The molten salt fast reactor as transmutation system in the view of the nuclear phase-out

The basic development and design of a molten salt reactor with fast neutron spectrum (Molten Salt Fast Reactor – MSFR) is the target of the EVOL project in FP7. The MSFR offers certain advantages in the view of transmutation compared to solid fuelled reactor types. In the first part, these advantages will be discussed in a comparison with the sodium cooled fast reactor technology and the research challenges will be analyzed.
In the second part, a strategy for the optimization of the transmutation efficiency is developed, based on the findings of a former study, for different configurations – core with U-238 fertile, a fertile free core and a core with Th-232 as fertile material. The study has identified advantageous use of Thorium as fertile material. The final aim of this study is dictated by the phase out decision of the German government. Transmutation in the German view thus is focused on the determination of the maximal transmutation efficiency and on an as much as possible reduced left over of transuranium elements (TRUs) in the end of reactor life core. This is a prerequisite, since there is no future reactor foreseen and the reminders have to be put into a final repository. This minimal left over is achieved by a two step operation, first a TRU burning phase with continuous feed in a salt configuration with Thorium as fertile material, second a deep burning phase utilizing the U-233 bred in the blanket of the core as feed. In the calculation results, the time evolution of different important isotopes will be analyzed for both phases. It will be demonstrated, that transmutation rates up to more than 90% can be reached, while the production of undesired high elements like Californium is very limited. Based on these results a rough approximation will be given on the required number of reactors for the transmutation of the German TRU stockpile and the left over will estimated. Additionally, the used tool HELIOS 1.10 and the adaptations needed for the simulation of a MSFR will be described.