• 방사성폐기물학회지
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• 제20권3호
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• pp.269-278
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• 2022

The buffer is a critical barrier component in an engineered barrier system, and its purpose is to prevent potential radionuclides from leaking out from a damaged canister by filling the void in the repository. No experimental parameters exist that can describe the buffer expansion phenomenon when Kyeongju bentonite, which is a buffer candidate material available in Korea, is exposed to groundwater. As conventional experiments to determine these parameters are time consuming and complicated, simple swelling pressure tests, numerical modeling, and machine learning are used in this study to obtain the parameters required to establish a numerical model that can simulate swelling. Swelling tests conducted using Kyeongju bentonite are emulated using the COMSOL Multiphysics numerical analysis tool. Relationships between the swelling phenomenon and mechanical parameters are determined via an artificial neural network. Subsequently, by inputting the swelling tests results into the network, the values for the mechanical parameters of Kyeongju bentonite are obtained. Sensitivity analysis is performed to identify the influential parameters. Results of the numerical analysis based on the identified mechanical parameters are consistent with the experimental values.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제15권3호
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• pp.223-231
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• 2011

During spray coating, especially in an air plasma spray (APS), pores, cracks, and splat boundaries are developed and those factors exert influence on thermomechanical properties such as elastic modulus, thermal conductivity, and coefficient of thermal expansion. Moreover, the thermo mechanical properties are crucial elements to determine the thermoelastic characteristics, for instance, temperature distribution, displacements, and stresses. Two types of thermal barrier coating (TBC) model, the dense and porous microstructures, are taken into account for the analysis of microstructural characterizations. $TriplexPro^{TM}$-200 system was applied to prepare TBC samples, and the METECO 204 C-NS powder is adopted for the relatively porous microstructure and METECO 204 NS powder for the dense microstructure in the top coat of TBCs. Governing partial differential equations were derived based on the thermoelastic theory and approximate estimates for the thermoelastic characteristics were obtained using a finite volume method for the governing equations.

• Bulletin of the Korean Chemical Society
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• 제15권8호
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• pp.658-662
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• 1994

Ab initio and extended Huckel calculations have been applied to discuss the electronic structure, ring inversion barrier, and geometry of the $Cp_2TiS_3$ compound. The deformation of four membered ring in the planar geometry is originated from a second-order Jahn-Teller distortion due to the small energy gap between HOMO and LUMO on the basis of extended Huckel calculations. The puckered $C_s$ geometry is stabilized by the interaction of the $x^2-y^2$ metal orbital with the hybrid orbital in sulfur. Ab initio calculations have been carried out to explore the ring inversion process for the model $Cl_2TiS_3$ compound. We have optimized $C_s$ and $C_{2v}$ structures of the model compound at the RHF level. The energy barriers for the ring inversion are sensitive to the used basis set. With 4-31$G^*$ for the Cl and S ligands, the barriers are computed to be 8.41 kcal/mol at MP2 and 8.02 kcal/mol at MP4 level.

• 한국항공우주학회지
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• 제37권11호
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• pp.1096-1103
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• 2009

연소기 헤드부는 극저온 유체인 액체산소가 고압으로 작동하고, 동시에 연소기의 추력으로 인한 하중을 받기 때문에, 극저온에서의 헤드의 구조 안정성 해석을 위한 재료의 변형 거동 예측은 매우 중요하다. 헤드부의 변형 거동을 예측하기 위해 재료의 저온에서의 인장 변형 거동을 묘사할 수 있는 구성 방정식을 Kocks의 전위 에너지 장벽 모델을 바탕으로 열적 요소와 비열적 요소의 결합으로 구성하였으며, 극저온에서 장애물들의 증가로 인한 응력의 열적 요소의 증가를 묘사하기 위해서, 장애물로 인해 발생하는 응력 요소를 Ramberg-Osgood 형태의 식으로 구성하였다. 본 모델은 극저온과 상온의 넓은 온도 영역에서 재료의 변형 거동을 잘 예측하였다.

• 터널과지하공간
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• 제29권1호
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• pp.38-51
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• 2019

Barcelona Basic Model(BBM)은 응력의 변화에 따른 부피변화뿐만 아니라 흡입력의 변화에 따른 팽윤거동을 설명할 수 있으며, 흡입력 변화에 따른 점착력과 선행압밀응력의 변화와 온도변화에 따른 선행압밀응력의 변화를 고려할 수 있다. 따라서, 고준위방사성폐기물 처분시스템에서 공학적방벽재로 고려되고 있는 벤토나이트 완충재의 열-수리-역학적 복합거동을 예측 및 분석하는 것에 많이 활용되고 있다. 그러나 우리나라의 암반 및 지반 공학자들에게 잘 알려져 있지 않기 때문에 BBM을 소개하고자 한다. BBM은 불포화 토질의 역학적 거동을 모사하기 위해 Modified Cam Clay(MCC) 모델을 확장하여 만들어 졌기 때문에 본 고에서는 먼저 MCC 모델을 간략하게 소개하고, 열-탄소성 모델인 BBM을 상세히 소개하였다.

• 방사성폐기물학회지
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• 제10권3호
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• pp.199-208
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• 2012

방사성폐기물처분을 위한 부지특성평가 기술 개발을 위해 지질특성조사와 수리지질특성조사가 1997년부터 지표기반 조사, 시추공 조사, 터널조사를 포함하여 수행되었다. 특히, 2006년에는 지하처분연구시설 (KURT, KAERI Underground Research Tunnel)을 건설하여 지하 환경에서 심부지질환경에 대한 연구 뿐 만 아니라 용질이동특성, 미생물특성, 공학적 방벽 시스템 연구 등 방사성폐기물처분을 위한 다양한 수행하고 있다. 본 연구는 한국원자력연구원내 건설된 지하처분연구시설 주변 지역을 연구지역으로 부지특성모델 구축의 일환으로 수행되었다. 연구지역의 지질모델구축을 위해 선형구조분석, 시추공/터널 조사, 지구물리탐사를 포함한 다양한 연구를 수행하여, 암질모델과 지질구조모델을 구축하였으며, 현장수리시험의 결과를 이용하여 암질모델과 지질구조모델을 포함한 지질모델에 입력된 요소에 대한 수리지질특성이 평가되었다.

• 연구논문집
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• 통권27호
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• pp.183-200
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• 1997

We have calculated the energy of three distinct grain configurations, namely completely connected, partially connected and unconnected configurations, evolving during a spheroidization of polycrystalline thin film by extending a geometrical model due to Miller et al. to the case of spheroidization at both the surface and film-substrate interface. "Stabilitl" diagram defining a stable region of each grain configuration has been established in terms of the ratio of grain size to film thickness vs. equilibrium wetting or dihedral angles at various interface energy conditions. The occurrence of spheroidization at the film-substrate interface significantly enlarges the stable region of unconnected grain configuration thereby greatly facilitating the occurrence of agglomeration. Complete separation of grain boundary is increasingly difficult with a reduction of equilibrium wetting angle. The condition for the occurrence of agglomeration differs depending on the equilibrium wetting or dihedral angles. The agglomeration occurs, at low equilibrium angles, via partially connected configuration containing stable holes centered at grain boundary vertices, whereas it occurs directly via completely connected configuration at large equilibrium angles except for the case having small surface and/or film-substrate interface energy. The initiation condition of agglomeration is defined by the equilibrium boundary condition between the partially connected and unconnected configurations for the former case, whereas it can, for the latter case, largely deviate from the equilibrium boundary condition between the completely connected and unconnected configurations because of the presence of a finite energy barrier to overcome to reach the unconnected grain configuration.

• Nuclear Engineering and Technology
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• 제49권2호
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• pp.434-441
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• 2017

Containment venting is one of several essential measures to protect the integrity of the final barrier of a nuclear reactor during severe accidents, by which the uncontrollable release of fission products can be avoided. The authors seek to develop an optimization approach to venting operations, from a simulation-based perspective, using an integrated severe accident code, THALES2/KICHE. The effectiveness of the containment-venting strategies needs to be verified via numerical simulations based on various settings of the venting conditions. The number of iterations, however, needs to be controlled to avoid cumbersome computational burden of integrated codes. Bayesian optimization is an efficient global optimization approach. By using a Gaussian process regression, a surrogate model of the "black-box" code is constructed. It can be updated simultaneously whenever new simulation results are acquired. With predictions via the surrogate model, upcoming locations of the most probable optimum can be revealed. The sampling procedure is adaptive. Compared with the case of pure random searches, the number of code queries is largely reduced for the optimum finding. One typical severe accident scenario of a boiling water reactor is chosen as an example. The research demonstrates the applicability of the Bayesian optimization approach to the design and establishment of containment-venting strategies during severe accidents.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1271-1287
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• 2004

In this article, vapor bubble nucleation in liquid and the evaporation process of a liquid droplet at its superheat limit were discussed from the viewpoint of molecular clustering (molecular cluster model for bubble nucleation). For the vapor bubble formation, the energy barrier against bubble nucleation was estimated by the molecular interaction due to the London dispersion force. Bubble nucleation by quantum tunneling in liquid helium under negative pressure near the absolute zero temperature and bubble nucleation on cavity free micro heaters were also presented as the homogenous nucleation processes.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2009년도 학술발표회 초록집
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• pp.511-515
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• 2009

본 연구에서는 소규모 연안 도시의 미래 에너지 공급원으로서 실용성을 검토하고 있는 연안 에너지 팜(energy farm)에 의한 파랑의 변형을 모의한다. 에너지 팜에 사용되는 부이는 파랑의 산란은 물론 파랑 에너지를 흡수하는 장치로서 해안선에 도달하는 파랑 에너지 저감에 영향을 미친다. 적용하는 파랑 모형은 해안 구조물에 의한 파랑 에너지 흡수와 산란을 동시에 구현하는 WADEM-PB(WAve Deformation Model-Permeable Barrier)이다.