NUCLEAR FUSSION

NUCLEAR FUSION

The process in which two or more light nuclei are combined into a single nucleus with the release of tremendous amount of energy is called as nuclear fusion. Like a fission reaction, the sum of masses before the fusion (i.e. of light nuclei) is more than the sum of masses after the fusion (i.e. of bigger nucleus) and this difference appears as the fusion energy. The most typical fusion reaction is the fusion of two deuterium nuclei into helium.
1H1 + 1H2 —> 2He4 + 21.6 MeV


For the fusion reaction to occur, the light nuclei are brought closer to each other (with a distance of 10–14 m). This is possible only at very high temperature to counter the repulsive force between nuclei. Due to this reason, the fusion reaction is very difficult to perform. The inner core of sun is at very high temperature, and is suitable for fusion, in fact the source of sun's and other star's energy is the nuclear fusion reaction








PLS ADD VEDIO CLIP OF NUCLEAR FUSION

The production of an abundant and clean energy is one of the grail of physics and modern technology. Among the candidates identified, nuclear fusion is among the favorites. After several decades of efforts, scientists are able to overcome one by one the obstacles they face in achieving control this form of energy. Two developments in this area have been announced in recent days.

The reactions of nuclear fusion

The nuclear fusion reactions are those that take place inside stars. In this process, nuclei of light atoms fuse to form heavier atoms. The reaction product, the same mass of fuel, 4 to 5 times more energy than fission reactions that are used in existing nuclear power plants. However, this nuclear energy is much more difficult to master.

Fusion reactions occur at temperatures of several tens of millions of degrees. In these circumstances, the matter is in the form of a plasma. The first challenge is therefore confined to this set of highly energetic charged particles. The second is to obtain a density very high regard for pushing the nuclei of atoms, which naturally repel the effect of electrical forces to meet and merge. In the case of a star, obtaining high temperatures and high densities is carried out simultaneously by the gravitational collapse of the star under its own weight. Fusion reactions occur when the energy required to offset the collapse and ensure stability of the star. At least until the total use of fuels which causes the death of the star.

Fission and fusion

To reproduce the nuclear fusion on Earth, we must succeed in maintaining a state controlled to a certain quantity of matter at temperatures and densities very high to cause fusion reactions and especially sustain the process to provide energy continuously. This condition is essential and is a difference between the reactions of fusion and fission.

The fission reactions occur in string. An neutron posted a solid nucleus destabilizes its energy causing fission into two nuclei of mass less and producing neutrons which in turn will cause the fission of nuclei. The reaction self-sustaining, continues as the fuel is available. This presents a major advantage to ensure the continued production of energy or when trying to make a very powerful bomb. Advantage can quickly become a disadvantage if the reaction gets carried away and causes the complete fusion reactor and radioactive pollution that ensues as happened at Chernobyl in 1986. The risk of runaway reactions is not the case in the process of nuclear fusion as soon as the temperature and / or density of matter are not met, the reaction stops.

The issue of energy production by fission is therefore to prevent the risk of runaway reaction while the production of fusion energy is to keep the system under conditions permitting the realization of reactions. The fission process is simple to implement, but risky when the merger is a complex process but does not present similar risks. Fusion has also other advantages over fission. The proposed reagents, deuterium and tritium (heavy isotope of hydrogen) are relatively abundant. Chemically equivalent to hydrogen, deuterium replaces in molecules of up to 0.015%. This may seem low but the abundance of hydrogen-water molecule contains two atoms to one oxygen atom, provides abundance of deuterium (it should however be extracted molecules). If tritium is different. This is a radioactive element with a period of very short life of just over 12 years. Thus there is only very small quantities naturally but its synthesis is under control for several decades. Combustible materials for nuclear fusion are far more abundant than those available for fission, that is to say uranium.

The other major advantage of fusion over fission of waste products. The reactions of nuclear fission produces radioactive waste whose lifetimes are very long, the order of several hundreds of thousands of years. The problem with these waste is not so much of their dangerousness as the difficulty to store securely over periods as long. What are the geological terrain that will remain stable for the next 200,000 years? How to ensure transmission of the memory of those storages? Simply put: what should we write about the waste to be sure of being understood in 100,000 years? In the case of fusion, radioactive waste, in much smaller amounts, have lifetimes shorter of the order of hundred years.

Control of energy production by nuclear fusion presents so many advantages: the existence of relatively abundant fuel, a very high ratio between the amount of fuel required and the energy produced a quantity of hazardous waste relatively low. However, the key processes occurring inside stars and to start the fusion reaction-the-gravitational collapse can not be reproduced on Earth. To create the conditions for nuclear fusion, two processes have been investigated: magnetic confinement and inertial confinement.