Incorporating natural and archaeological analogues as additional lines of argument within a safety assessment aligns with IAEA’s guidelines for post-closure safety assessments for radioactive waste repositories. Following, e.g., Côme & Chapman (1986) and IAEA (1999), these analogues can be defined as natural or man-made environments and/or materials that share common features or similarities with, and thus can provide useful information on, the repository system and its evolution over time. They allow processes and their effects to be observed on large temporal and spatial scales, similar to, or even exceeding, those relevant to safety assessment, providing insights into the durability of system components and into the effective isolation of radioactive materials in a repository. They can showcase the resilience of chosen barrier materials to potentially detrimental repository induced effects and to long-term degradation processes.

Analogues can usefully complement site-specific information, especially at the early stages of a programme where such information is limited. The three-stage Sectoral Plan for Deep Geological Repositories (SGT) in Switzerland has, since 2008 (BFE 2008), led to extensive exploration and studies of potentially suitable geological environments, yielding large amounts of geological and hydrological data, as well as experimental results elucidating the behaviour of relevant materials, including radionuclides, in such environments. Nonetheless, while this reduces reliance on natural and archaeological analogues to support the durability and performance of the repository barriers, information from analogues remains integral to the post-closure safety case and is summarised in the following sections.