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110-545: The Magnox Reprocessing Plant is a former nuclear reprocessing facility at Sellafield in northern England, which operated from 1964 to 2022. The plant used PUREX chemistry (based on tributyl phosphate (TBP)) to extract plutonium and uranium from used nuclear fuel originating primarily from Magnox reactors. The plant was originally constructed and operated by the United Kingdom Atomic Energy Authority (UKAEA), but in 1971 control

220-479: A nuclear proliferation risk as they can be configured to produce plutonium , as well as tritium gas used in boosted fission weapons . Reactor spent fuel can be reprocessed to yield up to 25% more nuclear fuel, which can be used in reactors again. Reprocessing can also significantly reduce the volume of nuclear waste, and has been practiced in Europe, Russia, India and Japan. Due to concerns of proliferation risks,

330-558: A " neutron howitzer ") produced a barium residue, which they reasoned was created by fission of the uranium nuclei. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening the possibility of a nuclear chain reaction . Subsequent studies in early 1939 (one of them by Szilárd and Fermi), revealed that several neutrons were indeed released during fission, making available

440-403: 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 robotic core dismantling technique. The current approximately 100-year decommissioning plan

550-441: A crucial role in generating large amounts of electricity with low carbon emissions, contributing significantly to the global energy mix. Just as conventional thermal power stations generate electricity by harnessing the thermal energy released from burning fossil fuels , nuclear reactors convert the energy released by controlled nuclear fission into thermal energy for further conversion to mechanical or electrical forms. When

660-445: A gas or a liquid metal (like liquid sodium or lead) or molten salt – is circulated past the reactor core to absorb the heat that it generates. The heat is carried away from the reactor and is then used to generate steam. Most reactor systems employ a cooling system that is physically separated from the water that will be boiled to produce pressurized steam for the turbines , like the pressurized water reactor . However, in some reactors

770-433: 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

880-442: A large fissile atomic nucleus such as uranium-235 , uranium-233 , or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, (the fission products ), releasing kinetic energy , gamma radiation , and free neutrons . A portion of these neutrons may be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This

990-424: A less effective moderator. In other reactors, the coolant acts as a poison by absorbing neutrons in the same way that the control rods do. In these reactors, power output can be increased by heating the coolant, which makes it a less dense poison. Nuclear reactors generally have automatic and manual systems to scram the reactor in an emergency shut down. These systems insert large amounts of poison (often boron in

1100-445: 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

1210-465: A non-oxidising covering to contain fission products. Magnox is short for mag nesium n on- ox idising. 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,

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1320-570: A number of ways: A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 10 joules per kilogram of uranium-235 versus 2.4 × 10 joules per kilogram of coal). The fission of one kilogram of uranium-235 releases about 19 billion kilocalories , so the energy released by 1 kg of uranium-235 corresponds to that released by burning 2.7 million kg of coal. A nuclear reactor coolant – usually water but sometimes

1430-465: A patent on reactors on 19 December 1944. Its issuance was delayed for 10 years because of wartime secrecy. "World's first nuclear power plant" is the claim made by signs at the site of the EBR-I , which is now a museum near Arco, Idaho . Originally called "Chicago Pile-4", it was carried out under the direction of Walter Zinn for Argonne National Laboratory . This experimental LMFBR operated by

1540-773: A pile (hence the name) of graphite blocks, embedded in which was natural uranium oxide 'pseudospheres' or 'briquettes'. Soon after the Chicago Pile, the Metallurgical Laboratory developed a number of nuclear reactors for the Manhattan Project starting in 1943. The primary purpose for the largest reactors (located at the Hanford Site in Washington ), was the mass production of plutonium for nuclear weapons. Fermi and Szilard applied for

1650-407: A planned typical lifetime of 30–40 years, though many of those have received renovations and life extensions of 15–20 years. Some believe nuclear power plants can operate for as long as 80 years or longer with proper maintenance and management. While most components of a nuclear power plant, such as steam generators, are replaced when they reach the end of their useful lifetime, the overall lifetime of

1760-431: 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

1870-471: A reactor. One such process is delayed neutron emission by a number of neutron-rich fission isotopes. These delayed neutrons account for about 0.65% of the total neutrons produced in fission, with the remainder (termed " prompt neutrons ") released immediately upon fission. The fission products which produce delayed neutrons have half-lives for their decay by neutron emission that range from milliseconds to as long as several minutes, and so considerable time

1980-529: A set of theoretical nuclear reactor designs. These are generally not expected to be available for commercial use before 2040–2050, although the World Nuclear Association suggested that some might enter commercial operation before 2030. Current reactors in operation around the world are generally considered second- or third-generation systems, with the first-generation systems having been retired some time ago. Research into these reactor types

2090-437: 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,

2200-613: A violent reaction called a "blowback" occurred in the First Generation Plant which contaminated that plant and 34 workers with ruthenium -106. Following this event the First Generation Plant was permanently closed. Over its lifetime, the Magnox plant handled over 55,000 tons of spent fuel from the UK's fleet of 11 Magnox plants as well as reprocessing Magnox fuel from Italy, Japan, and fast breeder fuel from Dounreay . In total,

2310-457: 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 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

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2420-408: 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

2530-413: Is inserted deeper into the reactor, it absorbs more neutrons than the material it displaces – often the moderator. This action results in fewer neutrons available to cause fission and reduces the reactor's power output. Conversely, extracting the control rod will result in an increase in the rate of fission events and an increase in power. The physics of radioactive decay also affects neutron populations in

2640-428: Is known as a nuclear chain reaction . To control such a nuclear chain reaction, control rods containing neutron poisons and neutron moderators are able to change the portion of neutrons that will go on to cause more fission. Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if monitoring or instrumentation detects unsafe conditions. The reactor core generates heat in

2750-405: Is mined, processed, enriched, used, possibly reprocessed and disposed of is known as the nuclear fuel cycle . Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel. Enrichment involves increasing the percentage of U-235 and is usually done by means of gaseous diffusion or gas centrifuge . The enriched result

2860-401: Is produced. Fission also produces iodine-135 , which in turn decays (with a half-life of 6.57 hours) to new xenon-135. When the reactor is shut down, iodine-135 continues to decay to xenon-135, making restarting the reactor more difficult for a day or two, as the xenon-135 decays into cesium-135, which is not nearly as poisonous as xenon-135, with a half-life of 9.2 hours. This temporary state is

2970-448: Is reaching or crossing their design lifetimes of 30 or 40 years. In 2014, Greenpeace warned that the lifetime extension of ageing nuclear power plants amounts to entering a new era of risk. It estimated the current European nuclear liability coverage in average to be too low by a factor of between 100 and 1,000 to cover the likely costs, while at the same time, the likelihood of a serious accident happening in Europe continues to increase as

3080-416: Is required to determine exactly when a reactor reaches the critical point. Keeping the reactor in the zone of chain reactivity where delayed neutrons are necessary to achieve a critical mass state allows mechanical devices or human operators to control a chain reaction in "real time"; otherwise the time between achievement of criticality and nuclear meltdown as a result of an exponential power surge from

3190-414: 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

3300-491: 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,

3410-521: 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 (734 to 680 °F). The Nuclear Decommissioning Authority (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

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3520-490: The Manhattan Project . Eventually, the first artificial nuclear reactor, Chicago Pile-1 , was constructed at the University of Chicago , by a team led by Italian physicist Enrico Fermi, in late 1942. By this time, the program had been pressured for a year by U.S. entry into the war. The Chicago Pile achieved criticality on 2 December 1942 at 3:25 PM. The reactor support structure was made of wood, which supported

3630-517: The PWR , BWR and PHWR designs above, and some are more radical departures. The former include the advanced boiling water reactor (ABWR), two of which are now operating with others under construction, and the planned passively safe Economic Simplified Boiling Water Reactor (ESBWR) and AP1000 units (see Nuclear Power 2010 Program ). Rolls-Royce aims to sell nuclear reactors for the production of synfuel for aircraft. Generation IV reactors are

3740-524: The U.S. Atomic Energy Commission produced 0.8 kW in a test on 20 December 1951 and 100 kW (electrical) the following day, having a design output of 200 kW (electrical). Besides the military uses of nuclear reactors, there were political reasons to pursue civilian use of atomic energy. U.S. President Dwight Eisenhower made his famous Atoms for Peace speech to the UN General Assembly on 8 December 1953. This diplomacy led to

3850-453: 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 (1,200 °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

3960-477: The coolant also acts as a neutron moderator . A moderator increases the power of the reactor by causing the fast neutrons that are released from fission to lose energy and become thermal neutrons. Thermal neutrons are more likely than fast neutrons to cause fission. If the coolant is a moderator, then temperature changes can affect the density of the coolant/moderator and therefore change power output. A higher temperature coolant would be less dense, and therefore

4070-661: The heat exchanger for the CO 2 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

4180-578: 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 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

4290-402: The "iodine pit." If the reactor has sufficient extra reactivity capacity, it can be restarted. As the extra xenon-135 is transmuted to xenon-136, which is much less a neutron poison, within a few hours the reactor experiences a "xenon burnoff (power) transient". Control rods must be further inserted to replace the neutron absorption of the lost xenon-135. Failure to properly follow such a procedure

4400-580: The 1986 Chernobyl disaster and 2011 Fukushima disaster . As of 2022 , the International Atomic Energy Agency reported there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world. The US Department of Energy classes reactors into generations, with the majority of the global fleet being Generation II reactors constructed from the 1960s to 1990s, and Generation IV reactors currently in development. Reactors can also be grouped by

4510-434: The AGR programme as one of the two most costly British government-sponsored project errors, alongside Concorde . Source: 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

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4620-476: 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

4730-467: The U and Pu before further processing in other plants. The plant contributed the majority of liquid discharges from the Sellafield site; around 132 Terabecquerels (TBq) annually. In 2014 Sellafield Ltd celebrated 50 years of Magnox Reprocessing from 1964 to 2014. Called "50 not out" to highlight that the plant was not shutting down, the events related to this celebration spoke about the history of Magnox and Reprocessing as well as design choices that led to

4840-678: The U.S. military sought other uses for nuclear reactor technology. Research by the Army led to the power stations for Camp Century, Greenland and McMurdo Station, Antarctica Army Nuclear Power Program . The Air Force Nuclear Bomber project resulted in the Molten-Salt Reactor Experiment . The U.S. Navy succeeded when they steamed the USS Nautilus (SSN-571) on nuclear power 17 January 1955. The first commercial nuclear power station, Calder Hall in Sellafield , England

4950-742: The UK's magnox reactor sites (apart from Calder Hall) are operated by Magnox Ltd , 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 Magnox South sites In January 2011 Magnox North Ltd and Magnox South Ltd recombined as Magnox Ltd . Following procurement and management issues with

5060-535: The United States does not engage in or encourage reprocessing. Reactors are also used in nuclear propulsion of vehicles. Nuclear marine propulsion of ships and submarines is largely restricted to naval use. Reactors have also been tested for nuclear aircraft propulsion and spacecraft propulsion . Reactor safety is maintained through various systems that control the rate of fission. The insertion of control rods, which absorb neutrons, can rapidly decrease

5170-518: 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

5280-569: The area was contaminated, like Fukushima, Three Mile Island, Sellafield, and Chernobyl. The British branch of the French concern EDF Energy , for example, extended the operating lives of its Advanced Gas-cooled Reactors (AGR) with only between 3 and 10 years. All seven AGR plants were expected to be shut down in 2022 and in decommissioning by 2028. Hinkley Point B was extended from 40 to 46 years, and closed. The same happened with Hunterston B , also after 46 years. An increasing number of reactors

5390-473: The basis of the plant operation. The unit comprised a set of mixing compartments where the solvent and aqueous liquids mixed. The mix then passed to an associated settler compartment where the solvent separated from the aqueous and forms two separate layers. These then left the settler compartment to the next mixer compartments. The solvent and aqueous flowed in opposite directions through the mixer settler stages (typically 8 or more), controlled by careful design of

5500-795: The beginning of his quest to produce the Einstein-Szilárd letter to alert the U.S. government. Shortly after, Nazi Germany invaded Poland in 1939, starting World War II in Europe. The U.S. was not yet officially at war, but in October, when the Einstein-Szilárd letter was delivered to him, Roosevelt commented that the purpose of doing the research was to make sure "the Nazis don't blow us up." The U.S. nuclear project followed, although with some delay as there remained skepticism (some of it from Enrico Fermi ) and also little action from

5610-485: 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

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5720-414: 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) of 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

5830-458: The choices of coolant and moderator. Almost 90% of global nuclear energy comes from pressurized water reactors and boiling water reactors , which use water as a coolant and moderator. Other designs include heavy water reactors , gas-cooled reactors , and fast breeder reactors , variously optimizing efficiency, safety, and fuel type , enrichment , and burnup . Small modular reactors are also an area of current development. These reactors play

5940-450: The closure date of the facility to be pushed back as no fuel will be reprocessed in this time. Magnox fuel reprocessing ceased on 17 July 2022, when the reprocessing plant completed its last batch of fuel after 58 years of operation. A total of 55,000 tonnes of fuel had been processed during those years. Magnox Magnox is a type of nuclear power / production reactor that was designed to run on natural uranium with graphite as

6050-524: 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 ,

6160-467: The complexities of handling actinides , but significant scientific and technical obstacles remain. Despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. The ITER project is currently leading the effort to harness fusion power. Thermal reactors generally depend on refined and enriched uranium . Some nuclear reactors can operate with a mixture of plutonium and uranium (see MOX ). The process by which uranium ore

6270-652: The contract, Magnox Ltd will become a subsidiary of the NDA in September 2019. Nuclear reactor Nuclear reactors have their origins in the World War II Allied Manhattan Project . The world's first artificial nuclear reactor, Chicago Pile-1, achieved criticality on 2 December 1942. Early reactor designs sought to produce weapons-grade plutonium for fission bombs , later incorporating grid electricity production in addition. In 1957, Shippingport Atomic Power Station became

6380-487: 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. The magnox reactors were considered at

6490-492: The critical mixer settler stages where the U and Pu were transferred into the aqueous phase, and fission products remained in the solvent phase. Separation of the U and Pu was achieved by adding a reductant, which caused the Pu, but not the U, to transfer into the aqueous phase. Once separated, further removal of fission products was undertaken by more mixer settler units. The U and Pu streams were then passed to evaporators to concentrate

6600-486: 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

6710-475: 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)

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6820-688: The dissemination of reactor technology to U.S. institutions and worldwide. The first nuclear power plant built for civil purposes was the AM-1 Obninsk Nuclear Power Plant , launched on 27 June 1954 in the Soviet Union . It produced around 5 MW (electrical). It was built after the F-1 (nuclear reactor) which was the first reactor to go critical in Europe, and was also built by the Soviet Union. After World War II,

6930-628: 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 , continues to operate as of 2016 . 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

7040-494: The energy of the neutrons that sustain the fission chain reaction : In principle, fusion power could be produced by nuclear fusion of elements such as the deuterium isotope of hydrogen . While an ongoing rich research topic since at least the 1940s, no self-sustaining fusion reactor for any purpose has ever been built. Used by thermal reactors: In 2003, the French Commissariat à l'Énergie Atomique (CEA)

7150-426: 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 (CO 2 ) 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

7260-469: The first mixer settler system where fission products were separated from the uranium (U) and plutonium (Pu) by extraction of the U/Pu into the solvent phase comprising tri-butyl-phosphate in odourless kerosene. This had the effect of reducing the radiation levels in subsequent stages of the process and the resulting degradation of the solvents. The solvent stream of U, Pu and remaining fission products passed to

7370-642: The first reactor dedicated to peaceful use; in Russia, in 1954, the first small nuclear power reactor APS-1 OBNINSK reached criticality. Other countries followed suit. Heat from nuclear fission is passed to a working fluid coolant (water or gas), which in turn runs through turbines . In commercial reactors, turbines drive electrical generator shafts. The heat can also be used for district heating , and industrial applications including desalination and hydrogen production . Some reactors are used to produce isotopes for medical and industrial use. Reactors pose

7480-587: 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

7590-407: The fission process generates heat, some of which can be converted into usable energy. A common method of harnessing this thermal energy is to use it to boil water to produce pressurized steam which will then drive a steam turbine that turns an alternator and generates electricity. Modern nuclear power plants are typically designed for a lifetime of 60 years, while older reactors were built with

7700-427: 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 CO 2 . 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

7810-529: The form of boric acid ) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated. Most types of reactors are sensitive to a process variously known as xenon poisoning, or the iodine pit . The common fission product Xenon-135 produced in the fission process acts as a neutron poison that absorbs neutrons and therefore tends to shut the reactor down. Xenon-135 accumulation can be controlled by keeping power levels high enough to destroy it by neutron absorption as fast as it

7920-424: The fuel rods. This allows the reactor to be constructed with an excess of fissionable material, which is nevertheless made relatively safe early in the reactor's fuel burn cycle by the presence of the neutron-absorbing material which is later replaced by normally produced long-lived neutron poisons (far longer-lived than xenon-135) which gradually accumulate over the fuel load's operating life. The energy released in

8030-447: The idea of nuclear fission as a neutron source, since that process was not yet discovered. Szilárd's ideas for nuclear reactors using neutron-mediated nuclear chain reactions in light elements proved unworkable. Inspiration for a new type of reactor using uranium came from the discovery by Otto Hahn , Lise Meitner , and Fritz Strassmann in 1938 that bombardment of uranium with neutrons (provided by an alpha-on-beryllium fusion reaction,

8140-537: 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

8250-423: 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 (called mag nesium n on- ox idising), 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

8360-434: The more common commercial light-water reactor which requires slightly enriched uranium . Graphite oxidizes readily in air, so the core is cooled with CO 2 , 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

8470-414: 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,

8580-442: 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 has been debate about whether

8690-459: 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

8800-449: The normal nuclear chain reaction, would be too short to allow for intervention. This last stage, where delayed neutrons are no longer required to maintain criticality, is known as the prompt critical point. There is a scale for describing criticality in numerical form, in which bare criticality is known as zero dollars and the prompt critical point is one dollar , and other points in the process interpolated in cents. In some reactors,

8910-581: The opportunity for the nuclear chain reaction that Szilárd had envisioned six years previously. On 2 August 1939, Albert Einstein signed a letter to President Franklin D. Roosevelt (written by Szilárd) suggesting that the discovery of uranium's fission could lead to the development of "extremely powerful bombs of a new type", giving impetus to the study of reactors and fission. Szilárd and Einstein knew each other well and had worked together years previously, but Einstein had never thought about this possibility for nuclear energy until Szilard reported it to him, at

9020-406: The physics of radioactive decay and are simply accounted for during the reactor's operation, while others are mechanisms engineered into the reactor design for a distinct purpose. The fastest method for adjusting levels of fission-inducing neutrons in a reactor is via movement of the control rods . Control rods are made of so-called neutron poisons and therefore absorb neutrons. When a control rod

9130-465: The plant has returned over 15,000 tons of uranium back into the fuel cycle. As of 2019, all Magnox reactors have now been retired from operation and defueled, with the last load of burnt-up Magnox fuel arrived at Sellafield in 2019. B205 ceased operations on 17 July 2022, when it was announced that it had worked through the remaining spent Magnox fuel stockpiles. Thus completing its mission which spanned nearly 6 decades. The process used mixer settlers as

9240-463: The power plant is limited by the life of components that cannot be replaced when aged by wear and neutron embrittlement , such as the reactor pressure vessel. At the end of their planned life span, plants may get an extension of the operating license for some 20 years and in the US even a "subsequent license renewal" (SLR) for an additional 20 years. Even when a license is extended, it does not guarantee

9350-442: The primary operational aim, magnox reactors were never capable of competing with the higher efficiency and higher fuel burnup of pressurised water reactors . 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

9460-429: 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

9570-572: The reactor fleet grows older. The neutron was discovered in 1932 by British physicist James Chadwick . The concept of a nuclear chain reaction brought about by nuclear reactions mediated by neutrons was first realized shortly thereafter, by Hungarian scientist Leó Szilárd , in 1933. He filed a patent for his idea of a simple reactor the following year while working at the Admiralty in London, England. However, Szilárd's idea did not incorporate

9680-422: 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

9790-416: The reactor will continue to operate, particularly in the face of safety concerns or incident. Many reactors are closed long before their license or design life expired and are decommissioned . The costs for replacements or improvements required for continued safe operation may be so high that they are not cost-effective. Or they may be shut down due to technical failure. Other ones have been shut down because

9900-437: The reactor's output, while other systems automatically shut down the reactor in the event of unsafe conditions. The buildup of neutron-absorbing fission products like xenon-135 can influence reactor behavior, requiring careful management to prevent issues such as the iodine pit , which can complicate reactor restarts. There have been two reactor accidents classed as an International Nuclear Event Scale Level 7 "major accident":

10010-454: 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

10120-530: 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

10230-410: 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

10340-422: 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

10450-599: The small number of officials in the government who were initially charged with moving the project forward. The following year, the U.S. Government received the Frisch–Peierls memorandum from the UK, which stated that the amount of uranium needed for a chain reaction was far lower than had previously been thought. The memorandum was a product of the MAUD Committee , which was working on the UK atomic bomb project, known as Tube Alloys , later to be subsumed within

10560-408: 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 (2.4 km), 10,000 within 5 miles (8.0 km) and 100,000 within 10 miles (16 km). In addition population around

10670-411: 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

10780-487: 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

10890-473: The transfer ports between the settler stages. The task to extract usable uranium and plutonium began with a process known as "decanning" where the magnesium fuel can was separated from the inner uranium rod. The uranium rod was then sheared and dropped into a hot nitric acid solution within the Dissolver Cell. The aqueous stream was conditioned to the correct temperature and acidity and then passed to

11000-531: The use of magnesium cladding and overall information about the Magnox Operating Programme. In 2020 due to coronavirus, Sellafield Ltd announced that the Magnox reprocessing plant will undergo a controlled shutdown to ensure less maintenance when it is eventually restarted. Whereas turning the facility off quickly in a response to reduced staff members on-site has a possibility to result in unnecessary maintenance or repair work. This will cause

11110-424: The water for the steam turbines is boiled directly by the reactor core ; for example the boiling water reactor . The rate of fission reactions within a reactor core can be adjusted by controlling the quantity of neutrons that are able to induce further fission events. Nuclear reactors typically employ several methods of neutron control to adjust the reactor's power output. Some of these methods arise naturally from

11220-642: The world's first commercial nuclear power station, while the last in Britain to shut down was Reactor 1 in Wylfa (on Anglesey ) 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

11330-425: Was a key step in the Chernobyl disaster . Reactors used in nuclear marine propulsion (especially nuclear submarines ) often cannot be run at continuous power around the clock in the same way that land-based power reactors are normally run, and in addition often need to have a very long core life without refueling . For this reason many designs use highly enriched uranium but incorporate burnable neutron poison in

11440-460: 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 ,

11550-788: Was officially started by the Generation ;IV International Forum (GIF) based on eight technology goals. The primary goals being to improve nuclear safety, improve proliferation resistance, minimize waste and natural resource utilization, and to decrease the cost to build and run such plants. Generation V reactors are designs which are theoretically possible, but which are not being actively considered or researched at present. Though some generation V reactors could potentially be built with current or near term technology, they trigger little interest for reasons of economics, practicality, or safety. Controlled nuclear fusion could in principle be used in fusion power plants to produce power without

11660-463: Was opened in 1956 with an initial capacity of 50 MW (later 200 MW). The first portable nuclear reactor "Alco PM-2A" was used to generate electrical power (2 MW) for Camp Century from 1960 to 1963. All commercial power reactors are based on nuclear fission . They generally use uranium and its product plutonium as nuclear fuel , though a thorium fuel cycle is also possible. Fission reactors can be divided roughly into two classes, depending on

11770-511: 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

11880-649: Was the first to refer to "Gen II" types in Nucleonics Week . The first mention of "Gen III" was in 2000, in conjunction with the launch of the Generation IV International Forum (GIF) plans. "Gen IV" was named in 2000, by the United States Department of Energy (DOE), for developing new plant types. More than a dozen advanced reactor designs are in various stages of development. Some are evolutionary from

11990-454: 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,

12100-493: Was transferred to British Nuclear Fuels Limited (BNFL). From 2005 the plant was operated by Sellafield Ltd. The plant was commissioned in 1964 as both a replacement for the UK's First Generation Reprocessing Plant, and to process spent fuel from the national fleet of Magnox reactors. The First generation Plant was then converted into a pre-handling plant for Magnox reprocessing and was recommissioned in 1969. In 1973, after both plants had been shut down for one year for maintenance,

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