IAEA COORDINATED RESEARCH PROJECT (CRP): The use of selected safety indicators (concentrations; fluxes) in the assessment of radioactive waste disposal. Report 6: Site-specific natural geochemical concentrations and fluxes at the Palmottu U-Th mineralisation (Finland) for use as indicators of nuclear waste repository safety

• Main Authors: Kaija, J., Rasilainen, Kari, Blomqvist, R.
• Format: Book
• Language: English
• Published: Geological Survey of Finland 2003
• Subjects: permafrost
• Online Access: https://cris.vtt.fi/en/publications/916f8d37-c5e7-4b51-8d6d-48d33f106f06; https://tupa.gtk.fi/julkaisu/ydinjate/yst_114.pdf

Research activities focused on field studies at the Palmottu U-Th mineralisation at Nummi-Pusula in southwestern Finland in order to increase the data on groundwater chemistry of the overburden, to gather additional information of the Quaternary deposit concentrations of the previously recognised Eastern Flow System and Palmottu Brook valley. Also U inventories were estimated for a 300 m x 500 m x 250 bedrock block. From the Palmottu uranium-thorium-mineralisation there are a lot of geochemical data available from mineral phases, bedrock, peat, soil cover, lake sediments, groundwater both in the overburden and in bedrock. Especially data about the uranium concentrations in different media is comprehensive. This data can be used for the PA repository performance assessment and related calculations. The main important contributions for the performance assessment of repositories for radioactive waste are summarized in the following: 1) there are indications in the oxygen isotope composition of the groundwater, which suggest that the site may have been subjected to deep (several hundred metres) penetration of glacial melt water. This melt water does not appear to have changed the reducing conditions prevailing below the upper hydraulically active zone. Another possible process, capable to generate the depleted oxygen isotope values is a freezing front under permafrost conditions, 2) Modelling of the redox and pH controls in a flow system supported that the rock would have sufficient redox buffering capacity to counteract deep penetration of oxidising conditions. Moreover, measured present-day redox potentials demonstrate that if oxidising conditions had penetrated to depth, the conditions have been restored to reducing, 3) Based on the occurrence of young uranophanes and uranium accumulations in association with fracture calcites, it can be concluded that a continuous alteration and oxygenating process is in progress at Palmottu. This process was also manifested by high concentrations of dissolved uranium in ...