RULET

The safe disposal of highly radioactive waste requires a detailed understanding of the long-term behaviour of radionuclides in the near field of deep geological repositories. The joint project RULET addresses this challenge by investigating the geochemical processes that determine the mobility and retention of important safety relevant fission, activation and decay products such as 99Tc, 79Se, 14C and 226Ra. The corrosion of iron-based waste canisters in a deep geological repository leads to the formation of Fe(II)-containing secondary phases, including carbonates and phyllosilicates. These phases significantly influence the redox environment and can serve as effective sinks for redox-sensitive radionuclides. RULET focuses on the formation, characterisation, and reactivity of these minerals with particular emphasis on their role in radionuclide retention through sorption, redox transformation and incorporation processes.

At IFN-2, our focus is on a comprehensive understanding of the retention mechanisms of 226Ra by carbonate minerals, based on thermodynamic and kinetic approaches for solid-solution–aqueous-solution systems. Our approach combines experimental investigations using microfluidics, advanced spectroscopic and microscopic techniques, and thermodynamic and atomistic modelling. Moreover, we examine the influence of the transport regime (diffusive/advective) on the incorporation of Se(IV) into Fe(II)-bearing carbonates with regard to their polymorphism and uptake kinetics. The results will contribute to the refinement of reactive transport models and support the development of robust safety assessments for deep geological disposal.