ABSTRACT:

The main objective of this study was to investigate the influence of stresses on radioactive nuclide transport in fractured rocks, based on Discrete Element Method (DEM) and a particle tracking approach. Matrix diffusion was also considered in the transport simulation. The results show that stresses not only influence the particle residence time in fracture network, but also change the particle transport paths significantly.

1 INTRODUCTION

Radioactive nuclides moving with the fluid flow in fractured rocks is one of the most important safety issues of nuclear waste repositories. The nuclides are retarded by sorption and diffusion in and out of the rock matrix as well. Since 1970s, a large number of analytical, semi-analytical and numerical schemes were proposed to simulate transport process in single fracture, regular fracture network, and complicated random fracture network. These results provided important insights to understanding transport phenomenon in fractured crystalline rocks like granite. Berkowitz (2002), Neuman (2005) systematically reviewed the developments of modeling flow and transport in fractured geological medium in the past. Nuclear waste repositories are usually located deep underground. If the fluid contains nuclides or other solutes, the transport phenomenon would also be influenced, indirectly, by in-field stresses. At present, few publications concerning with the stress effects on the transport process in fractured crystalline rocks are available. The main objective of this study was to investigate the influence of stresses on nuclide transport in fractured crystalline rocks where fluid flow is dominated by connected fractures, considering the realistic representation of fracture network geometry and stress-deformation behaviors of the fractures. This study is a part of the international DECOVALEX- 2011 project for numerical modeling of coupled thermo-hydro-mechanical (THM) processes of geological media for performance and safety assessments of nuclear waste repositories since 1992. More recently, chemical (C) processes have also been added.

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