Argon

Gases & Other

Density: 0.00166201 g/cm³

Atom density: 0.000025 atoms/b·cm

Argon at room conditions — cover gas above sodium in an SFR, where it keeps air away from the coolant.

Where these numbers come from

PNNL-15870 Rev. 2, "Argon" (id argon): density and full isotopic composition are taken from the compendium unchanged.

Open the compendium entry for the isotope-by-isotope table and the compendium's own notes.

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)
Ar-36 (18036)	3.0036e-3	3.3360e-3	8.3583e-8
Ar-38 (18038)	5.9774e-4	6.2900e-4	1.5759e-8
Ar-40 (18040)	9.9639e-1	9.9604e-1	2.4955e-5

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 Argon
c PNNL-15870 Rev. 2, "Argon" - reactormc.net/nrdp/material/argon; rho =
c 0.00166201 g/cm3 (use -0.00166201 on the cell card)
m39    18036.80c  -0.003004  $ Ar36
       18038.80c  -5.9774e-4  $ Ar38
       18040.80c  -0.996394  $ Ar40

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

Natural argon is 99.6% Ar-40, written as Ar-36/38/40 because ENDF/B-VII.1 has no natural argon evaluation. Ar-41 from Ar-40(n,γ) is the activation product that matters in a cover gas system.

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