4.21. The purpose of each revision of the safety case will depend on a number of factors, such as the stage of development of the disposal facility, and whether the safety case is to be submitted to the regulatory body as part of a formal licensing procedure or to obtain directions from the regulatory body. For each revision of the safety case, the operator should provide a clear description of its purpose, which, depending on the stage of development of the facility, could include:@@- Testing of initial ideas for safety concepts;@@- Site selection;@@- Demonstration of the safety of the disposal facility;@@- Optimization of the facility design;@@- Identification of safety related issues to be addressed by research and development programmes;@@- Definition or revision of limits, controls and conditions such as waste acceptance criteria;@@- Assessment of the maximum inventory that can be disposed of (the ‘radiological capacity’ of the facility);@@- Rationale for the duration of institutional control;@@- Input to monitoring and data acquisition programmes;@@- Periodic re-assessment as required by law or regulation;@@- Application to extend or upgrade the facility or to co-locate new plant or waste management facilities;@@- Closure of the facility, either at the planned end of the lifetime of the facility or as a consequence of non-compliance with the regulations;@@- Application to re-open the facility after closure for non-compliance or for other reasons;@@- Determination of whether remedial action is necessary.