Nuclear Energy

The energy released during nuclear fission or fusion, especially when used to generate electricity.

Energy is the power to do work, whether that work is moving, warming, growing, or lighting something. Energy is needed every day to make our world function.

Energy comes in many forms: thermal (heat), radiant (light), mechanical, electrical, chemical, and nuclear energy. All of these forms of energy are the result of different physical processes. Throughout history, people have tried to find substances whose potential energy can be changed into a form that is useful to humans. For example, wood is a useful energy source because when it is burned, it generates heat and light.

Scientists divide energy sources into two groups: renewable (an energy source that we can use over and over again and that will not run out) and nonrenewable (an energy source that we use up and that we cannot use again.) Some examples of renewable energy sources are sunlight (solar energy), moving water (hydropower), heat from within the earth (geothermal), and wind. Some examples of nonrenewable energy sources are coal, oil, and gas, which are fossil fuels that are formed from the remains of dead plants and animals over millions of years. All energy sources are used by people to do the work of heating, lighting, moving, or producing things in order to improve and sustain our lives.

Nuclear energy is produced from nonrenewable resources, but it is not a fossil fuel. Unlike most forms of energy that have been known to humans for a long time, it was discovered much more recently. It may have a big role to play in the future, but it can also be dangerous. Sound mysterious? Let's find out more.

It all starts with atoms. Atoms are the tiny particles that make up all matter -- gases, liquids, and solids -- water, air, food, cars, everything. Atoms are so small that you cannot see them. There are billions of atoms in the period at the end of this sentence!

Today, we know that at least 92 different kinds of atoms occur in nature. Each of these different kinds of atoms is a unique element, such as gold, oxygen, and carbon. All atoms are composed of smaller particles called protons, neutrons, and electrons. Atoms differ in the number of protons, neutrons, and electrons they contain. The center core of the atom, called the nucleus, contains the protons and neutrons, with the electrons moving around it.

Nuclear energy can be defined as the energy in the core of an atom. There is an enormous amount of energy present in the bonds that hold the nucleus together. In fact, the energy that holds the nucleus of an atom together is the strongest force known in nature. This energy can be released when those bonds are broken through nuclear fission, and this energy can be used to produce electricity.

Most nuclear power plants use uranium atoms as the energy fuel. Uranium is a common metal found in certain rocks worldwide. Because it is mined from the earth, it is considered to be nonrenewable. During nuclear fission, a neutron hits a uranium atom's nucleus and splits it, releasing a great amount of energy in the form of heat. More neutrons are also released when the atom splits. These neutrons go on to collide with other uranium atoms, and the process repeats over and over in a chain reaction. This reaction is carefully controlled in a nuclear power plant to produce a constant supply of heat, which turns water into steam. As in other types of power plants, this steam turns turbines and generates electricity.

Nuclear energy is also released in nuclear fusion. During fusion, two or more atoms combine to form a larger atom, and a huge amount of energy is released in the process. Nuclear fusion is what is happening in our sun and other stars; it is the source of their incredible light and heat energy. Scientists are researching ways to control the nuclear fusion reaction that would allow it to be used as a practical energy source for electricity and heat. For now, all nuclear power plants use nuclear fission to generate electricity.

Nuclear fission takes place inside the reactor of a nuclear power plant. Nuclear reactors are machines that contain and control fission chain reactions while releasing the desired amount of heat. The uranium fuel is at the core of the reactor. After being mined, uranium is processed into small pellets, less than an inch long, that are stacked in 12-foot metal fuel rods. A fuel assembly is composed of bundles of fuel rods, surrounded in the reactor by water. Control rods are used to control the rate of the chain reaction. The heat produced during nuclear fission in the reactor is used to boil water into steam, which turns turbines' blades. The turning turbines drive generators that make electricity, which then flows into transmission lines for the use of homes and businesses. The steam is cooled back into water in a cooling tower, and the water can be reused.

There are two main types of nuclear reactors that are used in power plants in the United States. In a boiling-water nuclear reactor, the reactor core heats water, which turns directly into steam in the reactor vessel. In a pressurized-water nuclear reactor, the fission-powered core heats water but keeps it under pressure to prevent the water from turning into steam. The superheated water flows through tubes in a steam generator, a giant cylinder filled with clean water. Eventually, the hot water in the tubes brings the clean water to a boil and turns it into steam. Learn more about how a nuclear power plant operates.

There are about 400 nuclear power plants operating in 31 countries around the world. In the United States, there are currently 61 operating nuclear power plants with 99 nuclear reactors. Nuclear power plants generate about 20% of electricity in the United States and about 14% worldwide. Although the U.S. generates more nuclear power than any other country, sixteen other countries obtain a larger percentage of their power from nuclear energy. For example, France gets 78% of its total electricity from nuclear energy.

There are advantages and disadvantages to all sources of energy. Nuclear energy has its pros and cons too.

Nuclear energy has some important benefits compared to other sources.

• Many power plants, including nuclear power plants, heat water to produce electricity. The basic process is the same: They all use steam from heated water to spin large turbines that generate electricity. The only difference is the source of the heat. Instead of burning coal to heat water, nuclear power plants use heat produced during nuclear fission to heat water. The process is predictable and reliable; a constant supply of energy for electricity is produced.
• Power plants that burn coal or oil produce a lot of air pollution or carbon dioxide while operating. Nuclear reactors do not produce these greenhouse gases, which contribute to global warming and climate change. Nuclear power is considered to be a "clean" source of energy.
• Although nuclear power plants are expensive to build, they are not expensive to run once they are operating. Although uranium is a nonrenewable resource, the supply is not a concern because so little is needed. Nuclear power plants can keep operating with fuel rods up to two years without refueling.
• It requires a small amount of uranium fuel to produce a large amount of energy. It would take 2,000 pounds of coal, 149 gallons of oil, 17,000 cubic feet of natural gas, or 5,000 pounds of wood to produce the same amount of energy as a one-inch pellet of uranium fuel!
• Because so much less uranium needs to be removed from the ground, the environmental impact of a uranium mine is less than mining or drilling for fossil fuels.

Nuclear energy also has some drawbacks, or risks, that are important to consider.

• The nuclear process creates radioactive waste. "Radioactive" refers to atoms that have an unstable nucleus and tend to break down to form more stable atoms. As they decay, they give off energy in the form of waves, rays, or small particles, which we call radiation. Exposure to high levels of certain types of radiation can be hazardous to people and other forms of life. The radioactivity of nuclear waste decreases over time, but some radioactive waste can remain dangerous to human health for thousands of years.
• There is low-level radioactive waste such as the leftover materials at uranium mills, and the tools, cleaning rags, and clothing that come into contact with small amounts of radioactive particles at nuclear power plants. There are special rules to govern the handling, storage, transportation, and disposal of such items so they don't come into contact with the outside environment.
• There is also high-level radioactive waste, such as spent (used-up) nuclear fuel rods. These rods still have a lot of heat and radiation left over from the fission process. These are often stored in pools of water or in dry storage containers using outdoor concrete or steel containers, near the reactors where the spent fuel assemblies were used. However, this is not a long-term solution. The United States does not currently have a permanent disposal facility for high-level nuclear waste.
• There is the possibility of an accident at a nuclear energy facility, where an uncontrolled nuclear reaction would contaminate the surrounding air and water. Environments that are contaminated by high levels of radiation are dangerous to live in or visit. There have been a few accidents in the past, the largest being at Three Mile Island in the U.S. (1979), Chernobyl in Ukraine (1986), and Fukushima in Japan (2011.) After each of these incidents, scientists studied what happened to find ways to make nuclear power plants safer.

Currently, the risk of a serious accident happening in the United States is very small, because there are so many safety features in place. U.S. reactors have containment vessels that are designed to withstand events like hurricanes, tornados, and earthquakes, and nuclear power plants are continually tested and monitored by the U.S. Nuclear Regulatory Commission (NRC).

Learn more about radiation, waste, and safety issues from the Office of Nuclear Energy.

Nuclear energy is a controversial topic, even among energy experts. Is nuclear fission a safe alternative to fossil fuels, or do the risks outweigh the benefits? People don't always agree. Because of its potential to help reduce the use of fossil fuels, scientists are continually researching ways to make nuclear energy safer. New technologies may result in nuclear energy taking a more significant role in the future.

The process of nuclear fission was first demonstrated by scientists about 80 years ago. In 1951, an experimental reactor in Idaho produced the first usable electric power from the atom, lighting four light bulbs. In 1953, the first boiling-water reactor was built in Idaho, and then, in July 1955, the town of Arco, Idaho, became the first American town to be powered by nuclear energy. The energy was provided by a reactor at the Idaho National Laboratory. Today, the Idaho National Laboratory continues to be an important center of nuclear energy research.

Learn more about the history of nuclear energy, and about the work of the Idaho National Laboratory.

Nuclear energy is the force that holds the nucleus together in an atom. When nuclear energy is used to generate electricity, it is known as nuclear power. But there are other uses of nuclear energy. Nuclear technology involves anything that utilizes those core atomic forces and reactions. Radiation and nuclear medicines are used to diagnose and treat many diseases. Nuclear energy is also used in agriculture, food safety, space exploration, and propelling submarines and ships -- even in things like smoke detectors and airport luggage screening. Nuclear science is part of everyday life and its uses will continue to grow in the future.