Graphite
C
Moderators & CoolantsDensity: 1.7 g/cm³
Atom density: 0.085238 atoms/b·cm
Nuclear-grade graphite moderator, for gas-cooled reactors (AGR, HTGR), RBMK, and molten-salt designs.
Where these numbers come from
PNNL-15870 Rev. 2, "Carbon, Graphite (reactor grade)" (id carbon-graphite-reactor-grade): 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) | 1.8427e-7 | 2.2103e-7 | 1.8840e-8 |
| B-11 (5011) | 8.1550e-7 | 8.8967e-7 | 7.5834e-8 |
| C-12 (6012) | 9.8843e-1 | 9.8930e-1 | 8.4326e-2 |
| C-13 (6013) | 1.1584e-2 | 1.0700e-2 | 9.1205e-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.
Bound scattering
ENDF/B-VII.1 has a thermal scattering law for this material as formulated, so the cards attach grph.20t. Free-gas scattering would misplace the thermal spectrum here.
Generated material cards
c Graphite
c PNNL-15870 Rev. 2, "Carbon, Graphite (reactor grade)" -
c reactormc.net/nrdp/material/graphite; rho = 1.7 g/cm3 (use -1.7 on the cell
c card)
m18 5010.80c -1.8427e-7 $ B10
5011.80c -8.1550e-7 $ B11
6000.80c -0.999999 $ C
mt18 grph.20tMCNP 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
Density runs 1.6–1.8 g/cm³ by grade and irradiation history. Nuclear grades are purified to a few ppm boron equivalent, because boron at ppm level competes with the graphite's own absorption. The card attaches grph.20t — treating graphite as a free gas is a real error, not a refinement.