Enhanced Defense in Depth: A Fundamental Approach for Innovative Nuclear Systems Recommended by INPRO

In May 2001, the IAEA initiated the “International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO)”. Having in mind that nuclear power will be an important option for meeting future electricity needs, the scope of INPRO covers nuclear reactors expected to come into service in the next fifty years, together with their associated fuel cycles. INPRO has been implemented in two phases. In the framework of its Phase 1A, the task group Safety of Innovative Nuclear Systems examined the needs to be met by innovative nuclear systems and defined, in a hierarchical order, a corresponding set of Basic Principles, User Requirements, and Criteria. In this context, an enhanced defense-in-depth strategy is considered as a dominant part in the fundamental safety approach. For each of the five levels of protection, a user requirement indicates the direction of the enhancement (e.g.: no need for evacuation, even in case of severe accidents) and, in general, more independence of the levels from each other shall be achieved.