Nuclear reactors can be classified according to different criteria. One of the criteria is the purpose for which they will be used. In this regard we distinguish the types of nuclear reactors used for civilian purposes, for military purposes or for research purposes.
Civil nuclear reactors use nuclear energy to generate power for electricity; military reactors create materials that can be used in nuclear weapons such as the atomic bomb; and research nuclear reactors used to develop weapons or energy production technology, for development purposes, for nuclear physics experimentation and to produce radioisotopes for medicine and research. Some reactors have a dual purpose, since they are used for the production of civilian energy and military materials.
Research nuclear reactors use neutrons generated during nuclear fission reactions to produce radioisotopes that are going to be used in other applications of nuclear energy such as nuclear medicine or to conduct studies on materials.
Classification of types of nuclear reactors by technical characteristics.
There are other classifications of nuclear reactor types depending on the criteria used. Among the most common criteria are:
According to the nuclear fuel used, we find the natural uranium nuclear reactors and the enriched uranium nuclear reactors. The nuclear fuel of natural uranium contains the same proportion of uranium found in nature, while in the enriched uranium fuel this proportion is artificially increased. Other reactors use mixed oxides of uranium and plutonium.
According to the speed of the neutrons, that is to say, of their kinetic energy, produced in the nuclear reactions of fission: the fast reactors and the thermal reactors are distinguished.
Depending on the moderator used, they may be nuclear reactors of heavy water, light water or graphite.
According to the material used as coolant: the most common materials are a gas (helium or carbon dioxide) or water (light or heavy). Sometimes these materials, at the same time, also act as a neutron moderator. You can also use water vapor, molten salts, air, or liquid metals as a coolant.
Nuclear reactors can also be distinguished by the type of nuclear reaction. Nuclear energy can be obtained in two ways: by nuclear fission reactions or by nuclear fusion reactions. In any case, at present, all the nuclear reactors in production are nuclear fission reactors. The nuclear fusion reactor is in the development phase. In this line exists the ITER project which is a fusion nuclear reactor in France for research and development purposes of this type of nuclear energy technology.
Nuclear power reactors
Nuclear power reactors are based on the use of thermal energy generated in nuclear fission reactions. The main and best known application of this type of reactors is the generation of electricity in nuclear power plants. However, these reactors are also used for the desalination of sea water, heating, or for propulsion systems.
The differences between the different types of nuclear power plants are based on the way the nuclear reactor works, which they use to produce electricity.
All nuclear power plants use one or several nuclear reactors to generate heat. This heat in the form of thermal energy is used to generate steam through certain thermodynamic processes and finally to operate a turbine. The characteristic that differentiates one nuclear power plant from another is based on the way the nuclear reactor works. From the different ways of operating the reactors we have a new classification of the types of nuclear reactors.
Pressure water reactor (PWR)
The pressurized water reactor (known by its acronym in English PWR) is the most used nuclear reactor in the world next to the boiling water reactor (BWR). This reactor has been developed mainly in the United States, RF Germany, France and Japan.
The nuclear fuel used is uranium enriched in oxide form.
The moderator and the coolant used can be water or graphite.
The thermal energy generated by the reactor core is transported by the cooling water that circulates at high pressure to a heat exchanger. The nuclear reactor is based on the principle that water subjected to high pressures can evaporate without reaching the boiling point, that is, at temperatures above 100 ° C. In the exchanger the steam cools and condenses, and returns to the reactor in a liquid state.
In the exchange there is a thermodynamic transfer of heat to a secondary water circuit. The water in the secondary circuit is converted into high pressure steam as a result of the amount of heat energy received in the exchanger. The steam is introduced into a turbine to convert this energy into mechanical energy and power an electric generator.
Boiling water reactor (BWR)
The boiling water reactor (known by the acronym in English BWR), is also frequently used. Technologically it has been developed mainly in the United States, Sweden and the German RF.
In this type of nuclear reactor, water is used as a coolant and moderator.
The nuclear fuel used is uranium enriched in oxide form since it facilitates the generation of nuclear fission.
The thermal energy generated by nuclear fission chain reactions is used to boil the water. The steam produced is introduced into a turbine that drives an electric generator. The steam that leaves the turbine passes through a condenser, where it is transformed back into liquid water. Later it returns to the nuclear reactor driven by a suitable pump.
Reactor of natural uranium, gas and graphite (GCR)
The natural uranium, gas and graphite reactor is a type of nuclear reactor that uses natural uranium in the form of metal as a nuclear fuel. The fuel is introduced into tubes of a magnesium alloy called magnox.
The neutron moderator used is graphite. The thermal cooler is gas, specifically carbon dioxide.
The technology of this type of nuclear reactor has been developed mainly in France and the United Kingdom.
Advanced gas reactor (AGR)
The advanced gas reactor (AGR) has been developed in the United Kingdom from the nuclear reactor of natural uranium-graphite-gas.
The main novelties are that nuclear fuel, in the form of enriched uranium oxide, is introduced in stainless steel tubes and that the vessel, made of prestressed concrete, contains the heat exchangers inside it.
High temperature gas cooled reactor (HTGCR)
The nuclear reactor cooled by gas at high temperature is a new evolution of the gas-cooled nuclear reactors. This type of nuclear reactor is developed in German RF, the United Kingdom and the United States.
The differences with respect to the advanced nuclear gas reactor (AGR) are mainly three:
- helium is replaced by carbon dioxide as a refrigerant,
- Ceramic fuel is used instead of metallic fuel
- the temperatures of the gas with which it works are much higher.
Heavy water nuclear reactor (HWR)
The heavy water nuclear reactor is a type of nuclear reactor developed mainly in Canada.
The fuel used to obtain nuclear energy is natural uranium, in the form of oxide, which is introduced into alloy zirconium tubes.
The main characteristic of the heavy water reactor is the use of heavy water as moderator and coolant.
In its most usual design, the nuclear fuel tubes are introduced into a vessel containing the moderator. The refrigerant is kept under pressure to maintain its liquid state. The steam is produced in heat exchangers through which light water circulates.
Fast breeder reactor (FBR)
There are several designs of FBR reactors, with Russian and French being the most advanced.
The main characteristic of fast reactors is that they do not use neutron moderators and that, therefore, most of the nuclear fissions are produced by fast neutrons.
The nucleus of this type of nuclear reactor consists of a fissionable zone, surrounded by a fertile zone in which natural uranium is transformed into plutonium. The uranium 233-thorium cycle can also be used.
The refrigerant is liquid sodium, steam is produced in heat exchangers. Its name of "reproductive" is due to the fact that in the fertile area there is a greater amount of fissile material than the one consumed by the reactor in its operation, that is, more new fuel than the one that is spent.