• 방사성폐기물학회지
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• 제6권1호
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• pp.55-63
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• 2008

고준위폐기물처분장의 완충재 물질로 사용되는 팽윤성 점토는 방벽재로서 그 기능을 제대로 발휘하기 위해 오랫동안 물리 화학적으로 안정해야 한다. 팽윤성 점토의 장기건전성 관련인 자들을 검토하고, 처분장 성능에 대한 각 인자의 중요성을 평가하였다. 검토결과, 붕괴 열에 의한 온도상승, 지하수 화학, 콘크리트에 의한 pH 증가, 유기물과 미생물, 방사선 조사 및 기계적 교란은 완충재물질로서 팽윤성 점토의 장기건전성에 중요한 인자임을 확인하였다. 본 연구는 고준위폐기물 처분장에서 팽윤성 점토의 완충재 설계를 위한 기초자료로 유용하게 활용될 것이다.

• 방사성폐기물학회지
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• 제15권4호
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• pp.301-312
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• 2017

The concept of deep borehole disposal (DBD) for high-level nuclear wastes has been around for about 40 years. Now, the Department of Energy (DOE) in the United States (U.S.) is re-examining this concept through recent studies at Sandia National Laboratory and a field test. With DBD, nuclear waste will be emplaced in boreholes at depths of 3 to 5 km in crystalline basement rocks. Thinking is that these settings will provide nearly intact rock and fluid density stratification, which together should act as a robust geologic barrier, requiring only minimal performance from the engineered components. The Nuclear Waste Technical Review Board (NWTRB) has raised concerns that the deep subsurface is more complicated, leading to science, engineering, and safety issues. However, given time and resources, DBD will evolve substantially in the ability to drill deep holes and make measurements there. A leap forward in technology for drilling could lead to other exciting geological applications. Possible innovations might include deep robotic mining, deep energy production, or crustal sequestration of $CO_2$, and new ideas for nuclear waste disposal. Novel technologies could be explored by Korean geologists through simple proof-of-concept experiments and technology demonstrations.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.186-186
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• 2010

소자의 축소화에 따라 floating gate 형의 flash 메모리 소자는 얇은 게이트 절연막 등의 이유로, 이웃 셀 간의 커플링 및 게이트 누설 전류와 같은 문제점을 지니고 있다. 이러한 문제점을 극복하기 위해 charge trap flash 메모리 (CTF) 소자가 연구되고 있지만, CTF 메모리 소자는 쓰기/지우기 속도와 데이터 보존 성능간의 trade-off 관계와 같은 문제점을 지니고 있다. 최근, 이를 극복하기 위한 방안으로, 다른 유전율을 갖는 유전체들을 적층시킨 터널 절연막을 이용한 Tunnel Barrier Engineered (TBE) 기술이 주목 받고 있다. 따라서, 본 논문에서는 TBE 기술을 적용한 MIS-capacitor를 높은 유전율을 가지는 Al2O3와 HfO2를 이용하여 제작하였다. 이를 위해 먼저 Si 기판 위에 Al2O3 /HfO2 /Al2O3 (AHA)를 Atomic Layer Deposition (ALD) 방법으로 약 2/1/3 nm의 두께를 가지도록 증착 하였고, Aluminum을 150 nm 증착 하여 게이트 전극으로 이용하였다. Capacitance-Voltage와 Current-Voltage 특성을 측정, 분석함으로써, AHA 구조를 가지는 터널 절연막의 전기적인 특성을 확인 하였다. 또한, high-k 물질을 이용한 터널 절연막을 급속 열처리 공정 (Rapid Thermal Annealing-RTA) 과 H2/N2분위기에서 후속열처리 공정 (Post-RTA)을 통하여 전기적인 특성을 개선 시켰다. 적층된 터널 절연막은 열처리를 통해 터널링 전류의 민감도의 향상과 함께 누설전류가 감소됨으로서 우수한 전기적인 특성이 나타남을 확인하였으며, 적층된 터널 절연막 구조와 적절한 열처리를 이용하여 빠른 쓰기/지우기 속도와 전기적인 특성이 향상된 비휘발성 메모리 소자를 기대할 수 있다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.315-321
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• 2003

본 연구에서는 고준위 방사성폐기물 심지층 처분시설의 규모 및 layout 설정에 필요한 요소인 처분터널 및 처분공 간격에 대한 분석을 수행하였다. 이를 위하여, 기준 처분개념 및 공학적 방벽개념을 바탕으로 처분터널 및 처분공 단면을 설정하고, 단층 및 복층 개념에 따른 처분동굴의 구조적, 열적 안정성을 분석하였다. 분석 결과를 바탕으로 설계에 있어서 주요한 인자 중의 하나인 굴착량을 최소화할 수 있는 처분동굴 및 처분공 간격을 제안하였다. 향후, 부지에 대한 불확실성을 줄이기 위하여 정확한 부지특성 자료를 통한 상세한 분석이 필요하다.

• Environmental Engineering Research
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• 제24권4호
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• pp.608-617
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• 2019

The adsorption of sulfamethoxazole (SMX) onto a NaOH-activated pine wood-derived biochar was investigated via batch experiments and models. Surprisingly, the maximum adsorption capacity of activated biochar for SMX (397.29 mg/g) was superior than those of pristine biochars from various feedstock, but comparable to those of commercially available activated carbons. Elovich kinetic and Freundlich isotherm models revealed the best fitted ones for the adsorption of SMX onto the activated biochar indicating chemisorptive interaction occurred on surface of the activated biochar. In addition, the intraparticle diffusion limitation was thought to be the major barrier for the adsorption of SMX on the activated biochar. The main mechanisms for the activated biochar would include hydrophobic, π-π interactions and hydrogen bonding. This was consistent with the changes in physicochemical properties of the activated biochar (e.g., increase in sp² and surface area, but decrease in the ratios of O/C and H/C).

• Journal of Microbiology and Biotechnology
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• 제22권2호
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• pp.234-238
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• 2012

Recombinant Escherichia coli displaying organophosphorus hydrolase (OPH) was used to overcome the diffusion barrier limitation of organophosphorus pesticides. A new anchor system derived from the N-terminal domain of ice-nucleation protein from Pseudomonas syringae InaV (InaV-N) was used to display OPH onto the surface. The designed sequence was cloned in the vector pET-28a(+) and then was expressed in E. coli. Tracing of the expression location of the recombinant protein using SDS-PAGE showed the presentation of OPH by InaV-N on the outer membrane, and the ability of recombinant E. coli to utilize diazinon as the sole source of energy, without growth inhibition, indicated its significant activity. The location of OPH was detected by comparing the activity of the outer membrane fraction with the inner membrane and cytoplasm fractions. Studies revealed that recombinant E. coli can degrade 50% of 2 mM chlorpyrifos in 2 min. It can be concluded that InaV-N can be used efficiently to display foreign functional protein, and these results highlight the high potential of an engineered bacterium to be used in bioremediation of pesticide-contaminated sources in the environment.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3359-3366
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• 2021

An engineered barrier system (EBS) for the deep geological disposal of high-level radioactive waste (HLW) is composed of a disposal canister, buffer material, gap-filling material, and backfill material. As the buffer fills the empty space between the disposal canisters and the near-field rock mass, heat energy from the canisters is released to the surrounding buffer material. It is vital that this heat energy is rapidly dissipated to the near-field rock mass, and thus the thermal conductivity of the buffer is a key parameter to consider when evaluating the safety of the overall disposal system. Therefore, to take into consideration the sizeable amount of heat being released from such canisters, this study investigated the thermal conductivity of Korean compacted bentonites and its variation within a temperature range of 25 ℃ to 80-90 ℃. As a result, thermal conductivity increased by 5-20% as the temperature increased. Furthermore, temperature had a greater effect under higher degrees of saturation and a lower impact under higher dry densities. This study also conducted a regression analysis with 147 sets of data to estimate the thermal conductivity of the compacted bentonite considering the initial dry density, water content, and variations in temperature. Furthermore, the Kriging method was adopted to establish an uncertainty metamodel of thermal conductivity to verify the regression model. The R² value of the regression model was 0.925, and the regression model and metamodel showed similar results.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1511-1518
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• 2021

In most countries, the thermal criteria for the engineered barrier system (EBS) is set to below 100 ℃ due to the possible illitization in the buffer, which will likely be detrimental to the performance and safety of the repository. On the other hand, if the thermal criteria for the EBS increases, the disposal density and the cost-effectiveness for the high-level radioactive wastes will dramatically increase. Thus, fundamentals on the thermal behavior of the buffer under the elevated temperatures is of crucial importance. Yet, the behaviors at the elevated temperatures of the bentonite under groundwater-saturated conditions have not been reported to-date. Here, we have developed an in-situ synchrotron-based method for the thermal behavior study of the buffer under the elevated temperatures (25-250 ℃), investigated dspacings of the montmorillonite in the Korean bentonite (i.e., Ca-type) at dry and KURT (KAERI Underground Research Tunnel) groundwater-saturated conditions (KJ-ii-dry and KJ-ii-wet), and compared the behaviors with that of MX-80 (i.e., Na-type, MX-80-wet). The hydration states analyzed show tri-, bi-, and mono-hydrated at 25, 120, and 250 ℃, respectively for KJ-ii-wet, whereas tri-, mono-, and de-hydrated at 25, 150, and 250 ℃, respectively for MX-80-wet. The Korean bentonite starts losing the interlayered water at lower temperatures; however, holds them better at higher temperatures as compared with MX-80.

• 방사성폐기물학회지
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• 제19권4호
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• pp.469-477
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• 2021

Safe storage of spent nuclear fuel in deep underground repositories necessitates an understanding of the long-term alteration of metal canisters and buffer materials. A small-scale laboratory alteration test was performed on metal (Cu or Fe) chips embedded in compacted bentonite blocks placed in anaerobic water for 1 year. Lactate, sulfate, and bacteria were separately added to the water to promote biochemical reactions in the system. The bentonite blocks immersed in the water were dismantled after 1 year, showing that their alteration was insignificant. However, the Cu chip exhibited some microscopic etch pits on its surface, wherein a slight sulfur component was detected. Overall, the Fe chip was more corroded than the Cu chip under the same conditions. The secondary phase of the Fe chip was locally found as carbonate materials, such as siderite (FeCO₃) and calcite ((Ca, Fe)CO₃). These secondary products can imply that the local carbonate occurrence on the Fe chip may be initiated and developed by an evolution (alteration) of bentonite and a diffusive provision of biogenic CO₂ gas. These laboratory scale results suggest that the actual long-term alteration of metal canisters/bentonite blocks in the engineered barrier could be possible by microbial activities.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.134-134
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• 2011

High-k dielectric materials such as $HfO_2$, $ZrO_2$ and $Al_2O_3$ increase gate capacitance and reduce gate leakage current in MOSFET structures. This behavior suggests that high-k materials will be promise candidates to substitute as a tunnel barrier. Furthermore, stack structure of low-k and high-k tunnel barrier named variable oxide thickness (VARIOT) is more efficient.[1] In this study, we fabricated the $WSi_2$ nanocrystals nonvolatile memory device with $SiO_2/HfO_2/Al_2O_3$ tunnel layer. The $WSi_2$ nano-floating gate capacitors were fabricated on p-type Si (100) wafers. After wafer cleaning, the phosphorus in-situ doped poly-Si layer with a thickness of 100 nm was deposited on isolated active region to confine source and drain. Then, on the gate region defined by using reactive ion etching, the barrier engineered multi-stack tunnel layers of $SiO_2/HfO_2/Al_2O_3$ (2 nm/1 nm/3 nm) were deposited the gate region on Si substrate by using atomic layer deposition. To fabricate $WSi_2$ nanocrystals, the ultrathin $WSi_2$ film with a thickness of 3-4 nm was deposited on the multi-stack tunnel layer by using direct current magnetron sputtering system [2]. Subsequently, the first post annealing process was carried out at $900^{\circ}C$ for 1 min by using rapid thermal annealing system in nitrogen gas ambient. The 15-nm-thick $SiO_2$ control layer was deposited by using ultra-high vacuum magnetron sputtering. For $SiO_2$ layer density, the second post annealing process was carried out at $900^{\circ}C$ for 30 seconds by using rapid thermal annealing system in nitrogen gas ambient. The aluminum gate electrodes of 200-nm thickness were formed by thermal evaporation. The electrical properties of devices were measured by using a HP 4156A precision semiconductor parameter analyzer with HP 41501A pulse generator, an Agillent 81104A 80MHz pulse/pattern generator and an Agillent E5250A low leakage switch mainframe. We will discuss the electrical properties for application next generation non-volatile memory device.