1 lecture #24 fusion engr 303i. 2 outline fusion →definition →atoms usually used previous...
Post on 22-Dec-2015
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TRANSCRIPT
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Outline
• Fusion→ Definition→ Atoms usually used
• Previous attempts at fusion
• Current attempts at fusion→ International Thermonuclear Experimental
Reactor (ITER)
• Summary→ Advantages→ Disadvantages
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Fusion - Definition• 2 lighter weight atoms bond together to form
1 heavier atom• As the 2 lighter atoms become close
together they repel each other with natural electrostatic forces
→ At very high temperatures these forces will be overcome and fusion will occur (100,000,000°C)
• The mass of the resulting atom is slightly less than the sum of the original 2 atoms
→ The difference in mass turned into energy→ E = mc2
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Fusion - Definition
Most commonly used atoms for fusion are isotopes of hydrogen:
→ Hydrogen→ Deuterium → Tritium
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Fusion - ReactionThe most common fusion reaction:
Deuterium + Tritium => Helium + neutron + energy
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Fusion Reaction Requirements• Need to heat small amounts of deuterium
and tritium atoms to 100,000,000°C• Need to contain and push these atoms
together long enough so they fuse• Need to recover the heat• Use the heat to make steam and then
electricity→ Part of that electricity could be used to make
more deuterium and tritium atoms from water→ If it works it is considered renewable because
of large amounts of deuterium and tritium in water
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Containment
Containment must be non-material
→ Any material will melt at the required temperatures
→ Inertial containment: High powered lasers keep atoms inside vessel
→ Magnetic containment: Magnetic fields hold the atoms inside vessel
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Inertial Containment• Laser beams
hold plasma in center (away from cooler walls)
• This method not used as much as next
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Magnetic Containment• Magnetic fields
keep plasma in center (away from walls)
• Total shape is a doughnut
• Difficult to keep center hot but magnets cold
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Magnetic Containment – Tokamak• Toroidal (doughnut-shaped) magnetic field for containing
plasma• Tokamak is an acronym from Russian words that mean: toroidal chamber in magnetic coils
• Made by Russian scientists who achieved much higher temperatures than US or British working with different shapes
Doughnut shape allows smooth, continuous magnetic field to be made from electric field
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Magnetic Containment – TokamakEarly 1980’s, Princeton University built Tokomak Fusion Test Reactor (TFTR)
→ Goal was to produce more power than put into magnetic fields, pumps, equipment - Never achieved the goal
http://www.pppl.gov/projects/pages/tftr.html
Also early 1980’s Joint European Torus (JET) was built in England
→ Q = power produced by fusion / input power→ Q = 1 is self–sustaining but no net production→ In 1997 produced Q = 0.7, best so farhttp://www.jet.efda.org/index.html
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Picture of Joint European TorusInside reactor before and during operation
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Japan Torus JT-60
• Did experiments with deuterium-deuterium fuel
• If used deuterium-tritium fuel they would have produced more power than power input
http://www-jt60.naka.jaea.go.jp/english/index-e.html
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International Thermonuclear Experimental Reactor (ITER)
To be built in France (2006 agreement)
→ Research fusion and show feasibility of full-scale fusion power reactor
→ 10 years of construction; 20 years operation→ $12.1 billion to construct→ Goal is to make 500 MW for up to 500
secondsPrevious results of TFTR, JET, JT were usually less than a second
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Advantages of Fusion
• Tritium is the only radioactive material used→ It only emits weak radiation→ It does not concentrate or linger in living organisms
• No long term waste products
• The temperature is high but no danger of nuclear melt down because very little radioactive material inside
• Considered renewable because of significant amount of water available to obtain deuterium and tritium
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Disadvantages of Fusion• Requires superconducting magnets at -270°C
• Very high temperature in center (100,000,000+°C)
• Chamber must be in complete vacuum
• Reactor cooled with liquid lithium that explodes on contact with air or water
• Inner wall of reactor replaced every 2-10 years
• Much larger and more costly than nuclear fission plants