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This article is about electricity generation from nuclear power. For the general topic of nuclear power, see Nuclear power.
Nuclear power plants are usually considered to be base load stations, since fuel is a small part of the cost of production.[3]
Contents
History
- For more history, see nuclear reactor, nuclear power and nuclear fission.
Systems
- This section has recently been translated from the German Wikipedia.
Nuclear reactors
Main article: Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most common use of nuclear reactors is for the generation of electric energy and for the propulsion of ships.The nuclear reactor is the heart of the plant. In its central part, the reactor core's heat is generated by controlled nuclear fission. With this heat, a coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines, which in turn powers either ship's propellers or electrical generators.
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 the environment. In addition, many reactors are equipped with a dome of concrete to protect the reactor against both internal casualties and external impacts.
In nuclear power plants, different types of reactors, nuclear fuels, and cooling circuits and moderators are used.
Steam turbine
Main article: Steam turbine
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 so
aligned to prevent debris from the destruction of a turbine in
operation from flying towards the reactor.[citation needed]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 is the outlet steam of the steam generator mounted an activity meter. In contrast, boiling water reactors and the steam turbine with radioactive water applied and therefore part of the control area of the nuclear power plant.
Generator
Main article: Electric generator
The generator converts kinetic energy supplied by the turbine into
electrical energy. Low-pole AC synchronous generators of high rated
power are used.Cooling system
A cooling system removes heat from the reactor core and transports it to another area of the plant, where the thermal energy can be harnessed to produce electricity or to do other useful work. Typically the hot coolant is used as a heat source for a boiler, and the pressurized steam from that boiler powers one or more steam turbine driven electrical generators.[6]Safety valves
In the event of an emergency, two independent 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 the BWR, the steam is directed into the condensate chamber and condenses there. The chambers on a heat exchanger are connected to the intermediate cooling circuit.Feedwater pump
The water level in the steam generator and 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 (Pressurized Water Reactor) or directly into the reactor vessel (Boiling Water Reactor).Emergency power supply
The emergency power supplies of a nuclear power plant are built up by several layers of redundancy, such as diesel generators, gas turbine generators and battery buffers. The battery backup provides uninterrupted coupling of the diesel/gas turbine units to the power supply network. If necessary, the emergency power supply allows the safe shut down of the nuclear reactor. Less important auxiliary systems such as, for example, heat tracing of pipelines are not supplied by these back ups. The majority of the required power is used to supply the feed pumps in order to cool the reactor and remove the decay heat after a shut down.People in a nuclear power plant
- Nuclear engineers
- Reactor operators
- Health physicists
- Emergency response team personnel
- Nuclear Regulatory Commission Resident Inspectors
Economics
Main article: Economics of new nuclear power plants
The economics of new nuclear power plants is a controversial subject,
and multi-billion dollar investments ride on the choice of an energy
source. Nuclear power plants typically have high capital costs, but low
direct fuel costs, with 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 plants. Cost estimates take into account plant decommissioning and nuclear waste storage or recycling costs in the United States due to the Price Anderson Act. With the prospect that all spent nuclear fuel/"nuclear waste" could potentially be recycled by using future reactors, generation IV reactors, that are being designed to completely close the nuclear fuel cycle.On the other hand, 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 futuristic Generation IV reactors promise 10000-30000% greater fuel efficiency and the elimination of nuclear waste.
In Eastern Europe, a number of long-established projects are struggling to find finance, notably Belene in Bulgaria and the additional reactors at Cernavoda in Romania, and some potential backers have pulled out.[8] Where cheap gas is available and its future supply relatively secure, this also poses a major problem for nuclear projects.[8]
Analysis of the economics of nuclear power must take into account who bears the risks of future uncertainties. To date all operating nuclear power plants were developed by state-owned or regulated utility monopolies[9] 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 plant suppliers and operators rather than consumers, which leads to a significantly different evaluation of the economics of new nuclear power plants.[10]
Following the 2011 Fukushima I nuclear accidents, costs are likely to go up for currently operating and new nuclear power plants, due to increased requirements for on-site spent fuel management and elevated design basis threats.[11] 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, this largely eliminates the necessity to spend more on redundant back up safety equipment.
Safety
There are trades to be made between safety, economic and technical properties of different reactor designs for particular applications. Historically these decisions were often made in private by scientists, regulators and engineers,[citation needed] but this may be considered problematic, and since Chernobyl and Three Mile Island, many involved now consider informed consent and morality to be primary considerations.[12]Complexity
Nuclear power plants are some of the most sophisticated and complex energy systems ever designed.[13] Any complex system, no matter how well it is designed and engineered, cannot be deemed failure-proof.[14] Veteran anti-nuclear activist and author Stephanie Cooke has argued:The reactors themselves were enormously complex machines with an incalculable number of things that could go wrong. When that happened at Three Mile Island in 1979, another fault line in the nuclear world was exposed. One malfunction led to another, and then to a series of others, until the core of the reactor itself began to melt, and even the world's most highly trained nuclear engineers did not know how to respond. The accident revealed serious deficiencies in a system that was meant to protect public health and safety.[15]The 1979 Three Mile Island accident inspired Perrow's book Normal Accidents, where a nuclear accident occurs, resulting from an unanticipated interaction of multiple failures in a complex system. TMI was an example of a normal accident because it was "unexpected, incomprehensible, uncontrollable and unavoidable".[16]
Perrow concluded that the failure at Three Mile Island was a consequence of the system's immense complexity. Such modern high-risk systems, he realized, were prone to failures however well they were managed. It was inevitable that they would eventually suffer what he termed a 'normal accident'. Therefore, he suggested, we might do better to contemplate a radical redesign, or if that was not possible, to abandon such technology entirely.[17] .A fundamental issue contributing to a nuclear power system's complexity is its extremely long lifetime. The timeframe from the start of construction of a commercial nuclear power station through the safe disposal of its last radioactive waste, may be 100 to 150 years.[13]
Failure modes of nuclear power plants
There are concerns that a combination of human and mechanical error at a nuclear facility could result in significant harm to people and the environment:[18]Operating nuclear reactors contain large amounts of radioactive fission products which, if dispersed, can pose a direct radiation hazard, contaminate soil and vegetation, and be ingested by humans and animals. Human exposure at high enough levels can cause both short-term illness and death and longer-term death by cancer and other diseases.[19]It is impossible for a commercial nuclear reactor to explode like a nuclear bomb since the fuel is never sufficiently enriched for this to occur.[20]
Nuclear reactors can fail in a variety of ways. Should the instability of the nuclear material generate unexpected behavior, it may result in an uncontrolled power excursion. Normally, the cooling system in a reactor is designed to be able to handle the excess heat this causes; however, should the reactor also experience a loss-of-coolant accident, then the fuel may melt or cause the vessel in which it is contained to overheat and melt. This event is called a nuclear meltdown.
After shutting down, for some time the reactor still needs external energy to power its cooling systems. Normally this energy is provided by the power grid to which that plant is connected, or by emergency diesel generators. Failure to provide power for the cooling systems, as happened in Fukushima I, can cause serious accidents.
Nuclear safety rules in the United States "do not adequately weigh the risk of a single event that would knock out electricity from the grid and from emergency generators, as a quake and tsunami recently did in Japan", Nuclear Regulatory Commission officials said in June 2011.[21]
Nuclear terrorists may intentionally cause such an incident.
Vulnerability of nuclear plants to attack
Nuclear reactors become preferred targets during military conflict and, over the past three decades, have been repeatedly attacked during military air strikes, occupations, invasions and campaigns:[22]- In September 1980, Iran bombed the Al Tuwaitha nuclear complex in Iraq, in Operation Scorch Sword.
- In June 1981, an Israeli air strike completely destroyed Iraq’s Osirak nuclear research facility.
- Between 1984 and 1987, Iraq bombed Iran’s Bushehr nuclear plant six times.
- In 1991, the U.S. bombed three nuclear reactors and an enrichment pilot facility in Iraq.
- In 1991, Iraq launched Scud missiles at Israel’s Dimona nuclear power plant.
- In September 2007, Israel bombed a Syrian reactor under construction.[22]
Attack from the air is an issue that has been highlighted since the September 11 attacks in the U.S. However, it was in 1972 when three hijackers took control of a domestic passenger flight along the east coast of the U.S. and threatened to crash the plane into a U.S. nuclear weapons plant in Oak Ridge, Tennessee. The plane got as close as 8,000 feet above the site before the hijackers’ demands were met.[24][25]
The most important barrier against the release of radioactivity in the event of an aircraft strike on a nuclear power plant is the containment building and its missile shield. Current NRC Chairman Dale Klein has said "Nuclear power plants are inherently robust structures that our studies show provide adequate protection in a hypothetical attack by an airplane. The NRC has also taken actions that require nuclear power plant operators to be able to manage large fires or explosions—no matter what has caused them."[26]
In addition, supporters point to large studies carried out by the U.S. Electric Power Research Institute that tested the robustness of both reactor and waste fuel storage and found that they should be able to sustain a terrorist attack comparable to the September 11 terrorist attacks in the U.S. Spent fuel is usually housed inside the plant's "protected zone"[27] or a spent nuclear fuel shipping cask; stealing it for use in a "dirty bomb" would be extremely difficult. Exposure to the intense radiation would almost certainly quickly incapacitate or kill anyone who attempts to do so.[28]
Plant location
The design of plants located in seismically active zones also requires the risk of earthquakes and tsunamis to be taken into account. Japan, India, China and the USA are among the countries to have plants in earthquake-prone regions. Damage caused to Japan's Kashiwazaki-Kariwa Nuclear Power Plant during the 2007 Chūetsu offshore earthquake[32][33] underlined concerns expressed by experts in Japan prior to the Fukushima accidents, who have warned of a genpatsu-shinsai (domino-effect nuclear power plant earthquake disaster).[34]
Multiple reactors
The Fukushima nuclear disaster illustrated the dangers of building multiple nuclear reactor units close to one another. This proximity triggered[citation needed] the parallel, chain-reaction accidents that led to hydrogen explosions damaging reactor buildings and water draining from open-air spent fuel pools -- a situation that was potentially more dangerous than the loss of reactor cooling itself. Because of the closeness of the reactors, Plant Director Masao Yoshida "was put in the position of trying to cope simultaneously with core meltdowns at three reactors and exposed fuel pools at three units".[35]Nuclear safety systems
Main article: Nuclear safety systems
The three primary objectives of nuclear safety systems as defined by the Nuclear Regulatory Commission
are to shut down the reactor, maintain it in a shutdown condition, and
prevent the release of radioactive material during events and accidents.[36]
These objectives are accomplished using a variety of equipment, which
is part of different systems, of which each performs specific functions.Routine emissions of radioactive materials
For the controversial debate on the health effects by the routine emissions, see Nuclear power debate#Health effects on population near nuclear power plants and workers and Environmental impact of nuclear power#Risk of cancer.
During everyday routine operations, emissions of radioactive
materials from nuclear plants are released to the outside of the plants
although they are quite slight amounts.[37][38][39][40] The daily emissions go into the air, water and soil.[38][39]NRC says, "nuclear power plants sometimes release radioactive gases and liquids into the environment under controlled, monitored conditions to ensure that they pose no danger to the public or the environment",[41] and "routine emissions during normal operation of a nuclear power plant are never lethal".[42]
According to the United Nations (UNSCEAR), regular nuclear power plant operation including the nuclear fuel cycle amounts to 0.0002 mSv (milli-Sievert) annually in average public radiation exposure; the legacy of the Chernobyl disaster is 0.002 mSv/yr as a global average as of a 2008 report; and natural radiation exposure averages 2.4 mSv annually although frequently varying depending on an individual's location from 1 to 13 mSv.[43]
The Japanese myth of absolute safety
In Japan, many government agencies and nuclear companies have promoted a public myth of "absolute safety" that nuclear power proponents had nurtured over decades.[44] The tsunami that began the Fukushima nuclear disaster could and should have been anticipated[45][verification needed] and in March 2012, Prime Minister Yoshihiko Noda acknowledged that the Japanese government shared the blame for the Fukushima disaster, saying that officials had been blinded to the country's "technological infallibility", and were all too steeped in a "safety myth".[46]In Japan, a national program to develop robots for use in nuclear emergencies was terminated in midstream because it "smacked too much of underlying danger". Japan, supposedly a major power in robotics, had none to send in to Fukushima during the disaster. Similarly, Japan’s Nuclear Safety Commission stipulated in its safety guidelines for light-water nuclear facilities that “the potential for extended loss of power need not be considered.” However, it was exactly such an extended loss of power to the cooling pumps that caused the meltdown at the Fukushima nuclear facilities.[47]
Controversy
Main article: Nuclear power debate
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.[54] Proponents advance the notion that nuclear power produces virtually no air pollution, in contrast to 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.[55]
Opponents say that nuclear power poses many threats to people and the environment. These threats include health risks and environmental damage from uranium mining, processing and transport, the risk of nuclear weapons proliferation or sabotage, and the unsolved problem of radioactive nuclear waste.[56][57][58] 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.[59][60] Critics do not believe that these risks can be reduced through new technology.[61] They argue that when all 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.[62][63][64]
Reprocessing
Main article: Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate
and recover fissionable plutonium from irradiated nuclear fuel.[65]
Reprocessing serves multiple purposes, whose relative importance has
changed over time. Originally reprocessing was used solely to extract
plutonium for producing nuclear weapons. With the commercialization of nuclear power, the reprocessed plutonium was recycled back into MOX nuclear fuel for thermal reactors.[66] The reprocessed uranium,
which constitutes the bulk of the spent fuel material, can in principle
also be re-used as fuel, but that is only economic when uranium prices
are high or disposal is expensive. Finally, the breeder reactor can employ not only the recycled plutonium and uranium in spent fuel, but all the actinides, closing the nuclear fuel cycle and potentially multiplying the energy extracted from natural uranium by more than 60 times.[67]Nuclear reprocessing reduces the volume of high-level waste, but by itself does not reduce radioactivity or heat generation and therefore does not eliminate the need for a geological waste repository. Reprocessing has been politically controversial because of the potential to contribute to nuclear proliferation, the potential vulnerability to nuclear terrorism, the political challenges of repository siting (a problem that applies equally to direct disposal of spent fuel), and because of its high cost compared to the once-through fuel cycle.[68] In the United States, the Obama administration stepped back from President Bush's plans for commercial-scale reprocessing and reverted to a program focused on reprocessing-related scientific research.[69]
Accident indemnification
The Vienna Convention on Civil Liability for Nuclear Damage puts in place an international framework for nuclear liability.[70] However states with a majority of the world's nuclear power plants, including the U.S., Russia, China and Japan, are not party to international nuclear liability conventions.In the U.S., insurance for nuclear or radiological incidents is covered (for facilities licensed through 2025) by the Price-Anderson Nuclear Industries Indemnity Act.
Under the Energy policy of the United Kingdom through its Nuclear Installations Act of 1965, liability is governed for nuclear damage for which a UK nuclear licensee is responsible. The Act requires compensation to be paid for damage up to a limit of £150 million by the liable operator for ten years after the incident. Between ten and thirty years afterwards, the Government meets this obligation. The Government is also liable for additional limited cross-border liability (about £300 million) under international conventions (Paris Convention on Third Party Liability in the Field of Nuclear Energy and Brussels Convention supplementary to the Paris Convention).[71]
Decommissioning
Main article: Nuclear decommissioning
Nuclear decommissioning is the dismantling of a nuclear power
plant and decontamination of the site to a state no longer requiring
protection from radiation for the general public. The main difference
from the dismantling of other power plants is the presence of radioactive material that requires special precautions.Generally speaking, nuclear plants were designed for a life of about 30 years.[citation needed] Newer plants are designed for a 40 to 60-year operating life.[citation needed]
Decommissioning involves many administrative and technical actions. It includes all clean-up of radioactivity and progressive demolition of the plant. Once a facility is decommissioned, there should no longer be any danger of a radioactive accident or to any persons visiting it. After a facility has been completely decommissioned it is released from regulatory control, and the licensee of the plant no longer has responsibility for its nuclear safety.
Historic accidents
Main article: Nuclear power accidents by country
The nuclear industry says that new technology and oversight have made nuclear plants much safer, but 57 small accidents have occurred since the Chernobyl disaster in 1986 until 2008. Two thirds of these mishaps occurred in the US.[74]
The French Atomic Energy Agency (CEA) has concluded that technical
innovation cannot eliminate the risk of human errors in nuclear plant
operation.[citation needed]According to Benjamin Sovacool, an interdisciplinary team from MIT in 2003 estimated that given the expected growth of nuclear power from 2005 – 2055, at least four serious nuclear accidents would be expected in that period.[74] However the MIT study Benjamin Sovacool references does not state this, instead the authors of the MIT study acknowledge that this estimated accident number does not take into account the existing, as of the time of publishing in 2003, and future, improvements in safety,[75] with the authors basing this assumed high accident rate, cited by Sovacool, only if none of the improvements in safety technology from 1970 to 2003 were implemented.[76] Therefore the figure the MIT team suggest, by their own account, would only be possible if the world nuclear fleet were to continue to operate and build old Generation II reactors and not learn from past mistakes, and that the world fleet would not include any of the presently(as of 2013) built, Generation III or in design phase Generation IV nuclear power plants between 2005 and 2055. The interdisciplinary team from MIT also went on to endorse that it was possible to make nuclear power safe,[76] going on to state that the substantial safety features of then under construction Generation III reactors appear "plausible" at reducing the serious accident rate to near zero with, amongst other features, the use of passive nuclear safety features, which are now part of the state of the art in nuclear reactor safety.[76]
Flexibility of nuclear power plants
It is often claimed that nuclear stations are inflexible in their output, implying that other forms of energy would be required to meet peak demand. While that is true for the vast majority of reactors, this is no longer true of at least some modern designs.[77]Nuclear plants are routinely used in load following mode on a large scale in France.[78] Unit A at the German Biblis Nuclear Power Plant is designed to in- and decrease its output 15% per minute between 40 and 100% of its nominal power.[79] Boiling water reactors normally have load-following capability, implemented by varying the recirculation water flow.[citation needed]
Future power plants
A number of new designs for nuclear power generation, collectively known as the Generation IV reactors, are the subject of active research and may be used for practical power generation in the future. Many of these new designs specifically attempt to make fission reactors cleaner, safer and/or less of a risk to the proliferation of nuclear weapons. Passively safe plants (such as the ESBWR) are available to be built[80] and other designs that are believed to be nearly fool-proof are being pursued.[81] Fusion reactors, which may be viable in the future, diminish or eliminate many of the risks associated with nuclear fission.[82]The 1600 MWe European Pressurized Reactor reactor is being built in Olkiluoto, Finland. A joint effort of French AREVA and German Siemens AG, it will be the largest reactor in the world. In December 2006 construction was about 18 months behind schedule so completion was expected 2010-2011.[83][84]
As of March 2007, there are seven nuclear power plants under construction in India, and five in China.[85]
In November 2011 Gulf Power stated that by the end of 2012 it hopes to finish buying off 4000 acres of land north of Pensacola, Florida in order to build a possible nuclear power plant.[86]
Russia has begun building the world’s first floating nuclear power plant. The £100 million vessel, the Lomonosov, is the first of seven plants that Moscow says will bring vital energy resources to remote Russian regions.[87]
By 2025, Southeast Asia nations would have a total of 29 nuclear power plants, Indonesia will have 4 nuclear power plants, Malaysia 4, Thailand 5 and Vietnam 16 from nothing at all in 2011.[88]
Expansion at two Nuclear Power Plants in the United States, Plant Vogtle and V. C. Summer Nuclear Power Plant, located in Georgia and South Carolina, respectively, are scheduled to be completed between 2016 and 2019. The two new Plant Vogtle reactors, and the two new reactors at Virgil C. Summer Nuclear Plant, represent the first nuclear power construction projects in the United States since the Three Mile Island nuclear accident in 1979.
See also
- List of nuclear reactors
- Nuclear power by country
- Nuclear Information and Resource Service
- Fossil-fuel power station
- Gerald W. Brown, American whistleblower on passive fire protection/circuit integrity deficiencies in US and Canadian plants
- Nuclear fuel cycle
- Containment building
- Safety engineering
- SCRAM
- U.S. Federal Emergency Management Agency (FEMA)
- Nuclear Regulatory Commission of the USA
- Auxiliary feedwater
- Uranium market
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