Types of nuclear reactors

We distinguish two types of nuclear reactors

  • Nuclear research reactors. This type of reactors used neutrons generated during nuclear fission reactions to produce radioisotopes that are going to be used in other applications of nuclear energy or materials for studies.
  • Nuclear power reactors. These reactors are based on the use of the thermal energy generated in the fission reactions. The main and most known application of this type of reactor is to generate electricity in nuclear power plants. However, also they are used for desalination of sea water, heating or to propulsion systems.

There are other classifications of the types of nuclear reactor depending on the criteria used. Among the most common criteria are:

  • According the nuclear fuel used we can find the nuclear reactors of natural uranium and enriched uranium nuclear. The nuclear fuel of natural uranium contains the same proportion of uranium than in nature, while in the enriched uranium fuel this proportion is artificially increased. Other reactors use mixed oxides of uranium and plutonium.
  • Depending on the speed of the neutrons produced in nuclear fission reactions: fast reactors and thermal reactors are distinguished.
  • According to the moderator used can be heavy-water nuclear reactors, light water or graphite reactors.
  • According to the material used as refrigerant: the most common materials are a gas (helium or carbon dioxide) or water (light or heavy). Sometimes these materials also act as a moderator. One can also use steam, molten salt, air, or liquid metal as coolant.

Differences between the different types of nuclear power plants are based on the type of nuclear reactor used to produce electricity. The way throug electricity is generated from the steam generated is similar in all nuclear power plants.

Types of nuclear power plants

The two major nuclear power reactors used are pressurized water reactor and boiling water reactor. But there are other types that we also will describe.

Pressurized water reactor (PWR)

The pressurized water reactor nuclear reactor is the most used in the world. It has been mainly developed in the USA, RF Germany, France and Japan.

This nuclear reactor uses enriched uranium as oxide form as nuclear fuel.

The moderator and coolant used can be water or graphite.

The energy generated by the reactor core is conveyed through the cooling water which flows at high pressure to a heat exchanger. The reactor is based on the principle that the water under high pressures can evaporate without reaching the boiling point, ie, at temperatures greater than 100 ° C. In the exchanger the vapor cools and condenses and returns to the reactor in liquid statge. In the exchanger there is heat transfer to a secondary water circuit. The water from the secondary circuit that comes from heat, produces steam, which is introduced into a turbine that drives an electric generator.

Boiling water reactor (BWR)

The boiling water reactor is also used frequently. Technologically it has been developed mainly in the United States, Sweden and RF German.

In this reactor, water is used as coolant and moderator.

The nuclear fuel is enriched uranium in oxide form and that facilitates the generation of nuclear fission.

The thermal energy generated by the chain reaction is used to boil water. The steam produced is introduced into a turbine that drives an electric generator. The steam from the turbine passes through a condenser where it is transformed back into liquid water. Subsequently the water returns to the reactor driven by a suitable pump.

Natural uranium reactor, gas-graphite (GCR)

This type of nuclear reactor uses natural uranium in the form of metal fuel. The fuel is introduced into tube of a magnesium alloy called Magnox.

The moderator used is graphite and the refrigerator is gas, carbon dioxide.

The technology of this type of nuclear reactor was developed mainly in France and the UK.

Advanced Gas Reactor (AGR)

It has developed in the UK from the natural uranium-graphite-gas nuclear reactor.

The main changes are that the nuclear fuel, in the form of enriched uranium oxide, is introduced into stainless steel tubes and that the vessel, made of pre-stressed concrete, contains heat exchangers inside.

Gas-cooled reactor at elevated temperature (HTGCR)

This nuclear reactor is a further evolution of gas-cooled nuclear reactors. Developed in R.F. German, UK and US.

The differences from the previous are mainly three:

  • Helium is replaced by carbon dioxide as a refrigerant.
  • The ceramic fuel is used instead of metal fuel.
  • The gas temperatures which it works are much higher.

Heavy water reactor (HWR)

This type of nuclear reactor has been developed primarily in Canada.

The fuel used is natural uranium in oxide form, which is inserted in zirconium alloy tubes.

Its main feature is the use of heavy water as moderator and coolant.

In its most common design, nuclear fuel tubes are introduced into a vessel containing the moderator. The coolant is maintained at pressure to maintain its liquid state. Steam is produced in a heat exchanger by circulating light water.

Fast breeder reactor (FBR)

There are various designs, with the Russian and French who are more advanced.

The main characteristic of fast reactor is that they don't use moderator and, therefore, most of the fissions produced are produced by fast neutrons.

The reactor core consists of a fissile area, surrounded by a fertile area where natural uranium is transformed into plutonium. Also the cycle uranium 233-thorium can be used.

The coolant is liquid sodium, the steam is produced in heat exchangers. His name "breeder" is due in the fertile area the reactor produces more amount of fissile material than it consumes in operation, it means that it generates more new fuel than the fuel that it spends.

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References

CCHEN - Tipos de Reactores Nucleares

Last review: September 18, 2015