1 Lecture #24 Fusion ENGR 303I

2 Outline Fusion →Definition →Atoms usually used Previous attempts at fusion Current attempts at fusion →International Thermonuclear Experimental Reactor (ITER) Summary →Advantages →Disadvantages

3 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 = mc 2

4 Fusion - Definition Most commonly used atoms for fusion are isotopes of hydrogen: →Hydrogen →Deuterium →Tritium

5 Fusion - Reaction The most common fusion reaction: Deuterium + Tritium => Helium + neutron + energy

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7 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

8 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

9 Inertial Containment Laser beams hold plasma in center (away from cooler walls) This method not used as much as next

10 Magnetic Containment Magnetic fields keep plasma in center (away from walls) Total shape is a doughnut Difficult to keep center hot but magnets cold

11 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

12 Magnetic Containment – Tokamak

13 Magnetic Containment – Tokamak Early 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 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 far

14 TFTR at Princeton

15 Picture of Joint European Torus Inside reactor before and during operation

16 Japan Torus JT-60 Did experiments with deuterium-deuterium fuel If used deuterium-tritium fuel they would have produced more power than power input

17 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 seconds Previous results of TFTR, JET, JT were usually less than a second

18 Drawing of ITER Much larger than a human

19 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

20 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

21 Shiva Nova NIF