Multiphysics Modelling of Solid Fission Products Transport in the Molten Salt Fast Reactor

Due to its innovative design and the strong coupling among thermal hydraulics, neutronics and fuel chemistry, the multiphysics approach has become a standard tool to address the design and analysis of the Molten Salt Fast Reactor (MSFR). Despite recent advancements, the integration of fission products (FPs) transport modelling has not been addressed yet. Some FP species are not expected to form stable compounds with the constituents of the liquid fuel salt and are likely to deposit on reactor surfaces in the form of solid precipitates, giving rise to potential issues such as formation of localised decay heat sources as well as deterioration of heat exchanger performance. The correct evaluation of solid FPs distribution is also crucial for the estimation of the radiological and decay heat inventory of the reactor, and to design effective FPs management and reprocessing strategies. The main goal of this work is therefore the extension of state-of-the-art MSFR multiphysics tools towards the modelling and simulation of solid FPs within the reactor. Several aspects are covered, including (i) the treatment of deposition of precipitated solid particles on reactor walls, both from the modelling and numerical viewpoint; (ii) the modelling of precipitation/dissolution of FP particles to account for local temperature variations; (iii) effects of turbulence closure modelling on the prediction of transported species, especially for complex geometries. An advection-diffusion-decay model is first integrated in an incompressible single-phase multiphysics MSFR solver based on the open-source CFD library OpenFOAM. Then the developed models are tested on two-dimensional MSFR cases, showing the role of RANS turbulence modelling on the prediction of particle transport and deposition. The development of a three-dimensional LES model for the MSFR is also addressed, suggesting the feasibility of more advanced turbulence modelling approaches in the context of multiphysics analysis of the MSFR. Preliminary results show interesting dynamic behaviour, with promising applications in a wide range of MSFR studies.