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.

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.

The present contribution provides an overview on the collaborative project iCROSS and reports selected results. The impact of considering complex coupled processes in repository subsystems for the assessment of the integrity of a given (generic) repository arrangement will be discussed. The interdisciplinary team combines experimental work in the lab, in the underground rock laboratory and environmental simulations in order to achieve process understanding across variable scales.