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

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 [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: /j.jnucmat

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–

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 [3] Taken from Chris Hardie’s Dphil thesis, 2012 Oxford University Fe-6Cr [3]

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

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 275 o C and 3.2MeV protons at 360 o C 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 Image Copyright Phil Champion. This work is licensed under the Creative Commons Attribution-Share Alike 2.0 Generic Licence. To view a copy of this licence, visit or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA.  Cyclotron 1-9MeV protons – 2.9MeV preferred set up ~10μA beam current up to 2cm diameter beam size Capable of ~10 -6 dpa/s in Iron which translates as ~0.05 dpa/day Temperature control up to 600 o C available now  Dynamitron 1-3MeV protons 100s of μA beam current easily possible, absolute maximum 2mA Up to 2cm diameter beam size ~ 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