Description of work
Task 1: Handling of the damaged zone in integrated PA (NAGRA, NRG and SCK•CEN)
Within this task, possible treatments of the damaged zone within the context of the performance assessment (PA) of a complete disposal system in clay will be identified. This task, to be executed early on in close cooperation with the End Users Group, will ensure that participants in the WP's 2-5 will be provided with a reasonable background on the stakes associated with the TDZ in the workings of a complete disposal system. In particular, this task should clearly identify
- how the damaged zone has been handled in previous PA exercises, the significance of available results of scoping calculations (e.g. from EC projects like BENIPA and national programmes) and typical PA needs;
- features, events and processes (FEPs) considered for scenario development purposes in PA that are potentially linked to the TDZ and its evolution;
- and safety functions of the host rock or the engineered barrier system that might be affected in any way by the TDZ.
Task 2: TDZ evolution and the Safety Case (NAGRA, NRG and SCK•CEN)
This task will build on the knowledge gained in WP's 2-5 to include or update a representation of the TDZ in the conceptual model of the evolution of a disposal system in clay and to clarify the specific impact of TDZ-related processes on the total performance of a repository for long-lived, highly radioactive waste.
With respect to Performance Assessment, the description of FEPs identified in Task 1 will be revised when required and new FEPs will be added if justified. The transferability of data and process-level modelling results acquired within TIMODAZ to the simplified models used in PA, either through the justification of basic PA assumptions or updated values of the parameters of current models (e.g. related to fluid flow and radionuclide transport in the damaged zone) will be investigated. The need to enhance the description of the TDZ in PA models will be assessed;
With respect to the basis for Safety Assessment, TIMODAZ results that can be used as arguments or evidence in a Safety Case (e.g.sealing) will be identified and formulated as such. The results will also be screened for possible interactions between the TDZ and the EBS that could jeopardize (or enhance) the safety functions attributed to EBS components. A statement will be made on the confidence about the level of understanding of the TDZ-related processes in performance assessments and their evolution in time. Finally, conclusions will be drawn over the thermal, mechanical and chemical conditions that can the favourable clay properties modifiy during the thermal period.
Task 3: Input from/to repository design (All)
The range of thermal loads and the expected evolution of temperature profiles arising from currently considered disposal system designs will be provided to WPs 2-5.
From the results of WPs 2-5 and Task 3 above, design options or optimizations that could minimise damage, or minimise the consequences of damage on long-term safety will be identified. Objective criteria will be sought for the admissible thermal load in typical repository systems in clays. Desirable properties and/or performance criteria for EBS components interacting with the TDZ (e.g. liner, buffer,…) will be specified when required.