The term of nuclear energy recovers two directions according to the context:
- At the Microscopic level , nuclear energy is the energy associated with the force of cohesion of the Nucléon S, the strong nuclear force (Proton S and Neutron S) within the core of the atoms. The transformations of the core releasing this energy are called nuclear reactions. The weak nuclear force , it, governs the reactions between particle S and Neutrino S;
- At the Macroscopic level , nuclear energy corresponds, on the one hand with the energy released by the reactions of nuclear Fusion within the star S, on the other hand with the civil and military uses of the energy released during the reactions of fission or fusion of the atomic nucleus.
Nuclear reactionsThe nuclear energy is produced by the cores of the atoms which undergo transformations, they are the nuclear reactions. These nuclear rearrangements lead to more stable configurations, the differential of energy (corresponding to the differential of Masse) then constitutes the energy released by the reaction. The applications of nuclear energy are based on this energy. The nuclear reactions at the base of the various applications are hereafter detailed.
See also: Nuclear fission
When a Neutron strikes the core some Isotope S heavy, there exists a probability that the impacted core is divided into two lighter cores. This reaction, which bears the name of Nuclear fission, results in a very important release of energy (about 200 MeV by event, to compare with energies chemical reactions, about EV).
This fission is accompanied by the emission of several neutrons which, under certain conditions, strike other cores and thus cause a chain reaction. In a nuclear reactor, this chain reaction is held at slow and controlled speed. In a bomb, it is propagated so quickly that it leads to an explosive reaction.
The importance of the energy emitted in fission comes owing to the fact that the energy binding by nucleon of the initial core is weaker than that of the produced cores (approximately 7,7 MeV by nucleon for the heavy elements, against 8,8 for iron). Most of energy finds in the form of kinetic energy neutrons and cores wire, energy recovered in the form of Chaleur in the engines.
See also: Generating thermoelectric with radioisotope
A body Radioactif naturally releases a flow slowly decreasing of heat. This heat can be used to generate electricity for small generators called generating thermoelectric with radioisotope. This application is very expensive, and delicate to use because of the strong radioactive environment. It is not thus used that for small powers, for example to feed in energy a Space probe which moves away from the Sun, and cannot use the photovoltaic solar panels.
See also: nuclear Fusion
Nuclear fusion is a reaction where two atomic nuclei are assembled to form a heavier core (for example a core of Deutérium and a core of Tritium are linked to form a core of Hélium more one neutron). The fusion of the light cores releases an enormous quantity of energy coming from the strong Interaction, much more important than the electrostatic repulsion between the components of the light cores. This results in a mass defect (cf energy binding ; E=mc ² ) ; the core resulting having a mass less raised than the sum from the masses of the cores of origin.
This reaction is however possible only at very high temperatures (several tens of million degrees) where the matter is with the state of plasma. These conditions are met within stars or during the explosion of a bomb with nuclear fission, which starts the thermonuclear explosion thus (Bombe H). Currently, no equipment makes it possible to produce energy by controlling the reactions fusion nuclear. Research is in hand in order to obtain a plasma over one sufficient duration, so that the energy of produced fusion is higher than that invested in the heating of the particles. Research is currently undertaken within an international framework in order to develop the civil use of the nuclear energy of fusion for the electric production.
Applications of nuclear energy
Uses of controlled reactions nuclearThe applications of nuclear energy concern, essentially, two fields:
- electrical production in nuclear plants;
- the marine Propulsion (mainly for the military fleets, in the submarines and the aircraft carriers).
Another application is the production of radioactive isotopes used in industry (Radiographie of welding for example) and in medicine (Nuclear medicine and Radiothérapie) Other uses were imagined, even tested, like the production of heat to feed a network of heating, the desalination of sea water or the production of hydrogen. These applications use nuclear reactors (also called atomic piles, when it is of low power, experimental use and production of radioisotopes).
The reactions of nuclear fission there are started, moderated and controlled in the heart: assembly of fuel and control rods crossed by a Coolant which extracts heat from it. This heat is then converted into electrical energy (or driving energy in marine Propulsion) via Turbine S (vapo-alternators).
See also: Nuclear industry
The first national park of nuclear plants is that of the the United States (104 nuclear reactors for a power of 99 GW), then of the France (59 nuclear reactors for a power of 63 GW). In proportion, the Lithuania is the second country depend on nuclear energy, with 69,6% of its electricity produced starting from the nuclear power according to IAEA, the France coming in first position with 78% from its electricity produced starting from the nuclear power (figures of the IAEA of the 2005, available on March 20th, 2007).
Production of nuclear energy of China in 2004: 50 TWh.
marine Propulsion (military and civil)
The buildings with nuclear propulsion use one or more nuclear reactors. Produced heat is transmitted to a coolant used to generate actuating steam:
- of the turbines coupled with the Propeller S of propulsion (propulsion with vapor);
- of the turbines coupled to alternators supplying with electrical energy all the building, and possibly of the electrical motors of propulsion (electric propulsion).
Approximately 400 ships with nuclear propulsion exist in the world, very mainly military, especially of the Sous-marins, but also of the Porte-avions and the Croiseur civil S, and some ships (Brise-glaces). Nuclear cargo liner S were also tested in the years 1960 and 1970 (American NS Savannah, German Otto Hahn and Japanese Mutsu ), but their exploitation did not prove to be profitable and, these experiments were abandoned.
And the exploitation capital costs of the nuclear propulsion make it truly interesting only for one military use and particularly for the submarines. This energy brings:
- a very great autonomy allowing to avoid in operations the constraint of the fuel supply (return to a port or supply with the sea). On the aircraft carriers, the space released by the absence of fuel compartment, makes it possible to devote more volume to storage of the fuel and ammunition of the aircraft.
- a propulsion completely independent of the atmosphere.
- Whereas the traditional submarines are constrained to go back on the surface (or to the periscopic immersion by using a Schnorchel) to supply the diesel engines in air (oxygen) and, thus to reload their electric batteries, after a few tens of hours of diving to the electrical motors (a few days for those equipped with propulsion AIP), making them thus detectable and vulnerable, the submarines with nuclear propulsion can remain several months in diving, thus preserving their discretion.
- They can also support in the duration important speeds in diving which a traditional submarine could not maintain any more few tens of minutes without entirely discharging its batteries.
The nuclear propulsion thus brings to the submarines an advantage determining, so much so that one can qualify the traditional submarines of simple submarines.
Certain space engines as Voyager already carried generating nuclear to feed their electronics. On the other hand the nuclear propulsion , if it would be possible, is still only considered. It would have the advantage of producing a push, certainly weak, but constant during all the way, whereas the current space engines - except those using solar energy - can produce only one initial push, or some adjustments of trajectory, because of the weak capacity of their tanks. This is why they are named ballistic , and it is also for that they should reach the escape velocity from the beginning. On long ways, interplanetary for example, this continuous acceleration could be overall more effective than initial acceleration used currently.
On paper, with a constant acceleration of 1 G on first half of the way and a deceleration of 1 G over the second, the closest stars would be with the range of a crew in ten years of voyage (clean time of the vessel), according to the restricted Relativité. However, several centuries would be passed outside. This would pose problems of political motivation for such a company.
But moreover, to suppose that one finds a process of acceleration adapted, it should well be seen that the contraction of time thus obtained rests on the fact that the mean velocity of the voyage is close to that of the light (relativistic contraction of time). If the average ratio meanwhile clean of the vessel and terrestrial time is of 100, (years for centuries), this implies an energy expense such as, even with an output of 100%, the mass of the spaceship would be divided per 1450 for acceleration outward journey, and the same factor for deceleration outward journey, then the same thing for the return. On its return, the mass of the vessel would be nothing any more but 2,3·10 - 13 that which it had with its departure. And this calculation is purely kinematic, and does not take into account the inevitable engineering problems.
Under these conditions, much of scientists want to limit the tests of nuclear propulsion because its advantages are far from being obvious, while if an accident occurs, the space pollution trained would be disastrous.
Uses of the not controlled nuclear reactions
See also: Nuclear weapon
The powers of the nuclear bombs go from the Kilotonne to the Mégatonne of equivalent TNT. The energy of a nuclear explosion is distributed primarily in the effect of breath (shock wave), the heating effect and radiations.
Types of weaponsThe nuclear weapons are of two types:
- the weapons with fission or “bombs has”: they use a critical mass of Uranium enriched or Plutonium, joined together by the implosion of a traditional explosive.
- weapons with fusion or bombs thermonuclear or “H-bombs”. The conditions of temperature and pressure necessary to the reaction of fusion of hydrogen isotopes (deuterium and tritium) is obtained by the explosion of a “starter” consisted a bomb with fission with plutonium.
The Bombe with neutrons is an alternative of thermonuclear bomb designed to maximize the share of the energy emitted in the form of radiations; it is supposed to destroy greatest forms of life in the vicinity of the target, while causing a minimum of property damages.
HistoryThe first use Militaire of a nuclear weapon (“Bombe has”) was in 1945, the dropping of two bombs on the cities Japan eases of Hiroshima and Nagasaki by the American Armée , in order to put a term at the Second world war. Since, this type of armament was the object only experimental tests (atmospheric then underground) then of data-processing modelings.
Doctrines of employmentIn the doctrines of use of the majority of the nuclear powers, one distinguishes:
- the Strategic nuclear weapon , instrument of the doctrines of nuclear deterrence or “not-employment”, intended to prevent a conflict,
- of the nuclear weapon Tactical, or battle, likely to be employed on military objectives during a conflict. The precision of the vectors helping, this type of weapon led to the miniaturization and the low powers ( Minis-nuke in the American journalese).
In the French doctrines of employment, there does not exist d'" tactique" arms; , but of the weapons of low power are definite like pre-strategic ; in this design, these weapons are used only incidentally for a military goal on the ground, their principal effect being that of a " ultimate avertissement" , of political nature, to warn the enemy leaders that the vital interests of France are from now on concerned, and that the next level of the reprisals will be thermonuclear.
Civil employmentCivil uses of the nuclear weapons were considered (for example, digging of underground cavities for the storage of gas).
The industry of the nuclear power
See also: Nuclear industry
The debate on nuclear energy
See also: Debate on nuclear energy
The civil applications of nuclear energy are discussed because, for their adversaires :
- of the risks of Nuclear accident serious on a nuclear reactor or during the fuel cycle ;
- of unsolved problems involved in management with very long run of the radioactive waste ;
- of the risk of Nuclear proliferation ;
- of the nuclear risk of Terrorism by the radioactive material diversion to use it like Toxic or to manufacture a “radiological Bomb”, or by the direct attack of a réacteur ;
- of the economic costs of the die of production of the nuclear power, the extraction of the ores to the management of waste.
However, the partisans insist on the fact que :
- the potential nuclear fuel resources would be higher than the supplys in hand for carbonaceous fuels (coal, gas, oil), especially if one manages to implement a die at fission using the Thorium, or dies with fusion ;
- the nuclear dies avoid charging the atmosphere in Carbon dioxide which is a Gaz with greenhouse effect.
The risks and the costs are not evaluated in the same way by the antinuclear pro and the , which also divides about the utility civil and military nuclear applications, in particular of the nuclear electrical production and Sortie appropriateness the civilian nuclear.
Research in the field of nuclear energy
- the United States, the European Union, Russia, Japan, China and South Korea met around the project ITER, programme of long-term study of the controlled nuclear Fusion. It is a research project which aims at the construction and the experimental exploitation of a Tokamak large-sized. The engine will be built with Cadarache in France. This project explores one of the branches of fusion, the Fusion by magnetic containment
Within the framework of the International forum generation IV, of the studies is carried out on the development of new dies of nuclear reactors to fission. The planning of this international program envisages the industrial startup of these engines by 2030-2040.
the study of the cycle of the Thorium is currently in hand and thorium could supplant the Uranium currently used, because the thorium reserves are more important than those of uranium. However, natural thorium is composed to 100% of the isotope 232 which is not fissile but fertile (like uranium 238). Its use is thus subjugated with the development of breeder reactors and the chemical processes of related reprocessing.
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