In the present paper we have attempted to associate quantified impacts with a forecasted nuclear energy development in different world regions, under a range of hypotheses on the energy demand growth. It gives results in terms of availability of uranium resources, required deployment of fuel cycle facilities and reactor types. In particular, the need to achieve short doubling times with future fast reactors is investigated and quantified in specific world regions. It has been found that a crucial feature of any world scenario study is to provide not only trends for an idealized “homogeneous” description of the global world, but also trends for different regions in the world. These regions may be selected using rather simple criteria (mostly of a geographical type), in order to apply different hypotheses for energy demand growth, fuel cycle strategies and the implementation of various reactor types for the different regions. This approach was an attempt to avoid focusing on selected countries, in particular on those where no new significant energy demand growth is expected, but instead to provide trends and conclusions that account for the features of countries that will be major players in the world energy development in the future.

Since a fast reactor core with uranium-plutonium fuel is not in its most reactive configuration under operating conditions, redistribution of the core materials (fuel, steel, sodium) during a core disruptive accident (CDA) may lead to recriticalities and as a consequence to severe nuclear power excursions. The prevention, or at least the mitigation, of core disruption is therefore of the utmost importance. In the current paper, we analyze an innovative fast reactor concept developed within the CP-ESFR European project, focusing on the phenomena affecting the initiation and the transition phases of an unprotected loss of flow (ULOF) accident. Key phenomena for the initiation phase are coolant boiling onset and further voiding of the core that lead to a reactivity increase in the case of a positive void reactivity effect. Therefore, the first level of optimization involves the reduction, by design, of the positive void effect in order to avoid entering a severe accident. If the core disruption cannot be avoided, the accident enters into the transition phase, characterized by the progression of core melting and recriticalities due to fuel compaction. Dedicated features that enhance and guarantee a sufficient and timely fuel discharge are considered for the optimization of this phase.