Simulating fusion neutron damage
using protons in ODS steels
Jack Haley
1. Fusion Power and radiation damage
2. Simulating neutron damage
3. Simulating with protons
4. Project plan
Fusion Power
• Deuterium and Tritium fuse to produce a
3.5MeV alpha particle and 14.1MeV neutron
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Fusion Power
• Neutrons cause hardening, embrittlement and swelling in components.
• Enormous demands placed on the structural steels
• ODS steels are excellent at handling the radiation
• ODS precipitates pin dislocations and act as sinks for defects and
Helium [1]
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[1] Brodrick, J., Hepburn, D. J., & Ackland, G. J. (2014). Mechanism for radiation
damage resistance in yttrium oxide dispersion strengthened steels. Journal of
Nuclear Materials, 445(1-3), 291–297. doi:10.1016/j.jnucmat.2013.10.045
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Simulating the neutrons
• Closest thing to fusion neutrons available fission neutrons
Lower energy (~2MeV)
Takes a long time
Makes samples radioactive
• Self ion irradiation is widely used
High dose rate
Many facilities available, eg JANNUS, MIAMI
Multi beam energies
In situ with TEM, Helium implantation
• Self ions irradiation behave like the primary knock on atom in neutron irradiation
Fission neutron PKA up to 200keV
Fusion neutron PKA up to 1MeV [2]
[2] Dierckx, R. (1987). The importance of the pka-energy for damage simulation
spectrum. Journal of Nuclear Materials, 144, 214–227.
Simulating with self-ions
Dose
SRIM damage calculation as a function of depth in Fe
2.9MeV Fe ions @ 2.2nA
-0.10
0.10
0.30
0.50
0.70
0.90
Depth (μm)
1.10
1.30
1.50
Simulating with self-ions
[3] Taken from Chris Hardie’s Dphil thesis, 2012
Oxford University
Simulating with self-ions
Size effect in micromechanical testing
• As sample size decreases, yield strength increases
Fe-6Cr
[3]
[3] Taken from Chris Hardie’s Dphil thesis, 2012
Oxford University
Simulating with protons
Dose
SRIM damage calculation as a function of depth in Fe
2.9MeV protons @ 100μA
Smooth Damage
Region
0.00
5.00
10.00
15.00
20.00
25.00
Depth (μm)
30.00
35.00
40.00
Simulating with protons
• Higher dose rate than neutrons, but much lower than heavy ions – need
higher currents
• Very different recoil energy (PKA <0.5keV) than fusion neutrons
Simulating with protons
• Dominant energy loss mechanism of proton is by ionization
• May be a problem with ODS steels – oxide precipitates could be degraded due
to the ionization
Energy
(eV/Ang/Ion)
Loss (eV/Ang/ion)
Energyloss
Energy Loss
Loss of
of 2.9MeV
2.9MeV protons
Fe ions in
Energy
inFe
Fe
1.0E+02
1.0E+02
EnergyLoss
LossbybyIonization
Ionization
Energy
EnergyLoss
LossbybyPhonons
Phonons
Energy
1.0E+00
1.0E+00
1.0E-02
1.0E-02
1.0E-04
1.0E-04
1.0E-06
1.0E-06
0.00E+00
0.0E+00
1.00E+05
5.0E+03
2.00E+05 1.0E+04
3.00E+05
Depth
Depth(Ang)
(Ang)
4.00E+05
1.5E+04
Protons in the literature
• Gary Was et al – Emulation of neutron irradiation effects with protons:
Validation of principle [4]
2002 paper studied:




Radiation Induced Segregation
Microstructure (dislocation loops)
Irradiation hardening
Susceptibility to IASCC
Found excellent agreement between fission neutrons irradiated at 275oC
and 3.2MeV protons at 360oC
• Higher temperature proton irradiation balances the increased displacement
rate by enhancing diffusion kinetics.
[4] Was, G. S. et. Al. (2002). Emulation of neutron irradiation effects with
protons : validation of principle, 300, 198–216.
Simulating with protons
• Still no proton studies on martensitic FeCr and ODS steel
• Recoil energy influence on the radiation induced damage is dependent on
 Composition
 Irradiation temperature
 Lattice structure
• There is no magic formula (yet!) for determining appropriate proton irradiation
conditions to reliably mimic neutron damage
Simulating with protons
• University of Birmingham has two particle accelerators available for proton
irradiation of materials
Accelerator facilities are housed in
 Cyclotron
the Medical
Physics
Buildingset up
1-9MeV protons
– 2.9MeV
preferred
~10μA beam current
to 2cm diameter beam size
at the up
University
Capable of ~10-6 dpa/s in Iron which translates as ~0.05 dpa/day
Temperature control up to 600oC available now
 Dynamitron
1-3MeV protons
100s of μA beam current easily possible, absolute maximum 2mA
Up to 2cm diameter beam size
~10-5 - 10-4 dpa/s
~1 dpa/day at 100 μA
Temperature control in the works
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Project plan
Key questions:
• How is the microstructural damage produced by proton, heavy
ion and fission neutrons different?
• What are the differences in mechanical properties?
• Is the proton damage representative of neutron damage under
any irradiation conditions?
Project plan
Next Steps
• Start work initially on FeCr binary alloys 0-15% Cr content
• ODS steels later
• Heavy ion irradiation at JANNUS in May
• Use Cyclotron in the summer for first proton irradiations, up to
0.6dpa to match neutron specimens at CCFE at same temperature
• Once Dynamitron is ready, use to irradiate at higher doses
Project plan
• Characterise the microstructural damage using TEM and relate this with
micromechanical tests

Dislocation loops

Hardening using nano-indentation and micro-cantilevers

Atom probe tomography?
• Dose and dose rate dependance
• Irradiation temperature dependence
• Composition dependence