Thermofluid simulation of hydrogen isotopologue mixtures during the solidification process

A typical inertial confinement fusion target comprises a central deuterium-tritium (D-T) gas surrounded by a solid D-T layer inside an outer ablator shell. However, because of the isotope effect, fractionation of the hydrogen isotopologues can occur during the solidification process. This inhomogeneity in the solid D-T layer may lead to a deterioration in the fusion reaction. Thus, effective methods are required to characterize isotopologue distribution and homogeneity in solid D-T layers. The distribution of isotopologues in a solid hydrogen mixture can be simulated numerically using computational fluid dynamics. In this study, thermofluid simulations of the mixture's solidification process were performed to investigate the mechanism behind component distribution and to analyze the factors affecting the homogeneity. A numerical simulation was conducted to model inhomogeneity formation during the solidification of hydrogen isotopologue mixtures in a 3D wedge-shaped cavity. The simulations revealed inhomogeneities in H₂-D_2, D₂-T₂, and D₂-DT-T₂ mixtures during solidification. For an H₂-D₂ mixture, the simulation showed good agreement with experimental results, validating the computational model. These simulation methods will be used for homogeneity analysis of the solid D-T layer in fuel pellets.