Usability of Monitoring at the Olkiluoto Repository Site for Safeguards

Volume: 56, June 2018, pages 28-35

Authors: E. Pentti¹ and O. Okko²

¹_{Pöyry Finland Ltd, Geoscientific Consulting,} ²_{Radiation and Nuclear Safety Authority, Nuclear Materials Safeguards}

Abstract:At the Olkiluoto repository site, the operator Posiva Oy runs a multidisciplinary monitoring programme targeted at studying environmental impact, improving the understanding of the natural properties of the site, verifying favourable conditions for long-term safety, and developing methods for monitoring the performance of engineered barriers. The usability of the data produced by the monitoring programme for the implementation of nuclear safeguards is assessed, primarily to detect the excavation of any undeclared underground premises.

Microseismic monitoring is currently the only method whose results, located seismic events in Olkiluoto and surroundings, are already used in implementing national safeguards. It is concluded that automatic hydraulic head measurements in deep drillholes and land use monitoring also produce relevant data and findings for safeguards purposes.

Hydraulic head is monitored in several drillholes that penetrate the rock volume where the repository will be excavated. These holes 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 national safeguards could apparently be achieved by examining material and reports that Posiva already delivers for other purposes. The IAEA can use these reports as open source information.

Keywords: monitoring; repository; safeguards; seismicity; hydrogeology

Reference guideline:

Pentti, E., & Okko, O. (2018). Usability of Monitoring at the Olkiluoto Repository Site for Safeguards. ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-proliferation, 56, 28-35. https://doi.org/10.3011/ESARDA.IJNSNP.2018.5