def METHOD_NAME():
    """Returns a control rod guide tube universe."""
    gt_inner_cell = openmc.Cell(fill=hot_water, region=-fuel_or)
    gt_clad_cell = openmc.Cell(fill=clad, region=+fuel_or & -clad_or)
    gt_outer_cell = openmc.Cell(fill=hot_water, region=+clad_or)
    univ = openmc.Universe(name='Guide Tube')
    univ.add_cells([gt_inner_cell, gt_clad_cell, gt_outer_cell])
    return univ