• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.4
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• pp.323-338
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• 2007

For the assessment of the performance and safety of a deep underground radioactive repository system, the thermal, hydraulic, mechanical, and chemical behaviors and their coupling should be studied. In order to analyze the THMC coupling behavior more effectively, which requires complex mathematical models and modelling techniques, DECOVALEX international cooperation project was launched in 1992. Since its beginning, four major stages of the project were successfully completed and THMC modelling techniques for various conditions could be developed. In this study, the current status and major achievements from the project were reviewed and possible benefits of the participation to the project were discussed.

• Tunnel and Underground Space
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• v.19 no.6
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• pp.507-516
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• 2009

In cases of high-level radioactive waste repositories, heat load is apparent by radioactive waste decay. The safety of a waste repository would be influenced by changing circumstances caused by heat transfer through rock. Thus, a ventilation system is necessary to secure the waste repository. The first priority for building an appropriate ventilation system is completing a computer simulation research with thermal rock properties and a heat transfer coefficient. In this study, the heat transfer coefficient in KURT was calculated using the measurement of inner circumstance factors that include dry bulb and wet bulb temperature, rock surface temperature, and barometric pressure. The heater that is 2 m in length and 5 kw in capacity heats the inside of rock in the research module by $90^{\circ}C$. As a result of determining the heat transfer coefficient in the heating section, the changes of heat transfer coefficient were found to be a maximum of 7.9%. The average heat transfer coefficient is approximately 4.533 w/$m^2{\cdot}K$.

• Nuclear Engineering and Technology
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• v.21 no.4
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• pp.267-276
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• 1989

A numerical model for nuclide migration through fractured rock media has been developed. Nuclide transport with groundwater in rock fissures and the diffusion of nuclides into rock matrix are considered one-dimensionally . In the safety assessment of the repository for radioactive waste, this one-dimensional model by the finite-difference scheme, which enables us not only to use more realistic boundary conditions but also to model the nonhomogeneous rock medium as the multilayered media, can be used effectively with the analytical mode. The solution by the numerical model will be verified analytically, and then extended to the double-layered rock medium transport model.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.203-212
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• 2009

The prediction of near field behavior around an underground high-level radioactive waste repository is important for the repository design as well as the safety assessment. In this study, a sensitivity analysis for seven parameters consisted of design parameters and material properties was carried out using a three-dimensional finite difference code. From the sensitivity analysis, it was found that the effects of borehole spacing, tunnel spacing, cooling time and rock thermal conductivity were more significant than the other parameters. For getting a statistical distribution of buffer and rock temperatures around the repository, an artificial neural network, backpropagation, was applied. The reliability of the trained neural network was tested with the cases with randomly chosen input parameters. When the parameter variation is within ${\pm}10%$, the prediction from the network was found to be reliable with about a 1% error. It was possible to calculate the temperature distribution for many cases quickly with the trained neural network. The buffer and rock temperatures showed a normal distribution with means of $98^{\circ}C$ and $83.9^{\circ}C$ standard deviations of $3.82^{\circ}C$ and $3.67^{\circ}C$, respectively. Using the neural network, it was also possible to estimate the required change in design parameters for reducing the buffer and rock temperatures for $1^{\circ}C$.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1996.03a
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• pp.43-54
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• 1996

장대 터널, 지하철, 양수발전소, 유류 비축기지, 핵폐기물 지하처분장 및 농축산물 지하 저장소 등 지하공간개발의 구상 및 그 건설이 활발한 가운데, 그 관련기술에 대한 관심이 고조되고 있다. 특히 지하공간개발을 위한 사전 설계단계 및 시공에 있어 국내ㆍ외적으로 현지암반 초기응력 측정은 중요한 요소로 대두되고 있다. (중략)

• Tunnel and Underground Space
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• v.17 no.1 s.66
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• pp.17-25
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• 2007

Research and development for disposal of contaminants including radioactive wastes in deep underground have been carried out from laboratory works. However, validation and reliability of the data from the laboratory are arguing issues because they are not obtained from real disposal situations. Underground research laboratory (URL) is not only a solution to overcome such limitations, but also a valuable facility for performance assessment as an engineering scale. However, it requires much budget, and environmental issues can give rise to social conflicts easily. Such considering points related to URL are discussed as well as current status of worldwide URLs are introduced. Furthermore study plans for solute transport in a small-scale underground research tunnel (KURT), which was authorized recently as an non-radioactive facility in Korea, also described.

• Computational Structural Engineering
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• v.18 no.1 s.67
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• pp.45-50
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• 2005

원자력 발전 과정에서 부산물로 발생되는 사용후 핵연료와 같은 고준위 방사성 폐기물은 수백 만년 동안 인간 및 자연 환경에 영향을 미치기 때문에 엄격한 관리가 요구된다. 이를 위하여 세계 각국에서는 스웨덴의 고준위방사성폐기물 처분개념인 KBS-3개념과 같이 고준위 방사성폐기물을 지하 500미터 심도의 암반에 영구 처분하기 위하여 많은 연구를 수행하고 있다. 이러한 연구 활동의 일환으로 고준위 방사성폐기물에서 발생하는 방사성 붕괴열로 인한 처분장 인접 암반에서의 응력 변화 및 이에 따른 주변 암반대에서의 지하수 유동 현상 규명을 위한 연구들 가운데 전산해석분야의 연구로 가장 활발히 진행되고 있는 것이 DECOVALEX 국제 공동 연구이다. 본고에서는 그 동안 진행되었던 DECOVALEX 연구 수행내용에 대하여 살펴보고자 한다.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.107-119
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• 2022

Excavation-Disturbed Zone (EDZ) is an important design factor in constructing final disposal facilities for spent nuclear fuel, since EDZ affects mechanical stability including a spacing between disposal holes, and the hydraulic properties within EDZ plays a significant role in estimating in-flow rate of groundwater as well as a subsequent corrosion rate of a canister. Thus, it is highly required to characterize in-situ EDZ with precision and control the EDZ occurrence while excavating disposal facilities and constructing relevant underground research facilities. In this report, we not only reviewed EDZ-related researches carried out in the ONKALO facility of Finland but also examined appropriate methods for field inspection and quality control of EDZ occurrence. From the review, GPR can be the most efficient method for in-situ characterization of EDZ since it does not demand drilling a borehole that may disturb a surrounding environment of caverns. And the EDZ occurrence was dominant at a cavern floor and it ranged from 0 to 70 cm. These can provide useful information in developing necessary EDZ-related regulations for domestic disposal facilities.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.419-434
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• 2020

In this study, the damage parameters of Mazars model for KURT (KAERI Underground Research Tunnel) granite are measured form uniaxial compressive and Brazilian tests under the simulated coupled condition of a deep geological disposal. The tests are conducted in three different temperatures (15℃, 45℃, and 75℃) and dry/saturated conditions. Major model parameters such as maximum effective tensile strain (𝜖_d0), A_t, B_t, A_c, and B_c differ from the typical reference values of concrete specimens. This is likely due to the difference in elastic modulus between rock and concrete. It is found that the saturation of specimens causes an increase in value of B_t and B_c while, the rise in temperature increases 𝜖_d0 and B_t and decreases B_c. The damage model obtained from this study will be used as the primary input parameters in the development of coupled Thermo-Hydro-Mechanical Damage numerical model in KAERI.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.587-609
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• 2019

Short-and long-term stabilities of bentonite, favored material as buffer in geological repositories for high-level waste were reviewed in this paper in addition to alternative design concepts of buffer to mitigate the thermal load from decay heat of SF (Spent Fuel) and further increase the disposal efficiency. It is generally reported that the irreversible changes in structure, hydraulic behavior, and swelling capacity are produced due to temperature increase and vapor flow between $150{\sim}250^{\circ}C$. Provided that the maximum temperature of bentonite is less than $150^{\circ}C$, however, the effects of temperature on the material, structural, and mineralogical stability seems to be minor. The maximum temperature in disposal system will constrain and determine the amount of waste to be disposed per unit area and be regarded as an important design parameter influencing the availability of disposal site. Thus, it is necessary to identify the effects of high temperature on the performance of buffer and allow for the thermal constraint greater than $100^{\circ}C$. In addition, the development of high-performance EBS (Engineered Barrier System) such as composite bentonite buffer mixed with graphite or silica and multi-layered buffer (i.e., highly thermal-conductive layer or insulating layer) should be taken into account to enhance the disposal efficiency in parallel with the development of multilayer repository. This will contribute to increase of reliability and securing the acceptance of the people with regard to a high-level waste disposal.