什么是核能？核电科学

Nuclear fission is a reaction where the nucleus of an atom splits into two or more smaller nuclei, while releasing energy.

For instance, when hit by a neutron, the nucleus of an atom of uranium-235 splits into two smaller nuclei, for example a barium nucleus and a krypton nucleus and two or three neutrons. These extra neutrons will hit other surrounding uranium-235 atoms, which will also split and generate additional neutrons in a multiplying effect, thus generating a chain reaction in a fraction of a second.

Each time the reaction occurs, there is a release of energy in the form of heat and radiation. The heat can be converted into electricity in a nuclear power plant, similarly to how heat from fossil fuels such as coal, gas and oil is used to generate electricity.

Inside nuclear power plants, nuclear reactors and their equipment contain and control the chain reactions, most commonly fuelled by uranium-235, to produce heat through fission. The heat warms the reactor’s cooling agent, typically water, to produce steam. The steam is then channelled to spin turbines, activating an electric generator to create low-carbon electricity.

Find more details about the different types of nuclear power reactors on this page.

Uranium is a metal that can be found in rocks all over the world. Uranium has several naturally occurring isotopes, which are forms of an element differing in mass and physical properties but with the same chemical properties. Uranium has two primordial isotopes: uranium-238 and uranium-235. Uranium-238 makes up the majority of the uranium in the world but cannot produce a fission chain reaction, while uranium-235 can be used to produce energy by fission but constitutes less than 1 per cent of the world’s uranium.

To make natural uranium more likely to undergo fission, it is necessary to increase the amount of uranium-235 in a given sample through a process called uranium enrichment. Once the uranium is enriched, it can be used effectively as nuclear fuel in power plants for three to five years, after which it is still radioactive and has to be disposed of following stringent guidelines to protect people and the environment. Used fuel, also referred to as spent fuel, can also be recycled into other types of fuel for use as new fuel in special nuclear power plants.

What is the Nuclear Fuel Cycle?

The operation of nuclear power plants produces waste with varying levels of radioactivity. These are managed differently depending on their level of radioactivity and purpose. See the animation below to learn more about this topic.

Radioactive Waste Management

The next generation of nuclear power plants, also called innovative advanced reactors, will generate much less nuclear waste than today’s reactors. It is expected that they could be under construction by 2030.

Nuclear power is a low-carbon source of energy, because unlike coal, oil or gas power plants, nuclear power plants practically do not produce CO₂ during their operation. Nuclear reactors generate close to one-third of the world’s carbon free electricity and are crucial in meeting climate change goals.

To find out more about nuclear power and the clean energy transition, read this edition of the IAEA Bulletin.

• The IAEA establishes and promotes international standards and guidance for the safe and secure use of nuclear energy to protect people and the environment.
• The IAEA supports existing and new nuclear programmes around the world by providing technical support and knowledge management. Through the Milestones Approach, the IAEA provides technical expertise and guidance to countries that want to develop a nuclear power programme as well as to those who are decommissioning theirs.
• Through its safeguards and verification activities, the IAEA oversees that nuclear material and technologies are not diverted from peaceful use.
• Review missions and advisory services led by the IAEA provide guidance on the activities necessary during the lifetime of production of nuclear energy: from the mining of uranium to the construction, maintenance and decommissioning of nuclear power plants and the management of nuclear waste.
• The IAEA administers a reserve of low enriched uranium (LEU) in Kazakhstan, which can be used as a last resort by countries that are in urgent need of LEU for peaceful purposes.

This article was first published on iaea.org on 2 August 2021.