The thermal conductivities of molten alkali fluorides (LiF, NaF, and KF) and their mixtures (LiF NaF, LiF KF, and NaF-KF binaries and LiF NaF KF ternary) are predicted using molecular dynamics simulation with the Green-Kubo method. A polarizable ion model is used to describe the interionic interactions. All the systems except LiF KF and LiF NaF-KF mixtures follow a scaling law: it is proportionnal to m(A)(-1/2)(N/V)(2/3), where m(A) is the arithmetic average of the ionic species masses in a given melt and N is the total number of ions included in the system volume V. In LiF KF and LiF-NaF-KF mixtures a significant departure from the scaling law is observed. By examining separately the effects of the cation mass and size asymmetry in LiF KF mixtures, we show that both of them account for half of the deviation. Finally, we observe that the temperature dependence of the thermal conductivity is very small in these molten fluorides.