• 한국환경농학회지
• /
• 제16권3호
• /
• pp.233-238
• /
• 1997

하천 수질예측 모형으로서 WASP5 모형을 선정하고, 복하천에 적용한 결과 다음과 같은 결과를 얻었다. 1. 년평균 유달율을 적용한 결과, 실측치와 계산치 사이에 큰 차이가 나타내므로 시간을 고려한 동적모의발생을 위해서는 계절에 따른 유달율의 변화를 반영하여야 할 것이다. 2. 월별 유달율을 고려한 부하량을 입력하여 계산한 결과, 실측치와 계산치가 거의 일치하므로 유역으로부터의 부하량을 이용한 하천수질 예측모형으로서 WASP5 모형의 활용이 기대된다. 3. GIS를 이용한 부하량 산정, 유역의 최적관리(BMP's)를 통한 발생량 저감, 처리장의 신${\cdot}$증설 등 경계조건이 변동된 경우, 본 WASP5모형에 시기별 유달율을 고려한 자료가 입력된다면 하천수질농도의 예측이나 수질개선효과의 파악이 용이할 것으로 판단된다.

• Nuclear Engineering and Technology
• /
• 제47권1호
• /
• pp.11-25
• /
• 2015

The accident at Japan's Fukushima Daiichi nuclear power plant in March 2011, caused by an earthquake and a subsequent tsunami, resulted in a failure of the power systems that are needed to cool the reactors at the plant. The accident progression in the absence of heat removal systems caused Units 1-3 to undergo fuel melting. Containment pressurization and hydrogen explosions ultimately resulted in the escape of radioactivity from reactor containments into the atmosphere and ocean. Problems in containment venting operation, leakage from primary containment boundary to the reactor building, improper functioning of standby gas treatment system (SGTS), unmitigated hydrogen accumulation in the reactor building were identified as some of the reasons those added-up in the severity of the accident. The Fukushima accident not only initiated worldwide demand for installation of adequate control and mitigation measures to minimize the potential source term to the environment but also advocated assessment of the existing mitigation systems performance behavior under a wide range of postulated accident scenarios. The uncertainty in estimating the released fraction of the radionuclides due to the Fukushima accident also underlined the need for comprehensive understanding of fission product behavior as a function of the thermal hydraulic conditions and the type of gaseous, aqueous, and solid materials available for interaction, e.g., gas components, decontamination paint, aerosols, and water pools. In the light of the Fukushima accident, additional experimental needs identified for hydrogen and fission product issues need to be investigated in an integrated and optimized way. Additionally, as more and more passive safety systems, such as passive autocatalytic recombiners and filtered containment venting systems are being retrofitted in current reactors and also planned for future reactors, identified hydrogen and fission product issues will need to be coupled with the operation of passive safety systems in phenomena oriented and coupled effects experiments. In the present paper, potential hydrogen and fission product issues raised by the Fukushima accident are discussed. The discussion focuses on hydrogen and fission product behavior inside nuclear power plant containments under severe accident conditions. The relevant experimental investigations conducted in the technical scale containment THAI (thermal hydraulics, hydrogen, aerosols, and iodine) test facility (9.2 m high, 3.2 m in diameter, and $60m^3$ volume) are discussed in the light of the Fukushima accident.

• Nuclear Engineering and Technology
• /
• 제50권1호
• /
• pp.132-139
• /
• 2018

Nanocrystalline reduced activation ferritic/martensitic (RAFM) steel samples were prepared using surface mechanical attrition treatment (SMAT). Un-SMATed and SMATed reduced activation ferritic/martensitic samples were irradiated by helium ions at $200^{\circ}C$ and $350^{\circ}C$ with 2 dpa and 8 dpa, respectively, to investigate the effects of grain boundaries (GBs) and temperature on the formation of He bubbles during irradiation. Experimental results show that He bubbles are preferentially trapped at GBs in all the irradiated samples. Bubble denuded zones are clearly observed near the GBs at $350^{\circ}C$, whereas the bubble denuded zones are not obvious in the samples irradiated at $200^{\circ}C$. The average bubble size increases and the bubble density decreases with an increasing irradiation temperature from $200^{\circ}C$ to $350^{\circ}C$. Both the average size and density of the bubbles increase with an increasing irradiation dose from 2 dpa to 8 dpa. Bubbles with smaller size and lower density were observed in the SMATed samples but not in the un-SMATed samples irradiated in the same conditions, which indicate that GBs play an important role during irradiation, and sink strength increases as grain size decreases.

• 한국전산구조공학회논문집
• /
• 제20권4호
• /
• pp.493-499
• /
• 2007

본 연구에서는 미분 가능한 함수가 Taylor 전개로 표현되고 그 계수들은 주어진 함수와 미분에 대한 근사값을 제공할 수 있다는 점에 착안하여 m차 Taylor 다항식을 구성하고 이동최소제곱법을 이용하여 그 계수들을 구했다. 계산된 근사함수와 미분을 콜로케이션 개념을 바탕으로 균열 문제를 포함하는 고체문제에 대한 지배 미분방정식에 적용하여 차분식 형태의 이산화된 계방정식을 구성하였다. 본 연구의 해석기법은 격자망(grid)에 의존적이고 근사함수가 없는 유한차분법과 형상함수의 미분과 약형식의 적분산정, 필수경계조건 처리가 어려운 Galerkin법 기반의 무요소법의 단점을 효과적으로 극복한 새로운 수치기법이다.

• 한국자기학회지
• /
• 제10권5호
• /
• pp.191-195
• /
• 2000

Fe$_{78}$Si$_{9}$B$_{13}$ 비정질 합금을 스위칭 전원의 평활용 쵸크 코어로 사용하기 위한 최적 열처리 조건을 조사하였다. 코어의 모양은 자기경로 상에 공극을 넣지 않는 무공극형으로 하였으며, 보다 효과적으로 쵸크 코어 특성을 얻기 위해 산화 분위기 중에서 열처리하였다. 이 합금에서 가장 양호한 쵸크 코어 특성은 44$0^{\circ}C$, 2시간의 열처리에 의하여 얻어졌으며, 그 때의 실효투자율은 180 정도로서 수 MHz의 높은 주파수 영역에 이르기까지 그 크기가 일정하게 유지되었다. 또 12A가지의 직류 바이어스 전류 또는 8,000 A/m의 직류 바이어스 자장을 가하여도 실효투자율의 저하가 나타나지 않는 우수한 직류중첩 특성을 나타내었다. 그리고 교류 자심 손실도 종래의 쵸크 코어에 비해 상당히 낮은 것으로 나타났다. 이와 같은 열처리 조건하에서 비정질상은 미세한 $\alpha$-Fe 결정상의 석출 입자를 포함하는 혼합상으로 변태하는데 , 상기의 쵸크코어 특성은 주로 이들 미세 결정 입자에 의해 효과적으로 자벽 이동이 억제되고 자구가 미세화 되는 것에 기인하는 것으로 생각되었다.

• 한국결정성장학회지
• /
• 제25권4호
• /
• pp.160-165
• /
• 2015

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, $Pb(Zr_xTi_{1-x}O_3)$, which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, $Na_{0.5}Bi_{0.5}TiO_3$ (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, $(Na_{0.5}Bi_{0.5})_{0.93}Ba_{0.7}TiO_3$ (abbreviated as NBT-7BT), at the region of MPB using 7 % $BaTiO_3$ as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

• 한국해양공학회지
• /
• 제10권2호
• /
• pp.77-87
• /
• 1996

The estimation of the remaining life for the aged components in power plant as well as chemical and peroleum plants has been recently coberned. The raw materials used in this syudy are the 1Cr-1Mo-0.25V rotor steel which intensified P and S compositions along with the nominal compositions of ASTM A470 standard. Five kinds of specimens with the different degradation levels were prepared by isothermal aging teat treatment at $630^{\circ}C$ The mechanical properties and fatigue strength of virgin and aged 1Cr-1Mo-0.25V rotor steel have been inbestigated through the hardness, tensile, fatigue test, SEM fractograph and EDS analysis at room temperature. Thus, the data of aged specimens were compared with those of virgin specimen to evaluate the aging effects. The main results obtained in this study are as follows; The decrease of the hardness due to degradation was distinguished until 50, 000hrs simulated service time. And is was confirmed that the considerable amount of P, Mn, Cr and S was precipitated at the grain boundary of aged material through the SEM and EDS analysis. The fatigue strength of 25, 000, 50, 000, 75, 000 and 100, 000hrs aged material was decreased 29.5%, 24.4%, 28.6%, 35.7% than that of virgin material at $10^7$ cycles of room temperature. The major cracks of virgin and aged materials initiated at the inclusions including Si, P and Mn compositions which were located at the outer periphery of the specimen.

• 한국주조공학회지
• /
• 제37권5호
• /
• pp.139-147
• /
• 2017

Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.

• 한국안전학회지
• /
• 제11권4호
• /
• pp.135-142
• /
• 1996

Prolonged in-plant personnel exposure to high noise levels results in permant hearing damage. There are no way to correct this hearing damage by treatment or use of hearing aids. Therefore, every employer is responsible for providing a workplace free of such hazards as excessive noise. This study was carried out to evalute and predict a given noise environment based on specific limit as the noise guarantee for a newly-founded petrochemical plant. The maximum total sound level should not exceed 85dBA in the work area, except where the area is defined as a restricted area and 70dBA at the plant boundary. Prediction of the noise levels within the plant area for a newly-founded petrochemical plant was achieved by dividing all plant area into 20m$\times$20m regular grid spaces and noise level inside the area or unit that in-plant personel exposure to high noise levels was estimated computed into 5m$\times$5m regular grid spaces. The noise level at the grid point that was propagated from each of the noise sources(equipments) computed using the methematical formula was defined as follows : $SPL_2$=$SPL_1-20log{\frac{r_2}{r_1}}$(dB) where $SPL_1$ =sound pressure level at distance $r_1$ from the source $SPL_2$=sound pressure level at distance $r_2$ from the source As a result, the equipments exceeded noise limit or irritaring noise levels were identified on the specific grid coordinates. As for equipments in the area that show high noise levels, appropriate counter-measures for noise control (by barriers, enclosure, silencers, or the change of equipments, for example) should be reviewed. Methods for identifying sources of noise applied in this study should be the model for prediction of the noise levels for any newly-founded plant.

• 한국도로학회논문집
• /
• 제9권4호
• /
• pp.105-116
• /
• 2007

회전교차로는 일반적인 신호교차로보다 안전성 향상 및 지체감소에 효과적이라고 한다. 회전교차로는 일반 평면교차로보다 자동차간 혹은 자동차와 보행자간의 상충횟수가 적고, 교차로 진입부와 교차로 내에서 감속운행하게 되며, 교차로를 통과할 때 대부분의 운전자가 비슷한 속도로 주행한다는 점 때문에 일반적인 교차로보다 안전성이 높은 기법으로 알려져 있다. 본 연구는 지방부 비신호 Y형 교차로에 대해 회전교차로로의 변환 가능성을 검토하기 위한 기초단계로써, 미시적 교통류 분석 S/W인 VISSIM을 활용하여 회전교차로 설치 전 후 모의실험을 수행하였다. 모의실험을 통하여 ROUNDABOUT의 운영 효율성을 평가하였으며, 현장조사 검증을 통해 설치준거를 제시하였다. 모의실험결과, 신호 및 비신호 Y형 교차로를 회전교차로로 변형하면 수용할 수 있는 교차로 전체교통량이 증가하고 안전성이 개선되는 것으로 분석되었다. 본 연구는 국내에서 최초로 미시적 시뮬레이션 모형을 활용하여 회전교차로의 운영효과를 평가하고, 교통량 및 회전교통량을 고려한 설치 가능 범위를 제시하였다는 점에서 그 의의를 찾을 수 있을 것이다.