B₄C (natural boron)

B₄C

Absorbers

Density: 2.52 g/cm³

Atom density: 0.137301 atoms/b·cm

Boron carbide with natural boron (19.9 at% B-10) — control rod and shutdown absorber, and the most common burnable absorber outside the fuel.

Where these numbers come from

PNNL-15870 Rev. 2, "Boron Carbide" (id boron-carbide): 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)
B-10 (5010)	1.4422e-1	1.5920e-1	2.1858e-2
B-11 (5011)	6.3827e-1	6.4080e-1	8.7983e-2
C-12 (6012)	2.1481e-1	1.9786e-1	2.7166e-2
C-13 (6013)	2.5176e-3	2.1400e-3	2.9382e-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 B4C (natural boron)
c PNNL-15870 Rev. 2, "Boron Carbide" - reactormc.net/nrdp/material/b4c-natural;
c rho = 2.52 g/cm3 (use -2.52 on the cell card)
m32    5010.80c  -0.144221  $ B10
       5011.80c  -0.638271  $ B11
       6000.80c  -0.217329  $ C

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

B-10 carries the absorption: 3840 barns thermal, via (n,α), which produces helium and swells the pellet over life. Carbon is elemental 6000 for ENDF/B-VII.1.

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