Fission Reactors: Overview


Fission reactors are engineered to fit one of three categories: power reactors, research reactors, and breeder reactors.

Power Reactors:
These reactors are used for the large amount of energy they produce. This power can be converted into electricity and then used by the public. Power reactors are also used on nuclear submarines to propel them for long periods of time with little fuel.

Research Reactors:
These reactors are used to produce specific radioisotopes used in the medical industry and other industries. Research reactors are also used as a neutron source, which is needed in various fields of research.

Breeder Reactors:
These reactors are used to produce additional fissile material to be used in other nuclear reactors. These reactors produce more fissile material than they need to run, thus creating more fuel than they use. They require an initial amount of fuel, and a supply of fertile material (natural uranium, depleted uranium, or thorium). Breeder reactors can use the waste material from other reactors to produce more useable material for other reactors, thus making nuclear power almost infinitely sustainable.

In general most nuclear reactors look something like the following (an example of a pressurized water reactor):


(http://media-1.web.britannica.com/eb-media/62/162162-004-0EED602E.jpg)

The main idea is that the reactor core heats up the coolant which is circulates through another working fluid which absorbs the heat from the coolant and circulates it through a steam turbine to produce electricity.

A closer look at the core and it's components:


(http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCSE/bytesize%20images/nuclearFissionOCR1.gif)

The core of a nuclear reactor consists of the several components: the fuel, coolant, moderator, concrete shield, and control rods, which are explained in more detail on the next page.

Another important aspect of nuclear reactors is what happens to used fuel. Eventually the concentration of fission fragments in the fuel reaches a point where the fuel rods need to be replaced with fresher fuel rods. However, the used fuel rods will still be emitting radiation and heat, so they cannot be disposed of easily. Usually, the used fuel rods are immediately placed into a separate cooling pool, where they will remain for years. After the used fuel has cooled enough, it is either reprocessed or put into long-term storage. [3]

Reprocessing:

Used fuel still contains a very large percentage of usable uranium, which can be separated and used again. About 3% of the used fuel will be high-level radioactive waste, which is buried deep underground. In some instances it may be easier or cheaper just to bury the used fuel outright, instead of trying to get the usable uranium out to use again. Either way, the used fuel has to be dealt with in a safe manor, as it is a highly dangerous material that can't just be left lying around. [3]



Next: Fission Reactors: Components
Previous: The Fission Process
Title Page