A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and a gas ( carbon dioxide or helium in extant designs) as coolant . Although there are many other types of reactor cooled by gas, the terms GCR and to a lesser extent gas cooled reactor are particularly used to refer to this type of reactor.
31-417: A high-temperature gas-cooled reactor (HTGR) is a type of gas-cooled nuclear reactor which use uranium fuel and graphite moderation to produce very high reactor core output temperatures. All existing HTGR reactors use helium coolant. The reactor core can be either a "prismatic block" (reminiscent of a conventional reactor core) or a " pebble-bed " core. China Huaneng Group currently operates HTR-PM ,
62-578: A 250 MW HTGR power plant in Shandong province , China. The high operating temperatures of HTGR reactors potentially enable applications such as process heat or hydrogen production via the thermochemical sulfur–iodine cycle . A proposed development of the HGTR is the Generation IV very-high-temperature reactor (VHTR) which would initially work with temperatures of 750 to 950 °C. The use of
93-441: A combustion chamber and scrubber unit supplied by fans and a refrigeration unit which cools the gas. A drier in series with the system removes moisture from the gas before it is supplied to the deck. Cargo tanks on gas carriers are not inerted, but the whole space around them is. Inert gas is produced on board commercial and military aircraft in order to passivate fuel tanks. On hot days, fuel vapour in fuel tanks may otherwise form
124-421: A fire and explosion prevention measure. At the bench scale, chemists perform experiments on air-sensitive compounds using air-free techniques developed to handle them under inert gas. Helium, neon, argon, krypton, xenon, and radon are inert gases. Inert gas is produced on board crude oil carriers (above 8,000 tonnes from Jan 1, 2016) by burning kerosene in a dedicated inert gas generator . The inert gas system
155-427: A flammable or explosive mixture which if oxidized, could have catastrophic consequences. Conventionally, Air Separation Modules (ASMs) have been used to generate inert gas. ASMs contain selectively permeable membranes. They are fed compressed air that is extracted from a compressor stage of a gas turbine engine. The pressure drives the separation of oxygen from the air due to the increased permeability of oxygen through
186-774: A high-temperature, gas-cooled reactor for power production was proposed by in 1944 by Farrington Daniels , then associate director of the chemistry division at the University of Chicago's Metallurgical Laboratory . Initially, Daniels envisaged a reactor using beryllium moderator. Development of this high temperature design proposal continued at the Power Pile Division of the Clinton Laboratories (known now as Oak Ridge National Laboratory ) until 1947. Professor Rudolf Schulten in Germany also played
217-448: A pebble bed core, the control rods will be inserted in the surrounding graphite reflector . Control can also be attained by adding pebbles containing neutron absorbers . The design takes advantage of the inherent safety characteristics of a helium-cooled, graphite-moderated core with specific design optimizations. The graphite has large thermal inertia and the helium coolant is single phase, inert, and has no reactivity effects. The core
248-600: A role in development during the 1950s. Peter Fortescue , whilst at General Atomics , was leader of the team responsible for the initial development of the High temperature gas-cooled reactor (HTGR), as well as the Gas-cooled fast reactor (GCFR) system. The Peach Bottom unit 1 reactor in the United States was the first HTGR to produce electricity, and did so very successfully, with operation from 1966 through 1974 as
279-432: A substitute for an inert gas. This is useful when an appropriate pseudo-inert gas can be found which is inexpensive and common. For example, carbon dioxide is sometimes used in gas mixtures for GMAW because it is not reactive to the weld pool created by arc welding. But it is reactive to the arc. The more carbon dioxide that is added to the inert gas, such as argon, will increase your penetration. The amount of carbon dioxide
310-529: A technology demonstrator. Fort St. Vrain Generating Station was one example of this design that operated as an HTGR from 1979 to 1989. Though the reactor was beset by some problems which led to its decommissioning due to economic factors, it served as proof of the HTGR concept in the United States (though no new commercial HTGRs have been developed there since). Experimental HTGRs have also existed in
341-534: A total of seven HTGR reactors had been constructed and operated. A further two HTGR reactors were brought on-line at China's HTR-PM site, in 2021/22. Additionally, from 1969 to 1971, the 3 MW Ultra-High Temperature Reactor Experiment (UHTREX) was operated by Los Alamos National Laboratory to develop the technology of high-temperature gas-cooled reactors. In UHTREX, unlike HTGR reactors, helium coolant contacted nuclear fuel directly, reaching temperatures in excess of 1300 °C. Gas-cooled reactor The GCR
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#1732791322271372-469: Is composed of graphite, has a high heat capacity and structural stability even at high temperatures. The fuel is coated uranium-oxycarbide which permits high burn-up (approaching 200 GWd/t) and retains fission products. The high average core-exit temperature of the VHTR (1,000 °C) permits emissions-free production of high grade process heat . Reactors are designed for 60 years of service. As of 2011,
403-473: Is graphite, although whether the reactor core is configured in graphite prismatic blocks or in graphite pebbles depends on the HTGR design. The fuel used in HTGRs is coated fuel particles, such as TRISO fuel particles. Coated fuel particles have fuel kernels, usually made of uranium dioxide , however, uranium carbide or uranium oxycarbide are also possibilities. Uranium oxycarbide combines uranium carbide with
434-612: Is in the fuel cladding material. Both types were mainly constructed in their countries of origin, with a few export sales: two Magnox plants to Italy and Japan , and one UNGG to Spain . More recently, GCRs based on the declassified drawings of the early Magnox reactors have been constructed by North Korea at the Yongbyon Nuclear Scientific Research Center . Both types used fuel cladding materials that were unsuitable for medium term storage under water, making reprocessing an essential part of
465-411: Is not necessarily elemental and is often a compound gas. Like the noble gases, the tendency for non-reactivity is due to the valence , the outermost electron shell , being complete in all the inert gases. This is a tendency, not a rule, as all noble gases and other "inert" gases can react to form compounds under some conditions. The inert gases are obtained by fractional distillation of air , with
496-647: Is often determined by what kind of transfer you will be using in GMAW. The most common is spray arc transfer, and the most commonly used gas mixture for spray arc transfer is 90% argon and 10% carbon dioxide. In underwater diving an inert gas is a component of the breathing mixture which is not metabolically active and serves to dilute the gas mixture. The inert gas may have effects on the diver, but these are thought to be mostly physical effects, such as tissue damage caused by bubbles in decompression sickness . The most common inert gas used in breathing gas for commercial diving
527-407: Is used to prevent the atmosphere in cargo tanks or bunkers from coming into the explosive range. Inert gases keep the oxygen content of the tank atmosphere below 5% (on crude carriers, less for product carriers and gas tankers), thus making any air/hydrocarbon gas mixture in the tank too rich (too high a fuel to oxygen ratio) to ignite. Inert gases are most important during discharging and during
558-552: The nuclear fuel cycle . Both types were, in their countries of origin, also designed and used to produce weapons-grade plutonium , but at the cost of major interruption to their use for power generation despite the provision of online refuelling . In the UK, the Magnox was replaced by the advanced gas-cooled reactor (AGR), an improved Generation II gas cooled reactor. In France, the UNGG
589-463: The ASMs in comparison to nitrogen. For fuel tank passivation, it is not necessary to remove all oxygen, but rather enough to stay below the lean flammability limit and the lean explosion limit. In contrast to the oxygen concentration of 21% in air, 10% to 12% in the ullage of a passivated fuel tank is common over the course of a flight. In gas tungsten arc welding (GTAW), inert gases are used to shield
620-858: The United Kingdom (the Dragon reactor ) and Germany ( AVR reactor and THTR-300 ), and currently exist in Japan (the High-temperature engineering test reactor using prismatic fuel with 30 MW th of capacity) and China (the HTR-10 , a pebble-bed design with 10 MW e of generation). Two full-scale pebble-bed HTGRs, the HTR-PM reactors, each with 100 MW of electrical production capacity, have gone operational in China as of 2021. The neutron moderator
651-550: The air from degrading a sample. Generally, all noble gases except oganesson ( helium , neon , argon , krypton , xenon , and radon ), nitrogen , and carbon dioxide are considered inert gases. The term inert gas is context-dependent because several of the inert gases, including nitrogen and carbon dioxide, can be made to react under certain conditions. Purified argon gas is the most commonly used inert gas due to its high natural abundance (78.3% N 2 , 1% Ar in air) and low relative cost. Unlike noble gases , an inert gas
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#1732791322271682-562: The ballast voyage when more hydrocarbon vapor is likely to be present in the tank atmosphere. Inert gas can also be used to purge the tank of the volatile atmosphere in preparation for gas freeing - replacing the atmosphere with breathable air - or vice versa. The flue gas system uses the boiler exhaust as its source, so it is important that the fuel/air ratio in the boiler burners is properly regulated to ensure that high-quality inert gases are produced. Too much air would result in an oxygen content exceeding 5%, and too much fuel oil would result in
713-457: The carryover of dangerous hydrocarbon gas. The flue gas is cleaned and cooled by the scrubber tower. Various safety devices prevent overpressure, the return of hydrocarbon gas to the engine room, or having a supply of IG with too high oxygen content. Gas tankers and product carriers cannot rely on flue gas systems (because they require IG with O 2 content of 1% or less) and so use inert gas generators instead. The inert gas generator consists of
744-420: The exception of helium which is separated from a few natural gas sources rich in this element, through cryogenic distillation or membrane separation. For specialized applications, purified inert gas shall be produced by specialized generators on-site. They are often used by chemical tankers and product carriers (smaller vessels). Benchtop specialized generators are also available for laboratories. Because of
775-473: The excess of reactivity. Helium has been the coolant used in all HTGRs to date. Helium is an inert gas , so it will generally not chemically react with any material. Additionally, exposing helium to neutron radiation does not make it radioactive, unlike most other possible coolants. In the prismatic designs, control rods are inserted in holes cut in the graphite blocks that make up the core. The VHTR will be controlled like current PBMR designs if it utilizes
806-623: The non-reactive properties of inert gases, they are often useful to prevent undesirable chemical reactions from taking place. Food is packed in an inert gas to remove oxygen gas. This prevents bacteria from growing. It also prevents chemical oxidation by oxygen in normal air. An example is the rancidification (caused by oxidation) of edible oils. In food packaging , inert gases are used as a passive preservative, in contrast to active preservatives like sodium benzoate (an antimicrobial ) or BHT (an antioxidant ). Historical documents may also be stored under inert gas to avoid degradation. For example,
837-479: The original documents of the U.S. Constitution are stored under humidified argon. Helium was previously used, but it was less suitable because it diffuses out of the case more quickly than argon. Inert gases are often used in the chemical industry. In a chemical manufacturing plant, reactions can be conducted under inert gas to minimize fire hazards or unwanted reactions. In such plants and in oil refineries, transfer lines and vessels can be purged with inert gas as
868-436: The tungsten from contamination. It also shields the fluid metal (created from the arc) from the reactive gases in air which can cause porosity in the solidified weld puddle. Inert gases are also used in gas metal arc welding (GMAW) for welding non-ferrous metals. Some gases which are not usually considered inert but which behave like inert gases in all the circumstances likely to be encountered in some use can often be used as
899-552: The uranium dioxide to reduce the oxygen stoichiometry. Less oxygen may lower the internal pressure in the TRISO particles caused by the formation of carbon monoxide, due to the oxidization of the porous carbon layer in the particle. The TRISO particles are either dispersed in a pebble for the pebble bed design or molded into compacts/rods that are then inserted into the hexagonal graphite blocks. The QUADRISO fuel concept conceived at Argonne National Laboratory has been used to better manage
930-1100: Was able to use natural uranium as fuel, enabling the countries that developed them to fabricate their own fuel without relying on other countries for supplies of enriched uranium , which was at the time of their development in the 1950s only available from the United States or the Soviet Union . The Canadian CANDU reactor, using heavy water as a moderator, was designed with the same goal of using natural uranium fuel for similar reasons. Historically thermal spectrum graphite-moderated gas-cooled reactors mostly competed with light water reactors , ultimately losing out to them after having seen some deployment in Britain and France. Heavy water reactor share some design considerations as both are capable in principle of using unenriched fuel but require online refueling to be viable power reactors. There were two main types of generation I GCR: The main difference between these two types
961-454: Was replaced by the pressurized water reactor (PWR). Gas-cooled reactor types include: Inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds . Though inert gases have a variety of applications, they are generally used to prevent unwanted chemical reactions with the oxygen ( oxidation ) and moisture ( hydrolysis ) in