Saturday, 19 March 2011

Nuclear power

Nuclear power is produced by controlled (i.e., non-explosive) nuclear reactions. Commercial and utility plants currently use nuclear fission reactions to heat water to produce steam, which is then used to generate electricity.

Nuclear power provides about 6% of the world's energy and 13–14% of the world's electricity,[1] with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity.[2] Also, more than 150 naval vessels using nuclear propulsion have been built.

Nuclear power is controversial and there is an ongoing debate about the use of nuclear energy.[3][4] Proponents, such as the World Nuclear Association and IAEA, contend that nuclear power is a sustainable energy source that reduces carbon emissions.[5] Anti-nuclear opponents, such as Greenpeace International and NIRS, believe that nuclear power poses many threats to people and the environment.[6][7][8]

Some serious nuclear and radiation accidents have occurred with nuclear-powered submarines and with nuclear power plants. Nuclear power plant accidents include the Chernobyl disaster (1986), Fukushima I nuclear accidents (2011), and the Three Mile Island accident (1979).[9] Nuclear submarine mishaps include the K-19 reactor accident (1961),[10] the K-27 reactor accident (1968),[11] and the K-431 reactor accident (1985).[9] International research is continuing into safety improvements such as passively safe plants,[12] and the possible future use of nuclear fusion.


As of 2005, nuclear power provided 6.3% of the world's energy and 15% of the world's electricity, with the U.S., France, and Japan together accounting for 56.5% of nuclear generated electricity.[2] In 2007, the IAEA reported there were 439 nuclear power reactors in operation in the world,[13] operating in 31 countries.[14] As of December 2009, the world had 436 reactors.[15] Since commercial nuclear energy began in the mid 1950s, 2008 was the first year that no new nuclear power plant was connected to the grid, although two were connected in 2009.[15][16]

Annual generation of nuclear power has been on a slight downward trend since 2007, decreasing 1.8% in 2009 to 2558 TWh with nuclear power meeting 13–14% of the world's electricity demand.[1] One factor in the nuclear power percentage decrease since 2007 has been the prolonged shutdown of large reactors at the Kashiwazaki-Kariwa Nuclear Power Plant in Japan following the Niigata-Chuetsu-Oki earthquake.[1]

The United States produces the most nuclear energy, with nuclear power providing 19%[17] of the electricity it consumes, while France produces the highest percentage of its electrical energy from nuclear reactors—80% as of 2006.[18] In the European Union as a whole, nuclear energy provides 30% of the electricity.[19] Nuclear energy policy differs among European Union countries, and some, such as Austria, Estonia, and Ireland, have no active nuclear power stations. In comparison, France has a large number of these plants, with 16 multi-unit stations in current use.

In the US, while the coal and gas electricity industry is projected to be worth $85 billion by 2013, nuclear power generators are forecast to be worth $18 billion.[20]

Many military and some civilian (such as some icebreaker) ships use nuclear marine propulsion, a form of nuclear propulsion.[21] A few space vehicles have been launched using full-fledged nuclear reactors: the Soviet RORSAT series and the American SNAP-10A.

International research is continuing into safety improvements such as passively safe plants,[22] the use of nuclear fusion, and additional uses of process heat such as hydrogen production (in support of a hydrogen economy), for desalinating sea water, and for use in district heating systems.
Nuclear fusion
Main articles: Nuclear fusion and Fusion power

Nuclear fusion reactions have the potential to be safer and generate less radioactive waste than fission.[23][24] These reactions appear potentially viable, though technically quite difficult and have yet to be created on a scale that could be used in a functional power plant. Fusion power has been under intense theoretical and experimental investigation since the 1950s.
Use in space

Both fission and fusion appear promising for space propulsion applications, generating higher mission velocities with less reaction mass. This is due to the much higher energy density of nuclear reactions: some 7 orders of magnitude (10,000,000 times) more energetic than the chemical reactions which power the current generation of rockets.

Radioactive decay has been used on a relatively small (few kW) scale, mostly to power space missions and experiments by using radioisotope thermoelectric generators such as those developed at Idaho National Laboratory.


Question book-new.svg
    This section needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (November 2010)
See also: Nuclear fission#History

The pursuit of nuclear energy for electricity generation began soon after the discovery in the early 20th century that radioactive elements, such as radium, released immense amounts of energy, according to the principle of mass–energy equivalence. However, means of harnessing such energy was impractical, because intensely radioactive elements were, by their very nature, short-lived (high energy release is correlated with short half-lives). However, the dream of harnessing "atomic energy" was quite strong, even it was dismissed by such fathers of nuclear physics like Ernest Rutherford as "moonshine." This situation, however, changed in the late 1930s, with the discovery of nuclear fission.

In 1932, James Chadwick discovered the neutron, which was immately recognized as a potential tool for nuclear experimentation because of its lack of an electric charge. Experimentation with bombardment of materials with neutrons led Frédéric and Irène Joliot-Curie to discover induced radioactivity in 1934, which allowed the creation of radium-like elements at much less the price of natural radium. Further work by Enrico Fermi in the 1930s focused on using slow neutrons to increase the effectiveness of induced radioactivity. Experiments bombarding uranium with neutrons led Fermi to believe he had created a new, transuranic element, which he dubbed hesperium.
Constructing the core of B-Reactor at Hanford Site during the Manhattan Project.

But in 1938, German chemists Otto Hahn[25] and Fritz Strassmann, along with Austrian physicist Lise Meitner[26] and Meitner's nephew, Otto Robert Frisch,[27] conducted experiments with the products of neutron-bombarded uranium, as a means of further investigating Fermi's claims. They determined that the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces, contradicting Fermi. This was an extremely surprising result: all other forms of nuclear decay involved only small changes to the mass of the nucleus, whereas this process—dubbed "fission" as a reference to biology—involved a complete rupture of the nucleus. Numerous scientists, including Leo Szilard, who was one of the first, recognized that if fission reactions released additional neutrons, a self-sustaining nuclear chain reaction could result. Once this was experimentally confirmed and announced by Frédéric Joliot-Curie in 1939, scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) petitioned their governments for support of nuclear fission research, just on the cusp of World War II.

In the United States, where Fermi and Szilard had both emigrated, this led to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, which built large reactors at the Hanford Site (formerly the town of Hanford, Washington) to breed plutonium for use in the first nuclear weapons, which were used on the cities of Hiroshima and Nagasaki. A parallel uranium enrichment effort also was pursued.
The first light bulbs ever lit by electricity generated by nuclear power at EBR-1 at what is now Idaho National Laboratory.

After World War II, the prospects of using "atomic energy" for good, rather than simply for war, were greatly advocated as a reason not to keep all nuclear research controlled by military organizations. However, most scientists agreed that civilian nuclear power would take at least a decade to master, and the fact that nuclear reactors also produced weapons-usable plutonium created a situation in which most national governments (such as those in the United States, the United Kingdom, Canada, and the USSR) attempted to keep reactor research under strict government control and classification. In the United States, reactor research was conducted by the U.S. Atomic Energy Commission, primarily at Oak Ridge, Tennessee, Hanford Site, and Argonne National Laboratory.

Work in the United States, United Kingdom, Canada, and USSR proceeded over the course of the late 1940s and early 1950s. Electricity was generated for the first time by a nuclear reactor on December 20, 1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW. Work was also strongly researched in the US on nuclear marine propulsion, with a test reactor being developed by 1953. (Eventually, the USS Nautilus, the first nuclear-powered submarine, would launch in 1955.) In 1953, US President Dwight Eisenhower gave his "Atoms for Peace" speech at the United Nations, emphasizing the need to develop "peaceful" uses of nuclear power quickly. This was followed by the 1954 Amendments to the Atomic Energy Act which allowed rapid declassification of U.S. reactor technology and encouraged development by the private sector.
Early years
Calder Hall nuclear power station in the United Kingdom was the world's first nuclear power station to produce electricity in commercial quantities.[28]
The Shippingport Atomic Power Station in Shippingport, Pennsylvania was the first commercial reactor in the USA and was opened in 1957.

On June 27, 1954, the USSR's Obninsk Nuclear Power Plant became the world's first nuclear power plant to generate electricity for a power grid, and produced around 5 megawatts of electric power.[29][30]

Later in 1954, Lewis Strauss, then chairman of the United States Atomic Energy Commission (U.S. AEC, forerunner of the U.S. Nuclear Regulatory Commission and the United States Department of Energy) spoke of electricity in the future being "too cheap to meter".[31] Strauss was referring to hydrogen fusion[32][33]—which was secretly being developed as part of Project Sherwood at the time—but Strauss's statement was interpreted as a promise of very cheap energy from nuclear fission. The U.S. AEC itself had issued far more conservative testimony regarding nuclear fission to the U.S. Congress only months before, projecting that "costs can be brought down... [to]... about the same as the cost of electricity from conventional sources..." Significant disappointment would develop later on, when the new nuclear plants did not provide energy "too cheap to meter."

In 1955 the United Nations' "First Geneva Conference", then the world's largest gathering of scientists and engineers, met to explore the technology. In 1957 EURATOM was launched alongside the European Economic Community (the latter is now the European Union). The same year also saw the launch of the International Atomic Energy Agency (IAEA).

The world's first commercial nuclear power station, Calder Hall in Sellafield, England was opened in 1956 with an initial capacity of 50 MW (later 200 MW).[28][34] The first commercial nuclear generator to become operational in the United States was the Shippingport Reactor (Pennsylvania, December 1957).

One of the first organizations to develop nuclear power was the U.S. Navy, for the purpose of propelling submarines and aircraft carriers. The first nuclear-powered submarine, USS Nautilus (SSN-571), was put to sea in December 1954.[35] Two U.S. nuclear submarines, USS Scorpion and USS Thresher, have been lost at sea. Several serious nuclear and radiation accidents have involved nuclear submarine mishaps.[11][9] The Soviet submarine K-19 reactor accident in 1961 resulted in 8 deaths and more than 30 other people were over-exposed to radiation.[10] The Soviet submarine K-27 reactor accident in 1968 resulted in 9 fatalities and 83 other injuries.[11]

The United States Army also had a nuclear power program, beginning in 1954. The SM-1 Nuclear Power Plant, at Ft. Belvoir, Virginia, was the first power reactor in the US to supply electrical energy to a commercial grid (VEPCO), in April 1957, before Shippingport. The SL-1 was a United States Army experimental nuclear power reactor which underwent a steam explosion and meltdown in 1961, killing its three operators.[36]
History of the use of nuclear power (top) and the number of active nuclear power plants (bottom).

Installed nuclear capacity initially rose relatively quickly, rising from less than 1 gigawatt (GW) in 1960 to 100 GW in the late 1970s, and 300 GW in the late 1980s. Since the late 1980s worldwide capacity has risen much more slowly, reaching 366 GW in 2005. Between around 1970 and 1990, more than 50 GW of capacity was under construction (peaking at over 150 GW in the late 70s and early 80s) — in 2005, around 25 GW of new capacity was planned. More than two-thirds of all nuclear plants ordered after January 1970 were eventually cancelled.[35] A total of 63 nuclear units were canceled in the USA between 1975 and 1980.[37]
Washington Public Power Supply System Nuclear Power Plants 3 and 5 were never completed.

During the 1970s and 1980s rising economic costs (related to extended construction times largely due to regulatory changes and pressure-group litigation)[38] and falling fossil fuel prices made nuclear power plants then under construction less attractive. In the 1980s (U.S.) and 1990s (Europe), flat load growth and electricity liberalization also made the addition of large new baseload capacity unattractive.

The 1973 oil crisis had a significant effect on countries, such as France and Japan, which had relied more heavily on oil for electric generation (39% and 73% respectively) to invest in nuclear power.[39][40] Today, nuclear power supplies about 80% and 30% of the electricity in those countries, respectively.

Some local opposition to nuclear power emerged in the early 1960s,[41] and in the late 1960s some members of the scientific community began to express their concerns.[42] These concerns related to nuclear accidents, nuclear proliferation, high cost of nuclear power plants, nuclear terrorism and radioactive waste disposal.[43] In the early 1970s, there were large protests about a proposed nuclear power plant in Wyhl, Germany. The project was cancelled in 1975 and anti-nuclear success at Wyhl inspired opposition to nuclear power in other parts of Europe and North America.[44][45] By the mid-1970s anti-nuclear activism had moved beyond local protests and politics to gain a wider appeal and influence, and nuclear power became an issue of major public protest.[46] Although it lacked a single co-ordinating organization, and did not have uniform goals, the movement's efforts gained a great deal of attention.[47] In some countries, the nuclear power conflict "reached an intensity unprecedented in the history of technology controversies".[48] In France, between 1975 and 1977, some 175,000 people protested against nuclear power in ten demonstrations.[49] In West Germany, between February 1975 and April 1979, some 280,000 people were involved in seven demonstrations at nuclear sites. Several site occupations were also attempted. In the aftermath of the Three Mile Island accident in 1979, some 120,000 people attended a demonstration against nuclear power in Bonn.[49] In May 1979, an estimated 70,000 people, including then governor of California Jerry Brown, attended a march and rally against nuclear power in Washington, D.C.[50][51] Anti-nuclear power groups emerged in every country that has had a nuclear power programme. Some of these anti-nuclear power organisations are reported to have developed considerable expertise on nuclear power and energy issues.[52]

Health and safety concerns, the 1979 accident at Three Mile Island, and the 1986 Chernobyl disaster played a part in stopping new plant construction in many countries,[53][54] although the public policy organization Brookings Institution suggests that new nuclear units have not been ordered in the U.S. because of soft demand for electricity, and cost overruns on nuclear plants due to regulatory issues and construction delays.[55]

Unlike the Three Mile Island accident, the much more serious Chernobyl accident did not increase regulations affecting Western reactors since the Chernobyl reactors were of the problematic RBMK design only used in the Soviet Union, for example lacking "robust" containment buildings.[56] Many of these reactors are still in use today. However, changes were made in both the reactors themselves (use of low enriched uranium) and in the control system (prevention of disabling safety systems) to reduce the possibility of a duplicate accident.

An international organization to promote safety awareness and professional development on operators in nuclear facilities was created: WANO; World Association of Nuclear Operators.

Opposition in Ireland and Poland prevented nuclear programs there, while Austria (1978), Sweden (1980) and Italy (1987) (influenced by Chernobyl) voted in referendums to oppose or phase out nuclear power. In July 2009, the Italian Parliament passed a law that canceled the results of an earlier referendum and allowed the immate start of the Italian nuclear program.[57] One Italian minister even called the nuclear phase-out a "terrible mistake

Nuclear reactor technology

Just as many conventional thermal power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear power plants convert the energy released from the nucleus of an atom, typically via nuclear fission.

When a relatively large fissile atomic nucleus (usually uranium-235 or plutonium-239) absorbs a neutron, a fission of the atom often results. Fission splits the atom into two or more smaller nuclei with kinetic energy (known as fission products) and also releases gamma radiation and free neutrons.[59] A portion of these neutrons may later be absorbed by other fissile atoms and create more fissions, which release more neutrons, and so on.[60]

This nuclear chain reaction can be controlled by using neutron poisons and neutron moderators to change the portion of neutrons that will go on to cause more fissions.[60] Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if unsafe conditions are detected.[61]
Three nuclear powered ships, (top to bottom) nuclear cruisers USS Bainbridge and USS Long Beach with USS Enterprise the first nuclear powered aircraft carrier in 1964. Crew members are spelling out Einstein's mass-energy equivalence formula E = mc2 on the flight deck.

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 will be used as a heat source for a boiler, and the pressurized steam from that boiler will power one or more steam turbine driven electrical generators.[62]

There are many different reactor designs, utilizing different fuels and coolants and incorporating different control schemes. Some of these designs have been engineered to meet a specific need. Reactors for nuclear submarines and large naval ships, for example, commonly use highly enriched uranium as a fuel. This fuel choice increases the reactor's power density and extends the usable life of the nuclear fuel load, but is more expensive and a greater risk to nuclear proliferation than some of the other nuclear fuels.[63]

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[64] and other designs that are believed to be nearly fool-proof are being pursued.[65] Fusion reactors, which may be viable in the future, diminish or eliminate many of the risks associated with nuclear fission.[66]

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, but this may be considered problematic, and since Chernobyl and Three Mile Island, many involved now consider informed consent and morality should be primary considerations

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 certain reactors, this is no longer true of at least some modern designs.[68] For a full discussion of the issues see[69]

Nuclear plants are routinely used in load following mode on a large scale in France.[70]

Boiling water reactors normally have load-following capability, implemented by varying the recirculation water flow.

Life cycle

A nuclear reactor is only part of the life-cycle for nuclear power. The process starts with mining (see Uranium mining). Uranium mines are underground, open-pit, or in-situ leach mines. In any case, the uranium ore is extracted, usually converted into a stable and compact form such as yellowcake, and then transported to a processing facility. Here, the yellowcake is converted to uranium hexafluoride, which is then enriched using various techniques. At this point, the enriched uranium, containing more than the natural 0.7% U-235, is used to make rods of the proper composition and geometry for the particular reactor that the fuel is destined for. The fuel rods will spend about 3 operational cycles (typically 6 years total now) inside the reactor, generally until about 3% of their uranium has been fissioned, then they will be moved to a spent fuel pool where the short lived isotopes generated by fission can decay away. After about 5 years in a spent fuel pool the spent fuel is radioactively and thermally cool enough to handle, and it can be moved to dry storage casks or reprocessed.

Conventional fuel resources

Uranium is a fairly common element in the Earth's crust. Uranium is approximately as common as tin or germanium in Earth's crust, and is about 40 times more common than silver.[71] Uranium is a constituent of most rocks, dirt, and of the oceans. The fact that uranium is so spread out is a problem because mining uranium is only economically feasible where there is a large concentration. Still, the world's present measured resources of uranium, economically recoverable at a price of 130 USD/kg, are enough to last for "at least a century" at current consumption rates.[72][73] This represents a higher level of assured resources than is normal for most minerals. On the basis of analogies with other metallic minerals, a doubling of price from present levels could be expected to create about a tenfold increase in measured resources, over time. However, the cost of nuclear power lies for the most part in the construction of the power station. Therefore the fuel's contribution to the overall cost of the electricity produced is relatively small, so even a large fuel price escalation will have relatively little effect on final price. For instance, typically a doubling of the uranium market price would increase the fuel cost for a light water reactor by 26% and the electricity cost about 7%, whereas doubling the price of natural gas would typically add 70% to the price of electricity from that source. At high enough prices, eventually extraction from sources such as granite and seawater become economically feasible.[74][75]

Current light water reactors make relatively inefficient use of nuclear fuel, fissioning only the very rare uranium-235 isotope. Nuclear reprocessing can make this waste reusable and more efficient reactor designs allow better use of the available resources.