MOX (mixed oxide, ~5% Pu)

(U,Pu)O₂

Fuels

Density: 11 g/cm³

Atom density: 0.073571 atoms/b·cm

Mixed-oxide fuel: reactor-grade plutonium in a depleted-uranium matrix (0.25 wt% U-235). Plutonium is 4.7 wt% of the heavy metal.

Where these numbers come from

PNNL-15870 Rev. 2, "Uranium-Plutonium, Mixed Oxide (MOX)" (id uranium-plutonium-mixed-oxide-mox): 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)
O-16 (8016)	1.1814e-1	6.6505e-1	4.8928e-2
O-17 (8017)	4.7828e-5	2.5333e-4	1.8638e-5
O-18 (8018)	2.7320e-4	1.3667e-3	1.0055e-4
Pu-238 (94238)	1.0298e-3	3.8950e-4	2.8656e-5
Pu-239 (94239)	2.2531e-2	8.4866e-3	6.2437e-4
Pu-240 (94240)	1.0751e-2	4.0324e-3	2.9667e-4
Pu-241 (94241)	3.9131e-3	1.4616e-3	1.0754e-4
Pu-242 (94242)	2.9658e-3	1.1032e-3	8.1163e-5
U-234 (92234)	1.0000e-5	3.8472e-6	2.8305e-7
U-235 (92235)	2.1009e-3	8.0479e-4	5.9210e-5
U-238 (92238)	8.3824e-1	3.1705e-1	2.3326e-2

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 (2.7320e-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 MOX (mixed oxide, ~5% Pu)
c PNNL-15870 Rev. 2, "Uranium-Plutonium, Mixed Oxide (MOX)" -
c reactormc.net/nrdp/material/mox-5pct; rho = 11 g/cm3 (use -11 on the cell
c card)
c O18 folded into O16: ENDF/B-VII.1 has no O18 evaluation (2.7320e-4 by weight,
c so the spectrum does not care).
m5    8016.80c  -0.118414  $ O16
      8017.80c  -4.7828e-5  $ O17
      94238.80c  -0.001030  $ Pu238
      94239.80c  -0.022531  $ Pu239
      94240.80c  -0.010751  $ Pu240
      94241.80c  -0.003913  $ Pu241
      94242.80c  -0.002966  $ Pu242
      92234.80c  -1.0000e-5  $ U234
      92235.80c  -0.002101  $ U235
      92238.80c  -0.838236  $ U238

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

The compendium's plutonium vector is Pu-238/239/240/241/242 = 2.5/54.7/26.1/9.5/7.2 wt%. Adjust the vector and the uranium enrichment to match a specific fuel: Pu-241 decays (14.3 y) and Pu-240 content follows burnup, so a vector is only right for one moment in the material's life.

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