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Environmental effects of nuclear power
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Nuclear power, as with all power sources, has an effect on the environment through the nuclear fuel cycle, through operation, and (in Europe) from the lingering effects of the Chernobyl accident.
ith any thermal power station, nuclear plants exchange 60 to 70% of their thermal energy by cycling with a body of water or by evaporating water through a cooling tower. This thermal efficiency is slightly less than that of coal fired power plants.
The cooling options are typically once-through cooling with river or sea water, pond cooling, or cooling towers.
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Encyclopedia
Nuclear power, as with all power sources, has an effect on the environment through the nuclear fuel cycle, through operation, and (in Europe) from the lingering effects of the Chernobyl accident.
Waste heat
As with any thermal power station, nuclear plants exchange 60 to 70% of their thermal energy by cycling with a body of water or by evaporating water through a cooling tower. This thermal efficiency is slightly less than that of coal fired power plants.
The cooling options are typically once-through cooling with river or sea water, pond cooling, or cooling towers. Many plants have an artificial lake like the Shearon Harris Nuclear Power Plant or the South Texas Nuclear Generating Station. Shearon Harris uses a cooling tower but South Texas does not and discharges back into the lake. The North Anna Nuclear Generating Station uses a cooling pond or artificial lake, which at one spot near the plant's discharge is often about 30 degrees warmer than in the other parts of the lake or in normal lakes (this is cited as an attraction of the area by some residents). The environmental effects on the artificial lakes are often weighted in arguments against construction of new plants, and during droughts have drawn media attention.
The Turkey Point Nuclear Generating Station is credited with helping the conservation status of the American Crocodile, largely an effect of the waste heat produced.
One researcher believes that increasing sea water temperature has a detrimental effect on sea life.
The Indian Point nuclear power plant in New York is in a hearing process to determine if a cooling system other than river water will be necessary (conditional upon the plants extending their operating licenses).
It is possible to use waste heat in cogeneration applications such as district heating. The principles of cogeneration and district heating with nuclear power are the same as any other form of thermal power production. One use of nuclear heat generation was with the Ågesta Nuclear Power Plant in Sweden. In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people.. However, district heating with nuclear power plants is less common than with other modes of waste heat generation: because of either sditing regulations and/or the NIMBY effect, nuclear stations are generally not built in densely populated areas. Waste heat is more commonly used in industrial applications..
During the Europe's 2003 and 2006 heat waves, French, Spanish and German utilities had to secure exemptions from regulations in order to discharge overheated water into the environment. Some nuclear reactors shut down.
Radioactive waste
High level waste
Around 300 tonnes of high-level waste is produced per month per nuclear reactor. Currently most spent nuclear fuel outside the U.S. is reprocessed for the useful components, leaving only a much smaller volume of short half-life waste to be stored. In the U.S. reprocessing is currently prohibited by executive order, and the spent nuclear fuel is therefore stored in dry cask storage facilities (this has the disadvantage of keeping the long-lived isotopes with the other waste, thus greatly extending the half-life of the waste).
Several methods have been suggested for final disposal of high-level waste, including deep burial in stable geological structures, transmutation, and removal to space. Currently, monitored retrieveable storage is the option being most prepared.
Some nuclear reactors, such as the Integral Fast Reactor, have been proposed that use a different nuclear fuel cycle that avoids producing waste containing long-lived radioactive isotopes or actually burns those isotopes from other plants.
Other waste
Moderate amounts of low-level waste are produced through chemical and volume control system (CVCS). This includes gas, liquid, and solid waste produced through the process of purifying the water through evaporation. Liquid waste is reprocessed continuously, and gas waste is filtered, compressed, stored to allow decay, diluted, and then discharged. The rate at which this is allowed is regulated and studies must prove that such discharge does not violate dose limits to a member of the public (see Radioactive effluent emissions).
Solid waste can be disposed of simply by placing it where it will not be disturbed for a few years. There are three low-level waste disposal sites in the United States in South Carolina, Utah, and Washington. Solid waste from the CVCS is combined with solid radwaste that comes from handling materials before it is buried off-site.
Environmental effects of accidents
Some possible accidents at nuclear power plants pose a risk of severe environmental contamination. The Chernobyl accident at an RBMK reactor (which did not have the usually-required containment building) released large amounts of radioactive contamination, killing many and rendering an area of land unusable to humans for an indeterminate period.
Radioactive effluent emissions
Most commercial nuclear power plants release gaseous and liquid radiological effluents into the environment as a byproduct of the Chemical Volume Control System, which are monitored in the US by the EPA and the NRC. Civilians living within of a nuclear power plant typically receive about 0.01 milli-rem per year. For comparison, the average person living at or above sea level receives at least 26 milli-rem from cosmic radiation.
The total amount of radioactivity released through this method depends on the power plant, the regulatory requirements, and the plant's performance. Atmospheric dispersion models combined with pathway models are employed to accurately approximate the dose to a member of the public from the effluents emitted. Effluent monitoring is conducted continuously at the plant.
Limits for the Canadian plants are shown below:
Effluent emissions for Nuclear power in the United States are regulated by 10 CFR 50.36(a)(2). For detailed information, consult the Nuclear Regulatory Commission's .
Boron letdown
Towards the end of each cycle of operation (typically 18 months to two years in length), each pressurized water reactor reduces the amount of boron in its primary coolant system (the water that flows past and cools the nuclear reactor core). As a consequence, some of this irradiated boron is discharged from the plant and into whatever body of water the plant's cooling water is drawn from. The maximum amount of radioactivity permitted in each volume of discharge is tightly regulated (see above).
Comparison to coal-fired generation
In terms of net radioactive release, the National Council on Radiation Protection and Measurements (NCRP) estimated the average radioactivity per short ton of coal is 17,100 millicuries/4,000,000 tons. With 154 coal plants in the United States, this amounts to emissions of 0.6319 TBq per year for a single plant, which still does not directly compare to the limits on nuclear plants (see above table) because coal emissions contain long lived isotopes and have different dispersion and intake pathways.
In terms of dose to a human living nearby, it is sometimes cited that coal plants release 100 times the radioactivity of nuclear plants. This comes from NCRP Reports No. 92 and No. 95 which estimated the dose to the population from 1000 MWe coal and nuclear plants at 490 person-rem/year and 4.8 person-rem/year respectively (a typical Chest x-ray gives a dose of about 6 milli-rem for comparsion). The Environmental Protection Agency estimates an added dose of 0.03 milli-rem per year for living within of a coal plant and 0.009 milli-ren for a nuclear plant for yearly radiation dose estimation.
Unlike coal-fired or oil-fired generation, nuclear power generation does not directly produce any sulfur dioxide, nitrogen oxides, or mercury (pollution from fossil fuels is blamed for 24,000 early deaths each year in the U.S. alone). However, as with all energy sources, there is some pollution associated with support activities such as manufacturing and transportation.
Carbon dioxide
Nuclear power operation does not produce carbon dioxide, leading the nuclear power industry and some environmentalists, such as Greenpeace co-founder Patrick Moore, to advocate it to reduce greenhouse gas emissions (which contribute to global warming). According to a 2007 story broadcast on 60 Minutes, nuclear power gives France the cleanest air of any industrialized country, and the cheapest electricity in all of Europe.
A fair comparison of the climate impacts from different energy sources can be made only by accounting for the emissions of all relevant greenhouse gases (GHGs) from the full energy chain (FENCH) of the energy sources. 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 either are 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).
Vattenfall comparative emissions study
A life cycle analysis centered around the Swedish Forsmark Nuclear Power Plant estimated carbon dioxide emissions at 3.10 g/kWh and 5.05 g/kWh in 2002 for the Torness Nuclear Power Station. This compares to 11 g/kWh for hydroelectric power, 950 g/kWh for installed coal, 900 g/kWh for oil and 600 g/kWh for natural gas generation in the United States in 1999.
The Swedish utility Vattenfall studied full life cycle emissions of nuclear, hydro, coal, gas, solar cell, peat, and wind, which the utility uses to produce electricity. The study concluded that nuclear power produced the smallest amount of CO2 of any of their electricity sources. Nuclear power produced 3.3 g/kWh of carbon dioxide, compared to 400 for natural gas and 700 for coal.
UK Parliamentary Office Study
In a study conducted in 2006 by the UK's Parliamentary Office of Science and Technology (POST), nuclear power's lifecycle was evaluated to emit the least amount of carbon dioxide (very close to wind power's lifecycle emissions) when compared to the other alternatives (fossil fuel, coal, and some renewable energy including biomass and PV solar panels). 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 CO2 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.
Storm and Smith publication
In 2001, Jan Willem Storm van Leeuwen and Philip Smith released a study, titled Is Nuclear Power Sustainable?, which was prepared for circulation during the April 2001 United Nations Commission on Sustainable Development meeting, and again during the continuation in Bonn in July 2001. The report claims 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 report concluded that nuclear power is not sustainable because of increasing energy inputs as lower-grade ores are used.
The study was strongly criticized by the World Nuclear Association (WNA), updated in 2002 and 2005 by Storm van Leeuwen, then dismissed again by the WNA in 2006 based on its own life-cycle-energy calculation. The WNA also listed several other independent life cycle analyses which show similar emissions per kilowatt-hour from nuclear power and from renewables such as hydro and wind power.
Other reports
A 2007 report by Frank Barnaby and James Kent lists several FENCH emissions of CO2 vary between 10 and 130 grams per kWh. Methodology from the Storm and Smith publication is cited, and similar conclusions are drawn from this literature study.
On 21 September 2005 the Oxford Research Group published a report, in the form of a memorandum to a committee of the British House of Commons, in which Storm repeated his results that, while nuclear plants do not generate carbon dioxide while they operate, the other steps necessary to produce nuclear power, including the mining of uranium and the storing of waste, result in substantial amounts of carbon dioxide pollution.
In 2000, Frans H. Koch of the International Energy Agency reported that, although it is correct that the nuclear life cycle produces greenhouse gases, these emissions are actually less than the life cycle emissions of some renewables, like solar and wind, and drastically less than fossil fuels.
Energy Cannibalism
Energy cannibalism refers to an effect where during rapid growth of the entire energy industry a need is created for energy that uses (or cannibalizes) the energy of existing power plants. Thus during rapid growth the industry as a whole produces no energy because new energy is used to fuel the embodied energy of future power plants. When this concept is applied to the nuclear energy industry the necessary growth rate was calculated to be 10.5% if it is to replace fossil fuels by 2050. This growth rate is very similar to the 10% limit due to energy payback for the nuclear power industry in the United States calculated in the same article from a life cycle analysis for energy. These results indicate that any energy policies with the intention of driving down greenhouse gas emissions with deployment of additional nuclear reactors will not be as effective as hoped unless the nuclear industry in the U.S. improves its efficiency considerably.
Water use
Nuclear plants require more, but not significantly more, cooling water than fossil-fuel power plants due to their slightly lower generation efficiencies.
Uranium mining can use large amounts of water - for example, the Roxby Downs mine in South Australia uses 35 million litres of water each day and plans to increase this to 150 million litres per day.
See also
External links
- Photo essay :
- PowerPoint :
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