Plant Operations

Three Mile Island Unit 1 is a pressurized water reactor that produces 852 million watts of electricity, which is enough to power 800,000 homes.

Nuclear energy comes from fission. Fission is the splitting of atoms. At a nuclear generating station, Uranium atoms are split through the process of fission, which releases neutrons, and in turn produces heat. The heat that is produced heats the water surrounding the nuclear fuel but it is safely kept under pressure to prevent it from boiling. The hot water is then pumped from the reactor vessel to a steam generator. There, the heat from the water is transferred to a second, separate supply of water. This water supply boils to make steam. The steam spins the turbine, which drives the electric generator to produce electricity. The electricity flows to the power grid and then ultimately to your home.

Pressurized Water Reactors are known as “PWRs.” They keep water under pressure so that it heats but does not boil. Water from the reactor and the water that is turned into steam are in separate pipes and never mix.

While some power plants burn oil, coal, or natural gas to produce electricity, nuclear power relies on small, half-inch long, uranium pellets. Each pellet is capable of releasing as much energy as one ton of coal. And a single ton of uranium releases energy equivalent to about 400,000 barrels of oil. But unlike fossil fuels, nuclear power releases no combustion products to the environment. It is clean energy.

The fission process explained above takes place within the nuclear reactor vessel. These reactor vessels contain the uranium pellets, stacked end-to-end in fuel rods. The fuel rods are arranged in bundles called fuel assemblies. These fuel assemblies make up the reactor core.

The faster the atoms split, the more heat that is produced. The rate at which the atoms are split is controlled by special rods, which absorb neutrons. These control rods fit into spaces between selected fuel rods. As the rods are raised, more heat is produced. As they are lowered, fission slows. When the control rods are fully lowered, fission stops.

At this point, water takes over. The heat produced by the fission process heats the water surrounding the nuclear fuel, but the water is kept under pressure to prevent it from boiling. The hot water is pumped from the reactor vessel to a steam generator. There, the heat from the water is transferred to a second, separate supply of water. This water supply boils to make steam. The steam spins the turbine, which drives the electric generator to produce electricity.