A methodology for scenario development based on understanding of long-term evolution of geological disposal systems

We have developed a “hybrid” scenario development method by combining bottom-up and top-down approaches and applied for the case of geological disposal of high-level waste. This approach provides a top-down perspective, by introducing a concept of safety functions for different periods and “storyboards”, which depict repository evolution with time on a range of spatial scales, and a bottom-up perspective, by identifying relationship between processes related to radionuclide migration and safety functions based on feature, event and process (FEP) management. Based on a trial study, we have specified work descriptions for each step of the hybrid scenario development methodology and confirmed that the storyboard provides a baseline and holistic overview for the FEP management and a common platform to involve close interaction with experts in various disciplines to understand the crossover phenomenological processes. We also confirmed that there is no conflict between the top-down approach and the bottom-up approach and the hybrid scenario development work frame fulfils the specified requirements for traceability, comprehensiveness, ease of understanding, integration of multidisciplinary knowledge and applicability to a staged approach to siting.