Skip to page content


Uranium (nuclear)

Energy Ant

File Scrub 1 ::::: EE ... nuclear_home-basics

Uranium (nuclear) Basics

The sun is basically a giant ball of hydrogen gas undergoing fusion and giving off vast amounts of energy in the process.
The sun is basically a giant ball of hydrogen gas undergoing fusion into helium gas and giving off vast amounts of energy in the process.

Source: NASA (public domain)

Did you know?

All nuclear power in the United States is used to generate electricity.

Drawing of how fission splits the uranium atom.

Source: Adapted from National Energy Education Development Project (public domain)

Nuclear energy is energy in the core of an atom

Atoms are the tiny particles in the molecules that make up gases, liquids, and solids. Atoms themselves are made up of three particles called protons, neutrons, and electrons. An atom has a nucleus (or core) containing protons and neutrons, which is surrounded by electrons. Protons carry a positive electrical charge and electrons carry a negative electrical charge. Neutrons do not have an electrical charge. Enormous energy is present in the bonds that hold the nucleus together. This nuclear energy can be released when those bonds are broken. The bonds can be broken through nuclear fission, and this energy can be used to produce electricity.

In nuclear fission, atoms are split apart, which releases energy. All nuclear power plants use nuclear fission, and most nuclear power plants use uranium atoms. During nuclear fission, a neutron collides with a uranium atom and splits it, releasing a large amount of energy in the form of heat and radiation. More neutrons are also released when a uranium atom splits. These neutrons continue to collide other uranium atoms, and the process repeats itself over and over again. This process is called a nuclear chain reaction. This reaction is controlled in nuclear power plant reactors to produce a desired amount of heat.

Nuclear energy can also be released in nuclear fusion, where atoms are combined or fused together to form a larger atom. Fusion is the source of energy in the sun and stars. Nuclear fusion is the subject of ongoing research as a source of energy for heat and electricity generation, but whether or not it will be a commercially viable technology is not yet clear because of the difficulty in controlling a fusion reaction.

Nuclear fuel—uranium

Uranium is the fuel most widely used by nuclear plants for nuclear fission. Uranium is considered a nonrenewable energy source, even though it is a common metal found in rocks worldwide. Nuclear power plants use a certain kind of uranium, referred to as U-235, for fuel because its atoms are easily split apart. Although uranium is about 100 times more common than silver, U-235 is relatively rare.

Most U.S. uranium ore is mined in the western United States. Once uranium is mined, the U-235 must be extracted and processed before it can be used as a fuel.

File Scrub L3 ::::: EE ... nuclear_home-basics ... nuclear_power_plants-basics

Nuclear Power Plants

Nuclear reactors in the United States may have large concrete domes covering the reactors, which are required to contain accidental releases of radiation. Not all nuclear power plants have cooling towers. Some nuclear power plants use water from lakes, rivers, or the ocean for cooling.
Photo of nuclear power plant

Source: Stock photography (copyrighted)

Nuclear power comes from nuclear fission

Many power plants, including nuclear power plants, heat water to produce electricity. These power plants use steam from heated water to spin large turbines that generate electricity. Nuclear power plants use heat produced during nuclear fission to heat water.

In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains uranium fuel.

The uranium fuel is formed into ceramic pellets. Each ceramic pellet produces roughly the same amount of energy as 150 gallons of oil. These energy-rich pellets are stacked end to end in 12-foot metal fuel rods. A bundle of fuel rods, sometimes hundreds, is called a fuel assembly. A reactor core contains many fuel assemblies.

The heat produced during nuclear fission in the reactor core is used to boil water into steam, which turns the turbine blades. As the turbine blades turn, they drive generators that make electricity. Afterward, the steam is cooled back into water in a separate structure at the power plant called a cooling tower. The water can then be reused.

Nuclear power plants generate about 20% of U.S. electricity

The United States has 99 nuclear reactors at 61 operating nuclear power plants located in 30 states. Thirty-five of the plants have 2 or more reactors. Nuclear power has supplied about one-fifth of annual U.S. electricity since 1990.

The United States generates more nuclear power than any other country

Of the 31 countries in the world that have commercial nuclear power plants, the United States has the most nuclear capacity and generation. France has the second-highest nuclear electricity generation and obtains about 75% of its total electricity from nuclear energy. Fifteen other countries generate more than 20% of their electricity from nuclear power.

Nuclear electricity generation by top five countries, 2014

Country Nuclear electricity generation (billion kilowatthours) Share of country's total electricity generation
United States 797 19%
France 418 78%
Russia 169 17%
South Korea 149 29%
China 124 2%

Source: U.S. Energy Information Administration, International Energy Statistics, as of May 24, 2017

File Scrub L3 ::::: EE ... nuclear_home-basics ... nuclear_power_plants-Types

Types of Nuclear Reactors

Diagram of a boiling water nuclear reactor
Diagram of a boiling water nuclear reactor.

Source: U.S. Nuclear Regulatory Commission (public domain)

Diagram of a pressurized nuclear water reactor
Diagram of a pressurized nuclear water reactor.

Source: U.S. Nuclear Regulatory Commission (public domain)

Nuclear reactors are machines that contain and control nuclear chain reactions while releasing heat at a controlled rate.

A nuclear power plant uses the heat that a nuclear reactor produces to turn water into steam, which then drives turbine generators that generate electricity.

U.S. nuclear power plants use two types of nuclear reactors

Nuclear power plants in the United States have either a boiling-water reactor or a pressurized-water reactor.

Boiling-water nuclear reactors

In a boiling-water reactor, the reactor core heats water, which turns directly into steam in the reactor vessel. The steam is used to power a turbine generator.

Pressurized-water nuclear reactors

In a pressurized-water reactor, the reactor core heats water and keeps it under pressure to prevent the water from turning into steam. This hot radioactive water flows through tubes in a steam generator.

A steam generator is a giant cylinder filled with nonradioactive water (or clean water). Inside the giant water-filled cylinder are thousands of tubes filled with the hot radioactive water from the reactor core that eventually bring the clean water to a boil and turn it into steam.

The radioactive water flows back to the reactor core to be reheated, and once reheated, returns to the steam generator. The clean water may come from one of several sources like oceans, lakes, or rivers.

What are small modular reactors?

The U.S. Department of Energy is supporting the design, certification, and commercialization of small modular reactors (SMRs). SMRS are about one-third the size of the reactors that are operating and under construction in the United States. SMRs have simple, compact designs that can be assembled in a factory and transported by train or truck to the power plant site. The size and simplicity of the SMRs could reduce the time it takes to construct a new nuclear power plant.

File Scrub L3 ::::: EE ... nuclear_home-basics ... nuclear_where-basics

Getting (Producing) Uranium

Uranium is the fuel most widely used by nuclear power plants for nuclear fission. In nuclear fission, energy is released when atoms are split apart to form smaller atoms. Nuclear power plants use the heat from nuclear fission to produce electricity.

Uranium is a common metal, but it must be processed into a fuel

Uranium is a common metal found in rocks all over the world. Uranium occurs in combination with small amounts of other elements. Economically recoverable uranium deposits have been discovered primarily in the western United States, Australia, Canada, Central Asia, Africa, and South America.

Nuclear power plants use a certain type of uranium, U-235, as fuel because its atoms are easily split apart. Although uranium is about 100 times more common than silver, U-235 is relatively rare.

After uranium is mined, the U-235 must be extracted and processed before it can be used as a fuel. Mined uranium ore typically yields one to four pounds of uranium concentrate (U3O8 or yellowcake) per ton, or 0.05% to 0.20% yellowcake.

Typical conventional uranium mill
Diagram of a Typical Conventional Uranium Mill

Source: U.S. Energy Information Administration (public domain)

The United States imports most of the uranium it uses as fuel

Owners and operators of U.S. nuclear power reactors purchased the equivalent of 50.6 million pounds of uranium in 2016. About 11% of the uranium delivered to U.S. reactors in 2016 was produced in the United States and 89% came from other countries.

Sources and shares of purchases of uranium produced in foreign countries in 2016:

  • Canada–25%
  • Kazakhstan–24%
  • Australia–20%
  • Russia–14%
  • Uzbekistan–4%
  • Malawi, Namibia, Niger, and South Africa–10%
  • Brazil, Bulgaria, China, Czech Republic, Germany, and Ukraine–2%

File Scrub L3 ::::: EE ... nuclear_home-basics ... nuclear_environment-basics

Nuclear Power & the Environment

Did you know?

Steam coming out of nuclear power plant cooling towers is just hot water.

Dry storage cask
Dry storage cask

Some canisters are designed to be placed vertically in robust above-ground concrete or steel structures.

Source: U.S. Nuclear Regulatory Commission (Public Domain)

Nuclear power reactors do not produce direct carbon dioxide emissions

Unlike fossil fuel-fired power plants, nuclear reactors do not produce air pollution or carbon dioxide while operating. However, the processes for mining and refining uranium ore and making reactor fuel all require large amounts of energy. Nuclear power plants also have large amounts of metal and concrete, which require large amounts of energy to manufacture. If fossil fuels are used for mining and refining uranium ore, or if fossil fuels are used when constructing the nuclear power plant, then the emissions from burning those fuels could be associated with the electricity that nuclear power plants generate.

Nuclear energy produces radioactive waste

The primary environmental concern related to nuclear power is the creation of radioactive wastes such as uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. These materials can remain radioactive and dangerous to human health for thousands of years. Radioactive wastes are subject to special regulations that govern their handling, transportation, storage, and disposal to protect human health and the environment. The U.S. Nuclear Regulatory Commission (NRC) regulates the operation of nuclear power plants.

Radioactive wastes are classified as low-level waste or high-level waste. The radioactivity in these wastes can range from just above natural background levels, like in uranium mill tailings, to much higher levels, like in used (spent) reactor fuel or in the parts inside a nuclear reactor. The radioactivity of nuclear waste decreases over time through a process called radioactive decay. The amount of time it takes for the radioactivity of radioactive material to decrease to half its original level is called the radioactive half-life. Radioactive waste with a short half-life is often stored temporarily before disposal to reduce potential radiation doses to workers who handle and transport the waste. This storage system also reduces the radiation levels at disposal sites.

By volume, most of the waste related to the nuclear power industry has a relatively low level of radioactivity. Uranium mill tailings contain the radioactive element radium, which decays to produce radon, a radioactive gas. Most uranium mill tailings are placed near the processing facility or mill where they come from. Uranium mill tailings are covered with a sealing barrier of material like clay to prevent radon from escaping into the atmosphere, and then the barrier is covered by a layer of soil, rocks, or other materials to prevent erosion of the sealing barrier.

The other types of low-level radioactive waste are the tools, protective clothing, wiping cloths, and other disposable items that become contaminated with small amounts of radioactive dust or particles at nuclear fuel processing facilities and nuclear power plants. These materials are subject to special regulations that govern their handling, storage, and disposal so they will not come in contact with the outside environment.

High-level radioactive waste consists of irradiated or spent nuclear reactor fuel (i.e., fuel that is no longer useful for producing electricity). The spent reactor fuel is in a solid form, consisting of small fuel pellets in long metal tubes called rods.

Spent reactor fuel storage and reactor decommissioning

Spent reactor fuel assemblies are highly radioactive, and initially, must be stored in specially designed pools of water. The water cools the fuel and acts as a radiation shield. Spent reactor fuel assemblies can also be stored in specially designed dry storage containers. An increasing number of reactor operators now store their older spent fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling. The United States does not currently have a permanent disposal facility for high-level nuclear waste.

When a nuclear reactor stops operating, it must be decommissioned. Decommissioning involves safely removing from service the reactor and all equipment that has become radioactive and reducing radioactivity to a level that permits other uses of the property. The U.S. Nuclear Regulatory Commission has strict rules governing nuclear power plant decommissioning that involve cleanup of radioactively contaminated power plant systems and structures and removal of the radioactive fuel.

Nuclear reactors and power plants have complex safety and security features

An uncontrolled nuclear reaction in a nuclear reactor could result in widespread contamination of air and water. The risk of this happening at nuclear power plants in the United States is considerably small because of the diverse and redundant barriers and numerous safety systems in place at nuclear power plants, the training and skills of the reactor operators, testing and maintenance activities, and the regulatory requirements and oversight of the U.S. Nuclear Regulatory Commission. A large area surrounding nuclear power plants is restricted and guarded by armed security teams. U.S. reactors also have containment vessels that are designed to withstand extreme weather events and earthquakes.