• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.19 no.1
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• pp.113-121
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• 2021

A safety assessment of radioactive waste repositories is a mandatory requirement process because there are possible radiological hazards owing to radionuclide migration from radioactive waste to the biosphere. For a reliable safety assessment, it is important to establish a parameter database that reflects the site-specific characteristics of the disposal facility and repository site. From this perspective, solubility, a major geochemical parameter, has been chosen as an important parameter for modeling the migration behavior of radionuclides. The solubilities were derived for Am, Ni, Tc, and U, which were major radionuclides in this study, and on-site groundwater data reflecting the operational conditions of the Gyeongju low and intermediate level radioactive waste (LILW) repository were applied to reflect the site-specific characteristics. The radiation dose was derived by applying the solubility and radionuclide inventory data to the RESRAD-OFFSITE code, and sensitivity analysis of the dose according to the solubility variation was performed. As a result, owing to the low amount of radionuclide inventory, the dose variation was insignificant. The derived solubility can be used as the main input data for the safety assessment of the Gyeongju LILW repository in the future.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.1
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• pp.1-9
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• 2013

The rare earth oxide wastes consisting of major 8 nuclides Y, La, Ce, Pr, Nd, Sm, Eu and Gd, are generated during the salt waste treatment of PyroGreen process. The final form of the rare earth is generated as the oxide state. In this study, six candidate glasses were developed to evaluate the feasibility for vitrifying the rare earth oxide wastes within the borosilicate glass system. The solubilities of the mixture of the rare earth oxide waste showed less than 25wt% at $1,200^{\circ}C$, less than 30wt% at $1,300^{\circ}C$, respectively. It means that solubility is increased with the temperature increment. The liquidus temperature of the homogeneous glass with 20wt% waste loading was determined as less than $950^{\circ}C$. In more than solubility of rare earth oxides glass, formation of rare earth-oxide-silicate crystal in glass-ceramic occurred as the secondary phase. As their viscosity at melting temperature $1,200{\sim}1,300^{\circ}C$ was less than 100 poise, electrical conductivity was higher than 1 S/cm, 20~25wt% waste loading glasses with good surface homogeneity are judged to have good operability in cold crucible induction melter. Other physicochemical properties of the developed glasses are going to be experimented in the future.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2019.05a
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• pp.287-288
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• 2019

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.19 no.3
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• pp.353-366
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• 2021

The solubilities of different multicomponent lanthanide oxide (Ln₂O₃) solid solutions including binary (Ln₁ and Ln₂ = La, Nd, Eu, or Tm), ternary (Ln₁, Ln₂, and Ln₃ = La, Nd, Eu, or Tm), and higher systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were studied after aging for four weeks at 60℃. Our recent study revealed that the phase transformations in binary ((La, Nd) and (La, Eu)) and ternary (La, Nd, Eu) systems are responsible for the formation of (La, Nd)(OH)₃, (La, Eu)(OH)₃, and (La, Nd, Eu)(OH)₃ solid solutions, respectively. The variations in the mole fractions of La³⁺, Nd³⁺, and Eu³⁺ in the sample solutions of these hydroxide solid solutions indicated that a thermodynamic equilibrium might account for the apparent La, Nd, and Eu solubilities. Conversely, the binary and ternary systems containing Tm₂O₃ as the heavy lanthanide oxide retained the oxide-based solid solutions, and their solubility behaviors were dominated by their congruent dissolutions. In the higher multicomponent system, the X-ray diffraction patterns of the solid phases, before and after contact with the aqueous phase indicated the formation of a stable oxide solid solution and their solubility behavior was explained by its congruent dissolution.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.4
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• pp.399-410
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• 2022

The solubility and species distribution of radionuclides in groundwater are essential data for the safety assessment of deep underground spent nuclear fuel (SNF) disposal systems. Americium is a major radionuclide responsible for the long-term radiotoxicity of SNF. In this study, the solubility of americium compounds was evaluated in synthetic groundwater (SynDB3), simulating groundwater from the DB3 site of the KAERI Underground Research Tunnel. Geochemical modeling was performed using the ThermoChimie_11a thermochemical database. Concentration of dissolved Am(III) in Syn-DB3 in the pH range of 6.4-10.5 was experimentally measured under over-saturation conditions by liquid scintillation counting over 70 d. The absorption spectra recorded for the same period suggest that Am(III) colloidal particles formed initially followed by rapid precipitation within 2 d. In the pH range of 7.5-10.5, the concentration of dissolved Am(III) converged to approximately 2×10^-7 M over 70 d, which is comparable to that of the amorphous AmCO₃OH(am) according to the modeling results. As the samples were aged for 70 d, a slow equilibrium process occurred between the solid and solution phases. There was no indication of transformation of the amorphous phase into the crystalline phase during the observation period.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2015.10a
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• pp.465-466
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• 2015

In this study, different amount of (fe(0)) were dissolve into different strength of phosphoric ($H_3PO_4$) acid and the optimum solubility was observed at 0.89M Fe(0) into 4M of $H_3PO_4$ acid. Different concentration of oxalic acid was added to determine the optimum precipitated condition. The dissolution kinetics of Fe(0) into $H_3PO_4$ acid was investigated at $40-50^{\circ}C$. The optimum Fe-oxalate precipitate was dried and thermal decomposition using DSC-TG was conducted. Approximately 52 wt(%) of oxalic acid was removed at $300^{\circ}C$. Iron oxides such as magnetite and hematite that may be formed on the surface of nuclear waste were also dissolved into the $H_3PO_4$ acid and the optimum solubility for magnetite is 0.005M while that for hematite is 0.02M in 8M $H_3PO_4$ acid, respectively.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2008.11a
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• pp.183-184
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• 2008

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.06a
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• pp.167-168
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• 2009

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2019.05a
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• pp.104-105
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• 2019

• Journal of Environmental Science International
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• v.13 no.1
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• pp.79-87
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• 2004

Esterification of soybean oil with methanol was investigated. First of all, liquid-liquid equilibriums for systems of soybean oil and methanol were measured at temperatures ranging from 40 to 65$^{\circ}C$. Profiles of conversion of soybean oil with time were determined from the glycerine content in reaction mixtures for the different kinds of catalysts, such as NaOH, CaO, Ca(OH)$_2$, MgO, Mg(OH)$_2$, and Ba(OH)$_2$. The effects of dose of catalyst, cosolvent and reaction temperature on final conversion were examined. Esterification of waste vegetable oil with methanol was investigated and compared to the case of soybean oil. Solubility of methanol in soybean oil was substantially greater than that of soybean oil in methanol. When the esterification reaction of soybean oil was catalyzed by solid catalyst, final conversion was strongly dependent on the alkalinity of the solid catalyst, and increased with the alkalinity of the metal. Hydroxides from the alkali metals were more effective than oxides. When Ca(OH)$_2$ was used for the esterification catalyst, maximum value of final conversion was measured at dose of 4％. When CHCl$_3$ as a cosolvent, was added into the reaction mixture of soybean oil which catalyzed by Ba(OH)$_2$, maximum value of final conversion was appeared at dose of 3％. When waste vegetable oil was catalyzed by NaOH and solid catalysts, high final conversion, over 90％, and fast reaction rate were obtained.