I believe the molten salt technology used for thermal energy storage is not directly related to molten salt nuclear reactors:

https://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_... (sodium nitrate, potassium nitrate and calcium nitrate)

https://en.wikipedia.org/wiki/Molten_salt_reactor#Fused_salt...

Many years ago when you could visit Dounreay nuclear power station I remember leaning they used liquid sodium as the main coolant. It was used to transfer heat our of the reactor from what I recall.