Great forces join the atomic nucleus, so when the atom splits great amount of energy is released. Albert Einstein could demonstrate that the mass can be changed to energy, written in the formula E=mc2, being "E" the energy, "m" the mass and "c" the light speed. In that case 1g of mass has the same calorific power as 2650 tons of coal. In the radioactive desintegration of uranium just 1/1000 part of the mass is changed into useful energy, like 2.37 tons of coal per gram of uranium.
The first impression that the world had from this great energy was the explosion caused by the atomic bomb in Hiroshima (1945). This bomb began a chain reaction to release the energy in a 1/1,000,000 of second, developing an explosive power of 60,000,000 tons of TNT.
It is very hard to release the energy stored in the atomic nucleus, so it is necessary to break the equilibrium between neutrons and protons, bombing the big nucleus with subatomic particles. The heaviest natural element on Earth is uranium, bombing its nucleus release energy and more neutrons that crash with other nucleus, producing a chain reaction.
This nuclear desintegration mean that the nuclei get divided in two new smaller nuclei and that belong to smaller elements in the periodic table. This nuclei aren't necessarily equal and aren't always the same elements, but the confined energy plus the great amounts of protons and neutrons in the uranium nucleus is partially released
Countries like England, France and Germany have been developed experimental reactors using plutonium, being produced 60 to 80 times more electric energy than in normal reactors, at the same time this close the uranium and plutonium cycle; in which conventional reactors produce little amounts of plutonium that is used with uranium in the new reactors, making more plutonium that can be reprocesed.
The difference in the scale of supply operations, reflects the difference in energy content between conventional and atomic fuels. One cubic foot of uranium has the same energy content as 1.7 million tons of coal, 7.2 million barrels of oil, or 32 billion cubic feet of natural gas. In today's atomic power plants only a very small fraction of the potential energy value of the fuel is extracted in a single cycle of operation, but even so a truck of atomic fuel substitutes for many trainloads of coal.
Even for every gram of atomic fuel actually consumed approximately on megawatt-day (A megawatt is 1000 kilowatts. To speak of a megawatt-day of heat means that heat is generated at a rate of 1000 kiliwatts over a period of 24 hours) of heat is released.
-What Atomic fuel is:
Atomic fuel means fuel for a nuclear reactor, reactors harness the energy of nuclear fission. The term atomic fuel also apply to the heat source in isotope generators, or nuclear batteries.
Atomic fuel consists basically of a mixture of fissionable and fertile materials. The essential ingredient is a fissionable material, a material that readily undergoes nuclear fission when struck by neutrons. The only naturally available fissionable material is uranium-235, an isotope of uranium constituting less than 1% of the element as found in nature (aproximately 0.7%).
Almost all the rest of the natural uranium element is the uranium-238, which is important for a different but related reason. For when neutrons strike uranium-238 a fussionable material is generaly formed, namely plutonium-239. So, although natural uranium actually contains only a little fissionable matter, almost all of it can be converted to fissionable matter.
For this property, the uranium-238 is called a fertile material. A second substance that has this property is the element thorium. Its fissionable derivative is still another isotope of uranium, uranium-233.
The physical form of the fuel is also important. Some work is being done with fluid fuels (solutions, sluries, or even molten fuel material) but, except for a few experimental systems, today's power reactors employ solid fuel in metallic or ceramic form.
Description of a Reactor
In the center section of reactor is located a fuel, which may consist of uranium, plutonium, or thorium. Any of the isotopes of these elements may be present in any combination, depending upon the design of the reactor. The fuel is generally in close proximity to, and intermingled with a moderating material such as hydrogen, beryllium, or any suitable light element. The moderating material is used to slow down fission neutrons to where they posses the desired energy spectrum. The combination of fuel, moderator, and associated structural components are called the core.
Passing through the core and in close contact with it is a heat-transfer material. Gases, water, or liquid metals may be used as the heat-transfer material. The moderator may also be circulated through the core and serve as the heat-transfer. Outside the core proper is a reflector which is used to conserve neutrons and bounce them back into the core in an optical-reflector sense. Surrounding the reflector is a biological shield with the purpose of attenuating the radiations emanating from the core. This shield is usually a combination shield which attenuates both neutrons and gamma rays. Inside the core or the reflector are located the control rods, the basic purpose of which is to regulate the power level of the core by controlling the rate of production of the number of neutrons.
These reactors extract the heat released from the nuclear chain reaction occurring when the isotope uranium-235 fissions. But natural uranium consists of about 0.7% U235 and the world resources of uranium can only provide enough of this material to last about 30 years.
Fast Reactors or Breeder Reactor
When thermal reactors operate they produce another material, plutonium, which can also be persuaded to undergo a nuclear chain reaction involving fission, with the release of heat. If this material is burned in another type of reactor it can produce more fissile material than it consumes. Hence these plants are called breeder reactors. Using breeder reactors we have also limitless supply of energy which we can use to produce electricity on a large scale.
At very high temperatures hydrogen nuclei will combine with a large release of heat and neutrons to form helium. It is essentially this reaction which heats at sun. The effect is achieved at lower temperatures with heavy hydrogen (deuterium or tritium). So far man has only achieved the reaction by heating up the deuterium with an atomic bomb (also called hydrogen bomb) but a large amount of research is on hand to find a way to initiate and control the reaction for use in the generation of electricity.
There are several misconceptions about fission power:
-Although it uses more readily available fuel (lithium not sea water, as is often sated) it is unlikely to be very cheap.
-Due to the high neutron fluxes which are inevible in the reactor there is likely to be very large amount of radioactive waste products arising from the reactor.
-The hazards of radiation will be no less than with thermal or fast reactors.
The nuclear energy is considered as a solution for the growing energetic problems in the world. In a fusion reaction, two atoms combine releasing great energy. This reaction takes place in the stars at high temperatures where all the particles are ions, and plasma is made.
Hydrogen from sea water is the fuel for the nuclear fusion. To produce energy it would be necessary to combine the nuclei of two hydrogen isotopes, getting helium. Deuterium is present in sea water; from every 6,500 hydrogen atoms, one is deuterium. The ocean has 1020g of this isotope. One kg of D2O (Deuterium Oxide) can provide the same energy than 200,000kg of coal or 1,900,000L of gasoline. In other words 1L of water is the same as 300L of gasoline in terms of energy.
Now a day, fusion energy can be produced just in extremely high temperatures, at least 100 million Celsius, where deuterium and tritium atoms make plasma. That is 5 or 6 times the temperature inside the sun. Plasma has no electrons, so there is no repelling force; when two nucleus crash, they fusion into hellium and great energy is released. Free neutrons are absorbed by lithium, forming tritium.
One of the most confused problems in the scientific research of plasmas is the container. Certanly, is impossible to contain the plasma at millions of celsius using normal material walls because it has very low density; the total pressure of an ideal gas or a plasma is proportional to its density and temperature. So the problem is keeping plasma under high pressure decreasing the plasma density around 1/10,000,000 of the density of solid matter. Energy is lost when particles penetrate the walls because plasma loses heat in 1/1,000,000 seconds. This lapse is extremely short to create and heat a plasma. So it is necessary to find something that can maintain the plasma isolated.
Around 1945, a magnetic field was suggested to isolate the plasma from the chamber that contains it. It is now known that a huge magnetic field can affect a particle's movement electrically charged making an spiral movement without losing heat. This teoric structure is named Magnetic Bottle, unfortunatelly it is unlikely to be made for at least 20 years.
Russian scientists are developing one container rounded by powerful magnets that can maintain the plasma enough time to start the reaction. This ractors are known as tokawaks and are the basis for future investigation about the application of this energy. In the United States a technique based on high energy lasser beams is being developed; the lasser keeps the plasma in the center of the reactor while acting as incident in the fuel from everywhere.