FusionWill it always be…
The power source of the future
Plasma in spherical tokamak START
TOKAMAKTen times
the temperature
of the sun
ITER – the WayCaderache, France, Open 2016
500Mw 400 seconds
ITER - costsCurrent 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 billionNuclear €2.2 billion Renewables €5.3 billion
Making electricityEnergy 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 materialFirst wallBlanket MaterialReaction pressure vesselElectronics… 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
SimulationsPrevious 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.
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.)
Dynamical system
Radiation inDefects producedDefects 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 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)SiCDiamond 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 coolantResist neutron bombardmentHigh 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 DamageWhen radiation hits metal – one atom
acquires enormous energy.
3D billiards with a million balls
Empty site – vacancy (red) Doubly-occupied site – interstitial
(green)
ClusteringCu 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 conservedHow to describe material transport?
Emergent interstitial features
Interstitials form 2D platelets (anisotropic strain).But these are really 1D dislocation loopsSimulation shows they move really fastCan 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 crystalCharged defects move and attract makingDipole defects move and attract makingStatic quadrupole defects, but captureDipoles making 6-mers move and attract..
Nothing can stop dislocations! (vacancy
pinning)339V_sr5_100K.mov
Unknown unknownsCopper particles in Steel
•bcc, commensurate 9R then fcc
•Embrittling effect small, large, smaller
Voids observed near a grain boundary
Drag impurities in, or out
Formation and growth of voids
HeliumUnavoidable in Fusion: D+T = He + nHelium 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
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
Confined Nuclear Fusion
ITER