Number collisions between different object types for fill can cause hard to understand errors

[MicahGale]

Bug Description

It appears that fill is based solely on object identifier irrespective of object type (e.g., Material, Universe, Lattice). This can sometimes cause unintended behavior, and cause false-alarm errors with circular dependencies. In the following example a cell and

Steps to Reproduce

MWE:

OD = 0.08
WALL = 0.005
LENGTH = 0.5
CAVITY_LENGTH = 0.3
R_SEED = 0.03
R_CAVITY = OD/2 - WALL
END_L = LENGTH - CAVITY_LENGTH
def generate_brach_problem():
    outer_cyl = openmc.model.RightCircularCylinder((0,0,0), LENGTH, OD / 2)
    inner_cyl = openmc.model.RightCircularCylinder((0,0,END_L/2),CAVITY_LENGTH, R_CAVITY)
    titanium = openmc.Material()
    titanium.add_element("Ti", 1.0)
    titanium.set_density("g/cm3", 4.5)
    capsule = openmc.Cell(region = -outer_cyl & +inner_cyl, fill = titanium)
    pallad = openmc.Material()
    pallad.add_element("Pd", 1.0)
    pallad.set_density("g/cm3", 12)
    seed_sp = openmc.Sphere(r=R_SEED)
    air = openmc.Material()
    air.add_element("N", 0.8)
    air.add_element("O", 0.2)
    air.set_density("g/cm3", 0.0012)

    seed = openmc.Universe( cells = [openmc.Cell(region = -seed_sp, fill = pallad),
                openmc.Cell(region = + seed_sp, fill = air)]
    )
    lattice = openmc.RectLattice()
    lattice.pitch = (1, 1, R_SEED * 2)
    lattice.universes = [[[seed]*5]]
    lattice.lower_left = (0,0, END_L /2)
    filler = openmc.Cell(region = -inner_cyl, fill = lattice)
    print(capsule, seed, lattice, filler)
    filler.plot()
    model = openmc.Model()
    model.geometry.root_universe = openmc.Universe(cells = [capsule, filler])
    model.geometry.plot(basis="xz")
    plt.show()

generate_brach_problem()

this Prints:

Cell
    ID             =    9
    Name           =    
    Fill           =    Material 7
    Region         =    (-15 16 -17 (18 | -19 | 20))
    Rotation       =    None
    Temperature    =    None
    Translation    =    None
    Volume         =    None
 Universe
    ID             =    3
    Name           =    
    Geom           =    CSG
    Cells          =    [10, 11]
 RectLattice
    ID             =    4
    Name           =    
    Shape          =    (5, 1, 1)
    Lower Left     =    (0, 0, 0.1)
    Pitch          =    (1, 1, 0.06)
    Outer          =    None
    Universes      
3 3 3 3 3  Cell
    ID             =    12
    Name           =    
    Fill           =    4
    Region         =    (-18 19 -20)
    Rotation       =    None
    Translation    =    None
    Volume         =    None

This leads to the error:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
Cell In[5], line 39
     36     model.geometry.plot(basis="xz")
     37     plt.show()
---> 39 generate_brach_problem()

Cell In[5], line 33, in generate_brach_problem()
     31 filler = openmc.Cell(region = -inner_cyl, fill = lattice)
     32 print(capsule, seed, lattice, filler)
---> 33 filler.plot()
     34 model = openmc.Model()
     35 model.geometry.root_universe = openmc.Universe(cells = [capsule, filler])

File /usr/local/lib/python3.9/dist-packages/openmc/cell.py:624, in Cell.plot(self, *args, **kwargs)
    622 u = openmc.Universe(cells=[self], universe_id=openmc.Universe.next_id + 1)
    623 openmc.Universe.used_ids.remove(u.id)
--> 624 return u.plot(*args, **kwargs)

File /usr/local/lib/python3.9/dist-packages/openmc/universe.py:446, in Universe.plot(self, origin, width, pixels, basis, color_by, colors, seed, openmc_exec, axes, legend, axis_units, legend_kwargs, outline, **kwargs)
    443 model.plots.append(plot)
    445 # Run OpenMC in geometry plotting mode
--> 446 model.plot_geometry(False, cwd=tmpdir, openmc_exec=openmc_exec)
    448 # Read image from file
    449 img_path = Path(tmpdir) / f'plot_{plot.id}.png'

File /usr/local/lib/python3.9/dist-packages/openmc/model/model.py:828, in Model.plot_geometry(self, output, cwd, openmc_exec)
    826 else:
    827     self.export_to_xml()
--> 828     openmc.plot_geometry(output=output, openmc_exec=openmc_exec)

File /usr/local/lib/python3.9/dist-packages/openmc/executor.py:154, in plot_geometry(output, openmc_exec, cwd, path_input)
    152 if path_input is not None:
    153     args += [path_input]
--> 154 _run(args, output, cwd)

File /usr/local/lib/python3.9/dist-packages/openmc/executor.py:125, in _run(args, output, cwd)
    122     error_msg = 'OpenMC aborted unexpectedly.'
    123 error_msg = ' '.join(error_msg.split())
--> 125 raise RuntimeError(error_msg)

RuntimeError: Cell 12 is filled with the same universe that it is contained in. application called MPI_Abort(MPI_COMM_WORLD, -1) - process 0 [unset]: write_line error; fd=-1 buf=:cmd=abort exitcode=-1 : system msg for write_line failure : Bad file descriptor

Environment

Openmc: v0.14.0