4.16. In the site selection process, some assumptions will have to be made regarding the detailed characteristics of the site and the design of the disposal facility and, therefore, the safety assessment will provide only preliminary estimates of how the disposal facility will perform. This is acceptable because the role of the safety case at this stage is only to determine whether a site is, in principle, suitable for a disposal facility. At later stages, more site specific data will be necessary and details of the proposed design will have been developed, which will allow operational and long term performance issues to be addressed in more detail in the safety case.