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Nuclear Energy

Nuclear Energy. G2 Reactions and Reactors. Reactions and Reactors. Energy is required to hold the protons and neutrons in an atom's nucleus together. Scientists have discovered ways to release the energy inside an atom.

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Nuclear Energy

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  1. Nuclear Energy G2 Reactions and Reactors

  2. Reactions and Reactors • Energy is required to hold the protons and neutrons in an atom's nucleus together • Scientists have discovered ways to release the energy inside an atom. • One way to release this energy is by splitting the nucleus of the atom apart • A reaction in which the nucleus of a large atom is split into smaller nuclei is called nuclearfission

  3. Nuclear Fission • Uranium-235 is the atom used most commonly in fission reactions • It splits when its nucleus is struck by a neutron • Releases energy • Forms new nuclei, called daughter nuclei. • Usually elements of barium or krypton • Change the number of protons • – change • the element into a different element • Most daughter nuclei are radioactive

  4. Nuclear Fission • energy • This continuous action of neutrons splitting atomic nuclei is called a chainreaction

  5. Nuclear Fission • When the nucleus of an atom of U-235 splits, the resulting nuclei have lessmass than the original nucleus • For example, the combined mass of a barium nucleus and a krypton nucleus is less than the mass of the original U-235 nucleus • Some of the missing mass is in the neutrons emitted during the fission reaction • The rest of the mass was converted directly into energy.

  6. Nuclear Reactors • Electricity is produced from nuclear fuel much the same way it is produced from fossil fuels • However, in nuclear reactors, heat is produced through the fission of nuclear material instead of burning • Nuclear fuel is usually about 97% U-238 and 3% U-235 • The U-238 is not fissionable, so it does not take part in the nuclear reaction

  7. Nuclear Reactors • In a typical American reactor, the fission of U-235 takes place inside a nuclear reactor vessel • This vessel can be as tall as 20 m, with steel walls at least 15 to 30 cm thick • The walls are surrounded by a large shield that keeps neutrons and other radiation from escaping • The reactor is housed inside a thick concretecontainment building • The fuel for the reactor consists of long rods filled with pellets that contain the fissionable U-235

  8. Nuclear Reactors • The fuel rods are positioned vertically in the center of the reactor so water can circulate between them • The water performs two functions • It acts as a coolant, which absorbs heat and keeps the core from melting • It also slows the movement of the neutrons released during the chain reaction • This helps to control the chain reaction

  9. Nuclear Reactors • The speed of the chain reaction is also regulated by controlrods • Control rods are made of cadmium, boron, or other materials that absorb neutrons • Lowering the rods slows the chain reaction by eliminating some of the neutrons • Raising the rods results in the absorption of fewer neutrons, and the speed of the chain reaction increases

  10. Nuclear Reactors • Raising or lowering the control rods also regulates the amount of heat produced • The temperature of the coolant water may reach temperatures above 275 oC • Hot water moves inside pipes to a heat exchanger, where it heats water for steam • The steam is then used to turn turbines connected to electric generators

  11. Nuclear Reactors • Nuclear Fission video • Nuclear Weapons video • Nuclear Weapons video

  12. Breeder Reactors • Over 99 percent of the naturally occurring uranium is the nonfissionable isotope, U-238 • However, U-238 can absorb a neutron, creating a fissionable atom of plutonium-239 (Pu-239) • Pu-239 can be used as a fuel in a nuclear reactor • A breeder reactor uses this process to produce new fuel while it generates usable energy. • U-238 is nonfissionable • Cannot be split • Cannot be used a fuel • Pu-239 is fissionable • Can be split • Can be used as fuel

  13. Breeder Reactors • During the reaction, U-238 captures a free neutron • Changes U-238 to a very unstable atom of U-239 • The U-239 changes by radioactive decay, which also releases energy, • into neptuniun-239 • The unstable neptuniun-239 decays again • Changes into a fissionable atom of Pu-239 • A breeder reactor can produce more fuel than it uses

  14. Breeder Reactors • Breeder reactors are not used in the United States • Because of concerns about nuclear terrorism • The plutonium produced by breeder reactors can be used to make atomic bombs as well as energy • If this material fell into the wronghands, the results could be horrific

  15. Section Review • Answer the questions in the section review

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