We have validated a neutral network force field model for pure molten FliNaK against self-diffusivity and local structure neutron scattering measurements. The temperature-dependent diffusivity of pure molten eutectic LiF-NaF-KF (46.5-11.5-42 molar %, Li-7 enriched) was measured using quasi-elastic neutron scattering (QENS). A stretched exponential model for the relaxation associated with diffusion was used to fit the measured QENS response over a Q range of 0.3 Å^-1 < Q < 0.9 Å^-1. The elemental-average cross-section weighted self-diffusion coefficient follows an Arrhenius behavior between 500 and 800 C with an activation energy of . The measured diffusivity is compared to molecular dynamics simulations using a neural network forcefield and good agreement is seen. The local structure of the same system was measured using neutron diffraction. A comparision of the measured static structure factor S(Q) agrees very well with the neutron-weighted NNFF model S(Q). This comparison demonstrates that the NNFF model has captured the local structure of molten FLiNaK.

Arrhenius plot showing comparison of the self-diffusivity QENS measurement of pure FLiNaK (solid line) and element-specific diffusvity from the NNFF model.

Comparision of neutron-weighted S(Q) from the NNFF model (solid line) and the measured S(Q) (open circles).

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