Translation. Region: Russian Federation –
Source: International Atomic Energy Agency –
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Where does nuclear energy come from? The scientific basis of nuclear energy
What's what in the nuclear sphere?
Learn more about nuclear energy in this article about how a nuclear power plant works, what the nuclear fuel cycle is, and what key nuclear energy challenges the IAEA addresses.
November 5, 2025
Andrea Galindo, IAEA Office of Public Information and Communication
Nuclear energy is a form of energy released from the nucleus—the central part of atoms, consisting of protons and neutrons. This energy can be generated by two physical processes: fission, when atomic nuclei split into several pieces, and fusion, when nuclei fuse together.
Nuclear energy, used worldwide today to generate electricity, is generated through nuclear fission, while fusion-based electricity generation technology is still in the research and experimental development phase. In this article, we will focus on nuclear fission. You can learn more about nuclear fusion from this article.
What is nuclear fission?
Graphic: A. Vargas/IAEA
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei, releasing energy.
For example, when a neutron strikes a uranium-235 atom, the nucleus splits into a barium nucleus, a krypton nucleus, and two or three more neutrons. These additional neutrons collide with other nearby uranium-235 nuclei, which also split and generate additional neutrons, resulting in a chain reaction within a fraction of a second.
Each time such a reaction is accompanied by the release of energy in the form of heat and radiationJust as heat from fossil fuels such as coal, gas, and oil is used to generate electricity, a nuclear power plant can convert this thermal energy into electricity.
How does a nuclear power plant work?
In a nuclear power plant reactor, a nuclear chain reaction is localized and controlled using appropriate equipment, most often using uranium-235 fuel, which produces heat through fission. This heat is used to heat the reactor coolant, typically water, to produce steam. The steam is then directed to turbines, causing them to rotate and activating an electric generator, producing electricity without carbon dioxide emissions.
Read more about the different types of nuclear power reactors at this page.
Pressurized water reactors (PWRs) are the most widely used nuclear reactors worldwide. Image: A. Vargas/IAEA
Uranium mining, enrichment and utilization
Uranium is a metal found in rocks throughout the world. Uranium has several natural occurrences. isotopes, which are forms of the element that differ in mass and physical properties but have the same chemical properties. Uranium has two primordial isotopes: uranium-238 and uranium-235. Uranium-238 accounts for the majority of the world's uranium but is incapable of undergoing a fission chain reaction, while uranium-235 can be used to generate energy through fission but accounts for less than 1 percent of the world's uranium reserves.
To increase the fissionability of natural uranium, the amount of uranium-235 it contains must be increased through a process called uranium enrichment. After enrichment, uranium can be used effectively for three to five years as nuclear fuel in nuclear power plants. After this period, it remains radioactive and must be disposed of in accordance with strict regulations to protect people and the environment. Used fuel, known as spent fuel, can also be reprocessed into other types of fuel, which can be used as new fuel for specialized nuclear power plants.
What is the nuclear fuel cycle?
The nuclear fuel cycle is a multi-stage production process necessary for generating electricity using uranium in nuclear power reactors. This cycle begins with uranium mining and ends with the disposal of radioactive waste.
Nuclear waste
Nuclear power plant operations generate waste with varying levels of radioactivity. Depending on the level of radioactivity and the final purpose, different waste management strategies are used. For more information on this topic, watch the animated video below.
Radioactive waste management
Radioactive waste accounts for a small share of total waste. It is a byproduct of millions of medical procedures performed each year, industrial and agricultural radiation use, and the operation of nuclear reactors, which produce approximately 10 percent of the world's electricity. This animated video explains how radioactive waste is managed to protect people and the environment from radiation today and in the future.
When operating the next generation of nuclear power plants based on so-called innovative advanced reactors much less will be formed nuclear wastethan today's reactors. Construction of such plants is expected to begin closer to 2030.
Nuclear energy and climate change
Nuclear energy is a low-carbon energy source because, unlike power plants burning coal, oil, or natural gas, nuclear power plants produce virtually no CO2 during operation. Nuclear power plants generate nearly a third of the world's carbon-free electricity and are crucial to achieving climate change goals.
Read more about Read more about nuclear power and the transition to clean energy in this issue of the IAEA Bulletin.
What role does the IAEA play?
The IAEA establishes international norms and guidelines for the safe and secure use of nuclear energy to protect people and the environment and promotes their implementation. The IAEA supports existing and new nuclear power programs worldwide by offering technical assistance and knowledge management services. Following milestone approachThe IAEA provides essential technical expertise and advice to countries decommissioning their nuclear facilities. As part of its activities in the field guarantees and verification The IAEA ensures that nuclear materials and technologies are not diverted from peaceful uses to other purposes. It provides a methodological framework for organizing the necessary activities throughout the entire life cycle of nuclear energy production, from uranium mining to the construction, maintenance, and decommissioning of nuclear power plants and nuclear waste management. peer review missions and advisory services under the supervision of the IAEA. The IAEA manages the stockpile. low-enriched uranium (LEU) in Kazakhstan, which can be used in case of emergency by countries urgently needing supplies of LEU for peaceful purposes.
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Please note: This information is raw content obtained directly from the source. It represents an accurate account of the source's assertions and does not necessarily reflect the position of MIL-OSI or its clients.