The production of energy by nuclear fission

The production of energy by nuclear fission in a nuclear reactor must be a controlled process. Neutrons released from the fission of lose most of their kinetic energy by passage through a moderator (graphite or D2O). They then undergo one of two nuclear reactions. The first is capture by leading to further fission the second 

The occurrence of a potentially catastrophic branching chain reaction is prevented by controlling the neutron concentration in the nuclear reactor by inserting boron-containing 

Estimates of the total radiation released from the Chernobyl disaster vary but it may have been as great as 

Atwood (1988) Journal of Chemical Education, vol. 65, p. 1037 - Chernobyl What happened  

The uses of radioisotopes in medicine are extremely important. Certain elements are readily absorbed by particular organs in a human body, and this is capitalized upon in the use of radiotracers (introduced by food or drug intake) to probe the function of human organs. An advantage of the technique is that it is non-invasive. 

The occurrence of a potentially catastrophic branching chain reaction is prevented by controlling the neutron concentration in the nuclear reactor by inserting boron-containing steel, boron carbide or cadmium control rods. The choice of material follows from the high cross-section for neutron capture exhibited by 5B and JJCd. 

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For the production of energy by nuclear fission the following features are decisive ... 

In Section 2.5, we discussed the production of energy by nuclear fission, and the reprocessing of nuclear fuels. We described how short-lived radioactive products decay during pond storage, and how uranium is converted into [U02][N03]2 and, finally, UFg. One of the complicating factors in this process is that the fuel to be reprocessed contains plutonium and fission products in addition to uranium. Two dilferent solvent extraction processes are needed to elfect separation. 

World-wide the production of energy by nuclear power amounts to about 470 GWe (1995) and increases by about 4% per year, although the problems with respect to the storage of the radioactive waste (fission products and actinides) are not yet solved in a satisfactory way. 

The production of electricity fiom nuclear fission energy is accompanied by formation of radioactive waste, of which the larger hazard is the presence of long-lived transuranium isotopes. The problems associated with this waste are still debated, but if the transuranium isotopes could be removed by exhaustive reprocessing and transmuted in special nuclear devices, the hazard of the waste would be drastically reduced (Chapter 12). This may require new selective extractants and diluents as well as new process schemes. Research in this field is very active. 

Such fission potentials might also have practical relevance. The possibility of transmutation of nuclear waste and the production of energy by accelerator-driven systems is under consideration. Accurate fission potentials are needed, particularly in the actinide region, to predict the fission cross sections for these applications. 

Reactors with other functions are also in use. For example, a breeder reactor is one in which new reactor fuel is manufactured. By far the most common material in any kind of nuclear reactor is uranium-238. This isotope of uranium does not undergo fission and does not, therefore, make any direct contribution to the production of energy. But the vast numbers of neutrons produced in the reactor core do react with uranium-238 in a different way, producing plutonium-239 as a product. This pluto-nium-239 can then be removed from the reactor core and used as a fuel in other reactors. Reactors whose primary function it is to generate plutonium-239 are known as breeder reactors. 

The uranium is consumed in the fission reaction. Energy generation by burning fossil fuels consumes fossil fuel chemicals and converts them to harmful combustion products. Nuclear reactors "bum" uranium and convert it to harmful fission products. Unlike fossil fuel materials, uranium has little other use than for the production of energy, like fossil fuels, there is a finite supply of the minerals used to produce the uranium for the fuel cycle. The worldwide amount of potential energy available by use of the burner reactor cycle is similar to that available from oil. If used at a high level the supplies of burner reactor uranium could be depleted in the middle of the next century. 

Currently, electrical power is produced in 103 nuclear power plants throughout the United States. Some countries produce less energy by nuclear fission than does the United States, but in others nuclear energy provides a much larger share of the total energy production (Figure 13.13). 

As it is now used, what is the principle or basis for the production of energy from uranium by nuclear fission Is this process actually used for energy production What are some of its environmental disadvantages What is one major advantage ... 

In nuclear chemistry, a fission reaction (see atomic energy) may be initiated by a neutron and may also result in the production of one or more neutrons, which if they reacted in like manner could start a chain reaction. Normally, moderators such as cadmium rods which absorb neutrons are placed In the reactor to control the rate of fission. 

In a nuclear power plant, heat must be transferred from the core to the turbines without any transfer of matter. This is because fission and neutron capture generate lethal radioactive products that cannot be allowed to escape from the core. A heat-transfer fluid such as liquid sodium metal flows around the core, absorbing the heat produced by nuclear fission. This hot fluid then flows through a steam generator, where its heat energy is used to vaporize... 

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate. Nuclear reactors are used for many purposes, but the most significant current uses are for the generation of electrical power and for the production of plutonium for use in nuclear weapons. Currently, all commercial nuclear reactors are based on nuclear fission. The amount of energy released by one kg 235U is equal to the energy from the combustion of 3000 tons of coal or the energy from an explosion of 20,000 tons of TNT (Trinitrotoluene, called commonly dynamite). 

The high amounts of energy liberated by nuclear fission and fusion led very early to the production of nuclear explosives, as already mentioned in section 11.1. 

For use in nuclear weapons, the concentration of °Pu in the plutonium should be low, because the presence of this nuclide leads to the production of appreciable amounts of neutrons by spontaneous fission if the concentration of °Pu is too high the neutron multiplication would start too early with a relatively small multiplication factor, and the energy release would be relatively low. Higher concentrations of " Pu also interfere, because of its transmutation into " Am with a half-life of only 14.35 y. To minimize the formation of " °Pu and " Pu, Pu for use in weapons is, in general, produced in special reactors by low bum-up (<20 000 MWth d per ton). 

Reactions with fast neutrons, such as (n, 2n), (n, p) and (n, a) reactions, are only of minor importance for production of radionuclides in nuclear reactors. However, special measures may be taken for irradiation of samples with high-energy neutrons. For instance, the samples may be irradiated in special fuel elements of ring-like cross section as shown in Fig. 12.1, or they may be irradiated in a receptacle made of enriched uranium. In both cases, the fast neutrons originating from the fission of enter the samples directly and their flux density is higher by about one order of magnitude than that at other places in the reactor. 

Nuclear fission is a process in which the nucleus of an atom splits, usually into two pieces. This reaction was discovered when a target of uranium was bombarded by neutrons. Eission fragments were shown to fly apart with a large release of energy. The fission reaction was the basis of the atomic bomb, which was developed by the United States during World War II. After the war, controlled energy release from fission was applied to the development of nuclear reactors. Reactors are utilized for production of electricity at nuclear power plants, for propulsion of ships and submarines, and for the creation of radioactive isotopes used in medicine and industry. 

The source of energy in a nuclear reactor is a fission reaction in which neutrons collide with nuelei of uranium-235 or plutonium-239 (the fuel), causing them to split apart. The products of a fission reaction include not only energy but also new elements (known as fission products) and free neutrons. A constant and reliable flow of neutrons is insured in the reactor by a moderator, which slows down the speed of neutrons, and by control rods, which limit the number of neutrons available in the reactor and, hence, the rate at which fission can occur. In a nuclear weapon, the fission chain reaction, once triggered, proceeds at an exponentially increasing rate, resulting in an explosion in a nuclear reactor, it proceeds at a steady, controlled rate. Most commercial nuclear power plants are incapable of undergoing an explosive nuclear chain reaction, even should their safety systems fail this is not true of all research reactors (e.g., some breeder reactors). 

When neutrons strike the nucleus of a large atom, they cause that nucleus to split apart into two roughly equal pieces known as fission products. In that process, additional neutrons and very large amounts of energy are also released. Only three isotopes are known to be fissionable, uranium-235, uranium-233, and plutonium-239. Of these, only the first, uranium-235, occurs naturally. Pluto-nium-239 is produced synthetically when nuclei of uranium-238 are struck by neutrons and transformed into plutonium. Since uranium-238 always occurs along with uranium-235 in a nuclear reactor, plutonium-239 is produced as a byproduct in all commercial reactors now in operation. As a result, it has become as important in the production of nuclear power as uranium-235. Uranium-233 can also be produced synthetically by the bombardment of thorium with neutrons. Thus far, however, this isotope has not been put to practical use in nuclear reactors. 

Safety trials were conducted to investigate the behaviour of the core of a nuclear device under simulated faulty detonation conditions. The core is destroyed by the conventional explosive detonation of such a device, with the production of finely divided plutonium and plutonium oxide which are widely dispersed if the test is not confined. Usually no fission takes place, though there was a very small fission energy release in three of the French underground safety trials. (Since there was some explosive yield, these three trials are sometimes counted as nuclear tests which would put the total number of underground nuclear tests at Mururoa and Fangataufa atolls at 140 rather than 137.) All of the 15 safety trials were carried out at Mururoa. 

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