• Tunnel and Underground Space
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• v.34 no.1
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• pp.28-53
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• 2024

In general, high-level radioactive waste (HLW) generated as a result of nuclear power generation should be disposed within the country. Determination of the disposal site and host rock for HLW deep geological repository is an important issue not only scientifically but also politically, economically, and socially. Considered host rock types worldwide for geological disposal include crystalline rocks, sedimentary rocks, volcanic rocks, and salt dome. However, South Korea consists of various rock types except salt dome. This paper not only analyzed the geological and rock mechanical characteristics on a nationwide scale with the preliminary results on various rock type studies for the disposal host rock, but also reviewed the characteristics and possibility of various rock types as a host rock through deep drilling surveys. Based on the nationwide screening for host rock types resulted from literature review, rock distributions, and detailed case studies, Jurassic granites and Cretaceous sedimentary rocks (Jinju and Jindong formations) were derived as a possible candidate host rock types for the geological disposal. However, since the analyzed data for candidate rock types from this study is not enough, it is suggested that the disposal rock type should be carefully determined from additional and detailed analysis on disposal depth, regional characteristics, multidisciplinary investigations, etc.

• Economic and Environmental Geology
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• v.57 no.4
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• pp.387-396
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• 2024

The geological disposal of high-level radioactive waste (HLW) involves permanently isolating the wastes in stable geological formations deep underground. Mudstone (siltstone and claystone) containing abundant clay minerals is proposed as a host rock for geological disposal of HLW because clay minerals have low permeability and high ion sorption/exchange capacity. Despite the widespread occurrence of sedimentary basins in Korea, there is a lack of evaluation of mudstone as host rocks for geological disposal. In this study, we utilized the JBH-1 borehole (7-754 m) obtained from the Jinju Formation to investigate the distribution trend and mineral compositions of mudstone. Additionally, we conducted comparative analyses with the Opalinus Clay in Switzerland considered as host rock of geological disposal of HLW. Claystone containing more than 40% clay minerals exhibit thick layers primarily in the upper section (7-350 m) of the JBH-1 borehole. While the clay minerals content of claystone does not show significant variation with depth, there are differences in the characteristics of feldspar and carbonate minerals. These mineralogical variations can led change in pore water chemistry and rock mechanical properties. The clay minerals content of claystone in the Jinju Formation is similar to that of the Opalinus Clay. However, there are notable differences in clay minerals composition. While the Opalinus Clay contains smectite-illite mixed-layer minerals, the Jinju Formation are dominated by illite indicating higher burial temperatures. This information will be useful for studying the host rock of HLW geological disposal site in Korea.

• Tunnel and Underground Space
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• v.34 no.3
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• pp.231-247
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• 2024

In the field of high-level radioactive waste disposal targeting deep rock environments, hydraulic characteristic information serves as the most important key factor in selecting relevant disposal sites, detailed design of disposal facilities, derivation of optimal construction plans, and safety evaluation during operation. Since various rock types are mixed and distributed in a small area in Korea, it is important to conduct preliminary work to analyze the hydrogeological characteristics of rock aquifers for various rock types and compile the resulting data into a database. In this paper, we obtained hydraulic conductivity data, which is the most representative field hydraulic characteristic of a high-depth volcanic bedrock aquifer, and also analyzed and evaluated the field data. To acquire field data, we used a high-performance hydraulic testing system developed in-house and applied standardized test methods and investigation procedures. In the process of hydraulic characteristic data analysis, hydraulic conductivity values were obtained for each depth, and the pattern of groundwater flow through permeable rock joints located in the test section was also evaluated. It is expected that the series of data acquisition methods, procedures, and analysis results proposed in this report can be used to build a database of hydraulic characteristics data for high-depth rock aquifers in Korea. In addition, it is expected that it will play a role in improving technical know-how to be applied to research on hydraulic characteristic according to various bedrock types in the future.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2015.10a
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• pp.245-246
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• 2015

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2001.03a
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• pp.40-60
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• 2001

핵변환 후 영구 처분될 가압경수로 및 중수로용 사용후핵연료에 대한 인간 생태계에 대한 영향을, 직접 처분하는 경우와 비교해 보았다 심지층 처분된 용기에 저장된 사용 후 핵연료로부터 유출된 방사성 핵종들이 공학적 방벽을 거쳐 결정질 기반암 내 균열대를 통해 지하수의 흐름을 따라 이동하면서 , 다양한 지질 및 암종을 거쳐 생태 환경으로 도달한다는 핵종 유출 시나리오 중 가장 보수적인 시나리오인 우물 시나리오에 대한 위해도를 평가하여 상대적인 환경친화성을 정량적으로 제시하였다. 현재 국내에 가속기와 미임계형 원자로를 함께 사용하는 핵변환시스템과 임계형 원자로와 같은 핵변환 시스템이 개념적인 수준에서 개발되고 있어, 이 연구를 통해 향후 핵변환시스템 연구에서 요구되는 항목들도 기술적 개선, 경제성 제고, 환경 친화성, 그리고 수용성측면에서 제시하였다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.2
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• pp.157-178
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• 2013

This study gives a conceptual and basic direction to develop a URL (underground research laboratory) program for establishing the performance and safety of a deep geological disposal system in Korea. The concept of deep geological disposal is one of the preferred methodologies for the final disposal of spent nuclear fuel (SNF). Advanced countries with radioactive waste disposal have developed their own disposal concepts reasonable to their social and environmental conditions and applied to their commercial projects. Deep geological disposal system is a multi-barrier system generally consisting of an engineered barrier and natural barrier. A disposal facility and its host environment can be relied on a necessary containment and isolation over timescales envisaged as several to tens of thousands of years. A disposal system is not allowed in the commercial stage of the disposal program without a validation and demonstration of the performance and safety of the system. All issues confirming performance and safety of a disposal system include investigation, analysis, assessment, design, construction, operation and closure from planning to closure of the deep geological repository. Advanced countries perform RD&D (research, development & demonstration) programs to validate the performance and safety of a disposal system using a URL facility located at the preferred rock area within their own territories. The results and processes from the URL program contribute to construct technical criteria and guidelines for site selection as well as suitability and safety assessment of the final disposal site. Furthermore, the URL program also plays a decisive role in promoting scientific understanding of the deep geological disposal system for stakeholders, such as the public, regulator, and experts.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.132-145
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• 2001

The purpose and need of the study is to quantify the advantage or disadvantage of the environmental friendliness of the partitioning of nuclear fuel cycle. To this end, a preliminary study on the quantitative effect of the partition on the permanent disposal of spent PWR and CANDU fuel (HLW) was carried out. Before any analysis, the so-called reference radionuclide release scenario from a potential repository embedded into a crystalline rock was developed. Firstly, the feature, event and processes (FEPs) which lead to the release of nuclides from waste disposed of in a repository and the transport to and through the biosphere were identified. Based on the selected FEPs, the ‘Well Scenario’which might be the worst case scenario was set up. For the given scenario, annual individual doses to a local resident exposed to radioactive hazard were estimated and compared to that from direct disposal. Even though partitioning and transmutation could be an ideal solution to reduce the inventory which eventually decreases the release time as well as the peaks in the annual dose and also minimize the repository area through the proper handling of nuclides, it should overcome major disadvantages such as echnical issues on the partitioning and transmutation system, cost, and public acceptance, and environment friendly issues. In this regard, some relevant issues are also discussed to show the direction for further studies.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.4
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• pp.305-311
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• 2012

Geology, hydrogeology, and geochemistry are the main technical siting factors of a geological repository for spent nuclear fuels. This paper focused on how rock's different geological conditions, such as topography, soils, rock types, structural geology, and geological events, influence the functions of the geological repository. In the context, the site selection criteria of various countries were analyzed with respect to the geological conditions. Each country established the criteria based on its important geological backgrounds. For example, it was necessary for Sweden to take into account the effect of ice age on the land uplift and sea level change, whereas Japan defined seismic activity and volcanism as the main siting factors of the geological repository. Therefore, the results of the paper seems to be helpful in preparing the siting criteria of geological repository in Korea.

• Tunnel and Underground Space
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• v.33 no.1
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• pp.10-28
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• 2023

Long-term shear behavior of the rock discontinuities should be analyzed and its stability should be evaluated to ensure the long-term stability of a high-level radioactive waste disposal repository. The long-term shear behavior of the discontinuities can be modeled with creep and RSF models. The shear creep test, velocity step test, and slide-hold-slide test can be performed to determine their model parameters or analyze the shear behavior by experiments under various conditions. Testing apparatuses for direct shear, triaxial compression, and biaxial shear were mainly used and improved to reproduce the thermo-hydro-mechanical conditions of local bedrock, and it was confirmed that the shear behavior could vary. In order to design a high-level radioactive waste disposal site in Korea, the long-term behavior of rock discontinuities should be investigated in consideration of rock types, thermo-hydro-mechanical conditions, metamorphism, and restoration of shear resistance.

• Tunnel and Underground Space
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• v.34 no.1
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• pp.71-87
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• 2024

In deep geological disposal of high-level radioactive waste, the surrounding rock at the immediate vicinity of the deposition hole may experience localized changes in permeability due to in-situ stress at depth, swelling pressure from resaturated bentonite buffer, and the heat generated from the decay of radioactive isotopes. In this study, experimental data on changes in permeability of granite, a promising candidate rock type in South Korea, were obtained by applying various confining pressures and temperature conditions expected in the actual disposal environment. By conducting the permeability test on KURT granite specimens under three or more hydrostatic pressure conditions, the relation in which the permeability decreases exponentially as the confining pressure increases was derived. The temperature-induced changes in permeability were found to be negligible at temperatures below the expected maximum of 90℃. In addition, by establishing a relation in which the initial permeability is proportional to the power of the initial porosity, it was possible to estimate permeability value for granite with a specific porosity under a certain confining pressure.