• Economic and Environmental Geology
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• v.56 no.6
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• pp.847-870
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• 2023

The safe disposal of high-level radioactive waste requires accurate predictions of the long-term geochemical behavior of radionuclides. To achieve this, the present study was conducted to model geochemical behaviors of uranium (U), plutonium (Pu), and palladium (Pd) under different hydrogeochemical conditions that represent deep groundwater in Korea. Geochemical modeling was performed for five types of South Korean deep groundwater environment: high-TDS saline groundwater (G1), low-pH CO₂-rich groundwater (G2), high-pH alkaline groundwater (G3), sulfate-rich groundwater (G4), and dilute (fresh) groundwater (G5). Under the pH and Eh (redox potential) ranges of 3 to 12 and ±0.2 V, respectively, the solubility and speciation of U, Pu, and Pd in deep groundwater were predicted. The result reveals that U(IV) exhibits high solubility within the neutral to alkaline pH range, even in reducing environment with Eh down to -0.2 V. Such high solubility of U is primarily attributed to the formation of Ca-U-CO₃ complexes, which is important in both G2 located along fault zones and G3 occurring in granitic bedrocks. On the other hand, the solubility of Pu is found to be highly dependent on pH, with the lowest solubility in neutral to alkaline conditions. The predominant species are Pu(IV) and Pu(III) and their removal is predicted to occur by sorption. Considering the migration by colloids, however, the role of colloid formation and migration are expected to promote the Pu mobility, especially in deep groundwater of G3 and G5 which have low ionic strengths. Palladium (Pd) exhibits the low solubility due to the precipitation as sulfides in reducing conditions. In oxidizing condition, anionic complexes such as Pd(OH)₃^-, PdCl₃(OH)₂^-, PdCl₄^2-, and Pd(CO₃)₂^2- would be removed by sorption onto metal (hydro)oxides. This study will improve the understanding of the fate and transport of radionuclides in deep groundwater conditions of South Korea and therefore contributes to develop strategies for safe high-level radioactive waste disposal.

• Economic and Environmental Geology
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• v.48 no.2
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• pp.131-145
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• 2015

Thermodynamic prediction of weathering products from primary aquifer minerals around underground disposal sites was investigated. The distribution of solubility quotients for kaolinite-smectite reactions showed the trend of reaching at equilibrium with Ca-, Mg-, and Na-smectite for deep groundwaters in granitic aquifers. The values of $10^{-14.56}$, $10^{-15.73}$, and $10^{-7.76}$ were proposed as equilibrium constants between kaolinite and Ca-, Mg-, and Na-smectite end members, respectively. On stability diagrams, most of deep groundwaters were located at equilibrium boundaries between stability fields of kaolinite and smectites or on stability fields of smectites and illite. Shallow groundwaters in basic rock aquifer were plotted at the same stability areas of deep granitic groundwaters on stability diagrams. The results indicated that the primiary mineralogical composition may be important to predict weathering products in deep aquifers.

• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.28-46
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• 2001

Natural gas is a mixture of hydrocarbon gases and impurities such as nitrogen, hydrogen sulfide, and carbon dioxide and a clean energy producing no pollution materials for combustion. Currently, the demand of the natural gas is rapidly increasing due to worldwide environmental problems. According to Hubbert's study in the past, the natural gas was predicted as rapidly depleted resources, and then the results led to high gas price and limitation of usage during 1980s. Afterward, the study of natural gas resources based on geology identified the additional natural gas resources that were not considered in Hubbert's study. They are unconventional gas, additional resources in the existed reservoirs, and natural gas in deep subsurface areas. Such additional resouces made the future of natural gas bright and pormised low and stable gas price in the future. Deep natural gas is defined as the gas existing at or below 15,000ft$(4,752{\cal}m)$ in depth from the surface. According to the study from the U.S. Geological Survey(USGS) in 1995, 1,412 TCF of technically recoverable natural gas was remained to be discovered or developed in the onshore of United States. A significant part of that resource base, 114 TCF, exists at deep sedimentary basins, and it shows wide distribution with various geological environments. In 1995, the deep gas contributed to $6.7\% of total supply amount of natural gas in the United States and is expected to be $18.7\% by 201.5. However, the development of the deep gas is a high risky business due to expensive investment and high portion of dry holes, although it is developed. Thus, for developing the deep gas economically, it is necessary to overcome many technical challenges. In this paper, for increasing success rate of the deep gas, 1) geologic and compositional characteristics, and production cost have been analyzed according to depth, 2) technical problems related to deep gas production have been summarized, and 3) finally future study areas for increasing application of the deep gas have been suggested. For reference, this paper was written based on the study results from USGS and Gas Research Institute(GRI), for the United States is doing the most active R&D in the deep gas area, and thus, has many reliable data.

• Economic and Environmental Geology
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• v.56 no.6
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• pp.729-744
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• 2023

The value of lithium has significantly increased due to the rising demand for electric cars and batteries. Lithium is primarily found in pegmatites, hydrothermally altered tuffaceous clays, and continental brines. Globally, groundwater-fed salt lakes and oil field brines are attracting attention as major sources of lithium in continental brines, accounting for about 70% of global lithium production. Recently, deep groundwater, especially geothermal water, is also studied for a potential source of lithium. Lithium concentrations in deep groundwater can increase through substantial water-rock reaction and mixing with brines. For the exploration of lithim in deep groundwater, it is important to understand its origin and behavior. Therefore, based on a nationwide preliminary study on the hydrogeochemical characteristics and evolution of thermal groundwater in South Korea, this study aims to investigate the distribution of lithium in the deep groundwater environment and understand the geochemical factors that affect its concentration. A total of 555 thermal groundwater samples were classified into five hydrochemical types showing distinct hydrogeochemical evolution. To investigate the enrichment mechanism, samples (n = 56) with lithium concentrations exceeding the 90th percentile (0.94 mg/L) were studied in detail. Lithium concentrations varied depending upon the type, with Na(Ca)-Cl type being the highest, followed by Ca(Na)-SO₄ type and low-pH Ca(Na)-HCO₃ type. In the Ca(Na)-Cl type, lithium enrichment is due to reverse cation exchange due to seawater intrusion. The enrichment of dissolved lithium in the Ca(Na)-SO₄ type groundwater occurring in Cretaceous volcanic sedimentary basins is related to the occurrence of hydrothermally altered clay minerals and volcanic activities, while enriched lithium in the low-pH Ca(Na)-HCO₃ type groundwater is due to enhanced weathering of basement rocks by ascending deep CO₂. This reconnaissance geochemical study provides valuable insights into hydrogeochemical evolution and economic lithium exploration in deep geologic environments.

• Proceedings of the KSEEG Conference
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• 2002.10a
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• pp.69-92
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• 2002

비금속 및 금속 광물자원의 탐사는 국가경영에 있어서 절대적으로 필요한 공공의 기반산업에 해당된다. 지금까지 수행되어 왔던 자원 탐사사업의 대부분은 비교적 개발이 용이한 천부 광상들에 집중되어 왔으며, 천부 광상들의 과도한 개발로 인하여 자원탐사의 범위가 점차 심부화 되고있는 실정이다. 지하 심부에 분포하는 광상들을 효율적으로 탐사해 내기 위해서는 분지 내 심부 퇴적층들에 대한 정밀한 대비와 평가가 요구된다. 그러나, 그 동안 천부 광상들의 평가에 적용되어 왔던 기재적 층서 원리들로는 심부에 분포하는 광상들을 도출해 내는데 한계가 있어 왔다 따라서, 분지 내 퇴적층들에 대한 보다 명확한 이해를 위해 새로운 고해상도의 층서틀 수립이 시급하다. 본 연구에서는 태백산분지 오오도비스 중기 퇴적층들에 대한 통합 층서적 접근을 통하여 고해상도 층서틀 수립에 대한 예를 제시하고자 한다. 이러한 통합 층서적 접근은 퇴적 분지의 지체 구조적 진화에 따른 층서를 규명하는데 있어서 보다 나은 통찰을 제공하고 있으며, 아울러 분지 내 비금속 및 금속 광물자원 탐사 및 개발사업의 효율성을 증대시키는데 사용될 수 있을 것이다. 따라서, 통합 층서적 접근을 통한 퇴적층들에 대한 고해상도 층서틀 수립은 분지 내에 부존 되어 있는 모든 형태의 자원 탐사 및 개발사업에 있어서 성공률을 극대화시킬 수 있는 새로운 층서적 규범으로 강조되어져야 한다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.495-498
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• 2004

대전시 유성구 한국원자력연구소 부근 지역의 심부 단열대 확인을 위해 BHTV 검층, 일정구간별 정압 주입시험을 실시하였다. BHTV 조사 결과 A Zone(100m～120m)과 B Zone(250m～280m)이 연결되었다고 판단되며, 일정구간별 정압주입시험을 통해 B Zone(250m～280m)과 C Zone(400～420m)의 연결성을 추측할 수 있었다. 또한, 시추공의 심도별 지하수위 자료를 통해 지하 250m 부근에서 그 상부와 하부의 지하수 시스템이 연속되지 않은 독립된 시스템을 갖는다고 추측된다. 이러한 결론은 MP system이 설치된 시추공의 구간별 압력변화 결과에 의해서도 확인된다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.354-357
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• 2004

방사성폐기물 처분 연구의 일환으로 대전 유성북부 화강암 지역내 200～500m 심도를 갖는 9개의 심부 시추공이 착정되었으며, 이중 3개 시추공에 대하여 다중패커시스템이 설치되어 장기적으로 심도별지하수의 수리특성, 화학특성 및 동위원소 특성이 모니터링 되고 있다. 다중패커시스템이 설치되기 전의시추공 지하수의 수리 및 지화학 특성은 심도에 따라 별다른 특성이 보이지 않지만, 다중패커시스템 설치 후, 심도에 따라 특징적인 수리 및 지화학특성을 보여주고 있다. 또한, 다중패커시스템이 설치된 시추공의 경우, 최상부 구간을 제외하고 모든 구간 지하수의 수리화학특성은 일정기간이 경과한 후에는 각 구간별로 거의 일정한 값으로 유지되고 있음을 보여준다. 그러나, 지하수의 함양특성이 크게 변하는 우기 동안에는 지하수 수두압이 심도 약350m의 구간까지 변화되는 특성을 보여주고 있다. 동위원소특성 역시 심도구간에 따라 특징적인 값을 보여주며, 장기적으로 일정한 구간별 특정 값을 보여주고 있다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.36-39
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• 2002

온양온천 지역 지하수에 대한 수질 조사결과, 심부 피압대수층에서 산출되는 온천수의 수질이 천층의 저온지하수에 강하게 영향을 받고 있음이 확인되었다. 본 연구에서는 이들 두 종류의 물 사이에서 매우 높은 상대적인 농도차이를 보이는 불소이온농도를 이용하여 천층지하수의 영향정도를 정량화할 수 있었다. 이 같은 방법으로 계산된 천층지하수 영향정도는 온천수취수정에 따라 다르게 나타나고 있었으나, 최소 10 %에서 최대 50%에 이르는 것으로 확인되었다. 이와 같은 관찰결과는 오염에 취약하지 않은 것으로 알려진 심부의 피압대수층도 과도한 양수가 이루어지게 되면 오염에 취약한 천층부의 지하수를 다량 심부로 유입시킴으로써, 점차 오염되어질 수 있음을 보여주는 것이다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.4
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• pp.491-505
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• 2018

As an alternative to deep geological disposal technology, which is considered as a reference concept, the domestic applicability of deep borehole disposal technology for high level radioactive waste, including spent fuel, has been preliminarily evaluated. Usually, the environment of deep borehole disposal, at a depth of 3 to 5 km, has more stable geological and geo-hydrological conditions. For this purpose, the characteristics of rock distribution in the domestic area were analyzed and drilling and investigation technologies for deep boreholes with large diameter were evaluated. Based on the results of these analyses, design criteria and requirements for the deep borehole disposal system were reviewed, and preliminary reference concept for a deep borehole disposal system, including disposal container and sealing system meeting the criteria and requirements, was developed. Subsequently, various performance assessments, including thermal stability analysis of the system and simulation of the disposal process, were performed in a 3D graphic disposal environment. With these analysis results, the preliminary evaluation of the domestic applicability of the deep borehole disposal system was performed from various points of view. In summary, due to disposal depth and simplicity, the deep borehole disposal system should bring many safety and economic benefits. However, to reduce uncertainty and to obtain the assent of the regulatory authority, an in-situ demonstration of this technology should be carried out. The current results can be used as input to establish a national high-level radioactive waste management policy. In addition, they may be provided as basic information necessary for stakeholders interested in deep borehole disposal technology.

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.181-184
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• 2001