Intermediate energy proton irradiation: An experimental and analytical foundation for bulk radiation damage testing

Fusion and next-generation fission power plants will require thermal and structural materials to perform under new, extreme conditions. Among mechanical, thermal, and corrosion or plasma exposure challenges, materials near the core of fusion and fission power plants will need to survive heavy exposure to high energy neutrons, outside of our current operating experience with fission reactors. Understanding the evolution of mechanical properties during radiation damage is essential to the design and commercial deployment of these systems. However, existing irradiation test methods are either extremely slow or not able to predict macroscopic property changes. In some applications, the shortcomings of existing methods could be addressed by a new technique - intermediate energy proton irradiation (IEPI) - using beams of 10 - 30 MeV protons to rapidly and uniformly damage bulk material specimens before direct testing of engineering properties. However, IEPI has seen relatively little use, and there has been little published work exploring the role IEPI could play in the future of nuclear materials development. This thesis presents a foundation for the use of IEPI to study radiation damage for future reactor conditions. Modeling of damage and beam heating shows that IEPI can achieve accelerated dose rates of 0.1 - 1 DPA/day in bulk irradiated structural materials, and doses exceeding 1 DPA/day in high thermal conductivity metals like copper and tungsten. Activation analysis shows experimental time savings that can range from 86-99+% when compared to irradiation and cool-down for reactor irradiation experiments. Calculated recoil energy transfers highlight that average recoil energies can mimic those of fusion plasma facing components, which are nearly an order of magnitude above fast reactors. Transmutation analysis highlights the ability to emulate fusion helium production levels of 10-30 ppm for common metals, where fission reactors cannot. Specifically for tungsten irradiation, protons are able to induce damage without confounding solid transmutation levels such as the 5% rhenium/dpa of high flux reactors. A first-of-its-kind IEPI facility was built using 12 MeV protons and custom miniature tensile testing. Dose rates exceeding 0.1 DPA/day were demonstrated with temperature control of ±5 − 10∘C. Tensile testing was demonstrated to be reproducible to within 20 MPa and 0.05 strain in both irradiated and unirradiated samples. Proton irradiated inconel samples up to 0.003 dpa were compared to neutron irradiated samples and showed favorable matching in irradiation hardening. Proton irradiated copper samples up to 0.1 dpa showed hardening and loss of ductility that was approximately 50% of past reactor irradiations, suggesting the impact of disparate recoil energies. In total, IEPI is shown to be a viable bulk irradiation technique with particular relevance to fusion plasma facing materials and fusion-relevant helium generation.

Name thesis:degree_name

Doctoral

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Nuclear Science and Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2021

Author dc:creator

• Jepeal, Steven Joseph

Advisor dc:contributor.advisor

• Hartwig, Zachary

Statement dc:rights

• In Copyright - Educational Use Permitted
• Copyright MIT

Licence dc:rights.uri

• http://rightsstatements.org/page/InC-EDU/1.0/

Handle dc:identifier.uri

https://hdl.handle.net/1721.1/139940

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/139940