Defence in depth considerations for inherent safety features and passive safety systems in advanced reactor technology designs

Defence in Depth (DiD) is a fundamental safety concept with a central objective to ensure that all safety activities, whether they be organizational, behavioural or equipment related, are subject to layers of overlapping provisions, so that, if a failure should occur, it would be compensated for or corrected without causing public harm. This idea of multiple levels of protection is the key feature of DiD and these levels are expected to be implemented during the design and operation of reactor facilities. Advanced reactor technologies are increasingly proposing to incorporate inherent safety features and passive safety systems in design with higher emphasis on earlier levels of DiD and physical barriers. Some considerations include addressing uncertainties with plant operating states, and failure modes due to limited operational experience and research and development. Nevertheless, it is important that fundamental safety objectives are achieved, including a balanced application of DiD. (author)