• Journal of the Korean Geophysical Society
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• v.8 no.4
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• pp.211-214
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• 2005

Low resistivity zone is observed at the lower part of a CFRD (Concrete Face Rockfill Dam). Generally, CFRD tends not to have any saturated zone within the body, but the result of resistivity survey shows that it is possible for the dam to be saturated under 20m depth with water. The level of reservoir was under 10 m from the crest. We suspect that this result may come from the wrong 2D inversion process ignoring the 3D geometry of dams. For the analysis of possibility of distortion by different geometry, we perform the 3D forward modeling for the dam and apply the 2D inversion process. And then we check the point of traditional interpretation of resistivity data. By the analysis, it is found that the result of 2D inversion process of 3D geometry of dams, seems to have deep relation with the reservoir level, and the complex 3D structure hide some internal electrical anomaly of dams from resistivity information.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.3
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• pp.191-208
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• 2024

In this study, a hydro-mechanical-damage coupled analysis model was developed to evaluate the structural safety of radioactive waste disposal structures. The Mazars damage model, widely used to model the fracture behavior of brittle materials such as rocks or concrete, was coupled with conventional hydro-mechanical analysis and the developed model was verified via theoretical solutions from literature. To derive the numerical input values for damage-coupled analysis, uniaxial compressive strength and Brazilian tensile strength tests were performed on concrete samples made using the mix ratio of the disposal concrete silo cured under dry and saturated conditions. The input factors derived from the laboratory-scale experiments were applied to a two-dimensional finite element model of the concrete silos at the Wolseong Nuclear Environmental Management Center in Gyeongju and numerical analysis was conducted to analyze the effects of damage consideration, analysis technique, and waste loading conditions. The hydro-mechanical-damage coupled model developed in this study will be applied to the long-term behavior and stability analysis of deep geological repositories for high-level radioactive waste disposal.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.5
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• pp.211-216
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• 2008

The artificial lightweight aggregate (ALA) was manufactured in a rotary kiln at $1125^{\circ}C$ using green body formed by pelletizing the batch powder composing of coal bottom ash (CBA) produced from power plant, clay and dredged soil (DS). The TCLP (Toxicity characteristic leaching procedure) results showed that the dissolution concentration of heavy metal ions of ALA fabricated in this study was below the limitation defined by the enforcement regulations of wastes management law in Korea. The ALA containing 60$\sim$70 wt% CBA had a bulk density of 1.45$\sim$1.49 and a water absorption of 17.2$\sim$18.5 %. The impact values for oven-dry state and saturated-surface dry state of ALA were 27.4$\pm$1.3 and 23.4$\pm$2.6 % respectively. The 28-days compressive strength of concrete made with various ALA was $22.7\sim27.8 N/mm^2$. The slump of concrete with ALA containing CBA 60 and 70 wt% were 7.9 and 14.3 cm respectively. The unit weight of concrete made with any ALA fabricated in this study was satisfied with the standard specifications of lightweight concrete for the civil engineering and construction presented by Korea as below $1.84 ton/m^3$.

• Magazine of the Korea Concrete Institute
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• v.9 no.1
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• pp.143-151
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• 1997

Chemical resistance of the cement mortar containing the Thermally Activated Diaomite(TAD) and H.M.(Heavy Metals) has been studied. The H.M.. extracted from EAF(Electrica1 Arc Furnace) Dust. were saturated with diatomite. The diatomite was then thermally activated at $750{\circ}C$ for 30minutes and powdeled. The powder was mixed with a portland cement on a weight basis from 0%. 2.5%. 5.0%. 10%. 20%. The optimum mixture. after those mixtures were subjected to compressive strength(7 and 28days) and leaching bchaviour of H.M.. was tested for its experiment on Wet/Dry cycles and chemical resistance(e.q. imrncrsion in 5%(Conc.) of H2S04, CaC12 and hlgSO4. It was shown that the cement, mortar containing 10% of' P.D. gave a rise to the remarkable increase in compressive strength. The compressive strength was generally decrease beyond the addition of 10% of P.D. The maximum $496kgf/cm^2$ of 28days compressive strength was acheiveti when 10% of P.D. was added to the cement mortar.

• Journal of the Korea Institute of Building Construction
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• v.8 no.4
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• pp.105-114
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• 2008

This study investigates the saturation level of surface dryness, quantity of adhesive mortar, and the alien substance content of recycled aggregates for concrete to develop an adequate quality testing method for understanding the properties of recycled aggregates, which differ greatly from preexisting aggregates. For tests that measure the saturation level of surface dryness, where detail methods are applied differently according to the tester, various testing methods from across world were compared and analyzed. This study revealed that when measuring the saturation level of surface dryness of a certain sample, aggregates must be supplemented immediately whenever the height of the sample becomes lower than the measuring mold, and allowing the tamper to free fall on the sample will provide the most accurate results. When measuring the quantity of adhesive mortar of recycled aggregates for concrete, an acid solution was used, and since the quantity of adhesive mortar increases as the particle sizes gets smaller, the sample for testing should represent the entire granularity. Sulfuric acid solution is adequate for immersion, and the concentration should be 20% for best results. According to the alien substance content measurement, which was examined by the naked eye, the error range caused by the difference in particle size was neglectable, and therefore the sample should be $2.5{\sim}5.0mm$ in size concerning the accuracy and measuring time. Also, for coarse recycled aggregates, the sample should amount to 1kg for measuring alien substance content by the naked eye, which proves that assortment by the naked eye is the most adequate method for measuring the alien substance content of a recycled aggregate.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.4
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• pp.267-274
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• 2014

The first Low- and Intermediate-Level Waste (LILW) disposal facility with 6 silos has been constructed in granite host rock saturated with groundwater in Korea. A two-dimensional numerical modeling on gas migration was carried out using TOUGH2 with EOS5 module in the disposal facility. Laboratory-scale experiments were also performed to measure the important properties of silo concrete related with gas migration. The gas entry pressure and relative gas permeability of the concrete was determined to be $0.97{\pm}0.15bar$ and $2.44{\times}10^{-17}m^2$, respectively. The results of the numerical modeling showed that hydrogen gas generated from radioactive wastes was dissolved in groundwater and migrated to biosphere as an aqueous phase. Only a small portion of hydrogen appeared as a gas phase after 1,000 years of gas generation. The results strongly suggested that hydrogen gas does not accumulate inside the disposal facility as a gas phase. Therefore, it is expected that there would be no harmful effects on the integrity of the silo concrete due to gas generation.

• Corrosion Science and Technology
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• v.17 no.5
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• pp.203-210
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• 2018

This paper compares the inhibition properties of aspartic and lactic acid salts with nitrite ions and their effect on critical chloride concentration. The tests were carried employing carbon steel specimens in saturated lime solution with varying pH in the range between13 to 13.6. The critical chloride concentration was estimated through multiple specimen potentiostatic tests at potentials in the usual range for passive rebar in the alkaline concrete of atmospheric structures. During tests, chloride salt was added every 48 h until all the specimens showed localized attacks. The cumulative distribution curves, i.e. the number of corroded specimens as a function of the chlorides concentration was obtained. Furthermore, IR spectra were recorded for the evaluation of the presence of the organic inhibitors on the passivity film. The results confirmed the inhibitory effect of 0.1M aspartate comparable with nitrite ions, at a similar concentration. Addition of calcium lactate did not result in an increase in the critical chloride concentration. However, the formation of a massive scale containing the substance that could reduce the corrosion propagation was observed.

• Nuclear Engineering and Technology
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• v.4 no.1
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• pp.39-45
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• 1972

In neutron shielding, the scattering effect is equally important as the attenuations in shielding materials. In the present study, the scattered dose equivalent was measured using a Rem counter for water, paraffin, borated paraffin, ordinary and heavy concrete, lead, iron, and tissue equivalent material in three different angles: 45$^{\circ}$, 90$^{\circ}$, and 135$^{\circ}$, respectively. The measurements were performed for the neutron, having the energies of 0.5, 1, 2, 5, and 18 MeV, which are produced from the Van do Graaff accelerator. The scattered dose equivalent ratios were increased with increasing the thickness of scattering materials and saturated at a certain thickness although they were different from one to other materials under study. The ratios were large for lead and iron while they were small for the hydrogen containing materials such as water and paraffin etc.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2889-2896
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• 2023

The waste acceptance criteria for heavy metals in mixed waste should be developed by reflecting the leaching behaviors that could highly depend on the repository design and environment surrounding the waste. The current standards widely used to evaluate the leaching characteristics of heavy metals would not be appropriate for the silo-type repository since they are developed for landfills, which are more common than a silo-type repository. This research aimed to explore the leaching behaviors of cementitious waste with Pb, Cd, and Sb metallic and oxide powders in an environment simulating a silo-type radioactive waste repository. The Toxicity Characteristic Leaching Procedure (TCLP) and the ANS 16.1 standard were employed with standard and two modified solutions: concrete-saturated deionized and underground water. The compositions and elemental distribution of leachates and specimens were analyzed using an inductively coupled plasma optical emission spectrometer (ICP-OES) and energy-dispersive X-ray spectroscopy combined with scanning electron microscopy (SEM-EDS). Lead and antimony demonstrated high leaching levels in the modified leaching solutions, while cadmium exhibited minimal leaching behavior and remained mainly within the cement matrix. The results emphasize the significance of understanding heavy metals' leaching behavior in the repository's geochemical environment, which could accelerate or mitigate the reaction.

• Computers and Concrete
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• v.32 no.6
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• pp.567-576
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• 2023

In this study, a 3D microstructure-based model is established to simulate the effective thermal conductivity of cement paste, covering varying influencing factors associated with microstructure and thermal transfer mechanisms. The virtual cement paste divided into colloidal C-S-H and heterogeneous paste are reconstructed based on its structural attributes. Using the two-level hierarchical cement pastes as inputs, a lattice Boltzmann model for heat conduction is presented to predict the thermal conductivity. The results suggest that due to the Knudsen effect induced by the nanoscale pore, the thermal conductivity of air in C-S-H gel pore is significantly decreased, maximumly accounting for 3.3% thermal conductivity of air at the macroscale. In the cement paste, the thermal conductivities of dried and saturated cement pastes are stable at the curing age larger than 100 h. The high water-to-cement ratio can decrease the thermal conductivity of cement paste.