Nuclear fuel is a material that is burning in the heart of the nuclear reactor through fission (fission) atoms of these materials in order to draw potential of nuclear energy in atoms. Heavy Elements used in nuclear fission (nuclear fission) is uranium 235 (Uranium 235) and plutonium-239 (Plotonium 239) factory of uranium 238 and uranium 233 (Uranium 233) factory of thorium (Thorium). The first element is a stainless fissionable uranium-235, a radioactive element available in nature mixed with uranium 238 rose 0.72% has been discovered in 1935. The half-life (half-life) of uranium-235 approximately 704 million years old compared to 4468 million years of uranium 238 which reduced the rate of natural uranium. The total amount of energy emitted by the fission of one atom of uranium-235 two hundred and two million electron volts (202.5 MeV = 3.24 × 10-11 J) while the amount of energy generated from fusion of one kilogram than 23.1 million kilowatt-hour (8.314 × 1013 joules), or more than three million times the energy produced by burning one kilogram of the finest types of coal (2.4 × 107 joules). A critical mass of uranium and of 235 non-envelope (untampered critical mass) 56 kg and can be reduced to a third or quarter of the uranium during the packing 235 with a layer of uranium 238, which works reflector of neutrons (tampered critical mass).
The uranium found in nature is a mixture of two isotopes of uranium isotopes (isotopes), namely uranium 238 (uranium-238) by (99.2742%) and uranium 235 (uranium-235) by (0.7204%). Natural uranium is available in abundance in the earth's crust where the ranking comes in abundance (abundance) in Grade 51 and is more abundant than many metals as silver (Silver) and tin (Tin) and antimony (Antimony). The amount of uranium found in the earth's crust to a hundred thousand billion tons (1017 kg) distributed in rocks, soil and ocean water at rates ranging between 2 and 15 parts per million. The uranium accumulates in some exceptionally rich mines in Kazakhstan, Canada and Australia, which have up rate in the rocks, which contain three percent. The world's reserves of natural uranium, which can be extracted economically not to exceed ten million tons, while the global production rate of fifty thousand tons of uranium per year. The average price per tonne of natural uranium (yellow cake) one hundred thousand US dollars per ton, but this contains only seven kilograms of fissionable uranium and responsible for thermal power generation.
Uranium is found in nature in the form of many of the most famous vehicles Alaoraninayat ore (uraninite) which consists primarily of uranium oxides and oxides of other metals. The first steps of uranium ore processing is the separation of uranium oxides from the rest of the raw ingredients to be the so-called yellow cake (Yellowcake), which contains more than 80% of the various uranium oxides that the most important (triuranium octoxide (U3O8)). The second step is to convert various uranium oxides into pure uranium dioxide (purified UO2) which can be used in some types of reactors Kmvaalat heavy water directly. Pure uranium metal is not used (pure uranium metal) as fuel in nuclear reactors because of the low degree of melting (melting point) which amounts to 1132 degrees Celsius. And it is often used instead of uranium oxides and metal oxides because its melting point higher than that of the pure metal, but the thermal conductivity (thermal conductivity) is low. Among the most famous oxides used in the reactors, uranium dioxide (Uranium dioxide UO2) which is in the form of black powder (black powder) and the degree of melting 2865 ° C.
The ratio of uranium fission in a stainless U-235 in natural uranium a low rate not exceeding seven per ten percent for this it is necessary to raise this percentage is determined by the type of use. In the atomic bombs it is required that the ratio is higher than ninety percent while the need for small nuclear reactors (compact nuclear reactors) used in submarines and aircraft carriers to the ratios of up to twenty percent and the most types of nuclear reactors and light water Vtaml rates ranging between 3% and 5% while some works by using natural uranium Kmvaalat heavy water. This is increasing the proportion of uranium-235 in natural uranium through the so-called enrichment process (enrichment process) A process by which remove uranium 238 from natural uranium rises so the proportion of uranium-235 in it. The enrichment process requires a very complicated equipment where they can not use chemical methods in the separation process for being two equals any of the same element that have the same chemical properties. The separation process are taking advantage of the small difference in atomic weight between the two isotopes are used mechanical methods as a centrifuge (gas centrifuge process), after conversion to uranium compounds in the gaseous state's sixth uranium hexafluoride (Uranium hexafluoride UF6). And use other methods to enrich uranium as a process of gaseous diffusion (gaseous diffusion process) which is made through the uranium hexafluoride gas to pass the membrane is made thin force of an alloy of silver and zinc allows the entry into force of uranium 235 at a rate higher than 238 because less weight. And it requires enriching one kilogram of uranium by 5% to ten kilograms of natural uranium, while necessary for the enrichment of one kilogram of uranium by 90% to more than 150 kg of natural uranium. And it called on the natural uranium is enriched resulting from the enrichment process with depleted uranium (depleted Uranium), where it has a low percentage of uranium-235 not exceeding three per ten percent, that is, they are lower than those in natural uranium. The Aln_khasab process is very expensive and therefore the price per kilogram of enriched uranium by 5% up to two thousand dollars.
The second element stainless fission is plutonium-239 (Plutonium-239), a radioactive element that is not available in nature relatively old palace, where the half-life (half-life) of 24 thousand years, that is, it may be hydrolyzed completely at the beginning of the land is before 4500 million years ago. The total amount of energy emitted by the fission of one atom of plutonium 239 two hundred and seven million electron volts (207.1 MeV = 3.318 × 10-11 J). The amount of energy produced by fission one kilogram of plutonium 239 is equal to 23.22 million kilowatt-hour (8.36 × 1013 joules), slightly higher than the uranium 235. The critical mass of plutonium-239 is the envelope (untampered critical mass) A ten kilogram can be reduced to one-third through the reflectors of neutrons (tampered critical mass). Since plutonium 239 industrial element does not exist in nature, it has been discovered by chance in 1940 after he was tossed uranium 238 with neutrons. Scientists have less than two years from the discovery of the construction of nuclear reactors for the purposes of plutonium production reactors, which generally have much which convert uranium 238 to plutonium-239 as a result of ejected neutrons. And generally have much reactors produce large quantities of plutonium and the cost is negligible with the cost of production of uranium 235 and most of it is used in the manufacture of fissile atomic bombs. And contributes to the plutonium as fuel energy-producing nuclear reactors in an indirect way as the U-238 contained in these reactors, uranium-235 turns into plutonium during the operation, and this in turn splits during operation as fissile uranium 235 thermal neutrons to produce energy by up to 30%. It can be used plutonium oxide 239 as fuel for nuclear reactors after mixing natural uranium oxide a certain percentage of so-called mixed oxide (MOX (mixed oxide) fuel).
The third element stainless fission is uranium 233 (Uranium-233), a radioactive element that is not available in nature relatively old palace, where the half-life (half-life) of 159 thousand years, that is, it may be hydrolyzed completely at the beginning of the land is before 4500 million years ago. The total amount of energy emitted by the fission of one atom of uranium 233. One hundred and ninety-eight million electron volts (197.9 MeV = 3.171 × 10-11 J). The amount of energy produced by fission one kilogram of uranium 233 is equal to 22.76 million kilowatt-hour (8.195 × 1013 joules), slightly less than the uranium-235 was discovered uranium 233 in 1946, after having been tossed thorium-232 (thorium-232) neutrons which turned into uranium 233 after holding it one of the neutrons and after a series of nuclear derogations (nuclear decay). And the production of uranium 233 from thorium 232 using thermal or fast reactors through the development of thorium rods with Alocodh rods in the reactor core. Despite the abundance of thorium in the earth's crust Khat more than four times the abundance of uranium, but the thorium fuel cycle (thorium fuel cycle) more expensive than uranium fuel cycle because natural uranium containing uranium 235 stainless fission while thorium does not contain any peer-fissionable. Some have been operating reactors using uranium 233, but in a limited and low cards, compared with uranium 235.
