A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nuclear fission is passed to a working fluid, which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. As of 2022, the International Atomic Energy Agency reports there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world.
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants. In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms. The heated, high pressure water then flows to a steam generator, where it transfers its thermal energy to lower pressure water of a secondary system where steam is generated. The steam then drives turbines, which spin an electric generator. In contrast to a boiling water reactor (BWR), pressure in the primary coolant loop prevents the water from boiling within the reactor. All light-water reactors use ordinary water as both coolant and neutron moderator. Most use anywhere from two to four vertically mounted steam generators; VVER reactors use horizontal steam generators.
A boiling water reactor (BWR) is a type of light water 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), which is also a type of light water nuclear reactor.
The RBMK is a class of graphite-moderated nuclear power reactor designed and built by the Soviet Union. The name refers to its design where, instead of a large steel pressure vessel surrounding the entire core, the core is surrounded by a cylindrical annular steel tank inside a concrete vault and each fuel assembly is enclosed in an individual 8 cm (inner) diameter pipe. The channels also contain the coolant, and are surrounded by graphite.
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 reactors are the most common type of nuclear reactor, and light-water reactors are the most common type of thermal-neutron reactor.
Passive nuclear safety is a design approach for safety features, implemented in a nuclear reactor, that does not require any active intervention on the part of the operator or electrical/electronic feedback in order to bring the reactor to a safe shutdown state, in the event of a particular type of emergency. Such design features tend to rely on the engineering of components such that their predicted behaviour would slow down, rather than accelerate the deterioration of the reactor state; they typically take advantage of natural forces or phenomena such as gravity, buoyancy, pressure differences, conduction or natural heat convection to accomplish safety functions without requiring an active power source. Many older common reactor designs use passive safety systems to a limited extent, rather, relying on active safety systems such as diesel powered motors. Some newer reactor designs feature more passive systems; the motivation being that they are highly reliable and reduce the cost associated with the installation and maintenance of systems that would otherwise require multiple trains of equipment and redundant safety class power supplies in order to achieve the same level of reliability. However, weak driving forces that power many passive safety features can pose significant challenges to effectiveness of a passive system, particularly in the short term following an accident.
A containment building is a reinforced steel, concrete or lead structure enclosing a nuclear reactor. It is designed, in any emergency, to contain the escape of radioactive steam or gas to a maximum pressure in the range of 275 to 550 kPa. The containment is the fourth and final barrier to radioactive release, the first being the fuel ceramic itself, the second being the metal fuel cladding tubes, the third being the reactor vessel and coolant system.
The advanced boiling water reactor (ABWR) is a Generation III boiling water reactor. The ABWR is currently offered by GE Hitachi Nuclear Energy (GEH) and Toshiba. The ABWR generates electrical power by using steam to power a turbine connected to a generator; the steam is boiled from water using heat generated by fission reactions within nuclear fuel. Kashiwazaki-Kariwa unit 6 is considered the first Generation III reactor in the world.
The supercritical water reactor (SCWR) is a concept Generation IV reactor, designed as a light water reactor (LWR) that operates at supercritical pressure. The term critical in this context refers to the critical point of water, and must not be confused with the concept of criticality of the nuclear reactor.
A steam generator is a heat exchanger used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactor between the primary and secondary coolant loops.
The Economic Simplified Boiling Water Reactor (ESBWR) is a passively safe generation III+ reactor design derived from its predecessor, the Simplified Boiling Water Reactor (SBWR) and from the Advanced Boiling Water Reactor (ABWR). All are designs by GE Hitachi Nuclear Energy (GEH), and are based on previous Boiling Water Reactor designs.
International Reactor Innovative and Secure (IRIS) is a Generation IV reactor design made by an international team of companies, laboratories, and universities and coordinated by Westinghouse. IRIS is hoped to open up new markets for nuclear power and make a bridge from Generation III reactor to Generation IV reactor technology. The design is not yet specific to reactor power output. Notably, a 335 MW output has been proposed, but it could be tweaked to be as low as a 100 MW unit.
The three primary objectives of nuclear reactor safety systems as defined by the U.S. Nuclear Regulatory Commission are to shut down the reactor, maintain it in a shutdown condition and prevent the release of radioactive material.
The MKER is a Russian third generation nuclear reactor design. It was a development of the RBMK nuclear power reactor. No reactor of such MKER type will continue to be developed, as ROSATOM have shelved the design.
The B&W mPower was a proposed small modular reactor designed by Babcock & Wilcox, and to be built by Generation mPower LLC, a joint venture of Babcock & Wilcox and Bechtel. It was a Generation III+ integral pressurized water reactor concept.
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment. Frequently, a chain of two coolant loops are used because the primary coolant loop takes on short-term radioactivity from the reactor.
GE Hitachi Nuclear Energy (GEH) is a provider of advanced reactors and nuclear services. It is headquartered in Wilmington, North Carolina, United States. Established in June 2007, GEH is a nuclear alliance created by General Electric and Hitachi. In Japan, the alliance is Hitachi-GE Nuclear Energy. In November 2015, Jay Wileman was appointed CEO.
Boiling water reactor safety systems are nuclear safety systems constructed within boiling water reactors in order to prevent or mitigate environmental and health hazards in the event of accident or natural disaster.
The Integral Molten Salt Reactor (IMSR) is a nuclear power plant design targeted at developing a commercial product for the small modular reactor (SMR) market. It employs molten salt reactor technology which is being developed by the Canadian company Terrestrial Energy. It is based closely on the denatured molten salt reactor (DMSR), a reactor design from Oak Ridge National Laboratory. It also incorporates elements found in the SmAHTR, a later design from the same laboratory. The IMSR belongs to the DMSR class of molten salt reactors (MSR) and hence is a "burner" reactor that employs a liquid fuel rather than a conventional solid fuel; this liquid contains the nuclear fuel and also serves as primary coolant.
An organic nuclear reactor, or organic cooled reactor (OCR), is a type of nuclear reactor that uses some form of organic fluid, typically a hydrocarbon substance like polychlorinated biphenyl (PCB), for cooling and sometimes as a neutron moderator as well.
