Geochemical far-field processes in performance assessment

The release and transport of radionuclides from underground repositories into the biosphere is influenced by geochemical processes and geological barriers, which play a crucial role in ensuring long-term safety. This study aims to provide an overview of recent advancements in modeling nonlinear sorption processes and colloid-facilitated contaminant transport and to assess the impact of these geochemical mechanisms on performance assessments for radioactive waste repositories. The methodology involves the application of models and data derived primarily from laboratory experiments, despite their inherent time limitations compared to the millennia-scale transport times required for thorough geosphere evaluations. To bridge this knowledge gap, investigations into geological analogues are suggested as a means to deepen understanding of the transport and retention of radionuclides under natural conditions, and to evaluate the applicability of laboratory findings to real-world scenarios. Ultimately, the paper highlights the importance of integrated computer codes, such as EMOS, in simulating contaminant dynamics and radiation exposure while emphasizing the role of geological formations in acting as barriers to nuclide transport into the biosphere.