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Thorium fuel cycle

Thorium fuel cycle

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The thorium fuel cycle is a nuclear fuel cycle
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 which the fuel is used during reactor operation, and steps in...

 that uses the naturally abundant isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

, , as the fertile material
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...

. In the reactor, is transmuted into the fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...

 artificial uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 isotope which is the nuclear fuel
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...

. Unlike natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...

, natural thorium contains only trace amounts of fissile material (such as ), which are insufficient to initiate a nuclear chain reaction
Nuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...

. Additional fissile material or another neutron source are necessary to initiate the fuel cycle. In a thorium-fueled reactor, absorbs neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s eventually to produce . This parallels the process in uranium reactors whereby fertile absorbs neutrons to form fissile . Depending on the design of the reactor and fuel cycle, the generated either fissions in situ
In situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...

 or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.

The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including thorium's greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation
Nuclear proliferation
Nuclear proliferation is a term now used to describe the spread of nuclear weapons, fissile material, and weapons-applicable nuclear technology and information, to nations which are not recognized as "Nuclear Weapon States" by the Treaty on the Nonproliferation of Nuclear Weapons, also known as the...

, and reduced plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

 and actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

 production.

History


Concerns about the limits of worldwide uranium resources
Uranium depletion
Uranium depletion is the result of extracting and consuming uranium, a non-renewable resource. The availability of high-grade uranium ore will deplete over time meaning the fuel will become more environmentally and economically expensive to extract....

 motivated initial interest in the thorium fuel cycle. It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material. However, for most countries, uranium was relatively abundant, and research in thorium fuel cycles waned. A notable exception was India's three stage nuclear power programme
India's three stage nuclear power programme
India's three stage nuclear power programme was formulated to use the available uranium and thorium reserves found in the monazite sands of coastal regions of South India. Importance of nuclear energy was recognised as soon as India became independent...

. In the twenty-first century thorium's potential for improving proliferation resistance and waste characteristics led to renewed interest in the mineral.

At Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...

 in the 1960s, the Molten-Salt Reactor Experiment
Molten-Salt Reactor Experiment
The Molten-Salt Reactor Experiment was an experimental molten-salt reactor at the Oak Ridge National Laboratory researching this technology through the 1960s; constructed by 1964, it went critical in 1965 and was operated until 1969....

 used as the fissile fuel as an experiment to demonstrate a part of the Molten Salt Breeder Reactor that was designed to operate on the thorium fuel cycle. Molten Salt Reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

 (MSR) experiments assessed thorium's feasibility, using thorium(IV) fluoride
Thorium(IV) fluoride
Thorium fluoride is an inorganic chemical compound. It is a white, hygroscopic powder which can be produced by reacting thorium with fluorine gas. At temperatures above 500 °C, it reacts with atmospheric moisture to produce ThOF2.-Uses:...

 dissolved in a molten salt
Molten salt
Molten salt refers to a salt that is in the liquid phase that is normally a solid at standard temperature and pressure . A salt which is normally liquid at STP is usually called a room temperature ionic liquid, although technically molten salts are a class of ionic liquids.-Uses:Molten salts have...

 fluid which eliminated the need to fabricate fuel elements. The MSR program was defunded in 1976.

In 2006, Carlo Rubbia
Carlo Rubbia
Carlo Rubbia Knight Grand Cross is an Italian particle physicist and inventor who shared the Nobel Prize in Physics in 1984 with Simon van der Meer for work leading to the discovery of the W and Z particles at CERN.-Biography:...

 proposed the concept of an energy amplifier
Energy amplifier
In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation...

 or "accelerator driven system" (ADS), which he saw as a novel and safe way to produce nuclear energy that exploited existing accelerator technologies. Rubbia's proposal offered the potential to incinerate high-activity nuclear waste and produce energy from natural thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 and depleted uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

.

Nuclear reactions with thorium



In the thorium cycle, fuel is formed when captures
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...

 a neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

 (whether in a fast reactor or thermal reactor
Thermal reactor
A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. Most power reactors are of this type. These type of reactors use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons...

) to become . This normally emits an electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 and an anti-neutrino  by
The thorium fuel cycle is a
nuclear fuel cycle
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 which the fuel is used during reactor operation, and steps in...

 that uses the naturally abundant isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

, {{SimpleNuclide2|Thorium|232|link=yes}}, as the fertile material
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...

. In the reactor, {{SimpleNuclide2|Thorium|232|link=yes}} is transmuted into the fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...

 artificial uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 isotope {{SimpleNuclide2|Uranium|233|link=yes}} which is the nuclear fuel
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...

. Unlike natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...

, natural thorium contains only trace amounts of fissile material (such as {{SimpleNuclide2|Thorium|231|link=yes}}), which are insufficient to initiate a nuclear chain reaction
Nuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...

. Additional fissile material or another neutron source are necessary to initiate the fuel cycle. In a thorium-fueled reactor, {{SimpleNuclide2|Thorium|232}} absorbs neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s eventually to produce {{SimpleNuclide2|Uranium|233}}. This parallels the process in uranium reactors whereby fertile {{SimpleNuclide2|Uranium|238|link=yes}} absorbs neutrons to form fissile {{SimpleNuclide2|Plutonium|239|link=yes}}. Depending on the design of the reactor and fuel cycle, the {{SimpleNuclide2|Uranium|233}} generated either fissions in situ
In situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...

 or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.

The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including thorium's greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation
Nuclear proliferation
Nuclear proliferation is a term now used to describe the spread of nuclear weapons, fissile material, and weapons-applicable nuclear technology and information, to nations which are not recognized as "Nuclear Weapon States" by the Treaty on the Nonproliferation of Nuclear Weapons, also known as the...

, and reduced plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

 and actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

 production.

History


Concerns about the limits of worldwide uranium resources
Uranium depletion
Uranium depletion is the result of extracting and consuming uranium, a non-renewable resource. The availability of high-grade uranium ore will deplete over time meaning the fuel will become more environmentally and economically expensive to extract....

 motivated initial interest in the thorium fuel cycle. It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material. However, for most countries, uranium was relatively abundant, and research in thorium fuel cycles waned. A notable exception was India's three stage nuclear power programme
India's three stage nuclear power programme
India's three stage nuclear power programme was formulated to use the available uranium and thorium reserves found in the monazite sands of coastal regions of South India. Importance of nuclear energy was recognised as soon as India became independent...

. In the twenty-first century thorium's potential for improving proliferation resistance and waste characteristics led to renewed interest in the mineral.

At Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...

 in the 1960s, the Molten-Salt Reactor Experiment
Molten-Salt Reactor Experiment
The Molten-Salt Reactor Experiment was an experimental molten-salt reactor at the Oak Ridge National Laboratory researching this technology through the 1960s; constructed by 1964, it went critical in 1965 and was operated until 1969....

 used {{SimpleNuclide2|Uranium|233}} as the fissile fuel as an experiment to demonstrate a part of the Molten Salt Breeder Reactor that was designed to operate on the thorium fuel cycle. Molten Salt Reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

 (MSR) experiments assessed thorium's feasibility, using thorium(IV) fluoride
Thorium(IV) fluoride
Thorium fluoride is an inorganic chemical compound. It is a white, hygroscopic powder which can be produced by reacting thorium with fluorine gas. At temperatures above 500 °C, it reacts with atmospheric moisture to produce ThOF2.-Uses:...

 dissolved in a molten salt
Molten salt
Molten salt refers to a salt that is in the liquid phase that is normally a solid at standard temperature and pressure . A salt which is normally liquid at STP is usually called a room temperature ionic liquid, although technically molten salts are a class of ionic liquids.-Uses:Molten salts have...

 fluid which eliminated the need to fabricate fuel elements. The MSR program was defunded in 1976.

In 2006, Carlo Rubbia
Carlo Rubbia
Carlo Rubbia Knight Grand Cross is an Italian particle physicist and inventor who shared the Nobel Prize in Physics in 1984 with Simon van der Meer for work leading to the discovery of the W and Z particles at CERN.-Biography:...

 proposed the concept of an energy amplifier
Energy amplifier
In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation...

 or "accelerator driven system" (ADS), which he saw as a novel and safe way to produce nuclear energy that exploited existing accelerator technologies. Rubbia's proposal offered the potential to incinerate high-activity nuclear waste and produce energy from natural thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 and depleted uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

.

Nuclear reactions with thorium


{{actinidesvsfissionproducts}}
In the thorium cycle, fuel is formed when {{SimpleNuclide2|Thorium|232}} captures
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...

 a neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

 (whether in a fast reactor or thermal reactor
Thermal reactor
A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. Most power reactors are of this type. These type of reactors use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons...

) to become {{SimpleNuclide2|Thorium|233|link=yes}}. This normally emits an electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 and an anti-neutrino ({{SubatomicParticle|Antineutrino}}) by
The thorium fuel cycle is a
nuclear fuel cycle
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 which the fuel is used during reactor operation, and steps in...

 that uses the naturally abundant isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

, {{SimpleNuclide2|Thorium|232|link=yes}}, as the fertile material
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...

. In the reactor, {{SimpleNuclide2|Thorium|232|link=yes}} is transmuted into the fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...

 artificial uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 isotope {{SimpleNuclide2|Uranium|233|link=yes}} which is the nuclear fuel
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...

. Unlike natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...

, natural thorium contains only trace amounts of fissile material (such as {{SimpleNuclide2|Thorium|231|link=yes}}), which are insufficient to initiate a nuclear chain reaction
Nuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...

. Additional fissile material or another neutron source are necessary to initiate the fuel cycle. In a thorium-fueled reactor, {{SimpleNuclide2|Thorium|232}} absorbs neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s eventually to produce {{SimpleNuclide2|Uranium|233}}. This parallels the process in uranium reactors whereby fertile {{SimpleNuclide2|Uranium|238|link=yes}} absorbs neutrons to form fissile {{SimpleNuclide2|Plutonium|239|link=yes}}. Depending on the design of the reactor and fuel cycle, the {{SimpleNuclide2|Uranium|233}} generated either fissions in situ
In situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...

 or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.

The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including thorium's greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation
Nuclear proliferation
Nuclear proliferation is a term now used to describe the spread of nuclear weapons, fissile material, and weapons-applicable nuclear technology and information, to nations which are not recognized as "Nuclear Weapon States" by the Treaty on the Nonproliferation of Nuclear Weapons, also known as the...

, and reduced plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

 and actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

 production.

History


Concerns about the limits of worldwide uranium resources
Uranium depletion
Uranium depletion is the result of extracting and consuming uranium, a non-renewable resource. The availability of high-grade uranium ore will deplete over time meaning the fuel will become more environmentally and economically expensive to extract....

 motivated initial interest in the thorium fuel cycle. It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material. However, for most countries, uranium was relatively abundant, and research in thorium fuel cycles waned. A notable exception was India's three stage nuclear power programme
India's three stage nuclear power programme
India's three stage nuclear power programme was formulated to use the available uranium and thorium reserves found in the monazite sands of coastal regions of South India. Importance of nuclear energy was recognised as soon as India became independent...

. In the twenty-first century thorium's potential for improving proliferation resistance and waste characteristics led to renewed interest in the mineral.

At Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...

 in the 1960s, the Molten-Salt Reactor Experiment
Molten-Salt Reactor Experiment
The Molten-Salt Reactor Experiment was an experimental molten-salt reactor at the Oak Ridge National Laboratory researching this technology through the 1960s; constructed by 1964, it went critical in 1965 and was operated until 1969....

 used {{SimpleNuclide2|Uranium|233}} as the fissile fuel as an experiment to demonstrate a part of the Molten Salt Breeder Reactor that was designed to operate on the thorium fuel cycle. Molten Salt Reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

 (MSR) experiments assessed thorium's feasibility, using thorium(IV) fluoride
Thorium(IV) fluoride
Thorium fluoride is an inorganic chemical compound. It is a white, hygroscopic powder which can be produced by reacting thorium with fluorine gas. At temperatures above 500 °C, it reacts with atmospheric moisture to produce ThOF2.-Uses:...

 dissolved in a molten salt
Molten salt
Molten salt refers to a salt that is in the liquid phase that is normally a solid at standard temperature and pressure . A salt which is normally liquid at STP is usually called a room temperature ionic liquid, although technically molten salts are a class of ionic liquids.-Uses:Molten salts have...

 fluid which eliminated the need to fabricate fuel elements. The MSR program was defunded in 1976.

In 2006, Carlo Rubbia
Carlo Rubbia
Carlo Rubbia Knight Grand Cross is an Italian particle physicist and inventor who shared the Nobel Prize in Physics in 1984 with Simon van der Meer for work leading to the discovery of the W and Z particles at CERN.-Biography:...

 proposed the concept of an energy amplifier
Energy amplifier
In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation...

 or "accelerator driven system" (ADS), which he saw as a novel and safe way to produce nuclear energy that exploited existing accelerator technologies. Rubbia's proposal offered the potential to incinerate high-activity nuclear waste and produce energy from natural thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 and depleted uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

.

Nuclear reactions with thorium


{{actinidesvsfissionproducts}}
In the thorium cycle, fuel is formed when {{SimpleNuclide2|Thorium|232}} captures
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...

 a neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

 (whether in a fast reactor or thermal reactor
Thermal reactor
A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. Most power reactors are of this type. These type of reactors use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons...

) to become {{SimpleNuclide2|Thorium|233|link=yes}}. This normally emits an electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 and an anti-neutrino ({{SubatomicParticle|Antineutrino}}) by {{SubatomicParticle
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...

 to become {{SimpleNuclide2|Protactinium|233|link=yes}}. This then emits another electron and anti-neutrino by a second {{SubatomicParticle|beta-}} decay to become {{SimpleNuclide2|Uranium|233}}, the fuel:

Fission product wastes


Nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 produces radioactive fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

s which can have half-lives from days to greater than 200,000 years. According to some toxicity studies, the thorium cycle can fully recycle actinide wastes and only emit fission product wastes, and after a few hundred years, the waste from a thorium reactor can be less toxic than the uranium ore that would have been used to produce low enriched uranium fuel for a light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

 of the same power.
Other studies assume some actinide losses and find that actinide wastes dominate thorium cycle waste radioactivity at some future periods.

Actinide wastes


In a reactor, when a neutron hits a fissile atom (such as certain isotopes of uranium), it either splits the nucleus or is captured and transmutes the atom. In the case of {{SimpleNuclide2|Uranium|233}}, the transmutations tend to produce useful nuclear fuels rather than transuranic wastes. When {{SimpleNuclide2|Uranium|233}} absorbs a neutron, it either fissions or becomes {{SimpleNuclide2|Uranium|234|link=yes}}. The chance of fissioning on absorption of a thermal neutron is about 92%; the capture-to-fission ratio of {{SimpleNuclide2|Uranium|233}}, therefore, is about 1:10 — which is better than the corresponding capture vs. fission ratios of {{SimpleNuclide2|Uranium|235|link=yes}} (about 1:6), or {{SimpleNuclide2|Plutonium|239}} (about 1:2), or {{SimpleNuclide2|Plutonium|241|link=yes}} (about 1:4).
The result is shorter-lived transuranic waste than in a reactor using the uranium-plutonium fuel cycle.
{{Thorium Cycle Transmutation}}
{{SimpleNuclide2|Uranium|234}}, like most actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

s with an even number of neutrons, is not fissile, but neutron capture produces fissile {{SimpleNuclide2|Uranium|235}}. If the fissile isotope fails to fission on neutron capture, it produces {{SimpleNuclide2|Uranium|236|link=yes}}, {{SimpleNuclide2|Neptunium|237|link=yes}}, {{SimpleNuclide2|Plutonium|238|link=yes}}, and eventually fissile {{SimpleNuclide2|Plutonium|239}} and heavier isotopes of plutonium
Isotopes of plutonium
Plutonium is an artificial element, except for trace quantities of primordial 244Pu, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940....

.
The {{SimpleNuclide2|Neptunium|237}} can be removed and stored as waste or retained and transmuted to plutonium, where more of it fissions, while the remainder becomes {{SimpleNuclide2|Plutonium|242|link=yes}}, then americium
Americium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...

 and curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...

, which in turn can be removed as waste or returned to reactors for further transmutation and fission.

However, the {{SimpleNuclide2|Protactinium|231|link=yes}} (with a half-life of {{val|3.27|e=4|u=years}}) formed via (n,2n) reactions with {{SimpleNuclide2|Thorium|232}} (yielding {{SimpleNuclide2|Thorium|231}} that decays to {{SimpleNuclide2|Protactinium|231|link=yes}}), while not a transuranic waste, is a major contributor to the long term radiotoxicity of spent nuclear fuel.

Uranium-232 contamination


Uranium-232 is also formed in this process, via (n,2n) reactions between fast neutrons and {{SimpleNuclide2|Uranium|233}}, {{SimpleNuclide2|Protactinium|233|link=yes}}, and {{SimpleNuclide2|Thorium|232}}:



Uranium-232 has a relatively short half-life ({{val|68.9|u=years}}), and some decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...

s emit high energy gamma radiation, such as {{SimpleNuclide2|Radon|224|link=yes}}, {{SimpleNuclide2|Bismuth|212|link=yes}} and particularly {{SimpleNuclide2|Thallium|208|link=yes}}. The full decay chain, along with half-lives and relevant gamma energies, is:
{{SimpleNuclide2|Uranium|232|link=yes}} decays to {{SimpleNuclide2|Thorium|228|link=yes}} where it joins decay chain of {{SimpleNuclide2








Thorium-cycle fuels produce hard gamma emissions, which damage electronics, limiting their use in military bomb triggers. {{SimpleNuclide2|Uranium|232}} cannot be chemically separated from {{SimpleNuclide2|Uranium|233}} from used nuclear fuel; however, chemical separation of thorium from uranium removes the decay product {{SimpleNuclide2|Thorium|228}} and the radiation from the rest of the decay chain, which gradually build up as {{SimpleNuclide2|Thorium|228}} reaccumulates. The hard gamma emissions also create a radiological hazard which requires remote handling during reprocessing.

Advantages as a nuclear fuel


Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, although present knowledge of reserves is limited. Current demand for thorium has been satisfied as a by-product of rare-earth
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

 extraction from monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...

 sands. Also, unlike uranium, mined thorium consists of a single isotope ({{SimpleNuclide2|Thorium|232}}). Consequently, it is useful in thermal reactors without the need for isotope separation.

Thorium-based fuels exhibit several attractive properties relative to uranium-based fuels. The thermal neutron absorption cross section
Nuclear cross section
The nuclear cross section of a nucleus is used to characterize the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a larger probability of interaction...

  and resonance integral (average of neutron cross sections over intermediate neutron energies) for {{SimpleNuclide2|Thorium|232}} are about three times and one third of the respective values for {{SimpleNuclide2|Uranium|238}}; consequently, fertile conversion of thorium is more efficient in a thermal reactor. Also, although the thermal neutron fission cross section of the resulting {{SimpleNuclide2|Uranium|233}} is comparable to {{SimpleNuclide2|Uranium|235}} and {{SimpleNuclide2|Plutonium|239}}, it has a much lower capture cross section than the latter two fissile isotopes, providing fewer non-fissile neutron absorptions and improved neutron economy
Neutron economy
Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production....

. Finally, the ratio of neutrons released per neutron absorbed (η) in {{SimpleNuclide2|Uranium|233}} is greater than two over a wide range of energies, including the thermal spectrum; as a result, thorium-based fuels can be the basis for a thermal breeder reactor.

Thorium-based fuels also display favorable physical and chemical properties which improve reactor and repository
Deep geological repository
A deep geological repository is a nuclear waste repository excavated deep within a stable geologic environment...

 performance. Compared to the predominant reactor fuel, uranium dioxide
Uranium dioxide
Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...

 , thorium dioxide
Thorium dioxide
Thorium dioxide , also called thorium oxide is a white, crystalline powder. It was formerly known as thoria or thorina. It is produced mainly as a by-product of lanthanide and uranium production.[1]...

  has a higher melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

, higher thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

, and lower coefficient of thermal expansion. Thorium dioxide also exhibits greater chemical stability
Chemical stability
Chemical stability when used in the technical sense in chemistry, means thermodynamic stability of a chemical system.Thermodynamic stability occurs when a system is in its lowest energy state, or chemical equilibrium with its environment. This may be a dynamic equilibrium, where individual atoms...

 and, unlike uranium dioxide, does not further oxidize.

Because the {{SimpleNuclide2|Uranium|233}} produced in thorium fuels is inevitably contaminated with {{SimpleNuclide2|Uranium|232}}, thorium-based used nuclear fuel possesses inherent proliferation
Nuclear proliferation
Nuclear proliferation is a term now used to describe the spread of nuclear weapons, fissile material, and weapons-applicable nuclear technology and information, to nations which are not recognized as "Nuclear Weapon States" by the Treaty on the Nonproliferation of Nuclear Weapons, also known as the...

 resistance. {{SimpleNuclide2|Uranium|232}} can not be chemically separated
Separation process
In chemistry and chemical engineering, a separation process, or simply a separation, is any mass transfer process used to convert a mixture of substances into two or more distinct product mixtures, at least one of which is enriched in one or more of the mixture's constituents. In some cases, a...

 from {{SimpleNuclide2|Uranium|233}} and has several decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...

s which emit high energy gamma radiation. These high energy photons are a radiological hazard
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

 that necessitate the use of remote handling
Remote handling
Remote handling is the synergistic combination of technology and engineering management systems to enable operators to safely, reliably and repeatedly perform manipulation of items without being in personal contact with those items.-Overview:...

 of separated uranium and aid in the passive detection
Nuclear detection
The threat of radiological attacks has led several organizations to develop specially designed nuclear detection systems. These systems differ in design and abilities.* * * Center for Neutron Research...

 of such materials.

The long term (on the order of roughly {{val|e=3}} to {{val|e=6|u=years}}) radiological hazard of conventional uranium-based used nuclear fuel is dominated by plutonium and other minor actinides, after which long-lived fission products become significant contributors again. A single neutron capture in {{SimpleNuclide2|Uranium|238}} is sufficient to produce transuranic elements, whereas six captures are generally necessary to do so from {{SimpleNuclide2|Thorium|232}}. 98–99% of thorium-cycle fuel nuclei would fission at either {{SimpleNuclide2|Uranium|233}} or {{SimpleNuclide2|Uranium|235}}, so fewer long-lived transuranics are produced. Because of this, thorium is a potentially attractive alternative to uranium in mixed oxide (MOX) fuels
MOX fuel
Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material. MOX fuel contains plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the...

 to minimize the generation of transuranics and maximize the destruction of plutonium.

Disadvantages as nuclear fuel


There are several challenges to the application of thorium as a nuclear fuel, particularly for solid fuel reactors.

Unlike uranium, natural thorium contains no fissile isotopes; fissile material, generally {{SimpleNuclide2|Uranium|233}}, {{SimpleNuclide2|Uranium|235}}, or plutonium, must be added to achieve criticality
Nuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...

. This, along with the high sintering
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...

 temperature necessary to make thorium-dioxide fuel, complicates fuel fabrication. Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...

 experimented with thorium tetrafluoride as fuel in a molten salt reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

 from 1964–1969, which was far easier to both process and separate from contaminants that slow or stop the chain reaction.

In an open fuel cycle (i.e. utilizing {{SimpleNuclide2|Uranium|233}} in situ), higher burnup
Burnup
In nuclear power technology, burnup is a measure of how much energy is extracted from a primary nuclear fuel source...

 is necessary to achieve a favorable neutron economy
Neutron economy
Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production....

. Although thorium dioxide performed well at burnups of 170,000 MWd/t and 150,000 MWd/t at Fort St. Vrain Generating Station
Fort St. Vrain Generating Station
Fort Saint Vrain Generating Station is a natural gas powered electricity generating facility located near the town of Platteville in northern Colorado in the United States. It currently has a capacity of just under 1000MW and is owned and operated by Xcel Energy, the successor to the plant's...

 and AVR
AVR reactor
The AVR reactor was a prototype pebble bed reactor at Jülich Research Centre in West Germany. Construction began in 1960, first grid connection was in 1967 and operation ceased in 1988....

 respectively, challenges complicate achieving this in light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

s (LWR), which compose the vast majority of existing power reactors.

Another challenge associated with a once-through thorium fuel cycle is the comparatively long interval over which {{SimpleNuclide2|Thorium|232}} breeds to {{SimpleNuclide2|Uranium|233}}. The half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of {{SimpleNuclide2|Protactinium|233}} is about 27 days, which is an order of magnitude longer than the half-life of {{SimpleNuclide2|Neptunium|239|link=yes}}. As a result, substantial {{SimpleNuclide2|Protactinium|233}} develops in thorium-based fuels. {{SimpleNuclide2|Protactinium|233}} is a significant neutron absorber, and although it eventually breeds
Breeder reactor
A breeder reactor is a nuclear reactor capable of generating more fissile material than it consumes because its neutron economy is high enough to breed fissile from fertile material like uranium-238 or thorium-232. Breeders were at first considered superior because of their superior fuel economy...

 into fissile {{SimpleNuclide2|Uranium|235}}, this requires two more neutron absorptions, which degrades neutron economy
Neutron economy
Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production....

 and increases the likelihood of transuranic production.

Alternatively, if solid thorium is used in a closed fuel cycle in which {{SimpleNuclide2|Uranium|233}} is recycled
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...

, remote handling
Remote handling
Remote handling is the synergistic combination of technology and engineering management systems to enable operators to safely, reliably and repeatedly perform manipulation of items without being in personal contact with those items.-Overview:...

 is necessary for fuel fabrication because of the high radiation levels resulting from the decay products of {{SimpleNuclide2|Uranium|232}}. This is also true of recycled thorium because of the presence of {{SimpleNuclide2|Thorium|228}}, which is part of the {{SimpleNuclide2|Uranium|232}} decay sequence. Further, unlike proven uranium fuel recycling technology (e.g. PUREX
PUREX
PUREX is an acronym standing for Plutonium - URanium EXtraction — de facto standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium from used nuclear fuel. It is based on liquid-liquid extraction ion-exchange.The PUREX process was invented by Herbert H. Anderson and...

), recycling technology for thorium (e.g. THOREX) is only under development.

Although the presence of {{SimpleNuclide2|Uranium|232}} complicates matters, {{SimpleNuclide2|Uranium|233}} has occasionally been used to produce fission weapons
Nuclear weapon design
Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three basic design types...

. The United States first tested {{SimpleNuclide2|Uranium|233}} as part of a bomb core in Operation Teapot
Operation Teapot
Operation Teapot was a series of fourteen nuclear test explosions conducted at the Nevada Test Site in the first half of 1955.During shot "Wasp", ground forces took part in Exercise Desert Rock VI which included an armored task force "Razor" moving to within 900 meters of ground zero, under the...

 in 1955. However, unlike plutonium, {{SimpleNuclide2|Uranium|233}} can be easily denatured
Denaturation (fissile materials)
Denaturation of fissile materials suitable for nuclear weapons is the process of transforming them into a form that is not suitable for weapons use and can not easily be reversely transformed...

 by mixing it with natural or depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

. Another option is to mix thorium fuels with small amounts of natural or depleted uranium during fabrication to ensure that {{SimpleNuclide2|Uranium|233}} concentrations at cycle end are acceptably low.

Though thorium-based fuels produce far less long-lived transuranics than uranium-based fuels,
some long-lived actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

 products constitute a long term radiological impact, especially {{SimpleNuclide2|Protactinium|231}}.

Advocates for liquid core and molten salt reactors claim that these technologies negate thorium's disadvantages. Since only one liquid core reactor using thorium has been built, it is hard to validate the exact benefits.{{Citation needed|date=April 2010}} The lack of relevance to the nuclear weapon industry can be seen as a disadvantage to the development of Thorium usage in power generation,{{Dubious|date=April 2010}} but a worldwide resurgence of nuclear power use could provide enough incentives and funding to negate this disadvantage.

Reactors


Thorium fuels have fueled several different reactor types, including light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

s, heavy water reactor
Heavy water reactor
A pressurised heavy water reactor is a nuclear power reactor, commonly using unenriched natural uranium as its fuel, that uses heavy water as its coolant and moderator. The heavy water coolant is kept under pressure in order to raise its boiling point, allowing it to be heated to higher...

s, high temperature gas reactors, sodium-cooled fast reactor
Sodium-cooled fast reactor
The sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced fast neutron reactor.It builds on two closely related existing projects, the LMFBR and the Integral Fast Reactor, with the objective of producing a fast-spectrum, sodium-cooled reactor.The reactors are...

s, and molten salt reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

s.

List of thorium-fueled reactors


From IAEA TECDOC-1450 "Thorium Fuel Cycle - Potential Benefits and Challenges", Table 1: Thorium utilization in different experimental and power reactors.
Name Country Type Power Fuel Operation period
AVR
AVR reactor
The AVR reactor was a prototype pebble bed reactor at Jülich Research Centre in West Germany. Construction began in 1960, first grid connection was in 1967 and operation ceased in 1988....

 
Germany HTGR, Experimental (Pebble bed reactor
Pebble bed reactor
The pebble bed reactor is a graphite-moderated, gas-cooled, nuclear reactor. It is a type of very high temperature reactor , one of the six classes of nuclear reactors in the Generation IV initiative...

)
015000 15 MW(e) Th+{{SimpleNuclide2|Uranium|235}} Driver Fuel, Coated fuel particles, Oxide & dicarbides 1967–1988
THTR-300
THTR-300
The THTR-300 was a thorium high-temperature nuclear reactor rated at 300 MW electric . The German state of North Rhine Westphalia, in the Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk GmbH financed the THTR-300’s construction. Operations started on the plant in Hamm-Uentrop,...

 
Germany HTGR, Power (Pebble Type
Pebble bed reactor
The pebble bed reactor is a graphite-moderated, gas-cooled, nuclear reactor. It is a type of very high temperature reactor , one of the six classes of nuclear reactors in the Generation IV initiative...

)
300000 300 MW(e) Th+{{SimpleNuclide2|Uranium|235}}, Driver Fuel, Coated fuel particles, Oxide & dicarbides 1985–1989
Lingen
Lingen Nuclear Power Plant
Lingen Nuclear Power Plant is an inactive nuclear power plant in Germany, close to Emsland Nuclear Power Plant.It once belonged to VEW, and now belongs to RWE Power AG....

 
Germany BWR Irradiation-testing 060000 60 MW(e) Test Fuel (Th,Pu)O2 pellets 1968; terminated in 1973
Dragon
Dragon reactor
Dragon was a high temperature gas cooled reactor at Winfrith in England operated by UKAEA. Its purpose was to test fuel and materials for the European high temperature reactor programme, and was built and managed as an OECD/NEA international project...

 (OECD-Euratom)
UK (also Sweden, Norway & Switzerland) HTGR, Experimental (Pin-in-Block Design) 020000 20 MWt Th+{{SimpleNuclide2|Uranium|235}} Driver Fuel, Coated fuel particles, Oxide & Dicarbides 1966–1973
Peach Bottom
Peach Bottom Nuclear Generating Station
Peach Bottom Atomic Power Station, a nuclear power plant, is located southeast of Harrisburg in Peach Bottom Township, York County, Pennsylvania, on the Susquehanna River on the Maryland border....

 
USA HTGR, Experimental (Prismatic Block) 040000 40 MW(e) Th+{{SimpleNuclide2|Uranium|235}} Driver Fuel, Coated fuel particles, Oxide & dicarbides 1966–1972
Fort St Vrain
Fort St. Vrain Generating Station
Fort Saint Vrain Generating Station is a natural gas powered electricity generating facility located near the town of Platteville in northern Colorado in the United States. It currently has a capacity of just under 1000MW and is owned and operated by Xcel Energy, the successor to the plant's...

 
USA HTGR, Power (Prismatic Block) 330000 330 MW(e) Th+{{SimpleNuclide2|Uranium|235}} Driver Fuel, Coated fuel particles, Dicarbide 1976–1989
MSRE ORNL  USA MSBR
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

 
007500 7.5 MWt {{SimpleNuclide2|Uranium|233}} Molten Fluorides 1964–1969
BORAX-IV & Elk River Station
Elk River Station
Elk River Station is an energy-from-waste plant operating in Elk River, Minnesota that generates 35 to 42 megawatts of electrical power.The site was originally built as a coal and oil-fired facility in 1950, then was converted to a nuclear power plant in 1963...

 
USA BWR (Pin Assemblies) 002400 2.4 MW(e); 24 MW(e) Th+235U Driver Fuel Oxide Pellets 1963 - 1968
Shippingport
Shippingport Reactor
The Shippingport Atomic Power Station, "the world’s first full-scale atomic electric power plant devoted exclusively to peacetime uses," was located near the present-day Beaver Valley Nuclear Generating Station on the Ohio River in Beaver...

 
USA LWBR PWR, (Pin Assemblies) 100000 100 MW(e) Th+{{SimpleNuclide2|Uranium|233}} Driver Fuel, Oxide Pellets 1977–1982
Indian Point 1  USA LWBR PWR, (Pin Assemblies) 285000 285 MW(e) Th+{{SimpleNuclide2|Uranium|233}} Driver Fuel, Oxide Pellets 1962–1980
SUSPOP/KSTR KEMA
KEMA
Established in 1927, KEMA is an independent knowledge leader and a global provider of high-quality services to the energy value chain, including business & technical consultancy, operational support, measurements & inspection, and testing & certification...

 
Netherlands Aqueous Homogenous Suspension (Pin Assemblies) 001000 1 MWt Th+HEU, Oxide Pellets 1974–1977
NRX
NRX
NRX was a heavy water moderated, light water cooled, nuclear research reactor at the Canadian Chalk River Laboratories, which came into operation in 1947 at a design power rating of 10 MW , increasing to 42 MW by 1954...

 & NRU
National Research Universal Reactor
The National Research Universal reactor, located in Chalk River, Ontario, is one of Canada’s national science facilities. It is a multipurpose science facility that serves three main roles....

 
Canada MTR (Pin Assemblies) 020000 20MW; 200MW (see) Th+{{SimpleNuclide2|Uranium|235}}, Test Fuel 1947 (NRX) + 1957 (NRU); Irradiation–testing of few fuel elements
CIRUS; DHRUVA
Dhruva reactor
The Dhruva reactor is India's largest nuclear research reactor. Located in the Mumbai suburb of Trombay at the Bhabha Atomic Research Centre , it is India's primary generator of weapons-grade plutonium-bearing spent fuel for its nuclear weapons program. Originally named the R-5, this pool-type...

; & KAMINI
KAMINI
KAMINI is a research reactor at Indira Gandhi Center for Atomic Research in Kalpakkam, India. Its first criticality was on October 29, 1996...

 
India MTR Thermal 040000 40 MWt; 100 MWt; 30 kWt (low power, research) Al+{{SimpleNuclide2|Uranium|233}} Driver Fuel, ‘J’ rod of Th & ThO2, ‘J’ rod of ThO2 1960-2010 (CIRUS); others in operation
KAPS 1 &2
Kakrapar Atomic Power Station
The Kakrapar Atomic Power Station is a nuclear power station in India, which lies in the proximity of the city of Surat in the state of Gujarat. It consists of two 220 MW pressurized water reactors with heavy water as moderator . KAPS-1 went critical on 3 September 1992 and began...

; KGS 1 & 2; RAPS 2, 3 & 4
Rajastan Atomic Power Project
The Rajasthan Atomic Power Station in India is located about from Kota by way of the Chambal River, approximately above the dam that holds the Rana Pratap Sagar lake. The plant lies in the Federal State Rajasthan, district Chittorgarh. The next locale is Tamlao, Rawatbhata is approx...

 
India PHWR, (Pin Assemblies) 220000 220 MW(e) ThO2 Pellets (For neutron flux flattening of initial core after start-up) 1980 (RAPS 2) +; continuing in all new PHWRs
FBTR
FBTR
The Fast Breeder Test Reactor is a breeder reactor located at Kalpakkam, India. The Indira Gandhi Center for Atomic Research and Bhabha Atomic Research Center jointly designed, constructed, and operate the reactor.-History:...

 
India LMFBR, (Pin Assemblies) 040000 40 MWt ThO2 blanket 1985; in operation

See also

  • Thorium
    Thorium
    Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

  • Nuclear fuel cycle
    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 which the fuel is used during reactor operation, and steps in...

  • Nuclear power
    Nuclear power
    Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

  • Nuclear fission
    Nuclear fission
    In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

  • Radioactive waste
    Radioactive waste
    Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...

  • World energy resources and consumption
    World energy resources and consumption
    ]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...

  • Uranium depletion
    Uranium depletion
    Uranium depletion is the result of extracting and consuming uranium, a non-renewable resource. The availability of high-grade uranium ore will deplete over time meaning the fuel will become more environmentally and economically expensive to extract....

  • Peak uranium
    Peak uranium
    Peak uranium is the point in time that the maximum global uranium production rate is reached. After that peak, the rate of production enters a terminal decline. While uranium is used in nuclear weapons, its primary use is for energy generation via nuclear fission of uranium-235 isotope in a nuclear...

  • Fuji MSR
  • Energy amplifier
    Energy amplifier
    In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation...

  • Alvin Radkowsky
    Alvin Radkowsky
    Alvin Radkowsky was a nuclear physicist and chief scientist at U.S. Navy nuclear propulsion division. His work in the 1950s led to major advances in nuclear-ship technology and civilian use of nuclear power.-Biography:...

  • Liquid fluoride thorium reactor
    Liquid fluoride thorium reactor
    The liquid fluoride thorium reactor is a thermal breeder reactor which uses the thorium fuel cycle in a fluoride-based molten salt fuel to achieve high operating temperatures at atmospheric pressure....

  • Weinberg Foundation
  • Flibe Energy
    Flibe Energy
    Flibe Energy is a company that intends to design, construct and operate small modular reactors based on liquid fluoride thorium reactor technology.-Corporation:...


External links


Recent interest in the thorium fuel cycle