Nuclear
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 with 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. Developing technology to harness nuclear fusion as a source of energy for heat and electricity generation is the subject of ongoing research, 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.
The sun is basically a giant ball of hydrogen gas undergoing fusion and giving off vast amounts of energy in the process.
Nuclear power comes from nuclear fission
Nuclear power plants heat water to produce steam. The steam is used 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 about 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, some with hundreds of rods, 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 blades of a steam turbine. As the turbine blades turn, they drive generators that make electricity. Nuclear plants cool the steam back into water in a separate structure at the power plant called a cooling tower or they use water from ponds, rivers, or the ocean. The cooled water is then reused to produce steam.
Nuclear power plants generate about 20% of U.S. electricity
As of January 2018, there were 99 operating nuclear reactors at 61 nuclear power plants in 30 states. Thirty-six of the plants have 2 or more reactors. Nuclear power has supplied about one-fifth of total annual U.S. electricity since 1990.
The United States generates more nuclear power than any other country
Of the 31 countries in the world with commercial nuclear power plants in 2015, the United States had the most nuclear electricity generation capacity and generated more electricity from nuclear energy than any other country. France had the second-highest nuclear electricity generation capacity and electricity generation and obtained about 78% of its total electricity generation from nuclear energy, the largest share of any other country. Fourteen other countries generated at least 20% of their electricity from nuclear power.
Top five nuclear electricity generation countries, 2015
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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.
What is the status of the U.S. nuclear industry?
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Electricity generation from commercial nuclear power plants in the United States began in the late 1950s. As of the end of December 2017, the United States had 99 operating commercial nuclear reactors at 61 nuclear power plants in 30 states. The average age of these nuclear reactors is about 37 years old. The oldest operating reactors, Nine Mile Point Unit 1 and Oyster Creek, began commercial operation in December 1969. The newest reactor to enter service, Watts Bar Unit 2, came online in 2016, the first reactor to come online since 1996 when the Watts Bar Unit 1 came online. Twenty shut down power reactors at 18 sites are being decommissioned.
Although six nuclear reactors have been shut down since 2013, total nuclear electricity generation capacity at the end of 2017 was about the same as total capacity in 2003, when the United States had 104 operating reactors. Power plant uprates—modifications to increase capacity—at nuclear power plants have made it possible for the entire operating nuclear reactor fleet to maintain a relatively consistent total electricity generation capacity. These uprates, combined with high capacity utilization rates (or capacity factors), have allowed nuclear power plants to maintain a consistent share of about 20% of total annual U.S. electricity generation since 1990. Some reactors have also increased annual electricity generation by shortening the length of time reactors are offline for refueling.
Thirty states have at least one commercial nuclear reactor
Most of U.S. commercial nuclear power reactors are located east of the Mississippi River. Illinois has more reactors than any state with 11 reactors at 6 plants, and at the end of 2017, had the largest total nuclear net summer electricity generation capacity of about 11,590 megawatts (MW). The largest reactor in the United States, with an electricity generating capacity of about 1,400 MW, is the Grand Gulf Nuclear Station, located in Port Gibson, Mississippi. The smallest operating reactors, each with a net summer generating capacity of about 520 MW, are at the Prairie Island nuclear plant in Red Wing, Minnesota. Two new nuclear reactors are under construction in Georgia, each with a planned electricity generation capacity of about 1,120 MW.
Many nuclear power plants have more than one reactor
The term power plant refers to an entire facility. A power plant may contain nuclear as well as non-nuclear electricity generating units. Each nuclear reactor located at a commercial nuclear power plant is unique and has its own personnel and equipment. The reactorprovides heat to make steam, which drives a turbine that, in turn, drives the generator that produces electricity.
Thirty-six U.S. nuclear power plants have at least two reactors. Although some foreign nuclear power plants have as many as eight reactors, only three U.S. nuclear power plants have more than two operational reactors: Palo Verde Nuclear Generating Station in Arizona, Browns Ferry Nuclear Power Plant in Alabama, and Oconee Nuclear Station in South Carolina.
Nuclear power plants are generally used more intensively than other power plants
For cost and technical reasons, nuclear power plants are generally used more intensively than coal- or natural gas-fired power plants (see capacity and generation charts at right). In 2017, the nuclear share of total U.S. electricity generating capacity was 9%, while the nuclear share of total electricity generation was about 20%.
Recent U.S. nuclear construction activity
In 2016, the Tennessee Valley Authority's (TVA) Watts Bar Unit 2 in Tennessee became the first new U.S. reactor to come online since 1996.
In February 2012, the U.S. Nuclear Regulatory Commission (NRC) voted to approve Southern Company's application to build and operate two new reactors, Units 3 and 4, at its Vogtle plant in Georgia. The new Vogtle reactors are the first new reactors to receive construction approval in more than 30 years.
In March 2012, the NRC voted to approve South Carolina Electric and Gas Company's application to build and operate two new reactors, Units 2 and 3, at its Virgil C. Summer plant in South Carolina. However, construction on these reactors stopped in 2017.
When will new reactors in the United States come online?
The two new reactors that are now under construction—Vogtle Units 3 and 4—are expected to come online between 2019 and 2020.
As of September 2017, the NRC had about 18 applications for new reactors in various stages of review. The NRC application review process can take up to five years to complete. Under current licensing regulations, a company that seeks to build a new reactor can use reactor designs that the NRC has previously approved. The design certification the NRC issues is independent of approvals of applications to construct or operate a new nuclear power plant. When the applicant uses an NRC-certified reactor design, that means that all safety issues related to the design have been resolved, and the focus of the NRC's review is the quality of construction. Construction of a nuclear power plant may take five years or more.
The U.S. Energy Information Administration (EIA) projects in the Annual Energy Outlook 2018 Reference case that new nuclear electricity generation capacity will be added in 2019 and 2020, but that capacity retirements and derating of some reactors will result in less total nuclear electricity generation capacity than in 2017 and in every year through 2050.