Uranium (nuclear)

Uranium (nuclear) Basics

Nuclear Energy Is Energy from Atoms

Nuclear energy is energy in the nucleus (core) of an atom. Atoms are tiny particles that make up every object in the universe. There is enormous energy in the bonds that hold atoms together.

Nuclear energy can be used to make electricity. But first the energy must be released. It can be released from atoms in two ways: nuclear fusion and nuclear fission.

In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Nuclear power plants use this energy to produce electricity.

In nuclear fusion, energy is released when atoms are combined or fused together to form a larger atom. This is how the sun produces energy. Fusion is the subject of ongoing research, but it is not yet clear that it will ever be a commercially viable technology for electricity generation.

Nuclear Fuel — Uranium

The fuel most widely used by nuclear plants for nuclear fission is uranium. Uranium is nonrenewable, though it is a common metal found in rocks all over the world. Nuclear plants use a certain kind of uranium, referred to as U-235. This kind of uranium is used as fuel because its atoms are easily split apart. Though uranium is quite common, about 100 times more common than silver, U-235 is relatively rare.

Most U.S. uranium 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.

During nuclear fission, a small particle called a neutron hits the uranium atom and splits it, releasing a great amount of energy as heat and radiation. More neutrons are also released. These neutrons go on to bombard other uranium atoms, and the process repeats itself over and over again. This is called a chain reaction.

Nuclear Power Plants

Nuclear Power Plants Generate About One-Fifth of U.S. Electricity

Nuclear power accounted for about 20% of the total net electricity generated in the United States in 2008, about as much as the electricity used in California, Texas, and New York, the three States with the most people. In 2008, there were 66 nuclear power plants (composed of 104 licensed nuclear reactors) throughout the United States. Most of the reactors are east of the Mississippi. The last new reactor to enter commercial service in the United States was the Tennessee Valley Authority’s Watts Bar 1 in Tennessee in 1996.

In 2008, TVA resumed construction on Watts Bar 2, which was about 80% complete when its construction was stopped in 1988. It is now expected to be completed in 2012.

Nuclear Power Comes from Fission

Most power plants, including nuclear plants, use heat to produce electricity. They rely on steam from heated water to spin large turbines, which generate electricity. Instead of burning fossil fuels to produce the steam, nuclear plants use heat given off during fission.

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 the uranium fuel.

The uranium fuel is formed into ceramic pellets. The pellets are about the size of your fingertip, but each one 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 given off during fission in the reactor core is used to boil water into steam, which turns the turbine blades. As they 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 be used again and again.

Types of Nuclear Reactors

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

A nuclear power plant uses the heat supplied by the nuclear reactor to turn water into steam, which drives turbine-generators that generate electricity.

There Are Two Types of U.S. Reactors

Just as there are different approaches to designing and building airplanes and automobiles, engineers have developed different types of nuclear power plants. Two types are used in the United States: boiling-water reactors and pressurized-water reactors.

Boiling-Water Reactors

In a boiling-water reactor, the water heated by the reactor core turns directly into steam in the reactor vessel and is then used to power the turbine-generator.

Pressurized-Water Reactors

In a pressurized-water reactor, the water heated by the reactor core is kept under pressure so that it does not turn to steam at all — it remains liquid. This hot radioactive water flows through a piece of equipment called a steam generator.

A steam generator is a giant cylinder with thousands of tubes in it that the hot radioactive water can flow through and heat up. Outside these hot tubes in the steam generator is nonradioactive water (or clean water), which eventually boils and turns to steam .

The radioactive water flows back to the reactor core, where it is reheated and then sent back to the steam generator. The clean water may come from one of several sources including oceans, lakes, or rivers.

Getting (Producing) Uranium

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

Uranium Is Found in Nature but Must Be Processed into Fuel

Uranium is nonrenewable, though it is a common metal found in rocks all over the world. Uranium occurs in nature in combination with small amounts of other elements.

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

Economically recoverable uranium deposits have been discovered principally in the western United States, Australia, Canada, Africa, and South America. Once 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% U3O8. The Nuclear Fuel Cycle describes uranium processing in more detail.

Most of Our Uranium Is Imported

Owners and operators of U.S. civilian nuclear power reactors purchased the equivalent of 53 million pounds of uranium during 2008. Uranium delivered to U.S. reactors in 2008 came from six continents:

• 14% of delivered uranium came from the United States
• 86% of delivered uranium was of foreign-origin:
  • 42% was from Australia and Canada
  • 33% originated in Kazakhstan, Russia and Uzbekistan
  • 11% came from Brazil, Czech Republic, Namibia, Niger, South Africa, and the United Kingdom

Nuclear Power & the Environment

Nuclear Power Plants Produce No Carbon Dioxide

The first sentence is questionable: is nuclear energy really "clean"?

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 require large amounts of energy. Nuclear power plants have large amounts of metal and concrete, which also require large amounts of energy to manufacture. If fossil fuels are used to make the electricity and manufacture the power plant materials, then the emissions from burning those fuels could be associated with the electricity that nuclear power plants generate.

Nuclear Energy Produces Radioactive Waste

The main environmental concerns for nuclear power are 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. They 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 regulates the operation of nuclear power plants.

Radioactive wastes are classified as low-level and high-level. The radioactivity in these wastes can range from just above natural background levels, as in mill tailings, to much higher levels, such as in spent reactor fuel or the parts inside a nuclear reactor. The radioactivity of nuclear waste decreases with the passage of time through a process called radioactive decay. The amount of time necessary to decrease the radioactivity of radioactive material to one-half the original level is called the radioactive half-life of the material. Radioactive waste with a short half-life is often stored temporarily before disposal in order to reduce potential radiation doses to workers who handle and transport the waste, as well as to reduce 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, and are covered with a barrier of a material such as clay to prevent radon from escaping into the atmosphere and then 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 get contaminated with small amounts of radioactive dust or particles at nuclear fuel processing facilities and power plants. These materials are subject to special regulation 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 used nuclear reactor fuel (i.e., fuel that has been used in a reactor to produce electricity). The used reactor fuel is in a solid form consisting of small fuel pellets in long metal tubes.

Spent Reactor Fuel Storage and Power Plant Decommissioning

Spent reactor fuel assemblies are highly radioactive and must initially be stored in specially designed pools resembling large swimming pools, where water cools the fuel and acts as a radiation shield, or 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. There is currently no permanent disposal facility in the United States for high-level nuclear waste. High-level waste is being stored at nuclear plants.

When a nuclear power plant stops operating, the facility must be decommissioned. This involves safely removing the plant from service and reducing radioactivity to a level that permits other uses of the property. The Nuclear Regulatory Commission has strict rules governing nuclear power plant decommissioning that involve cleanup of radioactively contaminated 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 can potentially result in widespread contamination of air and water with radioactivity for hundreds of miles around a reactor. The risk of this happening at nuclear power plants in the United States is considered to be very small due to the diverse and redundant barriers and numerous safety systems at nuclear power plants, the training and skills of the reactor operators, testing and maintenance activities, and the regulatory requirements and oversight of the Nuclear Regulatory Commission. A large area surrounding nuclear power plants is restricted and guarded by armed security teams. U.S. reactors have containment vessels that are designed to withstand extreme weather events and earthquakes.