Tunnel and Underground Space (터널과지하공간)

Korean Society for Rock Mechanics and Rock Engineering (한국암반공학회)
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Effect of Excavation and Thermal Stress on Slip Zone and Aperture Change Around Disposal Hole and Tunnel in Fractured Rock

굴착 및 열응력을 고려한 절리암반 내 처분공동 주변에서의 전단영역 및 균열간극 변화 분석

  • Hong, Suyeon (Department of Nuclear Safety Research, Korea Institute of Nuclear Safety) ;
  • Kwon, Saeha (Research Institute of Energy and Resources) ;
  • Min, Ki-Bok (Department of Energy Systems Engineering, Seoul National University) ;
  • Ji, Sung-Hoon (Radwaste Disposal Research Division, Korea Atomic Energy Research Institute)
  • 홍수연 (한국원자력안전기술원 원자력안전연구실) ;
  • 권새하 (서울대학교 에너지자원신기술연구소) ;
  • 민기복 (서울대학교 에너지시스템공학부) ;
  • 지성훈 (한국원자력연구원 방사성폐기물처분연구부)
  • Received : 2021.02.15
  • Accepted : 2021.04.20
  • Published : 2021.04.30
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Abstract

Deep geological disposal is one of the most prominent option for the permanent disposal of high-level radioactive waste(HLW) generated from nuclear power. There is a need for studies considering coupled thermo-hydro-mechanical behavior to assess the performance of the repository. In particular, the comprehensive analysis considering rock fracture properties and geometry is necessary. Therefore, in this study, sensitivity analyses are conducted using two-dimensional distinct element method simulator to quantitatively analyze the effects of joint angle, friction angle and stress ratio on slip zone and aperture around the disposal tunnel and hole in the fractured rocks. As a result of stress modeling after excavation, the effect of shear dilation dramatically increased as the friction angle decreased. The area where the aperture change was about 1.5 times of the initial aperture varied from 2.8 to 4.8 times, 4.3 to 10.7 times and 2.6 times to 4.2 times for the variation of joint angle, friction angle and stress ratio, respectively. The results obtained in the discrete fracture network model were similar to the uniformly jointed model, and the slip zone occurred within the region not exceeding three times of the opening radius in all models at the friction angle of 30°. As a result of modeling considering thermal stress in the disposal hole model, the aperture was closed in all models and most of the slip zone disappeared which had been caused by the excavation. This study can be used as basic data in the site selection guidelines for HLW disposal repository, and can be used for performance assessment of geological repository for HLW.

원자력발전으로 발생되는 고준위방사성폐기물의 영구처분 방법의 방안들 중 심층처분 방법은 가장 유력한 방법으로 제시된다. 처분시스템의 성능을 평가하기 위해서는 시스템 내에서의 열-수리-역학적인 복합거동을 고려한 연구가 필요하다. 특히 암반의 물성 및 절리의 기하학적 구조에 따른 일반적인 분석의 필요성이 대두된다. 따라서 본 연구에서는 2차원 개별요소법 시뮬레이터를 이용하여 균열이 존재하는 암반에 굴착된 처분터널 및 처분공 주변에서의 절리각, 마찰각, 응력비에 따른 전단영역 및 균열간극에 대한 영향을 정량적으로 분석하였다. 굴착 이후 응력 모델링의 결과, 마찰각이 작아질수록 전단팽창에 의한 영향이 급격히 증가하였다. 균열간극 변화량이 초기간극의 1.5배가 되는 영역은 절리각에 따라서는 공동 반경의 2.8배에서 4.8배, 마찰각에 따라서는 4.3배에서 10.7배, 응력비에 따라서는 2.6배에서 4.2배까지 변하였다. 암반균열망 모델에서도 유사한 결과를 얻었으며, 전단영역은 마찰각이 30도인 경우, 모든 모델에서 공동 반경의 3배를 넘지 않는 영역에서 발생하였다. 열응력을 고려한 처분공 모델에서의 해석 결과, 열응력 적용 이후 모든 모델에서 간극이 닫히고, 굴착으로 인해 발생했던 전단영역이 대부분 소멸되었다. 본 연구는 고준위방사성폐기물 처분장의 부지 선정 가이드라인에 기초 자료로 활용될 수 있으며, 처분장의 성능평가에 활용될 수 있을 것으로 전망한다.

Keywords

Acknowledgement

이 연구는 과학기술정보통신부의 재원으로 시행하는 한국연구재단의 원자력기술개발사업의 지원(과제번호 : NRF-2017M2A8A5014858)과 원자력안전재단의 지원(NSRM 1805020-0421-CG100)을 받아 수행되었습니다.

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