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Jeonghwan Hwang,Jung-Woo Kim 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2
Understanding the long-term geochemical evolution of engineered barrier system is crucial for conducting safety assessment in high-level radioactive waste disposal repository. One critical scenario to consider is the intrusion of seawater into the engineered barrier system, which may occur due to global sea level rise. Seawater is characterized by its high ionic strength and abundant dissolved cations, including Na, K, and Mg. When seawater infiltrates an engineered barrier, such dissolved cations displace interlayer cations within the montmorillonite and affect to precipitation/ dissolution of accessory minerals in bentonite buffer. These geochemical reactions change the porewater chemistry of bentonite buffer and influence the reactive transport of radionuclides when it leaked from the canister. In this study, the adaptive process-based total system performance assessment framework (APro), developed by the Korea Atomic Energy Research Institute, was utilized to simulate the geochemical evolution of engineered barrier system resulting from seawater intrusion. Here, the APro simulated the geochemical evolution in bentonite porewater and mineral composition by considering various geochemical reactions such as mineral precipitation/dissolution, temperature, redox processes, cation exchange, and surface complexation mechanisms. The simulation results showed that the seawater intrusion led to the dissolution of gypsum and partial precipitation of calcite, dolomite, and siderite within the engineered barrier system. Additionally, the composition of interlayer cation in montmorillonite was changed, with an increase in Na, K, and Mg and a decrease in Ca, because the concentrations of Na, K, and Mg in seawater were 2-10 times higher than those in the initial bentonite porewater. Further studies will evaluate the geochemical sorption and transport of leaked uranium-238 and iodine-129 by applying TDB-based sorption model.
Jeonghwan Hwang,Jung-Woo Kim 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1
In the engineered barrier system of deep geological disposal repository, complex physicochemical phenomena occur throughout the entire disposal time, consequently impacting the safety function. The bentonite buffer, a significant component of the engineered barrier system, can be geochemically altered due to the changes in host rock groundwater, temperature, and redox condition. Such changes may have direct or indirect effects on radionuclide migration in case of canister failure. Therefore, a modeling tool that accounts for coupled thermal-hydraulic-mechanical-chemical (THMC) processes is necessary for the safety assessment. To this end, the Korea Atomic Energy Research Institute (KAERI) has developed the APro, a modeling interface for conducting safety assessment of deep geological disposal repository. The APro considers coupled THMC processes that influence radionuclide migration. Here, the solute transport considering thermal and hydraulic processes are calculated using the COMSOL multi-physics, while geochemical reactions are carried out in PHREEQC. The two software are coupled using a sequential non-iterative operator splitting approach, and transport of non-water H, non-water O, and charge were additionally considered to enhance the coupling model stability. Finally, the applicability of APro to simulate long-term geochemical evolution of bentonite was demonstrated through benchmark studies to evaluate the effects of mineral precipitation/dissolution, temperature, redox, and seawater intrusion.
Jeonghwan Hwang,Won Woo Yoon,Weon Shik Han,Sungwook Choung,Jung-Woo Kim 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Multiple sorptive sites on natural illitic clays (e.g., frayed edge [FES], type II [TS], and planar sites [PS]) play an important role to diverse 137Cs immobilization in soil and aquifer environments. This study investigated the Cs sorption capabilities of 10 natural illitic clays at ranged Cs concentrations (1 ×10?7 to 1×10?3 mol·L?1) under various competing potassium concentration (distilled water to 1×10?1 mol·L?1). Additionally, multisite cation exchange model was performed to evaluate the best-fit sorption model and optimize the sorption capacities and affinities of multiple sorptive sites for Cs. Here, the experimental Cs sorption isotherms varied among 10 illtic clays, indicating different sorption capacities of Cs on illitic clays. The best-fit sorption model exhibited that variable Cs sorption of 10 illitic clays was significantly related to the sorption capacities at the FES (1.76 × 10?5 to 1.12×10?4 eq·kg?1), TS (1.59×10?3 to 9.76×10?3 eq·kg?1), and PS (2.14×10?2 to 1.51×10?1 eq·kg?1), respectively. The FES predominantly contributed to Cs sorption at low aqueous concentrations, whereas the TS and PS sorbed Cs at high concentrations. These sorption capabilities of multiple sorptive sites were correlated to illite contents and crystallinity of illitic clays, implicating that such parameters could be key factors to predict the Cs sorption for natural illitic clays in soil and aquifer environments. Finally, 1-D transport simulations represented that the severe Cs retardation occurred at low Cs concentration, implying that the FES predominantly affected to Cs transport in actual radioactive contamination sites (i.e., where low Cs concentration prevails), compared to the TS and/or PS.
Jeonghwan Hwang,Weon Shik Han,Jung-Woo Kim,Won Woo Yoon 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2
Montmorillonite plays a key role in engineered barrier systems in the high-level radioactive waste repository because of its large sorption capacity and high swelling pressure. However, the sorption capacity of montmorillonite can be largely varied dependent on the surrounding environments. This study conducted the batch simulation for U(VI) sorption on Na-montmorillonite by utilizing the cation exchange and surface complexation coupled (2SP-NE-SC/CE) model and evaluated the effects of physicochemical properties (i.e., pH, temperature, competing cations, U(VI) concentration, and carbonate species) on U(VI) sorption. The simulation demonstrated that the U(VI) sorption was affected by physicochemical properties: the pH and temperature relate to aqueous U(VI) speciation, the competing cations relate to the cation exchange process and selectivity, the U(VI) concentration relates to saturation at sorption sites. For example, the Kd (L kg?1) of Na-montmorillonite represented the largest values of 2.7×105 L kg?1 at neutral pH condition and had significantly decreased at acidic pH<3, showing non-linear and diverse U(VI) sorption at the ranged pH from 2 to 11. Additionally, the U(VI) sorption on montmorillonite significantly decreased in presence of carbonate species. The U(VI) sorption for long-term in actual porewater chemistry and temperature of high-level radioactive waste repository represented that the sorption capacity of Na-montmorillonite was affected by various external properties such as concentration of competing cation, temperature, pH, and carbonate species. These results indicate that geochemical sorption capacity of bentonite should be evaluated by considering both geological and aquifer environments in the high-level radioactive waste repository.
Jeonghwan Hwang,Weon Shik Han,Sungwook Choung,Wonwoo Yoon 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
Immobilization of dissolved Cs<SUP>+</SUP> is dominantly affected by geochemical sorption to illitic clays in aquifer environments. The illitic clays have multiple sorptive sites (e.g., frayed edge, type II, and planar sites), which cause variable Cs<SUP>+</SUP> immobilization. This study investigated the sorption capacities and contributions of multiple sorptive sites on illitic clays under various competing K<SUP>+</SUP> (DIW–1.0×10<SUP>-1</SUP> mol/L) and Cs<SUP>+</SUP> concentrations (1.0×10<SUP>−7</SUP>–1.0×10<SUP>−3</SUP> mol/L). Experimental results revealed that 10 illitic clays had diverse sorption isotherms for Cs<SUP>+</SUP> with varying Langmuir-Qmax (0.009–0.033 eq/kg). In addition, the competing K<SUP>+</SUP> disrupted Cs<SUP>+</SUP> sorption to illitic clays, decreasing Kd,Cs in the order of DIW<1.0×10<SUP>−3</SUP><1.0×10<SUP>−1</SUP> mol/L of K<SUP>+</SUP>. Multisite cation exchange model confirmed that the amount of sorbed Cs<SUP>+</SUP> was significantly linked to sorption capacities of multiple sorptive sites: frayed edge sites (2.30×10<SUP>−6</SUP>–1.06×10<SUP>−4</SUP> eq/kg), type II sites (2.30×10<SUP>−4</SUP>–4.80×10<SUP>−3</SUP> eq/kg), and planar sites (8.60×10<SUP>−3</SUP>–3.13×10<SUP>−2</SUP> eq/kg). The frayed edge sites predominantly sorbed Cs<SUP>+</SUP> at low Cs<SUP>+</SUP> concentrations, whereas the type II and planar sites contributed to Cs<SUP>+</SUP> sorption at relatively high concentrations. According to 1-D cation exchange transport simulations, the retardation factors ranged 1.26–125.78 depending on the types and capacities of multiple sorptive sites, implying that the sorption of individual sorptive sites plays an important role to Cs<SUP>+</SUP> immobilization in actual radioactive contamination sites.
Design and Implementation of Hadoop Based Smart Farm Integrated Management System
( Jeonghwan Hwang ),( Miok Kim ),( Hye-rim Lee ),( Sangyoung Lee ),( Banghun Kang ),( Yongbeen Cho ) 한국농업기계학회 2018 한국농업기계학회 학술발표논문집 Vol.23 No.1
We propose hadoop based smart farm integrated management system that efficiently collects smart farm big data generated through environmental sensor and greenhouse facilities installed in smart farm, and provides various big data services to farmers using collected smart farm big data. The proposed system consists of LoRA(Long Range) based smart farm data logger, hadoop based smart farm big data server and web server. The LoRA based smart farm data logger collects environmental data and facilities status data measured by smart farm devices such as sensor, controller and etc., and transmits these data the smart farm big data server via LoRA modem. The hadoop based smart farm big data server saves smart farm big data collected via the smart farm data logger to HDFS(Hadoop Distributed File System) periodically, and provides smart farm big data services through classification of saved data in real time and arrangement processing. The web server provides the analyzed results of the smart farm big data server to farmers via web or mobile. In this paper, we designed and developed components of the proposed smart farm integrated management system, and implemented to smart farm integrated control application and user(farmer) application to make it possible to monitor integrated smart farm environment, control integrated smart farm environment, serve smart farm productivity improvement model and etc.