Energy and energy sources

What is energy?

Energy is a physical magnitude that we associate with the ability of bodies to produce mechanical work, emit light, generate heat, etc. In all these manifestations there is a common substratum, which we call energy, which is specific to each body or material system according to its physical-chemical state, and whose content varies when this state is modified.

In physics, energy is one of the basic concepts due to its fundamental property: the total energy of an isolated system remains constant. Therefore, in the universe there can be no creation or disappearance of energy, but transfer from one system to another or transformation of energy from one form to another.

Energy is, therefore, a physical quantity that can manifest itself in different ways: potential, kinetic, chemical, electrical, magnetic, nuclear, radiant, etc., with the possibility that they transform each other but always respecting the principle of the conservation of energy.

What units are used to measure energy?

If the energy possessed by a body is manifested by doing work, the value of this work will be a measure of the energy it possesses. If, on the other hand, we have done work on a body and it has stored it in the form of energy, the measure of the work done on the body will give us the value of the energy that remains latent in the body. For all this, the energy released or accumulated will have the same units as the magnitude of work.

In the International System of units (SI) the unit of work and energy is the joule (J) defined as the work done by the force of 1 newton when it displaces its point of application 1 meter.

In nuclear physics, the electronvolt (eV) is used as a unit, defined as the energy acquired by an electron when passing from one point to another between which there is a potential difference of 1 volt.

Its relationship with the unit of the International System is:

1 eV= 1,602 x 10-19 J

For electrical energy, the kilowatt-hour (kWh)* is used as the production unit, defined as the work done during 1 hour by a machine that has a power of 1 kilowatt.

Its equivalence with the unit of the International System is:

1 kWh = 36x 105J

In order to evaluate the energy quality of the different energy sources, units based on the calorific power of each one of them are established. The most used in energy economics are kcal/kg, tec and toe.

• kcal/kg applied to a fuel indicates the number of kilocalories that we would obtain in the combustion of 1 kg of that fuel.

1 kcal = 4,186 x 103J.

• tec: equivalent ton of coal. It represents the energy released by the combustion of 1 ton of coal.

1 tec = 29,3 x 109J

• toe: equivalent ton of oil. it is equivalent to the energy released in the combustion of 1 ton of crude oil.

1 toe = 41,84 x 109J

Relationship between these units:

1 toe = 1,428 tec

What is potency?

The work done by a system in unit time is called power. Its unit in the International System (SI) is the watt, defined as the power of a machine that does the work of 1 joule in the time of 1 second. Its symbol is W. Multiples of this unit are often used.

They are the kilowatt (kW) and the horsepower (CV or HP).

• 1 kW = 103 W
• 1 CV ó HP = 735,5 W
• 1 MeV.s-1 = 1,602 x 10-13 W

Where does the energy we consume come from?

Almost all the energy available to us comes from the Sun. It is the cause of the winds, the evaporation of surface waters, the formation of clouds, the rains and, consequently, the waterfalls. Its heat and light are the basis of numerous chemical reactions essential for the development of plants and animals that over the centuries have given rise to fossil fuels: coal, oil…

If we remember the principle of conservation of energy, we will unquestionably affirm that energy is neither created nor destroyed, it is only transformed. Therefore, if we need to obtain energy, we will have to start from a body that has it stored and can undergo a transformation. These bodies are called sources of energy.

More broadly, we will call any natural or artificial system or reservoir that can supply us with energy a source of energy. The available amounts of energy from these sources are what is called an energy resource.

The Earth possesses enormous amounts of these resources. However, one of the problems that humanity has raised is obtaining and transforming them.

The most sought after energy sources are those in which concentrated energy is available (a lot of energy per unit of mass). This is the case of coal, oil, natural gas, uranium, etc. On the contrary, we have another type of energy sources called diffuse, in which there are difficulties for its capture and concentration. This is the case of solar energy, wind energy, etc.

In the former one must take into account, in addition to the energy content, impurities, location of the deposit, ease of exploitation, required technology; These are all reasons that directly affect the cost of obtaining that energy and therefore the profitability of the exploitation.

In the case of diffuse energies, the problem is not in the extraction, but in the concentration, storage and transformation. These data are important to make the economic balance of each source.

All energy sources are important, but from the point of view of their specific use, the different energy sources may or may not be substitutes for each other.

For example, for the production of electrical energy in a power station we can use coal, oil, natural gas or uranium. However, in a steel process, uranium could never replace coal, and as fuel, petroleum products (gasoline, kerosene) cannot be replaced by coal, uranium, wood…

How are energy sources classified?

Several criteria can be used to classify the different energy sources:

• Depending on whether or not they are renewable.
• Depending on the impact they have on the country's economy.
• Depending on its use.

We will call renewable energy sources those whose potential is inexhaustible because they come from the energy that reaches our planet continuously as a result of solar radiation or the gravitational attraction of other planets in our solar system. They are solar, wind, hydraulic, tidal and biomass energy.

Non-renewable energy sources are those that exist in a limited amount in nature. They are not renewed in the short term and that is why they are depleted when they are used. The world demand for energy is currently mainly satisfied with this type of sources. The most common are coal, oil, natural gas, and uranium.

If we attend to the second classification criterion, we will call conventional energy sources those that have an important participation in the energy balances of industrialized countries. This is the case of coal, oil, natural gas, hydraulics, nuclear.

On the contrary, non-conventional energy sources, or new energy sources, are those which, due to being in a stage of technological development in terms of their widespread use, do not have an appreciable participation in the coverage of the energy demand of those countries. This is the case of solar, wind, tidal and biomass energy.

According to its use, the energy sources can be classified into primary and secondary. The primary ones are those that are obtained directly from nature, as an example we have coal, oil, natural gas. It is a stored energy. The secondaries, also called useful or final, are obtained from the primaries through a transformation process by technical means. It is the case of electricity or fuels.

What is hydraulic energy and how is it harnessed?

We can consider hydraulic energy as the energy obtained from river water. It is a renewable energy source.

Indirectly it has the Sun as its origin. The heat evaporates the water from the seas forming clouds, which in turn will transform into rain or snow, thus ensuring the continuity of the cycle.

The greatest use of this energy is made in the waterfalls of the dams. The water is generally retained in reservoirs or swamps. These are large deposits that are generally formed artificially, closing the mouth of a valley by means of a dam or dam in which the waters of a river are retained. This stored water can be used later for irrigation, population supply or for the production of electricity in a hydroelectric power station.

Most of the hydraulic dams are used for the production of electrical energy. Countries with great hydraulic potential obtain most of their electricity from hydroelectric plants due to its great advantages, including that of being an inexhaustible resource that is renewed freely and constantly in nature, and the surplus can be used for other purposes.

But it also has drawbacks. It is not possible to make predictions, since they depend on annual hydraulicity, and dry or rainy years are not events that man can affect. Hydraulic sites are usually far from large populations, so it is necessary to transport the electricity produced through expensive networks. Another unfavorable aspect is the negative effect that the creation of a reservoir can have on the environment, with problems of channel alteration, erosion, incidences on populations, loss of fertile soil, etc.

These drawbacks, together with the large investments required in this type of power plant, and the increasingly difficult location of sites, are what prevent greater use of this energy source. However, hydropower continues to be the most widely used among renewable energy sources for the production of electrical energy.

What is solar energy and how is it harnessed?

Solar energy is that which reaches Earth in the form of electromagnetic radiation from the Sun, where it is generated by a process of nuclear fusion.

Fusion reactions are constantly taking place in the Sun: hydrogen atoms fuse to form a helium atom, releasing a large amount of energy. Of this, only a small part reaches Earth, since the rest is reflected towards outer space by the presence of the terrestrial atmosphere.

Solar energy reaches the Earth's surface in two different ways:

• Influencing objects illuminated by the Sun (direct radiation).
• By reflection of solar radiation absorbed by air and atmospheric dust (diffuse radiation).

The first is usable directly. Flat collectors and photovoltaic cells take advantage of the second, to some extent.

The advantages of solar energy are:

• It is inexhaustible on a human scale and non-polluting.
• Through suitable concentration processes, temperatures of up to 3,000 °C can be reached with it, which in principle allow high-performance thermodynamic cycles to be started.

The drawbacks of this power source are:

• It cannot be stored, so it has to be immediately transformed into another form of energy (heat, electricity, biomass).
• Its use requires the availability of collection systems with large surfaces and some of its main components are very expensive.
• It is discontinuous and random.

Therefore, the solar energy that reaches the Earth is free, but its transformation into useful energy is very expensive and, in many cases, is in the experimental phase.

The use of solar energy can be done in two ways: thermal and photovoltaic.

Thermal pathway: Transforms energy from the Sun into heat energy. This transformation can occur at low, medium and high temperatures.

Low temperature transformation: It is generally used for domestic heating, air conditioning of premises, water heating in hospitals, swimming pools… It is necessary to capture solar energy, for which a series of flat collectors are available that absorb solar radiation and the They are transmitted as heat to feed the heating system.

These systems take advantage of solar energy at temperatures ranging between 35 °C and 90 °C, currently being the main application of solar thermal energy in Spain.

Medium-temperature facilities: In these facilities, the temperatures obtained range between 90 °C and 200 °C, for which it is necessary to capture solar energy and concentrate it using special devices.

These facilities consist of a set of concentration collectors of different shapes:

Cylindrical-parabolic: they collect solar energy and transmit it to a fluid (thermal oil) in the form of heat.

Heliostats: generally made up of adjustable mirrors so that the incident radiation is reflected at a fixed point.

The applications of this type of installations are fundamentally industrial.

High temperature installations: These are thermoelectric plants. The temperature reached is higher than 400 °C. They are made up of a wide surface area of heliostats supported by supports that reflect solar radiation and concentrate it in a small receiving point. The receiver transmits solar radiation in the form of heat to a fluid (water, air, liquid metals) that circulates through a primary circuit. This is sent to a steam generator that converts the water that circulates through a secondary circuit into steam, which sets in motion a turbine-alternator group producing electrical energy.

The yield of these facilities is approximately 20%.

Photovoltaic conversion: Photovoltaic solar systems are made up of a set of solar or photovoltaic cells arranged in panels that directly transform solar energy into electrical energy. Sunlight carries energy in the form of a stream of photons. When these photons hit certain types of materials and under certain conditions, they cause an electric current. This is known as the photovoltaic effect.

Solar or photovoltaic cells are small elements made of a semiconductor crystalline element, silicon-germanium (Si-Ge). When incident on them, the photons produce a movement of electrons inside the cell and a potential difference appears between their ends that turns them into a small electrical generator. The cost of these cells is very high and the performance is low.

The development of these systems is linked to the technique of artificial satellites. In a first stage, due to the reliability of its operation, its low weight and its low maintenance needs, these systems were used to cover the energy needs of the satellites.

What is wind energy and how is it harnessed?

Wind energy is the energy produced by the wind. It was one of the first sources of energy used by man. Sailing ships and windmills are the first manifestations of the energetic use of wind energy. At present, there are systems to take advantage of the kinetic energy of the wind and transform it, later, into electrical energy through wind turbines..

This source of energy presents the advantages and disadvantages of solar energy: it is inexhaustible, clean, non-polluting and, once the installation for its capture is done, free. But at the same time it is dispersed, intermittent and occurs irregularly in terms of its intensity.
The main applications of wind energy in those places where the wind reaches regularly and with great intensity are:

• Windbombs. To raise the water, wheels with six to fifteen blades are used, which can pump from five hundred to six hundred l/h, a sufficient quantity to cover the needs of small farms.
• Production of electrical energy through wind turbines. To do this, a tower is installed at the top of which there is a rotor with multiple blades that are oriented in the direction of the wind. These rotors act on a generator that allows to obtain electrical energy.
  • Isolated wind turbines: They are installed in isolated areas where there is no electricity. Powers from ten to one hundred kW can be obtained.
  • Wind plants: They are made up of a certain number of wind turbines, and can reach a power of one hundred to six hundred kW.

En la actualidad, para lograr un mayor aprovechamiento de la energía eólica, se están desarrollando modelos de equipos encaminados a la producción de energía eléctrica con un menor tamaño, una mayor duración y un mantenimiento más sencillo y barato, procurando mitigar el impacto ambiental producido por los aerogeneradores.

What is biomass energy and how is it used?

It is the energy that can be obtained from organic compounds formed in natural processes. It is what is commonly called biomass.

Biomass energy can be achieved mainly:

• Establishing certain crops that can be subsequently transformed into energy (harvestable biomass).
• Taking advantage of forest, agricultural and domestic residues, later transforming them into fuel (residual biomass).
• Chemically or biologically transforming certain plant species to also convert them into fuel (methanol and ethanol).

The main application of harvestable biomass is the production of heat in a combustion process. For this purpose, herbaceous and woody plants are usually used, obtained in natural ecosystems, or in crops intended for this purpose (agro-energy). At present, work is being done on this type of crops, and in the future the harvestable biomass may be the most important source of biomass for energy purposes.

Residual biomass also offers, in principle, great prospects in terms of its energy use. This group includes forestry, agricultural and livestock waste, as well as waste produced in urban centers (mainly solid waste and wastewater). These prospects are limited due to the pollution that occurs when removing this waste and that is sometimes greater than the energy that can be generated, so this type of biomass is used above all in facilities that use their own waste, such as in farms, urban treatment plants or forest industries, places where, in addition to obtaining energy, waste disposal costs are saved.

Another large section of energy resources obtained from biomass is made up of liquid biofuels obtained from vegetable oils, intended to replace diesel in diesel engines, or bioethanol, obtained by fermentation of biomass for engines that use biomass. gasoline as fuel. These biofuels can be used in internal combustion engines, both in compression and spark ignition engines, being able to become a transition bridge between an era dominated by fossil fuels and another potentially open to the use of biomass.

What is geothermal energy and how is it harnessed?

We can consider it as the energy that the Earth contains in the form of heat, and that has been produced fundamentally in the disintegration of the radioactive substances in its nucleus. This heat tends to diffuse in the interior until escaping through the surface of the earth's crust. This energy would be enough to cover world needs if it could be used, but geothermal energy is diffuse energy and difficult to use.

The temperature is distributed irregularly according to the areas of the earth's crust. The pockets of magma that come from the deepest areas move towards areas of lower pressure. Upon contact, the rocks melt and release large amounts of gases that tend to escape through cracks and fissures in the crust, giving rise to volcanism, such as volcanic eruptions, gas outlets at high temperatures (fumaroles and solfataras). ), boiling water and steam outlet (geysers) and hot water outlets (thermal springs), although only some of these are usable.

Geothermal energy has been used by man since the earliest times. At present, attempts are being made to find a way to take advantage of this immense amount of energy that the Earth contains in the form of heat and that, except in isolated cases, is wasted or lost.
In the areas that we could call privileged (Iceland or Landerello -Italy-), the use of geothermal energy can be carried out at various temperatures.

• Low temperature: The heat that emerges at less than 100 °C is used directly in multiple applications: heating, domestic and sanitary hot water, swimming pools, greenhouses, dryers, etc. This use presents a significant drawback, and that is that, due to the low thermal level of the fluid, it has to be used in direct applications of heat, so the reservoir must be close to the center of consumption.
• Medium and high temperature: To extract the energy stored in the lithosphere we need the presence of an intermediate geothermal fluid (ammonia or freon) that acts as an energy transport vehicle. The geothermal fluid, once it reaches the surface, must undergo a series of transformations for its use. Geothermal fluids with a temperature higher than 150 °C are used for the direct production of electricity, through different types of cycles. If the temperature is between 100 °C and 150 °C, the use of this energy is in industrial processes.

At present, the lines of research are aimed at carrying out transformation projects of geothermal energy at low temperature, with smaller investments and less deep surveys, with fewer geological risks and exploitation and business set-up problems.

What is tidal energy and how is it harnessed?

Tidal energy is the energy developed by sea waters when they are in motion.

The tides are the result of the gravitational attraction exerted by the Sun and the Moon on our planet. In some places, the tidal difference frequently reaches several meters between low tide and high tide (low tide and high tide). Its industrial use is only possible in those coastal areas that meet certain topographic and maritime conditions in which the value of the amplitude of the tidal gap is comparable to a hydroelectric installation with a low height of water fall, but of considerable mass.

In some particular cases where the tide enters through a narrow passage, it is possible, by dikes, to allow the rising tide to enter it and to pass the water through the turbine when the tide recedes. This is the principle of tidal power stations.

Wave energy is much more difficult to master and the appropriate technology has not yet been achieved.

What is coal and what uses does it have?

Coal is a fossil fuel, the final result of a series of transformations on plant remains accumulated in swampy places, lagoons and fluvial deltas mainly, during the carboniferous period of the primary era.

Due to various chemical actions and pressure and temperature variations over long intervals of time, these vegetables are transformed into carbon in a process called carbonization. In summary, it can be said that after the deposition phase of the vegetables, the action of anaerobic bacteria begins (mainly on cellulose and lignin). The changes that give rise to the transformation of wood into charcoal are of two types: chemical and structural.

In chemicals, hydrogen and oxygen are released as the proportion of carbon increases. In some cases (such as anthracite) it constitutes almost the entire resulting product.

There are also structural changes. The fibrous structure of the wood is transformed into a different microcrystalline structure for each variety of coal, and its color changes from brown to black.

There are four different types of coals, due to the different kinds of vegetables from which they come and, above all, the duration and conditions (pressure and temperature) of the carbonization process. These are:

• Anthracite: It is a hard coal, completely charred. Very compact and bright. With pearlescent shine and black color.
• Coal: It is a hard coal, completely charred. Glossy black colour. Pearly luster with glossy and matt bands.
• Lignite: Blackish. It is a soft coal belonging (like peat) to times after the Carboniferous, so it has not undergone the complete carbonization process. It has the appearance of burnt wood and shine to pieces.
• Peat: It is the most recent of the coals. It is soft, brown in color, matt, light in weight and remains of plants can still be seen on it.

The calorific power of these coals varies from 7,000 to 2,000 kcal/kg, from anthracite and coal to lignite and peat. Likewise, its humidity ranges from 3% to 40% and volatile substances can range from 8% to 50%. As the main impurity we have sulfur (S) and nitrogen (N), which are released in the form of SO2 and NOX when the coal is burned to later join the water vapor and produce acid rain.

The most important applications of coal are:

• As domestic and industrial fuel.
• As a reducer in the steel industry.
• As raw material in the manufacture of lighting gas.
• As fuel in thermal power plants.

Anthracite is mainly used as domestic and industrial fuel. The dry distillation of coal gives rise to four fractions: ammonia, tar, gas and coke. The latter (hard, resistant and porous) is used in the metallurgy of iron and steel (iron industry). Brown coal is mainly used in thermal power plants to obtain electrical energy. Peat is used as domestic fuel.

What is natural gas and what uses does it have?

Natural gas is a mixture of gases among which methane is found in a greater proportion. The proportion in which this compound is found is from 75% to 95% of the total volume of the mixture, for this reason, natural gas is usually called methane. The rest of the components are ethane, propane, butane, nitrogen, carbon dioxide, hydrogen sulfide, helium, and argon.

The development of the use of natural gas has been carried out after the use of oil. The natural gas that appeared in almost all oil fields was burned as just another waste. Despite its enormous calorific value, it could not be used, due to the great problems posed by its storage and transport.

The need to find new sources of energy, the fine-tuning of gas liquefaction techniques and pipe welding procedures to withstand high pressures have made it possible to use all these energy resources. Natural gas is used:

• As domestic and industrial fuel: It has a great calorific value. Its combustion is adjustable and produces little pollution.
• As raw material in the petrochemical industry to obtain ammonia, methanol, ethylene, butadiene and propylene.

What is oil and what uses does it have?

Petroleum is a very dark or black mineral oil, less dense than water and with a characteristic pungent odor. It is formed by a mixture of hydrocarbons accompanied by sulfur, oxygen and nitrogen in variable amounts. Oil is found only in sedimentary rocks.

Petroleum originates from a raw material formed mainly by the remains of living aquatic, plant and animal organisms, which lived in the seas, lagoons, river mouths and in the vicinity of the sea. These remains were attacked in the muddy bottoms by anaerobic bacteria that consumed their oxygen, leaving only carbon and hydrogen molecules called hydrocarbons.

The pressure exerted by the enormous mass of sediments causes the expulsion of the liquid found between the layers of sedimentary rock. This liquid, oil, migrates down the slope for tens of kilometers until it finds a porous and incomprehensible rock whose holes it fills. This rock is called storage rock.

Crude oil is a mixture of hydrocarbons from the simplest (CH4, methane) to complex species with 40 carbon atoms. Oil, such as well mana, has very few applications. To obtain the various derivatives it is necessary to submit it to a refining process. The main operation of this is fractional distillation. In it we obtain, at different temperatures, a whole range of commercial products from crude oil. Gaseous substances such as methane, ethane, propane and butane; liquids such as gasoline, kerosene and fuel; solids such as paraffins and tars, are obtained at different temperatures in this process.

The oil fields are normally located very far from the places of consumption. Crude oil is normally transported by land through pipelines that go from the well to the nearest refinery or port of dispatch. Long-distance maritime transport is covered by tankers or oil tankers.

The main uses of oil are:

• As domestic and industrial fuel.
• As fuel and lubricant.
• To obtain basic raw materials in the petrochemical industry.

In order to satisfy the needs of the market, it has been necessary to develop transformation techniques that, by modifying the structure of the products obtained in fractional distillation, make it possible to obtain the substances that society demands. Among these techniques, the most
important are cracking and polymerization.

In the cracking operation, the breaking of a heavy molecule with many C atoms (fuel, for example) is achieved, giving rise to several light molecules (gasoline and gases, for example).

Polymerization is the union of several molecules of a compound called a monomer (eg ethylene), to form a molecule called a polymer (eg polyethylene). This process is of great importance in the petrochemical industry.

One of the most important applications of oil is its use as a raw material throughout the petrochemical industry. 60% of the chemical products found on the market and 80% of the organic sector come from petrochemicals. Fertilizers, plastics, antifreeze, detergents, synthetic rubber, dyes, explosives, plasticizing fibers, solvents… are products obtained from petroleum.

For all these reasons, we can affirm that oil plays an important role, not only in the field of energy supplies, but also in the chemical industry.

How is the nucleus of atoms made up?

The nucleus of atoms was discovered in 1911 by Rutherford from the analysis of α particles scattered by the atoms. It is from 1932, with the discovery of the neutron by Chadwick and with the reactions carried out by the Joliot-Curie spouses, when the nucleus began to have real importance.

The core has very small dimensions. It occupies the central part of the atom; in it resides all the positive charge and almost the entire atomic mass. It is made up mainly of protons and neutrons. Protons have a positive charge quantitatively equal to that of the electron (1.602 x 10-19 C). Neutrons are electrically neutral. The particles in the nucleus are called nucleons. The forces that hold the particles of the nucleus together, even overcoming the electrostatic repulsion between the protons, are forces of unknown nature and short range that only appear inside the nuclei and are called nuclear forces.

The energy accumulated by these nuclear forces is called binding or binding energy and is calculated using the Einstein relationship E = mc2 (energy = mass x square of the speed of light).

When determining the mass of the nucleus, we observe that it is less than the sum of the masses of the components. The difference between the two is called the mass defect (Δm) and the binding energy will be E = Δm.c2.

A part of the mass of the nucleus has been transformed into binding energy to hold the particles of the nucleus together. This energy is what is released in a nuclear reaction. Dividing the binding or binding energy by the number of components of the nucleus, the average energy per nucleon is obtained, a value that indicates the stability of the nucleus. If the average binding energy has a high value, it will be a stable nucleus. If its value is small, it will be unstable and will tend to emit some of its components to become another, more stable form. In this case the nucleus is radioactive.

Is nuclear energy the same as atomic energy?

The terms atomic energy and nuclear energy are synonymous and define the same concept. The reason for this double denomination is of historical origin. There are some countries that we can call "pioneers" in research related to the energy emitted by radioactive bodies and others that we can call "users" of said energy. Among the first we can include France and the United Kingdom, countries in which Becquerel, the Curies, Rutherford and their collaborators spoke of atomic energy in their communications and what they studied were "the large amounts of energy stored in radioactive atoms" . In the second group (in which we can include Spain) the term nuclear is the one that began to be used with rigor and precision.

There is an attempt to generalize the use of the term nuclear in all countries. However, it is difficult to stop talking about atomic energy due to the large number of official bodies and standards that implicitly carry this term.

What is nuclear fission?

Nuclear fission is a reaction in which a heavy nucleus, when bombarded with neutrons, breaks down into two nuclei, whose sizes are of the same order of magnitude, with great release of energy and the emission of two or three neutrons. These, in turn, can cause more fissions by interacting with new fissile nuclei that will emit new neutrons, and so on.

This multiplier effect is known as a chain reaction. In a small fraction of a second, the number of nuclei that have fissed releases energy 106 times greater than that obtained by burning a block of coal or exploding a stick of dynamite of the same mass. Because of the speed at which a nuclear reaction takes place, energy is released much faster than in a chemical reaction. This is the principle on which the atomic bomb is based. The conditions under which it was discovered and built are part of the history of humanity and are known to all.

If, on the other hand, only one of the neutrons released produces a subsequent fission, the number of fissions that take place per second is constant and the reaction is controlled. This is the principle of operation on which nuclear reactors are based, which are controllable sources of nuclear fission energy.

Which is nuclear fusion?

The reaction in which two very light nuclei unite to form a heavier and more stable nucleus, with great release of energy, is called nuclear fusion.

For fusion to take place, positively charged nuclei must approach each other overcoming repulsive electrostatic forces. The kinetic energy needed for the reacting nuclei to overcome the interactions can be supplied in the form of thermal energy or by using a particle accelerator.

The most viable solution is thermal fusion. These thermal fusion reactions, called thermonuclear reactions, occur in fusion reactors and mainly with hydrogen isotopes (protium: 11H, deuterium: 21H, and tritium: 31H).

Among the possible nuclear fusion reactions are:

21H + 21H→3 1H + 11H + 4MeV

21H + 21H→32He + 10n + 3,2 MeV

21H + 31H→42He + 10n + 17,6 MeV

The use of fusion energy by man involves research and development of technological systems that meet two fundamental requirements: heating and confinement. Heating to get a superheated gas (plasma) where the electrons come out of their orbits and where the nuclei can be controlled by a magnetic field; and confining, to keep matter in a plasma or ionized gas state, enclosed in the reactor cavity long enough for it to react.

These types of reactions are very attractive as a source of energy, since deuterium is not radioactive and occurs naturally and practically unlimited in nature. Tritium does not occur naturally and is also radioactive. However, research is basically focused on deuterium-tritium fusion reactions, because it releases more energy and the temperature at which fusion takes place is considerably lower than the others.

* Note: kW-h or kWh can be used interchangeably for the kilowatt-hour symbol.