Degree

Doctor of Philosophy (PhD)

Department

Geology & Geophysics

Document Type

Dissertation

Abstract

Understanding the potential processes of radionuclides released from nuclear waste forms is essential to the safe disposal and containment of nuclear waste. Iodoapatite, a potential waste form for radioiodine, was chosen as a model system to examine the impact by common aqueous anions on iodine release processes. Four semi-dynamic leaching tests were performed using 0.1 mol/L NaCl, Na2CO3, Na3PO4, and Na2SO4 solutions respectively under 90 °C, 1 bar, fixed S/V ratio 5/m (sample surface area to solution volume), and with 24-hour replacement of the leaching solutions. Solution analysis and surface characterization show that these ion-rich solutions accelerated the iodine release processes due to the increased ionic strength, reduced concentration coefficients of dissolved species, and elevated solution pH. Secondary phases produced by the experiments were observed at the leached surfaces. These produces were induced by ion-exchange, dissolution, and re-precipitation. This research suggests that maintaining neutral pH and low ion content in aqueous environments is imperative to ensure the safe disposal of radioactive iodine when contained by this apatite waste form.

Characterizing the behavior of petroleum-bearing fluids in natural reservoirs is challenging due to the heterogeneous composition of hydrocarbon systems. However, the fluid– rock interactions are important for recovering oil from the natural reservoirs. Molecular dynamics simulations were used to investigate the interactions of octane and octanethiol with kerogen and with calcite, respectively. To quantify their interactions, free energy surfaces were computed by umbrella sampling to obtain the minimum energy required to recover oil molecules from kerogen and from calcite surfaces. The effects of surface composition, oil molecular polarity, surface water, and size of the oil molecular cluster were examined through the calculations. The results suggest that (1) polar oil compounds require more energy to be recovered from the reservoir rocks than non-polar molecules, (2) isolated oil molecules or oil clusters of a smaller size are more difficult to be displaced than a larger size of molecular clusters, and (3) the presence of surface water reduces the energy required for oil recovery. This study provides an energetic perspective on the interfacial interactions for oil recovery in natural reservoirs.

Date

6-4-2020

Committee Chair

Wang, Jianwei

DOI

10.31390/gradschool_dissertations.5287

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