Nuclear Reactors
1 - What is a nuclear reactor?
A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, producing radionuclides (for industry and medicine), conducting research, and military purposes. All of the various designs of power-producing reactors accomplish the same simple task: spinning a generator. Many commercial reactors pass water over heat-producing fuel rods to generate steam and run a turbine. Some designs call for the passage of helium over a pile of heat-producing fuel pebbles. Yet another design uses liquid sodium as a coolant.
Components of nuclear reactors
The control room
Main components
- The core of the reactor contains all of the nuclear fuel and generates all of the heat. It contains low-enriched uranium (<5% U-235), control systems, and structural materials. The core can contain hundreds of thousands of individual fuel pins.
- The coolant is the material that passes through the core, transferring the heat from the fuel to a turbine. It could be water, heavy-water, liquid sodium, helium, or something else. In the US fleet of power reactors, water is the standard.
- The turbine transfers the heat from the coolant to electricity, just like in a fossil-fuel plant.
- The containment is the structure that separates the reactor from the environment. These are usually dome-shaped, made of high-density, steel-reinforced concrete. Chernobyl did not have a containment to speak of.
- Cooling towers are needed by some plants to dump the excess heat that cannot be converted to energy due to the laws of thermodynamics. These are the hyperbolic icons of nuclear energy. They emit only clean water vapor.
2 - The nuclear core
Fuel pins
The smallest unit of the reactor is the fuel pin. These are typically uranium-oxide (UO2). They are surrounded by a zirconium clad to keep fission products from escaping into the coolant.
Fuel assembly
Fuel assemblies are bundles of fuel pins. Fuel is put in and taken out of the reactor in assemblies. Click here to see a 3-D blowup diagram of an assembly.
Full core
This is a full core, made up of several hundred assemblies. Some assemblies are control assemblies. Various fuel assemblies around the core have different fuel in them. They vary in enrichment and age, among other parameters. The assemblies may also vary with height, with different enrichments at the top of the core from those at the bottom.
The next stop
Go on to our nuclear waste page to learn what nuclear waste is and what we can do about it.
References
- http://www.epa.gov/ttn/caaa/t3/reports/eurtc1.pdf
- http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html