Some nuclei can undergo fission on their own spontaneously, but only specific nuclei, like uranium-235, uranium-233, and plutonium-239, can sustain a fission chain reaction. The reactor core consists of nuclear fuel, control rods, moderator (coolant), and neutron reflector.The fission takes place in the nuclear reactor core.The multiplication factor is also influenced by other parameters such as temperature, fuel burnup, and reactor poisoning.Insertion of the rods decreases the parameter one or more (multiplication factor), thus decrease the power.Withdrawal of the rods increases the parameter one or more (multiplication factor), thus increase the power.Control rods contain material that absorbs neutrons ( boron, cadmium, …).For reactors using light water as moderators, enriched uranium fuel is required.Therefore the moderator is used to slow down neutrons (to increase the probability of fission).The probability that fission will occur depends on incident neutron energy.The chain reaction means if the reaction induces one or more reactions.
#Nuclear fission meaning free#
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Meitner and Frisch carried out further experiments, which showed that the U-235 fission could release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). She was the first to realize that Hahn’s barium and other lighter products from the neutron bombardment experiments were coming from the fission of U-235. When they finally published the results in 1939, they came to the attention of Lise Meitner, an Austrian-born physicist who had worked with Hahn on his nuclear experiments. When they finally identified one of the products as Barium-141, they were circumspective of publishing the finding because it was unexpected. Rather than the heavy elements they expected, they got several unidentified products. They attempted to create transuranic elements by bombarding uranium with neutrons. Nuclear fission of heavy elements was discovered on December 17, 1938, by Otto Hahn and his assistant Fritz Strassmann. In 2007, the IAEA reported 439 nuclear power reactors operating globally, operating in 31 countries. In 2011 nuclear power provided 10% of the world’s electricity.Since 1 gram of any fissile material contains about 2.5 x 10 21 nuclei, the fissioning of 1 gram of fissile material yields about one megawatt-day (MWd) of heat energy.About 3.1⋅10 10 fissions per second are required to produce a power of 1 W.The total energy released in a reactor is about 210 MeV per 235U fission.The fission process may produce 2, 3, or more free neutrons, and these neutrons can trigger further fission, and a chain reaction can occur.Some nuclei can undergo fission on their own spontaneously, but only specific nuclei, like uranium-235, uranium-233, and plutonium-239, can sustain a fission chain reaction.
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Neutron-induced nuclear fission is the process of the most significant practical importance in reactor physics.
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Nuclear fission is a nuclear reaction or a decay process in which the heavy nucleus splits into smaller parts (lighter nuclei). The fission process often produces free neutrons, photons (in the form of gamma rays) and releases a large amount of energy. Article Summary & FAQs What is nuclear fission?