Monitoring Disturbances in the Repository System during Construction Process: Experiences from Natural Decay Series Studies at the Pyhäsalmi Mine (Central Finland)

Abstract

Prior to the selection of the site for nuclear waste disposal, the performance of the repository is assessed based on general geological data of sites under investigation. Once the site has been selected, the results of the site investigations are used to establish the baseline condition to monitor and evaluate the induced processes during the construction of the repository. One of the processes considered is the change in hydraulic properties in the bedrock due to excavation of tunnels and other open spaces. Within this framework, the results of natural decay series studies in rock samples from the Pyhäsalmi mine collected in the nearby of a water-conducting fracture at the depths of 1275 and 1325 m may give insights on the influence of the excavation-induced changes, if any, in the groundwater flow. The spatial and temporal scale of these changes is also evaluated. The methodology used in this work could be applied to add confidence in the establishment of the baseline conditions to better assess the evolution of changes in groundwater flow patterns during and after construction of a repository system.