Year
2018
Abstract
At the Olkiluoto repository site, the operator Posiva Oy runs a multidisciplinary monitoring program targeted at studying environmental impact, improving the understanding of the natural properties of the site, verifying favorable conditions for long-term safety, and developing methods for monitoring the performance of engineered barriers. We assess the usability of the data produced by the monitoring program for the implementation of nuclear safeguards, primarily to detect the excavation of any undeclared underground rooms. Microseismic monitoring is currently the only methods whose results, located seismic events in Olkiluoto and surroundings, are already used in implementing national safeguards. We conclude that automatic hydraulic head measurements in deep drillholes and land use monitoring also produce relevant data for safeguards. Hydraulic head is monitored in several drillholes that penetrate the rock volume where the repository will be excavated. They are divided into sections, so that head can be measured separately at different depths. The monitored sections are often situated in hydrogeological zones, where fractures in the crystalline bedrock allow groundwater to flow significantly more freely than elsewhere. In some of these zones, a groundwater leak into a new tunnel or drillhole gives rise to a significant decrease of hydraulic head at such a large distance that it can be readily detected in several monitoring sections. Monitoring of land use is based on aerial photographs and maintaining a land use record. These sources are used to regularly update a land use grid covering the whole of Olkiluoto. The aerial photographs and land use grid can supplement other imagery used to verify the declaration of surface constructions. The inclusion of the results of hydraulic head and land use monitoring in the input for the implementation of safeguards could apparently be achieved by examining material and reports that Posiva already delivers for other purposes.