This report provides insights, guidance and a framework for Member States to conduct realistic safety assessments for research reactors in terms of external events. A graded approach to the safety of research reactors is presented based on the radiological hazard that a facility poses to the environment, the public and workers. This report supports the development of site specific guidelines for the actual design and safety assessment. It can also be used as background for the preparation of training material for research reactor staff for a self-assessment of the vulnerability of existing structures to external events.