• Tunnel and Underground Space
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• v.22 no.6
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• pp.429-437
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• 2012

This study predicted temperature in the disposal tunnels using computational fluid dynamics based on natural ventilation quantity that comes from high altitude and temperature differences that are the characteristics of high level waste repository. The result of the previous study that evaluated quantitatively natural ventilation quantity using a hydrostatic method and CFD shows that significant natural ventilation quantity is generated. From the result, this study performed the prediction of temperature in disposal tunnels by natural ventilation quantity by the caloric values of the wastes, at both deep geological repository and surface repository. The result of analysis shows that deep geological repository is effective for thermal control in the disposal tunnels due to heat transfer to rock and the generation of sufficient natural ventilation quantity, while surface repository was detrimental to thermal control, because surface repository was strongly affected by external temperature, and could not generate sufficient natural ventilation quantity. Moreover, this study found that in the case of deep geological repository with a depth of 200 m, the heatof about $10^{\circ}C$ was transferred to the depth of 500 m. Thus, it is considered that if the high level waste repository scheduled to be built in the country is designed placing an emphasis on thermal control, deep geological repository rather than surface repository is more appropriate.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.21 no.1
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• pp.149-164
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• 2023

As part of the safety case development for generic disposal sites in Korea, it is necessary to develop generic assessment models using various geosphere-biosphere interfaces (GBIs) and potentially exposed groups (PEGs) that reflect the natural environmental characteristics and the lifestyles of people in Korea. In this study, a unique modeling strategy was developed to systematically construct and select Korean generic biosphere assessment models. The strategy includes three process steps (combination, screening, and experts' scoring) for the biosphere system conditions. First, various conditions, such as climate, topography, GBIs, and PEGs, were combined in the biosphere system. Second, the combined calculation cases were configured into interrelation matrices to screen out some calculation cases that were highly unlikely or less significant in terms of the exposure dose. Finally, the selected calculation cases were prioritized based on expert judgment by scoring the knowledge, probability, and importance. The results of this study can be implemented in the development of biosphere assessment models for Korean generic sites. It is believed that this systematic methodology for selecting the candidate calculation cases can contribute to increasing the confidence of future site-specific biosphere assessment models.

• Geophysics and Geophysical Exploration
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• v.27 no.1
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• pp.69-83
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• 2024

Considering importance and specificity, site investigations for deep geological disposal of Spent Nuclear Fuel require stringent quality control, unlike general geotechnical investigations for tunnels and bridges. In this study, we present a case of selecting geophysical survey method for individual site investigation stage and preparing geophysical survey guideline. The proposed geophysical survey guidelines include procedures, considerations, and quality control for exploration planning, data acquisition, data processing, and interpretation. They comprehensively summarize the contents of airborne electromagnetic survey and seismic reflection survey.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.3
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• pp.239-256
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• 2017

In the process of site selection for a radioactive waste disposal, site characterization must be carried out to obtain input parameters to assess the safety and feasibility of deep geological repository. In this paper, methodologies of site characterization for radioactive waste disposal in Korea were suggested based on foreign cases of site characterization. The IAEA recommends that site characterization for radioactive waste disposal should be performed through stepwise processes, in which the site characterization period is divided into preliminary and detailed stages, in sequence. This methodology was followed by several foreign countries for their geological disposal programs. General properties related to geological environments were obtained at the preliminary site characterization stage; more detailed site characteristics were investigated during the detailed site characterization stage. The results of investigation of geology, hydro-geology, geochemistry, rock mechanics, solute transport and thermal properties at a site have to be combined and constructed in the form of a site descriptive model. Based on this site descriptive model, the site characteristics can be evaluated to assess suitability of site for radioactive waste disposal. According to foreign site characterization cases, 7 or 8 years are expected to be needed for site characterization; however, the time required may increase if the no proper national strategy is provided.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.4
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• pp.191-205
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• 2009

To characterize the geological features in the study area for high-level radioactive waste disposal research, KAERI (Korea Atomic Energy Research Institute) has been performing several geological investigations such as geophysical surveys and borehole drillings since 1997. Especially, the KURT (KAERI Underground Research Tunnel) constructed to understand the deep geological environments in 2006. Recently, the deep boreholes, which have 500 m depth inside the left research module of the KURT and 1,000 m depth outside the KURT, were drilled to confirm and validate the results from a geological model. The objective of this research was to investigate hydrogeological conditions using a 3-D geological model around the KURT. The geological analysis from the surface and borehole investigations determined four important geologicla elements including subsurface weathered zone, low-angled fractures zone, fracture zones and bedrock for the geological model. In addition, the geometries of these elements were also calculated for the three-dimensional model. The results from 3-D geological model in this study will be beneficial to understand hydrogeological environment in the study area as an important part of high-level radioactive waste disposal technology.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.4
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• pp.405-418
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• 2019

Based on spent fuels characteristics from domestic nuclear power plants and a disposal scenario from the current basic plan for high-level radioactive waste management, an improved disposal system has been proposed that enhances disposal efficiency and economic effectiveness compared to the existing disposal system. For this purpose, two disposal canisters concepts were derived from the length of the spent fuel generated from the nuclear power plants. In the disposal scenario, the acceptable amount of decay heat for each disposal container was determined, taking into account the discharge and disposal times of spent fuels in accordance with the current basic plan. Based on the determined decay heat of the two types of disposal canisters and the associated disposal system, thermal stability analyses were performed to confirm their suitability to the proposed disposal system design requirement and disposal efficiency assessment. The results of this study confirm 20% reduction in the disposal area and 20% increase in disposal density for the proposed disposal system compared to the existing system. These results can be used to establish a spent fuel management policy and to design a viable commercial disposal system.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.445-471
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• 2023

Long-term safety over millennia is the top priority consideration in the construction of disposal sites. However, ensuring the mechanical stability of deep geological repositories for spent fuel, a.k.a. radwaste, disposal during construction and operation is also crucial for safe operation of the repository. Imposing restrictions or limitations on tunnel support and lining materials such as shotcrete, concrete, grouting, which might compromise the sealing performance of backfill and buffer materials which are essential elements for the long-term safety of disposal sites, presents a highly challenging task for rock engineers and tunnelling experts. In this study, as part of an extensive exploration to aid in the proper selection of disposal sites, the anticipation of constructing a deep geological repository at a depth of 500 meters in an unknown state has been carried out. Through a review of 2D and 3D numerical analyses, the study aimed to explore the range of properties that ensure stability. Preliminary findings identified the potential range of rock properties that secure the stability of central and disposal tunnels, while the stability of the vertical tunnel network was confirmed through 3D analysis, outlining fundamental rock conditions necessary for the construction of disposal sites.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.1
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• pp.63-75
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• 2012

This paper gives some basic requirements and preferences of various geological environmental conditions for the final deep geological repository of spent nuclear fuel (SNF). This study also indicates how the requirements and preferences are to be considered prior to the selection of sites for a site investigation as well as the final disposal in Korea. The results of the study are based on the knowledge and experience from the IAEA and NEA/OECD as well as the advanced countries in SNF disposal project. This study discusses and suggests preliminary guideline of the disposal requirements including geological, mechanical, thermal, hydrogeological, chemical and transport properties of host rock with long term geological stabilities which influence the functions of a multi-barrier disposal system. To apply and determine whether requirements and preferences for a given parameter are satisfied at different stages during a site selection and suitability assessment of a final disposal site, the quantitative criteria in each area should be formulated with credibility through relevant research and development efforts for the deep geological environment during the site screening and selection processes as well as specific studies such as productions of safety cases and validation studies using a generic underground research laboratory (URL) in Korea.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3359-3366
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• 2021

An engineered barrier system (EBS) for the deep geological disposal of high-level radioactive waste (HLW) is composed of a disposal canister, buffer material, gap-filling material, and backfill material. As the buffer fills the empty space between the disposal canisters and the near-field rock mass, heat energy from the canisters is released to the surrounding buffer material. It is vital that this heat energy is rapidly dissipated to the near-field rock mass, and thus the thermal conductivity of the buffer is a key parameter to consider when evaluating the safety of the overall disposal system. Therefore, to take into consideration the sizeable amount of heat being released from such canisters, this study investigated the thermal conductivity of Korean compacted bentonites and its variation within a temperature range of 25 ℃ to 80-90 ℃. As a result, thermal conductivity increased by 5-20% as the temperature increased. Furthermore, temperature had a greater effect under higher degrees of saturation and a lower impact under higher dry densities. This study also conducted a regression analysis with 147 sets of data to estimate the thermal conductivity of the compacted bentonite considering the initial dry density, water content, and variations in temperature. Furthermore, the Kriging method was adopted to establish an uncertainty metamodel of thermal conductivity to verify the regression model. The R² value of the regression model was 0.925, and the regression model and metamodel showed similar results.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.3
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• pp.217-224
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• 2008

In deep geological disposal system, the integrity of a disposal canister having spent fuels is very important factor to assure the safety of the repository system. This disposal canister is one element of the engineered barriers to isolate and to delay the radioactivity release from human beings and the environment for a long time so that the toxicity does not affect the environment. The main requirement in designing the deep geological disposal system is to keep the buffer temperature below 100$^{\circ}C$ by the decay heat from the spent fuels in the canister in order to maintain the integrity of the buffer material. Also, the disposal canister can endure the hydraulic pressure in the depth of 500 m and the swelling pressure of the bentonite as a buffer. In this study, new concept of the disposal canister for the CANDU spent fuels which were considered to be disposed without any treatment was developed and the thermal stability and the structural integrity of the canister were analysed. The result of the thermal analysis showed that the temperature of the buffer was 88.9$^{\circ}C$ when 37 years have passed after emplacement of the canister and the spacings of the disposal tunnel and the deposition holes were 40 m and 3 m, respectively. In the case of structural analysis, the result showed that the safety factors of the normal and the extreme environment were 2.9 and 1.33, respectively. So, these results reveal that the canister meets the thermal and the structural requirements in the deep geological disposal system.