Value of abstraction in performance assessment – When is a higher level of detail necessary?

• Published in: Geomechanics for energy and the environment Vol. 39; no. 2352-3808; p. 100577
• Main Authors: Frank, Tanja, Becker, Dirk-Alexander, Benbow, Steven, Bond, Alexander, Jayne, Richard, LaForce, Tara, Wolf, Jens
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.09.2024; Elsevier
• Subjects: Domal salt; MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; Model uncertainty; Performance assessment; Radioactive waste disposal; Radionuclide transport simulation; Safety assessment; Radionuclide transport simulation; Safety assessment; Model uncertainty; Performance assessment; Radioactive waste disposal; Domal salt
• ISSN: 2352-3808; 2352-3808
• DOI: 10.1016/j.gete.2024.100577

In this study, different approaches in performance assessment (PA) of the long-term safety of a repository for radioactive waste were examined. This investigation was carried out as part of the DECOVALEX-2023 project, an international collaborative effort for research and model comparison. One specific task of the DECOVALEX-2023 project was the Salt Performance Assessment Modelling task (Salt PA), which aimed at comparing various models and methods employed in the performance assessment of deep geological repositories in salt. In the context of the Salt PA task, three distinct teams from SNL (United States), Quintessa Ltd (United Kingdom), and GRS (Germany) examined the consequences of employing different levels of abstractions when modelling the repository's geometry and implementing various features and processes, using the example of a simple hypothetical repository structure in domal salt. Each team applied their own tools: PFLOTRAN (SNL), QPAC (Quintessa) and LOPOS (GRS). These differ essentially regarding numerical concept and degree of detail in the representation of the underlying physical processes. The discussion focused on when simplifications can be appropriately applied and what consequences result from them. Furthermore, it was explored when and if a higher level of fidelity in geometry or physical processes is required. •Different modelling approaches for the same repository system in rock salt are compared.•Salt convergence and two-phase flow are taken into account.•Approaches use different levels of simplification and dimensionalities.•Approaches roughly agree about the consequences.•Results show that Richard’s equation is a fair approximation of two-phase flow.