Deep geological repositories (DGR) for radioactive waste place unique demands on geological site characterization. In particular, robust, yet efficient characterization strategies are needed to reduce geological uncertainties and assess the suitability of potential host rocks and their surrounding geological environment that act as natural barriers with respect to the long-term containment of radionuclides. This includes, among other aspects, the evaluation of geological structure, hydrogeological and hydrogeochemical conditions, potential transport pathways for radionuclides, geomechanical properties, and the continuity of low-permeable storage formations. While underground research laboratories (URL) have significantly advanced our knowledge about storage formations for nuclear waste disposal and the coupled processes governing their long-term evolution, an important challenge remains the transfer into a practical site characterization programme.

This session invites contributions on integrated approaches to DGR site characterization, from laboratory to regional scales. We welcome studies addressing the design and optimization of characterization programmes, including deep drilling, geological and structural investigations, hydrogeological and hydrogeochemical testing, borehole logging, geophysical imaging, laboratory analyses, monitoring concepts, and numerical modelling. Particular emphasis is placed on multidisciplinary workflows that combine complementary datasets to efficiently evaluate key repository relevant characteristics, reduce uncertainties, and support evidence-based site assessment.

Contributions from underground research laboratories, national site investigation programmes, and international collaborative projects are particularly encouraged, especially those demonstrating how fundamental research, methodological developments, and integrated characterization strategies can be translated into practical site characterization for deep geological repositories.