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80-540: The Fessenheim plant has two pressurized water reactors , which each generated 920 MWe . Construction at Fessenheim began in 1970 and the plant was commissioned in 1977. It is built alongside the Grand Canal d'Alsace , a canal channelling the Upper Rhine river, from which it drew 2.5 km (0.60 cu mi) of cooling water annually. The plant employed around 700 staff and 200 contractors, and indirectly supports

160-442: A (partially) closed nuclear fuel cycle . Water is a nontoxic, transparent, chemically unreactive (by comparison with e.g. NaK ) coolant that is liquid at room temperature which makes visual inspection and maintenance easier. It is also easy and cheap to obtain unlike heavy water or even nuclear graphite . Compared to reactors operating on natural uranium , PWRs can achieve a relatively high burnup . A typical PWR will exchange

240-508: A 8.9 km depth). Previously an earthquake of magnitude 4.7, was recorded in this southern third at Sierentz in July 1980. The last major earthquake in the region was the 1356 Basel earthquake , estimated to have had a M w magnitude of up to 7.1. A report commissioned by the Swiss canton of Basel-Stadt , published in 2007, concluded that the previous seismic evaluations undertaken by both EDF and, to

320-479: A CANDU reactor or any other heavy water reactor when ordinary light water is supplied to the reactor as an emergency coolant. Depending on burnup , boric acid or another neutron poison will have to be added to emergency coolant to avoid a criticality accident . PWRs are designed to be maintained in an undermoderated state, meaning that there is room for increased water volume or density to further increase moderation, because if moderation were near saturation, then

400-593: A French Regional Council has passed such a vote. On April 6 the Grand Council of Basel-Stadt also voted for the plant to be closed as did the council of the Urban Community of Strasbourg on April 12. The European Parliament's Green members also supported the closure demands and referred the matter to the European Commission . Around 3,800 people demonstrated near the plant on April 8; a larger demonstration

480-465: A PWR cannot exceed a temperature of 647 K (374 °C; 705 °F) or a pressure of 22.064 MPa (3200 psi or 218 atm), because those are the critical point of water. Supercritical water reactors are (as of 2022) only a proposed concept in which the coolant would never leave the supercritical state. However, as this requires even higher pressures than a PWR and can cause issues of corrosion, so far no such reactor has been built. Pressure in

560-405: A PWR design. Nuclear fuel in the reactor pressure vessel is engaged in a controlled fission chain reaction , which produces heat, heating the water in the primary coolant loop by thermal conduction through the fuel cladding. The hot primary coolant is pumped into a heat exchanger called the steam generator , where it flows through several thousand small tubes. Heat is transferred through

640-470: A PWR is not suitable for most industrial applications as those require temperatures in excess of 400 °C (752 °F). Radiolysis and certain accident scenarios which involve interactions between hot steam and zircalloy cladding can produce hydrogen from the cooling water leading to hydrogen explosions as a potential accident scenario. During the Fukushima nuclear accident a hydrogen explosion damaging

720-455: A PWR. It can, however, be used in a CANDU with only minimal reprocessing in a process called "DUPIC" - Direct Use of spent PWR fuel in CANDU. Thermal efficiency , while better than for boiling water reactors , cannot achieve the values of reactors with higher operating temperatures such as those cooled with high temperature gases, liquid metals or molten salts. Similarly process heat drawn from

800-408: A further 600 to 2,000 people during maintenance operations. The plant contributed around 16,000,000 euro in tax to the various local authorities, including providing the commune of Fessenheim with 70% of its revenue. In October 2009 the plant's third 10-yearly inspection on reactor 1 began, in advance of a decision on whether the plant could continue to operate for a further decade. A full decision

880-646: A given temperature set by the position of the control rods. In contrast, the Soviet RBMK reactor design used at Chernobyl, which uses graphite instead of water as the moderator and uses boiling water as the coolant, has a large positive thermal coefficient of reactivity. This means reactivity and heat generation increases when coolant and fuel temperatures increase, which makes the RBMK design less stable than pressurized water reactors at high operating temperature. In addition to its property of slowing down neutrons when serving as

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960-444: A heavy pressure vessel and hence increases construction costs. The higher pressure can increase the consequences of a loss-of-coolant accident . The reactor pressure vessel is manufactured from ductile steel but, as the plant is operated, neutron flux from the reactor causes this steel to become less ductile. Eventually the ductility of the steel will reach limits determined by the applicable boiler and pressure vessel standards, and

1040-515: A lesser extent, by the Institut de radioprotection et de sûreté nucléaire (Radioprotection and Nuclear Safety Institute, IRSN) had underestimated the risks involved. In particular, although the location of the fault in the Rhine Rift Valley that led to the 1356 Basel earthquake was sufficiently well known for national and regional purposes, its location was not known precisely enough to evaluate

1120-426: A moderator). The pressure in the primary coolant loop is typically 15–16 megapascals (150–160  bar ), which is notably higher than in other nuclear reactors , and nearly twice that of a boiling water reactor (BWR). As an effect of this, only localized boiling occurs and steam will recondense promptly in the bulk fluid. By contrast, in a boiling water reactor the primary coolant is designed to boil. Light water

1200-423: A moderator, water also has a property of absorbing neutrons, albeit to a lesser degree. When the coolant water temperature increases, the boiling increases, which creates voids. Thus there is less water to absorb thermal neutrons that have already been slowed by the graphite moderator, causing an increase in reactivity. This property is called the void coefficient of reactivity, and in an RBMK reactor like Chernobyl,

1280-459: A particular site. Studies conducted by other scientists have, for example, reached different conclusions about which faults might have been involved in the 1356 earthquake, its magnitude (ranging from 6.0 to 7.1 on the moment magnitude scale ), and the distance from the fault to the plant (ranging from 2 km (1.2 mi) to 40 km (25 mi) away, compared to the distances of 34 km (21 mi) and 29 km (18 mi) used by EDF and

1360-562: A pressurized water reactor (although the first power plant connected to the grid was at Obninsk , USSR), on insistence from Admiral Hyman G. Rickover that a viable commercial plant would include none of the "crazy thermodynamic cycles that everyone else wants to build". The United States Army Nuclear Power Program operated pressurized water reactors from 1954 to 1974. Three Mile Island Nuclear Generating Station initially operated two pressurized water reactor plants, TMI-1 and TMI-2. The partial meltdown of TMI-2 in 1979 essentially ended

1440-542: A quarter to a third of its fuel load every 18-24 months and have maintenance and inspection, that requires the reactor to be shut down, scheduled for this window. While more uranium ore is consumed per unit of electricity produced than in a natural uranium fueled reactor, the amount of spent fuel is less with the balance being depleted uranium whose radiological danger is lower than that of natural uranium. The coolant water must be highly pressurized to remain liquid at high temperatures. This requires high strength piping and

1520-469: A reduction in density of the moderator/coolant could reduce neutron absorption significantly while reducing moderation only slightly, making the void coefficient positive. Also, light water is actually a somewhat stronger moderator of neutrons than heavy water, though heavy water's neutron absorption is much lower. Because of these two facts, light water reactors have a relatively small moderator volume and therefore have compact cores. One next generation design,

1600-567: A secondary system where steam is generated. The steam then drives turbines, which spin an electric generator. In contrast to a boiling water reactor (BWR), pressure in the primary coolant loop prevents the water from boiling within the reactor. All light-water reactors use ordinary water as both coolant and neutron moderator . Most use anywhere from two to four vertically mounted steam generators; VVER reactors use horizontal steam generators. PWRs were originally designed to serve as nuclear marine propulsion for nuclear submarines and were used in

1680-420: A shaft used for propulsion . Direct mechanical action by expansion of the steam can be used for a steam-powered aircraft catapult or similar applications. District heating by the steam is used in some countries and direct heating is applied to internal plant applications. Two things are characteristic for the pressurized water reactor (PWR) when compared with other reactor types: coolant loop separation from

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1760-557: Is a multidisciplinary not-for-profit association of independent scientists who aim to spread information about the nuclear industry in France founded on December 15, 1975. In addition to providing a structure within which independent evaluations can take place, GSIEN aims to ensure that the French nuclear industry, one of the World's largest, provides open and honest information. In 1977 GSIEN

1840-514: Is a type of light-water nuclear reactor . PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan and Canada). In a PWR, the primary coolant ( water ) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms. The heated, high pressure water then flows to a steam generator , where it transfers its thermal energy to lower pressure water of

1920-548: Is built below the reactor in order to reduce the risk of polluting the aquifer. In August 2018, the plant was shut down during a heat wave to ensure that cooling water being released into the nearby river did not overheat it. Opposition to the Fessenheim plant dates back to the 1970s when its construction was proposed, and in June 1977 the pirate radio station Radio Verte Fessenheim (Green Radio Fessenheim) began broadcasting against

2000-455: Is expected on April 25. The group Stop Fessenheim have collected over 63,000 signatures through an online petition calling for Fessenheim's closure, and, on April 18, began a 366-day ' fasting relay' outside the préfecture office in Colmar . Although the plant was built with a 40-year operational life, on the plant's 30th anniversary, the anti nuclear group sortir du nucléaire called for

2080-402: Is generated per unit of uranium ore even though a higher burnup can be achieved. Nuclear reprocessing can "stretch" the fuel supply of both natural uranium and enriched uranium reactors but is virtually only practiced for light water reactors operating with lightly enriched fuel as spent fuel from e.g. CANDU reactors is very low in fissile material. Because water acts as a neutron moderator, it

2160-432: Is more dense (more collisions will occur). The use of water as a moderator is an important safety feature of PWRs, as an increase in temperature may cause the water to expand, giving greater 'gaps' between the water molecules and reducing the probability of thermalization — thereby reducing the extent to which neutrons are slowed and hence reducing the reactivity in the reactor. Therefore, if reactivity increases beyond normal,

2240-401: Is not possible to build a fast-neutron reactor with a PWR design. A reduced moderation water reactor may however achieve a breeding ratio greater than unity, though this reactor design has disadvantages of its own. Spent fuel from a PWR usually has a higher content of fissile material than natural uranium. Without nuclear reprocessing , this fissile material cannot be used as fuel in

2320-527: Is on an 18–24 month cycle. Approximately one third of the core is replaced each refueling, though some more modern refueling schemes may reduce refuel time to a few days and allow refueling to occur on a shorter periodicity. In PWRs reactor power can be viewed as following steam (turbine) demand due to the reactivity feedback of the temperature change caused by increased or decreased steam flow. (See: Negative temperature coefficient .) Boron and cadmium control rods are used to maintain primary system temperature at

2400-465: Is used as the primary coolant in a PWR. Water enters through the bottom of the reactor's core at about 548  K (275 °C; 527 °F) and is heated as it flows upwards through the reactor core to a temperature of about 588 K (315 °C; 599 °F). The water remains liquid despite the high temperature due to the high pressure in the primary coolant loop, usually around 155 bar (15.5  MPa 153  atm , 2,250  psi ). The water in

2480-480: The 2012 Presidential Election , François Hollande confirmed his plan to close the plant in 2017. In September 2012, he ordered to close the plant by the end of 2016. In September 2015, Ségolène Royal (Minister of Ecology, Sustainable Development and Energy since April 2014), said a closure before the end of the term of François Hollande (that ends in May 2017) would furthermore be her intention. Royal has suggested turning

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2560-452: The supercritical water reactor , is even less moderated. A less moderated neutron energy spectrum does worsen the capture/fission ratio for U and especially Pu, meaning that more fissile nuclei fail to fission on neutron absorption and instead capture the neutron to become a heavier nonfissile isotope, wasting one or more neutrons and increasing accumulation of heavy transuranic actinides, some of which have long half-lives. After enrichment,

2640-531: The uranium dioxide ( UO 2 ) powder is fired in a high-temperature, sintering furnace to create hard, ceramic pellets of enriched uranium dioxide. The cylindrical pellets are then clad in a corrosion-resistant zirconium metal alloy Zircaloy which are backfilled with helium to aid heat conduction and detect leakages. Zircaloy is chosen because of its mechanical properties and its low absorption cross section. The finished fuel rods are grouped in fuel assemblies, called fuel bundles, that are then used to build

2720-640: The 400), a petition signed initially by over 400 scientists, and ultimately by around 4,000, expressing their concern over a number of issues including 'secrecy' and 'official propaganda '. GSIEN was created following this petition, inspired in part by model of the Union of Concerned Scientists in the United States , with the objective of disseminating information to 'prevent nuclear officials from turning information into propaganda'. In 1998 Monique Sené , nuclear physicist, one of GSIEN's co-founders and its president,

2800-482: The Fessenheim Nuclear Power Plant, which was still under construction. This caused damage and delayed the completion of the plant. No one was injured. The bombing was claimed by a group named "Commando Puig Antich – Ulrike Meinhof". On the evening of June 2, 1980, unidentified people drove up to the gate of the power plant and fired guns at the guards. None of the guards were hit. After his victory in

2880-562: The Fessenheim plant is subject to particular risks from seismic activity and flooding, and there is an ongoing debate about the adequacy of its design in these respects. The majority of the Haut-Rhin département , including Fessenheim, is classified as being in a zone of moderate seismicity; the southern third is in a medium-risk zone. The most recent earthquake in this zone, with a magnitude of 3.9, took place on Saturday, 10 September 2022, 1.2km from Flaxlanden (epicenter 47.693°N 7.359°E with

2960-522: The French government to suspend the operation of Fessenheim while undertaking a safety review based on the lessons learned from Japan. The German state of Baden-Württemberg has called for a temporary closure in line with the 3-month shutdown of pre-1981 plants ordered in Germany. On March 29 the Franche-Comté Regional Council went further and voted for the plant to be closed, the first time

3040-531: The IRSN respectively). EDF also failed to take into account the possibility of a moderate local earthquake, which may have the potential to do greater damage than one which is larger but more distant, and the report was also critical of some aspects of the RFS 2001-01 assessment requirements. The report found that the design standards in force when the plant was built were similar to those that apply to present-day public buildings:

3120-587: The US, they were originally designed at the Oak Ridge National Laboratory for use as a nuclear submarine power plant with a fully operational submarine power plant located at the Idaho National Laboratory . Follow-on work was conducted by Westinghouse Bettis Atomic Power Laboratory . The first purely commercial nuclear power plant at Shippingport Atomic Power Station was originally designed as

3200-532: The calculation methods in the 1960s, the design took adequate account the consequences of a breach in the canal. In its initial report following the 1999 Blayais Nuclear Power Plant flood , the Institute for Nuclear Protection and Safety (now part of the Radioprotection and Nuclear Safety Institute ) called for the risk of flooding at Fessenheim to be re-examined due to the presence of the canal. On March 11, 2011,

3280-570: The containment building was a major concern, though the reactors at the plant were BWRs , which owing to the steam at the top of the pressure vessel by design carry a greater risk of this happening. Some reactors contain catalytic recombiners which let the hydrogen react with ambient oxygen in a non-explosive fashion. Groupement des scientifiques pour l%27information sur l%27%C3%A9nergie nucl%C3%A9aire The Groupement des scientifiques pour l'information sur l'énergie nucléaire GSIEN (Association of Scientists for Information on Nuclear Energy)

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3360-426: The core of the reactor. A typical PWR has fuel assemblies of 200 to 300 rods each, and a large reactor would have about 150–250 such assemblies with 80–100 tons of uranium in all. Generally, the fuel bundles consist of fuel rods bundled 14 × 14 to 17 × 17. A PWR produces on the order of 900 to 1,600 MW e . PWR fuel bundles are about 4 meters in length. Refuelings for most commercial PWRs

3440-544: The desired point. In order to decrease power, the operator throttles shut turbine inlet valves. This would result in less steam being drawn from the steam generators. This results in the primary loop increasing in temperature. The higher temperature causes the density of the primary reactor coolant water to decrease, allowing higher neutron speeds, thus less fission and decreased power output. This decrease of power will eventually result in primary system temperature returning to its previous steady-state value. The operator can control

3520-410: The event of an earthquake of magnitude 7.2, corresponding to the new seismic reference point proposed by the Swiss experts', the other on the 'redundancy of the cooling systems' in case of flooding. GSIEN has been commissioned to produce one of the reports. Although situated around 8 m (26 ft) below the level of the adjacent Grand Canal d'Alsace , it is not clear whether, taking into account

3600-399: The fast fission neutrons to be slowed (a process called moderation or thermalizing) in order to interact with the nuclear fuel and sustain the chain reaction. In PWRs the coolant water is used as a moderator by letting the neutrons undergo multiple collisions with light hydrogen atoms in the water, losing speed in the process. This "moderating" of neutrons will happen more often when the water

3680-548: The flawed RBMK control rods design. These design flaws, in addition to operator errors that pushed the reactor to its limits, are generally seen as the causes of the Chernobyl disaster . The Canadian CANDU heavy water reactor design have a slight positive void coefficient, these reactors mitigate this issues with a number of built-in advanced passive safety systems not found in the Soviet RBMK design. No criticality could occur in

3760-567: The growth in new construction of nuclear power plants in the United States for two decades. Watts Bar unit 2 (a Westinghouse 4-loop PWR) came online in 2016, becoming the first new nuclear reactor in the United States since 1996. The pressurized water reactor has several new Generation III reactor evolutionary designs: the AP1000 , VVER-1200, ACPR1000+, APR1400, Hualong One , IPWR-900 and EPR . The first AP1000 and EPR reactors were connected to

3840-460: The heaters or emptying the pressurizer. Pressure transients in the primary coolant system manifest as temperature transients in the pressurizer and are controlled through the use of automatic heaters and water spray, which raise and lower pressurizer temperature, respectively. The coolant is pumped around the primary circuit by powerful pumps. These pumps have a rate of ~100,000 gallons of coolant per minute. After picking up heat as it passes through

3920-518: The local Information and Oversight Commission announced that it had commissioned an urgent report on the 'redundancy of the cooling systems' in case of flooding and that another report 'to determine the areas to strengthen to guarantee the safety of the plant in the event of a breach in the canal', which had already started, was expected in June 2011. The station is built on top of a large aquifer (French Fossé rhénan , German Oberrhein-Aquifer ), contamination of which would be very harmful. A concrete slab

4000-510: The most deployed type of reactor globally, allowing for a wide range of suppliers of new plants and parts for existing plants. Due to long experience with their operation they are the closest thing to mature technology that exists in nuclear energy. PWRs - depending on type - can be fueled with MOX-fuel and/or the Russian Remix Fuel (which has a lower Pu and a higher U content than "regular" U/Pu MOX-fuel) allowing for

4080-430: The neutron activity correspondingly. An entire control system involving high pressure pumps (usually called the charging and letdown system) is required to remove water from the high pressure primary loop and re-inject the water back in with differing concentrations of boric acid. The reactor control rods, inserted through the reactor vessel head directly into the fuel bundles, are moved for the following reasons: to start up

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4160-480: The nucleus of a boron-10 atom which subsequently splits into a lithium-7 and tritium atom. Pressurized water reactors annually emit several hundred curies of tritium to the environment as part of normal operation. Natural uranium is only 0.7% uranium-235, the isotope necessary for thermal reactors. This makes it necessary to enrich the uranium fuel, which significantly increases the costs of fuel production. Compared to reactors operating on natural uranium, less energy

4240-539: The original design of the second commercial power plant at Shippingport Atomic Power Station . PWRs currently operating in the United States are considered Generation II reactors . Russia's VVER reactors are similar to US PWRs, but the VVER-1200 is not considered Generation II (see below). France operates many PWRs to generate the bulk of its electricity. Several hundred PWRs are used for marine propulsion in aircraft carriers , nuclear submarines and ice breakers . In

4320-545: The plant because of the seismic , flooding and other risks was rejected by the tribunal. A local association called Stop Fessenheim was formed in October 2005 and registered in the Canton of Munster, after having operated informally since 2004. The Fessenheim plant is one in a group of French nuclear power plants opposed by neighbouring countries, the other plants being Cattenom and Bugey . On May 3, 1975, two bombs exploded at

4400-411: The plant had been designed to accommodate movement, but it was not possible to determine whether or not the safety margins used would be adequate if a more realistic seismic evaluation were to be used. On March 11, 2011, the local Information and Oversight Commission announced that it was commissioning two independent second opinions, to be delivered as soon as possible, one on 'the safety of the plant in

4480-621: The plant into a Tesla factory. In June 2016, EDF demanded a settlement from the State for compensation. On 24 August 2016, Le Monde wrote that a settlement has been stipulated. On 9 April 2017, the plant was ordered to close after the Flamanville 3 unit comes online, expected to begin operation in late 2018, later reported to 2019, keeping the French nuclear generation capacity below the legal limit of 63.2 GWe. In November 2018, President Macron announced that both units would close in early 2020, which

4560-493: The plant's immediate closure. The Tri-national Nuclear Protection Action Group ATPN ( Action Tri nationale de Protection Nucléaire ), with members from France, Germany and Switzerland also campaigned for the plant to be closed and in 2008 unsuccessfully applied to the Strasbourg Administrative Tribunal ( Tribunal Administratif de Strasbourg ) to order its closure. On March 9, 2011, a further application to close

4640-467: The plant. There have been concerns about the seismic safety of the plant and, following the 2011 Fukushima I nuclear accidents , on March 21 the local Information and Oversight Commission for the plant called for the seismic risk to be re-evaluated based on a 7.2 magnitude earthquake; the plant was originally designed for a 6.7 magnitude earthquake. The Swiss cantons of Basel-Stadt , Basel-Landschaft and Jura have also said that they are going to ask

4720-637: The power grid in China in 2018. In 2020, NuScale Power became the first U.S. company to receive regulatory approval from the Nuclear Regulatory Commission for a small modular reactor with a modified PWR design. Also in 2020, the Energy Impact Center introduced the OPEN100 project, which published open-source blueprints for the construction of a 100 MW electric nuclear power plant with

4800-432: The pressure drop across the turbine, and hence the energy extracted from the steam, is maximized. Before being fed into the steam generator, the condensed steam (referred to as feedwater) is sometimes preheated in order to minimize thermal shock. The steam generated has other uses besides power generation. In nuclear ships and submarines, the steam is fed through a steam turbine connected to a set of speed reduction gears to

4880-518: The pressure vessel must be repaired or replaced. This might not be practical or economic, and so determines the life of the plant. Additional high pressure components such as reactor coolant pumps, pressurizer, and steam generators are also needed. This also increases the capital cost and complexity of a PWR power plant. The high temperature water coolant with boric acid dissolved in it is corrosive to carbon steel (but not stainless steel ); this can cause radioactive corrosion products to circulate in

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4960-419: The pressurized steam is fed through a steam turbine which drives an electrical generator connected to the electric grid for transmission. After passing through the turbine the secondary coolant (water-steam mixture) is cooled down and condensed in a condenser . The condenser converts the steam to a liquid so that it can be pumped back into the steam generator, and maintains a vacuum at the turbine outlet so that

5040-414: The pressurizer temperature and the highest temperature in the reactor core) of 30 °C (54 °F). As 345 °C is the boiling point of water at 155 bar, the liquid water is at the edge of a phase change. Thermal transients in the reactor coolant system result in large swings in pressurizer liquid/steam volume, and total pressurizer volume is designed around absorbing these transients without uncovering

5120-441: The primary circuit is maintained by a pressurizer, a separate vessel that is connected to the primary circuit and partially filled with water which is heated to the saturation temperature (boiling point) for the desired pressure by submerged electrical heaters. To achieve a pressure of 155 bars (15.5 MPa), the pressurizer temperature is maintained at 345 °C (653 °F), which gives a subcooling margin (the difference between

5200-423: The primary coolant loop. This not only limits the lifetime of the reactor, but the systems that filter out the corrosion products and adjust the boric acid concentration add significantly to the overall cost of the reactor and to radiation exposure. In one instance, this has resulted in severe corrosion to control rod drive mechanisms when the boric acid solution leaked through the seal between the mechanism itself and

5280-406: The primary system. Due to the requirement to load a pressurized water reactor's primary coolant loop with boron, undesirable radioactive secondary tritium production in the water is over 25 times greater than in boiling water reactors of similar power, owing to the latter's absence of the neutron moderating element in its coolant loop. The tritium is created by the absorption of a fast neutron in

5360-432: The reactor coolant and control the reactor power by adjusting the reactor coolant flow rate. PWR reactors are very stable due to their tendency to produce less power as temperatures increase; this makes the reactor easier to operate from a stability standpoint. PWR turbine cycle loop is separate from the primary loop, so the water in the secondary loop is not contaminated by radioactive materials. PWRs can passively scram

5440-455: The reactor core, the primary coolant transfers heat in a steam generator to water in a lower pressure secondary circuit, evaporating the secondary coolant to saturated steam — in most designs 6.2 MPa (60 atm, 900  psia ), 275 °C (530 °F) — for use in the steam turbine. The cooled primary coolant is then returned to the reactor vessel to be heated again. Pressurized water reactors, like all thermal reactor designs, require

5520-403: The reactor in case offsite power is lost to immediately stop the primary nuclear reaction. The control rods are held by electromagnets and fall by gravity when current is lost; full insertion safely shuts down the primary nuclear reaction. PWR technology is favoured by nations seeking to develop a nuclear navy; the compact reactors fit well in nuclear submarines and other nuclear ships. PWRs are

5600-428: The reactor, to shut down the primary nuclear reactions in the reactor, to accommodate short term transients, such as changes to load on the turbine, The control rods can also be used to compensate for nuclear poison inventory and to compensate for nuclear fuel depletion. However, these effects are more usually accommodated by altering the primary coolant boric acid concentration. In contrast, BWRs have no boron in

5680-431: The reduced moderation of neutrons will cause the chain reaction to slow down, producing less heat. This property, known as the negative temperature coefficient of reactivity, makes PWR reactors very stable. This process is referred to as 'Self-Regulating', i.e. the hotter the coolant becomes, the less reactive the plant becomes, shutting itself down slightly to compensate and vice versa. Thus the plant controls itself around

5760-426: The steady state operating temperature by addition of boric acid and/or movement of control rods. Reactivity adjustment to maintain 100% power as the fuel is burned up in most commercial PWRs is normally achieved by varying the concentration of boric acid dissolved in the primary reactor coolant. Boron readily absorbs neutrons and increasing or decreasing its concentration in the reactor coolant will therefore affect

5840-427: The steam system and pressure inside the primary coolant loop. In a PWR, there are two separate coolant loops (primary and secondary), which are both filled with demineralized/deionized water. A boiling water reactor, by contrast, has only one coolant loop, while more exotic designs such as breeder reactors use substances other than water for coolant and moderator (e.g. sodium in its liquid state as coolant or graphite as

5920-409: The void coefficient is positive, and fairly large, making it very hard to regulate when the reaction begins to run away. The RBMK reactors also have a flawed control rods design in which during rapid scrams, the graphite reaction enhancement tips of the rods would displace water at the bottom of the reactor and locally increase reactivity there. This is called the "positive scram effect" that is unique to

6000-414: The walls of these tubes to the lower pressure secondary coolant located on the shell side of the exchanger where the secondary coolant evaporates to pressurized steam. This transfer of heat is accomplished without mixing the two fluids to prevent the secondary coolant from becoming radioactive. Some common steam generator arrangements are u-tubes or single pass heat exchangers. In a nuclear power station,

6080-709: Was awarded the National Order of the Legion of Honour for her work as anti–nuclear power activist. Since its first edition in June 1976, GSIEN has published over 250 editions of its quarterly newsletter, la Gazette Nucléaire (the Nuclear Gazette). GSIEN has also published a number of books including Electro-nucléaire : danger (1977, ISBN   978-2-02-004711-1 ), Plutonium Sur Rhône (1981, ISBN   978-2-901968-47-4 ) GSIEN members have been invited by several Local Information Commissions to participate in

6160-558: Was first to provide an explanation of the causes and consequences of the Three Mile Island accident , while the authorities tried to play-down the incident, however GSIEN came to prominence at the time of the 1986 Chernobyl disaster when the press and public found that their independent information helped to compensate for the shortcomings in the official information. They subsequently became widely recognised after many of their members contributed to various overseas projects. GSIEN

6240-567: Was founded in the wake of the launch in 1974 of the Messmer Plan to switch all of France's electricity generation to nuclear power, which took place without public or parliamentary debate. The announcement of the Messmer Plan caused a split in the scientific community between those physicists (generally older) who favoured the plan, and those (generally younger) who were concerned about the potential risks, leading to l’Appel des 400 (the appeal of

6320-472: Was made in 2011, with permission to operate reactor 1 given. Reactor 1 was permanently shut down on February 22, 2020. The second reactor was inspected in mid April 2011. The local Information and Oversight Commission asked GSIEN to conduct a parallel independent inspection alongside the official inspection by the Nuclear Safety Authority . Reactor 2 shut down on 29 June 2020. Due to its location,

6400-618: Was refined in 2019 to unit 1 in February 2020 and unit 2 in June 2020. Representatives of the international and French nuclear industry spoke out against the closure. The World Nuclear Association and the Director General of the Société française d’énergie nucléaire argued that low-emission energy from Fessenheim will be replaced by energy generated by fossil fuel plants. Pressurized water reactor A pressurized water reactor ( PWR )

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