• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4005-4012
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• 2022

As high-level radioactive waste (HLW) generated from nuclear power plants is harmful to the human body, it must be safely disposed of by an engineered barrier system consisting of disposal canisters and buffer and backfill materials. A gap exists between the canister and buffer material in a HLW repository and between the buffer material and natural rock-this gap may reduce the water-blocking ability and heat transfer efficiency of the engineered barrier materials. Herein, the basic characteristics and thermal properties of granular bentonite, a candidate gap-filling material, were investigated, and their effects on the temperature change of the buffer material were analyzed numerically. Heat transfer by air conduction and convection in the gap were considered simultaneously. Moreover, by applying the Korean reference disposal system, changes in the properties of the buffer material were derived, and the basic design of the engineered barrier system was presented according to the gap filling material (GFM). The findings showed that a GFM with high initial thermal conductivity must be filled in the space between the buffer material and rock. Moreover, the target dry density of the buffer material varied according to the initial wet density, specific gravity, and water content values of the GFM.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.306-314
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• 2003

Engineered barrier test facility is specially designed to demonstrate the performance of engineered barrier system for the near-surface disposal facility under the domestic environmental conditions. Comprehensive measurement systems for the water content, temperature, matric potential are installed within each test cell. In this study, short-term monitoring of the behavior of multi-layered cover system is implemented with artificial rainfall system. The periodic measurement data are collected and analyzed by a dedicated database management system, and provide a basis for performance verification of the disposal cover design.

• 방사성폐기물학회지
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• 제2권1호
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• pp.23-34
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• 2004

To validate the previous conceptual design of cover system, construction of the engineered barrier test facility is completed and the performance tests of the disposal cover system are conducted. The disposal test facility is composed of the multi-purpose working space, the six test cells and the disposal information space for the PR center. The dedicated detection system measures the water content, the temperature, the matric potential of each cover layer and the accumulated water volume of lateral drainage. Short-term experiments on the disposal cover layer using the artificial rainfall system are implemented. The sand drainage layer shows the satisfactory performance as intended in the design stage. The artificial rainfall does not affect the temperature of cover layers. It is investigated that high water infiltration of the artificial rainfall changes the matric potential in each cover layer. This facility is expected to increase the public information about the national radioactive waste disposal program and the effort for the safety of the planned disposal facility.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4120-4124
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• 2023

High-level radioactive waste produced by nuclear power plants are disposed subterraneously utilizing an engineered barrier system (EBS). A gap inevitably exists between the disposal canisters and buffer materials, which may have a negative effect on the thermal transfer and water-blocking efficiency of the system. As few previous experimental works have quantified this effect, this study aimed to create an experimental model for investigating differences in the temperature changes of bentonite buffer in the presence and absence of air gaps between it and a surrounding stainless steel cell. Three test scenarios comprised an empty cell and cells partially or completely filled with bentonite. The temperature was measured inside the buffers and on the inner surface of their surrounding cells, which were artificially heated. The time required for the entire system to reach 100℃ was approximately 40% faster with no gap between the inner cell surface and the bentonite. This suggests that rock-buffer spaces should be filled in practice to ensure the rapid dissipation of heat from the buffer materials to their surroundings. However, it can be advantageous to retain buffer-canister gaps to lower the peak buffer temperature.

• 방사성폐기물학회지
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• 제10권4호
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• pp.281-294
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• 2012

현재까지 개발된 고준위폐기물 심지층처분장의 열-수리-역학적 복합거동 해석을 위한 전산 코드의 현황을 조사하고, 문헌에 보고된 각 코드에 의한 계산치와 현장실험 측정치의 비교 결과를 이용하여, 기존 전산 코드들의 신뢰도를 분석하였다. 개발된 전산코드들은 완충재가 없는 처분장에서는 붕괴열에 따른 암반의 열-수리-역학적 거동을 비교적 잘 모사하였으나, 포화 경암층에 위치한 완충재가 존재하는 처분장의 공학적방벽시스템 내에서 일어나는 열-수리-역학적 복합거동의 예측은 만족스럽지 못하였다. 현재 제안된 열-수리-역학적 복합거동 해석모델을 고준위폐기물 처분장 공학적방벽시스템의 거동 해석에 적용하기 위해서는 완충재 내의 수분함량 및 전 압력 분포를 보다 정교하게 모사할 수 있도록 수학적 모델의 개선이 필요하다.

• 터널과지하공간
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• 제17권6호
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• pp.464-474
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• 2007

고준위폐기물처분장의 성능 및 안전성 향상을 위해서 공학적방벽(engineered barrier)에 대한 실증이 필요하다. 우리나라 기준처분시스템에 대한 엔지니어링 규모의 실험장치(KENTEX)를 제작 설치하고, 공학적방벽에서의 열-수리-역학적 거동 규명을 위한 실증실험을 수행하였다. KENTEX 실험은 2005년 5월 31일에 시작되어 현재 성공적으로 진행 중에 있으며, 지금까지 얻어진 실험결과로부터 공학적방벽에서의 열-수리-역학적 거동에 대한 중간결론을 얻을 수 있었다. 벤토나이트 블록 내 온도는 실험 시작 후 수 주 만에 정상상태에 도달하였고, 온도분포는 히터에 가까울수록 높고 멀어질수록 낮은 값을 보였다. 수분함량은 히터 쪽보다는 지하수가 유입되는 실린더 벽면 부근에서 높은 값을 가졌고, 건조-습윤 과정에 의한 벤토나이트 블록의 수화는 측정위치에 따라 달랐다. 실험기간 동안 벤토나이트 블록에 작용하는 압력은 블록의 포화도 (그 결과, 팽윤압)이 증가할수록 증가하였다. 히터 부근에서는 벤토나이트의 열응력이나 블록 공극 내 증기압도 중요한 역할을 하였다.

• Geomechanics and Engineering
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• 제35권1호
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• pp.13-27
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• 2023

The model production for large-scale (lateral length ≥ 2.0 m) capillary barrier (CB) model tests is time and cost-intensive. To address these limitations, the framework of a small-scale CB (SSCB) model test under the lateral no-flow condition has been established. In this study, to validate the experimental methodology of the SSCB model test, a series of seepage analyses on the SSCB model test and engineered slopes in the same and additional test conditions was performed. First, the seepage behavior and diversion length (L_D) of the CB system were investigated under three rainfall conditions. In the seepage analysis for the engineered slopes with different slope angles and sand layer thicknesses, the L_D increased with the increase in the slope angle and sand layer thickness, although the increase rate of the L_D with the sand layer thickness exhibited an upper limit. The L_D values from the seepage analysis agreed well with the results estimated from the laboratory SSCB mode test. Therefore, it can be concluded that the experimental methodology of the SSCB model test is one of the promising alternatives to efficiently evaluate the water-shielding performance of the CB system for an engineered slope.

• 방사성폐기물학회지
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• 제18권2호
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• pp.133-141
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• 2020

고준위방사성폐기물의 처분은 고심도 암반내에 처분시스템을 구축하는 심층 처분방법이 고려된다. 심층 처분은 처분용기, 완충재, 뒷채움재, 근계암반의 설계 요소인 공학적방벽과 천연 방벽으로 구성된다. 공학적방벽 중에서 벤토나이트 완충재는 암반으로부터 유입되는 지하수 흐름을 최소화하고 핵종 유출을 저지하는 기능을 한다. 지하수 유입으로 인한 완충재의 수리전도도 특성 규명은 처분장 공학적방벽의 안정성 및 건전성에 대한 성능 평가에 있어 중요한 사안이다. 본 연구에서는 경주 벤토나이트를 이용하여 다양한 건조밀도와 온도 조건에 따라 포화 수리전도도 실험을 수행하였으며, 120개의 실험 결과를 다중 회귀 분석을 통해 수리전도도 추정 모델을 제시하였다. 실험 결과에서는 건조밀도가 커질수록 수리전도도가 감소하는 경향이 나타났다. 또한, 온도가 증가할수록 수리전도도가 증가하였다. 이러한 실험 결과들을 종합한 다중 회귀 분석 결과에서는 수리전도도 추정식의 결정계수(R²)가 0.93으로 높게 나타났다. 본 연구에서 제시된 수리전도도 추정식은 벤토나이트 완충재의 성능과 연관된 건조밀도와 온도의 영향을 고려하여 처분시스템의 공학적방벽 설계에 활용 될 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.1041-1048
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• 2021

An engineered barrier system (EBS) for the disposal of high-level radioactive waste (HLW) is composed of a disposal canister with spent fuel, a buffer material, a gap-filling material, and a backfill material. As the buffer is located in the empty space between the disposal canisters and the surrounding rock mass, it prevents the inflow of groundwater and retards the spill of radionuclides from the disposal canister. Due to the fact that the buffer gradually becomes saturated over a long time period, it is especially important to investigate its thermal-hydro-mechanical-chemical (THMC) properties considering variations of saturated condition. Therefore, this paper suggests a new method of measuring thermal conductivity and water suction for single compacted bentonite at various levels of saturation. This paper also highlights a convenient method of saturating compacted bentonite. The proposed method was verified with a previous method by comparing thermal conductivity and water suction with respect to water content. The relative error between the thermal conductivity and water suction values obtained through the proposed method and the previous method was determined as within 5% for compacted bentonite with a given water content.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.1191-1198
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• 2023

Bentonite buffer material is a critical component in an engineered barrier system (EBS) for disposing high-level radioactive waste (HLW). The bentonite buffer material protects the disposal canister from groundwater penetration and releases decay heat to the surrounding rock mass; thus, it should possess high thermal conductivity, low hydraulic conductivity, and moderate swelling pressure to safely dispose the HLWs. Bentonite clay is a suitable buffer material because it satisfies the safety criteria. Several additives have been suggested as mixtures with bentonite to increase the thermal-hydraulic-mechanical-chemical (THMC) properties of bentonite buffer materials. Therefore, this study investigated the geotechnical, mineralogical, and THMC properties of several candidate additives such as sand, graphite, granite, and SiC powders. Datasets obtained in this study can be used to select adequate additives to improve the THMC properties of the buffer material.