Anisotropic thermal analysis of the high-level nuclear waste in final geological repositories

  • 林 佩瑤

Student thesis: Master's Thesis

Abstract

After numerous years of international research and development there is a broad technical consensus that deep geological disposal which offers relatively enough space to accommodate the large volume of HLW accumulated over the years will provide for the safety of humankind and the environment now and far into the future In addition there is not yet an operating geological repository for high-level radioactive waste and there remains substantial public research about the underground rock mass of geological repository However most studies all consider the host rock as homogeneous and isotropic While in real cases underground host rock is inherently anisotropic and heterogeneous Besides many of them are thermally anisotropic indicating that there is a preferred direction of thermal conductivity Therefore in this thesis we extend the previous research (Salama A et al 2015) conducted to analyze thermal characteristics of HLW geological repositories by including the effect of anisotropy of thermal conductivity of host rock We reveal that differences in anisotropy of thermal conductivity of host rock with direction could have clear effects on temperature fields We also investigate the effect of dip angle on the temperature field This includes 0? 15? 30? 45? 60? 75?and 90? in additions to the isotropic case as a reference Furthermore we also consider the effect of anisotropy ratio on the temperature fields This includes ratios ranging from 1 1 to 1 5 The significant differences between this study with previous research are that we conducted the verification with analytical approach before the numerical simulation and also developed a chart for variation of peak rock wall temperature with the anisotropy ratio for different dip angles which can be used as an anisotropic case for HLW repositories reference In order to ensure feasibility and accuracy of the numerical model we conduct the numerical verification with analytical approach proposed by SKB (2009) before the thermal simulation for anisotropic cases The results of both approaches show pretty much the same overall trends As a result after the verification the same numerical model is feasibly used for the next anisotropic simulation In this study it is found that the temperature contours are shifted towards the direction of dip angle The temperature of anisotropic cases are all high than isotropic one Furthermore the peak buffer temperature is found to be higher when the dip angle is larger and vice versa Additionally the peak buffer temperature is also found to be higher when anisotropic ratio is larger Also we developed a chart of variation of peak buffer temperature with the anisotropy ratio for different dip angles and find that the peak buffer temperature meets the 100℃ design limit when anisotropy ratio is set to 1 3 The presented chart can be used as an anisotropic case for HLW repositories reference
Date of Award2016 Aug 17
Original languageEnglish
SupervisorChao-Shi Chen (Supervisor)

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