Fusion Energy
Nuclear Engineering, Imperial College London
Dr Jonathan Shimwell
This work was funded by the RCUK Energy Programme
[Grant number EP/P012450/1]
Image by Volker Steger
Jonathan.Shimwell@ukaea.uk
Objectives
 Why and when
 Reasons for selecting the DT reaction
 Methods of achieving nuclear fusion
 Lawson criteria
 Fusion technology
Fusion energy has excellent credentials
 Safe (no run away chain reactions)
 High energy density (337GJ/g)
 Clean (reaction waste product is helium)
 Low Carbon (no CO2 emitted during operation)
 Produces no long lived radioactivity (Only activated materials)
 An abundant and distributed fuel source (Lithium and Deuterium)
When will fusion be achieved?
 Funding
 The demand for a new energy source
 Political will
 Scientific and engineering capacity
 Unknown unknowns
"Fusion will be ready when society needs it"
Lev Artsimovich, Father of the Tokamak
by Jonathan Shimwell
Fusion Energy, Physics 303 course
The need for a new energy source
Data source WEC, BP, USGS and WNA data from presentation by Steven Cowley
Unknown unknowns
What is fusion
 A fusion reaction is the joining of two smaller atoms to form heavier ones.
 A large amount of energy is released during this process .
Deuterium (D)
Tritium (T)
Helium 4
3.5MeV
1/5 of the energy
Neutron
14.1MeV
4/5 of the energy
Helium 5
17.6MeV
Energy emitted from nuclear reactions
 Calculation of fusion energy from binding energy
H3 + H2 = He4 + n
Binding energy before = 3 x 2.83 + 2 x 1.11
Binding energy after = 4 x 7.07
Difference in binding energy is 17.57 MeV
 Calculation of fission energy from mass difference
U235 + n= Ba145 + Kr87 + 4n
Mass before = 235.04393u + 1.00866u
Mass after = 144.92752u + 86.91335u + 4 x 1.00866u
Mass difference = 0.17708u = 164.95MeV
proton mass = 1.672623E27 kg
neutron mass = 1.674929E27 kg
1 atomic mass unit = 1.660540E27 kg
Maximum energy emitted from fission and fusion per gram
17.6 MeV emitted per DT fusion
Assuming every D reacts with a T.
1 gram of material.
~200MeV emitted per U235 fission
Assuming 100% U235 enrichment .
Assuming ever U235 fissions.
Ignoring decay heat.
1 gram of material.
Typical fusion reactions
H2 + H2 = H3 + H1 Q=4MeV
H2 + H2 = He3 + n Q=3.3MeV
H2 + He3 = He4 + H1 Q=18.3MeV
N14 + H1 = O15 Q=7.35MeV
H2 + H1 = He3 Q=5.49MeV
C12 + H1 = N13 Q=12.86MeV
He3 + He3 = He4 + 2 H1 Q=1.95MeV
C13 + H1 = N14 Q=7.55MeV
H1 + H1 = H2 Q=0.42MeV
N15 + H1 = C12 + He4 Q=4.96MeV
H2 + H3 = He4 +n Q=17.6MeV
Fusion cross section
 The DT reaction has a higher probability of occurring
 The DT reaction has a lower threshold temperature
 The DT reaction releases large amounts of energy 17.6MeV
plot of energy distribution of neutron for different DD, DT and 150Kev, 20Kev
Main methods of achieving fusion
Magnetic
confinement
Gravitational
confinement
Inertial
confinement
Gravitation confinement
 The repulsive coulomb force is overcome by gravitational forces and tunneling
 Extremely large masses are required as gravity is a relatively weak force.
The CNO cycle
The ProtonProton reaction
Fusion research around the world
Fusion research around the world
Inertial Confinement
Inertial Confinement
Indirect drive
Direct drive
Inertial Confinement
Magnetic Confinement
Magnetic Confinement
Poloidal and toroidal magnets
Magnetic Confinement
Magnetic Confinement
Magnetic Confinement Roadmap
ITER reactor
800m3 plasma volume
500MW thermal
DEMO reactor
10003500m3 plasma volume
4000MW thermal
JET reactor
80m3 plasma volume
16MW thermal
Tore Supra
25m3 plasma volume
0MW thermal
Ignition
The point where a fusion reaction becomes selfsustaining instead of requiring a constant input of energy. In the case of DT fusion the plasma is heated by the energetic alpha particle that is emitted during fusion reactions. This is also known as self heated plasma
Lawson criteria
The lawson criteria defines the general requirements (temperature, density and confinement time) of a reactor to reach a self sustaining reaction (ignition).
Confinement time
Boltzmann constant
Temperature of electrons
Number density of electrons
Energy released per fission
Cross section of reaction
Average velocity of ions
Derivation of Lawson Criterion for DT fusion
Fusion Technology
Breeder blankets
 To generate sufficient tritium fuel to sustain the reactor.
 To convert kinetic energy of the neutrons to thermal energy.
 To shield the exterior components from neutrons.
Fuel Cycle
Fuel Cycle
Fuel Cycle
Fuel Cycle
Key reactions in breeder blankets
Questions
Which isotope is depleted?
Why at the front?
What is the best isotope for the front?
Neutron moderation
 Neutron spectra at different depths in the blanket.
 Neutrons are moderated by the material and lose energy.
 Neutrons are also captured and produced by some reactions.
Fuel Cycle
Neutron spectra at different depths in the blanket.
Neutrons are moderated by the material and lose energy.
Neutrons are also captured by some reactions.
Selecting suitable materials
Fuel Cycle  tritium breeding
Fuel Cycle  neutron multiplication
Neutron interaction
Material 1
Material 2
Neutron birth
(n,n')
(n,f)
(n,n')
(γ,γ')
(n,nγ')
(n,pn')
(n,f)
(n,2n)
(n,α)
(n,γ)
Neutron
Electron
Gamma
Alpha
Proton
Radioactivity
Target
Nuclide
n,2n
n,g
n,p
n,pn
n,d
n,t
n,nd
n,a
n,He3
n,pd
n = neutron
g = gamma
t = tritium
p = proton
d = deuterium
He = helium
Common neutron induced reactions
Neutron number
Proton number
Irradiation
Time
Number of atoms
Shut down
 New isotopes build up during irradiation

Radioactive isotopes decay and will eventually reach a point where decay rate is equal to activation rate.

Decay is more noticeable once the plasma is shutdown.
 The activity is related to the irradiation time and the nuclide half life.
 The decay process emits gamma rays leading to dose.
 The dose is dependent on the activity, the energy of the gamma and biological response.
Radioactivity  activation
Radioactivity  fission products
Atomic number
Percentage of fission products
Radioactivity  fission products
EU Roadmap for fusion energy
 3 main reactors (JET, ITER, DEMO) demonstrating large steps in understanding and performance.
Image source www.ccfe.ac.uk/mast_upgrade.aspx
 Many smaller reactors testing, validating and experimenting on different plasma physics regimes, component designs, materials and feeding into the design of larger ground breaking reactors
Lots of interesting physics to learn
Banana orbits
run away electrons
Stellarators
3D printing components
Neutral particle accelerators
Robotic maintainance
Plasma instabilities such as sausage, kink, balloon and elms
Further opportunists
Masters Degrees
PhD
Jobs
Fusion Energy Msc
The University of York
European Masters of Science in Nuclear Fusion and Engineering Physics
Organised by the European Commission
The physics and technology of nuclear reactors, MSc
University of Birmingham
Nuclear Energy, MPhil
University of Cambridge
Fusion Doctorial Training Network, PhD Organised by several universities and research organisations.
Doctoral Programme in nuclear fusion science and engineering
Organised by 18 European Universities
Nuclear First Doctorial Training Centre University of Manchester and University of Sheffield.
Summer placements, graduate recruitment and work experience at CCFE near Oxford
PhD open days hosted by UKAEA and CCFE with repreentatives from UK universities
Summer placements, graduate recruitment at Fusion 4 Energy in Barcelona
Summer placements, graduate recruitment at ITER in France
Fusenet the European fusion education network with funding oppertunities
Fusion Energy
By Jonathan Shimwell
Fusion Energy
Imperial College London Nuclear Engineering 2018
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