The turbines then function as pumps, raising water to the reservoir. The water can be used at a later time to produce electricity. Hydroelectric power plants cost less to operate than fossil-fueled plants and do not pollute the air. The number of hydroelectric power plants is limited, however, by the availability of water power and suitable locations for dams and reservoirs. Nuclear power plants generate about 17 percent of the world's electric power and about 21 percent of the electricity generated in the United States.
Nuclear plants produce electricity in much the same way that fossil-fueled plants do.
But instead of a fuel-burning combustion chamber, a nuclear power plant has a device called a nuclear reactor. Most nuclear plants use the element uranium as the fuel in their reactors. Heat from the nuclear fission is used to convert water into steam. The steam drives the steam turbine that runs the electric generator. After the steam has left the turbine, it is condensed and recycled through the plant.