Drillings and excavations
In the initial phase, bedrock in Olkiluoto was explored from the surface by drilling test holes and making test excavations. With the construction of ONKALO, surveys were carried out also underground. Posiva has analysed bedrock in ONKALO in detail, developed rock construction methods and implemented dozens of tests, demonstrations and drillholes.
For example, pilot holes have been drilled at the deposition depth to help determine the bedrock suitability for final disposal before the excavation of the deposition tunnels and the selection of the locations of the deposition holes. The drill core provides information about the bedrock rock types and rock cracking. In addition, pilot holes can be used to examine rock density, electrical conductivity, magnetism and water leaks in fractures.