1. What Is Nuclear Energy?

Nuclear energy is energy that comes from the nucleus (core) of an atom. Atoms are the particles that make up all objects in the universe. Atoms consist of neutrons, protons, and electrons.

Nuclear energy is released from an atom through one of two processes: nuclear fusion or nuclear fission. In nuclear fusion, energy is released when the nuclei of atoms are combined or fused together. This is how the sun produces energy. In nuclear fission, energy is released when the nuclei of atoms are split apart. Nuclear fission is the only method currently used by nuclear plants to generate electricity.

The fuel most widely used by nuclear power plants for fissioning is uranium. Uranium is the heaviest of the 92 naturally occurring elements and is classified as a metal. It is also one of the few elements that is easily fissioned. Uranium was formed when the earth was created and is found in rocks all over the world. Rocks that contain a lot of uranium are called uranium ore, or pitch-blende. Uranium, although abundant, is a nonrenewable energy source.

Two forms (isotopes) of uranium are found in nature, uranium-235 and uranium-238. These numbers refer to the number of neutrons and protons in each atom.

Uranium-235 is the form commonly used for energy production because, unlike uranium-238, its nucleus splits easily when bombarded by a neutron. During fissioning, the uranium-235 atom absorbs a bombarding neutron, causing its nucleus to split apart into two atoms of lighter weight. At the same time, the fission reaction releases energy in the form of heat, radiation, and more neutrons. The newly released neutrons go on to bombard other uranium atoms, and the process repeats itself over and over. This is called a chain reaction.

2. History of Nuclear Energy

Compared to other energy sources, nuclear energy is a very new way to produce energy. It wasn't until the early 1930s that scientists discovered that the nucleus of an atom made up of protons an neutrons. Then just a few years later, in 1938, two German scientists split the nucleus of the atom apart by bombarding it with a neutron--the process called "fission." Soon after a Hungarian scientist discovered the "chain reaction" and its ability to produce enormous amounts of energy. Under the dark cloud of World War II, nuclear fission was first used to make a bomb. After that war, nuclear fission was developed for generating electricity.

The first commercial nuclear power plant came on line in Shippingport, Pennsylvania in 1957. Since then, the industry has experienced dramatic shifts in fortune. Throughout the mid 1960s, government and industry experimented with demonstration and small commercial plant. A period of rapid expansion followed between 1965 and 1975. The Three Mile Island accident in 1979 abruptly stalled the growth. The public opposition that organized in response to the Three Mile Island accident has been so successful that no new plants have been ordered since then.

3. The Nuclear Fuel Cycle

The chain of steps from mining the uranium ore, through its use in a nuclear reactor, through disposal--is called the nuclear fuel cycle.

Mining. The first step in the nuclear fuel cycle is mining the uranium ore. Workers mine uranium ore much as coal miners mine coal-in deep underground mines or in open-pit surface mines. A ton of uranium ore in the United States typically contains three to four pounds of uranium.

Milling. After it has been mined uranium ore is crushed. The crushed ore is usually poured into an acid, which dissolves the uranium, but not the rest of the crushed rock. The acid solution is drained off and dried, leaving a yellow powder called "yellowcake," consisting mostly of uranium. This process of removing uranium from the ore is called uranium milling.

Conversion. The next step in the cycle is the conversion of the yellowcake into a gas called uranium hexafluoride, or UF6. The uranium hexafluoride is then shipped to a gaseous diffusion plant for enrichment.

Enrichment. Because less than one percent of uranium ore contains uranium-235, the form used for energy production, uranium must be treated to increase the concentration of uranium-235. This treatment process--called uranium enrichment--increases the percentage of uranium-235 from one to three percent. It typically takes place at a gaseous diffusion plant where the uranium hexafluoride is pumped through filters that contain extremely tiny holes. Because uranium-235 has three fewer neutrons and is one percent lighter than uranium-238, it moves through the holes more easily than uranium-238. This method increases the percentage of uranium-235 as the gas passes through thousands of filters.

Fuel Fabrication. The enriched uranium is then taken to a fuel fabrication plant where it is prepared for the nuclear reactor. Here, the uranium is made into a solid ceramic material and formed into small barrel-shaped pellets. These ceramic fuel pellets can withstand very high temperatures, just like the ceramic tiles on the space shuttle. Fuel pellets are about the size of your fingertip, yet each one can produce as much energy as 120 gallons of oil. The pellets are then stacked and sealed in 12-foot metal tubes called fuel rods. Finally, the fuel rods are bundled into groups called fuel assemblies.

Nuclear Reactor. The uranium fuel is now ready for use in a nuclear reactor. Fissioning takes place in the reactor core. Surrounding the core of the reactor is a shell called the reactor pressure vessel. To prevent heat or radiation leaks, the reactor core and the vessel are housed in an air-tight containment building made of steel and concrete several feet thick.

The reactor core houses approximately 200 fuel assemblies. Spaced between the fuel assemblies are movable control rods. Control rods absorb neutrons and slow down the nuclear chain reaction. They are called control rods because they help control the fissioning process. Water also flows up through the fuel assemblies and control rods to remove some of the heat of the nuclear chain reaction.

The nuclear reaction generates heat energy just as burning coal or oil generate heat energy. Likewise, the heat is used to boil water into steam which turns a turbine generator to produce electricity. Afterward, the steam is condensed back into water and cooled in a separate structure called a cooling tower. In this way, the water can be used again and again.

Spent Fuel Storage. Like most industries, nuclear power plants produce waste. One of the main concerns about nuclear power plants is not the amount of waste created, which is quite small compared to other industries, but the radioactivity of some of that waste. The fission process creates radioactive waste products. After three or so years, these waste products build up in the fuel rods making the chain reaction more difficult. Utility companies generally replace one-third of the fuel rods every 12 to 18 months to keep power plants in continuous operation. The fuel that is taken out of the reactor is called spent fuel. The spent fuel contains both radioactive waste products and some unused nuclear fuel.

The spent fuel is typically stored near the reactor in a deep pool of water called the spent fuel pool. During storage, the spent fuel cools down and begins to lose most of its radioactivity through radioactive decay. In three months, the spent fuel will lose 50 percent of its radiation; in one year, 80 percent; in 10 years, 90 percent. The spent fuel pool is intended as a temporary method for storing nuclear waste. Eventually, the spent fuel will be reprocessed and/or transported to a permanent federal disposal site.

Reprocessing. Spent fuel contains both radioactive waste products and unused nuclear fuel. In fact, about one-third of the nuclear fuel remains unused when the fuel rod must be replaced. Reprocessing separates the unused nuclear fuel from the waste products so that it can be used in a reactor again and again.

But currently American nuclear power plants store the spent fuel in spent fuel pools without reprocessing. Why? Mainly because reprocessing is more expensive than making new fuel from uranium ore.

4. Nuclear Waste Repositories, Use and Power Plants

Most scientists believe the safest way to store nuclear waste is in rock formations deep underground--called geological repositories. In 1982, the U.S. Congress agreed and passed the Nuclear Waste Policy Act. This law directed the U.S. Department of Energy to site, design, construct, and operate America's first repository by 1998. The repository will store radioactive waste from nuclear power plants and from defense weapons plants.

The same law also established the Nuclear Waste Fund to pay for the repository. People who use electricity from nuclear power plants contribute 1/10 of a cent for each kilowatt-hour of nuclear-generated electricity they use. An average American household, which uses about 7,500 kilowatt-hours a year, would contribute $7.50 a year to the fund if it got all its electricity from nuclear power. The nation contributed $600 million to the fund in 1993.

More recently, Congress passed the Nuclear Waste Policy Amendments Act in 1987. Among other things, this act proposed Yucca Mountain, Nevada as the nation's first repository site.

If the current plan is approved (it's not a done deal), nuclear waste will be sealed in steel canisters and stored in underground vaults located 1,000 feet below the surface by the year 2003.

Yucca Mountain is being studied as a repository site because it is dry (water won't percolate through the repository) and geologically stable (the chance of erupting volcanoes or damaging earthquakes is extremely slim). Another plus about the Yucca Mountain site is its isolation. Hardly anyone lives near it.

Although utility companies currently store their nuclear waste in pools of water at the power plant, some companies will run out of storage space by 1998--the original deadline for the opening of the repository. Utility companies are asking the Department of Energy to accept responsibility for the waste in 1998. The Department of Energy would need to store the waste in a temporary facility prior to its final burial at the repository.

How Much Nuclear Energy Do We Use?

Nuclear energy is an important source of electricity in the United States-it's second only to coal. Nuclear power provides about 21 percent of this country's electricity.

At the end of 1994, there were 109 nuclear power plants operating in the United States. No new plants are planned for the remaining decade.

In other parts of the world, nuclear energy is a growing source of electrical power. Nuclear energy now provides about 17 percent of the world's electricity. The United States, France, Japan, and Germany are the world leaders in producing electricity from nuclear power. France gets 75 percent of its electricity from nuclear power.

Licensing Nuclear Power Plants

Nuclear power plants must obtain a permit to start construction and, later, a license to begin operation.

Researchers conduct many studies to find the best site for a nuclear power plant. Detailed plans and reports are submitted to the Nuclear Regulatory Commission, the federal government agency responsible for licensing nuclear power plants and overseeing their construction and operation. When the builders of a nuclear power plant apply for a license, local hearings are held so people can testify and air their concerns and opinions. After a plant is built, the Nuclear Regulatory Commission places inspectors at the site to assure the plant is operating properly.

5. Economics of Nuclear Energy and the Environment

The cost of producing electricity from nuclear energy is somewhat higher than the cost of producing electricity from coal. Much of the cost of producing electricity at a nuclear plant comes not from the fuel source-uranium is very inexpensive at just $11 a ton-but from the cost of building the plant. Building a nuclear power plant is very expensive because of the high costs of licensing, construction, and inspection.

The cost of producing nuclear electricity is about two cents per kilowatt-hour (kWh). In comparison, the cost of producing electrical power from new coal plants is approximately four cents per kWh.

Uranium is an abundant natural resource that is found all over the world. At current rates of use, uranium resources could last more than 500 years. (A process called "breeding," which converts uranium into plutonium-an even better fuel--could extend uranium reserves for millions of years. Breeder reactors are already being used in France, but they are not planned for use in this country.) And because uranium is an extremely concentrated fuel source, it requires far less mining and transportation than other fuel sources for the energy it furnishes.

Nuclear Energy and the Environment

One of the best kept secrets about nuclear power its impact on the environment. There is very little. Generating electricity from nuclear power produces no air pollution because fuel is not burned as it is in coal and oil or gas-fired plants. In fact, using nuclear energy may become one way to solve pollution problem linked to acid rain and the greenhouse effect.

People are using more and more electricity. Some experts predict that we will have to use nuclear energy to produce the amount of electricity people need at cost they can afford. Whether or not we should use nuclear energy to produce electricity has become a controversial and sometimes highly emotional issue.