[en] Andra is currently in the license application process for a deep geological disposal facility for high level waste (HLW) and intermediate level waste (ILW) in a clay formation, the Callovo-Oxfordian, in the eastern part of France. This process started in 2011 by the development of an industrial design phase that consists of a proposed overall underground architecture for the repository and the definition of the operating principles, and the name given to the project was defined: the “Centre industriel de stockage en milieu géologique” (Cigéo, Industrial Center for Geological Disposal). The files and in particular the safety case that will support the license application result from a continuous increase in knowledge, project development, and associated safety assessment for several decades. Since the French Act in 1991 on the long term plan for the management of ILW and HLW in France, Andra is running a comprehensive research project including a broad combination of laboratory research, surface and drilling based site investigations, research in the Bure URL and model development. The preparation of the license application is thus the result of a stepwise accumulation of knowledge and iterative process including several safety cases as well as their regulatory review. The safety case development plays a key role in supporting the development of the technical solutions to manage HLW and ILW. It is based on successive “knowledge/design /safety” iterations. Each iteration involves scientific and technological knowledge acquisition, study of the layout designs consistent with this knowledge and safety assessment. Each safety case is associated with key milestones (reliability, siting, underground research, industrial design development, safety options, licensing) based on the “knowledge/design /safety” iteration providing lessons learnt. The successive iterations gradually help to guide the choice toward design solutions, R&D programmes, and safety studies. Andra collects and documents knowledge R&D data and analyses residual uncertainties in the knowledge. (author)