• Journal of the Korean Vacuum Society
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• v.20 no.2
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• pp.135-140
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• 2011

By investigating photoluminescence (PL) spectra (20 K) of undoped and Be-doped p-type GaSb/GaAs epilayers, the origin has been analyzed by the change due to doping density. We have observed that the PL peak shifts to higher energy and the full-width half-maximum (FWHM) decreases with increasing the doping density below ${\sim}10^{17}cm^{-3}$, contrasted to shift to low energy and increasing FWHM above the density of ${\sim}10^{17}cm^{-3}$. From the variation of the integrated PL intensities of three peaks dissolved by Gaussian fit, it has been analyzed that, as the density increases, the $Be[Be_{Ga}]$ acceptor level (0.794 eV) reduces, whereas the intrinsic defect of $A[Ga_{Sb}]$ (0.778 eV) enhances together with a new $Be^*$ level (0.787 eV) locating between A and Be. We have discussed that it is due to coexistence of the Be acceptor level (${\Delta}E=16meV$) and the complex level (${\Delta}E=23meV$), $Be^*[Ga_{Sb}-Be_{Ga}]$combined by Be and A, in Be-doped p-GaSb, and that the level density of $Be[Be_{Ga}]$ may be reduced above ${\sim}10^{17}cm^{-3}$.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.4
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• pp.281-294
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• 2012

The current status of the computer codes for the analysis of coupled thermal-hydrological-mechanical behavior occurred in a high-level waste repository was investigated. Based on the reported results on the comparison between the predictions using the computer codes and the experimental data from the in-situ tests, the reliability of the existing computer codes was analyzed. The presented codes simulated considerably well the coupled thermal-hydrological-mechanical behavior in the near-field rock of the repository without buffer, but the predictions for the engineered barrier system of the repository located at saturated hard rock were not satisfactory. To apply the current thermal-hydrological-mechanical models to the assessment of the performance of engineered barrier system, a major improvement on the mathematical models which analyze the distribution of water content and total pressure in the buffer is required.

• Tunnel and Underground Space
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• v.31 no.3
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• pp.167-183
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• 2021

It is essential to understand the complex thermo-hydro-mechanical-chemical (THMC) coupled behavior in the engineered barrier system and natural barrier system to secure the high-level radioactive waste repository's long-term safety. The heat from the high-level radioactive waste induces thermal pressurization and vaporization of groundwater in the repository system. Groundwater inflow affects the saturation variation in the engineered barrier system, and the saturation change influences the heat transfer and multi-phase flow characteristics in the buffer. Due to the complexity of the coupled behavior, a numerical simulation is a valuable tool to predict and evaluate the THMC interaction effect on the disposal system and safety assessment. To enhance the knowledge of THMC coupled interaction and validate modeling techniques in geological systems. DECOVALEX, an international cooperation project, was initiated in 1992, and KAERI has participated in the projects since 2008 in Korea. In this study, we introduced the main contents of all tasks in the DECOVALEX-2023, the current DECOVALEX phase, to the rock mechanics and geotechnical researchers in Korea.

• Proceedings of the Acoustical Society of Korea Conference
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• 1996.06a
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• pp.22-28
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• 1996

수동 소나 시스템에서 표적을 탐지, 식별하는데 가장 중요한 인자는 표적에서 발생되는 토날 신호 성분이다. 수중의 주변잡음과 표적소음이 복합된 환경하에서 표적의 토날 신호성분을 정확히 추출하는데는 신호 탐지 준위 설정이나 주변 잡음의 변화에 의해 어려움이 있다. 본 논문에서는 ASM 신경망을 이용하여 신호 탐지 준위 설정이나 주변잡음의 변화에 강인한 음향 표적의 토날 신호 탐지 방식을 제안한다. 모의 시뮬레이션 및 실제 표적 신호에 적용하여 우수한 토날 신호 탐지 성능을 보인다.

• Tunnel and Underground Space
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• v.31 no.5
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• pp.309-332
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• 2021

Natural barrier systems surrounding the geological repository for the high-level radioactive waste should guarantee the hydraulic performance for preventing or delaying the leakage of radionuclide. In the case of the behavior of a crystalline rock, the hydraulic performance tends to be decided by the existence of discontinuities, so the coupled hydro-mechanical(HM) processes on the discontinuities should be characterized. The discontinuum modelling can describe the complicated behavior of discontinuities including creation, propagation, deformation and slip, so it is appropriate to model the behavior of a crystalline rock. This paper investigated the coupled HM processes in discontinuum modelling such as UDEC, 3DEC, PFC, DDA, FRACOD and TOUGH-UDEC. Block-based discontinuum methods tend to describe the HM processes based on the fluid flow through the discontinuities, and some methods are combined with another numerical tool specialized in hydraulic analysis. Particle-based discontinuum modelling describes the overall HM processes based on the fluid flow among the particles. The discontinuum methods that are currently available have limitations: exclusive simulations for two-dimension, low hydraulic simulation efficiency, fracture-dominated fluid flow and simplified hydraulic analysis, so it could be improper to the modelling the geological repository. Based on the concepts of various discontinuum modelling compiled in this paper, the advanced numerical tools for describing the accurate coupled HM processes of the deep geological repository should be developed.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2008.05a
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• pp.165-166
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• 2008

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2012.05a
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• pp.279-280
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• 2012

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.501-518
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• 2019

The rock properties measured under in-situ geological condition can be used to increase the reliability in numerical simulations with regard to the long-term performance of a high-level waste repository. In this study, the change in mechanical properties of KURT (Korea atomic energy research institute Underground Research Tunnel) granite was evaluated under the simulated THM (Thermo-Hydro-Mechanical) coupled condition due to a deep geological formation in the disposal repository. The rock properties such as uniaxial compression strength, indirect tensile strength, elastic modulus and Poisson's ratio were measured under the coupled test conditions (M, HM, TM, THM). It was found that the mechanical properties of KURT granite is more susceptible to the change in saturation rather than temperature within the test condition of this study. The changes in uniaxial compression strength and indirect tensile strength from the rock samples of dried or saturated conditions showed the maximum relative error of about 20% and 13% respectively under the constant temperature condition. Therefore, it is necessary to use the material properties of rock measured under the coupled THM condition as input parameters for the numerical simulation of long-term performance assessment of a disposal repository

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.369-376
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• 2003

In this paper, a nonlinear structural analysis for the composite structure composed of the spent nuclear fuel disposal canister and the 50㎝ thick bentonite buffer is carried out to predict the collapse of the canister while the horizontal symmetric sudden rock movement of 10㎝ is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Elastoplastic material model is adopted. Drucket-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the canister(cast iron, copper). Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffet, the canister structure still endures elastic small strains and stresses below the yield strength. Hence, the 50㎝ thick bentonite buffet can protect the canister safely against the 10㎝ sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the canister structure due to the shear deformation of the bentonite buffer.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.11a
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• pp.263-264
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• 2009