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Magnox is a type of nuclear power/production reactor that was designed to run on
natural uranium Natural uranium (NU or Unat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes ...
with graphite as the moderator and
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
gas as the heat exchange coolant. It belongs to the wider class of gas-cooled reactors. The name comes from the
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
-
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
alloy used to clad the fuel rods inside the reactor. Like most other " Generation I nuclear reactors", the Magnox was designed with the dual purpose of producing
electrical power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billion ...
and
plutonium-239 Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three mai ...
for the nascent nuclear weapons programme in Britain. The name refers specifically to the United Kingdom design but is sometimes used generically to refer to any similar reactor. As with other plutonium-producing reactors, conserving
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
s is a key element of the design. In magnox, the neutrons are moderated in large blocks of
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...
. The efficiency of graphite as a moderator allows the Magnox to run using
natural uranium Natural uranium (NU or Unat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes ...
fuel, in contrast with the more common commercial light-water reactor which requires slightly enriched uranium. Graphite oxidizes readily in air, so the core is cooled with CO2, which is then pumped into a
heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...
to generate
steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...
to drive conventional
steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam tu ...
equipment for power production. The core is open on one end, so fuel elements can be added or removed while the reactor is still running. The "dual use" capability of the Magnox design led to the UK building up a large stockpile of fuel grade/"reactor grade" plutonium, with the aid of the B205 reprocessing facility. The low-to-interim burnup feature of the reactor design would become responsible for changes to US regulatory classifications after the US–UK "Reactor-grade" plutonium detonation test of the 1960s. Despite improvements to the design in later decades as electricity generation became the primary operational aim, magnox reactors were never capable of competing with the higher efficiency and higher fuel " burnup" of
pressurized water reactor 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 (with notable exceptions being the UK, Japan and Canada). In a PWR, the primary coolant (water) i ...
s. In total, only a few dozen reactors of this type were constructed, most of them in the UK from the 1950s to the 1970s, with very few exported to other countries. The first magnox reactor to come online was
Calder Hall Sellafield is a large multi-function nuclear site close to Seascale on the coast of Cumbria, England. As of August 2022, primary activities are nuclear waste processing and storage and nuclear decommissioning. Former activities included nuc ...
(at the
Sellafield Sellafield is a large multi-function nuclear site close to Seascale on the coast of Cumbria, England. As of August 2022, primary activities are nuclear waste processing and storage and nuclear decommissioning. Former activities included nuc ...
site) in 1956, frequently regarded as the "first commercial-scale electricity producing reactor in the world", while the last in Britain to shut down was Reactor 1 in Wylfa (on Ynys Môn) in 2015. ,
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and shares borders with China and Russia to the north, at the Yalu (Amnok) and T ...
remains the only operator to continue using Magnox style reactors, at the Yongbyon Nuclear Scientific Research Center. The Magnox design was superseded by the Advanced Gas-cooled Reactor, which is similarly cooled but includes changes to improve its economic performance.


General description


Windscale

The UK's first full-scale
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
was the Windscale Pile in
Sellafield Sellafield is a large multi-function nuclear site close to Seascale on the coast of Cumbria, England. As of August 2022, primary activities are nuclear waste processing and storage and nuclear decommissioning. Former activities included nuc ...
. The pile was designed for the production of
plutonium-239 Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three mai ...
which was bred in multi-week reactions taking place in
natural uranium Natural uranium (NU or Unat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes ...
fuel. Under normal conditions, natural uranium is not sensitive enough to its own
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
s to maintain a chain reaction. To improve the fuel's sensitivity to neutrons, 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 m ...
is used, in this case highly purified
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...
. The reactors consisted of a huge cube of this material (the "pile") made up of many smaller blocks and drilled through horizontally to make a large number of ''fuel channels''. Uranium fuel was placed in aluminium canisters and pushed into the channels in the front, pushing previous fuel canisters through the channel and out the back of the reactor where they fell into a pool of water. The system was designed to work at low temperatures and power levels and was air-cooled with the help of large fans. Graphite is flammable and presents a serious safety risk. This was demonstrated on 10 October 1957 when Unit 1 of the now two-unit site caught fire. The reactor burned for three days, and massive contamination was only avoided due to the addition of filtering systems that had previously been derided as unnecessary " follies".


Magnox

As the UK nuclear establishment began to turn its attention to
nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
, the need for more plutonium for weapons development remained acute. This led to an effort to adapt the basic Windscale design to a power-producing version that would also produce plutonium. In order to be economically useful the plant would have to run at much higher power levels, and in order to efficiently convert that power to electricity, it would have to run at higher temperatures. At these power levels, the fire risk is amplified and air cooling is no longer appropriate. In the case of the Magnox design, this led to the use of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
(CO2) as the coolant. There is no facility in the reactor to adjust the gas flow through the individual channels whilst at power, but gas flow was adjusted by using flow gags attached to the support strut which located into the
diagrid A diagrid (a portmanteau of diagonal grid) is a framework of diagonally intersecting metal, concrete, or wooden beams that is used in the construction of buildings and roofs. It requires less structural steel than a conventional steel f ...
. These gags were used to increase flow in the centre of the core and to reduce it at the periphery. Principal control over the reaction rate was provided by a number (48 at Chapelcross and Calder Hall)
boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the '' boron group'' it has t ...
-steel control rods which could be raised and lowered as required in vertical channels. At higher temperatures, aluminium is no longer structurally sound, which led to the development of the magnox alloy fuel cladding. Unfortunately, magnox is increasingly reactive with increasing temperature, and the use of this material limited the operational gas temperatures to , much lower than desirable for efficient steam generation. This limit also meant that the reactors had to be very large in order to generate any given power level, which was further amplified by the use of gas for cooling, as the low thermal capacity of the fluid required very high flow rates. The magnox fuel elements consisted of refined uranium enclosed in a loose-fitting magnox shell and then pressurized with
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
. The outside of the shell was typically finned in order to improve heat exchange with the CO2. Magnox alloy is reactive with water, which means it cannot be left in a cooling pond after extraction from the reactor for extended periods. In contrast to the Windscale layout, the Magnox design used vertical fuel channels. This required the fuel shells to lock together end-to-end, or to sit one on top the other to allow them to be pulled out of the channels from the top. Like the Windscale designs, the later Magnox reactors allowed access to the fuel channels and could be refuelled while operating. This was a key criterion for the design because its use of natural uranium leads to low burnup ratios and the requirement for frequent refuelling. For power use, the fuel canisters were left in the reactor as long as possible, while for plutonium production they were removed earlier. The complicated refuelling equipment proved to be less reliable than the reactor systems, and perhaps not advantageous overall. The entire reactor assembly was placed in a large pressure vessel. Due to the size of the pile, only the reactor core itself was placed within the steel pressure assembly, which was then surrounded by a concrete confinement building (or "biological shield"). As there was no water in the core, and thus no possibility of a steam explosion, the building was able to tightly wrap the pressure vessel, which helped reduce construction costs. In order to keep the size of the confinement building down, the early Magnox designs placed the
heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...
for the CO2 gas outside the dome, connected through piping. Although there were strengths with this approach in that maintenance and access was generally more straightforward, the major weakness was the radiation 'shine' emitted particularly from the unshielded top duct. The Magnox design was an evolution and never truly finalised, and later units differ considerably from earlier ones. As neutron fluxes increased in order to improve power densities problems with neutron embrittlement were encountered, particularly at low temperatures. Later units at Oldbury and Wylfa replaced the steel pressure vessels with
prestressed concrete Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" ( compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. Post-tensioned concreted ...
versions which also contained the heat exchangers and steam plant. Working pressure varies from 6.9 to 19.35
bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar * Chocolate bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a layer of cloud * Bar ( ...
for the steel vessels, and 24.8 and 27bar for the two concrete designs. No British construction company at the time was large enough to build all the power stations, so various competing consortiums were involved, adding to the differences between the stations; for example, nearly every power station used a different design of Magnox fuel element. Most of the Magnox builds suffered time overruns and cost escalation. For the initial start up of the reactor neutron sources were located within the core to provide sufficient neutrons to initiate the nuclear reaction. Other aspects of the design included the use of flux shaping or flattening bars or controls rods to even out (to some extent) the neutron flux density across the core. If not used, the flux in the centre would be very high relative to the outer areas leading to excessive central temperatures and lower power output limited by the temperature of the central areas. Each fuel channel would have several elements stacked one upon another to form a ''stringer''. This required the presence of a latching mechanism to allow the stack to be withdrawn and handled. This caused some problems as the Nimonic springs used contained cobalt, which became irradiated giving high gamma level when removed from the reactor. Additionally, thermocouples were attached to some elements and needed to be removed on fuel discharge from the reactor.


AGR

The "dual use" nature of the Magnox design leads to design compromises that limit its economic performance. As the Magnox design was being rolled out, work was already underway on the Advanced Gas-cooled Reactor (AGR) with the explicit intention of making the system more economical. Primary among the changes was the decision to run the reactor at much higher temperatures, about , which would greatly improve the efficiency when running the power-extracting
steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam tu ...
s. This was too hot for the magnox alloy, and the AGR originally intended to use a new
beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to for ...
-based cladding, but this proved too brittle. This was replaced by a
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
cladding, but this absorbed enough neutrons to affect criticality, and in turn required the design to operate on slightly enriched uranium rather than the Magnox's natural uranium, driving up fuel costs. Ultimately the economics of the system proved little better than Magnox. Former Treasury Economic Advisor, David Henderson, described the AGR programme as one of the two most costly British government-sponsored project errors, alongside
Concorde The Aérospatiale/BAC Concorde () is a retired Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC). Studies started in 1954, and France an ...
.


Technical information

Source:


Economics

The first Magnox reactors at
Calder Hall Sellafield is a large multi-function nuclear site close to Seascale on the coast of Cumbria, England. As of August 2022, primary activities are nuclear waste processing and storage and nuclear decommissioning. Former activities included nuc ...
were designed principally to produce plutonium for
nuclear weapons A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
. The production of plutonium from uranium by irradiation in a pile generates large quantities of heat which must be disposed of, and so generating steam from this heat, which could be used in a turbine to generate electricity, or as process heat in the nearby Windscale works, was seen as a kind of "free" by-product of an essential process. The Calder Hall reactors had low efficiency by today's standards, only 18.8%. The British government decided in 1957 that electricity generation by nuclear power would be promoted, and that there would be a building programme to achieve 5,000 to 6,000 MWe capacity by 1965, a quarter of UK's generating needs. Although Sir John Cockcroft had advised the government that electricity generated by nuclear power would be more expensive than that from coal, the government decided that nuclear power stations as alternatives to coal-fired power stations would be useful to reduce the bargaining power of the coal miners' unions, and so decided to go ahead. In 1960 a government
white paper A white paper is a report or guide that informs readers concisely about a complex issue and presents the issuing body's philosophy on the matter. It is meant to help readers understand an issue, solve a problem, or make a decision. A white paper ...
scaled back the building programme to 3,000MWe, acknowledging that coal generation was 25% cheaper. A government statement to the
House of Commons The House of Commons is the name for the elected lower house of the bicameral parliaments of the United Kingdom and Canada. In both of these countries, the Commons holds much more legislative power than the nominally upper house of parliament. T ...
in 1963 stated that nuclear generation was more than twice as expensive as coal. The "plutonium credit" which assigned a value to the plutonium produced was used to improve the economic case, although the operators of the power stations were never paid this credit. Once removed from the reactor, the used fuel elements are stored in cooling ponds (with the exception of Wylfa which has dry stores in a carbon dioxide atmosphere) where the decay heat is transferred to the pond water, and then removed by the pond water circulation, cooling and filtration system. The fact that fuel elements can only be stored for a limited period in water before the Magnox cladding deteriorates, and must therefore inevitably be reprocessed, added to the costs of the Magnox programme. Later reviews criticised the continuing development project by project instead of standardisation on the most economical design, and for persisting with the development of a reactor which achieved only two export orders. A retrospective evaluation of costs, using a low 5% discount rate on capital, estimated Magnox electricity costs were nearly 50% higher than coal power stations would have provided.


Safety

The Magnox reactors were considered at the time to have a considerable degree of inherent safety because of their simple design, low power density, and gas coolant. Because of this they were not provided with secondary containment features. A safety design principle at the time was that of the "maximum credible accident", and the assumption was made that if the plant were designed to withstand that, then all other lesser but similar events would be encompassed. Loss of coolant accidents (at least those considered in the design) would not cause large-scale fuel failure as the Magnox cladding would retain the bulk of the radioactive material, assuming the reactor was rapidly shutdown (a
SCRAM A scram or SCRAM is an emergency shutdown of a nuclear reactor effected by immediately terminating the fission reaction. It is also the name that is given to the manually operated kill switch that initiates the shutdown. In commercial reacto ...
), because the decay heat could be removed by natural circulation of air. As the coolant is already a gas, explosive pressure buildup from boiling is not a risk, as happened in the catastrophic steam explosion at the
Chernobyl accident The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR in the Soviet Union. It is one of only two nucl ...
. Failure of the reactor shutdown system to rapidly shut down the reactor, or failure of natural circulation, was not considered in the design. In 1967 Chapelcross experienced a fuel melt due to restricted gas flow in an individual channel and, although this was dealt with by the station crew without major incident, this event had not been designed or planned for, and the radioactivity released was greater than anticipated during the station design. Despite the belief in their inherently safe design, it was decided that the Magnox stations would not be built in heavily populated areas. The positioning constraint decided upon was that any 10-degree sector would have a population less than 500 within , 10,000 within and 100,000 within . In addition population around the site in all directions would be less than six times the 10-degree limits. Planning permission constraints would be used to prevent any large growth of population within five miles. In the older steel pressure vessel design, boilers and gas ducting are outside the concrete biological shield. Consequently, this design emits a significant amount of direct
gamma Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter r ...
and
neutron radiation Neutron radiation is a form of ionizing radiation that presents as free neutrons. Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new isotopes— ...
, termed direct "shine", from the reactors. For example, the most exposed members of the public living near Dungeness Magnox reactor in 2002 received 0.56
mSv mSv or MSV may refer to: * Maize streak virus, a plant disease * Medium-speed vehicle, US category * Medium Systems Vehicle, a class of fictional artificially intelligent starship in The Culture universe of late Scottish author Iain Banks * Millis ...
, over half the International Commission on Radiological Protection recommended maximum radiation dose limit for the public, from direct "shine" alone. The doses from the Oldbury and Wylfa reactors, which have concrete pressure vessels which encapsulate the complete gas circuit, are much lower.


Reactors built

In all, 11 power stations totalling 26 units were built in the United Kingdom where the design originated. In addition, one was exported to Tōkai in Japan and another to Latina in Italy. North Korea also developed their own Magnox reactors, based on the UK design which was made public at an Atoms for Peace conference. The first Magnox power station,
Calder Hall Sellafield is a large multi-function nuclear site close to Seascale on the coast of Cumbria, England. As of August 2022, primary activities are nuclear waste processing and storage and nuclear decommissioning. Former activities included nuc ...
, was the world's first nuclear power station to generate electrical power on an industrial scale (a power station in Obninsk, Russia started supplying the grid in very small non-commercial quantities on 1 December 1954). The first connection to the grid was on 27 August 1956, and the plant was officially opened by
Queen Elizabeth II Elizabeth II (Elizabeth Alexandra Mary; 21 April 1926 – 8 September 2022) was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until her death in 2022. She was queen regnant of 32 sovereign states during ...
on 17 October 1956. When the station closed on 31 March 2003, the first reactor had been in use for nearly 47 years. The first two stations (Calder Hall and Chapelcross) were originally owned by the
UKAEA The United Kingdom Atomic Energy Authority is a UK government research organisation responsible for the development of fusion energy. It is an executive non-departmental public body of the Department for Business, Energy and Industrial Strategy ...
and primarily used in their early life to produce weapons-grade
plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exh ...
, with two fuel loads per year. From 1964 they were mainly used on commercial fuel cycles and in April 1995 the UK Government announced that all production of plutonium for weapons purposes had ceased. The later and larger units were owned by the CEGB and operated on commercial fuel cycles. However Hinkley Point A and two other stations were modified so that weapons-grade plutonium could be extracted for military purposes should the need arise.


Derating to reduce corrosion

In early operation it was found that there was significant oxidation of mild steel components by the high temperature carbon dioxide coolant, requiring a reduction in
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
and power output. For example, the Latina reactor was derated in 1969 by 24%, from 210MWe to 160MWe, by the reduction of operating temperature from .


Last operating Magnox reactor

The
Nuclear Decommissioning Authority The Nuclear Decommissioning Authority (NDA) is a non-departmental public body of the Department for Business, Energy and Industrial Strategy, formed by the Energy Act 2004. It evolved from the Coal and Nuclear Liabilities Unit of the Department ...
(NDA) announced on 30 December 2015 that Wylfa Unit 1 – the world's last operating Magnox reactor – was closed. The unit had generated electricity for five years longer than originally planned. Two units at Wylfa were both scheduled to shut down at the end of 2012, but the NDA decided to shut down Unit 2 in April 2012 so that Unit 1 could continue operating in order to fully utilize existing stocks of fuel, which was no longer being manufactured. The small 5 MWe experimental reactor, based on the Magnox design, at Yongbyon in
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and shares borders with China and Russia to the north, at the Yalu (Amnok) and T ...
, continues to operate .


Magnox definitions


Magnox alloy

Magnox is also the name of an
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
—mainly of
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
with small amounts of
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
and other metals—used in cladding unenriched
uranium Uranium is a chemical element with the 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. Uranium is weak ...
metal fuel with a non-oxidising covering to contain fission products. Magnox is short for Magnesium non-oxidising. This material has the advantage of a low
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
capture cross-section, but has two major disadvantages: *It limits the maximum temperature, and hence the thermal efficiency, of the plant. *It reacts with water, preventing long-term storage of spent fuel under water. Magnox fuel incorporated cooling fins to provide maximum heat transfer despite low operating temperatures, making it expensive to produce. While the use of uranium metal rather than oxide made reprocessing more straightforward and therefore cheaper, the need to reprocess fuel a short time after removal from the reactor meant that the fission product hazard was severe. Expensive remote handling facilities were required to address this danger.


Magnox plants

The term magnox may also loosely refer to: *Three
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and shares borders with China and Russia to the north, at the Yalu (Amnok) and T ...
n reactors, all based on the declassified blueprints of the Calder Hall Magnox reactors: **A small 5 MWe experimental reactor at Yongbyon, operated from 1986 to 1994, and restarted in 2003. Plutonium from this reactor's spent fuel has been used in the
North Korea nuclear weapons program North Korea has a military nuclear weapons program and, as of early 2020, is estimated to have an arsenal of approximately 30 to 40 nuclear weapons and sufficient production of fissile material for six to seven nuclear weapons per year.
. **A 50 MWe reactor, also at Yongbyon, whose construction commenced in 1985 but was never finished in accord with the 1994 U.S.-North Korea Agreed Framework. **A 200 MWe reactor at
Taechon T'aechŏn County or Thaechŏn County (''in North Korean romanization'') is a ''kun'', or county, in central North P'yŏngan province, North Korea. It borders Taegwan and Tongch'ang to the north, Unsan and Nyŏngbyŏn to the east, Pakch'ŏn ...
, construction of which also halted in 1994. *Nine UNGG power reactors built in France, all now shut down. These were carbon dioxide-cooled, graphite reactors with natural uranium metal fuel, very similar in design and purpose to the British Magnox reactors except that the fuel cladding was
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
-
zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
alloy and that the bars were disposed horizontally (instead of vertically for Magnox).


Decommissioning

The
Nuclear Decommissioning Authority The Nuclear Decommissioning Authority (NDA) is a non-departmental public body of the Department for Business, Energy and Industrial Strategy, formed by the Energy Act 2004. It evolved from the Coal and Nuclear Liabilities Unit of the Department ...
(NDA) is responsible for the decommissioning of the UK Magnox power plants, at an estimated cost of £12.6billion. There has been debate about whether a 25 or 100-year decommissioning strategy should be adopted. After 80years short-lifetime radioactive material in the defuelled core would have decayed to the point that human access to the reactor structure would be possible, easing dismantling work. A shorter decommissioning strategy would require a robotic core dismantling technique. The current approximately 100-year decommissioning plan is called Safestore. A 130-year Deferred Safestore Strategy was also considered, with an estimated cost saving of £1.4 billion, but not selected. In addition the
Sellafield Sellafield is a large multi-function nuclear site close to Seascale on the coast of Cumbria, England. As of August 2022, primary activities are nuclear waste processing and storage and nuclear decommissioning. Former activities included nuc ...
site which, amongst other activities, reprocessed spent Magnox fuel, has an estimated decommissioning cost of £31.5billion. Magnox fuel was produced at Springfields near
Preston Preston is a place name, surname and given name that may refer to: Places England *Preston, Lancashire, an urban settlement **The City of Preston, Lancashire, a borough and non-metropolitan district which contains the settlement **County Boro ...
; estimated decommissioning cost is £371million. The total cost of decommissioning Magnox activities is likely to exceed £20billion, averaging about £2billion per productive reactor site. Calder Hall was opened in 1956 as the world's first commercial nuclear power station, and is a significant part of the UK's industrial heritage. The NDA is considering whether to preserve Calder Hall Reactor 1 as a museum site. All the UK's Magnox reactor sites (apart from Calder Hall) are operated by
Magnox Ltd Magnox Ltd is a nuclear decommissioning Site Licence Company (SLC) under the Nuclear Decommissioning Authority (NDA), a government body set up specifically to deal with the nuclear legacy under the Energy Act 2004. In September 2019, it became a ...
, a subsidiary of the NDA. Reactor Sites Management Company (RSMC), a NDA Site Licence Company (SLC), originally held the contract to manage Magnox Ltd on behalf of the NDA. In 2007, RSMC was acquired by American nuclear fuel cycle service provider EnergySolutions from British Nuclear Fuels. On 1 October 2008, Magnox Electric Ltd separated into two nuclear licensed companies, Magnox North Ltd and Magnox South Ltd. Magnox North sites * Chapelcross * Hunterston A * Oldbury * Trawsfynydd * Wylfa Magnox South sites * Berkeley * Bradwell * Dungeness A * Hinkley Point A In January 2011 Magnox North Ltd and Magnox South Ltd recombined as
Magnox Ltd Magnox Ltd is a nuclear decommissioning Site Licence Company (SLC) under the Nuclear Decommissioning Authority (NDA), a government body set up specifically to deal with the nuclear legacy under the Energy Act 2004. In September 2019, it became a ...
. Following procurement and management issues with the contract, Magnox Ltd will become a subsidiary of the NDA in September 2019.


List of Magnox reactors in the UK


Magnox reactors exported from the UK


See also

*
Nuclear power in the United Kingdom Nuclear power in the United Kingdom generated 16.1% of the country's electricity in 2020. , the UK has 9 operational nuclear reactors at five locations (8 advanced gas-cooled reactors (AGR) and one pressurised water reactor (PWR)), producing 5 ...
* UNGG, the similar class of reactors built in France * Edge of Darkness, 1985 British television drama about the nuclear industry, which went by the working title "Magnox".


References


External links


Energy''Solutions''Nuclear Sites Stakeholder Information
– Overview of each Magnox power station, provided by British Nuclear Group
Magnox Safety Reviews
September 2000, HSE Nuclear Installations Inspectorate
Magnox Electric plc’s strategy for decommissioning its nuclear licensed sites
February 2002, HSE Nuclear Installations Inspectorate
The decommissioning of commercial magnox gas cooled reactor power stations in the United Kingdom
G. Holt, Magnox Electric, IAEA meeting paper, 8–10 September 1997

21–23 September 1988, Ente Nazionale per l'Energia Electrica
Review of ageing processes and their influence on Safety and Performance at Wylfa Nuclear Power Station
John Large, 14 March 2001 – includes detailed diagrams
Magnox Fuel Element Design
– Atomic Energy Insights
Sellafield Magnox cooling ponds cleanup job commences
– Nuclear Engineering International
A ponderous hazard
– Nuclear Engineering International
British Nuclear Group image asset library
– A large collection of interior and exterior photographs of all the Magnox power stations in the UK. * {{Energy in the United Kingdom, sources Nuclear power reactor types Graphite moderated reactors Nuclear power in the United Kingdom