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Fission and Fusion.notebook
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April 16, 2012
Aug 310:37 AM
Fission and Fusion
Goals
Define nuclear fission, chain reaction, and nuclear fusion and distinguish between them
Explain how a fission reaction is used to generate power Discuss the possible benefits and the current difficulty of
controlling fusion reactions
Aug 310:39 AM
Nuclear Fission
In fission you start with a heavy atomic nucleus like U235 Bombard with smaller particles like neutrons or
or lighter nuclei Larger atom splits apart into smaller stable atoms Less nuclear binding energy is needed to hold the smaller
atoms together Remaining energy is released from the split nucleus
Aug 310:51 AM
Chain Reactions
Chain reactions are fusion reactions that run continuously Particles emitted from the initial reaction trigger the
continuation throughout the sample Particles are usually neutrons
Need a critical mass of the heavy element Need more neutrons to continue the chain
reaction Those extra neutrons come from the heavy
initial element Control of a chain reaction depends on the speed of the
neutrons
Aug 311:01 AM
Aug 311:04 AM
Nuclear Reactors
Nuclear reactors employ a controlled chain reaction. Control here refers to the speed of the reaction
Too fast = meltdown Methods of control
Control rods: used to absorb extra neutrons Moderators: used to slow the speed of emitted
neutrons Most commonly used moderator is water
which also serves as a coolant Sometimes "heavy" water (D2O deuterium
oxide) Other safety features
Shielding: absorbs radiation from the reaction,especially gamma rays
Aug 311:14 AM
Fission and Fusion.notebook
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April 16, 2012
Aug 311:19 AM
Major Nuclear Reactor Accidents
Three Mile Island Harrisburg, PA 1979 Partial meltdown of a reactor core Caused by loss of coolant due to a relief valve that was stuck open Occurred 12 days after the release of the film The China Syndrome,
which was about a nuclear accident in California In the movie one physicist mentions that the China Syndrome
would render "an area the size of Pennsylvania" uninhabitable! The unaffected reactor at TMI is still operating today.
Aug 311:33 AM
Major Nuclear Reactor Accidents
Chernobyl Soviet Union (now Ukraine) 1986
Reactor exploded during anexperiment
Worst reactor accident in history Caused by a combination of human
error and lack of safety features Human error: most of the
control rods were removed during the test
Safety: lack of operatinginstructions and poor design
Aug 311:51 AM
Major Nuclear Reactor Accidents
Fukushima Daichii Japan March 11, 2011 Earthquake and tsunami caused the accident
Cooling pumps were damaged on 4 different reactors 3 of the 4 reactors went into meltdown
Second only to Chernobyl in terms scope of disaster Both accidents have the highest rating on the International
Nuclear Event Scale at Level 7 (TMI is at Level 5)
Aug 312:46 PM
Fusion
The opposite process of fission Start with light nuclei Combine to form a heavier nucleus that is stable Releases more energy that fission Hydrogen bonds Stars are essentially great big fusion reactors
Aug 312:49 PM
Fusion
What's the problem? Currently uncontrollable High temperature needed to start the reaction
About 108 K We're working on it
Aug 312:57 PM
Fusion in Stars Nucleosynthesis
Start with hydrogen Hydrogen fuses to make helium
Small stars can only do this Covers most of the lives of all stars
Helium fuses to make carbon and oxygen The largest stars can further fuse elements to make metals
Include Ca, Cr, Fe, Ni, Cu The heaviest elements are formed when a star undergoes
supernova
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April 16, 2012
Aug 31:09 PM