Gadolinium Oxide

Gd₂O₃

Absorbers

Density: 7.41 g/cm³

Atom density: 0.06155 atoms/b·cm

Gadolinia burnable absorber, usually mixed into UO₂ pellets at a few weight percent. Gd-155 and Gd-157 have the largest thermal capture cross sections of any stable nuclides.

Where these numbers come from

Gd₂O₃ stoichiometry with natural gadolinium (abundances from the compendium's gadolinium entries). Density carried over from the previous NRDP entry; the oxide is not in the compendium.

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)
O-16 (8016)	1.3205e-1	5.9854e-1	3.6840e-2
O-17 (8017)	5.3459e-5	2.2800e-4	1.4033e-5
O-18 (8018)	3.0536e-4	1.2300e-3	7.5707e-5
Gd-152 (64152)	1.6763e-3	8.0000e-4	4.9240e-5
Gd-154 (64154)	1.8513e-2	8.7200e-3	5.3672e-4
Gd-155 (64155)	1.2650e-1	5.9200e-2	3.6438e-3
Gd-156 (64156)	1.7609e-1	8.1880e-2	5.0397e-3
Gd-157 (64157)	1.3550e-1	6.2600e-2	3.8530e-3
Gd-158 (64158)	2.1643e-1	9.9360e-2	6.1156e-3
Gd-160 (64160)	1.9288e-1	8.7440e-2	5.3819e-3

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.

What ENDF/B-VII.1 forced

O18 folded into O16: ENDF/B-VII.1 has no O18 evaluation (3.0536e-4 by weight, so the spectrum does not care).

The cards keep the material's mass and atom count; a nuclide the library cannot name hands its share to one it can. That is why a card row can differ slightly from the table above.

Generated material cards

MCNP

c Gadolinium Oxide
c ReactorMC NRDP derived material - reactormc.net/nrdp/material/gd2o3; rho =
c 7.41 g/cm3 (use -7.41 on the cell card)
c O18 folded into O16: ENDF/B-VII.1 has no O18 evaluation (3.0536e-4 by weight,
c so the spectrum does not care).
m35    8016.80c  -0.132354  $ O16
       8017.80c  -5.3459e-5  $ O17
       64152.80c  -0.001676  $ Gd152
       64154.80c  -0.018513  $ Gd154
       64155.80c  -0.126502  $ Gd155
       64156.80c  -0.176094  $ Gd156
       64157.80c  -0.135495  $ Gd157
       64158.80c  -0.216431  $ Gd158
       64160.80c  -0.192882  $ Gd160

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

Gd-157 is about 254,000 barns and Gd-155 about 61,000 barns thermal, so the absorber burns out quickly and by design — that is the point of a burnable poison. The burnout is fast enough that a depletion step size chosen for fuel will smear it.

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