Title Page
Contents
Abstract 12
CHAPTER 1. INTRODUCTION 14
CHAPTER 2. OBJECTIVES 22
CHAPTER 3. BACKGROUND 23
3.1. Uranium (U) 23
3.2. Bentonite as the buffer material in the SNF repository 27
CHAPTER 4. MATERIAL AND METHODS 33
4.1. Material 33
4.1.1. Preparation of the WRK bentonite 33
4.1.2. Preparation of the U 34
4.2. Characterizations of the WRK bentonite 35
4.2.1. Analyses for the physical characteristics of the WRK bentonite 35
4.2.2. Analyses for the mineral and chemical characteristics of the WRK bentonite 38
4.2.3. Analyses for the structural characteristics of the WRK bentonite 40
4.3. The U batch experiments for the WRK bentonite 42
4.3.1. Adsorption batch experiment for the effect of the reaction time 42
4.3.2. Desorption batch experiment for effect of the reaction time 44
4.4. The U adsorption kinetic model studies for the WRK bentonite 46
4.4.1. Pseudo 1st-order model 46
4.4.2. Pseudo 2nd-order model 47
CHAPTER 5. RESULTS AND DISCUSSION 49
5.1. Characterizations of the WRK bentonite 49
5.1.1. Physical characteristics of the WRK bentonite 49
5.1.2. Mineral and chemical characteristics of the WRK bentonite 51
5.1.3. Structural characteristics of the WRK bentonite 56
5.2. Investigation for the U adsorption efficiency and desorption rate on the WRK bentonite 60
5.2.1. Effect of the pH 60
5.2.2. The U adsorption efficiency on the WRK bentonite at various pH conditions 62
5.2.3. The U desorption rate on the WRK bentonite at various pH conditions 64
5.3. Comparison of the WRK bentonite characterizations before and after the U adsorption 66
5.3.1. XRD analysis before and after the U adsorption 66
5.3.2. XRF analysis before and after the U adsorption 68
5.3.3. SEM-EDS analysis before and after the U adsorption 69
5.4. Comparison of the U adsorption kinetic models on the WRK bentonite at various pH conditions 70
5.5. Understanding of the U adsorption mechanisms on the WRK bentonite at various pH conditions 72
5.5.1. The U adsorption mechanism on the WRK bentonite at pH 3, 5, and 6 72
5.5.2. The U adsorption mechanism on the WRK bentonite at pH 7, 10, and 11 77
CHAPTER 6. CONCLUSIONS 80
REFERENCES 81
요약 97
Table 1. Physical parameters to identify the WRK bentonite properties 36
Table 2. Conditions of the U adsorption batch experiments for reaction time at various pH conditions 43
Table 3. Conditions of the U desorption batch experiments for reaction time at various pH conditions 45
Table 4. Comparison of physical properties between the WRK bentonite and the KJ-II bentonite 50
Table 5. Results of the XRF analysis for the WRK bentonite, GMZ bentonite, and MX-80 bentonite 53
Table 6. Results of the XRF analysis for the WRK bentonite before and after the U adsorption 68
Table 7. Parameter values of two kinetic models for the WRK bentonite at various pH conditions 71
Table 8. Aqueous U species at pH 3, 5, and 6 72
Figure 1. Portion of electric source for the electricity generation of the South Korea in 2021 15
Figure 2. Portion of radionuclides present in the SNF 16
Figure 3. Saturation status of the temporary SNF storage facility in the nuclear plants in the South Korea 17
Figure 4. Schematic of the DGR for the HLW 18
Figure 5. Schematic of radionuclides behavior scenario in the SNF repository 20
Figure 6. The U aqueous speciation in solution at various pH conditions 25
Figure 7. Relative speciation (%) of carbon dioxide (CO₂), bicarbonate (HCO₃⁻), and carbonate (CO₃²⁻) in solution as a function of pH 25
Figure 8. The behavior of the U species released from SNF 26
Figure 9. Schematic of the typical montmorillonite structure 27
Figure 10. Schematic microstructure of the montmorillonite particles 28
Figure 11. The swelling property of the bentonite 29
Figure 12. Schematic of typical U adsorption mechanisms for the montmorillonite in the bentonite 30
Figure 13. The powdered the WRK bentonite (<150 µm in diameter) 33
Figure 14. Definition of parameters to assess physical properties of the WRK bentonite 35
Figure 15. Schematic for the swelling index measurement (KS K 0764, 2015) 37
Figure 16. Schematic of the U adsorption batch experiments for reaction time at various pH conditions 43
Figure 17. Schematic of the U desorption batch experiments for reaction time at various pH conditions 45
Figure 18. Schematic of the physical adsorption mechanism derived by the pseudo 1st-order model 47
Figure 19. Schematic of the chemical adsorption mechanism derived by the pseudo 2nd-order model 48
Figure 20. Result of the XRD analysis for the WRK bentonite 51
Figure 21. Result of the zeta potential analysis for the WRK bentonite 54
Figure 22. Results of the SEM analysis for the WRK bentonite (a: 5.00 kx; b: 30.00 kx) 56
Figure 23. Result of the TEM analysis for the WRK bentonite 56
Figure 24. Result of the FTIR analysis for the WRK bentonite 58
Figure 25. Result of the FTIR analysis for the GMZ bentonite 58
Figure 26. Results of the U adsorption efficiency on the WRK bentonite at various pH conditions (the reaction time of 48 h) 61
Figure 27. Results of the U adsorption efficiency on the WRK bentonite at various pH conditions 63
Figure 28. Results of the U desorption rate on the WRK bentonite at various pH conditions 65
Figure 29. Results of the XRD analysis for the WRK bentonite before and after the U adsorption 67
Figure 30. Results of the SEM-EDS analysis for the WRK bentonite before and after the U adsorption 69
Figure 31. Plots of the experimental U adsorption results on the pseudo 2nd-order model at various pH conditions 71
Figure 32. Results of the XRD analysis for the WRK bentonite before and after the U adsorption at pH 3 and 5 73
Figure 33. The pH changes of the supernatants before and after the U adsorption at pH 3, 5, and 6 74
Figure 34. The U adsorption mechanisms on the WRK bentonite at pH 3, 5, and 6 75
Figure 35. The U adsorption efficiency on the WRK bentonite at pH 3, 5, and 6 76
Figure 36. The U adsorption mechanisms on the WRK bentonite in presence of carbonate 78
Figure 37. Schematic of the formation of the anion U-hydroxyl complex 79
Figure 38. The U adsorption mechanisms on the WRK bentonite in absence of carbonate 79