UO2 (19.75% HALEU)

UO₂

Fuels

Density: 10.96 g/cm³

Atom density: 0.0734885 atoms/b·cm

Uranium dioxide at 19.75 wt% U-235 — high-assay low-enriched uranium, the working fuel of most advanced reactor and research reactor designs.

Where these numbers come from

UO₂ stoichiometry with uranium enriched to 19.75 wt% U-235; density from the compendium's UO₂ entry. The U-234/U-236 ratios are extrapolated from the compendium's LEU entry, which is an interpolation of cascade behaviour rather than a measured vector.

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)	1.1844e-1	6.6505e-1	4.8873e-2
O-17 (8017)	4.7949e-5	2.5333e-4	1.8617e-5
O-18 (8018)	2.7389e-4	1.3667e-3	1.0043e-4
U-234 (92234)	1.5490e-3	5.9443e-4	4.3684e-5
U-235 (92235)	1.7405e-1	6.6505e-2	4.8874e-3
U-236 (92236)	8.0061e-4	3.0462e-4	2.2386e-5
U-238 (92238)	7.0485e-1	2.6593e-1	1.9543e-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 (2.7389e-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 UO2 (19.75% HALEU)
c ReactorMC NRDP derived material - reactormc.net/nrdp/material/uo2-haleu; rho =
c 10.96 g/cm3 (use -10.96 on the cell card)
c O18 folded into O16: ENDF/B-VII.1 has no O18 evaluation (2.7389e-4 by weight,
c so the spectrum does not care).
m4    8016.80c  -0.118712  $ O16
      8017.80c  -4.7949e-5  $ O17
      92234.80c  -0.001549  $ U234
      92235.80c  -0.174045  $ U235
      92236.80c  -8.0061e-4  $ U236
      92238.80c  -0.704845  $ 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

19.75 wt% is just under the 20% ceiling that defines LEU. Used in microreactors, TRISO kernels, and research reactors.

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