• Tunnel and Underground Space
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• 제31권5호
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• pp.333-359
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• 2021

Gases such as hydrogen and radon can be generated around the canister in high-level radioactive waste disposal systems due to several reasons including the corrosion of metal materials. When the gas generation rate exceeds the gas diffusion rate in the low-permeability bentonite buffer, the gas phase will form and accumulate in the engineered barrier system. If the gas pressure exceeds the gas entry pressure, gas can migrate into the bentonite buffer, resulting in pathway dilation flow and advective flow. Because a sudden occurrence of dilation flow can cause radionuclide leakage out of the engineered barrier of the radioactive waste disposal system, it is necessary to understand the gas migration behavior in the bentonite buffer to quantitatively evaluate the long-term safety of the engineered barrier. Experimental research investigating the characteristics of gas migration in saturated bentonite and research developing numerical models capable of simulating such behaviors are being actively conducted worldwide. In this technical note, previous gas injection experiments and the numerical models proposed to verify such behaviors are introduced, and the future challenges necessary for the investigation of gas migration are summarized.

• Clean Technology
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• 제19권1호
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• pp.38-43
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• 2013

Vapor adsorption of hydrocarbon has been studied for stabilization after drying low-rank coal. The surface characteristics and the propensity of spontaneous combustion were observed for stabilized coal which was maintained with hydrocarbons as stabilizer at several conditions of residence time and temperature. Surface area of micropores in coal mainly decreased after vapor adsorption. As residence time and temperature of adsorption process increased, the propensity of spontaneous combustion decreased. The type of hydrocarbons did not effect on the propensity of spontaneous combustion. As the analysis results of this work, the amount of hydrocarbon adsorbates required to stabilize dried coal was 0.5 wt% or less of coal, and the stabilizing effect was induced by adsorption of low-molecular-weight hydrocarbons.

• Analytical Science and Technology
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• 제14권4호
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• pp.317-323
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• 2001

Dissolution procedures of Monsanto catalyst which has been used to produce acrylronitrile by ammoxidation of propylene have been studied. Optimum dissolution condition of the catalyst supported on silica was obtained by microwave digestion system with mixed of HCl, HF and $H_2O_2$. When a safety device was activated by increased pressure in microwave vessel, Bi, Fe, Mo, Sb and U were not volatilized even though silica was volatilized as $SiF_4$. Quantification results by this method were $SiO_2$ $50.5{\pm}0.4%$, $Sb_2O_3$ $29.6{\pm}0.6%$, $UO_2$ $10.2{\pm}0.1%$, $Fe_2O_3$ $6.1{\pm}0.1%$, $MoO_3$ $0.73{\pm}0.01%$ and $Bi_2O_3$ $0.49{\pm}0.01%$ by ICP-AES and the relative error was within ${\pm}10%$ except bismuth.

• Korean Journal of Materials Research
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• 제12권8호
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• pp.624-633
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• 2002

In order to improve the hydrogen storage capacity and the activation properties of the hydrogen storage alloys, the rare-earth metal alloy series, MmN $i_{4.5}$M $n_{0.5}$Z $r_{x}$(x=0, 0.025, 0.05, 0.1), are prepared by adding excess Zr in MmN $i_{4.5}$M $n_{0.5}$ alloy. The various parts in hydrogen storage vessel consisted of copper pipes reached the setting temperature within 4~5 minutes after heat addition, which indicated that storage vessel had a good heat conductivity required in application. The performance test on storage vessel filled with rare-earth metal alloys of 1000 gr was also conducted after hydrogen charging for 10 min at $18^{\circ}C$ under 10 atm. It showed that the average capacity of discharged hydrogen volume was found to be for $MmNi_{4.5}$ $Mn_{0.5}$ and $MmNi_{4.5}$ $Mn_{x}$ 0.5/$Zr_{samples}$ indicated that the released amount of hydrogen for this $AB_{5}$ type alloys was more than 92 % of theoretic value, and also it was found that the optimum discharging temperature for obtaining an appropriate pressure of 3 atm was determined to be $V^{\circ}C$ for $MmNi_{4.5}$ $Mn_{0.5}$$Zr_{x}$(x=0, 0.025, 0.05, 0.1) hydrogen storage alloys. The released amount of these hydrogen storage samples was 125 $\ell$ , 122.4 $\ell$ and 108.15 $\ell$/kg for $MmNi_{4.5}$ $Mn_{0.5}$ $Zr_{0.025}$ $MmNi_{4.5}$M $n_{0.5}$Z $r_{0.05}$, and MmN $i_{4.5}$ Mn_0.5$Zr_{0}$, at $70^{\circ}C$ respectively. Amount of the 2nd phases increase with increase on Zr contents in $MmNi_{4.5}$$Mn_{0.5}$ $Zr_{ 0.1}$/ alloy. This phenomenon indicates that$ ZrNi_3$ in $MmNi_{4.5}$ $Mn_{0.5}$ $Zr_{x}$ / phase, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage. As the Zr contents increase, the activation time and the plateau pressure decreases and sloping of the plateau pressure increases.creases.eases.s.

• Journal of Hydrogen and New Energy
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• 제9권4호
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• pp.169-176
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• 1998

An experimental study on effect of vapor-cooled heat stations in a 5.5 liter cryogenic vessel has been performed. The cryogenic vessel is made of stainless steel of thickness of 1mm and insulated by the combined insulation of vacuum, MLI(multi-layer insulation) and vapor-cooled radiation shield. Vapor-cooled heat stations are also constructed based on the 1-dimensional thermal analysis to reduce the heat inleak through a filling tube. Thermal analysis indicates that the vapor-cooled heat stations can substantially enhance the performance of vessel for cryogenic fluids with high $C_p/h_{fg}$ where $C_p$ the specific heat and $h_{fg}$ the heat of vaporization, such as $LH_2$ and LHe. The experimental results for $LN_2$ shows that the total heat inleak into inner vessel consists of 14% radiation and 86% conduction through the filling tube. Therefore, it is expected that the conduction heat in leak of the vessel for high $C_p/h_{fg}$ cryogenic fluids can be significantly reduced. powders. The amount of copper coating was 20wt%. In order to examine corrosion behavior of the electrodes, the corrosion current and the current density, in 6M KOH aqueous solution after removal of oxygen in the solution, were measured by potentiodynamic and cyclic voltamo methods. The results showed that Co in the alloy increased corrosion resistance of the electrode whereas Ni decreased the stability of the electrode during the charge-discharge cycles. The electrode used Si sealant as a binder showed a lower corrosion current density than the electrode used PTFE and the electrode used Cu-coated alloy powders showed the best corrosion resistance.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.119.1-119.1
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• 2016

크라이오 워터펌프(CWP)는 크라이오 펌프(CP)와 달리 10 K 활성탄 어레이는 장착하지 않고 100 K 정도로 냉각시킨 배플만을 사용하여 물의 배기속도를 최적화 하는 데 초점을 맞춘 진공펌프다. 용기 압력이 10-9 mbar 대가 될 때까지는 잔류기체의 90% 이상이 수분이므로 다른 기체들의 배기 보다는 물을 잘 배기하는 것이 배기시간을 단축하고 도달 진공도를 낮추는 첩경이라는 아이디어에 근거를 두고 있다. CWP는 물 흡착확률을 거의 1에 가깝게 만들어서 오리피스 컨덕턴스에 육박하는 이상적인 펌프를 제작할 수 있지만 용도상 직부형(close type), 통과형(in-line type) 및 내장형(in-vessel type) 등 세 가지 다른 형태에 따라 성능도 약간씩 다르다. CWP는 모든 기체에 반응하는 정통적인 CP에 비해 훨씬 간단하고 저렴하게 만들 수 있으면서도 진공 시스템에 큰 영향을 미칠 수 있지만 물 이외의 기체들을 배기할 펌프가 필요하다는 측면에서 활용에 제약이 있다. 만일 TMP를 이미 사용하고 있거나 작은 TMP를 추가로 달아서 충분히 작동이 가능한 시스템이면서 수분 발생이 많은 곳이나, 또 활성탄의 오염이나 산소 분위기 등 CP 투입이 꺼려지는 환경이라면 CWP 사용이 좋은 선택이 될 수 있다. CWP의 물 배기용량은 CP의 알곤이나 질소 배기용량에 준하는 크기로 0.5g/cm2 이상임이 실험적으로 입증되었다. 따라서 일반적인 상황에서 정상 작동시 대부분의 기체는 TMP로 배출하고 잔류 수분만 포집하므로 CP처럼 주기적인 재생이 필요 없다. 필요하다면 CWP는 금속 표면에 응축된 물을 드라이펌프 작동만으로 쉽게 제거할 수 있고 혹시 오염 물질이 붙어도 세척이 용이하다. 이런 사용상 융통성과 여러 가지 장점에도 불구하고 그동안 물배기에 대한 인식이 미흡하고, 또 부수적이고 추가적인 비용이 드는 것으로 생각되어 주목을 받지 못했지만 디스플레이와 반도체 산업을 필두로 물 분압을 낮추고 생산수율을 높이는 것에 점점 더 관심이 높아지면서 CWP에 대한 수요도 높아지고 있다. 본 보고에서는 20인치 통과형 CWP를 만들고 14인치 TMP에 얹어 복합 진공배기시스템을 구성한 후 물 배기속도와 알곤, 질소 및 수소 배기속도를 측정하고 예측치와 비교했다. 아울러 물 배기용량 측정 및 CWP의 온도제어와 펌프재생 특성 평가 결과도 정리했다.

• Microbiology and Biotechnology Letters
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• 제19권2호
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• pp.179-185
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• 1991

We examined optimum culture conditions of Rhodopseudomonas sphaeroides B5 for effective utilization of substrate and sunlight for hydrogen production. The optimum concentration range of DL-lactate as electron donor for hydrogen production by resting cells was from 5 to 50mM, and optimun CN ratio (lactate/glutamat) for maintenence of hydrogen production activity by growing cultures was from 5 to 6. Hydrogen production by the cultures of low cell density (0.36mg/ml dry cells) was saturated with 10 Klux light intensity. Under constant illumination of 50Klux which was set up as the average medium value of annual variation of sunlight intensity, hydrogen production with various cell densities in the culture resulted in highest production rate (132${\mu}$l/hr/mg dry cells) up to 0.64mg/ml dry cells. However, the amount of total hydrogen production was saturated with cell density of 2.1mg/ml dry cells. In addition to these, the optimum inner thickness pervious to light of the culture vessel for hydrogen production which was measured under sunlight was 5 cm.

• Journal of the Korean Institute of Gas
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• 제1권1호
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• pp.1-6
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• 1997

In case of using the electrical apparatus in the hazardous atmosphere which exist flammable gas mixtures, There is a dangerosity of gas explosion accident by the electrical spark. The most general method to prevent the explosion by the spark is to use the flame-proof type electrical apparatus to isolate the ignition source. from the flammable atmosphere. But actualy it is impossible to isolate the ignition sources from the atmosphere. So it was needed to find the safe gap which prevent ignition of flammable atmosphere by transmission of flame or heat when a flammable gas mixture exploded inside the apparatus. In this study we tried to find the maximum experimental safe gap(MESG) of $H_2$-air, and $CH_4$-air mixtures by using the 8 litre spherical vessel with 25mm flange. The experiment parameter were ignition position, concentration and initial pressure before explosion. From the experiment the ignition position was affected to the MESG. MESG value was minimum near the stoichiometric concentration of gas mixtures, and according to the increase of initial pressure MESG was decreased.

• Resources Recycling
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• 제7권2호
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• pp.16-22
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• 1998

Recently, the new technology for the recycling of waste plastics as an alternative he1 of blast furnace ha been developed. In this shldy, the test of plastics injection into a tuyere af the foundry blast furnace were carried out. The injection rate of plastics far this tcst facility war expressed as follows, ${W}_{s}=0.265\frac{{delta}PA}{U}_{g}$, where. Ws, AP, A and Ug are plastic conveying ratc (kgisec), pressure drop between feed hopper and blaqt pressure (alm), cross sectional area of conveying pipe (mi) and superficial velocity of transport air (mhzc) respcctiuely. From the results of semi-continuous test operation during 96 hours, the replacement raho mned out to be 1.38 according to the injection rate of 6. 4 kg-plasticsit-p. With increasing the rate of plaslics injcchon, the content of hydrogen in top gas became increased and the brick temperahlre at bzlly was also increased due to Lhe changes ot the combustion zone shape.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제37권3호
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• pp.353-358
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• 2013

The ultrasonic characteristics of 2.25Cr-1Mo steel were investigated in relation to the isothermal heat treatment temperature and time. Charpy impact tests and hardness tests were conducted on individual specimens with three different heat treatment conditions. A pulse-echo method with longitudinal waves was used to measure the attenuation and velocity of ultrasonic waves. The FATT (fracture appearance transition temperature) increased with an increase in the isothermal heat treatment time, which implies that the toughness decreased. As the isothermal heat treatment time and temperature increased, the longitudinal wave velocity and ultrasonic attenuation coefficient were raised.