FLiNaK

LiF-NaF-KF

Moderators & Coolants

Density: 2.09 g/cm³

Atom density: 0.0609643 atoms/b·cm

Lithium–sodium–potassium fluoride eutectic, used as a secondary coolant and heat-transfer salt in molten-salt designs.

Where these numbers come from

Eutectic LiF-NaF-KF at 46.5-11.5-42.0 mol% with natural lithium. Density carried over from the previous NRDP entry; not in the compendium and not re-derived here.

Material compositions from PNNL-15870 Rev. 2 (April 2021), R.S. Detwiler, R.J. McConn Jr., T.F. Grimes, S.A. Upton, and E.J. Engel, Compendium of Material Composition Data for Radiation Transport Modeling, Pacific Northwest National Laboratory. Full report (DOI 10.2172/1782721)

Composition

Nuclide (ZAID)	Weight fraction	Atom fraction	Atom density (atoms/b·cm)
Li-6 (3006)	5.1415e-3	1.7647e-2	1.0758e-3
Li-7 (3007)	7.3015e-2	2.1485e-1	1.3098e-2
F-19 (9019)	4.6011e-1	5.0000e-1	3.0482e-2
Na-23 (11023)	6.4030e-2	5.7500e-2	3.5054e-3
K-39 (19039)	3.6961e-1	1.9584e-1	1.1939e-2
K-40 (19040)	4.7561e-5	2.4570e-5	1.4979e-6
K-41 (19041)	2.8042e-2	1.4133e-2	8.6164e-4

This is the material as formulated. The cards below carry weight fractions, written negative, which is what MCNP and Serpent read as a mass basis.

Generated material cards

MCNP

c FLiNaK
c ReactorMC NRDP derived material - reactormc.net/nrdp/material/flinak; rho =
c 2.09 g/cm3 (use -2.09 on the cell card)
m22    3006.80c  -0.005141  $ Li6
       3007.80c  -0.073015  $ Li7
       9019.80c  -0.460114  $ F19
       11023.80c  -0.064030  $ Na23
       19039.80c  -0.369611  $ K39
       19040.80c  -4.7561e-5  $ K40
       19041.80c  -0.028042  $ K41

MCNP and Serpent cards use .80c (ENDF/B-VII.1 at 293.6 K) — renumber m1 and change the suffix to match your deck. SCONE compositions are atom densities in atoms/barn-cm with the .03 suffix matching temp 300. See the library reference before changing a suffix: the mapping is not portable between vendors.

Notes

Eutectic melting point is about 454 °C, and the density falls as it heats — set it for your operating temperature. Natural lithium is normal here: as a secondary, non-fuel-bearing salt, the Li-6 tritium production matters much less than in FLiBe.

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