Short answers, pulled from the story.
Nuclear power is the use of nuclear reactions to produce electricity, and the vast majority comes from the nuclear fission of uranium and plutonium. When a neutron splits a uranium-235 or plutonium nucleus, the reaction releases heat that boils water into steam, which drives a turbine connected to an electric generator.
Nuclear power plants supplied 2,602 terawatt hours of electricity in 2023, equivalent to about 9% of global electricity generation. That made nuclear the second largest low-carbon power source after hydroelectricity, though its share has fallen from 16.5% in 1997.
The Obninsk Nuclear Power Plant in the USSR became the world's first to generate electricity for a power grid on the 27th of June 1954, producing around 5 megawatts. The world's first commercial nuclear power station, Calder Hall at Windscale in England, connected to the national grid on the 27th of August 1956.
The 1986 Chernobyl disaster in the USSR is considered the worst nuclear disaster in history, with 56 direct deaths and cleanup costs estimated at about 68 billion US dollars in 2019 terms. The 2011 Fukushima Daiichi accident in Japan, caused by the Tohoku earthquake and tsunami, produced three core meltdowns and is ranked alongside Chernobyl at level 7 on the international scale.
Nuclear power has one of the lowest fatality rates per unit of energy generated, with a death rate of 0.03 per terawatt hour, making it the second safest energy source after solar power. Coal, petroleum, natural gas and hydropower have each caused more deaths per unit of energy due to air pollution and accidents.
Nuclear power emits no greenhouse gases during operation and has a median life-cycle emission intensity of 12 grams of CO2-equivalent per kilowatt hour, the lowest among commercial baseload sources, compared with 820 for coal and 490 for natural gas. As of 2021, nuclear reactors had helped avoid 72 billion tonnes of carbon dioxide emissions since 1970 compared to coal-fired generation.
France produces the highest percentage of its electricity from nuclear reactors, at 65% in 2023. The United States produces the most nuclear energy in absolute terms, with nuclear providing 19% of the electricity it consumes.