Thorium fuel cycles : a graphite-moderated molten salt reactor versus a fast spectrum solid fuel system

The aim of this paper is to compare two main options dedicated to long-term energy production with Thorium: solid fuel with fast spectrum and molten salt with moderated neutrons. In both cases, we have set up a speci c system and studied its behaviour until it reaches the Th/U equilibrium from two di erent starting fuels: Th/U and Th/Pu, with Pu coming from PWR spent fuel. All this work was done with the same computing methods based on the coupling between a validated neutron transport code and a numerical resolution of the evolution equations which takes into account the time dependence of the mean cross sections. Our results consist in precise time evolutions of physical parameters, inventories and waste production, allowing comparison of breeding performance and induced radiotoxicities. From this comparison, the molten salt solution appears to be more interesting than the solid fuel reactor for a quick transition to a signi cant Thorium fuel cycle.