UZrH₁.₆ (TRIGA fuel)

UZrH₁.₆

Fuels

Density: 5.97 g/cm³

Atom density: 0.0934176 atoms/b·cm

Uranium–zirconium hydride fuel used in TRIGA research reactors. The hydride matrix is what gives TRIGA its large prompt negative temperature coefficient.

Where these numbers come from

Standard TRIGA fuel meat: 8.5 wt% uranium at 19.75 wt% enrichment in a ZrH1.6 matrix. Atom fractions from a 100 g basis; density by ideal mixing of uranium metal (18.94 g/cm³) with ZrH1.6 (5.61 g/cm³, the compendium's Zr5H8).

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)
H-1 (1001)	1.5893e-2	6.0691e-1	5.6696e-2
Zr-90 (40090)	4.5590e-1	1.9516e-1	1.8231e-2
Zr-91 (40091)	1.0053e-1	4.2559e-2	3.9758e-3
Zr-92 (40092)	1.5535e-1	6.5053e-2	6.0771e-3
Zr-94 (40094)	1.6086e-1	6.5925e-2	6.1586e-3
Zr-96 (40096)	2.6468e-2	1.0621e-2	9.9217e-4
U-234 (92234)	1.4940e-4	2.4568e-5	2.2951e-6
U-235 (92235)	1.6787e-2	2.7487e-3	2.5677e-4
U-236 (92236)	7.7220e-5	1.2590e-5	1.1761e-6
U-238 (92238)	6.7984e-2	1.0991e-2	1.0267e-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.

Bound scattering

ENDF/B-VII.1 has a thermal scattering law for this material as formulated, so the cards attach h-zr.20t zr-h.20t. Free-gas scattering would misplace the thermal spectrum here.

Generated material cards

MCNP

c UZrH1.6 (TRIGA fuel)
c ReactorMC NRDP derived material - reactormc.net/nrdp/material/uzrh; rho = 5.97
c g/cm3 (use -5.97 on the cell card)
m8    1001.80c  -0.015893  $ H1
      40090.80c  -0.455904  $ Zr90
      40091.80c  -0.100528  $ Zr91
      40092.80c  -0.155349  $ Zr92
      40094.80c  -0.160860  $ Zr94
      40096.80c  -0.026468  $ Zr96
      92234.80c  -1.4940e-4  $ U234
      92235.80c  -0.016787  $ U235
      92236.80c  -7.7220e-5  $ U236
      92238.80c  -0.067984  $ U238
mt8   h-zr.20t zr-h.20t

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

Uranium is 8.5 wt% of the fuel meat here; TRIGA elements run 8.5–12 wt%, and density and H/Zr ratio vary with the element type. The previous version of this entry put uranium and zirconium at equal atom fractions, which is about 72 wt% uranium — an order of magnitude off its own note. Hydrogen and zirconium both need bound-scattering data (h-zr, zr-h): free-gas hydrogen in a hydride gets the thermal spectrum wrong.

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