existed as part of the conglomerate Al ...
, is a long-time promoter of the
thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...
, coining the term
liquid fluoride thorium reactor
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 ...
. In 2011, Sorensen founded Flibe Energy,
a company aimed at developing 20–50 MW LFTR reactor designs to power military bases. (It is easier to approve novel military designs than civilian power station designs in the US nuclear regulatory environment).
Transatomic Power pursued what it termed a waste-annihilating molten salt reactor (WAMSR), intended to consume existing
spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor an ...
, from 2011 until ceasing operation in 2018 and open-sourcing their research.
In January 2016, the
United States Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...
announced a $80m award fund to develop
Generation IV reactor
Generation IV reactors (Gen IV) are six nuclear reactor designs recognized by the Generation IV International Forum. The designs target improved safety, sustainability, efficiency, and cost.
The most developed Gen IV reactor design is the sodium ...
designs.
[
]
One of the two beneficiaries,
Southern Company
Southern Company is an American gas and electric utility holding company based in the southern United States. It is headquartered in Atlanta, Georgia, with executive offices also located in Birmingham, Alabama. The company is the second largest ...
will use the funding to develop a molten chloride
fast reactor
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as opposed t ...
(MCFR), a type of MSR developed earlier by British scientists.
In 2021, Tennessee Valley Authority
The Tennessee Valley Authority (TVA) is a federally owned electric utility corporation in the United States. TVA's service area covers all of Tennessee, portions of Alabama, Mississippi, and Kentucky, and small areas of Georgia, North Carolina ...
(TVA) and Kairos Power announced a TRISO
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoin ...
-fueled, fluoride salt-cooled 50MWt test reactor would be deployed at Oak Ridge, Tennessee. Also in 2021, Southern Company, in collaboration with TerraPower and the U.S. Department of Energy announced plans to build the Molten Chloride Reactor Experiment, the first fast-spectrum salt reactor at the Idaho National Laboratory
Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...
.
Abilene Christian University
Abilene Christian University (ACU) is a Private university, private Churches of Christ, Christian university in Abilene, Texas. It was founded in 1906 as ''Childers Classical Institute''. ACU is one of the largest private universities in the Sout ...
(ACU) has applied to the US Nuclear Regulatory Commission (NRC) for a construction licence for a 1MWt molten salt research reactor (MSRR), to be built on its campus in Abilene, Texas, as part of the Nuclear Energy eXperimental Testing (NEXT) laboratory. ACU plans for the MSRR to achieve criticality by December 2025.[ World nuclear news (wnn]
(19 Aug 2022) Application submitted for US molten salt research reactor
ACU is part of NEXT
*Brian Wan
Teledyne Brown Engineering is the prime contractor.
See also
* Aqueous homogeneous reactor
Aqueous homogeneous reactors (AHR) are a type of nuclear reactor in which soluble nuclear salts (usually uranium sulfate or uranium nitrate) are dissolved in water. The fuel is mixed with the coolant and the moderator, thus the name "homogeneo ...
* Integral fast reactor
The integral fast reactor (IFR, originally advanced liquid-metal reactor) is a design for a nuclear reactor using fast neutrons and no neutron moderator (a "fast" reactor). IFR would breed more fuel and is distinguished by a nuclear fuel cycle ...
* Nuclear aircraft
A nuclear-powered aircraft is a concept for an aircraft intended to be powered by nuclear energy. The intention was to produce a jet engine that would heat compressed air with heat from fission, instead of heat from burning fuel. During the Co ...
* Nuclear waste
Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...
Notes
References
Further reading
Energy from Thorium's Document Repository
Contains scanned versions of many of the U.S. government engineering reports, over ten thousand pages of construction and operation experience. This repository is the main reference for the aircraft reactor experiment and molten-salt fueled reactor's technical discussion.
*
Bruce Hoglund's Eclectic Interests Home Page
Nuclear Power, Thorium, Molten Salt reactors, etc.
INL MSR workshop summary
*
Material Considerations for Molten Salt Accelerator-based Plutonium Conversion Systems
J.H. Devan et al.
Nuclear goes retro – with a much greener outlook
M. Mitchell Waldrop
*
External links
Pacific Northwest National Laboratory – Molten Salt Reactor Fundamentals
YouTube
International Thorium Energy Organisation – www.IThEO.org
*
Idaho National Laboratory Molten Salt Reactor Fact Sheet
Energy from Thorium
Blog / Website
Google TechTalks – “Liquid Fluoride Thorium Reactor: What Fusion Wanted To Be” by Dr. Joe Bonometti NASA / Naval Postgraduate School
YouTube
Pebble Bed Advanced High Temperature Reactor
Thorium Remix
LFTR in 5 Minutes and other LFTR Documentaries.
Kun Chen from Chinese Academy of Sciences on China Thorium Molten Salt Reactor TMSR Program
Review of Molten Salt Reactor Technology
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{{DEFAULTSORT:Molten Salt Reactor
Graphite moderated reactors
Molten salt reactors