Acceptance of emplacement hole positions — stage 1 thermomechanical study

Abstract

The fraction of intended emplacement hole positions along a KBS3-type nuclear waste deposition tunnel that can actually be used for deposition of waste canisters will be an important issue during different stages of decision-making within the repository site selection, design and construction phases. Some criteria for rejecting positions will deal with long-time performance aspects, e.g. expected post-closure groundwater flow in fractures that intersect the deposition hole and connect to the tunnel or to nearby major fracture zones. Other criteria will be concerned with construction aspects, e.g. inflow into the open deposition hole during construction and emplacement, or the mechanical stability of the deposition hole walls. Acceptance or rejection of individual deposition hole positions will depend on the expected consequences of a number of processes: excavation of tunnel and emplacement hole, interaction with the swelling bentonite buffer, heating and subsequent cooling. Additional, hypothetical processes include effects of glaciation and seismic events. The consequences of these processes will depend on the arrangement of fractures in the nearfield, on the mechanical properties of the nearfield-and farfield rock, and on the initial stress field. This paper deals with the first stage of an ongoing numerical thermomechanical study, aimed at providing consequence descriptions that are relevant on the tunnel- and deposition hole scale. The results regard results from continuum analyses. Comparisons are made with recently developed analytical solutions for the temperature field and the thermoelastic stress- and strain fields around and within the volume occupied by the repository. The discussion focuses on the relevance of the results and the applicability of the numerical method.