CFD Simulations of the Molten Salt Fast Reactor
Résumé
The Molten Salt Fast Reactor (MSFR) is a fast-spectrum molten salt reactor (MSR) concept, where the fuel salt flows freely through a toroidal core (two meters high by two meters in diameter). This reactor presents several specificities compared to solid fuel reactors, in particular : the strong density feedback depending on the turbulent temperature field in the core ; the turbulent transport of the delayed neutron precursors through the core. These two aspects require the use of coupled neutronics – thermal-hydraulics to model the MSFR core. In CEA, a coupled tool combining the deterministic neutronics code APOLLO3® — and notably its S$_N$ -transport solver MINARET — and the CFD code TrioCFD is used. In a first stage, several thermal-hydraulics studies of the steady-state MSFR flow were performed.
The thermal power distribution was taken from a Monte Carlo calculation. RANS and LES approaches were used.
Different geometries were considered, from one sixteenth of the core to the full core. Our RANS model was compared to steady-state simulations realised by other partners, and used to determine several turbulent parameters (transverse Taylor microscale), in order to optimize the LES meshing. The high Reynolds number (106) as well as the large domain to model contribute to the high computational cost of the LES. They are nonetheless necessary, comparisons between LES and RANS models having revealed important discrepancies in the mean velocity field. These simulations also revealed a very turbulent instantaneous velocity field with several recirculation zones, leading to early estimations
of the power instabilities in the MSFR core.