Generation IV (Gen IV) reactors are

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

design technologies that are envisioned as successors of generation III reactors. The Generation IV International Forum (GIF) – an international organization that coordinates the development of generation IV reactors – specifically selected six reactor technologies as candidates for generation IV reactors. The designs target improved safety, sustainability, efficiency, and cost. The

World Nuclear Association World Nuclear Association is the international organization that promotes nuclear power and supports the companies that comprise the global nuclear industry. Its members come from all parts of the nuclear fuel cycle, including uranium mining ...

in 2015 suggested that some might enter commercial operation before 2030. No precise definition of a Generation IV reactor exists. The term refers to nuclear reactor technologies under development as of approximately 2000, and whose designs were intended to represent 'the future shape of nuclear energy', at least at that time. The six designs selected were: the gas-cooled fast reactor (GFR), the lead-cooled fast reactor (LFR), the molten salt reactor (MSR), the sodium-cooled fast reactor (SFR), the supercritical-water-cooled reactor (SCWR) and the very high-temperature reactor (VHTR). The sodium fast reactor has received the greatest share of funding that supports demonstration facilities. Moir and Teller consider the molten-salt reactor, a less developed technology, as potentially having the greatest inherent safety of the six models. The very-high-temperature reactor designs operate at much higher temperatures than prior generations. This allows for high temperature electrolysis or for sulfur–iodine cycle for the efficient production of hydrogen and the synthesis of

carbon-neutral fuel Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using Carbon dioxide, carbon dioxide (CO2) as a Raw material, feedstock. Proposed carbon-neutral fu ...

s. The majority of reactors in operation around the world are considered second generation and third generation reactor systems, as the majority of the first generation systems have been retired. China was the first country to operate a demonstration generation-IV reactor, the HTR-PM in Shidaowan,

Shandong Shandong is a coastal Provinces of China, province in East China. Shandong has played a major role in Chinese history since the beginning of Chinese civilization along the lower reaches of the Yellow River. It has served as a pivotal cultural ...

, which is a pebble-bed type high-temperature gas-cooled reactor. It was connected to the grid in December 2023, making it the world's first Gen IV reactor to enter commercial operation. In 2024, it was reported that China would also build the world’s first thorium molten salt nuclear power station, scheduled to be operational by 2029.

Generation IV International Forum

The Generation IV International Forum (GIF) is an international organization with its stated goal being ''"the development of concepts for one or more Generation IV systems that can be licensed, constructed, and operated in a manner that will provide a competitively priced and reliable supply of energy ... while satisfactorily addressing nuclear safety, waste, proliferation and public perception concerns."''''FAQ 2: When will Gen IV reactors be built?''
GEN IV International Forum. Published 1 October 2013. Accessed Nov. 2021) It coordinates the development of GEN IV technologies. It has been instrumental in coordinating research into the six types of Generation IV reactors, and in defining the scope and meaning of the term itself. As of 2021, active members include: Australia, Canada, China, the European Atomic Energy Community (Euratom), France, Japan, Russia, South Africa, South Korea, Switzerland, the United Kingdom and the United States. Non-active members include Argentina and Brazil. The Forum was initiated in January 2000 by the

Office of Nuclear Energy The Office of Nuclear Energy (NE) is an agency of the United States Department of Energy which promotes nuclear power as a resource capable of meeting the energy, environmental, and national security needs of the United States by resolving techni ...

of the

U.S. 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 energy production, the research and development of nuclear power, the military's nuclear we ...

's (DOE)''Origins of the GIF.''
GEN IV International Forum Nov 2021) ''"as a co-operative international endeavour seeking to develop the research necessary to test the feasibility and performance of fourth generation nuclear systems, and to make them available for industrial deployment by 2030."'' ''Welcome to Generation IV International forum.''
GIF (accessed Feb 2023) In November 2013, a brief overview of the reactor designs and activities by each forum member was made available. An update of the technology roadmap which details R&D objectives for the next decade was published in January 2014. In May 2019,

Terrestrial Energy Terrestrial Energy is a nuclear technology company working on Generation IV reactor, Generation IV nuclear technology. It expects its nuclear plant to produce cost-competitive, high-temperature thermal energy with zero emissions. The company is d ...

, the Canadian developer of a molten salt reactor, became the first private company to join GIF. At the forum's October 2021 meeting, the members agreed to create a task force on non-electric applications of nuclear heat, including district and industrial heat applications, desalination and large-scale hydrogen production.

Timelines

The GIF Forum has introduced development timelines for each of the six systems. Research and development is divided into three phases: * Viability: test basic concepts under relevant conditions; identify and resolve all "potential technical show-stoppers"; * Performance: verify and optimise "engineering-scale processes, phenomena and materials capabilities" under prototypical conditions; * Demonstration: complete and license the detailed design and carry out construction and operation of prototype or demonstration systems. In 2000, GIF stated, "After the performance phase is complete for each system, at least six years and several US$ billion will be required for detailed design and construction of a demonstration system."''A Technology Roadmap for Generation IV Nuclear Energy Systems''
p. 79-82 (4.5 MB). U.S. DOE Nuclear Energy Research Advisory Committee and the GIF, Dec 2002 In the Roadmap update of 2013, the performance and demonstration phases were considerably shifted to later dates, while no targets for the commercialisation phases are set. According to the GIF in 2013, "It will take at least two or three decades before the deployment of commercial Gen IV systems."

Reactor types

Many reactor types were considered initially; the list was then refined to focus on the most promising technologies.''Generation IV Nuclear Reactors''
World Nuclear Association, update Dec 2020 Three systems are nominally

thermal reactor A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and stru ...

s and three are

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, on average), as opposed to slow t ...

s. The ''very high temperature reactor'' (VHTR) potentially can provide high quality process heat. Fast reactors offer the possibility of burning

actinides The actinide () or actinoid () series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. Number 103, lawrencium, is also generally included despite being part ...

to further reduce waste and can breed more fuel than they consume. These systems offer significant advances in sustainability, safety and reliability, economics, proliferation resistance, and physical protection.

Thermal reactors

is a

that uses slow or

thermal neutrons The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...

. A

neutron moderator In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely ...

is used to slow the

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

s emitted by fission to make them more likely to be captured by the fuel.

Very-high-temperature reactor (VHTR)

The very-high-temperature reactor (VHTR) uses a graphite-moderated core with a once-through uranium fuel cycle, using helium or molten salt. This reactor design envisions an outlet temperature of 1,000 °C. The reactor core can be either a prismatic-block or a

pebble bed reactor The pebble-bed reactor (PBR) is a design for a graphite- moderated, gas-cooled nuclear reactor. It is a type of very-high-temperature reactor (VHTR), one of the six classes of nuclear reactors in the Generation IV initiative. The basic desig ...

design. The high temperatures enable applications such as process heat or

hydrogen production Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Article in press. Most hydrogen is ''gray hydrogen'' made through steam methane reforming. In this process, ...

via the thermochemical sulfur-iodine cycle process. In 2012, as part of its next generation nuclear plant competition,

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. Historically, the lab has been involved with nuclear research, although the labora ...

approved a design similar to

Areva Areva S.A. was a French multinational group specializing in nuclear power, active between 2001 and 2018. It was headquartered in Courbevoie, France. Before its 2016 corporate restructuring, Areva was majority-owned by the French state through t ...

's prismatic block Antares reactor to be deployed as a prototype by 2021. In January 2016,

X-energy X-energy is a private American nuclear reactor and fuel design engineering company. It is developing a Generation IV reactor, Generation IV high-temperature gas-cooled Pebble bed modular reactor, pebble-bed nuclear reactor design. It has receiv ...

was provided a five-year grant of up to $40 million by 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 energy production, the research and development of nuclear power, the military's nuclear w ...

to advance their reactor development. The Xe-100 is a PBMR that would generate 80

MWe The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor o ...

, or 320 MWe in a 'four-pack'. Since 2021, the Chinese government is operating a demonstration HTR-PM 200-MW high temperature

as a successor to its HTR-10.

Molten-salt reactor (MSR)

A molten salt reactor (MSR) is a type of reactor where the primary

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 corr ...

or the fuel itself is a molten salt mixture. It operates at high temperature and low pressure. Molten salt can be used for thermal, epithermal and fast reactors. Since 2005 the focus has been on fast spectrum MSRs (MSFR). Other designs include integral molten salt reactors (e.g. IMSR) and molten chloride salt fast reactors (MCSFR). Early thermal spectrum concepts and many current ones rely on

uranium tetrafluoride Uranium tetrafluoride is the inorganic compound with the formula UF4. It is a green solid with an insignificant vapor pressure and low solubility in water. Uranium in its tetravalent ( uranous) state is important in various technological process ...

(UF₄) or thorium tetrafluoride (ThF₄), dissolved in molten

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...

salt. The fluid reaches criticality by flowing into a core with a

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

moderator. The fuel may be dispersed in a graphite matrix. These designs are more accurately termed an epithermal reactor than a thermal reactor due to the higher average speed of the neutrons that cause the fission events. MCSFR does away with the graphite moderator. They achieve criticality using a sufficient volume of salt and fissile material. They can consume much more of the fuel and leave only short-lived waste. Most MSR designs are derived from the 1960s Molten-Salt Reactor Experiment (MSRE). Variants include the conceptual '' Dual fluid reactor'' that uses lead as a cooling medium with molten salt fuel, commonly a metal chloride, e.g.

plutonium(III) chloride Plutonium(III) chloride is a chemical compound with the formula PuCl3. This ionic plutonium salt can be prepared by reacting the metal with hydrochloric acid. Structure Plutonium atoms in crystalline PuCl3 are 9 coordinate, and the structure is ...

, to aid in greater closed-fuel cycle capabilities. Other notable approaches include the stable salt reactor (SSR) concept, which encases the molten salt in the well-established

fuel rod Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is usually based o ...

s of conventional reactors. This latter design was found to be the most competitive by consultancy firm Energy Process Development in 2015. Another design under development is TerraPower's molten chloride fast reactor. This concept mixes the liquid natural uranium and molten chloride coolant in the reactor core, reaching very high temperatures at atmospheric pressure. In 2025, the Molten Chloride Reactor Experiment (MCRE), a joint project between Idaho National Labs (INL),

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 located in Birmingham, Alabama. As of 2021 it is the second largest ut ...

and TerraPower, achieved a major milestone, when a prototype furnace created a fuel based on denatured uranium at the rate of per batch. It further completed a Molten Salt Flow Loop Test Bed, using stainless steel containing a slurry of lithium chloride-potassium chloride salts. Slurry properties such as temperature can be adjusted while the salts circulate. Five sensors analyze factors such as

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...

, fluid density, corrosion, and heat transfer rates. Another notable MSR feature is the possibility of a thermal spectrum nuclear waste-burner. Conventionally only fast spectrum reactors have been considered viable for utilization or reduction of the

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 and ...

. Thermal waste-burning was achieved by replacing a fraction of the

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

in the spent nuclear fuel with

thorium Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and ha ...

. The net production rate of

transuranic element The transuranium (or transuranic) elements are the chemical elements with atomic number greater than 92, which is the atomic number of uranium. All of them are radioactively unstable and decay into other elements. Except for neptunium and pluton ...

s (e.g.

plutonium Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...

and

americium Americium is a synthetic element, synthetic chemical element; it has Chemical symbol, symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element e ...

) is below the consumption rate, thus reducing the nuclear storage problem, without the

nuclear proliferation Nuclear proliferation is the spread of nuclear weapons to additional countries, particularly those not recognized as List of states with nuclear weapons, nuclear-weapon states by the Treaty on the Non-Proliferation of Nuclear Weapons, commonl ...

concerns and other technical issues associated with a

Supercritical-water-cooled reactor (SCWR)

The supercritical water reactor (SCWR) is a reduced moderation water reactor concept. Because the average speed of the fission-causing neutrons within the fuel is faster than

thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wit ...

s, it is more accurately termed an epithermal reactor than a thermal reactor. It uses

supercritical water Supercritical water oxidation (SCWO) is a process that occurs in water at temperatures and pressures above a mixture's thermodynamic critical point (thermodynamics), critical point. Under these conditions water becomes a fluid with unique proper ...

as the working fluid. SCWRs are basically

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 react ...

s (LWR) operating at higher pressure and temperatures with a direct, once-through heat exchange cycle. As commonly envisioned, it would operate on a direct cycle, much like a

boiling water reactor A boiling water reactor (BWR) is a type of nuclear reactor used for the generation of electrical power. It is the second most common type of electricity-generating nuclear reactor after the pressurized water reactor (PWR). BWR are thermal neutro ...

(BWR). Since it uses

(not to be confused with

critical mass In nuclear engineering, critical mass is the minimum mass of the fissile material needed for a sustained nuclear chain reaction in a particular setup. The critical mass of a fissionable material depends upon its nuclear properties (specific ...

) as the working fluid, it would have only one water phase. This makes the heat exchange method more similar to a pressurized water reactor ( PWR). It could operate at much higher temperatures than both current PWRs and BWRs. Supercritical water-cooled reactors (SCWRs) offer high

thermal efficiency In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For ...

(i.e., about 45% vs. about 33% efficiency for current LWRs) and considerable simplification. The mission of the SCWR is generation of low-cost

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

. It is built upon two proven technologies, LWRs, the most commonly deployed power generating reactors, and superheated

fossil fuel A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geolog ...

fired

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centra ...

s, also in wide use. 32 organizations in 13 countries are investigating the concept. SCWRs share the steam explosion and radioactive steam release hazards of BWRs and LWRs as well as the need for extremely expensive heavy duty pressure vessels, pipes, valves, and pumps. These shared problems are inherently more severe for SCWRs due to their higher temperatures. One SCWR design under development is the

VVER The water-water energetic reactor (WWER), or VVER (from ) is a series of pressurized water reactor designs originally developed in the Soviet Union, and now Russia, by OKB Gidropress. The idea of such a reactor was proposed at the Kurchatov Instit ...

-1700/393 (VVER-SCWR or VVER-SKD) – a Russian SCWR with double-inlet-core and a breeding ratio of 0.95.

Fast reactors

directly uses fission neutrons without moderation. Fast reactors can be configured to "burn", or fission, all

, and given enough time, therefore drastically reduce the actinides fraction in

produced by the present world fleet of thermal neutron

s, thus closing the fuel cycle. Alternatively, if configured differently, they can

breed A breed is a specific group of breedable domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist seve ...

more actinide fuel than they consume.

Gas-cooled fast reactor (GFR)

The gas-cooled fast reactor (GFR) features a fast-neutron spectrum and closed fuel cycle. The reactor is

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

-cooled. Its outlet temperature is 850 °C. It moves the very-high-temperature reactor (VHTR) to a more sustainable fuel cycle. It uses a direct

Brayton cycle The Brayton cycle, also known as the Joule cycle, is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. It is characterized by isentropic process, isentropic compre ...

gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...

for high thermal efficiency. Several fuel forms are under consideration: composite

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

fuel, advanced fuel particles, or ceramic-clad actinide compounds. Core configurations involve pin- or plate-based fuel assemblies or prismatic blocks. The European Sustainable Nuclear Industrial Initiative provided funding for three Generation IV reactor systems: * Allegro: a 100 MW_t gas-cooled fast reactor, planned for central or eastern Europe. The central European

Visegrád Group The Visegrád Group (also known as the Visegrád Four or the V4) is a cultural and political alliance of four Central European countries: the Czech Republic, Hungary, Poland, and Slovakia. The alliance aims to advance co-operation in military, e ...

are pursuing the technology. * GoFastR'':'' In 2013 German, British, and French institutes finished a 3-year collaboration study on the follow-on industrial scale design. They were funded by the EU's 7th FWP framework programme, with the goal of making a sustainable VHTR.

Sodium-cooled fast reactor (SFR)

Sodium-cooled fast reactors (SCFRs) have been operated in multiple countries since the 1980s. The two largest experimental sodium cooled fast reactors are in Russia, the BN-600 and the BN-800 (880 MWe gross). These NPPs are being used to provide operating experience and technological solutions that will be applied to the construction of the BN-1200 ( OKBM Afrikantov first Gen IV reactor). The largest ever operated was the French Superphenix reactor at over 1200 MW_e, successfully operating before decommissioning in 1996. In India, the Fast Breeder Test Reactor (FBTR) reached criticality in October 1985. In September 2002, fuel burn up efficiency in the FBTR for the first time reached the 100,000 megawatt-days per metric ton uranium (MWd/MTU) mark. This is considered an important milestone in Indian breeder reactor technology. Using that experience, the

Prototype Fast Breeder Reactor The Prototype Fast Breeder Reactor (PFBR) is a 500 MWe sodium-cooled, fast breeder reactor that is being constructed at the same site as the Madras Atomic Power Station in Kokkilamedu, near Kalpakkam, in Tamil Nadu state, India. The Indira ...

, a 500 MWe Sodium cooled fast reactor is being built at a cost of INR 5,677 crores (~US$900 million). After numerous delays, the government reported in March 2020 that the reactor might be operational in December 2021. The PFBR was to be followed by six more Commercial Fast Breeder Reactors (CFBRs) of 600 MW_e each. The Gen IV SFR is a project that builds on the oxide fueled

fast breeder reactor A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. These reactors can be Nuclear fuel, fueled with more-commonly available isotopes of uranium and Isotopes of thorium, thorium, such as uranium-238 and t ...

and the metal fueled

integral fast reactor The integral fast reactor (IFR), originally the advanced liquid-metal reactor (ALMR), is a design for a nuclear reactor using fast neutrons and no neutron moderator (a "fast" reactor). IFRs can breed more fuel and are distinguished by a nuclea ...

. Its goals are to increase the efficiency of uranium usage by

breeding Breeding is sexual reproduction that produces offspring, usually animals or plants. It can only occur between a male and a female animal or plant. Breeding may refer to: * Animal husbandry, through selected specimens such as dogs, horses, and rab ...

plutonium and eliminating

transuranic The transuranium (or transuranic) elements are the chemical elements with atomic number greater than 92, which is the atomic number of uranium. All of them are radioactively unstable and decay into other elements. Except for neptunium and pluton ...

isotopes. The reactor design uses an unmoderated core running on fast neutrons, designed to allow any transuranic isotope to be consumed (and in some cases used as fuel). SFR fuel expands when the reactor overheats, automatically slowing down the chain reaction, making it passively safe. One SFR reactor concept is cooled by liquid

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

and fueled by a metallic alloy of uranium and

, the nuclear waste of

s. The SFR fuel is contained in steel cladding. Liquid sodium fills the space between the clad elements that make up the fuel assembly. One of the design challenges is the risks of handling sodium, which reacts explosively if it comes into contact with water. The use of liquid metal instead of water as coolant allows the system to work at atmospheric pressure, reducing the risk of leakage. Ifr concept

The European Sustainable Nuclear Industrial Initiative funded three Generation IV reactor systems. Advanced Sodium Technical Reactor for Industrial Demonstration ( ASTRID) was a sodium-cooled fast reactor, that was cancelled in August 2019. Numerous progenitors of the Gen IV SFR exist. The 400 MW_t Fast Flux Test Facility operated for ten years at Hanford; the 20 MW_e EBR II operated for over thirty years at Idaho National Laboratory, but was shut down in 1994. GE Hitachi's

PRISM PRISM is a code name for a program under which the United States National Security Agency (NSA) collects internet communications from various U.S. internet companies. The program is also known by the SIGAD . PRISM collects stored internet ...

reactor is a modernized and commercial implementation of the Integral Fast Reactor (IFR), developed by

Argonne National Laboratory Argonne National Laboratory is a Federally funded research and development centers, federally funded research and development center in Lemont, Illinois, Lemont, Illinois, United States. Founded in 1946, the laboratory is owned by the United Sta ...

between 1984 and 1994. The primary purpose of PRISM is burning up

from other reactors, rather than breeding new fuel. The design reduces the half lives of the fissionable elements present in spent nuclear fuel while generating electricity largely as a byproduct.

Lead-cooled fast reactor (LFR)

The lead-cooled fast reactor (LFR) features a fast-neutron-spectrum

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

bismuth Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs nat ...

eutectic ( LBE) coolant with a closed fuel cycle. Proposals include a small 50 to 150 MW_e that features a long refueling interval, a modular system rated at 300 to 400 MW_e, and a large monolithic plant at 1,200 MW_e. The fuel is metal or nitride-based containing fertile uranium and

s. The reactor is cooled by natural

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

with a reactor outlet coolant temperature of 550-800 °C. The higher temperature enables the production of hydrogen by thermochemical processes. The European Sustainable Nuclear Industrial Initiative is funding a 100 MW_t LFR, an accelerator-driven sub-critical reactor called

MYRRHA Myrrha (; ), also known as Smyrna (), is the mother of Adonis in Greek mythology. She was transformed into a myrrh tree after having intercourse with her father, and gave birth to Adonis in tree form. Although the tale of Adonis has Semitic r ...

. It is to be built in

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

with construction expected by 2036. A reduced-power model called Guinevere was started up at Mol in March 2009 and became operational in 2012. Two other lead-cooled fast reactors under development are the SVBR-100, a modular 100 MW_e lead-bismuth cooled fast neutron reactor concept designed by OKB Gidropress in Russia and the BREST-OD-300 (Lead-cooled fast reactor) 300 MW_e, to be developed after the SVBR-100, it will dispense with the fertile blanket around the core and will supersede the sodium cooled BN-600 reactor design, to purportedly give enhanced proliferation resistance. Preparatory construction work commenced in May 2020.

Assessment

The GEN IV Forum reframes the reactor safety paradigm, from accepting that nuclear accidents can occur and should be mastered, to eliminating the physical possibility of an accident. Active and passive safety systems would be at least as effective as those of Generation III systems and render the most severe accidents physically impossible.''What is the risk of a severe accident resembling Chernobyl or Fukushima in a Gen IV design?''
GEN IV International Forum (accessed Nov. 2021).
"The aim of Generation IV systems is to maintain the high level of safety achieved by today's reactors, while shifting from the current principle of "mastering accidents" (i.e. accepting that accidents can occur, but taking care that the population is not affected) to the principle of "excluding accidents"." Relative to Gen II-III, advantages of Gen IV reactors include: * Nuclear waste that remains radioactive for a few centuries instead of millennia * 100–300x energy yield from the same amount of nuclear fuel * Broader range of fuels, including unencapsulated raw fuels (non-pebble MSR,

LFTR 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 c ...

). * Potential to burn existing nuclear waste and produce electricity: a closed fuel cycle. * Improved safety via features such as ambient pressure operation, automatic passive reactor shutdown, and alternate coolants. A specific risk of the SFR is related to using metallic sodium as a coolant. In case of a breach, sodium explosively reacts with water.

Argon Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

is used to prevent sodium oxidation. Argon can displace oxygen in the air and can pose hypoxia concerns for workers. This was a factor at the loop type Prototype Fast Breeder Reactor Monju at Tsuruga, Japan. Using lead or molten salt coolants mitigates this problem as they are less reactive and have a high freezing temperature and ambient pressure. Lead has much higher viscosity, much higher density, lower heat capacity, and more radioactive neutron activation products than sodium. Multiple proof of concept Gen IV designs have been built. For example, the reactors at Fort St. Vrain Generating Station and HTR-10 are similar to the proposed Gen IV VHTR designs, and the pool type EBR-II,

Phénix Phénix (French for phoenix) was a small-scale (gross 264/net 233 MWe) prototype fast breeder reactor, located at the Marcoule nuclear site, near Orange, France. It was a pool-type liquid-metal fast breeder reactor cooled with liquid sodium. ...

, BN-600 and BN-800 reactor are similar to the proposed pool type Gen IV SFR designs. Nuclear engineer

David Lochbaum David A. Lochbaum was the Director of the Nuclear Safety Project for the Union of Concerned Scientists (UCS). A nuclear engineer by training, he worked in nuclear power plants for nearly two decades. Lochbaum has written numerous articles and repo ...

cautions, "the problem with new reactors and accidents is twofold: scenarios arise that are impossible to plan for in simulations; and humans make mistakes". As one director of a U.S. research laboratory put it, "fabrication, construction, operation, and maintenance of new reactors will face a steep learning curve: advanced technologies will have a heightened risk of accidents and mistakes. The technology may be proven, but people are not".

Design projects

Emerging Structural Materials

Development of generation IV fission reactors has sparked significant interest in emerging radiation resistant materials. Structural materials and fuel cladding are integral to extending plant operating lifetime and safety. Since the discovery of the High-entropy alloy, these materials have been thoroughly investigated as a next generation nuclear power plant structural material. Chemically complex alloys and ceramics (see

High entropy oxide High-entropy oxides (HEOs) are complex oxides that contain five or more principal metal cations and have a single-phase crystal structure. The first HEO, (MgNiCuCoZn)0.2O in a rock salt structure, was reported in 2015 by Rost ''et al''. HEOs have ...

) such as high entropy carbide ceramics possess increased radiation resistance due to their unique electronic properties and atomic level heterogeneity. Chemical disorder and local lattice distortion have been proposed as mechanisms for improved radiation resistance, as well as increasing strength up to temperatures well above the relatively high operating temperatures of gen. IV reactors. High entropy alloys and ceramics have been demonstrated experimentally to possess low irradiation-induced swelling, resist void formation and subsequent helium bubble growth, and minimize other irradiation hardening and embrittlement effects. Although extremely promising as next generation nuclear reactor materials, high-entropy materials and specifically high-entropy ceramics are still in their infancy. The inherent chemical complexity of these materials offers limitless possibilities in terms of design and property modification, but complicates design paths. Limited study of irradiation resistance and creep strength on timescales relevant to reactor applications constrains high-entropy material scale up. A greater underlying understanding of nanometer-scale material properties is necessary; thus, these materials are likely to undergo significant research and development before scale up in generation IV or generation V reactors. Ongoing research at the basic material level includes studies of atomic level segregation at grain boundaries, defect migration rates, irradiation resistance at greater timescales, and further characterization of embrittlement and other material failure points as they compare to the standard ferritic-martensitic steels commonly used in gen. III reactor structural materials.

References

Bibliography

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External links

Article from Idaho National Laboratory detailing some current efforts at developing Gen. IV reactors.

Generation IV International Forum (GIF)

* ttps://web.archive.org/web/20060512033030/http://www.engr.utk.edu/nuclear/colloquia/slides/Gen%20IV%20U-Tenn%20Presentation.pdf Gen IV presentation
Science or Fiction - Is there a Future for Nuclear?
(Nov. 2007) - A publication from the Austrian Ecology Institute about 'Generation IV' and Fusion reactors. * "In the wake of a severe plant accident, advanced reactor designs are getting renewed attention." *
International Thorium Energy Committee - iThEC
{{Nuclear fission reactors Nuclear power reactor types Idaho National Laboratory