Coolant Void Effect Optimization of an Inert Matrix Pb-Cooled xADS Transmuter Core

This analysis arises from the necessity to 'improve' the reactivity coefficients of a xADTransmuter core fuelled by 'Uranium Free' fuel in MgO inert matrix. In fact, it was already highlighted that there is necessity of a 'second thoughts' of the safety criterions and/or design constrains as well as some concepts related to the suberitical systems, that is to 'trace back' the reactor safety reactivity coefficients to values consistent with the Subcritical System Concept. This appears possible without 'penalizations' of the core geometry assuring. in such a way, the possibility of using the 'natural convection' for the removal of the residual power. It is clear that, such solution need to be verified for each core configuration different from the analysed one, and verified in terms of Minor Actinides, loaded in the core, efficiency of the transmutation/burning process.