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Nuclear power

2007 Schools Wikipedia Selection. Related subjects: Engineering

   A nuclear power station. Fog rises from the hyperboloid shaped cooling
   towers. The nuclear reactors are inside the cylindrical containment
   buildings.
   Enlarge
   A nuclear power station. Fog rises from the hyperboloid shaped cooling
   towers. The nuclear reactors are inside the cylindrical containment
   buildings.

   Nuclear power is the controlled use of nuclear reactions to release
   energy for work including propulsion, heat, and the generation of
   electricity. Human use of nuclear power to do significant useful work
   is currently limited to nuclear fission and radioactive decay. Nuclear
   energy is produced when a fissile material, such as uranium-235 (
   ^235U), is concentrated such that nuclear fission takes place in a
   controlled chain reaction and creates heat — which is used to boil
   water, produce steam, and drive a steam turbine. The turbine can be
   used for mechanical work and also to generate electricity. Nuclear
   power is used to power most military submarines and aircraft carriers
   and provides 7% of the world's energy and 15.7% of the world's
   electricity. Nuclear energy policy differs between countries. The
   United States produces the most nuclear energy, with nuclear power
   providing 20% of the electricity it consumes, while France produces the
   highest percentage of its electrical energy from nuclear reactors—80%
   as of 2006.

   Nuclear energy uses an abundant, widely distributed fuel, and mitigates
   the greenhouse effect if used to replace fossil-fuel-derived
   electricity. International research is ongoing into various safety
   improvements, the use of nuclear fusion and additional uses such as the
   generation of hydrogen (in support of hydrogen economy schemes), for
   desalinating sea water, and for use in district heating systems.
   Construction of nuclear power plants declined following the 1979 Three
   Mile Island accident and the 1986 disaster at Chernobyl. Lately, there
   has been renewed interest in nuclear energy from national governments,
   the public, and some notable environmentalists due to increased oil
   prices, new passively safe designs of plants, and the low emission rate
   of greenhouse gas which some governments need to meet the standards of
   the Kyoto Protocol. A few reactors are under construction, and several
   new types of reactors are planned.

   The use of nuclear power is controversial because of the problem of
   storing radioactive waste for indefinite periods, the potential for
   possibly severe radioactive contamination by accident or sabotage, and
   the possibility that its use in some countries could lead to the
   proliferation of nuclear weapons. Proponents believe that these risks
   are small and can be further reduced by the technology in the new
   reactors. They further claim that the safety record is already good
   when compared to other fossil-fuel plants, that it releases much less
   radioactive waste than coal power, and that nuclear power is a
   sustainable energy source. Critics, including most major environmental
   groups, believe nuclear power is an uneconomic, unsound and potentially
   dangerous energy source, especially compared to renewable energy, and
   dispute whether the costs and risks can be reduced through new
   technology. There is concern in some countries over North Korea and
   Iran operating research reactors and fuel enrichment plants, since
   those countries refuse adequate IAEA oversight and are believed to be
   trying to develop nuclear weapons. North Korea admits that it is
   developing nuclear weapons, while the Iranian government vehemently
   denies the claims against Iran.

History

Origins

   The first successful experiment with nuclear fission was conducted in
   1938 in Berlin by the German physicists Otto Hahn, Lise Meitner and
   Fritz Strassmann.

   During the Second World War, a number of nations embarked on crash
   programs to develop nuclear energy, focusing first on the development
   of nuclear reactors. The first self-sustaining nuclear chain reaction
   was obtained at the University of Chicago by Enrico Fermi on December
   2, 1942, and reactors based on his research were used to produce the
   plutonium necessary for the " Fat Man" weapon dropped on Nagasaki,
   Japan. Several nations began their own construction of nuclear reactors
   at this point, primarily for weapons use, though research was also
   being conducted into their use for civilian electricity generation.

   Electricity was generated for the first time by a nuclear reactor on
   December 20, 1951 at the EBR-I experimental fast breeder station near
   Arco, Idaho, which initially produced about 100 kW.

   In 1952 a report by the Paley Commission (The President's Materials
   Policy Commission) for President Harry Truman made a "relatively
   pessimistic" assessment of nuclear power, and called for "aggressive
   research in the whole field of solar energy".

   A December 1953 speech by President Dwight Eisenhower, " Atoms for
   Peace", set the U.S. on a course of strong government support for the
   international use of nuclear power.

Early years

   The Beaver Valley Nuclear Generating Station in Shippingport,
   Pennsylvania was the first commercial reactor in the USA and was opened
   in 1957.
   Enlarge
   The Beaver Valley Nuclear Generating Station in Shippingport,
   Pennsylvania was the first commercial reactor in the USA and was opened
   in 1957.

   On June 27, 1954, the world's first nuclear power plant to generate
   electricity for a power grid started operations at Obninsk, USSR. The
   reactor was graphite moderated, water cooled and had a capacity of 5
   megawatts (MW). The world's first commercial nuclear power station,
   Calder Hall in Sellafield, England was opened in 1956, a gas-cooled
   Magnox reactor with an initial capacity of 50 MW (later 200 MW). The
   Shippingport Reactor ( Pennsylvania, 1957), a pressurized water
   reactor, was the first commercial nuclear generator to become
   operational in the United States.

   In 1954, the chairman of the United States Atomic Energy Commission
   (forerunner of the U.S. Nuclear Regulatory Commission) talked about
   electricity being "too cheap to meter" in the future, often misreported
   as a concrete statement about nuclear power, and foresaw 1000 nuclear
   plants on line in the USA by the year 2000.

   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).

   Thanks to the presence of the nearby Bettis Laboratory and the
   Shippingport power plant, Pittsburgh, Pennsylvania became the world's
   first nuclear powered city in 1960.

Development

   Installed nuclear capacity initially rose relatively quickly, rising
   from less than 1 gigawatt (GW) in 1960 to 100GW in the late 1970s, and
   300GW in the late 1980s. Since the late 1980s capacity has risen much
   more slowly, reaching 366GW in 2005, primarily due to Chinese expansion
   of nuclear power. Between around 1970 and 1990, more than 50GW of
   capacity was under construction (peaking at over 150GW in the late 70s
   and early 80s) — in 2005, around 25GW of new capacity was planned. More
   than two-thirds of all nuclear plants ordered after January 1970 were
   eventually cancelled.

   During the 1970s and 1980s rising economic costs (related to vastly
   extended construction times largely due to regulatory delays) 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 unnecessary.
   Washington Public Power Supply System Nuclear Power Plants 3 and 5 were
   never completed
   Enlarge
   Washington Public Power Supply System Nuclear Power Plants 3 and 5 were
   never completed

   A general movement against nuclear power arose during the last third of
   the 20th century, based on the fear of a possible nuclear accident and
   on fears of latent radiation, and on the opposition to nuclear waste
   production, transport and final storage. Perceived risks on the
   citizens health and safety, the 1979 accident at Three Mile Island and
   the 1986 Chernobyl accident played a key part in stopping new plant
   construction in many countries. Austria (1978), Sweden (1980) and Italy
   (1987) voted in referendums to oppose or phase out nuclear power, while
   opposition in Ireland prevented a nuclear programme there. However, the
   Brookings Institution suggests that new nuclear units have not been
   ordered primarily for economic reasons rather than fears of accidents.

   Financing for new reactors dried up when Wall Street's enthusiasm
   ended. Disillusionment was complete when new research discredited the
   claim (previously accepted as fact even by opponents) that nuclear
   power was still, despite all its problems, the most cost-effective
   source of electrity. Industry figures had omitted the factor of
   downtime. During the 1980s and early 1990s, the newest and biggest U.S.
   plants were actually producing only half the energy they were supposed
   to, due to shutdowns for refueling, routine maintenance, retrofitting,
   and frequent minor mishaps. Since that time, the capacity factor of
   existing nuclear power plants has increased dramatically, and has been
   near 90% in the current decade.

   As of 2006, the stated desire to use nuclear power for electricity
   generation has been suspected of being a cover for nuclear
   proliferation in the countries of Iran and North Korea.

Reactor types

Current technology

   There are two types of nuclear power sources in current use:
    1. The nuclear fission reactor produces heat through a controlled
       nuclear chain reaction in a critical mass of fissile material.
       All current nuclear power plants are critical fission reactors,
       which are the focus of this article. The output of fission reactors
       is controllable. There are several subtypes of critical fission
       reactors, which can be classified as Generation I, Generation II
       and Generation III. All reactors will be compared to the
       Pressurized Water Reactor (PWR), as that is the standard modern
       reactor design.
       The difference between fast-spectrum and thermal-spectrum reactors
       will be covered later. In general, fast-spectrum reactors will
       produce less waste, and the waste they do produce will have a
       vastly shorter halflife, but they are more difficult to build, and
       more expensive to operate. Fast reactors can also be breeders,
       whereas thermal reactors generally cannot.

        A. Pressurized water reactors (PWR)
                These are reactors cooled and moderated by high pressure,
                liquid (even at extreme temperatures) water. They are the
                majority of current reactors, and are generally considered
                the safest and most reliable technology currently in large
                scale deployment, although Three Mile Island is a reactor
                of this type. This is a thermal neutron reactor design.

        B. Boiling water reactors (BWR)
                These are reactors cooled and moderated by water, under
                slightly lower pressure. The water is allowed to boil in
                the reactor. The thermal efficiency of these reactors can
                be higher, and they can be simpler, and even potentially
                more stable and safe. Unfortunately, the boiling water
                puts more stress on many of the components, and increases
                the risk that radioactive water may escape in an accident.
                These reactors make up a substantial percentage of modern
                reactors. This is a thermal neutron reactor design.

        C. Pressurised Heavy Water Reactor (PHWR)
                A Canadian design, (known as CANDU) these reactors are
                heavy-water-cooled and -moderated Pressurized-Water
                reactors. Instead of using a single large containment
                vessel as in a PWR, the fuel is contained in hundreds of
                pressure tubes. These reactors are fuelled with natural
                uranium and are thermal neutron reactor designs. PHWRs can
                be refueled while at full power, which makes them very
                efficient in their use of uranium (it allows for precise
                flux control in the core). Most PHWR's exist within
                Canada, but units have been sold to Argentina, China,
                India (pre-NPT), Pakistan (pre-NPT), Romania, and South
                Korea. India also operates a number of PHWR's, often
                termed 'CANDU-derivatives', built after the 1974 Smiling
                Buddha nuclear weapon test.

        D. RBMKs
                A Soviet Union design, built to produce plutonium as well
                as power, the dangerous and unstable RBMKs are water
                cooled with a graphite moderator. RBMKs are in some
                respects similar to CANDU in that they are refuelable
                On-Load and employ a pressure tube design instead of a
                PWR-style pressure vessel. However, unlike CANDU they are
                very unstable and too large to have containment buildings.
                Because of this RBMK reactors are generally considered one
                of the most dangerous reactor designs in use. Chernobyl
                was an RBMK.

        E. Gas Cooled Reactor (GCR) and Advanced Gas Cooled Reactor (AGCR)
                These are generally graphite moderated and CO[2] cooled.
                They have a high thermal efficiency compared with PWRs and
                an excellent safety record. There are a number of
                operating reactors of this design, mostly in the United
                Kingdom. Older designs (i.e. Magnox stations) are either
                shut down or will be in the near future. However the AGCRs
                have an anticipated life of a further 10 to 20 years. This
                is a thermal neutron reactor design.

        F. Super Critical Water-cooled Reactor (SCWR)
                This is a theoretical reactor design that is part of the
                Gen-IV reactor project. It combines higher efficiency than
                a GCR with the safety of a PWR, though it is perhaps more
                technically challenging than either. The water is
                pressurized and heated past its critical point, until
                there is no difference between the liquid and gas states.
                An SCWR is similar to a BWR, except there is no boiling
                (as the water is critical), and the thermal efficiency is
                higher as the water behaves more like a classical gas.
                This is an epithermal neutron reactor design.

        G. Liquid Metal Fast Breeder Reactor (LMFBR)
                This is a reactor design that is cooled by liquid metal,
                and totally unmoderated. These reactors can function much
                like a PWR in terms of efficiency, and do not require much
                high pressure containment, as the liquid metal does not
                need to be kept at high pressure, even at very high
                temperatures. Superphénix in France was a reactor of this
                type, as was Fermi-I in the United States. The Monju
                reactor in Japan suffered a sodium leak in 1995 and is
                approved for restart in 2008. All three use/used liquid
                sodium. These reactors are fast neutron, not thermal
                neutron designs. These reactors come in two types:

              Lead Cooled
                      Using lead as the liquid metal provides excellent
                      radiation shielding, and allows for operation at
                      very high temperatures. Also, lead is (mostly)
                      transparent to neutrons, so fewer neutrons are lost
                      in the coolant, and the coolant does not become
                      radioactive. Unlike sodium, lead is mostly inert, so
                      there is less risk of explosion or accident, but
                      such large quantities of lead may be problematic
                      from toxicology and disposal points of view. Often a
                      reactor of this type would use a lead-bismuth
                      eutectic mixture. In this case, the bismuth would
                      present some minor radiation problems, as it is not
                      quite as transparent to neutrons, and can be
                      transmuted to a radioactive isotope more readily
                      than lead.

              Sodium cooled
                      Most LMFBRs are of this type. The sodium is
                      relatively easy to obtain and work with, and it also
                      manages to actually remove corrosion on the various
                      reactor parts immersed in it. However, sodium
                      explodes violently when exposed to water, so care
                      must be taken, but such explosions wouldn't be
                      vastly more violent than (for example) a leak of
                      superheated fluid from a CWR or PWR.

    2. The radioisotope thermoelectric generator produces heat through
       passive radioactive decay.

                Some radioisotope thermoelectric generators have been
                created to power space probes (for example, the Cassini
                probe), some lighthouses in the former Soviet Union, and
                some pacemakers. The heat output of these generators
                diminishes with time; the heat is converted to electricity
                utilising the thermoelectric effect.

How it works

   The key components common to most types of nuclear power plants are:
     * Nuclear fuel
     * Moderator
     * Coolant
     * Control rods
     * Pressure vessel
     * Emergency core cooling systems
     * Reactor Protective System
     * Steam generators (not in BWRs)
     * Containment building
     * Boiler feedwater pump
     * Turbine
     * Electrical generator
     * Condenser

   Conventional thermal power plants all have a heat source. Examples are
   gas, coal, or oil. For a nuclear power plant, this heat is provided by
   nuclear fission inside the nuclear reactor. When a relatively large
   fissile atomic nucleus (usually uranium-235 or plutonium-239) is struck
   by a neutron it forms two or more smaller nuclei as fission products,
   releasing energy and neutrons in a process called nuclear fission. The
   neutrons then trigger further fission. And so on. When this nuclear
   chain reaction is controlled, the energy released can be used to heat
   water, produce steam and drive a turbine that generates electricity. It
   should be noted that a nuclear explosive involves an uncontrolled chain
   reaction, and the rate of fission in a reactor is not capable of
   reaching sufficient levels to trigger a nuclear explosion because
   commercial reactor grade nuclear fuel is not enriched to a high enough
   level. (see enriched uranium)

   The chain reaction is controlled through the use of materials that
   absorb and moderate neutrons. In uranium-fueled reactors, neutrons must
   be moderated (slowed down) because slow neutrons are more likely to
   cause fission when colliding with a uranium-235 nucleus. Light water
   reactors use ordinary water to moderate and cool the reactors. When at
   operating temperatures if the temperature of the water increases, its
   density drops, and less neutrons passing through it are slowed enough
   to trigger further reactions. That negative feedback stabilizes the
   reaction rate.

Experimental technologies

   A number of other designs for nuclear power generation, the Generation
   IV reactors, are the subject of active research and may be used for
   practical power generation in the future. A number of the advanced
   nuclear reactor designs could also make critical fission reactors much
   cleaner, much safer and/or much less of a risk to the proliferation of
   nuclear weapons.
     * Integral Fast Reactor — The link at the end of this paragraph
       references an interview with Dr. Charles Till, former director of
       Argonne National Laboratory West in Idaho and outlines the Integral
       Fast Reactor and its advantages over current reactor design,
       especially in the areas of safety, efficient nuclear fuel usage and
       reduced waste. The IFR was built, tested and evaluated during the
       1980s and then retired under the Clinton administration in the
       1990s due to nuclear non-proliferation policies of the
       administration. Recycling spent fuel is the core of its design and
       it therefore produces a fraction of the waste of current reactors.
     * Pebble Bed Reactor — This reactor type is designed so high
       temperatures reduce power output by doppler broadening of the
       fuel's neutron cross-section. It uses ceramic fuels so its safe
       operating temperatures exceed the power-reduction temperature
       range. Most designs are cooled by inert helium, which cannot have
       steam explosions, and which does not easily absorb neutrons and
       become radioactive, or dissolve contaminants that can become
       radioactive. Typical designs have more layers (up to 7) of passive
       containment than light water reactors (usually 3). A unique feature
       that might aid safety is that the fuel-balls actually form the
       core's mechanism, and are replaced one-by-one as they age. The
       design of the fuel makes fuel reprocessing expensive.
     * SSTAR, Small, Sealed, Transportable, Autonomous Reactor is being
       primarily researched and developed in the US, intended as a fast
       breeder reactor that is tamper resistant and passively safe.
     * Subcritical reactors are designed to be safer and more stable, but
       pose a number of engineering and economic difficulties.
     * Controlled nuclear fusion could in principle be used in fusion
       power plants to produce safer, cleaner power, but significant
       scientific and technical obstacles remain. Several fusion reactors
       have been built, but as yet none has 'produced' more thermal energy
       than electrical energy consumed. Despite research having started in
       the 1950s, no commercial fusion reactor is expected before 2050.
       The ITER project is currently leading the effort to commercialize
       fusion power.
     * Thorium based reactors

          It is possible to convert Thorium-232 into U-233 in reactors
          specially designed for the purpose. In this way, Thorium , which
          is more plentiful than uranium, can be used to breed U-233
          nuclear fuel. U-233 is also believed to have favourable nuclear
          properties as compared to traditionally used U-235, including
          better neutron economy and lower production of long lived
          transuranic waste.

          + Advanced Heavy Water Reactor — A proposed heavy water
            moderated nuclear power reactor that will be the next
            generation design of the PHWR type. Under development in the
            Bhabha Atomic Research Centre (BARC).
          + KAMINI — A unique reactor using Uranium-233 isotope for fuel.
            Built by BARC and IGCAR Uses thorium.
          + India is also building a bigger scale FBTR or fast breeder
            thorium reactor to harness the power with the use of thorium.

Life cycle

   The Nuclear Fuel Cycle begins when uranium is mined, enriched, and
   manufactured into nuclear fuel, (1) which is delivered to a nuclear
   power plant. After usage in the power plant, the spent fuel is
   delivered to a reprocessing plant (2) or to a final repository (3) for
   geological disposition. In reprocessing 95% of spent fuel can be
   recycled to be returned to usage in a power plant (4).
   Enlarge
   The Nuclear Fuel Cycle begins when uranium is mined, enriched, and
   manufactured into nuclear fuel, (1) which is delivered to a nuclear
   power plant. After usage in the power plant, the spent fuel is
   delivered to a reprocessing plant (2) or to a final repository (3) for
   geological disposition. In reprocessing 95% of spent fuel can be
   recycled to be returned to usage in a power plant (4).
   Nuclear fuel — a compact, inert, insoluble solid.
   Enlarge
   Nuclear fuel — a compact, inert, insoluble solid.

   A nuclear reactor is only a small part of the life-cycle for nuclear
   power. The process starts with mining. Generally, uranium mines are
   either open-pit strip mines, or in-situ leach mines. In either case,
   the uranium ore is extracted, usually converted into a stable and
   compact form such as yellowcake, and then transported to a processing
   facility. At the reprocessing facility, 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 years 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 cooling pond, the spent fuel is
   radioactively cool enough to handle, and it can be moved to dry storage
   casks or reprocessed.

Reprocessing

   Reprocessing can recover up to 95% of the remaining uranium and
   plutonium in spent nuclear fuel, putting it into new mixed oxide fuel.
   Reprocessing of civilian fuel from power reactors is currently done on
   large scale in Britain, France and (formerly) Russia, will be in China
   and perhaps India, and is being done on an expanding scale in Japan.
   Iran has announced its intention to complete the nuclear fuel cycle via
   reprocessing, a move which has led to criticism from the United States
   and the International Atomic Energy Agency. Reprocessing of civilian
   nuclear fuel is not done in the United States due to proliferation
   concerns.

Solid waste

   Nuclear power produces spent fuel, a unique solid waste problem. Highly
   radioactive spent fuel needs to be handled with great care and
   forethought due to the long half-lives of the radioactive isotopes in
   the waste. In fact, fresh spent fuel is so radioactive that less than a
   minute's exposure to it will cause death. However, spent nuclear fuel
   becomes less radioactive over time. After 40 years, the radiation flux
   is 99.9% lower than it was the moment the reactor was last shut off,
   although still dangerously radioactive.

   Spent fuel is primarily composed of unconverted uranium, as well as
   significant quantities of transuranic actinides (plutonium and curium,
   mostly). In addition, about 3% of it is made of fission products. The
   actinides (uranium, plutonium, and curium) are responsible for the bulk
   of the long term radioactivity, whereas the fission products are
   responsible for the bulk of the short term radioactivity. It is
   possible through reprocessing to separate out the actinides and use
   them again for fuel, but this often requires special fast spectrum
   reactors, which produce a reduction in long term radioactivity within
   the remaining waste. In any case, the remaining waste will be
   substantially radioactive for at least 300 years even if the actinides
   are removed, and for up to thousands of years if the actinides are left
   in. Even in the most optimistic scenarios, complete consumption of all
   actinides, and using fast spectrum reactors to destroy some of the
   long-lived non-actinides as well, the waste must be segregated from the
   environment for at least several hundred years, and therefore this is
   properly categorized as a long-term problem. There are, however,
   chemical plants which also produce hazardous waste staying in the
   environment for hundreds of years.

   A large nuclear reactor produces 3 cubic metres (25-30 tonnes) of spent
   fuel each year. As of 2003, the United States had accumulated about
   49,000 metric tons of spent nuclear fuel from nuclear reactors. Unlike
   other countries, U.S. policy forbids recycling of used fuel and it is
   all treated as waste. After 10,000 years of radioactive decay,
   according to United States Environmental Protection Agency standards,
   the spent nuclear fuel will no longer pose a threat to public health
   and safety.

   The safe storage and disposal of nuclear waste is a difficult
   challenge. Because of potential harm from radiation, spent nuclear fuel
   must be stored in shielded basins of water, or in dry storage vaults or
   dry cask storage until its radioactivity decreases naturally ("decays")
   to safe levels. This can take days or thousands of years, depending on
   the type of fuel. Most waste is currently stored in temporary storage
   sites, requiring constant maintenance, while suitable permanent
   disposal methods are discussed. Underground storage at Yucca Mountain
   in U.S. has been proposed as permanent storage. See the article on the
   nuclear fuel cycle for more information.

   The nuclear industry produces a volume of low-level radioactive waste
   in the form of contaminated items like clothing, hand tools, water
   purifier resins, and (upon decommissioning) the materials of which the
   reactor itself is built. In the United States, the Nuclear Regulatory
   Commission has repeatedly attempted to allow low-level materials to be
   handled as normal waste: landfilled, recycled into consumer items, etc.
   Much low-level waste releases very low levels of radioactivity and is
   essentially considered radioactive waste because of its history. For
   example, according to the standards of the NRC, the radiation released
   by coffee is enough to treat it as low level waste. Overall, nuclear
   power produces far less waste material than fossil-fuel based power
   plants. Coal-burning plants are particularly noted for producing large
   amounts of radioactive ash due to concentrating naturally occurring
   radioactive material in the coal.

   In addition, the nuclear industry fuel cycle produces many tons of
   depleted uranium (DU) which consists of U-238 with the easily fissile
   U-235 isotope removed. U-238 is a tough metal with several commercial
   uses — for example, aircraft production, radiation shielding, and
   making bullets and armor — as it has a higher density than lead. There
   are concerns that U-238 may lead to health problems in groups exposed
   to this material excessively, like tank crews and civilians living in
   areas where large quantities of DU ammunition have been used.

   The amounts of waste can be reduced in several ways. Both nuclear
   reprocessing and fast breeder reactors can reduce the amounts of waste
   and increase the amount of energy gained per fuel unit. Subcritical
   reactors or fusion reactors could greatly reduce the time the waste has
   to be stored. Subcritical reactors may also be able to do the same to
   already existing waste. It has been argued that the best solution for
   the nuclear waste is above ground temporary storage since technology is
   rapidly changing. The current waste may well become valuable fuel in
   the future, particularly if it is not reprocessed, as in the U.S.

   In countries with nuclear power, radioactive wastes comprise less than
   1% of total industrial toxic wastes, which remain hazardous
   indefinitely unless they decompose or are treated so that they are less
   toxic or, ideally, completely non-toxic.

Economy

   Opponents of nuclear power argue that any of the environmental benefits
   are outweighed by safety compromises and by the costs related to
   construction and operation of nuclear power plants, including costs for
   spent-fuel disposal and plant retirement. Proponents of nuclear power
   respond that nuclear energy is the only power source which explicitly
   factors the estimated costs for waste containment and plant
   decommissioning into its overall cost, and that the quoted cost of
   fossil fuel plants is deceptively low for this reason. The cost of some
   renewables would be increased too if they included necessary back-up
   due to their intermittent nature.

   A UK Royal Academy of Engineering report in 2004 looked at electricity
   generation costs from new plants in the UK. In particular it aimed to
   develop "a robust approach to compare directly the costs of
   intermittent generation with more dependable sources of generation".
   This meant adding the cost of standby capacity for wind, as well as
   carbon values up to £30 (€45.44) per tonne CO[2] for coal and gas. Wind
   power was calculated to be more than twice as expensive as nuclear
   power. Without a carbon tax, the cost of production through coal,
   nuclear and gas ranged £0.022-0.026/ kWh and coal gasification was
   £0.032/kWh. When carbon tax was added (up to £0.025) coal came close to
   onshore wind (including back-up power) at £0.054/kWh — offshore wind is
   £0.072/kWh.

   Nuclear power remained at £0.023/kWh either way, as it produces
   negligible amounts of CO[2]. Nuclear figures included decommissioning
   costs.

   In one study, certain gas cogeneration plants were calculated to be
   three to four times more cost-effective than nuclear power, if all the
   heat produced was used onsite or in a local heating system. However,
   the study estimated only 25 year plant lifetimes (60 is now common),
   68% capacity factors were assumed (above 90% is now common), other
   conservatisms were applied, and nuclear power also produces heat which
   could be used in similar ways (although most nuclear power plants are
   located in remote areas). The study then found similar costs for
   nuclear power and most other forms of generation if not including
   external costs (such as back-up power).

Capital costs

   Generally, a nuclear power plant is significantly more expensive to
   build than an equivalent coal-fuelled or gas-fuelled plant. Coal is
   significantly more expensive than nuclear fuel, and natural gas
   significantly more expensive than coal — thus, capital costs aside,
   natural gas-generated power is the most expensive. However servicing
   the capital costs for a nuclear power dominate the costs of
   nuclear-generated electricity, contributing about 70% of costs
   (assuming a 10% discount rate).

   The recent liberalisation of the electricity market in many countries
   has made the economics of nuclear power generation less attractive.
   Previously a monopolistic provider could guarantee output requirements
   decades into the future. Private generating companies have to accept
   shorter output contracts and the risks of future competition, so desire
   a shorter return on investment period which favours generation plants
   with lower capital costs.

   In many countries, licensing, inspection and certification of nuclear
   power plants has added delays and construction costs to their
   construction. In the U.S. many new regulations were put in place after
   the Three Mile Island partial meltdown. Building gas-fired or
   coal-fired plants has not had these problems. Because a power plant
   does not yield profits during construction, longer construction times
   translate directly into higher interest charges on borrowed
   construction funds. However, the regulatory processes for siting,
   licensing, and constructing have been standardized since their
   introduction, to make construction of newer and safer designs more
   attractive to companies.

   In Japan and France, construction costs and delays are significantly
   diminished because of streamlined government licensing and
   certification procedures. In France, one model of reactor was
   type-certified, using a safety engineering process similar to the
   process used to certify aircraft models for safety. That is, rather
   than licensing individual reactors, the regulatory agency certified a
   particular design and its construction process to produce safe
   reactors. U.S. law permits type-licensing of reactors, a process which
   is about to be used.

   To encourage development of nuclear power, under the Nuclear Power 2010
   Program the U.S. Department of Energy (DOE) has offered interested
   parties the opportunity to introduce France's model for licensing and
   to subsidize 25% to 50% of the construction cost overruns due to delays
   for the first six new plants. Several applications were made, two sites
   have been chosen to receive new plants, and other projects are pending.

Operating costs

   In general, coal and nuclear plants have the same types of operating
   costs (operations and maintenance plus fuel costs). However, nuclear
   and coal differ in the relative size of those costs. Nuclear has lower
   fuel costs but higher operating and maintenance costs. In recent times
   in the United States savings due to lower fuel cost have not been low
   enough for nuclear to repay its higher investment cost. Thus no new
   nuclear reactors have been ordered in the United States since the
   1970s. Coal's operating cost advantages have only rarely been
   sufficient to encourage the construction of new coal based power
   generation. Around 90 to 95 percent of new power plant construction in
   the United States has been natural gas-fired.

   To be competitive in the current market, both the nuclear and coal
   industries must reduce new plant investment costs and construction
   time. The burden is clearly greater for nuclear producers than for coal
   producers, because investment costs are higher for nuclear plants.
   Operation and maintenance costs are particularly important because they
   represent a large portion of costs for nuclear power.

   One of the primary reasons for the uncompetitiveness of the U.S.
   nuclear industry has been the lack of any measure that provides an
   economic incentive to reduce carbon emissions ( carbon tax). Many
   economists and environmentalists have called for a mechanism to take
   into account the negative externalities of coal and gas consumption. In
   such an environment, it is argued that nuclear will become
   cost-competitive in the United States.

Subsidies

   Critics of nuclear power claim that it is the beneficiary of
   inappropriately large economic subsidies — mainly taking the forms of
   taxpayer-funded research and development and limitations on disaster
   liability — and that these subsidies, being subtle and indirect, are
   often overlooked when comparing the economics of nuclear against other
   forms of power generation. However, competing energy sources also
   receive subsidies. Fossil fuels receive large direct and indirect
   subsidies, like tax benefits and not having to pay for their pollution.
   Renewables receive large direct production subsidies and tax breaks in
   many nations.

   Energy research and development (R&D) for nuclear power has and
   continues to receive much larger state subsidies than R&D for renewable
   energy or fossil fuels. However, today most of this takes places in
   Japan and France: in most other nations renewable R&D get more money.
   In the U.S., public research money for nuclear fission declined from
   2,179 to 35 million dollars between 1980 and 2000. However, in order to
   restart the industry, the next six U.S. reactors will receive subsidies
   equal to those of renewables and, in the event of cost overruns due to
   delays, at least partial compensation for the overruns (see Nuclear
   Power 2010 Program).

   According to the DOE, insurance for nuclear or radiological incidents
   in the U.S., is subsidized by the Price-Anderson Nuclear Industries
   Indemnity Act. In July 2005, Congress extended this Act to newer
   facilities. In the UK, the Nuclear Installations Act of 1965 governs
   liability for nuclear damage for which a UK nuclear licensee is
   responsible. The Vienna Convention on Civil Liability for Nuclear
   Damage puts in place an international framework for nuclear liability.

Other economic issues

   Nuclear Power plants tend to be most competitive in areas where other
   fuel resources are not readily available — France, most notably, has
   almost no native supplies of fossil fuels. The province of Ontario,
   Canada is already using all of its best sites for hydroelectric power,
   and has minimal supplies of fossil fuels, so a number of nuclear plants
   have been built there. India too has few resources and is building new
   nuclear plants. Conversely, in the United Kingdom, according to the
   government's Department Of Trade And Industry, no further nuclear power
   stations are to be built, due to the high cost per unit of nuclear
   power compared to fossil fuels. However, the British government's chief
   scientific advisor David King reports that building one more generation
   of nuclear power plants may be necessary. China tops the list of
   planned new plants, due to its rapidly expanding economy and fervent
   construction in many types of energy projects.

   Most new gas-fired plants are intended for peak supply. The larger
   nuclear and coal plants cannot quickly adjust their instantaneous power
   production, and are generally intended for baseline supply. The market
   price for baseline power has not increased as rapidly as that for peak
   demand. Some new experimental reactors, notably pebble bed modular
   reactors, are specifically designed for peaking power.

   Any effort to construct a new nuclear facility around the world,
   whether an older design or a newer experimental design, must deal with
   NIMBY objections. Given the high profile of both the Three Mile Island
   and Chernobyl accidents, few municipalities welcome a new nuclear
   reactor, processing plant, transportation route, or experimental
   nuclear burial ground within their borders, and many have issued local
   ordinances prohibiting the development of nuclear power. However, a few
   U.S. areas with nuclear units are campaigning for more (see Nuclear
   Power 2010 Program).

   Current nuclear reactors return around 40-60 times the invested energy
   when using life cycle analysis. This is better than coal, natural gas,
   and current renewables except hydropower.

   The Rocky Mountain Institute gives other reasons why nuclear power
   plants may not be economical. In the U.S. this includes long lead times
   on risky investments, and the more cost-effective approach of investing
   in efficiency instead of new power plants.

   Nuclear power, coal, and wind power are currently the only realistic
   large scale energy sources that would be able to replace oil and
   natural gas after a peak in global oil and gas production has been
   reached (see peak oil). However, The Rocky Mountain Institute claims
   that in the U.S. increases in transportation efficiency and stronger,
   lighter cars would replace most oil usage with what it calls negawatts.
   Biofuels can then substitute for a significant portion of the remaining
   oil use. Efficiency, insulation, solar thermal, and solar photovoltaic
   technologies can substitute for most natural gas usage after a peak in
   production.

   Nuclear proponents often assert that renewable sources of power have
   not solved problems like intermittent output, high costs, and diffuse
   output which requires the use of large surface areas and much
   construction material and which increases distribution losses. For
   example, studies in Britain have shown that increasing wind power
   production contribution to 20% of all energy production, without costly
   pumped hydro or electrolysis/fuel cell storage, would only reduce coal
   or nuclear power plant capacity by 6.7% (from 59 to 55 GWe) since they
   must remain as backup in the absence of power storage. Nuclear
   proponents often claim that increasing the contribution of intermittent
   energy sources above that is not possible with current technology. Some
   renewable energy sources, such as solar, overlap well with peak
   electricial production and reduce the need of spare generating
   capacity. Future applications that use electricity when it is available
   (e.g. for pressurizing water systems, desalination, or hydrogen
   generation) would help to reduce the spare generation capacity required
   by both nuclear and renewable energy sources.

Concerns about nuclear power

Accident or attack

   Opponents argue that a major disadvantage of the use of nuclear
   reactors is the threat of a nuclear accident or terrorist attack and
   the possible resulting exposure to radiation.

   Proponents argue that the potential for a meltdown in
   non-Russian-designed reactors is very small due to the care taken in
   designing adequate safety systems, and that the nuclear industry has
   much better statistics regarding humans deaths from occupational
   accidents than coal or hydropower. While the Chernobyl accident caused
   great negative health, economic, environmental and psychological
   effects in a widespread area, the accident at Chernobyl was caused by a
   combination of the faulty RBMK reactor design, the lack of a properly
   designed containment building, poorly trained operators, and a
   non-existent safety culture. The RBMK design, unlike nearly all designs
   used in the Western world, featured a positive void coefficient,
   meaning that a malfunction could result in ever-increasing generation
   of heat and radiation until the reactor was breached. Even at Three
   Mile Island, the most severe civilian nuclear accident in the
   non-Soviet world, the reactor vessel and containment building were
   never breached, even though it had suffered a core meltdown, so that
   very little radiation (well below natural background radiation levels)
   was released into the environment.

   Design changes are being pursued in the hope of lessening some of the
   risks of fission reactors; in particular, automated and passively safe
   designs are being pursued. Fusion reactors which may come to exist in
   the future theoretically have little risk since the fuel contained in
   the reaction chamber is only enough to sustain the reaction for about a
   minute, whereas a fission reactor contains about a year's supply of
   fuel. Subcritical reactors never have a self sustained nuclear chain
   reaction.

   Opponents of nuclear power express concerns that nuclear waste is not
   well protected, and that it can be released in the event of terrorist
   attack, quoting a 1999 Russian incident where workers were caught
   trying to sell 5 grams of radioactive material on the open market, or
   the incident in 1993 where Russian workers were caught selling 4.5
   kilograms of enriched uranium. The UN has since called upon world
   leaders to improve security in order to prevent radioactive material
   falling into the hands of terrorists, sometimes leading to the guarding
   of nuclear shipments by thousands of police. Other energy sources, such
   as hydropower plants and LNG carriers, are more vulnerable to accidents
   and attacks. Proponents of nuclear power contend, however, that nuclear
   waste is already well protected, and state their argument that there
   has been no accident involving any form of nuclear waste from a
   civilian program worldwide. In addition, they point to large studies
   carried out by NRC and other agencies 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. Spent fuel is usually housed inside the plant's "protected
   zone" or a spent nuclear fuel shipping cask; stealing it for use in a
   "dirty bomb" is extremely difficult. Exposure to the intense radiation
   would almost certainly quickly incapacitate or kill any terrorists who
   attempt to do so.

   According to the Nuclear Regulatory Commission, 20 American states have
   requested stocks of potassium iodide which the NRC suggests should be
   available for those living within 10 miles of a nuclear power plant in
   the unlikely event of a severe accident.

Health effects on populations near nuclear plants

   Most of the human exposure to radiation comes from natural background
   radiation. Most of the remaining exposure comes from medical
   procedures. Several large studies in the U.S., Canada, and Europe have
   found no evidence of any increase in cancer mortality among people
   living near nuclear facilities. For example, in 1990, the National
   Cancer Institute (NCI) of the National Institutes of Health announced
   that, after doing a large-scale study which evaluated the mortality
   rates from 16 types of cancer, no increased incidence of cancer
   mortality was found for people living near 62 nuclear installations in
   the United States. The study also showed no increase in the incidence
   of childhood leukemia mortality in the study of surrounding counties
   after the start-up of the nuclear facilities. The NCI study, the
   broadest of its kind ever conducted, surveyed 900,000 cancer deaths in
   counties near nuclear facilities.

   Aside from the immediate effects of the Chernobyl accident (see above),
   there is continuing impact from soils containing radioactivity in
   Ukraine and Belarus. For this reason a Zone of alienation was
   established around the Chernobyl plant.

   In March, 2006, safety reviews found that several nuclear plants in the
   United States have been leaking water contaminated with tritium into
   the ground. (The discharges were intended to go through discharge pipes
   into rivers, at levels which would be below below regulatory limits.
   However, by leaking into the ground, very low levels of tritium reached
   drinking water supplies.) The attorney general of Illinois announced
   that she was filing a lawsuit against Exelon because of six such leaks,
   demanding that the utility provide substitute water supplies to
   residents although no well outside company property shows levels that
   exceed drinking water standards. According to the NRC, "The inspection
   determined that public health and safety has not been adversely
   affected and the dose consequence to the public that can be attributed
   to current onsite conditions is negligible with respect to NRC
   regulatory limits." However, the chairman of the Nuclear Regulatory
   Commission, said, "They're going to have to fix it."

Nuclear proliferation

   Opponents of nuclear power point out that nuclear technology is often
   dual-use, and much of the same materials and knowledge used in a
   civilian nuclear program can be used to develop nuclear weapons. This
   concern is known as nuclear proliferation and is a major reactor design
   criterion.

   The military and civil purposes for nuclear energy are intertwined in
   most countries with nuclear capabilities. In the U.S., for example, the
   first goal of the Department of Energy is "to advance the national,
   economic, and energy security of the United States; to promote
   scientific and technological innovation in support of that mission; and
   to ensure the environmental cleanup of the national nuclear weapons
   complex."

   The enriched uranium used in most nuclear reactors is not concentrated
   enough to build a bomb. Most nuclear reactors run on 4% enriched
   uranium; Little Boy used 90% enriched uranium; while lower enrichment
   levels could be used, the minimum bomb size would rapidly become
   infeasibly large as the level was decreased. However, the same plants
   and technology used to enrich uranium for power generation can be used
   to make the highly enriched uranium needed to build a bomb.

   In addition, the plutonium produced in power reactors, if concentrated
   through reprocessing, can be used for a bomb. While the plutonium
   resulting from normal reactor fuelling cycles is less than ideal for
   weapons use because of the concentration of Pu-240, a usable weapon can
   be produced from it. If the reactor is operated on very short fuelling
   cycles, bomb-grade plutonium can be produced. However, such operation
   would be virtually impossible to camouflage in many reactor designs, as
   the frequent shutdowns for refuelling would be obvious, for instance in
   satellite photographs.

   It is widely believed that the nuclear programs of India and Pakistan
   used CANDU reactors to produce fissionable materials for their weapons;
   however, this is not entirely accurate. Both Canada (by supplying the
   40 MW research reactor) and the United States (by supplying 21 tons of
   heavy water) supplied India with the technology necessary to create a
   nuclear weapons programme, dubbed CIRUS (Canada-India Reactor, United
   States). Because international policies did not dictate usage of
   nuclear technology transfers, India was able to use the technology to
   create a nuclear weapon. Pakistan is believed to have produced the
   material for its weapons from an indigenous enrichment program.

   To prevent weapons proliferation, safeguards on nuclear technology were
   published in the Nuclear Non-Proliferation Treaty (NPT) and monitored
   since 1968 by the International Atomic Energy Agency (IAEA). Nations
   signing the treaty are required to report to the IAEA what nuclear
   materials they hold and their location. They agree to accept visits by
   IAEA auditors and inspectors to verify independently their material
   reports and physically inspect the nuclear materials concerned to
   confirm physical inventories of them in exchange for access to nuclear
   materials and equipment on the global market.

   Several states did not sign the treaty and were able to use
   international nuclear technology (often procured for civilian purposes)
   to develop nuclear weapons (India, Pakistan, Israel, and South Africa).
   South Africa has since signed the NPT, and now holds the distinction of
   being the only known state to have indigenously produced nuclear
   weapons, and then verifiably dismantled them. Of those who have signed
   the treaty and received shipments of nuclear paraphernalia, many states
   have either claimed to, or been accused of, attempting to use
   supposedly civilian nuclear power plants for developing weapons,
   including Iran and North Korea. Certain types of reactors are more
   conducive to producing nuclear weapons materials than others, and a
   number of international disputes over proliferation have centered on
   the specific model of reactor being contracted for in a country
   suspected of nuclear weapon ambitions.

   New technology, like SSTAR, may lessen the risk of nuclear
   proliferation by providing sealed reactors with a limited
   self-contained fuel supply and with restrictions against tampering.

   One possible obstacle for expanding the use of nuclear power might be a
   limited supply of uranium ore, without which it would become necessary
   to build and operate breeder reactors. However, at current usage there
   is sufficient uranium for an extended period — "In summary, the actual
   recoverable uranium supply is likely to be enough to last several
   hundred (up to 1000) years, even using standard reactors." Breeder
   reactors have been banned in the U.S. since President Jimmy Carter's
   administration prohibited reprocessing because of what it regarded as
   the unacceptable risk of proliferation of weapons-grade materials.

   Some proponents of nuclear power agree that the risk of nuclear
   proliferation may be a reason to prevent nondemocratic developing
   nations from gaining any nuclear technology but argue that this is no
   reason for democratic developed nations to abandon their nuclear power
   plants. Especially since it seems that democracies never make war
   against each other (See the democratic peace theory).

   Proponents also note that nuclear power, like some other power sources,
   provides steady energy at a consistent price without competing for
   energy resources from other countries, something that may contribute to
   wars.

   In February, 2006, a new U.S. initiative, the Global Nuclear Energy
   Partnership was announced. It would be an international effort to
   reprocess fuel in a manner making proliferation infeasible, while
   making nuclear power available to developing countries.

Environmental effects

Air pollution

   Non-radioactive water vapour is the significant operating emission from
   nuclear power plants. Fission produces gases such as iodine-131 or
   Xenon-133 which have to be stored on-site for several half-lives until
   they have decayed to safe levels.

   Nuclear generation does not directly produce sulphur dioxide, nitrogen
   oxides, mercury or other pollutants associated with the combustion of
   fossil fuels (pollution from fossil fuels is blamed for many deaths
   each year in the U.S. alone). It also does not directly produce carbon
   dioxide, which has led some environmentalists to advocate increased
   reliance on nuclear energy as a means to reduce greenhouse gas
   emissions (which contribute to global warming).

   Like any power source (including renewables like wind and solar
   energy), the facilities to produce and distribute the electricity
   require energy to build and subsequently decommission. Mineral ores
   must be collected and processed to produce nuclear fuel. These
   processes are either directly powered by diesel and gasoline engines,
   or draw electricity from the power grid, which may be generated from
   fossil fuels. Life cycle analyses assess the amount of energy consumed
   by these processes (given today's mix of energy resources) and
   calculate, over the lifetime of a nuclear power plant, the amount of
   carbon dioxide saved (related to the amount of electricity produced by
   the plant) vs. the amount of carbon dioxide used (related to
   construction and fuel acquisition).

   Several life cycle analyses show similar emissions per kilowatt-hour
   from nuclear power and from renewables such as wind power. According to
   one life cycle study by van Leeuwen and Smith from 2001–2005, carbon
   dioxide emissions from nuclear power per kilowatt hour could range from
   20% to 120% of those for natural gas-fired power stations depending on
   the availability of high grade ores. The study was rebutted in detail
   by the World Nuclear Association.

   In 2006, a UK government advisory panel, The Sustainable Development
   Commission, concluded that if the UK's existing nuclear capacity were
   doubled, it would provide an 8% decrease in total UK CO[2] emissions by
   2035. This can be compared to the country's goal to reduce greenhouse
   gas emissions by 60 % by 2050. As of 2006, the UK government was to
   publish its official findings later in the year.

Waste heat in water systems

   Nuclear reactors require cooling, typically with water (sometimes
   indirectly). The process of extracting energy from a heat source,
   called the Rankine cycle, requires the steam to be cooled down. Rivers
   are the most common source of cooling water, as well as the destination
   for waste heat. The temperature of exhaust water must be regulated to
   avoid killing fish; long-term impact of hotter-than-natural water on
   ecosystems is an environmental concern. In most new facilites, this
   problem is solved by implementing cooling towers.

   The need to regulate exhaust temperature also limits generation
   capacity. On extremely hot days, which is when demand can be at its
   highest, the capacity of a nuclear plant may go down because the
   incoming water is warmer to begin with and is thus less effective as a
   coolant, per unit volume. This was a significant factor during the
   European heat wave of 2003. Engineers consider this in making improved
   power plant designs because increased cooling capacity will increase
   costs.

List of atomic energy groups

     * American Nuclear Society (United States)
     * Department of Energy (United States)
     * The Nuclear Energy Institute (United States)
     * Atomic Energy of Canada Limited (Canada)
     * Areva (France)
     * EDF (France)
     * MinAtom (Russia)
     * EnergoAtom (Ukraine)
     * Pakistan Atomic Energy Commission (Pakistan)
     * Atomic Energy Commission (India)
     * KazAtomProm (Kazakhstan)
     * Egyptian Atomic Energy Authority
     * United Kingdom Atomic Energy Authority (UKAEA)
     * EURATOM (Europe)
     * International Atomic Energy Agency (IAEA)

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