<?xml version='1.0' encoding='utf-8'?>
<model>
  <materials>
    <material depletable="true" id="1" name="fuel">
      <density units="g/cc" value="4.5" />
      <nuclide ao="1.0" name="U235" />
    </material>
    <material id="2" name="moderator">
      <density units="g/cc" value="1.0" />
      <nuclide ao="1.0" name="O16" />
      <nuclide ao="2.0" name="H1" />
      <sab name="c_H_in_H2O" />
    </material>
    <material id="3" name="iron">
      <density units="g/cc" value="7.9" />
      <nuclide ao="1.0" name="Fe56" />
    </material>
  </materials>
  <geometry>
    <cell fill="5" id="1" name="Cell 1" region="1 -2 3 -4" universe="0" />
    <cell id="101" material="1" name="cell 2" region="-5" universe="1" />
    <cell id="102" material="2" name="cell 3" region="5" universe="1" />
    <cell id="500" material="2" name="cell 4" universe="3" />
    <hex_lattice id="5" n_rings="2">
      <pitch>1.0</pitch>
      <outer>3</outer>
      <center>0.0 0.0</center>
      <universes>
 1
1 1
 1
1 1
 1</universes>
    </hex_lattice>
    <surface boundary="vacuum" coeffs="-3.0" id="1" name="left" type="x-plane" />
    <surface boundary="vacuum" coeffs="3.0" id="2" name="right" type="x-plane" />
    <surface boundary="vacuum" coeffs="-4.0" id="3" name="bottom" type="y-plane" />
    <surface boundary="vacuum" coeffs="4.0" id="4" name="top" type="y-plane" />
    <surface coeffs="0.0 0.0 0.4" id="5" type="z-cylinder" />
  </geometry>
  <settings>
    <run_mode>eigenvalue</run_mode>
    <particles>1000</particles>
    <batches>1</batches>
    <inactive>0</inactive>
    <source strength="1.0">
      <space type="box">
        <parameters>-1.0 -1.0 -1.0 1.0 1.0 1.0</parameters>
      </space>
    </source>
  </settings>
  <tallies>
    <filter id="1" type="distribcell">
      <bins>101</bins>
    </filter>
    <tally id="1">
      <filters>1</filters>
      <scores>total</scores>
    </tally>
  </tallies>
</model>
