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71-677: The site formerly operated two separate prototype nuclear reactors , trialling five different types of submarine reactor core . The site is located adjacent to the Dounreay civil nuclear site. When operational, the site housed and operated the prototype nuclear propulsion plants of the type operated by the Royal Navy in its submarine fleet. Originally it was known as the Admiralty Reactor Test Establishment (ARTE). For over 40   years Vulcan has been

142-498: A neutron , it splits into lighter nuclei, releasing energy, gamma radiation , and free neutrons, which can induce further fission in a self-sustaining chain reaction . The process is carefully controlled using control rods and neutron moderators to regulate the number of neutrons that continue the reaction, ensuring the reactor operates safely, although inherent control by means of delayed neutrons also plays an important role in reactor output control. The efficiency of nuclear fuel

213-479: 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,

284-558: 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

355-444: A cost of £270   million, before similar problems might arise on the submarines. This was not revealed to the public until 2014. Nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction . Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion . When a fissile nucleus like uranium-235 or plutonium-239 absorbs

426-441: 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

497-445: 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

568-442: 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

639-428: A large tamper . The nominal spherical critical mass for an untampered U nuclear weapon is 56 kilograms (123 lb), which would form a sphere 17.32 centimetres (6.82 in) in diameter. The material must be 85% or more of U and is known as weapons grade uranium, though for a crude and inefficient weapon 20% enrichment is sufficient (called weapon(s)-usable ). Even lower enrichment can be used, but this results in

710-424: 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

781-406: A minority (about 15%) result in the formation of uranium-236 . The fission of one atom of uranium-235 releases 202.5 MeV ( 3.24 × 10  J ) inside the reactor. That corresponds to 19.54 TJ/ mol , or 83.14 TJ/kg. Another 8.8 MeV escapes the reactor as anti-neutrinos. When 92 U nuclei are bombarded with neutrons, one of the many fission reactions that it can undergo

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852-570: 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

923-465: 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

994-773: 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

1065-407: 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

1136-471: 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

1207-529: 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

1278-453: Is fissile , i.e., it can sustain a nuclear chain reaction . It is the only fissile isotope that exists in nature as a primordial nuclide . Uranium-235 has a half-life of 703.8 million years. It was discovered in 1935 by Arthur Jeffrey Dempster . Its fission cross section for slow thermal neutrons is about 584.3 ± 1 barns . For fast neutrons it is on the order of 1 barn. Most neutron absorptions induce fission, though

1349-402: Is adjusted by the location of control rods containing elements that strongly absorb neutrons, e.g., boron , cadmium , or hafnium , in the reactor core. In nuclear bombs , the reaction is uncontrolled and the large amount of energy released creates a nuclear explosion . The Little Boy gun-type atomic bomb dropped on Hiroshima on August 6, 1945, was made of highly enriched uranium with

1420-413: 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

1491-428: 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

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1562-405: 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

1633-632: Is much higher than fossil fuels; the 5% enriched uranium used in the newest reactors has an energy density 120,000 times higher than coal. 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

1704-401: 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

1775-448: 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

1846-416: 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

1917-483: Is sometimes used in the reactors of nuclear submarines , research reactors and nuclear weapons . If at least one neutron from uranium-235 fission strikes another nucleus and causes it to fission, then the chain reaction will continue. If the reaction continues to sustain itself, it is said to be critical , and the mass of U required to produce the critical condition is said to be a critical mass. A critical chain reaction can be achieved at low concentrations of U if

1988-443: Is the following (shown in the adjacent image): Heavy water reactors and some graphite moderated reactors can use natural uranium, but light water reactors must use low enriched uranium because of the higher neutron absorption of light water. Uranium enrichment removes some of the uranium-238 and increases the proportion of uranium-235. Highly enriched uranium (HEU), which contains an even greater proportion of uranium-235,

2059-425: Is then converted into uranium dioxide powder, which is pressed and fired into pellet form. These pellets are stacked into tubes which are then sealed and called fuel rods . Many of these fuel rods are used in each nuclear reactor. Uranium-235 Uranium-235 ( U or U-235 ) is an isotope of uranium making up about 0.72% of natural uranium . Unlike the predominant isotope uranium-238 , it

2130-490: 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

2201-517: 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

Vulcan Naval Reactor Test Establishment - Misplaced Pages Continue

2272-524: 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

2343-477: 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

2414-402: 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

2485-580: 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

2556-736: 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

2627-535: 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

2698-569: 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

2769-795: 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

2840-458: 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

2911-467: 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

Vulcan Naval Reactor Test Establishment - Misplaced Pages Continue

2982-566: The cornerstone of the Royal Navy's nuclear propulsion programme, testing and proving the operation of five generations of reactor core. Its reactors have significantly led the operational submarine plants in terms of operation hours, proving systems, procedures and safety. The reactors were run at higher levels of intensity than those on submarines with the intention of discovering any system problems before they might be encountered on board submarines. Rolls-Royce , which designs and procures all

3053-688: 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,

3124-494: 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)

3195-642: 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

3266-3786: The fissile component of the primary stage; however, HEU (highly enriched uranium, in this case uranium that is 20% or more U) is frequently used in the secondary stage as an ignitor for the fusion fuel. U 92 235 → 7.038 × 10 8   y α Th 90 231 → 25.52   h β − Pa 91 231 → 3.276 × 10 4   y α Ac 89 227 { → 21.773   y 98.62 % β − Th 90 227 → 18.718   d α → 21.773   y 1.38 % α Fr 87 223 → 21.8   min β − } Ra 88 223 → 11.434   d α Rn 86 219 Rn 86 219 → 3.96   s α Po 84 215 { → 1.778   ms 99.99 % α Pb 82 211 → 36.1   min β − → 1.778   ms 2.3 × 10 − 4 % β − At 85 215 → 0.10   ms α } Bi 83 211 { → 2.13   min 99.73 % α Tl 81 207 → 4.77   min β − → 2.13   min 0.27 % β − Po 84 211 → 0.516   s α } Pb ( stable ) 82 207 {\displaystyle {\begin{array}{r}{\ce {^{235}_{92}U->[\alpha ][7.038\times 10^{8}\ {\ce {y}}]{^{231}_{90}Th}->[\beta ^{-}][25.52\ {\ce {h}}]{^{231}_{91}Pa}->[\alpha ][3.276\times 10^{4}\ {\ce {y}}]{^{227}_{89}Ac}}}{\begin{Bmatrix}{\ce {->[98.62\%\beta ^{-}][21.773\ {\ce {y}}]{^{227}_{90}Th}->[\alpha ][18.718\ {\ce {d}}]}}\\{\ce {->[1.38\%\alpha ][21.773\ {\ce {y}}]{^{223}_{87}Fr}->[\beta ^{-}][21.8\ {\ce {min}}]}}\end{Bmatrix}}{\ce {^{223}_{88}Ra->[\alpha ][11.434\ {\ce {d}}]{^{219}_{86}Rn}}}\\{\ce {^{219}_{86}Rn->[\alpha ][3.96\ {\ce {s}}]{^{215}_{84}Po}}}{\begin{Bmatrix}{\ce {->[99.99\%\alpha ][1.778\ {\ce {ms}}]{^{211}_{82}Pb}->[\beta ^{-}][36.1\ {\ce {min}}]}}\\{\ce {->[2.3\times 10^{-4}\%\beta ^{-}][1.778\ {\ce {ms}}]{^{215}_{85}At}->[\alpha ][0.10\ {\ce {ms}}]}}\end{Bmatrix}}{\ce {^{211}_{83}Bi}}{\begin{Bmatrix}{\ce {->[99.73\%\alpha ][2.13\ {\ce {min}}]{^{207}_{81}Tl}->[\beta ^{-}][4.77\ {\ce {min}}]}}\\{\ce {->[0.27\%\beta ^{-}][2.13\ {\ce {min}}]{^{211}_{84}Po}->[\alpha ][0.516\ {\ce {s}}]}}\end{Bmatrix}}{\ce {^{207}_{82}Pb_{(stable)}}}\end{array}}} Uranium-235 has many uses such as fuel for nuclear power plants and in nuclear weapons such as nuclear bombs . Some artificial satellites , such as

3337-407: 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

3408-529: 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

3479-424: 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

3550-447: 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,

3621-426: The neutrons from fission are moderated to lower their speed, since the probability for fission with slow neutrons is greater. A fission chain reaction produces intermediate mass fragments which are highly radioactive and produce further energy by their radioactive decay . Some of them produce neutrons, called delayed neutrons , which contribute to the fission chain reaction. The power output of nuclear reactors

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3692-449: 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,

3763-581: 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

3834-406: 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

3905-505: The plant was re-commissioned as LAIRD (Loss of Coolant Accident Investigation Rig Dounreay) a non-nuclear test rig, the only one of its kind in the world. LAIRD trials simulated loss of coolant accidents to prove the effectiveness of systems designed to protect the reactor in loss-of-coolant accidents. The second reactor, PWR2 , is housed in the Shore Test Facility (STF), was commissioned in 1987, and went critical with Core G

3976-463: 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

4047-572: 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

4118-657: The reactor plants for the Royal Navy from its Derby offices, operates Vulcan on behalf of the MoD and employs around 280 staff there, led by a small team of staff from the Royal Navy. Reactors developed include the PWR1 and PWR2 . In 2011, the MoD stated that NRTE could be scaled down or closed after 2015 when the current series of tests ends. Computer modelling and confidence in new reactor designs meant testing would no longer be necessary. The cost of decommissioning NRTE facilities when they become redundant, including nuclear waste disposal,

4189-416: 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

4260-437: 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":

4331-479: The removal of all fuel to the NDA Sellafield site. The first reactor, PWR1 , is known as Dounreay Submarine Prototype 1 (DSMP1). The reactor plant was recognised by the Royal Navy as one of Her Majesty's Submarines (HMS) and was commissioned as HMS Vulcan in 1963. It went critical in 1965. HMS Vulcan is a Rolls-Royce PWR 1 reactor plant and tested Cores A, B and Z before being shut down in 1984. In 1987,

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4402-462: The required critical mass rapidly increasing. Use of a large tamper, implosion geometries, trigger tubes, polonium triggers, tritium enhancement, and neutron reflectors can enable a more compact, economical weapon using one-fourth or less of the nominal critical mass, though this would likely only be possible in a country that already had extensive experience in engineering nuclear weapons. Most modern nuclear weapon designs use plutonium-239 as

4473-400: The same year. The plant was shut down in 1996, and work began to refit the plant with the current core, Core H, in February 1997. This work was completed in 2000 and after two years of safety justification the plant went critical in 2002. Vulcan Trials Operation and Maintenance (VTOM) (the programme under which Core H is tested) was completed and the reactor shut down on 21 July 2015. The reactor

4544-647: 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

4615-424: 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

4686-481: 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

4757-547: Was estimated at £2.1   billion in 2005. Its final reactor shut down on 21 July 2015, with post operational work continuing to 2022. In March 2020, it was reported that tenders were being issued to decontaminate and dismantle the reactor complex under a ten-year contract, ending in the creation of a "brownfield" site, which would be transferred to the Nuclear Decommissioning Authority . This decommissioning programme would start in 2023, following

4828-788: 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

4899-463: 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

4970-649: 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

5041-481: Was then to be de-fuelled and examined, and post-operational work was to continue to 2022; the site was then to be decommissioned along with facilities at neighbouring UKAEA Dounreay. In January 2012, radiation was detected in the reactor's coolant water, caused by a microscopic breach in fuel cladding. This discovery led to HMS  Vanguard being scheduled to be refuelled and contingency measures being applied to other Vanguard and Astute -class submarines , at

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