• Journal of Radiation Industry
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• v.17 no.4
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• pp.333-344
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• 2023

To validate the numerical model used in the study of deep disposal of spent nuclear fuel, we selected benchmark cases and performed numerical model validation. We selected the DECOVALEX-THMC Task D_THM1 FEBEX Type benchmark case, which was conducted from 2003 to 2007. We analyzed the thermal-hydraulic (TH) behavior using the finite element program CODE_BRIGHT and verified the results against previous studies. The temperature results were similar to the results of DECOVALEX-THMC Task D. The saturation results showed a similar trend to the results of DECOVALEX-THMC Task D, but the time to reach full saturation was different.

• Computers and Concrete
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• v.26 no.1
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• pp.75-94
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• 2020

The aim of this research is to investigate free vibration of a novel five layer Timoshenko microbeam which consists of a transversely flexible porous core made of Al-foam, two graphen platelets (GPL) nanocomposite reinforced layers to enhance the mechanical behavior of the structure as well as two piezo-magneto-electric face sheets layers. This microbeam is subjected to a thermal load and resting on Pasternak's foundation. To accomplish the analysis, constitutive equations of each layer are derived by means of nonlocal strain gradient theory (NSGT) to capture size dependent effects. Then, the Hamilton's principle is employed to obtain the equations of motion for five layer Timoshenko microbeam. They are subsequently solved analytically by applying Navier's method so that discretized governing equations are determined in form of dynamic matrix giving the possibility to gain the natural frequencies of the Timoshenko microbeam. Eventually, after a validation study, the numerical results are presented to study and discuss the influences of various parameters such as nonlocal parameter, strain gradient parameter, aspect ratio, porosity, various volume fraction and distributions of graphene platelets, temperature change and elastic foundation coefficients on natural frequencies of the sandwich microbeam.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.1-8
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• 2013

Coolant rubber hoses for automotive radiators can degrade under thermal and mechanical loadings and thus fail owing to the influences of locally formed electricity. In this study, an advanced test method was developed to simulate the failure of a rubber hose. The aging behavior of carbon-black-filled ethylene-propylene diene monomer (EPDM) rubber used as a radiator hose material under a combination of electrochemical stresses and tensile strain was analyzed. The changing behaviors of the current and the resistance as a function of the aging time were analyzed in consideration of the tensile strain, voltage, and aging temperature. Sectioned specimens clarified the failure mechanisms of the aged skin layer under the combined electrochemical stresses.

• Journal of Powder Materials
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• v.20 no.4
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• pp.275-279
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• 2013

Fe-based oxide dispersion strengthened (ODS) powders were produced by high energy ball milling, followed by spark plasma sintering (SPS) for consolidation. The mixed powders of 84Fe-14Cr-$2Y_2O_3$ (wt%) were mechanically milled for 10 and 90 mins, and then consolidated at different temperatures ($900{\sim}1100^{\circ}C$). Mechanically-Alloyed (MAed) particles were examined by means of cross-sectional images using scanning electron microscopy (SEM). Both mechanical alloying and sintering behavior was investigated by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). To confirm the thermal behavior of $Y_2O_3$, a replica method was applied after the SPS process. From the SEM observation, MAed powders milled for 10 min showed a lamella structure consisting of rich regions of Fe and Cr, while both regions were fully alloyed after 90 min. The results of sintering behavior clearly indicate that as the SPS temperature increased, micro-sized defects decreased and the density of consolidated ODS alloys increased. TEM images revealed that precipitates smaller than 50 nm consisted of $YCrO_3$.

• Journal of the Korean Ceramic Society
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• v.44 no.8
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• pp.451-456
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• 2007

This paper presents results and observations obtained from a study of sintering behavior and crystallization in $Li_2O-Al_2O_3-SiO_2$ (LAS) Glass by screen printing method. The variable experimental conditions were determined carefully by Thermal-Mechanical Analyzer (TMA), Differential Thermal Analyzer (DTA) for setting the optimum transparent sintering conditions in LAS glass system, $10.5Li_2O-14.7Al_2O_3-58.1SiO_2-16.7B_2O_3(wt%)$, such as glass-ceramics which usually have low crystallization temperatures. Crystallization glasses generated during sintering was observed from diffraction patterns by X-Ray Diffraction (XRD), transmittance by UV-Vis spectrometer. Finally, the optimum sintering condition of LAS glass and the relation between factors and results in several sintering conditions were given by using Response Surface Methodology (RSM). From this study, we confirmed that crystallization interrupted densification during glass powder sintering. Furthermore, we observed that main effect of factors in glass powder sintering with concurrent crystallization depended on experimental conditions from main effects plot by MINTAB-14.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1659-1666
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• 2010

In this study, a new type of wire-woven cellular metal named WBD(wire-woven bulk diamond) was developed. Like WBK(wire-woven bulk Kagome), WBD is composed of helically formed wires; WBK was introduced a few years ago, and its mechanical, thermal properties, and engineering applications have been extensively investigated. The number of wires that pass by one another at each cross point in WBD is four, whereas that in WBK is three. The mechanical behavior of WBD subjected to compression was investigated and the results were compared to those for WBK. For a given slenderness ratio the density and yield strength of WBD were about twice as high as those for WBK, but elastic stiffness of WBD was not that higher than that for WBK.

• Nuclear Engineering and Technology
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• v.56 no.10
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• pp.4018-4030
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• 2024

The in-vessel retention through external reactor vessel cooling (IVR-ERVC) strategy is a key management strategy for early termination of a nuclear severe accident that can threaten the integrity of the reactor vessel. To simulate the physical phenomena of the molten corium, the smoothed particle hydrodynamic (SPH) method is utilized in this study. The SPH method is a Lagrangian computational fluid dynamic (CFD) method that can simulate multi-fluid stratification, turbulence, natural circulation, radiative heat transfer, thermal ablation, and crust formation. To address the external vessel cooling, it is coupled with a conventional 1-D nuclear system analysis method. The 1-D system analysis code can calculate the two-phase natural circulation of cooling water and the convective heat transfer on the external reactor vessel wall. These two simulation codes exchange the temperature and heat flux of the reactor vessel outer wall. This study numerically simulated the IVR-ERVC strategy for a Korean high-power reactor and compared it with the traditional lumped parameter method (LPM). Unlike LPM, this study provides localized detailed data about the thermal hydraulic behavior of molten corium and visualization of phenomena in the IVR-ERVC strategy. This enhances our understanding of the phenomena in IVR-ERVC strategy and introduces new perspectives.

• Composites Research
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• v.30 no.6
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• pp.422-428
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• 2017

The moisture absorption behavior, tensile properties, and thermal analysis properties of MWCNT embedded nanocomposites exposed to temperature and moisture were evaluated. The contents of MWCNT were 0 wt%, 1 wt%, and 2 wt%, respectively. The specimens were exposed to immersed conditions at $25^{\circ}C$ and $75^{\circ}C$ for up to 600 hours. According to the results, the apparent moisture content increased as the exposure time increased, but the difference between the maximum moisture content and the moisture content at 600 hours was almost constant. The tensile modulus decreased with increasing exposure time and the degree of decrease was increased significantly as the MWCNT content and exposure temperature increased. The tensile strength decreased with longer exposure time without MWCNT, but increased with MWCNT due to the reinforcing effect of MWCNT. The storage modulus, glass transition temperature, tan d peak magnitude were low as the exposure time increased, but tan d curves with two peaks appeared when exposed to high exposure temperature for more than 300 hours.

• 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.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.189-207
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• 2023

In the present study, the thermoshearing experiment on a rough rock fracture were modeled using a three-dimensional grain-based distinct element model (GBDEM). The experiment was conducted by the Korea Institute of Construction Technology to investigate the progressive shear failure of fracture under the influence of thermal stress in a critical stress state. The numerical model employs an assembly of multiple polyhedral grains and their interfaces to represent the rock sample, and calculates the coupled thermo-mechanical behavior of the grains (blocks) and the interfaces (contacts) using 3DEC, a DEM code. The primary focus was on simulating the temperature evolution, generation of thermal stress, and shear and normal displacements of the fracture. Two fracture models, namely the mated fracture model and the unmated fracture model, were constructed based on the degree of surface matedness, and their respective behaviors were compared and analyzed. By leveraging the advantage of the DEM, the contact area between the fracture surfaces was continuously monitored during the simulation, enabling an examination of its influence on shear behavior. The numerical results demonstrated distinct differences depending on the degree of the surface matedness at the initial stage. In the mated fracture model, where the surfaces were in almost full contact, the characteristic stages of peak stress and residual stress commonly observed in shear behavior of natural rock joints were reasonably replicated, despite exhibiting discrepancies with the experimental results. The analysis of contact area variation over time confirmed that our numerical model effectively simulated the abrupt normal dilation and shear slip, stress softening phenomenon, and transition to the residual state that occur during the peak stress stage. The unmated fracture model, which closely resembled the experimental specimen, showed qualitative agreement with the experimental observations, including heat transfer characteristics, the progressive shear failure process induced by heating, and the increase in thermal stress. However, there were some mismatches between the numerical and experimental results regarding the onset of fracture slip and the magnitudes of fracture stress and displacement. This research was conducted as part of DECOVALEX-2023 Task G, and we expect the numerical model to be enhanced through continued collaboration with other research teams and validated in further studies.