Treatment of chemical evolutions in national programmes: EURAD ACED Deliverable 2.4

The broader scope of the workpackage ACED is the assessment of the chemical evolution at the disposal cell scale involving interacting materials and thermal, hydraulic and/or chemical gradients by considering ILW and HLW disposal concepts representative for different concepts throughout Europe. There are a number of elements, especially at the interface scale, which are common for both HLW and ILW disposal cells. On the other hand, the disposal cells for ILW and HLW also have specific elements only relevant for either one of the two such as involved processes, features et cetera. Therefore having both ILW and HLW as separate study objects in the evaluation of the methodologies for process integration and model abstraction will allow for a much broader application of the outcomes of this work package for the different national programmes. Processed waste is considered in ACED and includes a vitrified waste form for High Level Waste (HLW) and a cementitious waste form for Intermediated Level Waste (ILW). Disposal of these waste forms in a geological disposal facility hosted in either crystalline or sedimentary rock types are investigated. Both rock types are porous materials and the chemical composition of their pore waters may induce mineral changes in the engineered barrier system. The virgin pore water chemistry in these host rocks is influenced by carbonates and clay minerals but thermodynamic modelling is required to determine the pore water chemistry in clay host rocks while this modelling may not always be appropriate to determine the pore water chemistry in fractures in crystalline rocks due mixing of groundwaters and biological processes that also have an impact on the porewater chemistry at the depth of the disposal facility. The evolved pore waters from the engineered system chemically affect the host rock locally. A systematic understanding of the chemical evolution from the waste form up till the host rock can be used for a robust assessment of the impact of these processes. Disposal cells in ACED treat the chemical evolution from the waste form until the host rock. An integration of the available knowledge of the chemical evolution can be performed in a safety assessment. There may be current European practices why the chemical evolutions for disposal are included in safety assessments and safety cases and how the chemical evolutions at disposal cell scale have been treated. A collection of the conceptualisations of the chemical evolutions and which parts have been modelled in Europe could prevent duplication of work already done. Organisations from eight EU countries participate in the ACED task for the current handling of the chemical evolution: Belgium, Czech, Finland, France, Germany, Lithuania, Netherlands and Spain They have described the characteristics of the disposal cells considered in their national programmes and the considered chemical evolutions. Organisations from other European countries with nuclear power plants that participate in EURAD and Switzerland have been asked to contribute to this deliverable. Waste management Organisations (WMOs) usually write the safety cases and the safety assessments is the backbone in the safety case. Therefore preferably WMOs from the missing European countries have been asked to complete a template in which details were asked, specifically references for the materials in the disposal cell, a narrative of the post-closure phase, conceptual and mathematical model for the disposal cell. These country contributions in this Deliverable 2.4 as well as Deliverable 2.5: Analysis of experiments and numerical studies on interfaces, are contributions to the initial State of the Art (Deliverable 2.1). The country contributions can also be used to define experimental conditions that are representative for the chemical evolution of the disposal concepts considered in Europe such as temperature at interfaces and these contributions have been used to define the disposal cells that are used for the modelling work in ACED.