4.10. In accordance with the requirements in Ref. [IAEA SSR-5 (2011)], the development of the safety case should be an iterative process that evolves with the development of the disposal facility. According to Ref. [IAEA SSR-5 (2011)], the formality and level of technical detail of the safety case will depend on the stage of development of the project, the decision in hand and specific national requirements. The step by step approach adopted for development of disposal facilities provides a basis for decision making relating to the siting, design, excavation and construction, operation and closure of facilities, and should allow the identification of issues that require further attention in order to improve the understanding of aspects influencing the safety of the disposal system and/or to reduce remaining uncertainties by appropriate design choices.