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

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• Deuterium and Tritium fuse to produce a 3.5MeV alpha particle and 14.1MeV neutron

• 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]

Fusion Power

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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

Simulating the neutrons

• Closest thing to fusion neutrons available fission neutronsLower energy (~2MeV)Takes a long timeMakes samples radioactive

• Self ion irradiation is widely used High dose rateMany facilities available, eg JANNUS, MIAMIMulti beam energiesIn 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.

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Simulating with self-ions

-0.10 0.10 0.30 0.50 0.70 0.90 1.10 1.30 1.50

SRIM damage calculation as a function of depth in Fe

Depth (μm)

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2.9MeV Fe ions @ 2.2nA

Simulating with self-ions

[3] Taken from Chris Hardie’s Dphil thesis, 2012Oxford University

Simulating with self-ions

Size effect in micromechanical testing

• As sample size decreases, yield strength increases

[3] Taken from Chris Hardie’s Dphil thesis, 2012Oxford University

Fe-6Cr

[3]

Simulating with protons

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SRIM damage calculation as a function of depth in Fe

Depth (μm)

Dos

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Smooth Damage Re-gion

2.9MeV protons @ 100μA

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

0.0E+00 2.0E+03 4.0E+03 6.0E+03 8.0E+03 1.0E+04 1.2E+04 1.4E+041.0E-06

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Energy Loss of 2.9MeV Fe ions in Fe

Energy Loss by Ionization

Energy Loss by Phonons

Depth (Ang)

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Ang

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0.00E+00 1.00E+05 2.00E+05 3.00E+05 4.00E+051.0E+00

1.0E+02

Energy Loss of 2.9MeV protons in Fe

Energy Loss by Ionization

Energy Loss by Phonons

Depth (Ang)

Ener

gy L

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eV/A

ng/I

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• 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.

Protons in the literature

• 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

Simulating with protons

Accelerator facilities are housed in the Medical Physics Building

at the University

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Cyclotron1-9MeV protons – 2.9MeV preferred set up~10μA beam current up to 2cm diameter beam sizeCapable of ~10-6 dpa/s in Iron which translates as ~0.05

dpa/dayTemperature control up to 600oC available now

Dynamitron 1-3MeV protons100s of μA beam current easily possible, absolute

maximum 2mAUp to 2cm diameter beam size

~10-5 - 10-4 dpa/s~1 dpa/day at 100 μA Temperature control in the works

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