Multiphysics modeling approach for the analysis of noble metals deposition in the Molten Salt Fast Reactor

Noble metals exhibit very low solubility in fluorine salts, leading to accumulation on reactor surfaces, which negatively impacts performance and safety. In this work, a new modeling capability of the OpenFOAM multiphysics solver, developed at Politecnico di Milano is proposed to analyze the deposition of noble metal fission products in the Molten Salt Fast Reactor (MSFR). To model the particle migration towards reactor walls, a tailored particle transport model and custom boundary condition were implemented. Verification against an analytical solution confirmed accuracy, followed by a sensitivity analysis on mesh refinement, which demonstrated strong dependence on wall-adjacent cell size. Simulating the reactor in full geometry and accounting for all nuclides in the salt demands high-performance computational resources, even for steady state conditions. To reduce computational effort, the deposition velocity (or mass transfer coefficient) obtained from a highly refined mesh was applied to coarser meshes using the tailored boundary conditions. This approach, combined with a single pseudo-nuclide representing the noble metals family, significantly reduces computational demand. Different mesh types were tested for steady-state reactor core simulations, showing that the deposition velocity-based strategy provides satisfactory results for the quantities of interest. Preliminary results are also presented for decay heat generated by radioactive particle deposits. The developed capability to describe noble metal behavior advances the multiphysics solver and contributes to the MSFR's design optimization.