High-level Radioactive Waste Disposal Facility Research Articles

The importance of surface ruptures and fault damage zones in earthquake hazard assessment: a review and new suggestions

Abstract Large earthquakes (M W > c. 6) generate surface ruptures and strong ground motions, resulting in extensive property damage and loss of lives. The earthquake damage and causality levels depend, for example, on the earthquake magnitude, seismic wave characteristics, the distance from the epicentre, the depth of earthquake and the foundation of related area . However, these factors cannot all be known for future earthquakes, because the exact times and locations of earthquakes cannot be predicted with the current technology. Thus, it is only possible to prepare for earthquakes by implementing anti-seismic design codes based on the local geological conditions. With accurate information about the locations of active faults or potential surface ruptures and deformation patterns, earthquake-prone areas could be avoided during site selection, especially for important facilities such as nuclear power plants and high-level radioactive waste disposal facilities. In this study, we investigated several factors for earthquake hazard estimation, focusing on the fault damage zones and respect distances. Fault damage zones around faults are mainly controlled by fault types, tip modes, exposed locations and slip senses along the fault. The characteristics of geological faults and earthquake ruptures show asymmetrical displacements and damage patterns, making it difficult to estimate respect distances and surface deformations. Therefore, both the respect distance and fault damage zone should be considered when identifying safe regions. This information will facilitate earthquake hazard assessment and appropriate site selection to reduce earthquake hazards in earthquake-prone areas.

The Core Agenda of Public Debate on the Cigéo Project in France

원자력 발전은 상대적으로 저렴한 발전비용으로 우리나라 경제성장의 밑거름이 되었던 에너지원으 로 알려져 있으나 방사성 폐기물 처리에 대해서는 논란이 지속적으로 발생하고 있다. 본 연구에서는 프랑스의 고준위 방폐장인 Cigéo의 설치에 대한 정책 수립과정과 공론화 과정을 살펴보고, 시맨틱네트워크 분석(Semantic Network Analysis)을 통해 프랑스의 고준위 방폐장 건설과정에서 제시되었던 여러 가지 핵심적인 의제들을 파악하였다. 분석결과 연결중심성이 높은 상위 10위의 주제어는 토론사업, 폐기물, 저장, 공공의, 질문, 위험, 시민, 참여, 부지 등이다. 프랑스의 사례를 볼 때 우리나라의 고준위 방폐장 설치단계에서 다양한 정책행위자들의 참여와 토론을 유도하고, 현세대와 미래세대간의 형평성을 고려해야 하는 한편, 사전적으로 관련 법제도를 정비해야 한다는 정책적 시사점을 제시할 수 있다.Nuclear power generation has been the cornerstone of economic growth due to low generation costs in Korea, but the disposal of radioactive waste continues to be controversial. Looking back on the controversy at the time of the establishment of low-level radioactive waste disposal facilities, it is expected that the establishment of high-level radioactive waste disposal facilities will lead to enormous social conflicts, urgently seeking social consensus. In this study, we examined the process of establishing the policy and public debate on the installation of Cigeo, a high-level radioactive waste disposal facility in France. In addition, through SNA (semantic network analysis), we identified several key agenda items which had been presented during the installation process, including debate, business, waste, storage, public, question, danger, citizen, participation, and site. Based on the case of Cigeo, we suggested several policy implications that it is necessary to promote participation and discussion of various policy actors and to consider intergenerational equity as well as preemptive legal action.

Numerical study on the shear-flow behavior and transport process in rough rock fractures

This paper presents a systematic research for understanding mechanical shearing effects on the fluid flow and the solute transport behavior of rough fractures through a numerical simulation approach. The aperture fields were modeled based on a real rock fracture geometry and the normal displacement obtained from the shear-flow test. The fluid flow through the rough fracture under shear was simulated using a finite element code that solves the Reynolds equation, and the transport behavior through the rough fracture under shear was simulated calculating the advection–dispersion equation. The results show that the fracture apertures increase as the shear displacement increases, with a few major flow channels detected through the fracture. The shear-induced flow channels increase both flow connectivity and transport connectivity, which accelerate the movement of solutes in a particular direction and lead to early breakthrough of the contaminants. Adsorption, acting as a retardation term, has a decisive influence on the transport process. These results can give a basic knowledge of the hydromechanical and solute transport progress through fracture, and will be helpful to safety assessment for high-level radioactive waste disposal facilities.

Gas breakthrough and emission through unsaturated compacted clay in landfill final cover

Determination of gas transport parameters in compacted clay plays a vital role for evaluating the effectiveness of soil barriers. The gas breakthrough pressure has been widely studied for saturated swelling clay buffer commonly used in high-level radioactive waste disposal facility where the generated gas pressure is very high (in the order of MPa). However, compacted clay in landfill cover is usually unsaturated and the generated landfill gas pressure is normally low (typically less than 10kPa). Furthermore, effects of clay thickness and degree of saturation on gas breakthrough and emission rate in the context of unsaturated landfill cover has not been quantitatively investigated in previous studies. The feasibility of using unsaturated compacted clay as gas barrier in landfill covers is thus worthwhile to be explored over a wide range of landfill gas pressures under various degrees of saturation and clay thicknesses. In this study, to evaluate the effectiveness of unsaturated compacted clay to minimize gas emission, one-dimensional soil column tests were carried out on unsaturated compacted clay to determine gas breakthrough pressures at ultimate limit state (high pressure range) and gas emission rates at serviceability limit state (low pressure range). Various degrees of saturation and thicknesses of unsaturated clay sample were considered. Moreover, numerical simulations were carried out using a coupled gas–water flow finite element program (CODE-BRIGHT) to better understand the experimental results by extending the clay thickness and varying the degree of saturation to a broader range that is typical at different climate conditions. The results of experimental study and numerical simulation reveal that as the degree of saturation and thickness of clay increase, the gas breakthrough pressure increases but the gas emission rate decreases significantly. Under a gas pressure of 10kPa (the upper bound limit of typical landfill gas pressure), a 0.6m or thicker compacted clay is able to prevent gas breakthrough at degree of saturation of 60% or above (in humid regions). Furthermore, to meet the limit of gas emission rate set by the Australian guideline, a 0.6m-thick clay layer may be sufficient even at low degree of saturation (i.e., 10% like in arid regions).

A STUDY OF THE PRESSURE SOLUTION AND DEFORMATION OF QUARTZ CRYSTALS AT HIGH pH AND UNDER HIGH STRESS

Bentonite is generally used as a buffer material in high-level radioactive waste disposal facilities and consists of 50% quartz by weight. Quartz strongly affects the behavior of bentonite over very long periods. For this reason, quartz dissolution experiment was performed under high-pressure and high-alkalinity conditions based on the conditions found in a high-level radioactive waste disposal facility located deep underground. In this study, two quartz dissolution experiments were conducted on 1) quartz beads under low-pressure and high-alkalinity conditions and 2) a single quartz crystal under high-pressure and high-alkalinity conditions. Following the experiments, a confocal laser scanning microscope (CLSM) was used to observe the surfaces of experimental samples. Numerical analyses using the finite element method (FEM) were also performed to quantify the deformation of contact area. Quartz dissolution was observed in both experiments. This deformation was due to a concentrated compressive stress field, as indicated by the quartz deformation of the contact area through the FEM analysis. According to the numerical results, a high compressive stress field acted upon the neighboring contact area, which showed a rapid dissolution rate compared to other areas of the sample.

Berthierine-like mineral formation and stability during the interaction of kaolinite with metallic iron at 90 C under anoxic and oxic conditions

The interaction between metallic iron and kaolinite was studied in conditions relevant to those that may be encountered in a high-level radioactive waste disposal facility in geological formation. Experiments were carried out under anoxic atmosphere at 90 °C and in chloride solutions to simulate conditions close to disposal facilities. KGa-2 kaolinite was put in contact with powdered metallic iron in batch experiments for durations of 1, 3, and 9 months. Solutions extracted from the end-products were analyzed (pH, Eh, conductivity, and cation concentrations). End-products were characterized by a set of chemical (oxide analyses, CEC, EDXS) and mineralogical techniques (SEM, TEM, XRD, and FTIR), textural analyses (nitrogen adsorption and low-pressure argon adsorption), XPS, and Mossbauer spectroscopy. In another set of experiments the system was changed from anoxic to oxic conditions to evaluate the stability of the system in the presence of O2. The interaction between metallic iron and kaolinite led to a fast initial reaction as major modifications took place during the first month. The partial oxidation of metallic iron resulted in a pH increase and negative Eh values. Iron was not found in solution but in two new Fe-rich phases: magnetite in very low amounts and a Fe-rich clay phase, belonging to the berthierine family. The Si and Al of the berthierine are derived from the partial alkaline dissolution of kaolinite, mostly along edge faces. TEM-EDXS local analyses showed that the composition of resulting particles consisted in mixtures of berthierine and kaolinite layers. Clay particles became thicker with the epitaxial growth of berthierine layers on the basal surfaces of pristine kaolinite. Neoformed berthierine was not stable in the presence of O2 at 90 °C. Berthierine layers dissolved, iron was mobilized to form iron oxides and oxyhydroxides while kaolinite layers recrystallized from released Al and Si.

Swelling characteristics of bentonites in artificial seawater

Bentonite is currently designated for use as a buffer material for the repository of high-level radioactive waste because such a material requires swelling characteristics to seal the waste. A high-level radioactive waste disposal facility may be built in a coastal area of Japan because transportation of this waste by ships is feasible. Therefore, it is important to investigate the effects of seawater on a bentonite-based buffer. This study is intended to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five common types of bentonite. The experiments described herein clarify the relations between the influence of seawater grade and compaction density, type of exchangeable cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, suitable specifications have been defined for a bentonite-based buffer that can withstand the effects of seawater.

XANES−EXAFS Analysis of Se Solid-Phase Reaction Products Formed upon Contacting Se(IV) with FeS2and FeS

The solid-phase Se speciation after short-term (3 weeks) contact of selenite [Se(IV)] oxyanions with pyrite (FeS2) and troilite (FeS) was investigated using X-ray absorption spectroscopy (XAS; X-ray absorption near-edge spectroscopy-extended X-ray absorption fine structure (XANES-EXAFS)). It was found that the nature of the sulfide mineral dictates the final speciation since respectively Se(0) and FeSe(x) were formed, meaning that the reaction mechanism is different and that these phases cannot be regarded as geochemically similar. The experimental results support the previously proposed sorption/ reduction mechanism for the reaction of selenite with pyrite. In the presence of troilite the reduction proceeds through the intermediate formation of Se(0) by reduction of selenite with dissolved sulfide. XAS data recorded for the FeS2 and FeS were compared with different Se reference phases, ranging in oxidation state from -II to +IV, used for validation of the XAS analysis methodology. This methodology can in principle be used to analyze Se phases formed in "in situ" geochemical conditions such as high-level radioactive waste disposal facilities.

Theoretical Equations on Hydraulic Conductivities of Bentonite-Based Buffer and Backfill for Underground Disposal of Radioactive Wastes

Compacted bentonite and sand-bentonite mixtures are sought as buffer and backfill materials for high-level radioactive waste disposal facilities because they have very low permeability. To establish specifications such as the dry density and sand-bentonite mass ratio for buffer and backfill materials, we must quantitatively evaluate a material’s hydraulic conductivities. This study presents theoretical new equations for evaluating the hydraulic conductivity of compacted bentonites and sand-bentonite mixtures. New equations are proposed for evaluating the flow velocity of interlayer water between two montmorillonite parallel-plate layers considering the swelling behaviors of montmorillonite. Furthermore, a prediction method for hydraulic conductivity of compacted bentonite and sand-bentonite mixtures is presented by combining new equations with previous equations for evaluating swelling behavior of montmorillonite in bentonite. The applicability of this method is clarified by comparing predicted results wi...

366. 高レベル放射性廃棄物処分地選定の社会的受容性を高めるための課題に関する考察

366. 高レベル放射性廃棄物処分地選定の社会的受容性を高めるための課題に関する考察