Coupled Computational Fluid Dynamics and Computational Thermodynamics Simulations for Chemically Reacting Flows with Phase Transformations: A Fluoride Volatility Process Example

Abstract

This study presents the development of a novel computational capability for chemically reacting flows with phase transformation that can be applied to complex multi-component systems. This is done by coupling Computational Fluid Dynamic (CFD) using OpenFOAM and Computational Thermodynamics (CT) using Thermochimica and the Joint Research Centre Molten Salt Database (JRCMSD). To illustrate this capability, the Fluorite Volatility Process (FVP) is modelled because it is the first step to clean up irradiated fuel salt in the Molten Salt Fast Reactor design and needs to be better understood. Local chemical equilibrium is assumed, which means that chemical kinetics is solely governed by mass transport. FVP recovers nuclear fuel UF4(liq) by injection of fluorine gas (F2), forming UF6(gas). The vaporization rate of UF4 is investigated on four different molten salt systems, using different dynamic viscosities and temperatures. The vaporization rate was shown to be clearly dependent on both thermochemical and thermophysical properties. Higher viscosities promoted larger bubbles, which delayed the chemical reaction. Results were compared to already available experimental data, showing good agreement. The applicability of coupling CFD with Thermochimica showed to be promising and expands interpretations on multiphysics systems and will be later applied to more complex scenarios.