Nuclear power has various environmental impacts, both positive and negative, including the construction and operation of the plant, the nuclear fuel cycle, and the effects of nuclear accidents. Nuclear power plants do not burn fossil fuels and so do not directly emit carbon dioxide. The carbon dioxide emitted during mining, enrichment, fabrication and transport of fuel is small when compared with the carbon dioxide emitted by fossil fuels of similar energy yield, however, these plants still produce other environmentally damaging wastes. Nuclear energy and renewable energy have reduced environmental costs by decreasing emissions resulting from energy consumption.
There is a catastrophic risk potential if containment fails, which in nuclear reactors can be brought about by overheated fuels melting and releasing large quantities of fission products into the environment. In normal operation, nuclear power plants release less radioactive material than coal power plants whose fly ash contains significant amounts of thorium, uranium and their daughter nuclides.
A large nuclear power plant may reject waste heat to a natural body of water; this can result in undesirable increase of the water temperature with adverse effect on aquatic life. Alternatives include cooling towers.
Mining of uranium ore can disrupt the environment around the mine. However, with modern in-situ leaching technology this impact can be reduced compared to "classical" underground or open-pit mining. Disposal of spent nuclear fuel is controversial, with many proposed long-term storage schemes under intense review and criticism. Diversion of fresh- or low-burnup spent fuel to weapons production presents a risk of nuclear proliferation, however all nuclear weapons states derived the material for their first nuclear weapon from (non-power) research reactors or dedicated "production reactors" and/or uranium enrichment. Finally, some parts the structure of the reactor itself becomes radioactive through neutron activation and will require decades of storage before it can be economically dismantled and in turn disposed of as waste. Measures like reducing the cobalt content in steel to decrease the amount of cobalt-60 produced by neutron capture can reduce the amount of radioactive material produced and the radiotoxicity that originates from this material. However, part of the issue is not radiological but regulatory as most countries assume any given object that originates from the "hot" (radioactive) area of a nuclear power plant or a facility in the nuclear fuel cycle is ipso facto radioactive, even if no contamination or neutron irradiation induced radioactivity is detectable.
Waste streams Nuclear power has at least three waste streams that may impact the environment:Benjamin K. Sovacool. A Critical Evaluation of Nuclear Power and Renewable Electricity in Asia, Journal Contemporary Asia, Vol. 40, No. 3, August 2010, pp. 376. Spent nuclear fuel at the reactor site (including fission products and plutonium waste) Tailings and waste rock at uranium mining mills Releases of ill-defined quantities of radioactive materials during accidents Nuclear reprocessing and breeder reactors which can decrease the need for storage of spent fuel in a deep geological repository have faced economic and political hurdles but are in some use in Russia, India, China, Japan and France, which are among the countries with the highest nuclear energy production outside the United States. However, the U.S. has not undertaken significant efforts towards either reprocessing or breeder reactors since the 1970s instead relying on the once through fuel cycle.
Radioactive waste
High-level waste
The spent nuclear fuel from uranium-235 and plutonium-239 nuclear fission contains a wide variety of carcinogenic radionuclide isotopes such as strontium-90, iodine-131, and caesium-137. Such waste includes some of the most long-lived transuranic elements such as americium-241 and isotopes of plutonium. The most long-lived radioactive wastes, including spent nuclear fuel, usually must be contained and isolated from the environment for a long period of time. Spent nuclear fuel storage is mostly a problem in the United States, following a 1977 prohibition by then-President Jimmy Carter on nuclear fuel recycling. France, The United Kingdom, and Japan are some of the countries that have rejected the repository solution. Spent nuclear fuel produced by some types of reactors is a valuable asset, not simply waste.
Disposal of these wastes in specially-engineered underground repositories is the preferred long-term storage solution.NEA – Moving forward with geological disposal The International Panel on Fissile Materials has said: It is widely accepted that spent nuclear fuel and high-level reprocessing and plutonium wastes require well-designed storage for long periods of time, to minimize releases of the contained radioactivity into the environment. Safeguards are also required to ensure that neither plutonium nor highly enriched uranium is diverted to weapon use. There is general agreement that placing spent nuclear fuel in repositories hundreds of meters below the surface would be safer than indefinite storage of spent fuel on the surface.
When designing long-term storage facilities, there are several crucial considerations, including the specific type of radioactive waste, the containers enclosing the waste, other engineered barriers or seals around the containers, the tunnels housing the containers, and the geologic makeup of the surrounding area.US DOE – Radioactive waste: an international concern
The ability of natural geologic barriers to isolate radioactive waste is demonstrated by the natural nuclear fission reactors at Oklo, Africa. During their long reaction period, about 5.4 metric tons of fission products, 1.5 metric tons of plutonium, and other transuranic elements were generated in the uranium ore body. These elements remain immobile and stable to this day, a span of almost 2 billion years.R. Naudet. 1976. The Oklos nuclear reactors: 1800 millions years ago. Interdisciplinary Science Reviews, 1(1) p.72-84.
Despite long-standing agreement among many experts that geological disposal can be safe, technologically feasible, and environmentally sound, a large part of the general public in many countries remains skeptical.Vandenbosch, Robert, and Susanne E. Vandenbosch. 2007. Nuclear waste stalemate. Salt Lake City: University of Utah Press. One of the challenges facing the supporters of these efforts is to demonstrate confidently that a repository will contain waste for so long that future containment breaches will pose no significant health or environmental risks.
Nuclear reprocessing does not eliminate the need for a repository, but it reduces the required volume, the need for long-term heat dissipation, and the long-term radiation hazard. Reprocessing does not eliminate the political and social challenges to repository siting.
The countries that have made the most progress towards a repository for high-level radioactive waste have typically started with public consultations and made voluntary siting a necessary condition. This consensus-seeking approach is believed to have a greater chance of success than top-down modes of decision making, but the process is necessarily slow, and there is "inadequate experience around the world to know if it will succeed in all existing and aspiring nuclear nations."M.V. Ramana. Nuclear Power: Economic, Safety, Health, and Environmental Issues of Near-Term Technologies, Annual Review of Environment and Resources, 2009, 34, p. 145. Moreover, many communities do not want to host a nuclear waste repository as they are "concerned about their community becoming a de facto site for waste for thousands of years, the health and environmental consequences of an accident, and lower property values."Benjamin K. Sovacool (2011). Contesting the Future of Nuclear Power: A Critical Global Assessment of Atomic Energy, World Scientific, p. 144; See also Nuclear Nebraska.
In a 2010 Presidential Memorandum, U.S. President Obama established the Blue Ribbon Commission on America's Nuclear Future. The commission, composed of fifteen members, conducted an extensive two-year study of nuclear waste disposal. During their research, the Commission visited Finland, France, Japan, Russia, Sweden, and the UK, and in 2012, the Commission submitted its final report. The Commission did not issue recommendations for a specific site but rather presented a comprehensive recommendation for disposal strategies. One major recommendation was that "the United States should undertake an integrated nuclear waste management program that leads to the timely development of one or more permanent deep geological facilities for the safe disposal of spent fuel and high-level nuclear waste."
Pressurized heavy water reactors like the Canadian CANDU or the Indian IPHWR do not need enriched fuel and can operate using natural uranium. This allows better use of the energy contained in the initial uranium ore (while higher enrichment allows higher burnup, the amount of natural uranium needed to produce this fuel increases faster than the achievable burnup) and reduces the energy needed in fuel manufacturing as the conversion of the yellowcake to uranium hexafluoride and back into an oxide fuel as well as the energy-intensive enrichment process can be skipped.
Other waste
Moderate amounts of low-level waste are managed through a chemical and volume control system (CVCS). This includes gas, liquid, and solid waste produced via 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 pose public health risks (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.NRC. Radioactive Waste: Production, Storage, Disposal (NUREG/BR-0216, Rev. 2) Solid waste from the CVCS is combined with solid waste that comes from handling materials before it is buried off-site.NRC. Radioactive Waste Management
Power plant emission
Radioactive gases and effluents Most commercial nuclear power plants release gaseous and liquid radiological effluents into the environment as a byproduct of the Chemical Volume Control System. These effluents are monitored in the US by the EPA and the NRC. Civilians living within of a nuclear power plant typically receive about 0.1 μSv per year.ANS dosechart [American Nuclear Society] For comparison, the average person living at or above sea level receives at least 260 μSv per year from cosmic radiation.
All reactors in the United States are required by law to have a containment building. The walls of containment buildings are several feet thick and made of concrete designed to stop the release of any radiation emitted by the reactor into the environment. For comparison:
The total amount of radioactivity released through the CVCS 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 exposure to a member of the public from the effluents emitted. Effluent monitoring is conducted continuously at the plant.
Tritium + Tritium Effluent Limits Country Limit (Bq/L) Australia 76,103 Finland 30,000 WHO 10,000 Switzerland 10,000 Russia 7,700 Ontario, Canada 7,000 European Union 1001 United States 740 California Public Health Goal 14.8