Magnox is a type of nuclear power/production reactor that was designed to run on natural uranium with graphite as the moderator and carbon dioxide gas as the heat exchange coolant. It belongs to the wider class of gas cooled reactors. The name comes from the magnesium-aluminium 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 and plutonium-239 for the nascent nuclear weapons program in Britain. The name refers specifically to the United Kingdom design but is sometimes used generically to refer to any similar reactor.
Like other plutonium-producing reactors, conserving neutrons is a key element of the design. In magnox, the neutrons are moderated in large blocks of graphite. The efficiency of graphite as a moderator allows the Magnox to run using natural uranium 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 to generate steam to drive conventional steam turbine 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 improving its electricity generating capabilities in later decades, marked by the transition to electric-power becoming the primary operational aim, magnox reactors were never capable of consistently generating high efficiency/high fuel "burn-ups" due to the handicap of its design and natural uranium heritage, compared with pressurized water reactors, the most widespread power-reactor design.
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 (at the Sellafield 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. As of 2016, North Korea 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.
The UK's first full-scale nuclear reactor was the Windscale Pile in Sellafield. The pile was designed for the production of plutonium-239 which was bred in multi-week reactions taking place in natural uranium fuel. Under normal conditions, natural uranium is not sensitive enough to its own neutrons to maintain a chain reaction. To improve the fuel's sensitivity to neutrons, a neutron moderator is used, in this case highly purified graphite.
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".
As the UK nuclear establishment began to turn its attention to nuclear power, the need for more plutonium 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 (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. 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-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 360 °C (680 °F), 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. 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 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 versions which also contained the heat exchangers and steam plant. Working pressure varies from 6.9 to 19.35 bar for the steel vessels, and 24.8 and 27 bar 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.
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 650 °C (1,202 °F), which would greatly improve the efficiency when running the power-extracting steam turbines. This was too hot for the magnox alloy, and the AGR originally intended to use a new beryllium-based cladding, but this proved too brittle. This was replaced by a stainless steel 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.
It differs from real:
|Thermal output (gross), MW||182||1875||835|
|Electrical output (gross), MW||46||590||280|
|Number of fuel channels||1696||6150||3320|
|Active core diameter||9,45 m||17,4 m||12,8 m|
|Active core height||6,4 m||9,2 m||8,5 m|
|Mean gas pressure||7 bar||26,2 bar||25,6 bar|
|Mean inlet gas temperature °C||140||247||245|
|Mean outlet gas temperature °C||336||414||410|
|Total gas flow||891 kg/s||10254 kg/s||4627 kg/s|
|Material||Natural uranium metal||Natural uranium metal||Natural uranium metal|
|Mass of uranium in tonnes||120||595||293|
|Pressure vessel internal diameter||11,28 m||29,3 m||23,5 m|
|Pressure vessel internal height||21,3 m||—||18,3 m|
|Number of generators||2||2||1|
The first Magnox reactors at Calder Hall were designed principally to produce plutonium for nuclear weapons. 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 scaled back the building programme to 3,000 MWe, acknowledging that coal generation was 25% cheaper. A government statement to the House of Commons 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.
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), 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. 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 1.5 miles, 10,000 within 5 miles and 100,000 within 10 miles. 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 and neutron radiation, 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, 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.
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, 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 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 and primarily used in their early life to produce weapons-grade plutonium, 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.
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 and power output. For example, the Latina reactor was derated in 1969 by 24%, from 210 MWe to 160 MWe, by the reduction of operating temperature from 390 to 360 °C.
The Nuclear Decommissioning Authority (NDA) announced on December 30, 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.
Magnox is also the name of an alloy—mainly of magnesium with small amounts of aluminium and other metals—used in cladding unenriched uranium 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 capture cross-section, but has two major disadvantages:
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.
The term magnox may also loosely refer to:
The Nuclear Decommissioning Authority (NDA) is responsible for the decommissioning of the UK Magnox power plants, at an estimated cost of £12.6 billion. There is currently debate about whether a 25 or 100 year decommissioning strategy should be adopted. After 80 years 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 fully robotic core dismantling technique.
In addition the Sellafield site which, amongst other activities, reprocessed spent Magnox fuel, has an estimated decommissioning cost of £31.5 billion. Magnox fuel was produced at Springfields near Preston; estimated decommissioning cost is £371 million. The total cost of decommissioning Magnox activities is likely to exceed £20 billion, averaging about £2 billion 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, a Site Licence Company (SLC) of the NDA. Reactor Sites Management Company (RSMC) holds 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
Magnox South sites
In January 2011 Magnox North Ltd and Magnox South Ltd recombined as Magnox Ltd. Following procurement and management issues with the contract, Magnox Ltd will become a subsidiary of the NDA on September 2019.
|Name||Location||Location (GeoHack)||Number of units||Production per unit||Total production||First grid connection||Shut down|
|Calder Hall||near Whitehaven, Cumbria||NY025042||4||50 MWe||200 MWe||1956||2003|
|Chapelcross||near Annan, Dumfries and Galloway||NY2161169707||4||60 MWe||240 MWe||1959||2004|
|Berkeley||Gloucestershire||ST659994||2||138 MWe||276 MWe||1962||1989|
|Bradwell||near Southminster, Essex||TM001087||2||121 MWe||242 MWe||1962||2002|
|Hunterston "A"||between West Kilbride and Fairlie North Ayrshire||NS183513||2||180 MWe||360 MWe||1964||1990|
|Hinkley Point "A"||near Bridgwater, Somerset||TR330623||2||235 MWe||470 MWe||1965||1999|
|Trawsfynydd||Gwynedd||SH690381||2||195 MWe||390 MWe||1965||1991|
|Dungeness "A"||Kent||TR074170||2||219 MWe||438 MWe||1966||2006|
|Sizewell "A"||near Leiston, Suffolk||TM472634||2||210 MWe||420 MWe||1966||2006|
|Oldbury||near Thornbury, South Gloucestershire||ST606945||2||217 MWe||434 MWe||1968||2012|
|Wylfa||Anglesey||SH350937||2||490 MWe||980 MWe||1971||2015|
|Name||Location||Number of units||Production per unit||Total production||First grid connection||Shut down|
|Latina||Italy||1||160 MWe||160 MWe||1963||1987 following Italian referendum on nuclear power|
|Tokai Mura||Japan||1||166 MWe||166 MWe||1966||1998|
the Central Electricity Generating Board has agreed to a small modification in the design of Hinkley Point and of the next two stations in its programme so as to enable plutonium suitable for military purposes to be extracted should the need arise.
An Advanced Gas-cooled Reactor (AGR) is a type of nuclear reactor designed and operated in the United Kingdom. These are the second generation of British gas-cooled reactors, using graphite as the neutron moderator and carbon dioxide as coolant. They have been the backbone of the UK's nuclear generation fleet since the 1980s.
The AGR was developed from the Magnox reactor, the UK's first-generation reactor design. The first Magnox reactors had been optimised for generating plutonium, and for this reason it incorporated a number of features that are not necessarily the best for economic performance. Primary among these requirements was the Magnox's ability to run on natural uranium, which demanded the use of a coolant with a low neutron cross section, in this case CO2, and efficient neutron moderator, graphite. Magnox also ran relatively cool compared to other power-producing designs, which made it less efficient extracting power from the reactor core.
The AGR retained the Magnox's graphite moderator and CO2 coolant but increased its operating temperature to improve efficiency when converted to steam. The steam it produced was deliberately identical to that from a coal fired plant, allowing the same turbines and generation equipment to be used. During the initial design stages the system was forced to switch the tubing enclosing the fuel pellets from beryllium to stainless steel. Steel has a higher cross section and this change demanded the switch to enriched uranium fuel to maintain criticality. As part of this change, the new design had higher burnup of 18,000 MWt-days per tonne of fuel, requiring less frequent refuelling.
The first prototype AGR became operational in 1962, but the first commercial AGR did not come online until 1976. A total of fourteen AGR reactors at six sites were built between 1976 and 1988. All of these are configured with two reactors in a single building. Each reactor has a design thermal power output of 1,500 MWt driving a 660 MWe turbine-alternator set. The various AGR stations produce outputs in the range 555 MWe to 670 MWe though some run at lower than design output due to operational restrictions.Berkeley Nuclear Power Station
Berkeley nuclear power station is a disused Magnox power station situated on the bank of the River Severn in Gloucestershire, England.Bradwell nuclear power station
Bradwell nuclear power station is a partially decommissioned Magnox power station located on the Dengie peninsula at the mouth of the River Blackwater, Essex.
As of 2016, China General Nuclear Power Group and China National Nuclear Corporation are considering Bradwell for the site of a new nuclear power station.Chapelcross nuclear power station
Chapelcross was a Magnox nuclear power plant near Annan in Dumfries and Galloway in southwest Scotland, in operation from 1959 to 2004. It was the sister plant to the Calder Hall plant in Cumbria, England; both were commissioned and originally operated by the United Kingdom Atomic Energy Authority.
The primary purpose of both plants was to produce weapons-grade plutonium for the UK's nuclear weapons programme, but they also generated electrical power for the National Grid.Eastwood v Magnox Electric plc
Eastwood v Magnox Electric plc  UKHL 35 is a UK labour law case concerning damages for wrongful dismissal, which were held to not be limited if a breach of contract occurs during the performance of the contract, rather than at the point of termination.Gas-cooled reactor
A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and carbon dioxide 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.
The GCR 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.Hinkley Point A nuclear power station
Hinkley Point A nuclear power station is a decommissioned Magnox Nuclear power station located on a 19.4-hectare (48-acre) site in Somerset on the Bristol Channel coast, 5 miles (8 km) west of the River Parrett estuary.Hunterston A nuclear power station
Hunterston A nuclear power station was a Magnox power station located at Hunterston in Ayrshire, Scotland, adjacent to Hunterston B and is currently being decommissioned.List of nuclear reactors
This is a list of all the commercial nuclear reactors in the world, sorted by country, with operational status. The list only includes civilian nuclear power reactors used to generate electricity for a power grid. All commercial nuclear reactors use nuclear fission. As of April 2018, there are 449 operable power reactors in the world, with a combined electrical capacity of 394 GW. Additionally, there are 58 reactors under construction and 154 reactors planned, with a combined capacity of 63 GW and 157 GW, respectively.
Over 300 more reactors are proposed. For non-power reactors, see List of nuclear research reactors. Where not otherwise specified, all information is sourced from the Power Reactor Information System (PRIS) of the International Atomic Energy Agency (IAEA).Magnox (alloy)
Magnox is an alloy—mainly of magnesium with small amounts of aluminium and other metals—used in cladding unenriched uranium metal fuel with a non-oxidising covering to contain fission products in nuclear reactors.
Magnox is short for Magnesium non-oxidising.
This material has the advantage of a low neutron capture cross section, but has two major disadvantages:
It limits the maximum temperature (to about 415Celsius), and hence the thermal efficiency, of the plant.
It reacts with water, preventing long-term storage of spent fuel under water in spent fuel pools.The magnox alloy Al80 has a composition of 0.8% aluminium and 0.004% beryllium.Magnox Ltd
Magnox Ltd is a nuclear decommissioning Site Licence Company (SLC) controlled by Cavendish Fluor Partnership, its designated Parent Body Organisation (PBO). It operates under contract for the Nuclear Decommissioning Authority (NDA), a government body set up specifically to deal with the nuclear legacy under the Energy Act 2004.
Magnox Ltd is responsible for the decommissioning of ten Magnox nuclear power stations and two former research facilities in the United Kingdom. The twelve sites are Berkeley, Bradwell, Chapelcross, Dungeness A, Hinkley Point A, Hunterston A, Oldbury, Sizewell A, Trawsfynydd, Wylfa Harwell and Winfrith. All the sites have ceased production. In addition, as part of the Trawsfynydd unit, Magnox Ltd operates a hydro-electric power station at Maentwrog.
The only Magnox power station in the UK not managed by Magnox Ltd is Calder Hall, which is part of the Sellafield site and is controlled by another SLC, Sellafield Ltd.
In September 2019 Magnox Ltd will become a subsidiary of the NDA.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 of Trade and Industry. It came into existence during late 2004, and took on its main functions on 1 April 2005. Its purpose is to deliver the decommissioning and clean-up of the UK’s civil nuclear legacy in a safe and cost-effective manner, and where possible to accelerate programmes of work that reduce hazard. The NDA does not directly manage the UK's nuclear sites. It oversees the work through contracts with specially designed companies known as Site Licence Companies. The NDA determines the overall strategy and priorities for managing decommissioning.
Although the NDA itself employs only 300 staff, its annual budget is £3.2 billion. The vast majority of the NDA budget is spent through contracts with Site Licence Companies, who also sub contract to other companies which provide special services. The NDA aims to do this by introducing innovation and contractor expertise through a series of competitions similar to the model that has been used in the United States.
In April 2017, the NDA lost a legal case in the Supreme Court regarding the procurement of a sizeable contract for the decommissioning of 12 different Magnox nuclear facilities when EnergySolutions EU Ltd. (now called ATK Energy EU Ltd.) challenged a decision in connection with ATK’s unsuccessful bid. In February 2018 the UK parliament's Public Accounts Committee (PAC) concluded that the NDA had "dramatically under-estimated" costs and "completely failed" in the procurement and management of the Magnox Ltd contract, which was one of the highest value contracts let by the government. An independent inquiry into the deal was set up.Oldbury Nuclear Power Station
Oldbury nuclear power station is a decommissioned nuclear power station located on the south bank of the River Severn close to the village of Oldbury-on-Severn in South Gloucestershire, England. It was operated by Magnox Limited on behalf of the Nuclear Decommissioning Authority (NDA). Oldbury is one of four stations located close to the mouth of the River Severn and the Bristol Channel, the others being Berkeley, Hinkley Point A, and Hinkley Point B.Scottish Nuclear
Scottish Nuclear was formed as a precursor to the privatization of the Electricity Supply Industry in Scotland on 1 April 1990. A purpose-built headquarters was built in 1992 in the new town of East Kilbride.
It consisted of the nuclear assets of the South of Scotland Electricity Board, which were later absorbed into the 1996 founded companies - Magnox Electric and British Energy.Sellafield
Sellafield is a nuclear fuel reprocessing and nuclear decommissioning site, close to the village of Seascale on the coast of the Irish Sea in Cumbria, England. The site is served by Sellafield railway station.
Sellafield incorporates the original nuclear reactor site at Windscale, which as of August 2019 is undergoing decommissioning and dismantling, and Calder Hall, a neighbour of Windscale, which is also undergoing decommissioning and dismantling of its four nuclear power generating reactors.
It is the site of the world's first nuclear power station to generate electricity on an industrial scale.Steam-generating heavy water reactor
Steam Generating Heavy Water Reactor (SGHWR) is a United Kingdom design for commercial nuclear reactors. It is similar to the Canadian CANDU reactor designs in that it uses a low-pressure reactor vessel containing high-pressure piping for the coolant, which reduces construction costs and complexity.
SGHWR was a heavy water moderated reactor, which used ordinary (light) water as coolant, in contrast with earlier UK designs that used graphite moderators which led to very large reactor sizes. Unlike CANDU, the SGHWR uses slightly enriched uranium fuel, which allows for higher burnup and more economical fuel cycles. The modern CANDU ACR-1000 reactor design uses a similar concept, as does the Italian CIRENE, hosted at Latina Nuclear Power Plant.
Only a single SGHWR was ever built, the small 100 MW prototype reactor at Winfrith, often known simply as the "Winfrith Reactor". It was connected to the grid in 1967 and ceased operation in 1990 after 23 successful years.  It was owned by the United Kingdom Atomic Energy Authority. Decommissioning is now being carried out by Magnox Ltd on behalf of the Nuclear Decommissioning Authority.
A similar design was the Gentilly Nuclear Generating Station in Quebec, but this was not successful and shut down after a short lifetime.Trawsfynydd nuclear power station
Trawsfynydd nuclear power station (Welsh: Atomfa Trawsfynydd) is a former Magnox power station situated in Snowdonia National Park in Gwynedd, Wales. The plant, which became operational in 1965, was the only nuclear power station in the UK to be built inland, with cooling water that was taken from the man-made Llyn Trawsfynydd reservoir. It was closed in 1991. Work to completely decommission the site is expected to take almost 100 years.UNGG reactor
The UNGG (Uranium Naturel Graphite Gaz) is an obsolete nuclear power reactor design developed in France. It was graphite moderated, cooled by carbon dioxide, and fueled with natural uranium metal. The first generation of French nuclear power stations were UNGGs, as was Vandellos unit 1 in Spain. Of ten units built, all were shut down by end 1994, most for economic reasons due to staffing costs.
The UNGG and the Magnox are the two main types of gas cooled reactor (GCR). A UNGG reactor is often referred to simply as a GCR in English documents, or sometimes loosely as a Magnox. It was developed independently of and in parallel to the British Magnox design, and to meet similar requirements of simultaneous production of electric power and plutonium. The first UNGG reactors at Marcoule used horizontal fuel channels and a concrete containment structure. Chinon A1 used vertical fuel channels, as did the British Magnox reactors, and a steel pressure-vessel.The fuel cladding material was magnesium-zirconium alloy in the UNGG, as opposed to magnesium-aluminium in Magnox. As both claddings react with water, they can be stored in a spent fuel pool for short times only, making short-term reprocessing of the fuel essential, and requiring heavily shielded facilities for this.
The programme was a succession of units, with changes to the design increasing power output. In the experimental phase they were built by the Commissariat à l'Énergie Atomique (CEA), and later by Électricité de France (EDF). The largest UNGG reactor build was Bugey 1 with a net electrical output of 540 MW.Wylfa Nuclear Power Station
Wylfa Nuclear Power Station (Welsh: Atomfa'r Wylfa) is a former Magnox power station situated west of Cemaes Bay on the island of Anglesey, North Wales. Construction of the two 490 MW nuclear reactors, known as "Reactor 1" and "Reactor 2", began in 1963. They became operational in 1971. Wylfa was located on the coast because seawater was used as a coolant.
In 2012, Reactor 2 was shut down. Three years later, Reactor 1 was switched off on 30 December 2015 so ending 44 years of operation at the site.
Wylfa Newydd (literally New Wylfa) is a proposed new nuclear station on a site adjacent to the old plant. An application to build two advanced boiling water reactors was submitted by Horizon Nuclear Power to the Office of Nuclear Regulation on 4 April 2017.
Types of nuclear fission reactor