In the United States, Department of Energy has determined that nuclear power accounts for about 21% of the total electricity generated in the United States, an amount comparable to all the electricity used in California, Texas, and New York. In 2002, there were 65 nuclear power plants throughout the United States, located mostly on the East Coast and in the Midwest.
A nuclear power plant operates essentially the same way as a fossil fuel plant, with one difference: the source of heat. The process that produces the heat in a nuclear power plant is the fissioning—or splitting—of uranium atoms. That heat boils water to make the steam that turns the turbine generator, just as in a fossil fuel plant. The part of the plant where the heat is produced is called the reactor core.
As you probably know, atoms are made up of three major particles components: protons, neutrons, and electrons. The most common fissionable atom is an isotope (the specific member of the atom’s family) of uranium known as Uranium-235 (U235), which is the fuel used in most types of nuclear reactors today. Although uranium is fairly common—about 100 times more common than silver—U235 is relatively rare. Most U.S. uranium is mined in the western United States. Once uranium is mined, the U235 must be extracted and processed before it can be used as a uranium fuel. In its final usable state, the nuclear fuel will be in the form of a pellet roughly 1 inch (2.54 centimeters) long, which can generate approximately the same amount of electricity as 1 ton (0.91 metric tons) of coal.
There are two different types of nuclear power plants that are being used in the United States: pressurized-water reactors (PWRs) and boiling-water reactors (BWRs). In a PWR, the water passing through the reactor core is kept under pressure so that it does not turn to steam at all—it remains liquid. Steam to drive the turbine is generated in a separate piece of equipment called a steam generator. A steam generator is a giant cylinder with thousands of tubes in it through which the hot, radioactive water can flow. Outside the tubes in the steam generator, a “clean” water or non-radioactive water boils and eventually turns to steam. It may come from one of several sources—oceans, lakes, or rivers. The radioactive water flows back to the reactor core, where it is reheated, only to flow back to the steam generator. Roughly 70 percent of the reactors operating in the United States are PWR. In the BWR, the water, heated by the reactor core, turns directly into steam in the reactor vessel and is then used to power the turbine generator.
Nuclear reactors acted as machines that control the chain reactions, at the same time releasing heat in a controlled time. If being used in electric power plants, nuclear reactors provide the heat in purposes to turn water into steam, which then drives turbine generators. As the result, the electricity then distributed to homes, schools, hospitals, factories, office buildings, rail systems, and other customers through electricity transmission line.
The reactor core is composed of four main elements: fuel, control rods, coolant, and a moderator. The nuclear fuel is stored in fuel rods. The fuel consists of pellets of enriched uranium dioxide that are packed into thin metal rods roughly 12 feet (3.7 m) long. Large groups of these rods can be connected in order to allow the power plant to operate for long periods of time.
The control rods are used to regulate (control) the rate of the nuclear chain reaction. For example, if they are pulled out of the core, it speeds up the reaction. Conversely, if they are inserted, the reaction slows down. A coolant—usually water—is pumped through the reactor to carry away the extreme heat generated by fissioning of the fuel in the nuclear reaction. This is comparable to the water in the cooling system of a car, which carries away the heat built up in the engine. A moderator is used to slow down the speed at which energized atoms travel. Water is commonly used for this purpose. This is important because reducing the speed enables atoms to be more likely to split. This split- ting is what releases the energy.
Although it may seem like a highly efficient and clean method of producing energy, nuclear power generation does have by-product nuclear power waste associated with it in the forms of radioactive waste and hot water. On the positive side, based on studies conducted by the U.S. Department of Energy, because nuclear-generated electricity does not emit carbon dioxide into the atmosphere, nuclear power plants in the United States prevent about as much greenhouse emissions as taking 5 billion cars off the streets and highways. Radioactive wastes are the principal environmental concern about using nuclear power. Most nuclear power waste is low-level nuclear waste: ordinary trash, tools, protective clothing, wiping cloths, and disposable items that have been contaminated with small amounts of radioactive dust or particles. These materials are subject to special regulations that govern their storage so they will not come in contact with the outside environment.
The irradiated fuel assemblies are highly radioactive and must be stored in specially designed pools resembling large swimming pools (water cools the fuel and acts as a radiation shield) or in specially designed dry storage containers. The older and less radioactive fuel is kept in a dry storage facility, which consists of special concrete- reinforced containers. The U.S. Department of Energy’s long-range plan is for this spent fuel to be stored deep in the Earth in a geologic repository, at Yucca Mountain, Nevada. Currently, all spent (used) fuel is stored at the power plant at which it was used.
