Radiation reactors
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Radiation reactors

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    Radiation reactors Radiation reactors Presentation Transcript

    • RadiationNuclear Reactors
    • Nuclear Reactions Uranium is a fairly common element on Earth and was incorporated into the planet during the planets formation U-238 makes up 99 percent of the uranium on the planet Uranium-235 makes up about 0.7 percent of the remaining uranium found naturally Uranium-235 has an interesting property
    • Nuclear Reactions U-235 decays naturally, just as U-238 does, by alpha radiation U-235 also undergoes spontaneous fission a small percentage of the time Fission is defined as “the splitting of an atom” Also, U-235 is one of the few materials that can undergo induced fission
    • Nuclear Reactions If a free neutron runs into a U-235 nucleus, the nucleus will absorb the neutron without hesitation, become unstable and split immediately The probability of a U-235 atom capturing a neutron as it passes by is fairly high In a reaction two or three neutrons are ejected from each fission causing other fissions to occur
    • Nuclear Reactions Theprocess of capturing the neutron and splitting happens very quickly  (1 x 10-12 seconds) picoseconds An incredible amount of energy is released, in the form of heat and gamma radiation, when a single atom splits The energy is released because the products and the neutrons, together, weigh less than the original U-235 atom
    • Nuclear Reactions The difference in weight is converted directly to energy at a rate governed by the equation E = mc2 a pound of highly enriched uranium used to power a nuclear submarine or nuclear aircraft carrier is equal to about a million gallons of gasoline a pound of uranium is smaller than a baseball and a million gallons of gasoline would fill a five-story building
    • Nuclear Reactions In order for a reactor to work, a sample of uranium must be enriched , so that it contains two to three percent or more of uranium-235 Weapons-grade uranium is composed of 90 percent
    • Nuclear Power uranium is formed into pellets with approximately the same diameter as a dime and an inch long These pellets are then placed in rods that are “super critical” meaning they would over heat and melt if left alone To prevent this, control rods made of a material that absorbs neutrons are inserted
    • Nuclear Power The depth the rods are inserted into the uranium, determines the amount of fission taking place All the way in… the reactions stop All the way out….the reactions increase until meltdown occurs The uranium bundle acts as an extremely high-energy source of heat. It heats the water and turns it to steam
    • Nuclear Power The steam drives a steam turbine, which spins a generator to produce power In some plants the steam contacts other water and turns it to steam… this way, the radioactive water never touches the turbine there is little difference between a nuclear plant and a coal or oil-fired plant except for the source of the heat used
    • Nuclear Power The reactors pressure vessel is typically housed inside a concrete liner that acts as a radiation shield the containment vessel is protected by an outer concrete building that is strong enough to survive such things as crashing jet airliners
    • Nuclear Power Uranium-235 is not the only possible fuel for a power plant. Another fissionable material is plutonium-239
    • Nuclear Power Plutonium-239 can be created by U-238 fission, therefore some reactors are used to make weapons grade plutonium If fact, the first reactors every produced were used for this purpose…. Atomic bombs Research reactors work on the same principals as power reactors, however are used for other purposes
    • Nuclear Power They can be used to expose materials to high levels of radiation To bombard elements with neutrons to create new isotopes And can be used to work on new energy possibilities How safe are they? Do they hurt the environment?
    • Nuclear Safety Compared with a coal-fired power plant, nuclear power plants are a dream come true from an environmental standpoint coal-fired power plant actually releases more radioactivity into the atmosphere than a properly-functioning nuclear power plant Fossils fuel plants (oil/coal) release huge amounts of carbon into the atmosphere, C-14 is radioactive
    • Nuclear Safety There are also drawbacks with nuclear power… Mining and purifying uranium has not, historically, been a very clean process Improperly-functioning nuclear power plants can create big problems i.e. The Chernobyl Spent fuel from nuclear power plants is toxic for centuries and there is no safe permanent storage facility for it, yet
    • Nuclear Safety Transporting nuclear fuel to and from plants also poses some risk Unfortunately, there are less new nuclear power plants being constructed due to these risks At some point however, there will be no more fossil fuel and we will have no choice but to build more nuclear power plants
    • Reactor Types There are a couple different types of reactors, all use the same principle of nuclear fission The four types are … Graphite Moderated Reactor Fast Breeder Reactor (FBR) Liquid Metal (LMFBR) (most common type of breeder)
    • Reactor Types LightWater Reactor (LWR) Heavy Water Reactor (HWR) There are two types of light water reactors  Boilingwater reactor  Pressurized water reactor Boiling water reactor  CoolantType - water  Moderator Type – water
    • Reactor Types Fuel - uranium-dioxide (UO2) Comments - steam generated inside the reactor goes directly to the turbine
    • Reactor Types Pressurized water reactor  Coolant Type - water  Moderator Type – water  Fuel - uranium-dioxide (UO2)  Comments - steam is generated outside the reactor in a secondary heat transfer loop
    • Reactor Types Heavy Water reactors work just like light water reactors, however, instead of using water H2O…. Normal hydrogen is replaced with deuterium H2
    • Reactor Types There are two types of Graphite moderated reactors…  Gas Cooled  Water Cooled Gas Cooled  Coolant Type - gas (carbon dioxide or helium)  Moderator Type – graphite  Fuel -- uranium
    • Reactor Types Comments - used in Britain, and France
    • Reactor Types Water Cooled Reactors  Coolant Type – water  Moderator Type – graphite  Fuel -- uranium  Comments - used in USA & former Soviet Union, e.g. Chernobyl
    • Reactor Types Fast Breeder Reactor (FBR)  Coolant Type – molten liquid sodium  Moderator Type – none required  Fuel - plutonium dioxide and uranium dioxide in various arrangements  Comments - breeder reactors are designed to produce more fissile material than they consume