고준위폐기물을 심지층에 처분하기 위한 공학적방벽의 구성 요소로는 처분용기, 완충재, 뒷채움재 등이 있다. 이 중 완충재는 처분용기와 근계암반 사이의 빈 공간에 설치되는 물질로써, 주변 지하수로부터 처분용기를 보호하며 방사성 핵종의 유출을 저지하는 등의 역할을 한다. 또한 처분용기에서 발생하는 고온의 열량은 완충재로 직접 전파되기에 완충재의 열전도도는 처분시스템의 안전성 평가에 있어 매우 중요하다고 할 수 있다. 따라서 본 연구에서는 국내 경주산 압축 벤토나이트 완충재의 열전도도 특성을 규명하였으며 실제 처분용기에서 발생되는 고온의 특성을 반영하여 상온에서 80~90℃까지의 범위에서 압축 벤토나이트의 열전도도를 측정하였다. 온도증가에 따라 압축 벤토나이트의 열전도도는 5~20% 가량 증가하였으며 초기 포화도가 클수록 열전도도 증가는 더 크게 나타났다.
고준위폐기물을 심지층에 처분하기 위한 공학적방벽의 구성 요소로는 처분용기, 완충재, 뒷채움재 등이 있다. 이 중 완충재는 처분용기와 근계암반 사이의 빈 공간에 설치되는 물질로써, 주변 지하수로부터 처분용기를 보호하며 방사성 핵종의 유출을 저지하는 등의 역할을 한다. 또한 처분용기에서 발생하는 고온의 열량은 완충재로 직접 전파되기에 완충재의 열전도도는 처분시스템의 안전성 평가에 있어 매우 중요하다고 할 수 있다. 따라서 본 연구에서는 국내 경주산 압축 벤토나이트 완충재의 열전도도 특성을 규명하였으며 실제 처분용기에서 발생되는 고온의 특성을 반영하여 상온에서 80~90℃까지의 범위에서 압축 벤토나이트의 열전도도를 측정하였다. 온도증가에 따라 압축 벤토나이트의 열전도도는 5~20% 가량 증가하였으며 초기 포화도가 클수록 열전도도 증가는 더 크게 나타났다.
An engineered barrier system (EBS) for the geological disposal of high-level radioactive waste (HLW) consists of a disposal canister packed with spent fuel, buffer material, backfill material, and gap-filling material. The buffer material fills the space between the canister and the near-field rock,...
An engineered barrier system (EBS) for the geological disposal of high-level radioactive waste (HLW) consists of a disposal canister packed with spent fuel, buffer material, backfill material, and gap-filling material. The buffer material fills the space between the canister and the near-field rock, thus serving to restrain the release of radionuclides and protect the canister from groundwater penetration. Furthermore, as significant amounts of heat energy are released from the canister to the surrounding rock, the thermal conductivity of the buffer plays an important role in maintaining the safety of the entire disposal system. Therefore, given the high levels of heat released from disposal canisters, this study measured the thermal conductivities of compacted bentonite buffers from Gyeongju under temperature variations ranging 25 to 80~90℃. There was a 5~20% increase in thermal conductivity as the temperature increased, and the temperature effect increased as the degree of saturation increased.
An engineered barrier system (EBS) for the geological disposal of high-level radioactive waste (HLW) consists of a disposal canister packed with spent fuel, buffer material, backfill material, and gap-filling material. The buffer material fills the space between the canister and the near-field rock, thus serving to restrain the release of radionuclides and protect the canister from groundwater penetration. Furthermore, as significant amounts of heat energy are released from the canister to the surrounding rock, the thermal conductivity of the buffer plays an important role in maintaining the safety of the entire disposal system. Therefore, given the high levels of heat released from disposal canisters, this study measured the thermal conductivities of compacted bentonite buffers from Gyeongju under temperature variations ranging 25 to 80~90℃. There was a 5~20% increase in thermal conductivity as the temperature increased, and the temperature effect increased as the degree of saturation increased.
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제안 방법
Therefore, this study measured the thermal conductivity of compacted bentonite produced in Korea for temperatures ranging from room temperature to 80~90℃, with consideration of the degree of saturation and dry density.
In disposal environments, bentonite buffers inevitably undergo temperature increases due to the high-temperature decay heat from the disposal canister in addition to groundwater inflow from the surrounding rock. With the thermal conductivity of compacted bentonite buffers being one of the most important parameters in the safety assessment of EBS, this study evaluated thermal conductivity variations in compacted Gyeongju bentonite by considering temperature increases and various initial water contents.
대상 데이터
The reference materials used in this experiment were Quartz (1.42 W/(m·K)),silicon rubber (0.24 W/(m·K)), and Styrofoam (0.036W/(m·K)) [17].
이론/모형
Thermal conductivity was measured for temperatures in the range of 25℃ to 80~90℃ according to various initial water contents. The thermal conductivity of the compacted bentonite was measured using a QTM-500 instrument based on the principle of the transient hot wire method. The compacted bentonite samples and probe were completely sealed with heat resistant tape and placed in a convection oven to measure thermal conductivity according to temperature variations.
Using the transient hot wire method, the thermal conductivity of the compacted bentonite was measured using a QTM-500 (Kyoto Electronics) instrument. The transient hot wire method is a principle for thermal conductivity measurement according to Equation (1): it involves the heating time and temperature rise relationship between heating wires when a constant amount of heat is applied toa heating wire in a medium [17].
성능/효과
As heat transfer by water does not occur under dry conditions, thermal conductivity did not exhibit significant increases. The results showed that the higher the dry density of the compacted bentonite, the smaller the increase in thermal conductivity. The thermal conductivity of the compacted bentonite in the three-phase system, in which soil particles, water, and air are all present, tended to increase as the temperature increased.
Through this study, it was found that the thermal conductivity of compacted bentonite increases by 5~20% as temperature increases, depending on the water content. Considering the mid to long-term conditions of actual disposal environments, even though heat is generated from disposal canisters, groundwater penetration form the nearfield rock continuously increases the degree of saturation of the buffer, which naturally leads to an increase in the thermal conductivity of the bentonite buffer.
후속연구
Additionally, the thermal-hydro-mechanical properties and the thermal conductivity of bentonite buffers at the set temperature of 100℃ or higher should be investigated with consideration of actual complex repository conditions.
In addition, the thermal conductivity of bentonite buffers was determined to increase to a greater degree in the temperature range of 80~90℃. Thus, the test results from this study can be effectively used to evaluate the soundness of bentonite buffers: the results are expected to be used as important data for repository design and engineering barrier performance evaluations for the goal of raising the maximum buffer temperature or reducing the overall disposal area.
M.V. Villar, P.L. Martin, and J.M. Barcala, "Modification of physical, mechanical and hydraulic properties of bentonite by thermo-hydraulic gradients", Eng. Geol., 81, 284-297 (2006).
P. Wersin, L.H. Johnson, and M. Snellman, "Impact of iron related released from steel components on the performance of the bentonite buffer: A preliminary assessment within the framework of the KBS-3H disposal concept", Materials Research Society Symposium Proceedings, 932, 95-102 (2006).
M.J. Kim, S.R. Lee, S. Yoon, J.S. Jeon, and M.S. Kim, "Effect of thermal properties of bentonite buffer on temperature variation", J. Korean Geotech Soc., 34(1), 17-24 (2018).
K.A. Daniel, J.F. Harrington, S.G. Zihms, and A.C. Wiseall, "Bentonite permeability at elevated temperature", Geoscience, 7, 3 (2017).
B.M. Das, "Principle of geotechnical engineering", 6th edition, Nelson (2006).
S. Yoon, M.J. Kim, S.R. Lee, and G.Y. Kim, "Thermal conductivity estimation model of compacted bentonite buffer materials for a high-level radioactive waste repository", Nucl. Technol., 204, 213-226 (2018).
Y. Xu, D. Sun, Z. Zeng, and H. Lv, "Temperature dependence of apparent thermal conductivity of compacted bentonite as buffer material for high-level radioactive waste repository", Appl. Clay Sci. 174, 10-14 (2019).
C. Ould-Lahoucine, H. Sakashita, and T. Kumada, "Measurement of thermal conductivity of buffer materials and evaluation of existing correlation predicting it", Nucl. Eng. Des., 216, 1-11 (2002).
J.W. Lee, H.J. Choi, and J.Y. Lee, "Thermal conductivity of compacted bentonite as a buffer material for a high-level radioactive waste repository", Ann. Nucl. Energy, 94, 848-855 (2016).
S. Yoon, W.Cho, C. Lee, and G.Y. Kim, "Thermal conductivity of Korean compacted bentnonite buffer materials for a nuclear waste repository", Energies, 11, 2269 (2018).
M. Yoo, H.J. Choi, M.S.Lee, and S.Y. Lee, "Measurement of properties of domestic bentonite for a buffer of an HLW repository", J. Nucl. Fuel Cycle Waste Technol., 14(2), 135-147 (2016).
M.S. Lee, H.J. Choi, J.O. Lee, and J.P. Lee, "Improvement of the thermal conductivity of a compact bentonite buffer", Korea Atomic Energy Research Institute Technical Report, KAERI/TR-5311/2013 (2013).
J.O. Lee, W.J. Cho, and S. Kwon, "Thermal-hydromechanical properties of reference bentonite buffer for a Korean HLW repository", Tunnel and Underground Space, 21(4), 264-273 (2011).
J.R. Phillip and D.A.D. Vries, "Moisture movement in porous materials under temperature gradients", Trans. Am. Geophys. Union, 38, 222-232 (1957).
K.M. Smith, T. Sakaki, S.E. Howington, J.F. Peters, and T.H. Illangasekare, "Temperature dependence of thermal properties of sands across a wide range of temperatures ( $30-70^{\circ}C$ )", Vadose Zone J., 138(4), 2256-2265 (2013).
A. Beziat, M. Dardaine, and V. Gabis, "Effect of compaction pressure and water content on the thermal conductivity of some natural clays", Clays and Clay Miner., 36(5), 462-466 (1998).
M.V. Villar, "Thermo-hydro-mechanical characterization and process in the clay barrier of a high level radioactive waste repository", State of the Art Report. Informes Tecnicos Ciemat 1044, Octubre (2004)
Y.A. Cengez and A.J. Ghajar, "Heat and mass transfer: fundamentals and applications", Fourth edition, McGraw Hill Education (2011)
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