FLiBe

Li₂BeF₄

Moderators & Coolants

Density: 1.94 g/cm³

Lithium fluoride–beryllium fluoride molten salt (2LiF-BeF₂). Primary coolant/fuel carrier for fluoride-salt-cooled and molten salt reactors. Li-7 enriched to 99.995% to minimize tritium production.

Composition

Nuclide / Element	Fraction
Li-6	0.000014
Li-7	0.285700
Be-9	0.142857
F-19	0.571429

Code output

MCNP

c FLiBe (Li2BeF4) - Li-7 enriched to 99.995%
c Density: 1.94 g/cm3 (use -1.94 on cell card)
c Atom fractions for 2 Li + 1 Be + 4 F = 7 atoms
m21    3006.80c  0.000014  $ Li-6
       3007.80c  0.285700  $ Li-7
       4009.80c  0.142857  $ Be-9
       9019.80c  0.571429  $ F-19

Notes

Li-7 enrichment to 99.995% is critical for MSR designs to limit tritium production from Li-6(n,α)T. Density varies with temperature: roughly ρ = 2.413 − 4.88×10⁻⁴·T(K) g/cm³.

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