Nuclear technology uses the energy released by splitting the atoms of certain elements. It was first developed in the 1940s, and during the Second World War research initially focused on producing bombs. In the 1950s attention turned to the peaceful use of nuclear fission, controlling it for power generation. For more information, see page on History of Nuclear Energy.

Here is some background information on nuclear energy:

  • Nuclear power stations started operation in the 1950s;
  • Nuclear energy now provides about 10 percent of the world’s electricity from about 440 power reactors;
  • Nuclear was the world’s second largest source of low-carbon power (28 percent of the total in 2019); and 
  • Over 50 countries utilize nuclear energy in about 220 research reactors. In addition to research, these reactors are used for the production of medical and industrial isotopes, as well as for training.

Civil nuclear power can now boast more than 18,000 reactor years of experience, and nuclear power plants are operational in 32 countries worldwide. In fact, through regional transmission grids, many more countries depend in part on nuclear-generated power; Italy and Denmark, for example, get almost 10 percent of their electricity from imported nuclear power.

When the commercial nuclear industry began in the 1960s, there were clear boundaries between the industries of the East and West. Today, the nuclear industry is characterized by international commerce. A reactor under construction in Asia today may have components supplied from South Korea, Canada, Japan, France, Germany, Russia, and other countries. Similarly, uranium from Australia or Namibia may end up in a reactor in the UAE, having been converted in France, enriched in the Netherlands, de-converted in the UK and fabricated in South Korea.

The uses of nuclear technology extend well beyond the provision of low-carbon energy. It helps control the spread of disease, assists doctors in their diagnosis and treatment of patients, and powers our most ambitious missions to explore space. These varied uses position nuclear technologies at the heart of the world’s efforts to achieve sustainable development. For more information, see page on Nuclear Energy and Sustainable Development.

World Nuclear Association updated on their website “The Nuclear Power in World” in January 2023 which reflects the current situation with nuclear reactors around the world:

  • Reactors Operable: 438 with the capacity to generate 394,876 Mwe annually;
  • Reactors Under Construction: 59 with the capacity to generate 60,902 Mwe; and
  • Reactors Shutdown: 207 with the capacity to generate 99,196 Mwe.

It’s recognized that there is a clear need for new generating capacity around the world, both to replace old fossil fuel units, especially coal-fired ones, which emit a lot of carbon dioxide (CO2) and to meet increased demand for electricity in many countries.

According to World Nuclear Association the share of electricity generated by burning fossil fuels was 66.5 percent in 2005.  Regrettably, despite the strong support for and growth in intermittent renewable electricity sources in recent years, the fossil fuel contribution to power generation has not changed significantly in the last 15 years or so as in 2019, 63 percent of electricity was generated from the burning of fossil fuels.

The world has seen the following two scenarios:

  • The Organization for Economic Co-operation and Development (OECD): The OECD International Energy Agency publishes annual scenarios related to energy. In its World Energy Outlook 2021 there is an ambitious ‘Sustainable Development Scenario’ which is consistent with the provision of clean and reliable energy and a reduction of air pollution, among other aims. In this decarbonization scenario, electricity generation from nuclear increases by almost 75 percent by 2050 to 4714 TWh, and capacity grows to 669 GWe; and
  • The World Nuclear Association: Has put forward a more ambitious scenario than this – the Harmony programme proposes the addition of 1000 GWe of new nuclear capacity by 2050, to provide 25 percent of electricity then (about 10,000 TWh) from 1250 GWe of capacity (after allowing for retirements). Providing one-quarter of the world’s electricity through nuclear would substantially reduce CO2 emissions and improve air quality.

In 2021 nuclear plants supplied 2653 TWh of electricity, up from 2553 TWh in 2020:

World Nuclear Electricity Production by Geographical Jurisdictions

Source: World Nuclear Association, IAEA PIS


Thirteen countries in 2020 produced at least one-quarter of their electricity from nuclear. France gets around 70 PERCENT of its electricity from nuclear energy, while Ukraine, Slovakia, Belgium and Hungary get about half from nuclear. Japan was used to relying on nuclear power for more than one-quarter of its electricity and is expected to return to somewhere near that level.


Source: IAEA Pris

The performance of nuclear reactors has improved substantially over time. Over the last 40 years the proportion of reactors reaching high capacity factors has increased significantly. For example, 68 percent of reactors achieved a capacity factor higher than 80 percent in 2021, compared to less than 30 percent in the 1970s, whereas only 6 percent of reactors had a capacity factor lower than 50 percent in 2021, compared to just over 20 percent in the 1970s.


Source: World Nuclear Association, IAEA Pris

Nuclear energy is defined as a source of power which is created from energy released by a nuclear reaction. Nuclear reactors serve three general purposes:

  1.  Civilian Reactors are used to generate energy for electricity and sometimes also steam for district heating; military reactors create materials that can be used in nuclear weapons; and research reactors are used to develop weapons or energy production technology, for training purposes, for nuclear physics experimentation, and for producing radio-isotopes for medicine and research;

Source: C&EN

2.  Military Reactors create materials that can be used in nuclear weapons; and


3.  Research Reactors are used to develop weapons or energy production technology, for training purposes, for nuclear physics experimentation, and for producing radio-isotopes for medicine and research. The chemical composition of the fuel, the type of coolant, and other details important to reactor operation depend on reactor design. Most designs have some flexibility as to the type of fuel that can be used. Some reactors are dual-purpose in that they are used for civilian power and military materials production. The two tables below give information about civilian and military reactors.


The focus of this book is on the Civilian and Research Reactors.

The global demand for electricity will continue to intensify and in order to meet this demand, future electricity generation will need a range of options and these options must be low carbon if the global objective is to reduce greenhouse gas (GHG) emissions significantly.  The good news is that nuclear generation provides reliable supplies of electricity, with very low carbon emissions and relatively small amounts of waste that can be safely stored and eventually disposed of.

The reality is that each method opted to generate electricity, generates Greenhouse Gases (GHGs) in varying quantities throughout the life cycle – construction, operation, and decommissioning.  Some generation methods such as coal fired power plants release the majority of GHGs when their carbon-containing fossil fuels are burnt, producing carbon dioxide (CO2). Others, such as wind power and nuclear power, give rise to much less emissions, these being during construction and decommissioning, or mining and fuel preparation in the case of nuclear.  Comparing the lifecycle emissions of electrical generation allows for a fair comparison of the different generation methods on a per kilowatt-hour basis. The lower the value, the fewer GHG emissions are released.

Here is an important consideration.  Nuclear power plants produce no GHG emissions during operation, and over the course of its life-cycle, nuclear produces about the same amount of carbon dioxide-equivalent emissions per unit of electricity as wind, and one-third of the emissions per unit of electricity when compared with solar.

Average life-cycle carbon dioxide-equivalent emissions for different electricity generators (Source: IPCC)

Perhaps another important factor about the generation of nuclear electricity is the cost.  Here is a graph designed to illustrate the breakdown of Operating Costs associated with Coal, Gas, and Gas Generation:

It should be kept in mind that nuclear technology is not just used to supply electricity to the grid; it is in a wide variety of other uses such as medicine, heating and space travel.  For instance:

  • Nuclear Medicine:  Nuclear medicine uses radiation to allow doctors to make a quick, accurate diagnosis of the functioning of person’s specific organs, or to treat them. Radiotherapy can be used to treat some medical conditions, especially cancer, using radiation to weaken or destroy particular targeted cells.
    • Tens of millions of patients are treated with nuclear medicine each year;
    • Over 10,000 hospitals worldwide use radioisotopes in medicine, and about     90  percent of the procedures are for diagnosis.  The most common radioisotope used in diagnosis is technetium-99, with some 30 million procedures per year, accounting for 80 percent of all nuclear medicine procedures worldwide; and
    • Modern industry also uses radioisotopes in a variety of ways. Sealed radioactive   sources are used in industrial radiography, gauging applications and mineral analysis.
  • Heat for Desalination: Heat from nuclear reactors can be used directly, instead or as well as being used to generate electricity. This heat can be used for district heating, as process heat for industry or for desalination plants, used to make clean drinkable water from seawater; and
  • Space Missions:  Radioisotope thermal generators are used in space missions. The heat generated by the decay of a radioactive source, often Plutonium-238, is used to generate electricity.  The Voyager space probes, the Cassini mission to Saturn, the Galileo mission to Jupiter and the New Horizons mission to Pluto all are powered by RTGs. The Spirit and Opportunity Mars rovers have used a mix of solar panels for electricity and RTGs for heat. The latest Mars rover, Curiosity, is much bigger and uses RTGs for heat and electricity as solar panels would not be able to supply enough electricity.

In the future, electricity or heat from nuclear power plants could be used to make hydrogen. Hydrogen can be used in fuel cells to power cars, or can be burnt to provide heat in place of gas, without producing emissions that would cause climate change.

Updated on 31 January 2023.

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