ACED: Assessment of chemical evolution of ILW and HLW disposal cells (EURAD WP)

The ACED WP was selected for inclusion in the first phase of EURAD as it addresses the following activities, which are relevant to Theme 3 “Engineered barrier system (EBS) properties, function and long-term performance” in Phase 1 and 2 of the EURAD Roadmap:

• Improved understanding of the interactions occurring at the interfaces between waste packages and different barriers in the disposal system
• Improved description of the spatial and temporal evolution and transformations affecting the porous media and degrading materials in the near field of HLW and ILW disposal systems
• And concerns also the high priority item for phase 1 in performance assessment and systems models
• Improved understanding of the role of physical/chemical processes at different scales and linking bottom-up and top-down approaches in performance assessment

The work will allow us to ascertain to what level of detail and complexity the processes should be incorporated in safety- and performance-related models. The information gained through study of the more generic but European representative HLW and ILW disposal cells can later be used and adapted for more specific, national disposal cell designs.

The WP outcomes will impact the safety case in various ways, for example, with respect to material specifications and establishment of requirements for deposition scenarios. The representative designs for ILW and HLW are set in both crystalline and sedimentary rock types, representing interests of the WMOs as end-users. The work in this WP is carried out by a large number of partners, with a good balance between WMO, TSO and RE representatives, which demonstrates the high level of interest in this subject area.

This WP aims to improve the methodology used to integrate knowledge on the geochemical processes in and between the materials in disposal cells for ILW and HLW waste in order to understand and assess the long-term evolution of such a complex system. A multi-process and multi-scale modelling framework will enable the assessment of the chemical evolution at various material interfaces and thermal, hydraulic and/or chemical gradients, from the microscale to the disposal cell scale (ILW, HLW), considering the near-field environment and the host rock over larger temporal scales. Starting from small-scale process understanding, the WP seeks to identify which detailed geochemical processes need to be included for representative assessments of the chemical evolution to be made, taking into account requirements relating to repository design and safety assessments.