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The environmental impact of nuclear power results from the nuclear fuel cycle, operation, and the effects of nuclear accidents.

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Banana equivalent dose (BED) is an informal measurement of ionizing radiation exposure, intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. Bananas contain naturally occurring radioactive isotopes, particularly potassium-40 (40K), one of several naturally-occurring isotopes of potassium. One BED is often correlated to 10−7 sievert ; however, in practice, this dose is not cumulative, as the principal radioactive component is excreted to maintain metabolic equilibrium. The BED is only meant to inform the public about the existence of very low levels of natural radioactivity within a natural food and is not a formally adopted dose measurement.

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A Blue Ribbon Commission on America's Nuclear Future was appointed by President Obama to look into future options for existing and future nuclear waste, following the ending of work on the incomplete Yucca Mountain Repository. At present there are 70 nuclear power plant sites where 65,000 tons of spent fuel is stored in the USA. Each year, more than 2,000 tons are added to this total. Nine states have "explicit moratoria on new nuclear power until a storage solution emerges". A deep geological repository seems to be the favored approach to storing nuclear waste.

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The following table compares the nuclear accidents at the Chernobyl (1986) and Fukushima Daiichi (2011) nuclear power plants, the only INES level 7 nuclear accidents to date.

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Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. The amount and spread of fallout is a product of the size of the weapon and the altitude at which it is detonated. Fallout may get entrained with the products of a pyrocumulus cloud and fall as black rain. This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron-activated by exposure, is a form of radioactive contamination.

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Nuclear safety is defined by the International Atomic Energy Agency (IAEA) as "The achievement of proper operating conditions, prevention of accidents or mitigation of accident consequences, resulting in protection of workers, the public and the environment from undue radiation hazards". The IAEA defines nuclear security as "The prevention and detection of and response to, theft, sabotage, unauthorized access, illegal transfer or other malicious acts involving nuclear material, other radioactive substances or their associated facilities".

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Nuclear winter is a severe and prolonged global climatic cooling effect hypothesized to occur after widespread firestorms following a nuclear war. The hypothesis is based on the fact that such fires can inject soot into the stratosphere, where it can block some direct sunlight from reaching the surface of the Earth. It is speculated that the resulting cooling would lead to widespread crop failure and famine. When developing computer models of nuclear-winter scenarios, researchers use the conventional bombing of Hamburg, and the Hiroshima firestorm in World War II as example cases where soot might have been injected into the stratosphere, alongside modern observations of natural, large-area wildfire-firestorms.

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Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a by-product of various nuclear technology processes. Industries generating radioactive waste include nuclear medicine, nuclear research, nuclear power, manufacturing, construction, coal and rare-earth mining, and nuclear weapons reprocessing. Radioactive waste is regulated by government agencies in order to protect human health and the environment.