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.

Chernobyl

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.

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.

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.

absorb
Verb

to soak up.

Noun

layers of gases surrounding a planet or other celestial body.

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.

Noun

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

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.

Noun

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

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.

Noun

heat energy generated within the Earth.

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.

Noun

water found in an aquifer.

helium
Noun

a light, colorless gas with the chemical symbol He.

Noun

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

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.

Noun

process of extracting ore from the Earth.

molten
Adjective

solid material turned to liquid by heat.

Noun

energy released by reactions among the nuclei of atoms.

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.

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.

Noun

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

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

poisonous.

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.

Noun

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

vapor
Noun

visible liquid suspended in the air, such as fog.

victim
Noun

person or organization that suffers from the act of another.

Noun

movement of water between atmosphere, land, and ocean.

xenon
Noun

chemical element with the symbol Xe.