Misplaced Pages

#431568

96-489: The Fukushima Daini Nuclear Power Plant ( 福島第二原子力発電所 , Fukushima Daini ( pronunciation ) Genshiryoku Hatsudensho , Fukushima II NPP, 2F) is a nuclear power plant located on a 150 ha (370-acre) site in the town of Naraha and Tomioka in the Futaba District of Fukushima Prefecture , Japan. The Tokyo Electric Power Company (TEPCO) runs the plant. After the 2011 Tōhoku earthquake and tsunami ,

192-433: A brief period. Often they are used to provide electrical power until the plant electrical supply can be switched to the batteries and/or diesel generators. Batteries often form the final redundant backup electrical system and are also capable of providing sufficient electrical power to shut down a plant. Containment systems are designed to prevent the release of radioactive material into the environment. The fuel cladding

288-465: A condenser. The condenser is a heat exchanger which is connected to a secondary side such as a river or a cooling tower . The water is then pumped back into the steam generator and the cycle begins again. The water-steam cycle corresponds to the Rankine cycle . The nuclear reactor is the heart of the station. In its central part, the reactor's core produces heat due to nuclear fission. With this heat,

384-442: A coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. The heat from nuclear fission is used to raise steam, which runs through turbines , which in turn power the electrical generators. Nuclear reactors usually rely on uranium to fuel the chain reaction. Uranium is a very heavy metal that is abundant on Earth and is found in sea water as well as most rocks. Naturally occurring uranium

480-402: A facility has been completely decommissioned it is released from regulatory control, and the licensee of the station no longer has responsibility for its nuclear safety. Generally speaking, nuclear stations were originally designed for a life of about 30 years. Newer stations are designed for a 40 to 60-year operating life. The Centurion Reactor is a future class of nuclear reactor that

576-438: A full melt-down, the fuel would most likely end up on the concrete floor of the primary containment building. Concrete can withstand a great deal of heat, so the thick flat concrete floor in the primary containment will often be sufficient protection against the so-called China Syndrome . The Chernobyl plant didn't have a containment building, but the core was eventually stopped by the concrete foundation. Due to concerns that

672-516: A large body of water in which to dissipate the heat, water is recirculated via a cooling tower . The failure of half of the ESWS pumps was one of the factors that endangered safety in the 1999 Blayais Nuclear Power Plant flood , while a total loss occurred during the Fukushima I and Fukushima II nuclear accidents in 2011. Emergency core cooling systems (ECCS) are designed to safely shut down

768-425: A maximum intensity of VII (Very strong) . 14 people were injured and more than 1,900 homes briefly lost electricity. Though a warning of a possible tsunami of 3 m (9.8 ft) in height was issued, a 60 cm (24 in) wave was reported by NHK in the port of Onahama of Iwaki, Fukushima ; a 90 cm (35 in) wave hit Sōma, Fukushima ; and another wave 1 m (3 ft 3 in) in height struck

864-521: A negative pressure within the secondary containment to limit the release of radioactive material. Each SGTS train generally consists of a mist eliminator/roughing filter; an electric heater; a prefilter; two absolute ( HEPA ) filters; an activated charcoal filter; an exhaust fan; and associated valves, ductwork, dampers, instrumentation and controls. The signals that trip the SGTS system are plant-specific; however, automatic trips are generally associated with

960-440: A nuclear reactor during accident conditions. The ECCS allows the plant to respond to a variety of accident conditions (e.g. LOCAs ) and additionally introduce redundancy so that the plant can be shut down even with one or more subsystem failures. In most plants, ECCS is composed of the following systems: The High Pressure Coolant Injection (HPCI) System consists of a pump or pumps that have sufficient pressure to inject coolant into

1056-404: A nuclear reactor heats the reactor coolant. The coolant may be water or gas, or even liquid metal, depending on the type of reactor. The reactor coolant then goes to a steam generator and heats water to produce steam. The pressurized steam is then usually fed to a multi-stage steam turbine . After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in

SECTION 10

#1732773158432

1152-683: A nuclear reactor was used to generate electricity was on December 21, 1951, at the Experimental Breeder Reactor I , powering four light bulbs. On June 27, 1954, the world's first nuclear power station to generate electricity for a power grid , the Obninsk Nuclear Power Plant , commenced operations in Obninsk , in the Soviet Union . The world's first full scale power station, Calder Hall in

1248-483: A nuclear station is smaller than the fuel cost for operation of coal or gas plants. Since most of the cost of nuclear power plant is capital cost, there is almost no cost saving by running it at less than full capacity. Nuclear power plants are routinely used in load following mode on a large scale in France, although "it is generally accepted that this is not an ideal economic situation for nuclear stations". Unit A at

1344-516: A number of long-established projects are struggling to find financing, notably Belene in Bulgaria and the additional reactors at Cernavodă in Romania , and some potential backers have pulled out. Where cheap gas is available and its future supply relatively secure, this also poses a major problem for nuclear projects. Analysis of the economics of nuclear power must take into account who bears

1440-444: A previous goal aimed to reduce nuclear electricity generation share to lower than fifty percent by 2025, this target was postponed to 2035 in 2019 and ultimately discarded in 2023. Russia continues to export the most nuclear power plants in the world, with projects across various countries: as of July 2023, Russia was constructing 19 out of 22 reactors constructed by foreign vendors; however, some exporting projects were canceled due to

1536-413: A series of pumps and spargers that spray coolant into the upper portion of the primary containment structure. It is designed to condense the steam into liquid within the primary containment structure in order to prevent overpressure and overtemperature, which could lead to leakage, followed by involuntary depressurization. This system is often driven by a steam turbine to provide enough water to safely cool

1632-591: A significantly different evaluation of the economics of new nuclear power stations. Following the 2011 Fukushima nuclear accident in Japan , costs are likely to go up for currently operating and new nuclear power stations, due to increased requirements for on-site spent fuel management and elevated design basis threats. However many designs, such as the currently under construction AP1000, use passive nuclear safety cooling systems, unlike those of Fukushima I which required active cooling systems, which largely eliminates

1728-413: A slight decrease from the 2653 TWh produced in 2021. Thirteen countries generated at least one-quarter of their electricity from nuclear sources. Notably, France relies on nuclear energy for about 70% of its electricity needs, while Ukraine , Slovakia , Belgium , and Hungary source around half their power from nuclear. Japan , which previously depended on nuclear for over a quarter of its electricity,

1824-427: A small enough volume to become supercritical. Most reactors require continuous temperature control to prevent a core meltdown , which has occurred on a few occasions through accident or natural disaster, releasing radiation and making the surrounding area uninhabitable. Plants must be defended against theft of nuclear material and attack by enemy military planes or missiles. The most serious accidents to date have been

1920-482: A three-year research study of offshore floating nuclear power generation. In October 2022, NuScale Power and Canadian company Prodigy announced a joint project to bring a North American small modular reactor based floating plant to market. The economics of nuclear power plants is a controversial subject, and multibillion-dollar investments ride on the choice of an energy source. Nuclear power stations typically have high capital costs, but low direct fuel costs, with

2016-425: A ton, from their Rad Waste Building to other locations onsite. The steam-powered reactor core isolation cooling system (RCIC) in all 4 units was activated and ran as needed to maintain water level. At the same time, operators utilized the safety relief valve systems to keep the reactor pressures from getting too high by dumping the heat to the suppression pools. In unit 3, one seawater pump remained operational and

SECTION 20

#1732773158432

2112-580: A worldwide perspective, long-term waste storage costs are uncertain. Construction, or capital cost aside, measures to mitigate global warming such as a carbon tax or carbon emissions trading , increasingly favor the economics of nuclear power. Further efficiencies are hoped to be achieved through more advanced reactor designs, Generation III reactors promise to be at least 17% more fuel efficient, and have lower capital costs, while Generation IV reactors promise further gains in fuel efficiency and significant reductions in nuclear waste. In Eastern Europe,

2208-496: Is a thermal power station in which the heat source is a nuclear reactor . As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces electricity . As of September 2023 , the International Atomic Energy Agency reported that there were 410 nuclear power reactors in operation in 32 countries around

2304-468: Is a mode of operation of a residual heat removal system, also known as an RHR or RHS but is generally called LPCI. It is also not a stand-alone valve or system. This system uses spargers (pipes fitted with an array of many small spray nozzles) within the reactor pressure vessel to spray water directly onto the fuel rods, suppressing the generation of steam. Reactor designs can include core spray in high-pressure and low-pressure modes. This system consists of

2400-409: Is about 1/3 of solar and 1/45 of natural gas and 1/75 of coal . Newer models, like HPR1000 , produce even less carbon dioxide during the whole operating life, as little as 1/8 of power plants using gen II reactors for 1.31g/kWh. Emergency Core Cooling System A reactor protection system is designed to immediately terminate the nuclear reaction. By breaking the nuclear chain reaction ,

2496-527: Is anticipated to resume similar levels of nuclear energy utilization. Over the last 15 years, the United States has seen a significant improvement in the operational performance of its nuclear power plants, enhancing their utilization and efficiency, adding the output equivalent to 19 new 1000 MWe reactors without actual construction. In France, nuclear power plants still produce over sixty percent of this country's total power generation in 2022. While

2592-503: Is being designed to last 100 years. One of the major limiting wear factors is the deterioration of the reactor's pressure vessel under the action of neutron bombardment, however in 2018 Rosatom announced it had developed a thermal annealing technique for reactor pressure vessels which ameliorates radiation damage and extends service life by between 15 and 30 years. Nuclear stations are used primarily for base load because of economic considerations. The fuel cost of operations for

2688-431: Is found in two different isotopes : uranium-238 (U-238), accounting for 99.3% and uranium-235 (U-235) accounting for about 0.7%. U-238 has 146 neutrons and U-235 has 143 neutrons. Different isotopes have different behaviors. For instance, U-235 is fissile which means that it is easily split and gives off a lot of energy making it ideal for nuclear energy. On the other hand, U-238 does not have that property despite it being

2784-665: Is the first layer of protection around the nuclear fuel and is designed to protect the fuel from corrosion that would spread fuel material throughout the reactor coolant circuit. In most reactors it takes the form of a sealed metallic or ceramic layer. It also serves to trap fission products, especially those that are gaseous at the reactor's operating temperature , such as krypton , xenon and iodine . Cladding does not constitute shielding, and must be developed such that it absorbs as little radiation as possible. For this reason, materials such as magnesium and zirconium are used for their low neutron capture cross sections. The reactor vessel

2880-408: Is the first layer of shielding around the nuclear fuel and usually is designed to trap most of the radiation released during a nuclear reaction. The reactor vessel is also designed to withstand high pressures. The primary containment system usually consists of a large metal and/or concrete structure (often cylindrical or bulb shaped) that contains the reactor vessel. In most reactors it also contains

2976-429: Is the only nuclear facility that does not use a natural body of water for cooling, instead it uses treated sewage from the greater Phoenix metropolitan area. The water coming from the cooling body of water is either pumped back to the water source at a warmer temperature or returns to a cooling tower where it either cools for more uses or evaporates into water vapor that rises out the top of the tower. The water level in

Fukushima Daini Nuclear Power Plant - Misplaced Pages Continue

3072-489: The BWR , the steam is directed into the suppression chamber and condenses there. The chambers on a heat exchanger are connected to the intermediate cooling circuit. The main condenser is a large cross-flow shell and tube heat exchanger that takes wet vapor, a mixture of liquid water and steam at saturation conditions, from the turbine-generator exhaust and condenses it back into sub-cooled liquid water so it can be pumped back to

3168-560: The Fukushima Daiichi Nuclear Power Plant site after the 6.9 shock. Chief Cabinet Secretary Yoshihide Suga said that the third reactor's spent fuel pool cooling systems at Fukushima Daini had stopped as a result of the earthquake; TEPCO later reported the restart of the spent fuel cooling system after only 100 minutes of stoppage. On 31 July 2019, the TEPCO board of directors decided to decommission

3264-496: The Russian invasion of Ukraine . Meanwhile, China continues to advance in nuclear energy: having 25 reactors under construction by late 2023, China is the country with the most reactors being built at one time in the world. Nuclear decommissioning is the dismantling of a nuclear power station and decontamination of the site to a state no longer requiring protection from radiation for the general public. The main difference from

3360-678: The UAE launched the Arab region's first-ever nuclear energy plant. Unit 1 of the Barakah plant in the Al Dhafrah region of Abu Dhabi commenced generating heat on the first day of its launch, while the remaining 3 Units are being built. However, Nuclear Consulting Group head, Paul Dorfman, warned the Gulf nation's investment into the plant as a risk "further destabilizing the volatile Gulf region, damaging

3456-657: The United Kingdom , opened on October 17, 1956 and was also meant to produce plutonium . The world's first full scale power station solely devoted to electricity production was the Shippingport Atomic Power Station in Pennsylvania , United States, which was connected to the grid on December 18, 1957. The conversion to electrical energy takes place indirectly, as in conventional thermal power stations. The fission in

3552-424: The 1970s and 1980s, when it "reached an intensity unprecedented in the history of technology controversies," in some countries. Proponents argue that nuclear power is a sustainable energy source which reduces carbon emissions and can increase energy security if its use supplants a dependence on imported fuels. Proponents advance the notion that nuclear power produces virtually no air pollution, in contrast to

3648-485: The 1979 Three Mile Island accident , the 1986 Chernobyl disaster , and the 2011 Fukushima Daiichi nuclear disaster , corresponding to the beginning of the operation of generation II reactors . Professor of sociology Charles Perrow states that multiple and unexpected failures are built into society's complex and tightly coupled nuclear reactor systems. Such accidents are unavoidable and cannot be designed around. An interdisciplinary team from MIT has estimated that given

3744-572: The Brussels supplementary convention, and the Vienna Convention on Civil Liability for Nuclear Damage . However states with a majority of the world's nuclear power stations, including the U.S., Russia, China and Japan, are not party to international nuclear liability conventions. The nuclear power debate about the deployment and use of nuclear fission reactors to generate electricity from nuclear fuel for civilian purposes peaked during

3840-609: The ECCS and does not have a low coolant accident function. For pressurized water reactors, this system acts in the secondary cooling circuit and is called Turbine driven auxiliary feedwater system . Under normal conditions, nuclear power plants receive power from generator. However, during an accident a plant may lose access to this power supply and thus may be required to generate its own power to supply its emergency systems. These electrical systems usually consist of diesel generators and batteries . Diesel generators are employed to power

3936-568: The Fukushima II Nuclear Power Plant are BWR-5 type with electric power of 1,100 MW each (net output: 1,067 MW each). The reactors for units 1 and 3 were supplied by Toshiba , and for units 2 and 4 by Hitachi . Units 1–3 were built by Kajima while the unit 4 was built by Shimizu and Takenaka . The Fukushima Daini plant is connected to the rest of the power grid by the Tomioka Line ( 富岡線 ) to

Fukushima Daini Nuclear Power Plant - Misplaced Pages Continue

4032-529: The MUWC system to the HPCS. While the water level was maintained in the three cores using emergency water injection, pressures in the containment vessel continued to rise due to lack of suppression pool cooling and the operators prepared to vent the containments making restoration of heat removal urgent. Unit 1 was prioritized as it had the highest drywell pressure. The ultimate heat sink was restored on March 13 when

4128-557: The Shin-Fukushima (New Fukushima) substation. In January 1989, an impeller blade on one of the reactor coolant pumps in Unit 3 broke at a weld, causing a large amount of metal debris to flow throughout the primary loop. As a result, the reactor was shut down for a considerable length of time. The March 11, 2011 Tōhoku earthquake resulted in maximum horizontal ground accelerations of 0.21 g (2.10 m/s) to 0.28 (2.77 m/s) at

4224-407: The alloys used also are required to have at least a low coefficient of thermal expansion so that they do not jam under high temperatures, and they have to be self-lubricating metal on metal, because at the temperatures experienced by nuclear reactor cores oil lubrication would foul too quickly. Boiling water reactors are able to SCRAM the reactor completely with the help of their control rods. In

4320-413: The bottom of the containment building. The AREVA EPR , SNR-300, SWR1000, ESBWR, and Atmea I reactors have core catchers. The ABWR has a thick layer of basaltic concrete floor specifically designed to catch the core. A standby gas treatment system (SGTS) is part of the secondary containment system. The SGTS system filters and pumps air from secondary containment to the environment and maintains

4416-446: The case of a loss of coolant accident (LOCA), the water-loss of the primary cooling system can be compensated with normal water pumped into the cooling circuit. On the other hand, the standby liquid control (SLC) system (SLCS) consists of a solution containing boric acid , which acts as a neutron poison and rapidly floods the core in case of problems with the stopping of the chain reaction. Pressurized water reactors also can SCRAM

4512-557: The chief viable alternative of fossil fuel. Proponents also believe that nuclear power is the only viable course to achieve energy independence for most Western countries. They emphasize that the risks of storing waste are small and can be further reduced by using the latest technology in newer reactors, and the operational safety record in the Western world is excellent when compared to the other major kinds of power plants. Opponents say that nuclear power poses many threats to people and

4608-456: The core would melt its way through the concrete, a " core catching device " was invented, and a mine was quickly dug under the plant with the intention to install such a device. The device contains a quantity of metal designed to melt, diluting the corium and increasing its heat conductivity; the diluted metallic mass could then be cooled by water circulating in the floor. Today, all new Russian-designed reactors are equipped with core-catchers in

4704-493: The costs of fuel extraction, processing, use and spent fuel storage internalized costs. Therefore, comparison with other power generation methods is strongly dependent on assumptions about construction timescales and capital financing for nuclear stations. Cost estimates take into account station decommissioning and nuclear waste storage or recycling costs in the United States due to the Price Anderson Act . With

4800-424: The destruction of a turbine in operation from flying towards the reactor. In the case of a pressurized water reactor, the steam turbine is separated from the nuclear system. To detect a leak in the steam generator and thus the passage of radioactive water at an early stage, an activity meter is mounted to track the outlet steam of the steam generator. In contrast, boiling water reactors pass radioactive water through

4896-458: The dismantling of other power stations is the presence of radioactive material that requires special precautions to remove and safely relocate to a waste repository. Decommissioning involves many administrative and technical actions. It includes all clean-up of radioactivity and progressive demolition of the station. Once a facility is decommissioned, there should no longer be any danger of a radioactive accident or to any persons visiting it. After

SECTION 50

#1732773158432

4992-551: The electric heaters and a high temperature condition in the charcoal filters. In case of a radioactive release, most plants have a system designed to remove radioactivity from the air to reduce the effects of the radioactivity release on the employees and public. This system usually consists of containment ventilation that removes radioactivity and steam from primary containment. Control room ventilation ensures that plant operators are protected. This system often consists of activated charcoal filters that remove radioactive isotopes from

5088-534: The energy-intensive stages of the nuclear fuel chain are considered, from uranium mining to nuclear decommissioning , nuclear power is not a low-carbon electricity source despite the possibility of refinement and long-term storage being powered by a nuclear facility. Those countries that do not contain uranium mines cannot achieve energy independence through existing nuclear power technologies. Actual construction costs often exceed estimates, and spent fuel management costs are difficult to define. On 1 August 2020,

5184-402: The environment and raising the possibility of nuclear proliferation." Nuclear power plants do not produce greenhouse gases during operation. Older nuclear power plants, like ones using second-generation reactors , produce approximately the same amount of carbon dioxide during the whole life cycle of nuclear power plants for an average of about 11g/kWh, as much power generated by wind , which

5280-775: The environment, and that costs do not justify benefits. Threats include health risks and environmental damage from uranium mining , processing and transport, the risk of nuclear weapons proliferation or sabotage, and the problem of radioactive nuclear waste . Another environmental issue is discharge of hot water into the sea. The hot water modifies the environmental conditions for marine flora and fauna. They also contend that reactors themselves are enormously complex machines where many things can and do go wrong, and there have been many serious nuclear accidents . Critics do not believe that these risks can be reduced through new technology , despite rapid advancements in containment procedures and storage methods. Opponents argue that when all

5376-411: The environment. In addition, many reactors are equipped with a dome of concrete to protect the reactor against both internal casualties and external impacts. The purpose of the steam turbine is to convert the heat contained in steam into mechanical energy. The engine house with the steam turbine is usually structurally separated from the main reactor building. It is aligned so as to prevent debris from

5472-422: The evacuation order for Naraha was completely lifted, allowing residents to return and reconstruction efforts to begin. Naraha is the first of a number of towns in the area to have had its evacuation order removed. On Tuesday, November 22, 2016, a magnitude 6.9 earthquake struck Japan 37 km (23 mi) east southeast of Namie , Fukushima Prefecture at a depth of 11.3 km (7.0 mi). The shock had

5568-525: The expected growth of nuclear power from 2005 to 2055, at least four serious nuclear accidents would be expected in that period. The MIT study does not take into account improvements in safety since 1970. Nuclear power works under an insurance framework that limits or structures accident liabilities in accordance with the Paris Convention on Third Party Liability in the Field of Nuclear Energy ,

5664-521: The four reactors at Fukushima Daini automatically shut down . While the sister plant Fukushima Daiichi Nuclear Power Plant , approximately 12 km (7.5 mi) to the north, suffered extensive damage, the Daini Plant was back under control within two days, reaching cold shutdown. The plant has not been operating since, and in July 2019 a decision to decommission the plant was made. All reactors in

5760-465: The high pressure systems. Some depressurization systems are automatic in function, while others may require operators to manually activate them. In pressurized water reactors with large dry or ice condenser containments, the valves of the system are called Pilot-operated relief valves . An LPCI is an emergency system which consists of a pump that injects a coolant into the reactor vessel once it has been depressurized. In some nuclear power plants an LPCI

5856-406: The hot coolant is used as a heat source for a boiler, and the pressurized steam from that drives one or more steam turbine driven electrical generators . In the event of an emergency, safety valves can be used to prevent pipes from bursting or the reactor from exploding. The valves are designed so that they can derive all of the supplied flow rates with little increase in pressure. In the case of

SECTION 60

#1732773158432

5952-426: The hours over which the fixed cost of construction can be amortized. Nuclear power plants have a carbon footprint comparable to that of renewable energy such as solar farms and wind farms , and much lower than fossil fuels such as natural gas and coal . Nuclear power plants are among the safest modes of electricity generation, comparable to solar and wind power plants. The first time that heat from

6048-513: The loss of the ultimate heat sink and damage to some of the electrical infrastructure. Operators prepared for this and set up an alternate injection line using a non-emergency system known as the Makeup Water Condensate (MUWC) system to maintain water level which was an accident mitigation method TEPCO put in place at all its nuclear plants. The system was started and stopped in all 4 units, including unit 3, as needed to maintain

6144-607: The need to spend more on redundant back up safety equipment. According to the World Nuclear Association , as of March 2020: The Russian state nuclear company Rosatom is the largest player in international nuclear power market, building nuclear plants around the world. Whereas Russian oil and gas were subject to international sanctions after the Russian full-scale invasion of Ukraine in February 2022, Rosatom

6240-483: The now decommissioned German Biblis Nuclear Power Plant was designed to modulate its output 15% per minute between 40% and 100% of its nominal power. Russia has led in the practical development of floating nuclear power stations , which can be transported to the desired location and occasionally relocated or moved for easier decommissioning. In 2022, the United States Department of Energy funded

6336-402: The plant site, which is well below the design basis. The design basis accident for an earthquake was between 0.42 g (4.15 m/s) and 0.52 g (5.12 m/s) and for a tsunami was 5.2 m. All four units were automatically shut down ( scram ) immediately after the earthquake, and the diesel engines were started to power the reactor cooling. A worker died of injuries from the earthquake when he

6432-474: The plant's seawater pumps, used to cool reactors, to fail. Of the plant's four reactors, three were in danger of meltdown. One external high-voltage power line still functioned, allowing plant staff in the central control room to monitor data on internal reactor temperatures and water levels. 2,000 employees of the plant worked to stabilize the reactors. Some employees connected over 9 kilometers of cabling using 200-meter sections of cable, each weighing more than

6528-409: The plant, in response to local demands for a decision. Decommissioning is expected to take more than 40 years to complete, and will include moving spent nuclear fuel from spent fuel pools to on-site dry cask storage . Nuclear power plant A nuclear power plant ( NPP ), also known as a nuclear power station ( NPS ), nuclear generating station ( NGS ) or atomic power station ( APS )

6624-474: The prospect that all spent nuclear fuel could potentially be recycled by using future reactors, generation IV reactors are being designed to completely close the nuclear fuel cycle . However, up to now, there has not been any actual bulk recycling of waste from a NPP, and on-site temporary storage is still being used at almost all plant sites due to construction problems for deep geological repositories . Only Finland has stable repository plans, therefore from

6720-467: The radioactively contaminated systems. The primary containment system is designed to withstand strong internal pressures resulting from a leak or intentional depressurization of the reactor vessel. Some plants have a secondary containment system that encompasses the primary system. This is very common in BWRs because most of the steam systems, including the turbine, contain radioactive materials. In case of

6816-475: The reactor and drywell. Operators had to also prepare an alternate injection line for each unit, as the RCIC can run indefinitely only while there is sufficient pressure and steam in the reactor to drive its turbine. Once the reactor pressure drops below a certain level, the RCIC shuts down automatically. The normal electrically driven Emergency Core Cooling Systems (ECCS) were for the most part unavailable due to

6912-427: The reactor by the condensate and feedwater pumps. In the main condenser, the wet vapor turbine exhaust come into contact with thousands of tubes that have much colder water flowing through them on the other side. The cooling water typically come from a natural body of water such as a river or lake. Palo Verde Nuclear Generating Station , located in the desert about 97 kilometres (60 mi) west of Phoenix, Arizona,

7008-477: The reactor completely with the help of their control rods. PWRs also use boric acid to make fine adjustments to reactor power level, or reactivity, using their Chemical and Volume Control System (CVCS). In the case of LOCA, PWRs have three sources of backup cooling water, high pressure injection (HPI), low pressure injection (LPI), and core flood tanks (CFTs). They all use water with a high concentration of boron. The essential service water system (ESWS) circulates

7104-399: The reactor if the reactor building is isolated from the control and turbine buildings. Steam turbine driven cooling pumps with pneumatic controls can run at mechanically controlled adjustable speeds, without battery power, emergency generator, or off-site electrical power. The Isolation cooling system is a defensive system against a condition known as station blackout. This system is not part of

7200-445: The reactor vessel while it is pressurized. It is designed to monitor the level of coolant in the reactor vessel and automatically inject coolant when the level drops below a threshold. This system is normally the first line of defense for a reactor since it can be used while the reactor vessel is still highly pressurized. The Automatic Depressurization System (ADS) consists of a series of valves which open to vent steam several feet under

7296-756: The reactors using the Low Pressure Coolant Injection (LPCI) mode as needed. When the suppression pool was cooled down to below 100 °C, the RHR was switched to the shutdown cooling mode and brought the reactors to a cold shutdown. Coolant temperatures below 100 °C ( cold shutdown ) were reached in reactor 2 about 34 hours after the emergency shut down ( scram ). Reactors 1 and 3 followed at 1:24 and 3:52 on March 14 and Reactor 4 at 7:00 on March 15. By March 15, all four reactors of Fukushima II reached cold shutdown, which remained non-threatening. The loss of cooling water at reactors 1, 2 and 4

7392-402: The residual heat removal system (RHR) was started to cool the suppression pool and later brought the reactor to cold shutdown on March 12. In units 1, 2, and 4 heat removal was unavailable, so the suppression pools began heating up and on March 12, the water temperature in the pools of units 1, 2, and 4 reached 100 °C between 05:30 and 06:10 JST , removing the ability to remove pressure from

7488-540: The risks of future uncertainties. To date all operating nuclear power stations were developed by state-owned or regulated utilities where many of the risks associated with construction costs, operating performance, fuel price, and other factors were borne by consumers rather than suppliers. Many countries have now liberalized the electricity market where these risks and the risk of cheaper competitors emerging before capital costs are recovered, are borne by station suppliers and operators rather than consumers, which leads to

7584-407: The same element. Different isotopes also have different half-lives . U-238 has a longer half-life than U-235, so it takes longer to decay over time. This also means that U-238 is less radioactive than U-235. Since nuclear fission creates radioactivity, the reactor core is surrounded by a protective shield. This containment absorbs radiation and prevents radioactive material from being released into

7680-498: The service seawater system pumps in the pump room were repaired in units 1, 2 and 4. This allowed the restoration of the normal ECCS and heat removal systems to operable status and cooling was switched to the Residual Heat Removal System (RHR) portion of the ECCS. The RHR systems were first activated to cool down the suppression pools (torus) and drywells to operable status, and water injections were made to

7776-607: The site during emergency situations. They are usually sized such that a single one can provide all the required power for a facility to shut down during an emergency. Facilities have multiple generators for redundancy. Additionally, systems that are required to shut down the reactor have separate electrical sources (often separate generators) so that they do not affect shutdown capability. Loss of electrical power can occur suddenly and can damage or undermine equipment. To prevent damage, motor-generators can be tied to flywheels that can provide uninterrupted electrical power to equipment for

7872-512: The source of heat is eliminated. Other systems can then be used to remove decay heat from the core. All nuclear plants have some form of reactor protection system. Control rods are a series of rods that can be quickly inserted into the reactor core to absorb neutrons and rapidly terminate the nuclear reaction. They are typically composed of actinides , lanthanides , transition metals , and boron , in various alloys with structural backing such as steel. In addition to being neutron absorbent,

7968-693: The steam generator and the nuclear reactor is controlled using the feedwater system. The feedwater pump has the task of taking the water from the condensate system, increasing the pressure and forcing it into either the steam generators—in the case of a pressurized water reactor — or directly into the reactor, for boiling water reactors . Continuous power supply to the plant is critical to ensure safe operation. Most nuclear stations require at least two distinct sources of offsite power for redundancy. These are usually provided by multiple transformers that are sufficiently separated and can receive power from multiple transmission lines. In addition, in some nuclear stations,

8064-487: The steam turbine, so the turbine is kept as part of the radiologically controlled area of the nuclear power station. The electric generator converts mechanical power supplied by the turbine into electrical power. Low-pole AC synchronous generators of high rated power are used. A cooling system removes heat from the reactor core and transports it to another area of the station, where the thermal energy can be harnessed to produce electricity or to do other useful work. Typically

8160-532: The surface of a large pool of liquid water (known as the wetwell or torus) in pressure suppression type containments (typically used in boiling water reactor designs), or directly into the primary containment structure in other types of containments, such as large-dry or ice-condenser containments (typically used in pressurized water reactor designs). The actuation of these valves depressurizes the reactor vessel and allows lower pressure coolant injection systems to function, which have very large capacities in comparison to

8256-477: The turbine generator can power the station's loads while the station is online, without requiring external power. This is achieved via station service transformers which tap power from the generator output before they reach the step-up transformer. Nuclear power plants generate approximately 10% of global electricity, sourced from around 440 reactors worldwide. They are recognized as a significant provider of low-carbon electricity , accounting for about one-quarter of

8352-534: The water level. The RCICs in each unit later shut down due to low reactor pressure. The MUWC and the makeup water purification and filtering (MUPF) systems were also used to try to cool the suppression pool and drywell in addition to the reactor to prevent the drywell pressure from getting too high. Operators were later able to restore the High Pressure Core Spray portion of the ECCS in unit 4 and switched emergency water injection for unit 4 from

8448-502: The water that cools the plant's heat exchangers and other components before dissipating the heat into the environment. Because this includes cooling the systems that remove decay heat from both the primary system and the spent fuel rod cooling ponds, the ESWS is a safety-critical system. Since the water is frequently drawn from an adjacent river, the sea, or other large body of water, the system can be fouled by seaweed, marine organisms, oil pollution, ice and debris. In locations without

8544-530: The water were beginning to corrode. Approximately 3,000 tons of the water was found to contain radioactive substances, and Japan's Fisheries Agency refused permission to release that water back into the ocean. On December 26, 2011, the Prime Minister officially cancelled the nuclear emergency declaration for the Fukushima Daini plant officially ending the incident. On February 8, 2012, the plant

8640-459: The world's supply in this category. As of 2020, nuclear power stood as the second-largest source of low-carbon energy, making up 26% of the total. Nuclear power facilities are active in 32 countries or regions, and their influence extends beyond these nations through regional transmission grids, especially in Europe. In 2022, nuclear power plants generated 2545 terawatt-hours (TWh) of electricity,

8736-402: The world, and 57 nuclear power reactors under construction. Building a nuclear power plant often spans five to ten years, which can accrue significant financial costs, depending on how the initial investments are financed. Because of this high construction cost and lower operations, maintenance, and fuel costs, nuclear plants are usually used for base load generation, because this maximizes

8832-500: Was classified a level 3 on the International Nuclear Event Scale (serious incident) by Japanese authorities as of March 18. Officials made preparations for release of pressure from the plant on March 12, but no pressure release was necessary. An evacuation order was issued to the people living within 3 kilometres (1.9 mi) of the plant, subsequently expanded to 10 km (6.2 mi). Air traffic

8928-477: Was not targeted by sanctions. However, some countries, especially in Europe, scaled back or cancelled planned nuclear power plants that were to be built by Rosatom. Modern nuclear reactor designs have had numerous safety improvements since the first-generation nuclear reactors. A nuclear power plant cannot explode like a nuclear weapon because the fuel for uranium reactors is not enriched enough, and nuclear weapons require precision explosives to force fuel into

9024-474: Was opened to news media for the first time since the 2011 Tōhoku earthquake and tsunami. The evacuation order was partly rescinded for Daini evacuees in August 2012. Some of the residents, such as the 7200 at Naraha , were permitted to return during daylight hours only, but others were ordered to remain away. The area did not become seriously contaminated and was safe to visit without protective clothing. In 2015,

9120-420: Was restricted in a 10 km (6.2 mi) radius around the plant, according to a NOTAM . These zones were later superseded by the 20 km evacuation and 30 km no-fly zones around Fukushima Daiichi on March 12 and 15, respectively. As of June 2011, 7,000 tons of seawater from the tsunami remained in the plant. The plant planned to release it all back into the ocean, as the tanks and structures holding

9216-484: Was trapped in the crane operating console of the exhaust stack. The tsunami that followed the earthquake and inundated the plant was initially estimated by TEPCO to be 14 meters high, which would have been more than twice the designed height. Other sources give the tsunami height at Fukushima Daini plant at 9-meter-high, while the Fukushima Daiichi plant was hit by a 13-meter-high tsunami. The tsunami caused

#431568