Confidence in the findings of safety assessment requires a sound scientific understanding of the repository system and its evolution and that uncertainties are identified and, where possible, quantified. Nagra’s scientific understanding relevant to the post-closure safety of the proposed repository system and its associated uncertainties has been developed through an interdisciplinary and collaborative programme of RD&D and site characterisation. Understanding of the long-term behaviour of the repository system and its geological setting is supported by wide ranging information, including:

• field observations and monitoring activities,

• laboratory experiments, field testing and demonstration/verification activities,

• modelling studies,

• literature surveys, and

• expert elicitation.

The following paragraphs summarise the assessment basis relevant to the safety assessment of a geological repository for both HLW and L/ILW. A detailed description, including references to data sources, can be found in the referenced reports.