Potential of thorium molten salt reactors: Detailed 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 Th-232/U-233 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 the plutonium 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 Th-232/U-233 MSBR-like systems from the existing French PWRs demonstrate the advantage of an upstream U-233 production in other reactors, allowing a direct start of the MSBR-like systems with U-233. This finally leads us to explore alternatives to some MSBR features, for energy production with Th-232/U-233 fuel from the start. We thus test different options, especially in terms of core neutronics optimization and reprocessing unit adaptation. (C) 2004 Published by Elsevier Ltd.