• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.330-335
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• 2017

The demand for electric motor fuel cells has surged in the automotive industry, leading to a recent increase in the demand for square aluminum cans used as fuel cell battery casings. The air vent located on the bottom of the rectangular battery casing prevents large explosions by intermittent pressure release prior to the accumulation of abnormally high pressures. Conventionally, the square cup battery casing is produced via six-step deep drawing, with the outer shape of the vent being manufactured by welding to the square battery casing. On the other hand, this study directly incorporated the air vent outlet into the bottom surface of the rectangular casing. The product of a coupled finite element analysis technique applying the thickness and contour generated from the square cup multi-step deep drawing formation analysis was used as the forging input shape. The results yielded increased prediction accuracy and the advanced prediction of defects, such as swelling and fracture. Based on the results of the initial analyses, two of the generated forging shapes were determined to be suitable, with the optimal forging shape being determined by molding analysis. The results presented here were validated by mold fabrication and a subsequent comparison of the actual and analytical results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3442-3447
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• 2014

A simple method to evaluate the hygroscopic characteristics of polymer of microelectronic plastic package is suggested. To evaluate the characteristics, specimens were prepared, and the internally absorbed moisture masses were measured as a function of the absorbing time and calculated numerically. The hygroscopic pressure ratio was calculated by heat transfer analysis supported by commercial FEM code because the hygroscopic diffusion equation has the same form as the heat transfer equation. The moisture masses were then summed by the self developed code. The nonconductive polymers had quite different characteristics for the different lots, even though they were the same products. The absorbed moisture mass variations were calculated for several different characteristics, and the optimal curve of the mass variation close to experimental data was selected, whose solubility and diffusivity were affected by the hygroscopic characteristics of the material. The method can be useful in the industrial fields to quickly characterize the polymer material of the semiconductor package because the fast correspondence is normally required in industry. The weight changes in the aluminum-nonconductive-polymer joint due to moisture absorption were measured. The deformed system was also measured using the Moire Interferometry system and compared with the results of finite element analysis.

• Clean Technology
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• v.23 no.4
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• pp.357-363
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• 2017

In this study, the supercritical carbon dioxide ($scCO_2$)/ n-butyl acetate (n-BA) co-solvent system was employed to remove an unexposed negative photoresist (PR) from the surface of a silicon wafer. In addition, the selectivity of the $scCO_2$/n-BA co-solvent system was confirmed for the unexposed and exposed negative PR. Optimum conditions for removal of the unexposed PR were obtained from various conditions such as pressure, temperature and n-BA ratio. The n-BA was highly soluble in $scCO_2$ without cloud point and phase separation in mostly experimental conditions. However, the $scCO_2$/n-BA co-solvent was phase separated at 100 bar, above $80^{\circ}C$. The unexposed and exposed PR was swelled in $scCO_2$ solvent at all experimental conditions. The complete removal of unexposed PR was achieved from the reaction condition of 160 bar, 10 min, $40^{\circ}C$ and 75 wt% n-BA in $scCO_2$, as measured by ellipsometry. The exposed photoresist showed high stability in the $scCO_2$/n-BA co-solvent system, which indicated that the $scCO_2$/n-BA co-solvent system has high selectivity for the PR removal in photo lithograph process. The $scCO_2$/n-BA co-solvent system not only prevent swelling of exposed PR, but also provide efficient and powful performance to removal unexposed PR.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.13 no.4
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• pp.283-293
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• 2015

The buffer is a key component of the engineered barrier system in a high-level radioactive waste (HLW) repository. The present study reviewed the requirements and functional criteria of the buffer reported in literature, and also based on the results, proposed an approach to establish a buffer concept which is applicable to an HLW repository in Korea. The hydraulic conductivity, radionuclide-retarding capacity (equilibrium distribution coefficient and diffusion coefficient), swelling pressure, thermal conductivity, mechanical properties, organic carbon content, and illitization rate were considered as major technical parameters for the functional criteria of the buffer. Domestic bentonite (Ca-bentonite) and, as an alternative, MX-80 (Na-bentonite) were proposed for the buffer of an HLW repository in Korea. The technical specifications for those proposed bentonites were set to parameter values that conservatively satisfy Korea's functional criteria for the Ca-bentonite and Swedish criteria for the Na-bentonite. The thickness of the buffer was determined by evaluating the means of shear behavior, radionuclide release, and heat conduction, which resulted in the proper buffer thickness of 0.25 to 0.5 m. However, the final thickness of the buffer should be determined by considering coupled thermal-hydraulic-mechanical evaluation and economics and engineering aspects as well.

• Journal of Radiation Protection and Research
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• v.31 no.1
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• pp.37-46
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• 2006

For the first step to develop a reference disposal container of spent fuel to be used in a deep geological repository, this paper examined safe dimensions of the disposal container on the points of nuclear criticality and radiation safety and mechanical structural safety and provided basic information for dimensioning the container and configuration of the container components, and establishing the favorable and safe disposal conditions. When the safety factor for stress due to the external loads (hydrostatic and swelling pressure) is taken as 2.0, the safe diameter of the filler material to provide enough container strength under the assumed external loads is found to be 112cm with 13cm spacing between inner baskets in PWR container. Also the thickness of the thinner section between the fuel basket and the surface of the cast insert is determined to be 150 mm. Regarding these dimensions of the container, the PWR fuel container is sketched to accommodate 4 square assemblies or 297 CANDU fuel 297 bundles (33 circle tubes x 9 stacks). However the top and bottom parts need to be checked again through the detail radiation shielding analysis with respects to the emplacement position and handling processes of the disposal container.

• Nuclear Engineering and Technology
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• v.20 no.2
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• pp.88-104
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• 1988

The FUel Rod Analysis(FURA) code is developed using two-dimensional finite element methods for axisymmetric and plane stress analysis of fuel rod. It predicts the thermal and mechanical behavior of fuel rod during normal and load follow operations. To evaluate the exact temperature distribution and the inner gas pressure, the radial deformation of pellet and clad, the fission gas release are considered over the full-length of fuel rod. The thermal element equation is derived using Galerkin's techniques. The displacement element equation is derived using the principle of virtual works. The mechanical analysis can accommodate various components of strain: elastic, plastic, creep and thermal strain as well as strain due to swelling, relocation and densification. The 4-node quadratic isoparametric elements are adopted, and the geometric model is confined to a half-pellet-height region with the assumption that pellet-pellet interaction is symmetrical. The pellet cracking and crack healing, pellet-cladding interaction are modelled. The Newton-Raphson iteration with an implicit algorithm is applied to perform the analysis of non-linear material behavior accurately and stably. The pellet and cladding model has been compared with both analytical solutions and experimental results. The observed and predicted results are in good agreement. The general behavior of fuel rod is calculated by axisymmetric system and the cladding behavior against radial crack is used by plane stress system. The sensitivity of strain aging of PWR fuel cladding tube due to load following is evaluated in terms of linear power, load cycle frequency and amplitude.

• Membrane Journal
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• v.21 no.4
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• pp.367-376
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• 2011

Huge amount of $CH_4$ mixtures has been emitted from landfills and organic wastes via anaerobic digestion. The recovery of high purity $CH_4$ from these gases has two merits: reduction of green house gases and production of renewable fuels. Membrane technology based on polymeric materials can be used in this application. In this study, asymmetric gas separation hollow fiber membranes were fabricated to develop the membrane-based bio-gas purification process. Polyethersulfone (PES) was chosen as a polymer materials because of high $CO_2$ permeability of 3.4 barrer and $CO_2/CH_4$ selectivity of 50[1]. Acetone was used as a non-solvent additive because of its unique swelling power for PES and highly volatile character. The prepared PES hollow fiber showed excellent separation properties: 36 GPU of $CO_2$ permeance and 46 of $CO_2/CH_4$ selectivity at optimized preparation conditions: 9wt% acetone content, 10cm air-gap and 4wt% PDMS coating processes. With the PES hollow fiber membranes developed, mixed $CO_2/CH_4$ test was done by changing various operating conditions such as pressures and feed compositions to meet the highest recovery of CH4 with 95% purity. High $CH_4$ recovery of 58 wt% was observed at 10 atm feed pressure for the 50 vol% of $CO_2$ in $CO_2/CH_4$ mixture.

• Korean Journal of Acupuncture
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• v.22 no.1
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• pp.7-21
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• 2005

Objectives : In the present study, the effect of electroacupuncture (EA) applied to SI6 and won-rak point on the ankle sprain model was examined. A common source of persistent pain in humans is the lateral ankle sprain. Methods : To model this condition, the rat's right ankle was bent repeatedly, overextending lateral ligaments, for 4 min under enflurane anesthesia. The rat subsequently showed swelling of the ankle and a reduced stepping force of the affected limb for the next several days. The reduced stepping force of the limb was presumably due to a painful ankle. EA was applied to the several acupuncture point on the contralateral forelimb for 30 min under gaseous anesthesia. After the termination of EA, behavioral tests measuring stepping force and Paw volume were Periodically conducted during the next 4 h and 18 h respectively. Results : EA applied to $SI_6$ with won-rak point produced more powerful improvement of stepping force of the sprained foot than to $SI_6$ alone lasting for at least 4 h. However, neigher $KI_4$ point nor $BL_{64}$ point produced any significant increase of weight bearing force. The improvement of stepping pressure was interpreted as an analgesic effect. The analgesic effect was specific to the acupuncture point since the analgesic effort on the ankle sprain pain model could not be mimicked by EA applied to $KI_4$ or $BL_{64}$. In addition, EA applied to $SI_6$ with won-rak combination point showed inhibitory effect on the paw edema induced by ankle sprain. Also, COX-2 protein expression increased by ankle sprain were suppressed by the EA stimulation. Conclusion : These data suggest that EA with won-rak combination point produces a more potent analgesic effect on the ankle sprain pain model in the rat and that EA with won-rak combination point induced anti-inflammatory effect through the suppression of COX-2 protein expression.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.221-242
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• 2021

A numerical study of the performance assesment of coupled thermo-hydro-mechanical (THM) processes in improved Korean reference disposal system (KRS⁺) for high-level radioactive waste is conducted using TOUGH2-MP/FLAC3D simulator. Decay heat from high-level radioactive waste increases the temperature of the repository, and it decreases as decay heat is reduced. The maximum temperature of the repository is below a maximum temperature criterion of 100℃. Saturation of bentonite buffer adjacent to the canister is initially reduced due to pore water evaporation induced by temperature increase. Bentonite buffer is saturated 250 years after the disposal of high-level radioactive waste by inflow of groundwater from the surrounding rock mass. Initial saturation of rock mass decreases as groundwater in rock mass is moved to bentnonite buffer by suction, but rock mass is saturated after inflow of groundwater from the far-field area. Stress changes at rock mass are compared to the Mohr-Coulomb failure criterion and the spalling strength in order to investigate the potential rock failure by thermal stress and swelling pressure. Additional simulations are conducted with the reduced spacing of deposition holes. The maximum temperature of bentonite buffer exceeds 100℃ as deposition hole spacing is smaller than 5.5 m. However, temperature of about 56.1% volume of bentonite buffer is below 90℃. The methodology of numerical modeling used in this study can be applied to the performance assessment of coupled THM processes for high-level radioactive waste repositories with various input parameters and geological conditions such as site-specific stress models and geothermal gradients.

• Tunnel and Underground Space
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• v.32 no.1
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• pp.59-77
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• 2022

Currently, the design reference temperature of the buffer material for disposing of high-level radioactive waste is less than 100℃, so if the heat dissipation capacity of the buffer material is improved, the spacings of the disposal tunnel and the deposition hole in the repository can be reduced. First of all, this study tries to analyze the criteria for thermal-hydraulic-mechanical performance of the buffer materials and to investigate the researches regarding the enhanced buffer materials with improved thermal conductivity. First, the thermal conductivity should be as high as possible and is affected by dry density, water content, temperature, mineral composition, and bentonite type. the organic content of the buffer material can have a significant effect on the corrosion performance of a canister, so the organic content should be low. In addition, hydraulic conductivity of the buffer material should be less than that of near-field rock and swelling pressure should be appropriate for buffer materials to function properly. For the development of enhanced buffer materials, additives such as sand, graphite, and graphite oxide are typically used, and a thermal conductivity can be greatly improved with a very small amount of graphite addition compared to sand.