In Switzerland, legal regulations and guidelines require the disposal of all types of radioactive waste in deep geological repositories. Following a comparison of candidate siting regions, the National Cooperative for the Disposal of Radioactive Waste (Nagra) identified the most suitable siting region, and in November 2024, applied for a general license for a combined repository for both high-level waste (HLW) and low- and intermediate-level waste (L/ILW). The documentation submitted to the regulatory authorities included the demonstration of post-closure safety of the repository. The overriding post-closure safety objective of a deep geological repository is the long-term protection of humans and the environment from the effects of ionising radiation, without imposing undue burdens and obligations on future generations.

This Research Topic showcases the long-term safety case of the planned deep geological repository for both HLW and L/ILW. The synthesis of the post-closure safety case, which is the outcome of the safety assessment, is presented. This includes the process of gathering all relevant evidence and arguments, and carrying out the analyses required for the demonstration of the safety of the disposal system during the post-closure phase. The safety assessment follows a traceable, transparent, and auditable process.

This Research Topic presents the following:
• The current safety and repository concept and provisional repository design, for which the safety case has been developed
• The methodology adopted for the safety assessment, which provides the central elements of the safety case
• The scientific underpinnings of the assessment. This includes aspects such as the integrated understanding of the geology of Northern Switzerland, the repository-induced effects covering the properties and interactions between the engineered barriers and the waste, as well as the phenomenological understanding of the expected evolution of the repository
• The performance assessment, which comprises an analysis of the thermal, hydraulic, mechanical, and chemical evolution of the repository system
• Safety scenarios developed to capture the uncertainty inherent in the ways in which the disposal system can evolve over time, considering all relevant sources, as well as demonstrating system robustness
• The analysis of radiological consequences, including an evaluation of radionuclide release rates to the surface environment as a function of time for the various safety scenarios, complemented by analyses linked to future human actions and the excavation of the repository by erosion processes.

Topic Editors, Nikitas Diomidis and Olivier Leupin, declare that they are affiliated with Nagra, and Paul Smith declares that they have provided consultancy services to Nagra over a period of several years.

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The Safety Case for a Deep Geological Repository in Switzerland