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151-735: The AGR was developed from the Magnox reactor, the UK's first-generation reactor design. The first Magnox design had been optimised for generating plutonium , and for this reason it had features that were not the most economic for power generation. Primary among these was the requirement to run on natural uranium , which required a coolant with a low neutron cross section , in this case carbon dioxide , and an efficient neutron moderator , graphite . The Magnox design also ran relatively cool gas temperatures compared to other power-producing designs, which resulted in less efficient steam conditions. The AGR design retained

302-447: 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

453-403: 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

604-586: A 300 MW e SMR version of the CANDU, the CANDU SMR , which it began to highlight on its website. In 2020, the CANDU SMR was not selected for further design work for a Canadian demonstration project. SNC-Lavalin is still looking at marketing a 300 MW SMR in part due to projected demand due to climate change mitigation . The basic operation of the CANDU design is similar to other nuclear reactors. Fission reactions in

755-544: A CANDU plant therefore includes monitoring tritium in the surrounding environment (and publishing the results). In some CANDU reactors the tritium is periodically extracted. Typical emissions from CANDU plants in Canada are less than 1% of the national regulatory limit, which is based on International Commission on Radiological Protection (ICRP) guidelines (for example, the maximal permitted drinking-water concentration for tritium in Canada, 7,000  Bq /L, corresponds to 1/10 of

906-508: A CANDU-6 reactor, began operating in 1983. Following statements from the in-coming Parti Québécois government in September 2012 that Gentilly would close, the operator, Hydro-Québec , decided to cancel a previously announced refurbishment of the plant and announced its shutdown at the end of 2012, citing economic reasons for the decision. The company has started a 50-year decommissioning process estimated to cost $ 1.8 billion. In parallel with

1057-496: 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

1208-401: A defect was found by a regular inspection in one of the eight pod boilers of Heysham reactor A1. The reactor resumed operation at a lower output level with this pod boiler disabled, until June 2014 when more detailed inspections confirmed a crack in the boiler spine. As a precaution Heysham A2 and the sister Hartlepool station were also closed down for an eight weeks' inspection. In October 2014

1359-736: A fusion reactor and so dozens of kilograms being required for a fleet. Between 1.5 to 2.1 kilograms (3.3 to 4.6 lb) of tritium were recovered annually at the Darlington separation facility by 2003, of which a minor fraction was sold. Consequently, the Canadian Nuclear Laboratories in 2024 announced a decades-long program to refurbish existing CANDU plants and equip them with tritium breeding facilities. The 1998 Operation Shakti test series in India included one bomb of about 45 kilotons of TNT (190 TJ) yield that India has publicly claimed

1510-482: A higher neutron cross section and this change required the use of enriched uranium fuel to compensate. This change resulted in a higher burnup of 18,000 MW t -days per tonne of fuel, enabling less frequent refuelling. The prototype AGR became operational at Windscale in 1962, but the first commercial AGR did not come on-line 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

1661-425: A larger moderator-to-fuel ratio and a larger core for the same power output. Although a calandria-based core is cheaper to build, its size increases the cost for standard features like the containment building . Generally nuclear plant construction and operations are ≈65% of overall lifetime cost; for CANDU, costs are dominated by construction even more. Fueling CANDU is cheaper than other reactors, costing only ≈10% of

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1812-1024: A level 2 incident on the International Nuclear Event Scale . As of August 2022, there are four nuclear generating stations each with two operating AGRs in the United Kingdom, all of which are owned and operated by EDF Energy : In 2005 British Energy announced a 10-year life extension at Dungeness B, that would see the station continue operating until 2018, and in 2007 announced a 5-year life extension of Hinkley Point B and Hunterston B until 2016. Life extensions at other AGRs will be considered at least three years before their scheduled closure dates. From 2006 Hinkley Point B and Hunterston B have been restricted to about 70% of normal MWe output because of boiler-related problems requiring that they operate at reduced boiler temperatures. In 2013 these two stations' power increased to about 80% of normal output following some plant modifications. In 2006 AGRs made

1963-599: A lower concentration of fissile atoms than light-water reactors, allowing it to use some alternative fuels; for example, " recovered uranium " (RU) from used LWR fuel. CANDU was designed for natural uranium with only 0.7%  U, so reprocessed uranium with 0.9%  U is a comparatively rich fuel. This extracts a further 30–40% energy from the uranium. The Qinshan CANDU reactor in China has used recovered uranium. The DUPIC ( Direct Use of spent PWR fuel in CANDU ) process under development can recycle it even without reprocessing. The fuel

2114-455: 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 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

2265-457: A modified and 'debugged' Hinkley design with much greater seismic margin, and have proved to be the most successful performers of the fleet. Former Treasury Economic Advisor, David Henderson , described the AGR programme as one of the two most costly British government-sponsored project errors, the other being Concorde . When the government started on privatising the electricity generation industry in

2416-523: A nearby source, such as a lake, river, or ocean. Newer CANDU plants, such as the Darlington Nuclear Generating Station near Toronto , Ontario, use a diffuser to spread the warm outlet water over a larger volume and limit the effects on the environment. Although all CANDU plants to date have used open-cycle cooling, modern CANDU designs are capable of using cooling towers instead. Where the CANDU design differs from most other designs

2567-445: 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

2718-457: A new kind of crack in the graphite moderator bricks was found at the Hunterston B reactor. This keyway root crack has been previously theorised but not observed. The existence of this type of crack does not immediately affect the safety of a reactor – however if the number of cracks exceed a threshold the reactor would be decommissioned, as the cracks cannot be repaired. In January 2015 Dungeness B

2869-465: 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,

3020-576: A number of imposed construction delays led to roughly a doubling of the cost of the Darlington Nuclear Generating Station near Toronto, Ontario. Technical problems and redesigns added about another billion to the resulting $ 14.4 billion price. In contrast, in 2002 two CANDU 6 reactors at Qinshan in China were completed on-schedule and on-budget, an achievement attributed to tight control over scope and schedule. In terms of safeguards against nuclear weapons proliferation , CANDUs meet

3171-481: A partnership between Atomic Energy of Canada Limited (AECL), the Hydro-Electric Power Commission of Ontario , Canadian General Electric , and other companies. There have been two major types of CANDU reactors, the original design of around 500  MW e that was intended to be used in multi-reactor installations in large plants, and the rationalized CANDU 6 in the 600 MW e class that

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3322-525: A partnership with China National Nuclear Corporation . SNC Lavalin, the successor to AECL, is pursuing new CANDU 6 reactor sales in Argentina (Atucha 3), as well as China and Britain. Sales effort for the ACR reactor has ended. In 2017, a consultation with industry led Natural Resources Canada to establish a "SMR Roadmap" targeting the development of small modular reactors (SMRs). In response, SNC-Lavalin developed

3473-402: A pressure tube. The newer CANFLEX bundle has 43 fuel elements, with two element sizes (so the power rating can be increased without melting the hottest fuel elements). It is about 10 centimetres (3.9 in) in diameter, 0.5 metres (20 in) long, weighs about 20 kilograms (44 lb), and is intended to eventually replace the 37-element bundle. To allow the neutrons to flow freely between

3624-431: 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

3775-421: A response from the rest of the reactor, allowing various negative feedbacks to stabilize the reaction. On the other hand, the fission neutrons are thoroughly slowed down before they reach another fuel rod, meaning that it takes neutrons a longer time to get from one part of the reactor to the other. Thus if the chain reaction accelerates in one section of the reactor, the change will propagate itself only slowly to

3926-447: A similar generation. The light-water designs spent, on average, about half the time being refueled or maintained. Since the 1980s, dramatic improvements in LWR outage management have narrowed the gap, with several units achieving capacity factors ~90% and higher, with an overall US fleet performance of 92% in 2010. The latest-generation CANDU 6 reactors have an 88–90% CF, but overall performance

4077-531: A similar level of international certification as other reactors. The plutonium for India's first nuclear detonation, Operation Smiling Buddha in 1974, was produced in a CIRUS reactor supplied by Canada and partially paid for by the Canadian government using heavy water supplied by the United States. In addition to its two PHWR reactors, India has some safeguarded pressurised heavy-water reactors (PHWRs) based on

4228-442: A single building, and each reactor has a design thermal power output of 1,500 MW t driving a 660 MW e 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. The AGR was designed such that the final steam conditions at the boiler stop valve were identical to that of conventional coal-fired power stations , thus

4379-524: A statement confirming that cracking of graphite bricks is a known symptom of extensive neutron bombardment and that they were working on a solution to the monitoring problem. Also, they stated that the reactors were examined every three years as part of "statutory outages". On 17 December 2010, EDF Energy announced a 5-year life extension for both Heysham 1 and Hartlepool to enable further generation until 2019. In February 2012 EDF announced it expected 7-year life extensions on average across all AGRs, including

4530-437: 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,

4681-469: A unit of a coolant is a function of the temperature; by pressurizing the core, the water can be heated to much greater temperatures before boiling , thereby removing more heat and allowing the core to be smaller and more efficient. Building a pressure vessel of the required size is a significant challenge, and at the time of the CANDU's design, Canada's heavy industry lacked the requisite experience and capability to cast and machine reactor pressure vessels of

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4832-401: A variety of major subcontractors. In consequence the first three CEGB stations, whilst sharing the same design concept and the same fuel pin design, were completely different in detail design. This also resulted in the three consortia having to compete for the same limited number of expert staff, the need for each design to have a unique (and very complex) safety case, and the need to support for

4983-440: A very large pressure vessel would be needed. The low U density in natural uranium also implies that less of the fuel will be consumed before the fission rate drops too low to sustain criticality, because the ratio of U to fission products + U is lower. In CANDU most of the moderator is at lower temperatures than in other designs, reducing the spread of speeds and the overall speed of the moderator particles. This means that most of

5134-427: A wide range of fuels other than enriched uranium, e.g., natural uranium, reprocessed uranium, thorium , plutonium , and used LWR fuel. Given the expense of enrichment, this can make fuel much cheaper. There is an initial investment into the tonnes of 99.75% pure heavy water to fill the core and heat-transfer system. In the case of the Darlington plant, costs released as part of a freedom of information act request put

5285-464: A year or two later, proved to be significantly better than the Dungeness design, and indeed were commissioned ahead of Dungeness. The next AGR design, built at Heysham 1 and Hartlepool, sought to reduce overall cost of design by reducing the footprint of the station and the number of ancillary systems. However this led to difficulties in construction. The final two AGRs at Torness and Heysham 2 returned to

5436-430: Is 10–12 days. Tritium is generated in the fuel of all reactors; CANDU reactors generate tritium also in their coolant and moderator, due to neutron capture in heavy hydrogen. Some of this tritium escapes into containment and is generally recovered; a small percentage (about 1%) escapes containment and is considered a routine radioactive emission (also higher than from an LWR of comparable size). Responsible operation of

5587-435: 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 (called mag nesium n on- ox idising), used to clad the fuel rods inside the reactor. Like most other generation I nuclear reactors ,

5738-613: Is also capable of creating tritium more efficiently by irradiation of lithium-6 in reactors. Tritium , H, is a radioactive isotope of hydrogen , with a half-life of 12.3 years. It is produced in small amounts in nature (about 4 kg per year globally) by cosmic ray interactions in the upper atmosphere. Tritium is considered a weak radionuclide because of its low-energy radioactive emissions ( beta particle energy up to 18.6 keV). The beta particles travel 6 mm in air and only penetrate skin up to 6 micrometers. The biological half-life of inhaled, ingested, or absorbed tritium

5889-451: 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

6040-442: Is carried out within the boiler tubes. This necessitates the use of ultra pure water to minimise the buildup of salts in the evaporator and subsequent corrosion problems. The AGR was intended to be a superior British alternative to American light water reactor designs. It was promoted as a development of the operationally (if not economically) successful Magnox design, and was chosen from a multitude of competing British alternatives -

6191-522: Is designed to be used in single stand-alone units or in small multi-unit plants. CANDU 6 units were built in Quebec and New Brunswick , as well as Pakistan, Argentina, South Korea, Romania, and China. A single example of a non-CANDU 6 design was sold to India. The multi-unit design was used only in Ontario , Canada, and grew in size and power as more units were installed in the province, reaching ~880 MW e in

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6342-473: Is dominated by the older Canadian units with CFs on the order of 80%. Refurbished units had historically demonstrated poor performance, on the order of 65%. This has since improved with the return of Bruce units A1 and A2 to operation, which have post-refurbishment (2013+) capacity factors of 90.78% and 90.38%, respectively. Some CANDU plants suffered from cost overruns during construction, often from external factors such as government action. For instance,

6493-417: Is in the details of the fissile core and the primary cooling loop. Natural uranium consists of a mix of mostly uranium-238 with small amounts of uranium-235 and trace amounts of other isotopes. Fission in these elements releases high-energy neutrons , which can cause other U atoms in the fuel to undergo fission as well. This process is much more effective when the neutron energies are much lower than what

6644-400: Is much less expensive as well. A further unique feature of heavy-water moderation is the greater stability of the chain reaction . This is due to the relatively low binding energy of the deuterium nucleus (2.2 MeV), leading to some energetic neutrons and especially gamma rays breaking the deuterium nuclei apart to produce extra neutrons. Both gammas produced directly by fission and by

6795-443: 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

6946-406: Is normally kept relatively cool. Heat generated by fission products would initially be at about 7% of full reactor power, which requires significant cooling. The CANDU designs have several emergency cooling systems, as well as having limited self-pumping capability through thermal means (the steam generator is well above the reactor). Even in the event of a catastrophic accident and core meltdown ,

7097-524: Is not attractive for weapons, but can be used as fuel (instead of being simply nuclear waste), while consuming weapons-grade plutonium eliminates a proliferation hazard. If the aim is explicitly to utilize plutonium or other actinides from spent fuel, then special inert-matrix fuels are proposed to do this more efficiently than MOX. Since they contain no uranium, these fuels do not breed any extra plutonium. The neutron economy of heavy-water moderation and precise control of on-line refueling allow CANDU to use

7248-408: Is not possible to keep the reaction going in natural uranium. CANDU replaces this "light" water with heavy water . Heavy water's extra neutron decreases its ability to absorb excess neutrons, resulting in a better neutron economy . This allows CANDU to run on unenriched natural uranium , or uranium mixed with a wide variety of other materials such as plutonium and thorium . This was a major goal of

7399-552: Is one of the many reasons for the cooler mass of moderator in the calandria, as even a serious steam incident in the core would not have a major impact on the overall moderation cycle. Only if the moderator itself starts to boil would there be any significant effect, and the large thermal mass ensures that this will occur slowly. The deliberately "sluggish" response of the fission process in CANDU allows controllers more time to diagnose and deal with problems. The fuel channels can only maintain criticality if they are mechanically sound. If

7550-519: Is sintered in air (oxidized), then in hydrogen (reduced) to break it into a powder, which is then formed into CANDU fuel pellets. CANDU reactors can also breed fuel from the more abundant thorium . This is being investigated by India to take advantage of its natural thorium reserves. Even better than LWRs , CANDU can utilize a mix of uranium and plutonium oxides ( MOX fuel ), the plutonium either from dismantled nuclear weapons or reprocessed reactor fuel. The mix of isotopes in reprocessed plutonium

7701-495: Is thought to have produced the plutonium for India's more recent (1998) Operation Shakti nuclear tests. Although heavy water is relatively immune to neutron capture, a small amount of the deuterium turns into tritium in this way. This tritium is extracted from some CANDU plants in Canada, mainly to improve safety in case of heavy-water leakage. The gas is stockpiled and used in a variety of commercial products, notably "powerless" lighting systems and medical devices. In 1985 what

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7852-414: 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

8003-487: 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,

8154-517: 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

8305-404: 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

8456-500: 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

8607-414: The overnight cost of the plant (four reactors totalling 3,512 MW e net capacity) at $ 5.117 billion CAD (about US$ 4.2 billion at early-1990s exchange rates). Total capital costs including interest were $ 14.319 billion CAD (about US$ 11.9 billion) with the heavy water accounting for $ 1.528 billion, or 11%, of this. Since heavy water is less efficient than light water at slowing neutrons, CANDU needs

8758-461: The 1960s. Despite improvements to the design in later decades as electricity generation became the primary operational aim, magnox reactors were never capable of competing with the higher efficiency and higher fuel burnup of 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

8909-445: The 1980s, a cost analysis for potential investors revealed that true operating costs had been obscured for many years. Decommissioning costs especially had been significantly underestimated. These uncertainties caused nuclear power to be omitted from the privatisation at that time. The small-scale prototype AGR at Sellafield (Windscale) has been decommissioned as of 2010 – the core and pressure vessel decommissioned leaving only

9060-434: 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

9211-543: The CANDU design, and two safeguarded light-water reactors supplied by the US. Plutonium has been extracted from the spent fuel from all of these reactors; India mainly relies on an Indian designed and built military reactor called Dhruva . The design is believed to be derived from the CIRUS reactor, with the Dhruva being scaled-up for more efficient plutonium production. It is this reactor which

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9362-399: The CANDU design; by operating on natural uranium the cost of enrichment is removed. This also presents an advantage in nuclear proliferation terms, as there is no need for enrichment facilities, which might also be used for weapons. In conventional light-water reactor (LWR) designs, the entire fissile core is placed in a large pressure vessel . The amount of heat that can be removed by

9513-709: The CANDU ;6 design, which first went into operation in the early 1980s. CANDU 6 was essentially a version of the Pickering power plant that was redesigned to be able to be built in single-reactor units. CANDU 6 was used in several installations outside Ontario, including the Gentilly-2 in Quebec, and Point Lepreau Nuclear Generating Station in New Brunswick. CANDU 6 forms the majority of foreign CANDU systems, including

9664-456: The ICRP's dose limit for members of the public). Tritium emissions from other CANDU plants are similarly low. In general, there is significant public controversy about radioactive emissions from nuclear power plants, and for CANDU plants one of the main concerns is tritium. In 2007 Greenpeace published a critique of tritium emissions from Canadian nuclear power plants by Ian Fairlie . This report

9815-463: The Magnox's graphite moderator and carbon dioxide coolant but increased the cooling gas operating temperature to improve steam conditions. These were made identical to those of a coal fired plant, allowing the same design of turbines and generation equipment to be used. During the initial design stages it was found necessary to switch the fuel cladding from beryllium to stainless steel . However, steel has

9966-471: 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

10117-739: 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

10268-408: The building "Golf Ball" visible. This project was also a study of what is required to decommission a nuclear reactor safely. In October 2016 it was announced that super-articulated control rods would be installed at Hunterston B and Hinkley Point B because of concerns about the stability of the reactors' graphite cores. In early 2018 a slightly higher rate of new keyway root cracks than modelled

10419-481: 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

10570-417: The bundles, the tubes and bundles are made of neutron-transparent zircaloy ( zirconium + 2.5% wt niobium ). Natural uranium is a mix of isotopes : approximately 99.28% uranium-238 and 0.72% uranium-235 by atom fraction. Nuclear power reactors are usually operated at constant power for long periods of time, which requires a constant rate of fission over time. In order to keep the fission rate constant,

10721-413: 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

10872-497: The classic CANDU design, experimental variants were being developed. WR-1 , located at the AECL 's Whiteshell Laboratories in Pinawa, Manitoba , used vertical pressure tubes and organic oil as the primary coolant. The oil used has a higher boiling point than water, allowing the reactor to operate at higher temperatures and lower pressures than a conventional reactor. WR-1's outlet temperature

11023-516: 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 ,

11174-425: The contract, Magnox Ltd will become a subsidiary of the NDA in September 2019. CANDU The CANDU ( CANada Deuterium Uranium ) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water ) moderator and its use of (originally, natural ) uranium fuel. CANDU reactors were first developed in the late 1950s and 1960s by

11325-503: The controllers to adjust reactivity across the fuel mass, as different portions would normally burn at different rates depending on their position. The adjuster rods can also be used to slow or stop criticality. Because these rods are inserted into the low-pressure calandria, not the high-pressure fuel tubes, they would not be "ejected" by steam, a design issue for many pressurized-water reactors. There are two independent, fast-acting safety shutdown systems as well. Shutoff rods are held above

11476-487: 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

11627-414: The decay of fission fragments have enough energy, and the half-lives of the fission fragments range from seconds to hours or even years. The slow response of these gamma-generated neutrons delays the response of the reactor and gives the operators extra time in case of an emergency. Since gamma rays travel for meters through water, an increased rate of chain reaction in one part of the reactor will produce

11778-410: The decision to construct the first multi-unit station in Pickering, Ontario. Pickering A, consisting of Units 1 to 4, went into service in 1971. Pickering B with units 5 to 8 came online in 1983, giving a full-station capacity of 4,120 MW e . The station is very close to the city of Toronto , in order to reduce transmission costs. A series of improvements to the basic Pickering design led to

11929-551: The defuelling phase with immediate effect. On 15 December 2021 EDF announced that Heysham 2 and Torness are expected to close in March 2028. On 7 January 2022 Hunterston B reactor 4 was shut down for the last time, ending production after nearly 47 years. Reactor 3 had moved to the defuelling phase in November 2021. On 1 August 2022 Hinkley Point B Reactor 3 was shut down, Reactor 4 was shut down on 6 July 2022. Magnox Magnox

12080-481: 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

12231-429: The designs exported to Argentina, Romania, China and South Korea. Only India operates a CANDU system that is not based on the CANDU 6 design. The economics of nuclear power plants generally scale well with size. This improvement at larger sizes is offset by the sudden appearance of large quantities of power on the grid, which leads to a lowering of electricity prices through supply and demand effects. Predictions in

12382-475: 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)

12533-618: 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

12684-422: The enrichment level of the fuel was raised to allow for the higher neutron capture losses of stainless steel cladding. This significantly increased the cost of the power produced by an AGR. The carbon dioxide coolant circulates through the core, reaching 640 °C (1,184 °F) and a pressure of around 40 bar (580 psi), and then passes through boiler (steam generator) assemblies outside the core but still within

12835-464: The first nuclear-generated electricity in Canada and ran successfully from 1962 to 1987. The second CANDU was the Douglas Point reactor, a more powerful version rated at roughly 200 MW e and located near Kincardine , Ontario. It went into service in 1968 and ran until 1984. Uniquely among CANDU stations, Douglas Point had an oil-filled window with a view of the east reactor face, even when

12986-576: 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

13137-429: The fuel is not critical in light water. This means that cooling the core with water from nearby sources will not add to the reactivity of the fuel mass. Normally the rate of fission is controlled by light-water compartments called liquid zone controllers, which absorb excess neutrons, and by adjuster rods, which can be raised or lowered in the core to control the neutron flux. These are used for normal operation, allowing

13288-430: The fuel is supplied and reprocessed by an internationally approved supplier. The main advantage of heavy water moderator over light water is the reduced absorption of the neutrons that sustain the chain reaction, allowing a lower concentration of fissile atoms (to the point of using unenriched natural uranium fuel). Deuterium ("heavy hydrogen") already has the extra neutron that light hydrogen would absorb, reducing

13439-475: The fuel material is usually U, most reactor designs are based on thin fuel rods separated by moderator, allowing the neutrons to travel in the moderator before entering the fuel again. More neutrons are released than the minimum needed to maintain the chain reaction; when uranium-238 absorbs neutrons, plutonium is created, which helps to make up for the depletion of uranium-235. Eventually the build-up of fission products that are more neutron-absorbing than U slows

13590-454: The fuel must be enriched , increasing the amount of U to a usable level. In light-water reactors , the fuel is typically enriched to between 2% and 5% U (the leftover fraction with less U is called depleted uranium ). Enrichment facilities are expensive to build and operate. They may also pose a proliferation concern, as they can be used to enrich the U much further, up to weapons-grade material (90% or more U). This can be remedied if

13741-505: 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) of boron -steel control rods which could be raised and lowered as required in vertical channels. At higher temperatures, aluminium

13892-454: The graphite, ensuring that the graphite core temperatures do not vary too much from those seen in a magnox station. The superheater outlet temperature and pressure were designed to be 2,485  psi (170 bar) and 543 °C. The fuel is uranium dioxide pellets, enriched to 2.5-3.5%, in stainless steel tubes. The original design concept of the AGR was to use a beryllium based cladding. When this proved unsuitable due to brittle fracture,

14043-417: The heat from the pressure tubes from leaking into the surrounding moderator, each pressure tube is enclosed in a calandria tube. Carbon dioxide gas in the gap between the two tubes acts as an insulator. The moderator tank also acts as a large heat sink that provides an additional safety feature. In a conventional pressurized water reactor , refuelling the system requires to shut down the core and to open

14194-483: The helium cooled very-high-temperature reactor , the steam-generating heavy water reactor and the fast-breeder reactor - as well as the American light water pressurised and boiling water reactors (PWR and BWR) and Canadian CANDU designs. The CEGB conducted a detailed economic appraisal of the competing designs and concluded that the AGR proposed for Dungeness B would generate the cheapest electricity, cheaper than any of

14345-445: The inter-fuel pellet fission reaction. This will not stop heat production from fission product decay, which would continue to supply a considerable heat output. If this process further weakens the fuel bundles, the pressure tube they are in will eventually bend far enough to touch the calandria tube, allowing heat to be efficiently transferred into the moderator tank. The moderator vessel has a considerable thermal capability on its own and

14496-500: The life of the programme three (later four) different AGR reactor designs. The AGR stations proved to be complex and difficult to construct. Notoriously bad labour relations at the time added to the problems. The lead station, Dungeness B, was ordered in 1965 with a target completion date of 1970. After problems with nearly every aspect of the reactor design it finally began generating electricity in 1983, 13 years late. The following reactor designs at Hinkley Point and Hunterston, ordered

14647-451: The lower energy limit is the energy where the neutrons are in thermal equilibrium with the moderator. When neutrons approach this lower energy limit, they are referred to as " thermal neutrons ." During moderation it helps to separate the neutrons and uranium, since U has a large affinity for intermediate-energy neutrons ("resonance" absorption), but is only easily fissioned by the few energetic neutrons above ≈1.5–2  MeV . Since most of

14798-529: The magnox was designed with the dual purpose of producing electrical power and plutonium-239 for the nascent nuclear weapons programme in Britain . The name refers specifically to the United Kingdom design but is sometimes used generically to refer to any similar reactor. As with other plutonium-producing reactors, conserving neutrons is a key element of the design. In magnox, the neutrons are moderated in large blocks of graphite . The efficiency of graphite as

14949-434: The mid-1990s, when further trials led to a fuel rod becoming stuck in a reactor core. Only refuelling at part load or when shut down is now undertaken at AGRs. The pre-stressed concrete pressure vessel contains the reactor core and the boilers. To minimise the number of penetrations into the vessel (and thus reduce the number of possible breach sites) the boilers are of the once through design where all boiling and superheating

15100-442: 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

15251-459: 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

15402-416: The neutrons released by fission must produce an equal number of fissions in other fuel atoms. This balance is referred to as " criticality ." Neutrons released by nuclear fission are fairly energetic and don't readily get absorbed (or "captured") by the surrounding fissile material . In order to improve the capture rate, the neutron energy must be reduced, or "moderated", to be as low as possible. In practice,

15553-411: The neutrons will end up at a lower energy and be more likely to cause fission, so CANDU not only "burns" natural uranium, but it does so more effectively as well. Overall, CANDU reactors use 30–40% less mined uranium than light-water reactors per unit of electricity produced. This is a major advantage of the heavy-water design; it not only requires less fuel, but as the fuel does not have to be enriched, it

15704-480: The news when documents were obtained under the Freedom of Information Act 2000 by The Guardian which claimed that British Energy were unaware of the extent of the cracking of graphite bricks in the cores of their reactors. It was also claimed that British Energy did not know why the cracking had occurred and that they were unable to monitor the cores without first shutting down the reactors. British Energy later issued

15855-475: The other end. A significant operational advantage of online refuelling is that a failed or leaking fuel bundle can be removed from the core once it has been located, thus reducing the radiation levels in the primary cooling loop. Each fuel bundle is a cylinder assembled from thin tubes filled with ceramic pellets of uranium oxide fuel (fuel elements). In older designs, the bundle had 28 or 37 half-meter-long fuel elements with 12–13 such assemblies lying end-to-end in

16006-404: 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 (CO 2 ) as the coolant. There is no facility in the reactor to adjust

16157-422: The post– World War II era to explore nuclear energy while lacking access to enrichment facilities. War-era enrichment systems were extremely expensive to build and operate, whereas the heavy water solution allowed the use of natural uranium in the experimental ZEEP reactor. A much less expensive enrichment system was developed, but the United States classified work on the cheaper gas centrifuge process. The CANDU

16308-404: The pressure vessel. In CANDU, only the single tube being refuelled needs to be depressurized. This allows the CANDU system to be continually refuelled without shutting down, another major design goal. In modern systems, two robotic machines attach to the reactor faces and open the end caps of a pressure tube. One machine pushes in the new fuel, whereby the depleted fuel is pushed out and collected at

16459-427: The reaction and calls for refuelling. Light water makes an excellent moderator: the light hydrogen atoms are very close in mass to a neutron and can absorb a lot of energy in a single collision (like a collision of two billiard balls). However, light hydrogen can absorb neutrons, reducing the number available to react with the small amount of U in natural uranium, preventing criticality. In order to allow criticality,

16610-427: The reactions release naturally. Most reactors use some form of neutron moderator to lower the energy of the neutrons, or " thermalize " them, which makes the reaction more efficient. The energy lost by the neutrons during this moderation process heats the moderator, and this heat is extracted for power. Most commercial reactor designs use normal water as the moderator. Water absorbs some of the neutrons, enough that it

16761-412: The reactor by electromagnets and drop under gravity into the core to quickly end criticality. This system works even in the event of a complete power failure, as the electromagnets only hold the rods out of the reactor when power is available. A secondary system injects a high-pressure gadolinium nitrate neutron absorber solution into the calandria. A heavy-water design can sustain a chain reaction with

16912-455: The reactor core heat pressurized water in a primary cooling loop . A heat exchanger , also known as a steam generator , transfers the heat to a secondary cooling loop , which powers a steam turbine with an electric generator attached to it (for a typical Rankine thermodynamic cycle ). The exhaust steam from the turbines is then cooled, condensed and returned as feedwater to the steam generator. The final cooling often uses cooling water from

17063-498: 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

17214-422: 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

17365-529: The reactor was operating. Douglas Point was originally planned to be a two-unit station, but the second unit was cancelled because of the success of the larger 515 MW e units at Pickering . Gentilly-1 , in Bécancour, Quebec , near Trois-Rivières , Quebec, was also an experimental version of CANDU, using a boiling light-water coolant and vertical pressure tubes, but was not considered successful and closed after seven years of fitful operation. Gentilly-2,

17516-454: 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

17667-515: 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

17818-411: The recently life-extended Heysham 1 and Hartlepool. These life extensions are subject to detailed review and approval, and are not included in the table above. On 4 December 2012 EDF announced that Hinkley Point B and Hunterston B had been given 7-year life extensions, from 2016 to 2023. On 5 November 2013 EDF announced that Hartlepool had been given a 5-year life extension, from 2019 to 2024. In 2013

17969-542: The required size. This problem is amplified by natural uranium fuel's lower fissile density, which requires a larger reactor core. This issue was so major that even the relatively small pressure vessel originally intended for use in the NPD prior to its mid-construction redesign could not be fabricated domestically and had to be manufactured in Scotland instead. Domestic development of the technology required to produce pressure vessels of

18120-421: The rest of the core, giving time to respond in an emergency. The independence of the neutrons' energies from the nuclear fuel used is what allows such fuel flexibility in a CANDU reactor, since every fuel bundle will experience the same environment and affect its neighbors in the same way, whether the fissile material is uranium-235, uranium-233 or plutonium . Canada developed the heavy-water-moderated design in

18271-502: The rival designs and the best coal-fired stations. There were great hopes for the AGR design. An ambitious construction programme of five twin reactor stations, Dungeness B , Hinkley Point B , Hunterston B , Hartlepool and Heysham was quickly rolled out, and export orders were eagerly anticipated. For political reasons the CEGB was instructed to spread the 'first generation' orders between three different 'design & build' consortia and

18422-405: The same design of turbo-generator plant could be used. The mean temperature of the hot coolant leaving the reactor core was designed to be 648 °C (1,198 °F). In order to obtain these high temperatures, yet ensure useful graphite core life (graphite reacts with CO 2 at high temperature) a re-entrant flow of coolant at the lower boiler outlet temperature of 278 °C is utilised to cool

18573-510: The same power output, and the fuel burnup of 27,000 MW(th) days per tonne for type 2 fuel and up to 34,000 MW(th) days per tonne for robust fuel at discharge is lower than the 40,000 MW(th) days per ton of PWRs so the fuel is used less efficiently, countering the thermal efficiency advantage. Like the magnox, CANDU , IPHWR , and RBMK reactors, and in contrast to light water reactors , AGRs are designed to be refuelled without being shut down first (see Online refuelling ). This on-load refuelling

18724-422: 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

18875-733: The size of the confinement building down, the early magnox designs placed 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

19026-496: The size required for commercial-scale heavy water moderated power reactors was thought to be very unlikely. In CANDU the fuel bundles of about 10 cm diameter are composed of many smaller metal tubes. The bundles are contained in pressure tubes within a larger vessel containing additional heavy water acting purely as a moderator. This larger vessel, known as a calandria, is not pressurized and remains at much lower temperatures, making it much easier to fabricate. In order to prevent

19177-408: 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

19328-411: 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

19479-521: The steel-lined, reinforced concrete pressure vessel. Control rods penetrate the graphite moderator and a secondary system involves injecting nitrogen into the coolant to absorb thermal neutrons to stop the fission process if the control rods fail to enter the core. A tertiary shutdown system which operates by injecting boron beads into the reactor is included in case the reactor has to be depressurized with insufficient control rods lowered. This would mean that nitrogen pressure cannot be maintained. The AGR

19630-410: The temperature of the fuel bundles increases to the point where they are mechanically unstable, their horizontal layout means that they will bend under gravity, shifting the layout of the bundles and reducing the efficiency of the reactions. Because the original fuel arrangement is optimal for a chain reaction, and the natural uranium fuel has little excess reactivity, any significant deformation will stop

19781-418: The tendency to capture neutrons. Deuterium has twice the mass of a single neutron (vs light hydrogen, which has about the same mass); the mismatch means that more collisions are needed to moderate the neutrons, requiring a larger thickness of moderator between the fuel rods. This increases the size of the reactor core and the leakage of neutrons. It is also the practical reason for the calandria design, otherwise,

19932-487: 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

20083-408: The total, so the overall price per kWh electricity is comparable. The next-generation Advanced CANDU reactor (ACR) mitigates these disadvantages by having light-water coolant and using a more compact core with less moderator. When first introduced, CANDUs offered much better capacity factor (ratio of power generated to what would be generated by running at full power, 100% of the time) than LWRs of

20234-574: The units installed at the Darlington Nuclear Generating Station . An effort to rationalize the larger units in a fashion similar to CANDU 6 led to the CANDU 9 . By the early 2000s, sales prospects for the original CANDU designs were dwindling due to the introduction of newer designs from other companies. AECL responded by cancelling CANDU 9 development and moving to the Advanced CANDU reactor (ACR) design. ACR failed to find any buyers; its last potential sale

20385-534: Was Calder Hall (at the Sellafield site) in 1956, frequently regarded as 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

20536-596: Was a hydrogen bomb. An offhand comment in the BARC publication Heavy Water – Properties, Production and Analysis appears to suggest that the tritium was extracted from the heavy water in the CANDU and PHWR reactors in commercial operation. Janes Intelligence Review quotes the Chairman of the Indian Atomic Energy Commission as admitting to the tritium extraction plant, but refusing to comment on its use. India

20687-440: 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

20838-490: Was about 490 °C compared to the CANDU 6's nominal 310 °C; the higher temperature and thus thermodynamic efficiency offsets to some degree the fact that oils have about half the heat capacity of water. The higher temperatures also result in more efficient conversion to steam, and ultimately, electricity. WR-1 operated successfully for many years and promised a significantly higher efficiency than water-cooled versions. The successes at NPD and Douglas Point led to

20989-496: Was an important part of the economic case for choosing the AGR over other reactor types, and in 1965 allowed the Central Electricity Generating Board (CEGB) and the government to claim that the AGR would produce electricity cheaper than the best coal-fired power stations. However, fuel assembly vibration problems arose during on-load refuelling at full power, so in 1988 full power refuelling was suspended until

21140-460: Was criticized by Richard Osborne. The CANDU development effort has gone through four major stages over time. The first systems were experimental and prototype machines of limited power. These were replaced by a second generation of machines of 500 to 600 MW e (the CANDU 6), a series of larger machines of 900 MW e , and finally developing into the CANDU 9 and ACR-1000 effort. The first heavy-water-moderated design in Canada

21291-431: Was designed to have a high thermal efficiency (electricity generated/heat generated ratio) of about 41%, which is better than a modern pressurized water reactor (PWR) with a typical thermal efficiency of 34%. This is due to the higher coolant outlet temperature of about 640 °C (1,184 °F) practical with gas cooling, compared to about 325 °C (617 °F) for PWRs. However the reactor core has to be larger for

21442-657: Was for an expansion at Darlington, but this was cancelled in 2009. In October 2011, the Canadian Federal Government licensed the CANDU design to Candu Energy (a wholly owned subsidiary of SNC-Lavalin, now the AtkinsRéalis Group Inc. ), which also acquired the former reactor development and marketing division of AECL at that time. Candu Energy offers support services for existing sites and is completing formerly stalled installations in Romania and Argentina through

21593-427: 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 CO 2 . Magnox alloy is reactive with water, which means it cannot be left in

21744-541: Was given a ten-year life extension, with an upgrade to control room computer systems and improved flood defences, taking the accounting closure date to 2028. In February 2016, EDF extended the life of four of its eight nuclear power plants in the UK. Heysham 1 and Hartlepool had their life extended by five years until 2024, while Heysham 2 and Torness had their closure dates pushed back by seven years to 2030. On 7 June 2021, EDF announced that Dungeness B, which had been in an extended outage since September 2018, would move into

21895-531: Was observed in Hunterston B Reactor 3 during a scheduled outage, and EDF announced in May 2018 that the outage would be extended for further investigation, analysis and modelling. In 2018 inspections ordered by the ONR at Dungeness B showed that seismic restraints, pipework and storage vessels were "corroded to an unacceptable condition", and that would have been the state when the reactor was operating. The ONR classified this as

22046-426: 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 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

22197-427: 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

22348-643: Was the ZEEP , which started operation just after the end of World War II . ZEEP was joined by several other experimental machines, including the NRX in 1947 and NRU in 1957. These efforts led to the first CANDU-type reactor, the Nuclear Power Demonstration (NPD), in Rolphton, Ontario. It was intended as a proof-of-concept and rated for only 22  MW e , a very low power for a commercial power reactor. NPD produced

22499-449: 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,

22650-548: Was then Ontario Hydro sparked controversy in Ontario due to its plans to sell tritium to the United States. The plan, by law, involved sales to non-military applications only, but some speculated that the exports could have freed American tritium for the United States nuclear weapons program. Future demands appear to outstrip production, in particular the demands of future generations of experimental fusion reactors like ITER , with up to 10kg of tritium being required in order to start up

22801-462: Was therefore designed to use natural uranium. The CANDU includes a number of active and passive safety features in its design. Some of these are a side effect of the physical layout of the system. CANDU designs have a positive void coefficient , as well as a small power coefficient, normally considered bad in reactor design. This implies that steam generated in the coolant will increase the reaction rate, which in turn would generate more steam. This

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