• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3884-3897
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• 2024

This study investigates the creep behavior of bentonite-sand mixtures as potential buffer materials for low-level radioactive waste (LLW) repositories, with a specific case study in Taiwan. To assess the long-term hydro-mechanical properties, constant-volume swelling pressure, hydraulic conductivity, strain-controlled shear, and stress-controlled shear tests were conducted on MX80 and KV1 bentonite-sand mixtures. The experimental results indicate that MX80-sand 70/30 mixtures are prioritized as the buffer materials with 2.10 MPa swelling pressure and 1 × 10^-13 m/s hydraulic conductivity. However, the shear strength of mixtures was reduced by almost 50 % when fully saturated. Furthermore, this study proposed a novel stress-controlled direct shear apparatus to retrieve the creep model parameters. The numerical method based on the creep model efficiently supports and simulates the saturation process and creep displacement. The finite element method (FEM) result predicts that the buffer of both bentonite-sand mixtures will achieve an average degree of saturation of 95 % at the end of three decades and full saturation in 100 years. The simulated creep displacement results at key nodes suggest that both top and bottom parts in the buffer, assembled from MX80-sand 70/30 mixtures or KV1-sand 70/30 mixtures, will have almost equivalent values of 4 mm in the horizontal and 2 mm in the vertical directions eventually.

• Korean Journal of Materials Research
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• v.19 no.10
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• pp.544-549
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• 2009

Activated carbon (AC) with very large surface area has high capacitance per weight. However, such activation methods tend to suffer from low yields, below 50%, and are low in electrode density and capacitance per volume. Carbon NanoFibers (CNFs) had high surface area polarizability, high electrical conductivity and chemical stability, as well as extremely high mechanical strength and modulus, which make them an important material for electrochemical capacitors. The electrochemical properties of immobilized CNF electrodes were studied for use as in electrical double layer capacitor (EDLC) applications. Immobilized CNFs on Ni foam grown by thermal chemical vapor deposition (CVD) were successfully fabricated. CNFs had a uniform diameter range from 50 to 60 nm. Surface area was 56 m$^2$/g. CNF electrodes were compared with AC and multi wall carbon nanotube (MWNT) electrodes. The electrochemical performance of the various electrodes was examined with aqueous electrolyte of 2M KOH. Equivalent series resistance (ESR) of the CNF electrodes was lower than that of AC and MWNT electrodes. The specific capacitance of 47.5 F/g of the CNF electrodes was achieved with discharge current density of 1 mA/cm$^2$.

• Journal of the Korean earth science society
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• v.35 no.2
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• pp.104-114
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• 2014

The variation of acidity, conductivity, and ion components in precipitation depending on the dominant wind direction was investigated from January, 2009 to December 2009 in Busan, Korea. Both southwesterly and northeasterly winds were dominant in Busan area. The volume-weighted mean acidity showed pH 7, and the high conductivity indicated 200 ${\mu}scm^{-1}$ in westerly wind. The volume-weighted mean equivalent concentration showed higher value of $K^+$ and $Cl^-$ in all wind directions. The composition ratio of $NO{_3}^-/SO{_4}^{2-}$ showed over 3 in northerly wind. The neutralization factors have been found to have higher value for potassium ion in northeasterly, easterly, southwesterly, and westerly winds compared with different wind directions, which indicated significant neutralization of acidic components over the region by potassium. Also, the concentration of sea salt has been found over 800 ${\mu}sm^{-3}$ in northeasterly and southwesterly winds. Air masses passing through Manchuria, Inner Mongolia plateau, China, and Russia in spring, autumn, and winter covered Busan, Korea in northerly, westerly, and northwesterly winds. However, air masses passing through the ocean in summer covered Busan, Korea in easterly, northeasterly, and southwesterly winds. Therefore, the variation of acidity, conductivity, and ionic components contained in precipitation shows each seasonal characteristics with prevailing wind systems between the continental and coastal area in Busan, Korea.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1832-1837
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• 2011

This paper presents the optimal permanent magnet shape on the rotor of an interior permanent magnet motor to reduce the core losses and improve the performance. As permanent magnet has conductivity inherently, it causes huge amount of eddy current losses by the slot harmonics with concentrated winding. This loss is roughly 100 times larger than that of distributed winding in high speed operation and it cannot be ignored, especially on traction motors. Each eddy current loss on permanent magnet has been investigated in detail by using FEM(Finite Element Method) instead of EMCNM(Equivalent Magnetic Circuit Network Method) in order to consider saturation and non-linear magnetic property. Simulation-based DOE(Design Of Experiment) is also applied to avoid large number of analyses according to each design parameter and consider expected interactions among parameters. Consequently, the optimal design to reduce the core loss on the permanent magnet while maintaining or improving motor performance is proposed by an optimization algorithm using regression equation derived and lastly, the core loss reduction on the proposed shape of the permanent magnet is verified by FEM.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.168.1-168.1
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• 2010

본 연구에서는 기존 지중열교환기용 뒤채움재인 벤토나이트 그라우트의 대안으로 시멘트 그라우트의 물리적 역학적 특성을 평가하였다. 실내 시험을 통하여 시멘트 그라우트의 배합비 및 첨가재에 따라 열전도도와 유동성, 일축압축강도에 미치는 영향을 평가하였다. 또한, 실제 지중열교환기용 파이프 내 순환유체의 온도변화가 시멘트 그라우트의 재료적 안정성에 미치는 영향을 검토하기 위해 $-5^{\circ}C$와 $50^{\circ}C$를 한 주기로 하여 일축압축강도를 반복적으로 측정하였다. 냉난방 운전에 따른 시멘트 그라우트와 순환 파이프 접촉면의 양호한 부착성 유지 여부를 판단하기 위해 시멘트 그라우트에 HDPE 파이프를 삽입한 시료의 등가 투수계수를 Flexible wall permeameter를 이용하여 장기간 측정하였다. 순환유체의 온도변화 모사에 따른 일축압축강도는 주기가 반복될수록 강도가 감소하는 경향이 나타났다. HDPE파이프를 삽입한 시료의 등가 투수계수는 순환수의 온도에 따라 증감하다가 $1.02{\times}10^{-9}cm/sec$로 수렴하였다.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1684-1685
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• 2011

This paper presents a theoretical and numerical analysis for thermal isolation of silicon micro-structures, especially for a large size with poor thermal conductivity, as well as straightforward solution for such an issue. Additional metal patterns underneath the silicon structures effectively reduces the thermal isolation. Heat transfer mechanism is analyzed using an equivalent circuit of thermal network including plasma, a heat source, heat capacitors, and thermal resistances. The FEM simulation was carried out to investigate the temperature change of silicon micro-structures according to process time. The temperature of silicon micro-structures with 2 ${\mu}m$ thick chrome layer at a steady state is $86^{\circ}C$, an approximately 40% decrease from the silicon microstructure without thin metal ($122^{\circ}C$)

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1169_1170
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• 2009

This paper introduces insulator pollutant accumulate pattern in the tunnel of korea railroad. To accomplish this goal, effective sample collecting method was proposed for the first step. Dust at the surface was collected directly. Distilled water and brush was used while collecting. Through this method dust is easily and accurately collected. The second step is pollutant analysis. Several analyze item is selected such as quantity, conductivity, contact angle, Optical Microscope(OM), IR, Equivalent Salt Deposit Density(ESDD), and ICP-AES. The third step, best represent tunnel was selected considering location, length and natural surroundings. Also to consider the difference at inside the tunnel, several bracket insulators were selected along to the location. To make the result precise, above procedure was repeated several times at the same target. Finally relation among type of train, numbers of movement, surroundings, length will be considered in combination with the pollution. With this result pollute map for KORAIL could be accomplished and inspect period will be optimized case by case.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.6
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• pp.589-598
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• 1998

This study was conducted to investigate the chemical characteristics of Precipitation at Seoul, Yangpyong, Hongchon and Inje in the central part of Korean peninsula during the period from March 1994 to November 1997. The precipitation samples were collected by automatic wet-only sampler. The samples were analyzed for major anions (SO42-, NO3-, Cl-, F-) and cations(NH4+, Ca2+, Mg+, Na+, K+), in addition to acidity and electrical conductivity. The analytical instrument for water soluble ionic components was ion chromatography. The volume - weighted mean PH were 4.73, 4.87, 4.89 and 4.81 at Seoul, Yangpyong, Hongchon and Inje, respectively. The sums of cation concentrations was slightly greater than the sums of anion concentrations. Also, the highest ion component was SO42- in anions and NH4+ in cations. The mean equivalent ratios of SO42- to NO3- were found by 2.96, 2.71, 2.43 and 2.25 at Seoul, Yangpyong, Hongchon and Inje, respectively. The factor analysis was conducted in order to make the large and diverse data set as manageable levels and to qualitatively examine the relationship between the variables. It showed that major sources of pollutants in precipitation were from the anthropogenic in Seoul, the natural in Hongchon, and the anthropogenic and natural in Yangpyong and Inje.

• Proceedings of the KIEE Conference
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• 1999.11a
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• pp.1-3
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• 1999

EM (ElectroMagnetic) pump is used for the purpose of transporting liquid sodium coolant with electrical conductivity in the LMR(Liquid Metal Reactor). (In the present study, pilot EM pump has been designed by using of equivalent circuit method which is commonly employed to analyze linear induction machines for the test of removal of residual heat. The length and diameter of the pump have fixed values of 840 mm and 101.6 mm each by taking account of geometrical size of circulation loop for the installation of EM pump. Flowrate versus developing pressure is related from Laithwaite's standard design formula and the characteristic analyses of developing force and efficiency are carried out according to change of input frequency. From the characteristic curve, input frequency of 13 Hz is determined as the design frequency. On the other hand, The annular air gap size of 6.05 mm is selected not to bring about too much hydraulic loss. Resultantly design analysis makes pump have the electrical input of 604 VA and the hydrodynamical capacity of 1.3 bars and 40 l/min.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.292-293
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• 2006

We have Investigated dielectric properties depending on bias voltage in organic lightemitting diodes using 8-hydroxyquinoline aluminum($Alq_3$) as an electron transport and emissive material. We analyzed the dielectric properties of organic light emitting diodes using impedance characteristics measurement by the auto-balancing bridge technique and equivalent cirrcuit of ITO/$Alq_3$/Al. Impedance characteristics was measured complex impedance Z and phase ${\theta}$ in the frequency range of 40 [Hz] to $10^8$ [Hz]. We obtained complex electrical conductivity, dielectric constant, and loss tangent ($tan{\delta}$) of the device at room temperature. From these analyses, we are able to interpret a conduction mechanism and dielectric properties contributed by an interfacial and orientational polarization.