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Sungjune Sohn,Keunyoung Lee,Min Ku Jeon 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2
Various dry active wastes (DAWs) have been accumulated in nuclear power plants since the DAWs are mostly combustible. KAERI has developed a thermochemical treatment process for the used decontamination paper as an operational waste to substitute for incineration process and to decontaminate radionuclides from the DAWs. The thermochemical process is composed of thermal decomposition in a closed vessel, chlorination of carbonated DAWs, separation of soluble chlorides captured in water by hydroxide precipitation, and immobilization of the precipitate. This study examined the third and fourth steps in the process to immobilize Co-60 by fabricating a stable wasteform. Precipitation behaviors were investigated in the chloride solution by adding 10 M KOH. It was shown that the precipitates were composed of Mg(OH)2 and Al(OH)3. Then, the glass-ceramic wasteform for the precipitates were produced by adding additive mixtures in which silica and boron oxide were blended with various ratios. The wasteform was evaluated in terms of volume reduction ratio, bulk density, compressive strength, and leachability.
Immobilization of C-14 Waste by Cement Wasteform
Sungjune Sohn,Hyung-Ju Kim,Maengkyo Oh,Keunyoung Lee 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Radioactive carbon, C-14, can be generated by the neutron capture reaction of O-17 during the nuclear power plant operation. Since C-14 is classified as an intermediate level waste radionuclide, it is required that an effective separation process for C-14. C-14 is mainly absorbed on activated carbon in the air cleanup system. Therefore, the main generation source of C-14 during the nuclear power plant decommissioning is spent activated carbon. KAERI has been developing the treatment of spent activated carbon. In this process, C-14 can be desorbed as a gaseous oxide form from the spent activated carbon at high-temperature vacuum conditions. This radioactive carbon dioxide can be captured into alkaline earth metal incorporated glass and can be transformed into carbonate form. However, the carbonate (e.g. CaCO3 and SrCO3) is dispersive. When the radioactive carbonates are disposed into a geological repository, they should be immobilized to remove future uncertainty. This study examined the stabilization/immobilization of the radioactive carbonates by the cement hydration process. Cement wasteform incorporated with calcium carbonate and strontium carbonate was produced under various waste loading (e.g. 20wt%, 40wt%, and 60wt% of CaCO3 and SrCO3, respectively). Then we evaluated mechanical and chemical durability by measuring compressive strength and leachability according to standard test methods specified in the waste acceptance criteria of the Gyeongju low and intermediate level waste repository (WAC-SIL-2022-1). Also, microstructure and thermal characteristics were investigated by SEM-EDS and TGA analysis.
Sohn, Sunyoung,Lee, Changhyun,Jung, Sungjune,Kim, Hwa-Min American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.11
<P>To improve the hydrophilicity of SiO2 and SnO2 binary metal oxide nano-composite films, the effect of the deposition rate and composition ratio during facing target sputtering was investigated. The wettability of the SiO2 and SnO2 films was measured by water contact angle, because wettability affects self-cleaning and anti-fog properties. A (SiO2)(30)(SnO2)(70) film fabricated with optimized processing conditions showed a high transmittance over 85% in the visible range, which is an important parameter for industrial applications such as for automobiles, windows, and mobile phones. We confirmed that the composition ratio and oxygen content are independent of the material's hydrophilicity, which instead is highly dependent on the deposition ratio.</P>
Highly-twisted pyrene derivative for pure-blue organic light emitting diodes
Sohn, Sunyoung,Wu, Xinwei,Park, Kwang Hun,Ahn, Hyungju,Jung, Sungjune,Kwon, Soon-Ki,Kim, Yun-Hi Elsevier 2019 Journal of industrial and engineering chemistry Vol.78 No.-
<P><B>Abstract</B></P> <P>The new fluorescent blue host material, 1,3,6,8-tetrakis(2,5-dimethylbiphenyl-4-yl)pyrene (BD4PP), was synthesized for pure-blue organic light-emitting diodes (OLEDs). BD4PP has highly twisted and steric structure for efficient fluorescence, and has high thermal stability of 492°C. BD4PP host doped with 5wt.% 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) or 5wt. % 1,4-bis[2-(3-<I>N</I>-ethylcarbazoryl)-vinyl]benzene (BCzVB) showed high device efficiencies due to wide bandgap (˜ 3.1eV) and electron-rich host. An OLED with the BD4PP:BCzVB emitter showed higher current and external quantum efficiencies of 4.41cd/A and 3.80% with color coordinates (0.16, 0.13) compared to those of the BD4PP:BCzVBi (3.63cd/A and 3.62%) with color coordinates (0.16, 0.11) and non-doped BD4PP (2.01cd/A and 1.61%) with color coordinates (0.18, 0.13).</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Park, Jaeyeong,Choi, Sungyeol,Sohn, Sungjune,Kim, Kwang-Rag,Hwang, Il Soon The Electrochemical Society 2014 Journal of the Electrochemical Society Vol.161 No.3
<P>This study examines zirconium electrochemical redox behaviors in LiCl-KCl-ZrCl4 at 500 degrees C. Cyclic voltammetries are conducted with tungsten working and counter electrode. Four oxidation peaks and three reduction peaks are observed and redox reactions which could contribute to each peak are determined based on electrolysis results and peak height changes of cyclic voltammogram according to scan rates and ranges. Zr(IV) could be reduced into ZrCl when cathode potential is more negative than -1.1 V (vs. 1 wt% Ag/AgCl) and ZrCl would be reduced into Zr metal if cathode potential become more negative than -1.2 V. ZrCl and Zr metal could be oxidized into mainly Zr(IV) in LiCl-KCl-ZrCl4(1 wt%). Zr(II) could exist in the molten salt but the concentration might be small because heights of cyclic voltammogram peaks related to redox reactions of Zr(II) are relatively small. Based on cyclic voltammetry results, suggestions for the electrorefining of irradiated Zircaloy-4 cladding are proposed. High cathodic current density is preferred to recover zirconium as a metal state and low anodic current density is required to prevent dissolution of elements which are more reductive than zirconium. (C) 2013 The Electrochemical Society. All rights reserved.</P>
Reference Electrode at Molten Salt: A Comparative Analysis of Electroceramic Membranes
Yoon, Seokjoo,Kang, Dokyu,Sohn, Sungjune,Park, Jaeyeong,Lee, Minho,Choi, Sungyeol Korean Radioactive Waste Society 2020 방사성폐기물학회지 Vol.18 No.2
A reference electrode is important for controlling electrochemical reactions. Evaluating properties such as the reduction potential of the elements is necessary to optimize the electrochemical processes in pyroprocessing, especially in a multicomponent environment. In molten chloride systems, which are widely used in pyroprocessing, a reference electrode is made by enclosing the silver wire and molten salt solution containing silver chloride into the membranes. However, owing to the high temperature of the molten salt, the choice of the membrane for the reference electrode is limited. In this study, three types of electroceramic, mullite, Pyrex, and quartz, were compared as reference electrode membranes. They are widely used in molten salt electrochemical processes. The potential measurements between the two reference electrode systems showed that the mullite membrane has potential deviations of approximately 50 mV or less at temperatures higher than 650℃, Pyrex at temperatures lower than 500℃, and quartz at temperatures higher than 800℃. Cyclic voltammograms with different membranes showed a significant potential shift when different membranes were utilized. This research demonstrated the uncertainties of potential measurement by a single membrane and the potential shift that occurs because of the use of different membranes.
Park, Jaeyeong,Choi, Sungyeol,Sohn, Sungjune,Hwang, Il Soon The Electrochemical Society 2017 Journal of the Electrochemical Society Vol.164 No.12
<P>To achieve a better understanding of Zircaloy-4 electrorefining in LiCl-KCl at 500 degrees C, redox behaviors of Zr, Sn, Cr, Fe and Co, were examined by cyclic voltammetry using tungsten working and counter electrode. Zr metal can be produced from Zr4+ through two step reduction and ZrCl is generated as an intermediate product. As ZrCl4 concentration decreases, ZrCl would be easily reduced into Zr metal. In addition, Zr2+ formation would be unlikely at low ZrCl4 concentration. The redox reactions of the other elements are much simpler than Zr. The reduction of Zr4+ into ZrCl was close to irreversible but the reduction reactions of the other elements are close to reversible. The diffusion coefficients and apparent reduction potentials were calculated using equations for a reversible or irreversible reaction. The diffusion coefficients are in the order of 10(-9) m(2)/s and Zr is less reductive than other elements. (C) 2017 The Electrochemical Society. All rights reserved.</P>