Decisions associated with radioactive waste management are made in the presence of irreducible and reducible uncertainties. Here, the identification of such uncertainties (namely numerical ones), their ranking according to relevance, their categorization, the elucidation of internal dependencies and cross-interactions is addressed. Suitable methodologies to analyse and illustrate complex uncertainty patterns are discussed.

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.