Potential of thorium molten salt reactorsdetailed calculations and concept evolution with a view to large scale energy production

We discuss here the concept of Thorium Molten Salt Reactor dedicated to future nuclear energy production. The fuel of such reactors being liquid, it can be easily reprocessed to overcome neutronic limits. In the late sixties, the MSBR project showed that breeding is possible with thorium in a thermal spectrum, provided that an efficient pyrochemical reprocessing is added. With tools developed around the Monte Carlo MCNP code, we first re-evaluate the performance of a MSBR-like reference system with 232Th/233U fuel. We find an important reduction of inventories and induced radiotoxicities at equilibrium compared to other fuel cycles, with a doubling time of about thirty years. We then study how to start this interesting reference system with theplutonium from PWR spent fuel. Such a transition appears slow and difficult, since it is very sensitive to the fissile quality of the plutonium used. Deployment scenarios of 232Th/233U MSBR-like systems from the existing French PWRs demonstrate the advantage of an upstream 233U production in other reactors, allowing a direct start of the MSBR-like systems with 233U. This finally leads us to explore alternatives to some MSBR features, for energy production with 232Th/233U fuel from the start. We thus test different options, especially in terms of core neutronics optimization and reprocessing unit adaptation.