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12-Fusion (About Fusion (What determines what reaction might be best for a…
12-Fusion
About Fusion
Example reactions
2H-3H
good Q, 17.6MeV
cross section high
reaction rate higher at lower temperatures
likely way forward
Left of Fe
Lots of energy
energy produced per gram around 2x bigger than fission
Occur in sun
What determines what reaction might be best for a reactor
Q-value
can reach 1-20MeV
cross section
temperature
Hot ion plasma has to be confined
Pros
Safe-no runaway chain reactions
clean-harmless waste
low carbon, no CO2 emission
high energy density
no long lived radioactivity
abundant fuel sources
Cons
high r&d costs
low political will
scientific capabilities
competition with oil
Confinement
Aim is to overcome the repulsive coulomb force of protons
Gravitational confinement
lots of mass required
like on sun
can't do on earth
inertial confinement
typically used laser beams to compress and confine a fuel pellet
pulsed so hard to sustain a reaction
magnetic confinement
use magnetic fields to confine the plasma
better developed
likely the way forward
Tokamak
Deuterium and tritium fuel
Deuterium is abundant
from sea water
tritium rarer
can be made in tokamak
when neutrons escaping plasma interact with lithium in a 'blanket'
must be breed in the reactor
breeder blankets
Be is important to increase the neutron flux
Ignition and Lawson criteria
fusion reaction must be self sustaining, instead of needing a constant source of energy
Lawson criteria maths:
Heat used to heat steam and power turbines
heat exchanger
JET and ITER