Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT) (방사성폐기물학회지)

Korean Radioactive Waste Society (한국방사성폐기물학회)
권호 표지
DOI QR코드

DOI QR Code

Numerical Analysis of Coupled Thermo-Hydro-Mechanical (THM) Behavior at Korean Reference Disposal System (KRS) Using TOUGH2-MP/FLAC3D Simulator

TOUGH2-MP/FLAC3D를 이용한 한국형 기준 처분시스템에서의 열-수리-역학적 복합거동 특성 평가

  • Received : 2019.02.08
  • Accepted : 2019.04.01
  • Published : 2019.06.30
Download PDF
⟨ Previous Next ⟩

Abstract

For design and performance assessment of a high-level radioactive waste (HLW) disposal system, it is necessary to understand the characteristics of coupled thermo-hydro-mechanical (THM) behavior. However, in previous studies for the Korean Reference HLW Disposal System (KRS), thermal analysis was performed to determine the spacing of disposal tunnels and interval of disposition holes without consideration of the coupled THM behavior. Therefore, in this study, TOUGH2-MP/FLAC3D is used to conduct THM modeling for performance assessment of the Korean Reference HLW Disposal System (KRS). The peak temperature remains below the temperature limit of $100^{\circ}C$ for the whole period. A rapid rise of temperature caused by decay heat occurs in the early years, and then temperature begins to decrease as decay heat from the waste decreases. The peak temperature at the bentonite buffer is around $96.2^{\circ}C$ after about 3 years, and peak temperature at the rockmass is $68.2^{\circ}C$ after about 17 years. Saturation of the bentonite block near the canister decreases in the early stage, because water evaporation occurs owing to temperature increase. Then, saturation of the bentonite buffer and backfill increases because of water intake from the rockmass, and bentonite buffer and backfill are fully saturated after about 266 years. The stress is calculated to investigate the effect of thermal stress and swelling pressure on the mechanical behavior of the rockmass. The calculated stress is compared to a spalling criterion and the Mohr-Coulumb criterion for investigation of potential failure. The stress at the rockmass remains below the spalling strength and Mohr-Coulumb criterion for the whole period. The methodology of using the TOUGH2-MP/FLAC3D simulator can be applied to predict the long-term behavior of the KRS under various conditions; these methods will be useful for the design and performance assessment of alternative concepts such as multi-layer and multi-canister concepts for geological spent fuel repositories.

고준위방사성폐기물의 처분터널 및 처분공 간격을 결정하고 처분시스템의 성능을 평가하기 위해서는 열-수리-역학적인 복합 거동 변화에 대한 이해가 반드시 필요하고 이를 반영하여 해석해야만 한다. 하지만 한국형 기준 처분시스템에서의 처분터널 및 처분공 간격을 결정하기 위해 수행된 기존의 연구들은 이러한 복합거동 특성을 반영하지 않고 열 해석 결과만을 근거로 처분시스템을 설계하였다. 따라서 본 연구에서는 열-수리-역학적인 복합거동 특성을 반영하여 한국형 기준 처분시스템의 성능을 TOUGH2-MP/FLAC3D를 이용하여 평가하였다. 고준위방사성폐기물이 처분된 이후 방사성 붕괴열에 의해 처분시스템의 온도는 급격히 증가하다가 붕괴열의 감소로 온도는 서서히 감소하였으며, 해석 기간 1,000년 동안 벤토나이트 완충재의 최고 온도는 설계 기준인 $100^{\circ}C$ 이하로 유지되는 것으로 나타났다. 처분용기와 벤토나이트 완충재의 계면에서의 최고 온도는 약 3.21년이 지난 시점에 용기의 중간 지점에서 약 $96.2^{\circ}C$로 나타났으며, 암반에서의 최고 온도는 폐쇄 후 약 17년이 지난 시점에서 약 $68.2^{\circ}C$로 계산되었다. 처분용기 부근 벤토나이트 완충재는 처분 초기에 온도 변화에 따른 건조현상이 발생하여 포화도가 감소하지만, 시간이 지남에 따라 주변 암반으로부터의 지하수 유입에 의해 포화도가 증가하는 것으로 계산되었다. 이후, 벤토나이트 완충재 및 뒷채움재 모두 약 266년 이후 완전히 포화되는 것으로 계산되었다. 처분시스템에서의 온도 변화에 따른 열응력 그리고 벤토나이트 완충재 및 뒷채움재의 팽윤압으로 인한 응력 변화가 처분장 주변 암반에 미치는 영향을 평가하고자 수치해석에서 계산된 응력을 스폴링 강도(spalling strength)와 Mohr-coulomb 파괴 기준식과 비교하였다. 계산 결과 일축압축강도와 스폴링 강도에 도달하지 않는 것으로 나타나 처분시스템이 스폴링에 의한 파괴는 나타나지 않을 것으로 판단되며, Mohr-coulomb 파괴 기준 역시 충족하는 것으로 나타났다. 본 연구에서 사용된 수치해석 코드와 방법론은 다양한 조건에서의 한국형 기준 처분시스템에 대한 성능평가뿐만 아니라, 복층 처분시스템에 대한 설계와 성능평가에 활용될 수 있을 것으로 판단된다.

Keywords

References

  1. Swedish Nuclear Fuel and Waste Management Company, Choice of Method - Evaluation of Strategies and Systems for Disposal of Spent Nuclear Fuel, SKB report, SKB P-10-47 (2010).
  2. World Nuclear News. November 29 2016. "Construction to Start on Finnish Repository", Accessed Jan. 4 2018. Available from: http://www.world-nuclear-news.org/WS-Construction-to-start-on-Finnish-repository-2911164.html.
  3. World Nuclear News. June 25 2015. "Preliminary Findings Positive for Swedish Repository", Accessed Jan. 4 2018. Available from: http://www.world-nuclear-news. org/WR-Preliminary-findings-positive-for-Swedish-repository-2506154.html.
  4. J. Lee, D. Cho, H. Choi, and J. Choi, "Concept of a Korean Reference Disposal System for Spent Fuels", J. Nucl. Sci. Technol., 44(12), 1565-1573 (2007). https://doi.org/10.1080/18811248.2007.9711407
  5. H.J. Choi, J.Y. Lee, D.G. Cho, S.K. Kim, S.S. Kim, K.Y. Kim, J.T. Jeong, M.S. Lee, J.W. Choi, J.W. Lee, K.S. Chun, and P.O. Kim, Korean Reference HLW Disposal System, Korea Atomic Energy Research Institute Technical Report, KAERI/TR-3563/2008 (2008).
  6. Swedish Nuclear Fuel and Waste Management Company, Design Premises for a KBS-3V Repository based on Results from the Safety Assessment SR-Can and Some Subsequent Analyses, SKB Technical Report, SKB TR-09-22 (2009).
  7. K. Ikonen, Thermal Condition of Open KBS-3H Tunnel, Swedish Nuclear Fuel and Waste Management Company Technical Report, SKB R-08-24 (2008).
  8. P. Wersin, L.H. Johnson, and I.G. Mckinley, H12 Project to establish technical basis for HLW disposal in Japan, Support Report 2 JNC TN1410 200-003, Japan Nuclear Cycle Development Institute (2000).
  9. J. Salas, C. Sena, and D. Arcos, "Hydrogeochemical Evolution of the Bentonite Buffer in a KBS-3 Repository for Radioactive Waste. Reactive Transport Modelling of the LOT A2 Experiment", Appl. Clay Sci., 101, 521-532 (2014). https://doi.org/10.1016/j.clay.2014.09.016
  10. Polytechnic University of Catalonia, CODE BRIGHT User's Guide: A 3-D Program for Thermo-Hydro-Mechanical Analysis in Geological Media (2004).
  11. W.J. Cho, J.O. Lee, and C.H. Kang, "A Compilation and Evaluation of Thermal and Mechanical Properties of Bentonite-based Buffer Materials for a Highlevel Waste Repository", Nucl. Eng. Technol., 34(1), 90-103 (2002).
  12. M.V. Villar, Thermo-Hydro-Mechanical Characterisation of a Bentonite from Cabo de Gata. A Study Applied to the Use of Bentonite as Sealing Material in High Level Radioactive Waste Repositories, Publicacion Tecnica ENRESA 01/2002 (2002).
  13. A.M. Tang, Y.J. Cui, and T.T. Le, "A Study on the Thermal Conductivity of Compacted Bentonites", Appl. Clay Sci., 41(3-4), 181-189 (2008). https://doi.org/10.1016/j.clay.2007.11.001
  14. K. Pruess, C.M. Oldenburg, and G.J. Moridis, TOUGH2 User's Guide, Version 2.0, Lawrence Berkeley National Laboratory Report, LBNL-43134 (1999).
  15. Itasca Consulting Group, Inc., FLAC3D - Fast Lagrangian Analysis of Continua in 3Dimensions User's Guide, Version 4.0 (2009).
  16. J. Rutqvist, "Status of the TOUGH-FLAC Simulator and Recent Applications Related to Coupled Fluid Flow and Crustal Deformations", Comput. Geosci., 37(6), 739-750 (2011). https://doi.org/10.1016/j.cageo.2010.08.006
  17. J. Rutqvist, Y.-S. Wu, C.-F. Tsang, and G. Bodvarsson, "A Modeling Approach for Analysis of Coupled Multiphase Fluid Flow, Heat Transfer, and Deformation in Fractured Porous Rock", Int. J. Rock Mech. Min. Sci., 39(4), 429-442 (2002). https://doi.org/10.1016/S1365-1609(02)00022-9
  18. J. Lee, C. Lee, and G.Y. Kim, Development of TOUGH2-MP/FLAC3D Simulator for the Coupled Thermal-hydraulic-mechanical Analysis in Porous Media, Korea Atomic Energy Research Institute Report, KAERI/TR-6737/2016 (2016).
  19. K. Zhang, Y.-S. Wu, and K. Pruess, User's Guide for TOUGH2-MP - A Massively Parallel Version of the TOUGH2 code, Lawrence Berkeley National Laboratory Report, LBNL-315E (2008).
  20. Itasca Consulting Group, Inc., FLAC3D - Fast Lagrangian Analysis of Continua in 3Dimensions User's Guide, Version 5.0 (2012).
  21. J. Rutqvist and C.-F. Tsang, Review of SKB's Work on Coupled THM Processes Within SR-Can: External Review Contribution in Support of SKI's and SSI's Review of SR-Can, Swedish Nuclear Power Inspectorate Technical Report, SKI Report 2008:08 (2008).
  22. W.J. Cho, C. Lee, and G.Y. Kim, "Feasibility Analysis of the Multilayer and Multicanister Concepts for a Geological Spent Fuel Repository", Nucl. Technol., 200(3), 225-240 (2017). https://doi.org/10.1080/00295450.2017.1369804
  23. M.V. Villar and A. Lloret, "Variation of the Intrinsic Permeability of Expansive Clays upon Saturation", In: K. Adachi, M. Fukue (eds.), 259-266, Clay Science for Engineering, Balkema, Rotterdam (2001).
  24. L.J. Klinkenberg, "The Permeability of Porous Mediato Liquid and Gases", Drill. Prod. Prac., American Petroleum Institute, 200-213 (1941).
  25. J. Rutqvist, Y. Ijiri, and H. Yamamoto, "Implementation of the Barcelona Basic Model into TOUGHFLAC for simulations of the geomechanical behavior of unsaturated soils", Comput. Geosci., 37(6), 751-762 (2011). https://doi.org/10.1016/j.cageo.2010.10.011
  26. J.O. Lee and W.J. Cho, Thermal-hydro-mechanical Properties of Reference Bentonite Buffer for a Korean HLW Repository, Korea Atomic Energy Research Institute Technical Report, KAERI/TR-3729/2009 (2009).
  27. S. Yoon, C. Lee, and G.Y. Kim, Investigation of the Thermal Conductivity for Compacted Bentonite Buffer, Korea Atomic Energy Research Institute Technical Report, KAERI/TR-6877/2017 (2017).
  28. C. Lee, "Characterization of Thermal-Mechanical Behavior of Rock Mass in the Excavation Damaged Zone at KURT", Ph.D. Dissertation, Seoul National University, 2012.
  29. W.J. Cho and S.K. Kwon, "Estimation of the Thermal Conductivity for Partially Saturated Granite", Eng. Geol., 115(1-2), 132-138 (2010). https://doi.org/10.1016/j.enggeo.2010.06.007
  30. W.J. Cho, J.W. Lee, and S. Kwon, Analysis of Thermohydro-mechanical Behavior of the Engineered Barrier System of a High-level Waste Repository, Korea Atomic Energy Research Institute Technical Report, KAERI/TR-4142/2010 (2010).
  31. G.A. Nicholson and Z.T. Bieniawski, "A Nonlinear Deformation Modulus Based on Rock Mass Classification", Int. J. Min. Geo-Eng., 8(3), 181-202 (1990). https://doi.org/10.1007/BF01554041
  32. V.K. Mehrotra, "Estimation of Engineering Parameters of Rock Mass", Ph.D. Dissertation, University of Roorkee, 1992.
  33. H.S. Mitri, R. Edrissi, and J. Henning, "Finite Element Modeling of Cable-bolted Slopes in Hard Rock Underground Mines", Proc. of the SME Annual Meeting, 94-116, February 14-17, 1994, Albuquerque.
  34. S.A.L. Read, L.R. Richards, and N.D. Perrin, "Applicability of the Hoek-Brown Failure Criterion to New Zealand Greywacke Rocks", Proc. of the 9th International Society of Rock Mechanics Congress, vol. 2, 655-660, August 25-28, 1999, Paris.
  35. B.S. Chun, Y.J. Lee, and S.H. Jung, "The Evaluation for Estimation Method of Deformation Modulus of Rock Mass Using RMR System", J. Korean Geoenviron. Soc., 7(2), 25-32 (2006).
  36. H. Sonmez, H.A. Gokceoglu, A. Nefeslioglu, and A. Kayabasi, "Estimation of Rock Modulus: For intact rocks with an artificial neural network and for rock masses with a new empirical equation", Int. J. Rock Mech. Min. Sci., 43(2), 224-235 (2006). https://doi.org/10.1016/j.ijrmms.2005.06.007
  37. S.S. Kang, H.Y. Kim, and B.A. Jang, "Correlation of in situ modulus of deformation with degree of weathering, RMR and Q-system", Environ. Earth Sci., 69(8), 2671-2678 (2013). https://doi.org/10.1007/s12665-012-2088-y
  38. E. Hoek and E.T. Brown, Underground excavations in rock, 1st ed., 527, CRC Press, London (1980).
  39. T. Ramamurthy, "Stability of Rock Mass. 8th IGS Annual lecture", Indian Geotech. J., 16(1), 1-74 (1986).
  40. G.S. Kalamaras and Z.T. Bieniawski, "A Rock Mass Strength Concept for Coal Incorporating the Effect of Time", Proc. of the 8th ISRM Congress, vol. 1, 295-302, September 25-29, 1995, Tokyo.
  41. P.R. Sheorey, Empirical rock failure criterion, 176, Balkema, Rotterdam (1997).
  42. O. Aydan and S. Dalgic, "Prediction of Deformation Behavior of 3-lanes Bolu Tunnels Through Squeezing Rocks of North Anatolian Fault Zone (NAFZ)", Proc. of the Reg. Symp. on Sedimentary Rock Eng., 228-233, 1998, Taipei.
  43. Z.T. Bieniawski, Engineering rock mass classifications, Wiley, New York (1989).
  44. G.W. Kim, "Revaluation of 'Geomechanics classifications of rock masses'", Geotech. Eng. Tunn. Technol. / Proc. of the Korean Geotechnical Society Spring '93 National Conference, 33-40, March 27, 1993, Seoul.
  45. R. Trueman, "An Evaluation of Strata Support Techniques in Dual Life Gateroads", Ph.D. Dissertation, University of Wales Cardiff, 1988.
  46. O. Aydan, T. Akagi, and T. Kawamoto, "The Squeezing Potential of Rocks Around Tunnels; Theory and prediction", Rock Mech. Rock Eng., 26(2), 137-163 (1993). https://doi.org/10.1007/BF01023620
  47. O. Aydan and T. Kawamoto, "The Stability Assessment of a Large Underground Opening at Great Depth", Proc. of the 17th International Mining Congress and Exhibition of Turkey (IMCET 2001), vol. 1, 277-288, June 19-22, 2001, Ankara.
  48. K. Thuro, R.J. Plinninger, S. Zah, and S. Schutz, "Scale Effects in Rock Strength Properties. Part 1: Unconfined Compressive Test and Brazilian Test", In: Sarkka P, Eloranta J (eds.), Proc. of ISRM Regional Symposium : Eurock 2001, 169-174, June 3-7, 2001, Espoo.
  49. A. Gens, "The Role of Geotechnical Engineering for Nuclear Energy Utilisation", In: Vanisek P et al. (eds.), Proc. of the XIII ECSMGE, Vol. 3, Special Lecture 2, August 25-28, 2003, Prague.
  50. J. Rutqvist, M. Chijimatsu, L. Jing, A. Millard, T.S. Nguyen, A. Rejeb, Y. Sugita, and C.F. Tsang, "A numerical study of THM effects on the near-field safety of a hypothetical nuclear waste repository-BMT1 of the DECOVALEX III project. Part 3: Effects of THM coupling in sparsely fractured rocks", Int. J. Rock Mech. Min. Sci., 42(5-6), 745-755 (2005). https://doi.org/10.1016/j.ijrmms.2005.03.012
  51. J.C. Jaeger and N.G.W. Cook, Fundamentals of Rock Mechanics, Chapman and Hall, London (1979).
  52. D. Martin, Preliminary assessment of potential underground stability (wedge and spalling) at Forsmark, Simpevarp and Laxemar sites, Swedish Nuclear Fuel and Waste Management Company Report, SKB R-05-71 (2005).

Cited by

  1. 온도 변화를 고려한 압축 벤토나이트 완충재의 수분흡입력 평가 vol.35, pp.11, 2019, https://doi.org/10.7843/kgs.2019.35.11.7
  2. Numerical analysis of coupled thermo-hydro-mechanical behavior in single- and multi-layer repository concepts for high-level radioactive waste disposal vol.103, 2020, https://doi.org/10.1016/j.tust.2020.103452
  3. 고준위방사성폐기물 처분장 내 열-수리-역학-화학적 복합거동 해석을 위한 국제공동연구 DECOVALEX-2023에서 수행 중인 연구 과제 소개 vol.31, pp.3, 2019, https://doi.org/10.7474/tus.2021.31.3.167