Generating electricity through nuclear power requires several major systems. Various designs of reactors heat water to make steam to turn turbines, which power generators. The steam turbine and generation components of nuclear power are essentially the same as used for fossil-fuel power generation and some solar power designs. Generating electricity from nuclear power does not release carbon dioxide like fossil fuels, but disposal of spent nuclear fuel remains a problem.
Nuclear Energy Becomes Heat Energy
Nuclear reactors have a core of uranium or plutonium as nuclear fuel, whose reaction rate is moderated by "control rods" of various materials capable of absorbing free neutrons from the fission reaction. In most designs, water also serves to moderate the reaction, by reducing the speed of the neutrons. The energy from the reaction heats the water to make steam; the water is under pressure to raise its boiling point, like in an automotive cooling system.
Boiling Water Reactors
The simplest design is a "boiling water reactor" in which the steam goes directly from the reactor to apply pressure to the turbines, before being cooled and pumped back to the reactor. The water and steam are pressurized to 70 times atmospheric pressure to raise the boiling point. The Georgia State University Department of Physics and Astronomy's HyperPhysics site describes a safety risk in this design: if the fuel leaks into the water and makes it radioactive, the contaminated water also contaminates the rest of the loop.
Pressurized Water Reactors
A more complex design called a "pressurized water reactor" runs at 160 times atmospheric pressure and much higher temperature. It has a primary high-pressure hot-water loop circulating through the reactor core, then through a heat exchanger, which heats a secondary loop of water to make steam for the turbines. With this design, any contamination from leaked fuel remains sealed in the primary loop. They are more efficient than the boiling water reactor design, but they're also more costly to construct.
Another design called a "liquid metal fast breeder reactor" cools the reactor core with a primary loop of liquid sodium at a temperature of approximately 500 degrees Celsius (932 degrees Fahrenheit). The sodium does not moderate the neutrons as water systems do. This feeds a heat exchanger that heats a secondary liquid sodium loop. The secondary loop then heats a water loop, which makes steam for the turbines. The "breeder" function is the reactor's ability to use uranium-235 to bombard uranium-238 to make fissionable plutonium-239; this design creates more nuclear fuel than it uses. Uranium-238 is 140 times more abundant than uranium-235.
- Georgia State University Department of Physics and Astronomy HyperPhysics: Boiling Water Reactor
- Georgia State University Department of Physics and Astronomy HyperPhysics: Liquid-Metal, Fast-Breeder Reactor
- Georgia State University Department of Physics and Astronomy HyperPhysics: Fast Breeder Reactors
- Photo Credit marcduf/iStock/Getty Images
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