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Intro. Into Nuclear Energy
And you
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What are the fundamental forces of the Universe???
Gravitational Force (interaction of massive bodies) Electromagnetic Force (interaction of charged particles) Weak Nuclear Force (short distance – responsible for radioactive decay of subatomic particles) Strong Nuclear Force (binds nucleons together despite electrostatic repulsion of protons – very strong force – only acts at very small distances)
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How it relates to nuclear Energy
Let’s discuss really big atoms – like Uranium -235 92 protons, 143 neutrons U The large number of neutrons help the nucleus to stay together (keeps P+s apart) Stays together due to strong nuclear force
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Fission reactions Breaking apart of nuclei 14156Ba 23592U
10 n 23592U Δ U n U 9236 Kr U Release of large amounts of energy Process takes about s Starts a chain reaction!!!!!
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E = mc2
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Historical highlight E = mc2 small amounts of mass converted to E
Started ~ 1940 in U.S. Manhattan project Did not take place in Manhattan Very fast pace A great deal of knowledge of atomic physics was learned in this time period
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Not just used for bombs!!! Fission used in nuclear reactions as well
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Where does the U-235 come from?
Mined Uranium is a combination of Uranium isotopes. Most is U-238, some U-237, and less than 1% is U-235 Enrichment = separation of isotopes to isolate U-235 to use in nuclear reactors
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What happens when you have large amounts of U-235?
When you have enough U-235, and therefore, enough slow moving neutrons to have a self sustaining nuclear reaction going in a reaction = critical mass. Is that all you need? No, you need something else to slow down the neutrons
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How you say?? The use of a moderator (graphite or heavy water) to slow down the neutrons that bombard the U-235 (too fast = bounce off)
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So why don’t the nuclear reactors just blow up like a bomb?
The use of control rods (Cd or B) help to slow down the reaction if it gets going too fast – they absorb neutrons (so they are not hitting the U-235) The control rods are adjustable – so they can be changed in their orientation – to control the rate of the nuclear reaction What if the reaction goes too fast? Meltdown (like 3 mile island or Chernobyl)
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How does the reactor work?
Shield molten Na steam to turbine (generates electricity) Core reactor heat exchanger Fuel rods water
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What do we do with the waste?
Left over 238U undergoes radioactive decay Fission daughter products also undergo decay β decay 238U ½ life = 4.5 x 109 year What is to be done with it???????
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Fusion reactions Put together small nuclei to make a larger nuclei
P+ + P+ 22He (fusion on the Sun) Enormous E released (high TO, P plasma gas) Very hard to start fusion reaction Net E gain is so large – that it melts everything!
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Example (Deuterium) 21H 42He + 10n smash together 31H (Tritium)
Non radioactive products 100 mill oC fusion plasma Contain in a magnetic chamber ~ 2035 (hopefully)
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