- atom - energy of fission - nuclear reactor - reactors of drive and search(research) - reactors fast-breeder reactors - the cycle of the fuel - security - risks radiologiques-

- systems of safety(security) - Tchernobyl - reprocessing of the fuel - Managements of waste - Nuclear Fusion

The energy of any system is characterized by its capacity to supply a work, a heat or radiations. The total energy of a system always keeps(preserves), but she can be transferred to another system or change shape.

Till the end of the XVIII-th century, the wood established(constituted) the main fuel. The energy, stored by plants during their cycle of life, results from that of the sun. Since the industrial revolution, the men(people) arranged fossil fuels, coal and petroleum, stemming also from a stocking of the solar energy. When some coal is burned, its atoms of hydrogen and carbon harmonize with the atoms of oxygen of the air(sight), it(he) forms then some water and the dioxide of carbon (carbon dioxide). Furthermore, the heat is freed(released), about 1,6.10-18 kilowatts - hours (a kw / hour), that is about 10 électronvolts ( eV ) by atom of carbon, quantity of energy which is characteristic chemical reactions. A part(party) of this energy is used to maintain the fuel in a temperature such as the reaction of combustion continues.


An atom is established(constituted) by a pit in charge of(core in charge of,loaded with) positively and by electrons in charge of(loaded with) negatively. The pit(core), concentrating the main part of the mass of the atom is established(constituted) by neutrons and by protons bound(connected) among them by nuclear forces much more intense than electric forces binding(connecting) electrons to the pit(core). The number of mass A of a pit(core) corresponds among nucléons (neutrons or protons) which it contains and the atomic number Z corresponds to its number of protons in charge of(loaded with) positively. One notes such a pit(core) ". The expression 235U represents l'uranium-235. See Isotopic.

The energy of connection of a pit(core) measures the cohesion of its neutrons and its protons by the nuclear forces. The energy of connection by nucléon, necessities to extract a neutron or a proton of a pit(core), depends on the number of mass A. The curve of the energy of connection (to refer to the document) shows that if two light pits merge to form a heavier pit(core) or if a heavy pit(core) divides in two lighter pits, pits so formed are more strongly bound(connected) and the energy will be freed(released).

The fusion of two light pits of hydrogen "! Heavy! ", deutérons ( fH ) 1 MeV produces 3,25 MeV by produced neutron (! =! 1 million of électronvolts). The fission of a heavy pit(core) as 235U, provoked by the absorption of a neutron, generates products of fission as for

The cesium 140, the rubidium 93, as well as neutrons and energy of 200 MeV. Such a reaction produces an energy 10 million times more important than that of a classic chemical reaction.


Nuclear energy of fission

Both main characteristics of the fission are a big liberation of energy and an existence of a chain reaction. The process of fission introduced during the absorption of a neutron by l'uranium-235 frees(releases) on average 2,5 neutrons of the pit(core) having undergone a fission. These neutrons so freed(released) provoke quickly the fission of several other atoms, freeing(releasing) in turn supplementary neutrons which introduce auto-spoken nuclear fission, or chain reactions.

The natural uranium contains only 0,71 p. 100 d'uranium-235, the consisting rest d'uranium-238, the not cleavable isotope. A quantity given by natural uranium, whatever it is, can not maintain only a chain reaction because, only, l'uranium-235 is easily cleavable. The probability that a neutron produced by fission and having an initial energy of 1 MeV leads(infers) itself a fission is relatively weak. She can be however increased by hundreds of time by slowing down this neutron by elasticated collisions with a moderator established(constituted) by light pits as the hydrogen, the deuterium or the carbon. It is on the base of the conception of reactors producing some energy by fission.

In December, 1942, the Italian physicist Enrico Fermi realized the first nuclear reaction in chain(channel). It(he) used some natural uranium spread in a pile of pure graphite, one of the forms of the carbon. In her(it) "! Pile! " Of Fermi, the neutrons were slowed down by some graphite used as moderator to make possible a chain reaction.


Reactors with nuclear energy

The first nuclear reactors of big turntable ladder were built in 1944 in the United States for the production of nuclear weapons. The fuel was the metal natural uranium and the moderator of the graphite. The plutonium was made in these sites by absorption of neutron by l'uranium-238, the produced heat not being used.

Reactors with light water and with heavy water

Several types of reactors characterized by their fuel, their moderator and their cooler, were built worldwide to produce some electricity. Many use the oxide of enriched uranium isotopiquement in about 3 p. 100 d'uranium-235. The moderator and the cooler are some common very cleansed water. A reactor of this type is called reactor to light water, or reactor of type LWR (Light Water Reactor).

Reactors with pressurized water, or reactors of type PWR (Pressurized Water Reactor) are a first type of reactors with light water (or of type LWR) and work with some water used as cooler in a pressure about 150 atm. This one circulates in the heart of the reactor where she(it) is warmed in about 325! °C. The overheated water passes in a generator of vapor where thermic heat exchangers warm a second buckle containing some water with weaker pressure which is vaporized. This vapor feeds one or several turbines, is then condensed and returns to the generator of vapor. This secondary buckle is isolated by some water of the heart of the reactor and is not so radioactive. A third circuit of water resulting from a lake, from a river or from a cooling tower is used to condense the vapor. The dimensions of a typical reactor working under pressure are: 15 m of height, 5 m of diameter and 25 cms in thickness of wall. The heart contains about 82 t of oxide of uranium, arranged in bundles in fine tubes resisting to the corrosion.

In boilers, or reactors of type BWR (Boiling Water Reactor), a second type of reactor with light water, the water of refrigeration is kept(guarded) for a lower pressure and is boiling in the heart of the reactor. The produced vapor feeds directly the turbine, is condensed, then sent back(dismissed) in the reactor. Although the vapor is radioactive, the return is not decreased by a heat exchanger of heat interposed between the reactor and the turbine. As for reactors with pressurized water, the water of refrigeration of the condenseur results from an independent source, as a lake or a river.

In working order, and even after a stop(ruling), a big reactor of 1 000 MW possesses a radioactivity of several billion curies (This). The radiations emitted(uttered) by the reactor during its functioning and by the products of fission after its stop(ruling) are absorbed by thick concrete protections surrounding the reactor and the primary system of cooling. The other safeties(securities) are installed(settled) in case of dysfunction of the main systems of cooling. Furthermore, the installation is protected by a building(ship) in concrete and steel foreseen to hold(retain) the radioactive elements which could escape in case of flight(leak).

At the beginning of 1950's, period of development of nuclear power stations, the enriched uranium was available only in the United States and in the USSR. The nuclear programs of Canada, France and United Kingdom concentrated so on reactors with natural uranium in which the common water can not be used as moderator, because it absorbs too many neutrons. It led(drove) the Canadian engineers to develop a reactor cooled and moderated with the oxide of deuterium ( D2O) or the heavy water. The Canadian system deuterium - uranium developed in the other countries, as India and Argentina(Argentine).

In France, the initial model of reactor with bars of metal natural uranium using some graphite as moderator and the dioxide of gas carbon under pressure as the cooler was abandoned for reactors to water pressurized by American conception when the enriched uranium became available. Russia and the other States stemming from the USSR have an important program of nuclear energy based on the graphite and the pressurized water ( PWR).


Reactors of drive

Similar nuclear installations in reactors with pressurized water are used for the drive of certain aircraft carrier. Reactors for the submarine drive are generally smaller and use some more enriched uranium, what gives more compact hearts. The United States, United Kingdom, Russia and France possess all nuclear submarines stemming from this technique. The Soviet citizens built the first nuclear icebreaker, the Lenin.

Research reactors

Various nuclear reactors of small size were built in many countries for the education, the forming(training), the search(research) and the manufacture of radioactive isotopes. These reactors work generally on levels of power close to 1 MW and are more easily started and stopped than the big.

A type of reactor used usually for the search(research) and the production of radioactive isotopes is "! Reactor - swimming pool! ". The heart is established(constituted) by more or less strongly enriched uranium immersed in a big quantity of water used as cooler and moderator. Materials can be directly placed inside or near the heart of the reactor to be irradiated by the neutrons. Various radioactive isotopes can be so produced for the medicine, the search(research) and the industry. Useful neutrons for scientific experiences(experiments) can be also extracted from the heart of the reactor.


Reactors fast-breeder reactors

The essential characteristic of a reactor fast-breeder reactor is that it produces more fuel than it consumes it thanks to the absorption of the superfluous neutrons by a material which, itself, will be transformed into fissile material. Several types of reactors fast-breeder reactors are technically practicable. The one that is the object of the big interest uses l'uranium-238 who, when he absorbs neutrons, is transformed into plutonium by a nuclear reaction called bêta destruction. The sequence of the nuclear reactions is represented by

In this process, a neutron gives a proton and a bêta particle.

When the plutonium 239 absorbs a neutron, a fission can occur with a liberation of 2,8 neutrons on average. In a reactor in functioning, one of these neutrons is necessary to provoke another fission and maintain the chain reaction. On average, 1,5 neutron is lost by absorption in the structure of the reactor or in the cooler. It remains 1,3 neutron being able to be absorbed by l'uranium-238 to produce more plutonium, according to the reactions of the equation ( 1 ).

The system of fast-breeder reactor on which concentrated the biggest efforts of development is the fast reactor with metal settles(liquidates) ( LMFBR). To obtain the maximum of plutonium 239, the speed of the neutrons provoking the fission should remain high, with an energy equal or close to their initial energy. All the moderating materials which could slow down the neutrons, as the water, should be excluded from the reactor. One uses the liquid sodium which has very good properties of thermic transfer. The sodium liquefies in about 100! °C and enter boiling only from 900! °C. The main inconveniences are the big chemical ability to react with the air(sight) and the water and its high level of radioactivity led(inferred) in the reactor.

The development of the fast fast-breeder reactors with liquid metal began in the United States towards 1950.

In a fast-breeder reactor of big dimensions, a heart of the reactor is established(constituted) by thousand tubes of stainless steel of weak thickness containing the fuel. This one is formed by a mixture of oxides, plutonium 239 and uranium. Around the heart is situated a region called coverage of the fast-breeder reactor, containing tubes of even typical filled(performed) only with oxide of uranium. The heart and the coverage, in their completeness, measure about 3 m of height for about a diameter 5 m and are maintained in a big tub containing the sodium melted in about 500! °C. This tub contains also pumps and thermic heat exchangers which intervene to extract the heat of the heart. The vapor is produced in a secondary buckle containing some sodium separated from the radioactive cooler by heat exchangers of heat situated in the tub of the reactor. The whole this nuclear reactor is situated in a big surrounding wall(speaker) of steel seclusion and in concrete. The first big nuclear reactor of this type built for the production of the electricity is Super-Phénix, put in service in France in 1984.

Such a fast-breeder reactor produces appreciably more fuel than it consumes it. In a big reactor, the production of fuel in excess during twenty years is sufficient(self-important) to load(charge) another reactor of equivalent power. The fast-breeder reactor allows to obtain a return about 45 p. 100, sharply superior to the return on 35 p. 100 of the reactors with light water.


The cycle of the nuclear fuel

The cycle of the fuel uranium includes numerous stages. The passage in a power plant establishes(constitutes) only a part(party) of the whole cycle. The uranium, containing 0,7 p. 100 d'uranium-235, is obtained from an ore which is concentrated by grinding, then sent to a factory of transformation where it is converted in hexafluorure of uranium gas ( UF6). This gas is enriched in about 3 p. 100, then transformed into powder of oxide of uranium, and finally into pastilles of ceramic of oxide. Pastilles are then placed in bars resisting to the corrosion, these are assembled in elements of fuel, then sent to the nuclear power station.

A reactor with typical pressurized water ( 1 000 MW) uses about 200 elements of fuel, the third(third party) of which is replaced every year because of the exhaustion of l'uranium-235 and of the forming(training) of products of fission which absorb the neutrons. At the end of its cycle of life, the fuel is extremely radioactive because of the products of fission which it contains!; it(he) emits(utters) so a considerable quantity of residual energy. The unloaded(unburdened) fuel is left during one year or more in swimming pools of stocking containing some water. At the end of the period of cooling, the elements of exhausted fuel are sent in very protected containers, either towards installations of permanent stocking, or towards factory of chemical reprocessing. There, the unused uranium and the plutonium produced in the reactor are got back and the radioactive waste is concentrated and stokés.

The exhausted fuel still practically contains everything l'uranium-238 of departure, about the third(third party) of l'uranium-235 and a small quantity of the plutonium produced in the reactor. When this exhausted fuel is intended for a permanent stocking, this potential of energy is not used. When this fuel is redeemed(pensioned off), the uranium is recycled in the factory of enrichment by broadcasting(distribution) and the got back plutonium 239 can be used in the place of l'uranium-235 in the new elements of fuel.

In the cycle of the fuel of the first described fast-breeder reactors, the plutonium produced in the reactor is always recycled to be used in a new fuel. The raw material of the factory of manufacture of the elements of fuel is established(constituted) d'uranium-238 recycled, of impoverished uranium resulting from the factory of separation isotopique and, partially , of got back plutonium 239. It(he) does not need there in uranium resulting from deposit, because the current reserves are sufficient(self-important) to feed reactors fast-breeder reactors during several centuries. As the fast-breeder reactor produces more plutonium 239 than it needs it for its own food, about 20 p. 100 of the got back plutonium are stored for the starting up of new fast-breeder reactors.

The final stage(stadium) of all the cycles of fuel is the long-term stocking of the highly radioactive waste which remain dangerous biologically during thousands of years. Several technologies seem satisfactory for a stocking of waste without danger, but no large-scale installation was built to confirm a process. The elements of fuel are stored in deposits(warehouses) protected and watched to be available later, either are transformed into stable compounds. They are in that case fixed in ceramic or glasses, arranged in cartridges of stainless steel intended to be buried very profoundly in the ground.


Nuclear Criminal Investigation Department

The anxiety of the public to the nuclear energy is due to two important elements. The first one is the high level of radioactivity of the various stages of the cycle of the nuclear fuel, including the final stage(stadium) of the cycle. The second is bound(connected) to the fact that nuclear fuel uranium 235 and plutonium 239 are materials used for the manufacture of nuclear weapons. To see Radioactive, consequences(fall-out).

In the 1950's, it was foreseen that the nuclear energy would supply a plentiful and little expensive energy. The energy-consuming industries hoped that the nuclear would replace more and more rare fossil fuels and would lower the cost of the electricity. The public opinion was rather favorable to this new source of energy. However, reserves were emitted(uttered) gradually, when a bigger importance was granted(tuned) to the questions getting(touching) the security and the proliferation of atomic weapons. Numerous movements opposed to the nuclear and the governmental rules became complex and strict. Sweden, for example, intends to limit its program to about ten reactors, whereas Austria stopped(arrested) his. On the contrary, United Kingdom, France and Japan develop the nuclear in a important way. In 1994, about 19,6 p. 100 of the electricity produced in the United States were of nuclear origin, against about 27,6 p. 100 in United Kingdom and 77,1 p. 100 in France.


Radiological risks

The radioactive compounds emit(utter) ionisantes and penetrating radiations which damage tissues. The unit of measure of the radioactive doses received by a human being is the millisievert ( mSv ). The measures of the quantities of radiation absorbed by the body are corrected according to the nature of the radiations, because the effects are different. A person receives annually a dose about 2,5 mSv due to the natural sources of radiation. The staff of a power plant receives about 4,5 mSv, is about the same dose as the crew of plane (who is more exposed(explained) to space rays). A dose of 5 Sv (5 000 mSv) has good chances to be mortal. An important population exposed(explained) to weak levels of radiation will undergo about a supplementary cancer for 10 successful Sv on the whole (sum(dream) all the individual doses). See Radiations, biologic effects.

The radiological risks can result from various stages(stadiums) of the cycle of the nuclear fuel. The radon, the radioactive gas, is a pollutant of the common(current) air(sight) in the substratum mines of uranium. The mining activities and of grinding of the ore produce a big quantity of waste which stays in opened sky and which contains still small concentrations of uranium. This waste should be confined in waterproof ponds and covered with a thick coat(layer) of earth(ground) to avoid that they contaminate the biosphere.

The factories of enrichment of uranium and manufacture of the fuel contain big quantities of hexafluorure of uranium, corrosive gas. The radiological risk is however weak and the usual precautions observed with a product presenting a classic chemical risk are sufficient(self-important) to assure(insure) the safety(security) of the technicians.


Systems of safety(security) of reactors

The safety(security) of the reactor itself received the biggest attention. Nevertheless, during the functioning of a reactor, a small fraction of the radioactive effluents is inevitably loosened. The dose received by the population living near a nuclear site represents generally a weak percentage of the one that corresponds to the natural radioactivity. The big concerns(preoccupations) concern in fact the radioactive flights(leaks) provoked by accidents for which the fuel is damaged and the systems of safety(security) do not work correctly. The main danger is a degradation more or less pushed by some fuel which can go to its fusion. The products of fission circulate then in the cooler and, if the cooling circuit is failing, the products of fission penetrate into the building(ship) of the reactor.

The functioning of a reactor rests(bases) on an instrumentation of controls - commands(-orders) of the systems of safety(security) elaborated having to led(driven) to the stop(ruling) during abnormal circumstances. The conception of reactors with pressurized water includes a system of supplementary safety(security) consisting of an injection of bore in the liquid of refroidisement to absorb the neutrons and stop(arrest) a possible chain reaction. Reactors with light water work under high pressure of cooler. In the case of a break of important channeling, the cooler would escape brutally in the form of vapor and the heart would not be cooled any more normally. To face this possible danger, systems of emergency cooling start automatically by the loss of pressure of the primary cooler. In the case of a flight(leak) of vapor in the surrounding wall(speaker) of seclusion, provoked by a break of the circuit of the primary cooler, coolings by irrigation are activated(started) to condense the vapor and avoid a dangerous ascent of the pressure in the surrounding wall(speaker).



On April 26, 1986, an important accident put in emotion the world population. One of four reactors of Tchernobyl ( Ukraine's ) power plant exploded and burned. According to the official report, published in August, the accident had been provoked by not authorized attempts. The reactor was not able to to be controlled, there were two explosions, the lid of the reactor was flabbergasted and the heart ignited by burning in temperatures of the order of 1 500! °C. Very high doses of radiation reached(affected) the population close to the reactor and a cloud of radioaktive fallouts extended westward. The radioactive products, discovered(found) by Swedish observers on April 28, spread(displayed) over Scandinavia and over the North of Europe. Contrary to most of the reactors of the western countries, Tchernobyl's reactor had no building(ship) of seclusion. Such a structure would have prevented the radioactive products from escaping from the site. About 135 000 persons were evacuated in a beam(shelf) of 30 km of the power plant. More than thirty technicians of the power plant and rescuers which intervened on the site during the accident died. The factory was covered with concrete. In 1988 however, three other Tchernobyl's reactors were again in functioning


Reprocessing of the fuel

The stage(stadium) of reprocessing of the fuel contains several radiological risks. One of these corresponds to the escape of products of fission if a flight(leak) should occur on the chemical installation and the building(ship) which surrounds him(it). The other one is consequence of the weak regular escape of radioactive sluggish gases as the xenon and the krypton. The reprocessing is at present made in France and in United Kingdom. Japan is finalizing(working out) its own factory.

An important question lifting(raising) anxieties concerns the separation of the plutonium 239 by the chemical reprocessing, because this compound can be used for the manufacture of nuclear weapons. Improved safety measures and greater inspection of the international Agency of the atomic energy present the best guarantees against the risk of diversion of the plutonium.


Management of waste

The last stage(stadium) of the nuclear cycle, the management of waste, remains one of the the most controversial subjects. The main question is not, in that case , the current danger, but that caused for the future generations, because a lot of nuclear waste remains radioactive during thousands of years. The technology of preparation and packaging of waste is relatively sure. The difficulties result from the choice of places of stocking of goods and of the way of storing waste. A permanent, but potentially accessible(approachable) stocking, in stable geologic formings(trainings), seems to be the best solution.


Nuclear fusion

The obtaining of nuclear energy occurs by the coalescence of two light pits in a heavier pit(core), as indicates it the minimum of the curve of energy of connection (to refer to the joined document). The energy emitted(uttered) by the Sun is due to these fusions in the deep regions of this one. In the pressures and enormous temperatures which reign there, the pits of hydrogen harmonize by series of reactions retranscribed in the equation below:

And supply the major part of the energy emitted(uttered) by the Sun. The other reactions in stars more massive than the Sun lead(drive) to the same result.

The artificial nuclear fusion was realized at first at the beginning of 1930's by bombarding a target containing some deuterium, isotope of the hydrogen of number of mass 2, with deutérons (pits of the deuterium) of high energy in a cyclotron (to see Particles, accelerator of). To accelerate the bundle of deutérons, a big quantity of energy was necessary, but the biggest part(party) of this one was transformed in the form of heat in the target. No useful energy was so produced in this way. During 1950's, the first productions of nuclear energy of large-scale fusion were realized during the attempts of the thermonuclear weapons by the United States, Soviet Union, United Kingdom and France. Such a broadcast(emission,issue) of energy, brief and uncontrolled, can not be used to produce some electricity. (See Nuclear, arm(equip)).

In the fissions presented first, the neutron, not carrying(wearing) electric load(responsibility), can easily approach a fissile pit(core) and react with this one, as for example with l'uranium-235. In a fusion, on the other hand, pits having to reacted carry(wear) each a positive electric load(responsibility), the aversion which results from it should be surmounted. It occurs when the temperature of the gas having to reacted reaches(affects) values enough high, 50 in 100 million degrees. For a gas established(constituted) by the heavy isotopes of the hydrogen, the deuterium and tritium, the fusion occurs in such temperatures

By freeing(releasing) about 17,6 MeV by fusion. The energy demonstrates itself at first in the form of kinetic energy of the pit(core) d'hélium-4 and of the neutron, but stemming from the reaction, this energy is quickly transformed into heat spreading(diffusing) in the gas and the materials around this one.

If the density of the gas is sufficient(self-important) (in such temperatures a pressure of 10-5 atm is sufficient(self-important), what corresponds almost to the space), the pit(core) d'hélium-4 containing the energy can transfer her(it) to the surrounding hydrogen and allow a fusion in chain(channel) which maintains the temperature. In these conditions, one says that one "! Nuclear ignition! " Occurred.

In temperatures superior to 100 000! °C, all the atoms of hydrogen are totally ionized. The gas is formed by a mixture electrically neutral of pits in charge of(loaded with) positively and electrons free, in charge of(loaded with) negatively. This state of the material(subject) is called a plasma.

A plasma having a sufficient(self-important) temperature for the fusion can not be confined with classic materials. The plasma would cool very quickly and the walls of bowls would be destroyed(annulled). However, as a plasma is established(constituted) by pits and by loaded(charged) electrons which move in spirals squeezed(tightened) around the lines of magnetic field, he can be confined in a space subjected to an appropriate magnetic field.

The fundamental problem to be resolved to obtain conditions of controlled nuclear fusion is to warm the plasma and to confine a sufficiency of reagent pits during a rather long time to allow the liberation of more energy than it is necessary to warm and confine the gas.

This condition is filled(performed) when the product of the time of seclusion t by the density n some plasma is superior to a noted value L, about equal in 1020 m-3.s. The relation n.t! >! L is called criterion of Lawson, L being the number of Lawson. The final problem is to get this energy and to transform it into electricity.

Numerous methods of magnetic seclusion of plasma were tried since 1950 in the United States, in ex-Soviet Union, in United Kingdom, in Japan and in France. Thermonuclear reactions were obtained, but the number of Lawson is only rarely exceeded 1018 old. However, a system, Tokamak, conceived originally by Igor Tamm and Andreï Sakharov in Soviet Union, gave encouraging results, at the beginning of 1960's.

The room(chamber) of seclusion of Tokamak has the shape of a tore having about a small diameter 1 m and about a big diameter 3 m. A toroïdal magnetic field about teslas ( T ) 5 is established inside this room(chamber) (corresponding field in about 100 000 times the ground magnetic field). A longitudinal current of several million amperes ( A ) is led(inferred) in the plasma. The lines of the magnetic field so created are internal spirals in the tore and confine the plasma.

After the promising results of several small Tokamaks, two big installations were built at the beginning of 1980's, the one at Princeton's university in the United States and the other one in Soviet Union. In Tokamak, the heater of the plasma is obtained by the effect Joule due to the very important toroïdal current. The addition of an additional heater by injection of neutral bundle in these new big installations should allow to reach(affect) the conditions of ignition.

Another possible way towards the energy of fusion is that of the inertiel seclusion. According to this technique, the fuel, tritium or the deuterium, is contained in a tiny pastille which is bombarded everywhere by a pulsed laser beam. It provokes an implosion of the pastille by activating(starting) a thermonuclear reaction with ignition of the fuel. Several laboratories, in the United States and somewhere else study at present this technique. The progress of the search(research) on the fusion was promising, but the development of systems which produce more energy than they consume will still take it probably decades, as far as the search(research) is expensive.

Nevertheless, certain progress was obtained at the beginning of 1990's. In 1991, for the first time, a significant quantity of energy, about 1,7 millions of W, was produced by nuclear fusion controlled in the laboratory of the JET (Joined European Torus), in United Kingdom. In December, 1993, researchers at Princeton's university realized a controlled fusion by obtaining 5,6 millions of W with the trial reactor Tokamak. However, these recent experiences(experiments) both consumed more energy than they produced it.

If the energy of fusion became available, she(it) would offer three advantages: 1) the existence from an unlimited source of fuel, the water of the oceans, because the used fuel is some deuterium, an isotope of the hydrogen which is in quantity in the water!; 2) the absence of risk of accident of reactor, because the used quantity of fuel is very weak!; 3) a lesser radioactivity and an ease of manipulation of waste with regard to those of the fission.

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