Assessment of Chemical Evolution of ILW and HLW Disposal Cells (ACED)

‘What’

This WP improves the methodology to integrate knowledge on the geochemical processes in and between the materials in a disposal cell for ILW and HLW waste in order to understand and assess the long-term evolution of such complex system. A multi-process and multi-scale modelling framework will enable the assessment of the chemical evolution at various materials 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 for larger temporal scales. Starting from small-scale process understanding, it seeks to which detail geochemical processes need to be included for representative assessments of the chemical evolution in view of the needs in repository design and safety assessment.

‘Why’

The WP ACED is included already in the first EJP EURAD as it covers an important number of high priority items of the roadmap of EURAD. These are in particular the EBS systems understanding in phase 1 and 2:

• 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

More concrete: the work will allow identifying to which detail and complexity these processes should be incorporated in models for different type of safety and performance related studies. 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 outcomes will impact the safety case in different ways such as with respect to material specifications and establishment of requirements for deposition scenarios. The representative designs are set for ILW and HLW in both crystalline and sedimentary rock types, representing prevailing designs of the WMOs as end-users. The clear interest of the mandated actors in this WP is demonstrated by the fact that the WP work is carried out by a large number of partners, with a good balance between WMO, TSO and RE representatives.
 

Closing words from WP Leader

ACED significantly improves our understanding and modelling of the chemical evolution at different scales relevant for ILW and HLW disposal cells; insight was gained by elucidating experiments at interfaces of two or more materials; modelling allowed for extrapolation of longer time scales. Through many interactions between the partners, a solid basis has been obtained for further studies – internationally or within national programmes.