• Nuclear energy is the energy in the nucleus, or core, of an atom. Atoms are tiny units that make up all matter in the universe, and energy is what holds the nucleus together. There is a huge amount of energy in an atom's dense nucleus. In fact, the power that holds the nucleus together is officially called the "strong force."

    Nuclear energy can be used to create electricity, but it must first be released from the atom. In the process of nuclear fission, atoms are split to release that energy.

    A nuclear reactor, or power plant, is a series of machines that can control nuclear fission to produce electricity. The fuel that nuclear reactors use to produce nuclear fission is pellets of the element uranium. In a nuclear reactor, atoms of uranium are forced to break apart. As they split, the atoms release tiny particles called fission products. Fission products cause other uranium atoms to split, starting a chain reaction. The energy released from this chain reaction creates heat.

    The heat created by nuclear fission warms the reactor's cooling agent. A cooling agent is usually water, but some nuclear reactors use liquid metal or molten salt. The cooling agent, heated by nuclear fission, produces steam. The steam turns turbines, or wheels turned by a flowing current. The turbines drive generators, or engines that create electricity.

    Rods of material called nuclear poison can adjust how much electricity is produced. Nuclear poisons are materials, such as a type of the element xenon, that absorb some of the fission products created by nuclear fission. The more rods of nuclear poison that are present during the chain reaction, the slower and more controlled the reaction will be. Removing the rods will allow a stronger chain reaction and create more electricity.

    As of 2011, about 15 percent of the world's electricity is generated by nuclear power plants. The United States has more than 100 reactors, although it creates most of its electricity from fossil fuels and hydroelectric energy. Nations such as Lithuania, France, and Slovakia create almost all of their electricity from nuclear power plants.

    Nuclear Food: Uranium

    Uranium is the fuel most widely used to produce nuclear energy. That's because uranium atoms split apart relatively easily. Uranium is also a very common element, found in rocks all over the world. However, the specific type of uranium used to produce nuclear energy, called U-235, is rare. U-235 makes up less than one percent of the uranium in the world.

    Although some of the uranium the United States uses is mined in this country, most is imported. The U.S. gets uranium from Australia, Canada, Kazakhstan, Russia, and Uzbekistan. Once uranium is mined, it must be extracted from other minerals. It must also be processed before it can be used.

    Because nuclear fuel can be used to create nuclear weapons as well as nuclear reactors, only nations that are part of the Nuclear Non-Proliferation Treaty (NPT) are allowed to import uranium or plutonium, another nuclear fuel. The treaty promotes the peaceful use of nuclear fuel, as well as limiting the spread of nuclear weapons.

    A typical nuclear reactor uses about 200 tons of uranium every year. Complex processes allow some uranium and plutonium to be re-enriched or recycled. This reduces the amount of mining, extracting, and processing that needs to be done.

    Nuclear Energy and People

    Nuclear energy produces electricity that can be used to power homes, schools, businesses, and hospitals. The first nuclear reactor to produce electricity was located near Arco, Idaho. The Experimental Breeder Reactor began powering itself in 1951. The first nuclear power plant designed to provide energy to a community was established in Obninsk, Russia, in 1954.

    Building nuclear reactors requires a high level of technology, and only the countries that have signed the Nuclear Non-Proliferation Treaty can get the uranium or plutonium that is required. For these reasons, most nuclear power plants are located in the developed world.

    Nuclear power plants produce renewable, clean energy. They do not pollute the air or release greenhouse gases. They can be built in urban or rural areas, and do not radically alter the environment around them.

    The steam powering the turbines and generators is ultimately recycled. It is cooled down in a separate structure called a cooling tower. The steam turns back into water and can be used again to produce more electricity. Excess steam is simply recycled into the atmosphere, where it does little harm as clean water vapor.

    However, the byproduct of nuclear energy is radioactive material. Radioactive material is a collection of unstable atomic nuclei. These nuclei lose their energy and can affect many materials around them, including organisms and the environment. Radioactive material can be extremely toxic, causing burns and increasing the risk for cancers, blood diseases, and bone decay.

    Radioactive waste is what is left over from the operation of a nuclear reactor. Radioactive waste is mostly protective clothing worn by workers, tools, and any other material that have been in contact with radioactive dust. Radioactive waste is long-lasting. Materials like clothes and tools can stay radioactive for thousands of years. The government regulates how these materials are disposed of so they don't contaminate anything else.

    Used fuel and rods of nuclear poison are extremely radioactive. The used uranium pellets must be stored in special containers that look like large swimming pools. Water cools the fuel and insulates the outside from contact with the radioactivity. Some nuclear plants store their used fuel in dry storage tanks above ground.

    The storage sites for radioactive waste have become very controversial in the United States. For years, the government planned to construct an enormous nuclear waste facility near Yucca Mountain, Nevada, for instance. Environmental groups and local citizens protested the plan. They worried about radioactive waste leaking into the water supply and the Yucca Mountain environment, about 130 kilometers (80 miles) from the large urban area of Las Vegas, Nevada. Although the government began investigating the site in 1978, it stopped planning for a nuclear waste facility in Yucca Mountain in 2009.


    Critics of nuclear energy worry that the storage facilities for radioactive waste will leak, crack, or erode. Radioactive material could then contaminate the soil and groundwater near the facility. This could lead to serious health problems for the people and organisms in the area. All communities would have to be evacuated.

    This is what happened in Chernobyl, Ukraine, in 1986. A steam explosion at one of the power plants four nuclear reactors caused a fire, called a plume. This plume was highly radioactive, creating a cloud of radioactive particles that fell to the ground, called fallout. The fallout spread over the Chernobyl facility, as well as the surrounding area. The fallout drifted with the wind, and the particles entered the water cycle as rain. Radioactivity traced to Chernobyl fell as rain over Scotland and Ireland. Most of the radioactive fallout fell in Belarus.

    The environmental impact of the Chernobyl disaster was immediate. For kilometers around the facility, the pine forest dried up and died. The red color of the dead pines earned this area the nickname the Red Forest. Fish from the nearby Pripyat River had so much radioactivity that people could no longer eat them. Cattle and horses in the area died.

    More than 100,000 people were relocated after the disaster, but the number of human victims of Chernobyl is difficult to determine. The effects of radiation poisoning only appear after many years. Cancers and other diseases can be very difficult to trace to a single source.

    Future of Nuclear Energy

    Nuclear reactors use fission, or the splitting of atoms, to produce energy. Nuclear energy can also be produced through fusion, or joining (fusing) atoms together. The sun, for instance, is constantly undergoing nuclear fusion as hydrogen atoms fuse to form helium. Because all life on our planet depends on the sun, you could say that nuclear fusion makes life on Earth possible.

    Nuclear power plants do not have the capability to safely and reliably produce energy from nuclear fusion. It's not clear whether the process will ever be an option for producing electricity. Nuclear engineers are researching nuclear fusion, however, because the process will likely be safe and cost-effective.

    nuclear energy
    The cesium-137 in this tank will "cool it" for more than a decade before being moved to a nuclear-waste storage site.

    Three Mile Island
    The worst nuclear accident in the United States happened at the Three Mile Island facility near Harrisburg, Pennsylvania, in 1979. The cooling system in one of the two reactors malfunctioned, leading to an emission of radioactive fallout. No deaths or injuries were directly linked to the accident.

    Nuclear Tectonics
    The decay of uranium deep inside the Earth is responsible for most of the planet's geothermal energy, causing plate tectonics and continental drift.

  • Term Part of Speech Definition Encyclopedic Entry
    absorb Verb

    to soak up.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    atom Noun

    the basic unit of an element, composed of three major parts: electrons, protons, and neutrons.

    boiling-water reactor Noun

    type of nuclear power plant where steam is used to power generators.

    burn Noun

    injury caused by heat.

    byproduct Noun

    substance that is created by the production of another material.

    cancer Noun

    growth of abnormal cells in the body.

    capability Noun

    ability to perform a task.

    cattle Noun

    cows and oxen.

    chain reaction Noun

    series of events where the previous event causes the next event.

    Chernobyl disaster Noun

    (1986) major accident at the nuclear power plant in Chernobyl, Ukraine.

    clean energy Noun

    electrical energy that does not pollute the atmosphere, water, or earth.

    contaminate Verb

    to poison or make hazardous.

    continental drift Noun

    the movement of continents resulting from the motion of tectonic plates.

    Encyclopedic Entry: continental drift
    controversial Noun

    questionable or leading to argument.

    cooling agent Noun

    material used in a nuclear power plant, usually water, that is warmed by heat from nuclear fission.

    cooling tower Noun

    structure in a nuclear power plant where steam is cooled until it turns back into water.

    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    decay Verb

    to rot or decompose.

    determine Verb

    to decide.

    developed country Noun

    a nation that has high levels of economic activity, health care, and education.

    disaster Noun

    terrible and damaging event.

    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    emission Noun

    discharge or release.

    enormous Adjective

    very large.

    environmental impact Noun

    incident or activity's total effect on the surrounding environment.

    erode Verb

    to wear away.

    evacuate Verb

    to leave or remove from a dangerous place.

    extract Verb

    to pull out.

    facility Noun

    a building or room that serves a specific function.

    fallout Noun

    airborne radioactive particles that eventually fall to the ground, usually the result of a nuclear explosion.

    forest Noun

    ecosystem filled with trees and underbrush.

    fossil fuel Noun

    coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

    fuel Noun

    material that provides power or energy.

    fuse Verb

    to combine or meld together.

    generate Verb

    to create or begin.

    generator Noun

    machine that converts one type of energy to another, such as mechanical energy to electricity.

    geothermal energy Noun

    heat energy generated within the Earth.

    Encyclopedic Entry: geothermal energy
    greenhouse gas Noun

    gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.

    groundwater Noun

    water found in an aquifer.

    Encyclopedic Entry: groundwater
    helium Noun

    a light, colorless gas with the chemical symbol He.

    hydroelectric energy Noun

    energy generated by moving water converted to electricity. Also known as hydroelectricity.

    Encyclopedic Entry: hydroelectric energy
    hydrogen Noun

    chemical element with the symbol H, whose most common isotope consists of a single electron and a single proton.

    immediate Adjective

    quickly or right away.

    import Noun

    good traded from another area.

    insulate Verb

    to cover with material to prevent the escape of energy (such as heat) or sound.

    liquid Noun

    state of matter with no fixed shape and molecules that remain loosely bound with each other.

    malfunction Verb

    to not work correctly.

    metal Noun

    category of elements that are usually solid and shiny at room temperature.

    mineral Noun

    inorganic material that has a characteristic chemical composition and specific crystal structure.

    mining Noun

    process of extracting ore from the Earth.

    molten Adjective

    solid material turned to liquid by heat.

    nuclear energy Noun

    energy released by reactions among the nuclei of atoms.

    Encyclopedic Entry: nuclear energy
    nuclear fission Noun

    process where the nucleus of an atom splits, releasing energy.

    nuclear fusion Noun

    process where the nuclei of one element, usually hydrogen, fuse with each other to form the nuclei of another element, usually helium.

    Nuclear Non-Proliferation Treaty (NPT) Noun

    (1970) international agreement to limit the spread of nuclear weapons.

    nuclear poison Noun

    materials that absorb some of the products produced in nuclear fission reactions.

    nuclear reactor Noun

    machinery that can control nuclear fission, usually producing electricity.

    nuclear waste Noun

    material that has been exposed to radioactivity. Also called radioactive waste.

    nuclear weapon Noun

    explosive device that draws power from the splitting and combining of atomic nuclei.

    nucleus Noun

    positively charged central region of an atom, containing protons and neutrons.

    particle Noun

    small piece of material.

    pellet Noun

    small, rounded object.

    pine Noun

    type of evergreen tree with needle-shaped leaves.

    plate tectonics Noun

    movement and interaction of the Earth's plates.

    plume Noun

    single, upward flow of a fluid, such as water or smoke.

    plutonium Noun

    chemical element with the symbol Pu. Used to make nuclear weapons and as a power source.

    pollute Verb

    to introduce harmful materials into a natural environment.

    power plant Noun

    industrial facility for the generation of electric energy.

    pressurized-water reactor Noun

    type of nuclear power plant where a flow of water is used to power generators.

    radiation poisoning Noun

    set of illnesses, including burns, cancers, and organ damage, that results from exposure to radioactive material.

    radically Adverb

    completely or extremely.

    radioactive Adjective

    having unstable atomic nuclei and emitting subatomic particles and radiation.

    radioactive waste Noun

    byproduct of nuclear fission that emits a type of heat, or radiation, that can damage the tissue of living organisms.

    recycle Verb

    to clean or process in order to make suitable for reuse.

    Red Forest Noun

    dead pine forest surrounding the nuclear power plant in Chernobyl, Ukraine.

    regulate Verb

    to determine and administer a set of rules for an activity.

    relocate Verb

    to move a residence or business from one place to another.

    rural area Noun

    regions with low population density and large amounts of undeveloped land. Also called "the country."

    Encyclopedic Entry: rural area
    salt Noun

    (sodium chloride, NaCl) crystalline mineral often used as a seasoning or preservative for food.

    steam Noun

    water vapor.

    storage tank Noun

    large container in which liquid is usually stored.

    strong force Noun

    power that binds parts of an atom's nucleus together. Also called the nuclear force.

    technology Noun

    the science of using tools and complex machines to make human life easier or more profitable.

    Three Mile Island disaster Noun

    (1979) accident at a nuclear reactor near Harrisburg, Pennsylvania.

    toxic Adjective


    turbine Noun

    machine that captures the energy of a moving fluid, such as air or water.

    U-235 Noun

    uranium isotope often used to produce nuclear fission.

    universe Noun

    all known matter, energy, and space.

    unstable atomic nuclei Noun

    radioactive material, or the nucleus of an atom that has an unbalanced number of protons or neutrons. Unstable atomic nuclei lose energy by emitting radiation and subatomic particles.

    uranium Noun

    chemical element with the symbol U. Fuel used to produce nuclear energy.

    urban area Noun

    developed, densely populated area where most inhabitants have nonagricultural jobs.

    Encyclopedic Entry: urban area
    vapor Noun

    visible liquid suspended in the air, such as fog.

    victim Noun

    person or organization that suffers from the act of another.

    water cycle Noun

    movement of water between atmosphere, land, and ocean.

    Encyclopedic Entry: water cycle
    xenon Noun

    chemical element with the symbol Xe.