materials.xml

<?xml version="1.0"?>
<materials>
  <!-- Set default xs set to 71c, which is ENDF-B/VII.0 at 600K -->
  <default_xs>71c</default_xs>

  <!-- 3.1 w/o enriched UO2 -->
  <material id="1">
    <density units="sum" />
    <nuclide name="U-235"   ao="7.18132E-4" />
    <nuclide name="U-238"   ao="2.21546E-2" />
    <nuclide name="O-16"    ao="4.57642E-2" />
  </material>

  <!-- Cladding -->
  <material id="2">
    <density units="sum" />
    <nuclide name="Zr-90"  ao="2.18865E-2" />
    <nuclide name="Zr-91"  ao="4.77292E-3" />
    <nuclide name="Zr-92"  ao="7.29551E-3" />
    <nuclide name="Zr-94"  ao="7.39335E-3" />
    <nuclide name="Zr-96"  ao="1.19110E-3" />
</material>

  <!-- Water -->
  <material id="3">
    <density units="sum" />
    <nuclide name="O-16"   ao="2.20729E-2" />
    <nuclide name="H-1"    ao="4.41459E-2" />
    <!--
      Set the thermal scattering table to H-H20
      16t is the library for 600K
    -->
    <sab name="lwtr" xs="16t" />
  </material>

</materials>