Degree

Doctor of Philosophy (PhD)

Department

Department of Mechanical and Industrial Engineering

Document Type

Dissertation

Abstract

The growing demand for nuclear power in the United States and worldwide is accountable for addressing the major concern of radioactive waste, involving the technical challenges of maintaining the nuclear fuel cycle and immobilizing high-level wastes for safe disposal in geological storage. The appropriate selection of waste forms for spent nuclear fuel such as fission products and radionuclides can be effective means for a feasible and sustainable nuclear fuel cycle. But highly volatile radionuclides such as iodine (129) are of specific concern due to its extraordinary long half-life (15.7 million years). Due to its poor solubility and high volatility at traditional glass processing temperatures (~1000 oC), iodine is not suitable for processing using traditional vitrification routes. As a result, significant researches have been done to develop a viable waste form for immobilizing iodine. Among the most proposed waste forms, apatite-based ceramics have been proposed as promising candidates for immobilization of iodine due to its high-level nuclear waste loading, high chemical stability, structure flexibility, promising thermal and radiational stability, and low leaching rate. In this study, we introduce the first reported instance of solid-state synthesis of barium vanado iodoapatite (Ba5(VO4)3I) by a high-energy ball milling machine and spark plasma sintering (SPS) technique. Various characterization tools were used to characterize the synthesized materials. Understanding the mechanism of releasing radionuclides stored in nuclear waste forms in different environments is also crucial for the secure removal of nuclear waste. The effect of aqueous environment on iodine release of SPS sintered barium iodoapatite was investigated by conducting semi-dynamic leaching tests on bulk samples. The experimental analysis revealed that the iodine release rate from iodoapatite is affected by the solution chemistry. Irradiation experiments were conducted by using energetic ions and electrons to simulate radiation effects by α-decay and β-decay events, respectively in order to understand the radiation tolerance of this synthesized apatite structure and the underlying physics for the design of advanced nuclear waste forms. The results indicated that the SPS-sintered pellets can have significantly enhanced radiation tolerance of the iodoapatite against displacive radiation-induced amorphization due to the improved crystallinity by the highly efficient sintering process.

Date

3-25-2021

Committee Chair

Lu, Fengyuan

Available for download on Thursday, March 14, 2024

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