Fusion and fission of the atom
What is nuclear fusion?
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Updated June 01, 2013
Atoms are the building blocks of all matter identified on this Earth but also in the universe.
There is no atom present in the space that is not here on Earth, and vice versa.
Nuclear fusion is a process in which two atomic nuclei together to form a heavier nucleus. Fusion is the source of natural energy from the sun and stars.
The fusion of light nuclei generates huge amounts of energy, it's the whole point of nuclear fusion that can theoretically produce 3-4 times more energy than fission, the same mass of fuel.
A nuclear fusion reaction thus requires that two nuclei stick together and this is very costly in energy because the kernels tend to repel because of their electrical charges, both positive.
The energy needed for melting temperatures are huge, several tens of millions of degrees, as in the heart of stars. When light nuclei fuse, the nucleus thus created ends up in an unstable state and tries to find a stable state of lower energy.
For that it ejects one or more particles (photon, neutron, proton, helium nucleus, according type reaction).
Electricity generation using nuclear fission for a long time, but nuclear fusion is still controlled by the researchers who are experimenting since the 1950s.
It is in Cadarache, France in 2018, we will commission the biggest machine ever nuclear is the ITER (International Thermonuclear Experimental Reactor). The fusion research is to demonstrate that this energy source can be used to generate electricity in a safe and friendly environment, with abundant fuel resources, to meet the needs of a world population growing.
These machines are likely to be commissioned before the end of the 21st century, if by then, no major disasters on existing fission power plants, could constrain the programs.
What is nuclear fission?
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With nuclear fission, scientists are working with heavy nuclei. Fission products are the remains of a heavy nucleus of uranium or plutonium that was fragmented following the capture of a neutron.
The nucleus of uranium or plutonium is generally fragmented into two pieces of unequal sizes, a lightweight core with 80 to 110 nucleons and a heavier nucleus of 130 to 155 nucleons.
The distribution of fission products depends little kernel that fission uranium-235 or plutonium-239.
Both fragments are highly unstable radioactive at the time of their creation.
A nucleus of uranium-235 containing 143 neutrons and 92 protons is 61% neutrons, while for stable heavy and light fragments should contain less than 57%.
Stability will be at the cost of a cascade of beta decay that convert neutrons into protons.
Nuclear fission is the breakup of a nucleus into two lighter nuclei. This is accompanied by a burst of heat, i.e. energy.
Fission releases energy giant, for comparison, 1 gram of uranium-235 releases as much energy as the burning of several tons of coal, and 69 000 times more energy than 1 gram of oil.
The neutrons released by fission are high energy and if we do not slow down, they can induce new fissions and the reaction continues and accelerates.
This is what happens in nuclear reactors, the reaction self-sustaining.
But, if allowed to increase the number of neutrons present, the reaction can become explosive, in the case of the atomic bomb (bomb).
Time to return to stability is extremely variable. Some days are enough for a fission product at 140 nucleons, while a fragment of 137 nucleons will another 30 years to 99 nucleons, 210 000 years.
Spent fuel discharged from a reactor after two or three years of operation still contains a significant fraction of fission fragments unstable.
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Where do we stand on nuclear power?
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In 2009, there are 59 reactors in France the second-generation pressurized water reactors (PWR) at 19 sites. The average age of nuclear power in France in 2009, is 22 years. In the World, there are 439 nuclear reactors. The production of nuclear power in France in 2007 was 419 TWh (Tera = 1012).
Worldwide production is 2600 TWh, supplying around 15% of electricity. In France, the production of electrical energy is distributed as follows: 77% is nuclear, 11.5% comes from hydropower, 10% is original hydrocarbon (gas) is 1.5% of RES, half of which comes from wind power. Regarding energy globally, i.e. all the energy we consume (gas, oil, electricity, solar...), the breakdown is as follows: 42% comes from electricity, 33% oil, 14.6% gas, 4.7% of renewable (solar, wind). The third-generation reactors that will replace the second generation in 2020, are under construction (EPR). With the same amount of fuel, a third generation reactor will produce 15% more electricity than the second generation of reactors.
It is also more powerful, 1600 megawatts, compared with 900 to 1300 megawatts for the second generation. And the fourth generation?
The energy will always be achieved by fission.
The Generation IV reactors will be much more powerful because they neutrons accelerated to break the atoms, and thus will be faster as uranium and plutonium will be burned better.
The energy produced will be 50 times larger. Industrialization is scheduled for the decade 2040.
Of France will build a prototype by 2020.
Not until the 2040s that the energy produced by fusion of light nuclei (as in nuclear reactions inside the Sun), will take over. Nuclear fusion could theoretically produce 3-4 times more energy than fission, same mass of fuel.
It is anticipated by 2030 a 60% increase in the number of nuclear reactors around the world, according to the International Atomic Energy Agency (IAEA).
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Image: Distribution of nuclear power plants in Europe. Source: IAEA (International emergence of Atomic Energy).