Doctoral Dissertations
Date of Award
12-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Nuclear Engineering
Major Professor
Steven John Zinkle
Committee Members
Maik Kurt Lang, Khalid Hattar, Haixuan Xu
Abstract
Structural materials play a crucial role in both extending the operating lifetime of existing nuclear reactors and in developing new Gen IV reactors and fusion reactor concepts.
Irradiation can cause prominent damage to reactor concrete aggregates, which limits the operating lifetime of the existing nuclear reactors. To develop an improved understanding of irradiation effects in concrete, three mineral analogues of concrete aggregates (limestone, marble, and quartzite) were irradiated by 5.5 MeV He ions and 13 MeV Ni ions at room temperature. The role of knock-on damage and irradiation spectrum on amorphization, radiation-induced volume expansion (RIVE), and mechanical property changes are discussed. Moreover, the dose dependence of RIVE in quartz was found to exhibit a delay compared to the amorphization behavior. The superior irradiation resistance of calcite phase compared to quartz phase implies there could be advantages to using calcareous aggregates and lowering the usage of siliceous aggregates for concrete in nuclear power plants for extended operation beyond 60 years.
For fusion reactor and Gen IV reactor concepts with higher operating temperatures and doses, high temperature helium embrittlement (HTHE) is considered a major lifetime limit mechanism for potential structural materials. To study HTHE effects, 4.5 MeV He irradiations were performed on Haynes 244, 316L stainless steel (SS), and Fe-9%Cr with different He implantation rates and pre-deformation conditions, with and without elastic stress of ~100 MPa during irradiation at 750 °C. No obvious He implantation rate effect was observed within the ranges (25-250 appm/h) studied. Although elastic stress alone did not significantly accelerate HTHE, enhanced nucleation of GB cavities with increasing GB He concentrations was observed in 316L SS with increasing pre-existing dislocations. Although Haynes 244 after standard aging (STD) had high dislocation line density, it showed good HTHE resistance due to its high matrix precipitate sink strength. A very large GB cavity was observed in pre-deformed Fe-9%Cr, implies that it might also experience HTHE problem under plastic deformation. Therefore, this work highlights the pivotal role of plasticity on HTHE and the importance of including high density of matrix precipitates in both FCC and BCC alloys for good HTHE resistance.
Recommended Citation
Qi, Zehui, "Microstructural evolution in ion-irradiated minerals and alloys. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/13630