Separation of CsF from FLiNaK molten salt via directional solidification

Abstract

BackgroundFluoride molten salt servers as a coolant and fuel carrier in molten salt reactors (MSRs). Over time of operation, fuel composition of MSR includes uranium, thorium, fission products, and carrier salt. Separating the fission products and recycling the valuable components enhances the reactor's operational efficiency and minimizes radioactive waste. Leveraging the phase equilibrium properties of multi-component mixtures and elemental migration during solidification, can effectively separate materials.PurposeThis study aims at the directional solidification technology of fuel composition of MSR with emphasis on the separation of CsF from FLiNaK molten salt.MethodsFirstly, a certain mass of CsF and FLiNaK eutectic salt were taken to prepare simulated sample of typical fuel composition by mechanical mixing, and completely melt the mixed salt by heating and waiting for the molten salt to cool naturally before using it for directional solidification separation experiments. Then, the concentration distribution of a typical fission product CsF in the FLiNaK molten salt system, subjected to directional solidification under different technological conditions, was investigated using a self-developed cold-rod directional solidification experimental device.ResultsThe experimental results indicate that, by controlling the cooling solidification rate, the Cs element concentration in the solidified salt exhibits a radial gradient distribution, decreasing from the inner to the outer layers. In comparison to the liquid phase, the Cs element concentration in the outer solidified salt shows a substantial reduction, with a maximum decrease of approximately 90%.ConclusionsThe results show that it is feasible to separate fission products via directional solidification in fuel salts. With its straightforward process and absence of by-product generation, this technology shows promise for separating fission products in fuel salts.

Keywords

• molten salt reactor
• fuel salt
• fission products
• directional solidification