Fusion
Will it always be…
The power source of the future
Plasma in spherical tokamak START
TOKAMAK
Ten times the
temperature of
the sun
ITER – the Way
Caderache, France,
Open 2016
500Mw 400 seconds
ITER - costs
Current estimate total €5 billion (JET on budget)
Double LHC, Half SSC (at cancellation) 10% Space Station
Indicative Single-year EU subsidies to existing generation
methods 2001 (European Environmental Agency, 2004)
Coal €13 billion
Oil/gas €8.7 billion
Nuclear €2.2 billion
Renewables €5.3 billion
Making electricity
Energy is primarily contained in
neutrons, alpha particles.
Capture these in a “blanket”, heat up
water, sodium, Pb etc.
Heat exchanger to run a steam engine.
None of this will be done at ITER.
Next Machine, DEMO, will make power
DEMO – Non-commercial
power generation
Materials
Plasma facing material
First wall
Blanket Material
Reaction pressure vessel
Electronics… Magnets…
Challenges for fusion
materials technology
•Low Activation – decommissionability
•Very high heat loads for materials
facing the plasma
•Damage to the structure caused by
high-energy neutrons
•Production of tritium in situ
•Helium embrittlement
•Sputtering on surface & poisoning of plasma
by heavy ions
Radiation
Damage
Simulations
Radiation damages the materials from which a
reactor is made. This determines reactor lifetimes.
A non-equilibrium process, it has unknown scaling
with time and dose. Modelling required.
Edinburgh: Graeme Ackland and Derek Hepburn
First principles studies of “primary damage” (point
defects).
Simplified atomistic force models for metals.
Molecular dynamics of evolution of damage, and
emergent objects (dislocation loops, hardening,
voids, etc.)
Previous Edinburgh Funding:
Four EU FP6/7 PDRA grants with
various industrial partners (EDF,
SCK, FZK)
ITEM, PERFORM, PERFECT,
GETMAT
One EPSRC PDRA joint with
Culham & Oxford
Total value to Edinburgh
~£500,000
SUPA funding: none.
Dynamical system
Radiation in
Defects produced
Defects recombine or
migrate to sinks
Sinks grow (voids lead to
swelling) and may
saturate (grain
boundary segregation)
Not at Thermodynamic
Equilibrium
Voids in Si after
10keV a irradiation
•Vanadium swells (vacancies form voids)
•V + Fe brittle, doesn’t swell
•V + Fe + Cr neither - but why?
International Fusion Materials
Irradiation Facility (IFMIF)
Environments – First Wall
Bombarded by 14MeV neutrons (alphas are
contained by magnetic field).
At 500oC for commercial reactor.
200 dpa (five year lifetime)
Immune to radiation damage in presence of He.
Immune to transmutation to long lived
isotopes.
Weldable, formable, corrosion resistant etc.
etc.
Must not poison plasma, sputter
Candidates – First Wall
Vanadium (+Cr,Ti).
Ferritic/Martensitic Stainless Steel (FeCr)
Oxide Dispersion Strengthening (ODS)
SiC
Diamond coating
Environment - Blanket
Immediately behind the
first wall
Protect the magnets from
radiation (ITER)
Convert neutron energy to
heat (DEMO)
Produce tritium for
reaction (DEMO)
Liquid – avoid damage –
water, LiPb
Environment – Pressure
Vessel
Contain coolant
Resist neutron bombardment
High temperature
Stainless steel
Multiscale modelling of
fusion materials
•Engineering properties depend on
•microstructures that depend on
•properties of defects that depend on
•interatomic interactions that depend on
•electronic structure of the material
How materials deform
Creep – 0D (point defects)
My Video\nhcreep[1].mov
Dislocations – 1D (line defects)
My Video\dislox[1].mov
Edinburgh Speciality:
Interatomic potentials
Computational elegance -Want force on atoms
as a function of atomic degrees of freedom
only. Simulate billions of atoms (microns)
Use insight from quantum mechanics – beyond
pair potentials
Energy as a functional of pairwise interactions
Fit parameters of the functional to relevant
properties of the material (phase diagram,
defect formation etc)
Atomistic simulations
Interstitial defects in body-centred cubic Fe
<110> diffuses slowly, <111> quickly
Not an atom moving - Impurities pin defects.
Radiation Damage
When radiation hits metal – one atom
acquires enormous energy.
3D billiards with a million balls
Empty site – vacancy (red)
Doubly-occupied site – interstitial (green)
Clustering
Cu 25keV cascade 100K 74FP.mov
Vacancies - the theory of
nothing
Vacancies cluster near initial event 3D
void
But … a 3D void comprising vacancies
can collapse to form a 2D platelet
Or, if top and bottom of platelet match,
the only defect is a 1D loop around
the edge.
Vacancies are not conserved
How to describe material transport?
Emergent interstitial features
Interstitials form 2D platelets (anisotropic strain).
But these are really 1D dislocation loops
Simulation shows they move really fast
Can sweep up defects as they go through the material
(nanoscale cleaners?)
Which are the important
defects?
We don’t know.
Maybe all lengthscales are important?
e.g. Ionic crystal
Charged defects move and attract making
Dipole defects move and attract making
Static quadrupole defects, but capture
Dipoles making 6-mers move and attract..
Nothing can stop dislocations!
(vacancy pinning)
339V_sr5_100K.mov
Unknown unknowns
Copper particles in Steel
•bcc, commensurate 9R then fcc
•Embrittling effect small, large, smaller
Formation and growth of voids
Voids observed near a grain boundary
Drag impurities in, or out
Helium
Unavoidable in Fusion: D+T = He + n
Helium hates being in metals – goes to voids,
causes swelling attracts other He, emits
interstitials.
He voids nucleate on grain boundaries and cause
embrittlement
Introduce other sinks (precipitates) to capture He,
or “nanopipes” to extract it to the surface – need
to understand what attracts it.
Formation and growth of voids
Experiment versus KMC theory.
Summary – not much known
Radiation damage is a unique environment
Driven, complex system – thermodynamics
need not apply – extrapolation dangerous
Experimental study of 14MeV neutrons
expensive (IFMIF) but necessary
Where can simulation focus, enhance, or
replace experimentation?
Who would believe it?
The energy source of the future?
Maybe…
The fusion reactions
REACTION 1:
D + D = He3 + n
REACTION 2:
D + T = He4 + n
Confined Nuclear Fusion
Very high energy and pressure
Various test projects
We know how to do it.
Nuclear issues resolved
Plasma control is not (Torus/sphere)
Materials issues are not
ITER