5.6. A safety case has to be prepared early in the development of a geological disposal facility to guide activities in research and development, site characterization, design and planning [1]. The safety assessment process should involve calculations to evaluate the robustness of the proposed conceptual model(s) in terms of its potential to meet regulatory requirements and to determine the relevant radionuclides, pathways and release mechanisms for which further knowledge is necessary and on which the focus should be set. Scoping calculations are often based on limited data, for example, from searches of the literature, material specifications, laboratory studies and studies of natural analogues, preliminary site investigations and characterization of the waste. Acquisition of data will continue throughout the step by step process until the disposal facility is permanently closed or the proposed concept is determined to be unacceptable.