ANALYZING ADVANCED COMPOSITE SHIELD MATERIALS FOR FUSION AND SPACE REACTOR APPLICATIONS

Author

Mediha Merve Karatas, University of Tennessee, KnoxvilleFollow

Date of Award

12-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

Steven John Zinkle

Committee Members

Steven John Zinkle, Khalid Hattar, David Donovan, David Sprouster

Abstract

Two feasibility issues associated with high performance composite radiation shields for nuclear energy systems were investigated. The first research thrust involved identification of sintering aids for reducing the sintering temperature of HfH₂-ceramic matrix in order to suppress hydrogen dissociative loss from the HfH₂ particles during consolidation. The second research thrust involved quantification of the impact of uniformly distributed incoherent hydride particles on the effective diffusion, solubility and permeability of hydrogen isotopes of composite radiation shields.

LiF was chosen as a sintering aid for ZrN and MgO ceramic matrix powders to investigate whether sintering enhancement could be achieved during spark plasma sintering (SPS). LiF additions up to 2%wt did not affect SPS sintering for ZrN whereas a strong reduction in sintering temperature occurred for MgO. The mechanisms responsible for the difference in sintering behavior of these two ceramics were investigated by modeling and advanced characterization techniques. The conventional hypothesis of enhanced consolidation due to LiF liquid phase sintering appears to be invalid since LiF doping did not result in sintering temperature reduction in ZrN, and did not strongly affect MgO sintering above and below the LiF melting temperature. An alternative mechanism is proposed based on enhanced self-diffusion due to creation of Schottky vacancies by the monovalent LiF dopant in the divalent ceramic matrix. Differences in effectiveness of LiF doping for MgO vs. ZrN are attributed to much lower LiF solubility in ZrN, with a corresponding reduction inSchottky vacancy production.

Hydrogen isotope permeation measurements on sintered MgO and metal matrix composite Fe-HfH₂ samples were obtained. The results were compared with model predictions considering H permeation in the metal or ceramic matrix and trapping of diffusing H isotopes at the incoherent particle-matrix interfaces of the distributed HfH₂ particles that can produce significant increases in effective solubility and decreases in effective diffusivity, with a resultant increase in effective permeability at low temperatures. An interfacial trap binding energy for H isotopes of ~1 eV and incoherent interface trap thickness of ~1% the matrix lattice plane spacing provided reasonable agreement between experimental measurement and model predictions of effective diffusivity and permeability in the composite.

Recommended Citation

Karatas, Mediha Merve, "ANALYZING ADVANCED COMPOSITE SHIELD MATERIALS FOR FUSION AND SPACE REACTOR APPLICATIONS. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/13608