Nuclear power plants were once thought to produce the least expensive power, even cheaper than hydroelectric plants. Today, they have proven to be more "risky" due to high costs of construction and operation, concerns over nuclear waste disposal, and the general uncertainty surrounding the deregulation of the electric utility industry. In fact, no new reactors have been ordered in the United States since 1978. Yet, nuclear power is still a significant source of electricity for us, accounting for 22 percent of utilities' net power generation in the United States.
Nuclear powered steam generating plants are similar to fossil fired plants in that they use steam to drive a turbine and generator to make electricity. In a nuclear powered steam generating plant, heat is produced to boil water into steam from the slow, controlled nuclear reaction known as "fission", or splitting of atoms.
The reactor is comprised of a core containing nuclear fuel, water, control rods, and an enclosed steel container called a reactor vessel. As the control rods are lifted out of the core containing the nuclear material, the nuclear reaction begins and heat is produced.
There are two distinct types of nuclear plants: boiling water and pressurized water reactor designs. The boiling water reactor is the older design where the heat produced from the nuclear reaction boils water in the reactor vessel itself. Steam is then piped directly to the turbine that drives the generator to produce electricity.
The newer design employed by most nuclear power plants in the U.S. is called a pressurized water reactor. The heat generated by the nuclear reaction in a pressurized water reactor is absorbed and carried to the steam generator by water under very high pressure which is then used to produce steam.