This paper describes the deep geological repository concept considered by Nagra in support of its recent general licence application and the methodology used by Nagra to demonstrate its post-closure safety. The concept presented is for a deep geological repository for high-level waste (HLW) and for low- and intermediate-level waste (L/ILW) located in the Opalinus Clay host rock in Switzerland. The safety and repository concept is based on geological and engineered barriers which together perform