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Two-dimensional thermal-mechanical analyses of a hypothetical repository in tuff were performed using a boundary-element computer code, with the objective of investing the relative stability of several waste emplacement panel access drifts. The drifts were assumed to be located within a central shaft pillar, within a small pillar between adjacent panels, or a t the repository perimeter. The results of analyses indicate that matrix failure is unlikely and that the extent of activation of pre-existing joints is influenced by the drift location and the initial state of stress. The results also show that several years after waste emplacement the influence of the initial state of stress is small compared to the influence of thermally induced stresses. Regions of joint activation are seen to be most extensive around the drifts between adjacent panels. The predicted extent of such activation was small when it was assumed that the joints were vertical or near vertical. More extensive regions of activation of shallow dipping joints were noted. However, joints of such orientation are believed to occur relatively infrequently in the candidate horizon for waste emplacement and the activation of the shallow dipping joints does not necessarily lead to drift stability concerns.