Energy fission reactor

Uranium dioxide fuel is irradiated in a reactor for periods of one to two years to produce fission energy. Upon removal, the used or spent fuel contains a large inventory of fission products. These are largely contained in the oxide matrix and the sealed fuel tubing. 

The two nuclei on the right side are just two of the many possible products of the fission process. Since more than one neutron is released in each process, the fission reaction is a self-propagating, or chain reaction. Neutrons released by one fission event may induce other fissions. When fission reactions are run under controlled conditions in a nuclear reactor, the energy released by... 

One of the fascinating features of fission power is the breeding of fission fuel from nonfissionable uranium-238. Breeding occurs when small amounts of fissionable isotopes are mixed with uranium-238 in a reactor. Fission liberates neutrons that convert the relatively abundant nonfissionable uranium-238 to uranium-239, which beta-decays to neptunium-239, which in turn beta-decays to fissionable plutonium-239. So in addition to the abundant energy produced, fission fuel is bred from relatively abundant uranium-238 in the process. 

Nuclear fission energy for the commercial production of electricity has been with us since the 1950s. In the United States, about 20 percent of all electrical energy now originates from 103 nuclear fission reactors situated throughout the country. Other countries also depend on nuclear fission energy, as is shown in Figure 19.13. Worldwide, there are about 442 nuclear reactors in operation and 29 currently under construction. 

Because of their intimate link with energy production in nuclear reactors, fission products and their nuclear data have long occupied an important position in reactor technology. In recent years, interest in short-lived fission-product decay data has increased markedly, as their relevance to different areas of research and technology has become recognized. In addition to their importance for estimation of the fission-product decay-heat source term in nuclear reactors, the increasing attention being focused on the assessment of the hazards associated with the release, transport and... 

In a reactor, the energy per fission, including the energy of the delayed neutrons and of the fission products, is 200 MeV. To produce 1 MW thermal energy, 3.1 x 1016 fissions per second are required. If the half-life of the fission product is short compared with the duration of operation of the reactor, its activity comes into equilibrium when creation by fission equals radioactive decay. Assuming a constant level of power for a duration of Tsecs, the activity is 3.1 x 104/(1 — exp—AT) TBq per MW. Some fission products themselves absorb neutrons (the socalled reactor poisons) and for them the calculation of activity is more complicated. Figure 2.2 shows the combined activity of 1 g of fission products formed in an instantaneous burst of fission and also from 1 g of fission products formed over a period of a year (Walton, 1961). The activity from a short burst decays approximately as t-1 2. 

D. We will still be using fossil fuels, oil, gas and coal, but their usage will be curtailed because there will have been a dramatic increase of harnessing of solar energy, wind energy, fusion and fission energy, and other sources. We propose that fusion reactors may become the usable energy source of choice, because of minimum problems of disposal and because of uses of the fissionable products (tritium). These are less of a security risk than fission products (which are plutonium and uranium). 

Plutonium— A man-made element that is created from uranium-238 by neutron bombardment and can be used as a material for fission energy. Radioactive waste—The radioactive fragments produced by fission, which accumulate in the fuel rods of a nuclear reactor and eventually must be removed. 

This was the first man-made radionuclide. From that time on many species of radionuclides were produced by bombardment of elements with charged particles using the various types of accelerators. In addition, practical use of fission energy allowed production of a great amount of artificial radionuclides, not only by neutron irradiation generated with nuclear reactors, but also by processing spent fuel. 

If the operational conditions and design of a reactor are adjusted to maximize the amount of Pu produced it is possible to operate the reactor to produce more fertile isotopes than were originally used to start the reactor. This operational mode is called the breeder reactor. The breeder reactor can greatly extend the amount of potential energy available from uranium because it is possible to use the 99.3% U present in natural uranium, as fuel. It is also possible to use thorium (Th" ) in a breeder reactor to produce fertile U. The use of the breeder reactor will extend the lifetime of the nuclear fission energy source to several hundred years. 

Fission energy can be obtained from uranium, using the uranium once-through option and the uranium-plutonium fuel cycle, and from thorium, by the thorium-uranium fuel cycle. Each fuel cycle offers a number of alternative routes with respect to reactor type, reprocessing, and waste handling. Although the uranium based cycles are described with special reference to light water reactors, the cycles also apply to the old uranium fueled gas cooled reactors. 

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