Model Based Performance Assessment in Support of the Safety Assessment for a Geological Repository
Nagra (2024): Model Based Performance Assessment in Support of the Safety Assessment for a Geological Repository. Nagra Arbeitsbericht NAB 24-25.
This report documents the development of a robust modelling workflow and delivers the associated model-based analyses for the performance assessments of an exemplary repository implementation at the Haberstal site. The modelling tools and analyses are implemented on the level of the total barrier system, as well focused on the high-level waste and low-/intermediate-level waste disposal areas, respectively.
In particular, a comprehensive description of numerical models used in the performance assessment is provided with all input data, technical specifications, and links within the performance assessment model chain. The abstraction methodology is elaborated in detail, including a discussion on the treatment of conceptual uncertainty, the assumptions and justifications of choices made in model implementations, as well as the extensive model benchmarking performed within the performance assessment model chain. The implementation of the model chain for the model-based assessments and the role and usage of each model is explained. The modelling performed for the total system assessments is described in detail for the expected barrier performance as well as several deterministic scenarios representing deviations therefrom. In addition, probabilistic simulations considering parametric uncertainty are presented for high-level waste and low‑/intermediate-level waste, for the expected performance and several scenarios that address individual barriers of the repository system.
The analysis of modelling results confirms on the one hand the confidence in the performance assessment model chain and on the other hand the robustness of the barrier system in the exemplary repository implementation. The latter is demonstrated comprehensively from the perspectives of the total system as well as of barrier components, gained by the multitude of modelling tools for a broad range of uncertainties and scenarios associated with the evolution of the repository system.
The modelling results presented here are used in the synthesis of the performance assessment for quantitative assessment with regards to safety functions of the barrier system and the associated performance margins. The latter is not addressed in the present report.