THEREDA represents a web-based system of programs enabling access to thermodynamic reference data for the needs of the final disposal of radioactive waste in Germany. It is the only polythermal database worldwide that covers the entire system of oceanic salts, including acids, bases and carbonates. THEREDA aims at calculation of solubilities in high-saline solutions and uses the Pitzer approach.

In the last few years, we have studied the immobilization of the long-lived fission product technetium-99 (⁹⁹Tc) by various Fe(II) minerals. Those minerals enable the reduction of Tc(VII) to Tc(IV), which is crucial to decrease the migration of technetium in the environment. In the future, we want to analyze Tc immobilization strategies under more complex systems that could, in a more realistic way, improve environmental conditions.

The immobilization of trivalent actinides (Am, Cm) and their less toxic homologue (Eu) in feldspar, a very common mineral in our earth crust, was studied by sorption experiments and spectroscopic studies. The speciation was identified and used to gain thermodynamic parameters to develop a surface complexation model. To sum up, feldspar, a main component of crystalline rock, is suitable for retaining radionuclides in a deep radioactive waste repository.

In the presentation, results from the European Joint Programme on Radioactive Waste Management (EURAD) strategic study, Uncertainty Management multi-Actor Network (UMAN), related to the management of uncertainties associated with human aspects, will be presented.

The Repository Site Selection Act explicitly emphasises that targeting the disposal of high-level radioactive waste is a so-called learning process. We are of the opinion that the procedure and the available data should be combined with geoscientific knowledge to support the identification of siting regions. We propose this workshop and invite all experts who have dealt with the search for a repository site from a geoscientific perspective.