In the context of the safety of a nuclear waste repository, we have investigated the uranium(VI) reduction by different microbial strains from deep geological layers. The results showed significant differences between the reduction behavior of sulfate- and iron-reducing bacteria. The investigated sulfate-reducing microorganism showed a speciation-dependent uranium(VI) reduction. In contrast, the iron reducer was able to reduce different uranium(VI) complexes and showed an uptake of uranium.

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.

Capturing the state of knowledge in radioactive waste management is a very important activity for supporting member states with the implementation of their national programmes towards the safe and effective management of waste. This requires the involvement of experts sharing their expertise and knowledge with the wider community. During the past 3 years, we have gained valuable insights into the procedures of involving experts and knowledge sharing, and the lessons learnt are shown here.

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.