Molten Salt Fast Reactor: Shift from Burner to Breeder

The nuclear reactors currently in operation utilise only a small fraction of the available natural uranium. By continuing in this track, known resources will be depleted too soon. Furthermore, Light Water Reactors (LWR) need to be shut down periodically so that refueling can take place. On top of that, their spent fuel must be safely stored for thousands of years. These unfortunate facts call for nuclear reactors which can convert non-fissile isotopes to fissile ones and produce less long-lived transuranic elements. Such a reactor is the Molten Salt Fast Reactor (MSFR). In this project in-house developed codes were used for neutronics (DALTON) and burnup (LOWFAT) calculations. The isotopic evolution of nuclides in the core and in the fertile blanket was simulated for two different initial core loadings: a mixture containing 233U as the fissile material and a mixture with transuranium elements (TRU) produced by a LWR. Moreover, the transition from the second configuration (actinide burner) to the first one was investigated. The results showed a huge reduction in the share of the initial isotopes for the TRU-started MSFR after one century of operation. The amount of 233U in the reactor core at that time is equal to the amount needed to create an initial inventory of a 233U-started MSFR, while the 233U to keep the reactor critical can be covered by the 233U bred by the 233Pa extraction from the fertile blanket. Both these facts lead to the conclusion that a transition from a burner to a breeder MSFR is possible.