Nuclear reactors typically use enriched uranium as fuel.
A nuclear reactor is a device that can produce and maintain nuclear fission chain reactions in a controlled manner . These chain reactions, in turn, are used to generate energy and obtain fissile materials.
The reactors are part of a nuclear power plant . This is the name given to the industrial plant that, appealing to the reactions promoted by the reactors thanks to the use of nuclear fuel, generates the heat that mobilizes alternators capable of converting mechanical energy into electrical energy .
Main concepts
To understand what a nuclear reactor is, you must first be clear about several concepts. Nuclear fission is a class of reaction in which the nucleus of a spent atom splits into at least two nuclei of lighter atoms (which are known as fission products ). This splitting is caused by the capture of an incident neutron; As a result of the process, gamma rays, neutrons and enormous amounts of nuclear energy are emitted.
An atom is considered to be the essential unit of a chemical element. It is made up of a nucleus (which houses neutrons and protons , referred to in this framework as nucleons ) with electrons attached to it. Protons attract electrons by the electromagnetic force, while protons and neutrons located in the nucleus are attracted to each other by the nuclear force. An atom that houses more than 150 nucleons is classified as a heavy atom .
Returning to the idea of nuclear fission, it is a reaction that involves the division of the nucleus of a heavy atom by the capture of a neutron , giving rise to nuclei of less heavy atoms that are more stable. As part of the reaction, more neutrons are also generated which, hitting other fissile nuclei, cause new fission reactions and so on. That's why we talk about a chain reaction .
The chain reaction requires a certain geometric configuration of the fissile or fissile material (that is, that can undergo the fission reaction) and that the so-called critical mass be exceeded: the minimum amount of material that is needed to maintain the reaction in question. Although it is possible for nuclear fission to occur spontaneously, the intervention of neutrons with the appropriate energy is always needed.
At this point, we can return to the concept of a nuclear reactor: a device that is capable of causing, maintaining and controlling fission chain reactions. For this, they use a nuclear fuel made up of fissile elements (such as isotopes of uranium or plutonium ) so that, inside the reactor, nuclear fission takes place without the need for another source of neutrons.
An accident can cause a nuclear reactor to release radioactivity.
Components of a nuclear reactor
A nuclear reactor consists of several parts and components that are involved in its operation. It features a steel structure that contains the nuclear fuel rods according to a specific geometric pattern to enable the chain reaction.
To promote the chain reaction, a nuclear moderator is usually used, whose function is to reduce the speed of the neutrons that are produced so that they can promote new reactions. Water is the most used moderator. Reflectors are also used that minimize the neutron output and increase the efficiency of the device.
The nuclear coolant , meanwhile, is responsible for conduction of the heat produced by the process to a turbine that generates electrical energy or to a heat exchanger.
On the other hand, each nuclear reactor has control bars or rods made of material with the capacity to absorb neutrons. Thus, if the chain reaction needs to be interrupted, boron or cadmium rods are inserted into the steel vessel.
It should be noted that shielding is developed around the nuclear reactor to prevent the emission of gamma rays. Such shielding is usually made with concrete , preventing radiation leakage and contributing to nuclear safety.
A nuclear reactor is capable of developing the production of radioisotopes.
Positive and negative aspects
Nuclear power plants, whose central component are nuclear reactors, make it possible to produce heat to generate electrical energy, transmute elements (creating radioactive isotopes ) and achieve nuclear propulsion for submarines and ships, for example. Even recognizing the importance of its applications, it is possible to highlight the advantages of its use and also warn about its risks.
The almost zero emission of pollutants into the atmosphere and the low volume of waste they generate are two of its favorable aspects. As disadvantages, the possibility of an accident (as happened in Chernobyl , Fukushima or Three Mile Island ) or a terrorist attack that generates radioactive contamination is usually referred to. Nuclear waste is also hazardous to health and can remain dangerous for thousands of years.
Types of nuclear reactor
A first distinction is made between thermal reactors and fast reactors . Thermal reactors, which are the most common, use a nuclear moderator, unlike fast reactors.
Among the thermal reactors, the light water reactor ( PWR ), the boiling water reactor ( BWR ), the heavy water reactor ( PHWR ), the graphite reactor and the high temperature gas reactor ( HTGR ) appear. inter alia. If we focus on fast reactors, we find the lead-cooled fast reactor and the sodium-cooled fast reactor , for example.