# Plot behavior for cells with no region

**URL:** <https://openmc.discourse.group/t/plot-behavior-for-cells-with-no-region/3106>\
**Category:** User Support\
**Created:** [June 16, 2023, 7:33pm UTC](https://openmc.discourse.group/t/plot-behavior-for-cells-with-no-region/3106 "2023-06-16T19:33:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![LukeSeifert](https://avatars.discourse-cdn.com/v4/letter/l/50afbb/32.png) [@LukeSeifert](https://openmc.discourse.group/u/LukeSeifert)\
**Post date:** [June 16, 2023, 7:33pm UTC](https://openmc.discourse.group/t/plot-behavior-for-cells-with-no-region/3106/1 "2023-06-16T19:33:07Z")

</div>

Hi all,

I am running simulations with transfer rates where I use a cell not present in the geometry to store nuclides removed from fuel salt. However, I noticed that when I set a cell’s region to None and used the plot run mode, all of the white space where no geometry is defined became colored the same as the material I gave to the cell with a None region. I’ve included an example below showing what I mean.

```auto
import openmc

x_min = openmc.XPlane(-1, boundary_type='vacuum')
x_max = openmc.XPlane(1, boundary_type='vacuum')
y_min = openmc.YPlane(-1, boundary_type='vacuum')
y_max = openmc.YPlane(1, boundary_type='vacuum')
z_min = openmc.ZPlane(-1, boundary_type='vacuum')
z_max = openmc.ZPlane(1, boundary_type='vacuum')

block_inside = (+x_min & -x_max & 
                +y_min & -y_max & 
                +z_min & -z_max)

fuel = openmc.Material()
fuel.set_density('g/cc', 10)
fuel.add_element('U', 1)

test = openmc.Material()
test.set_density('g/cc', 100)
test.add_element('U', 1)

mats = openmc.Materials(
    (fuel,
     test)
)
mats.export_to_xml()

fuel_cube = openmc.Cell()
fuel_cube.fill = fuel
fuel_cube.region = block_inside

empty_cell = openmc.Cell()
empty_cell.fill = test

root = openmc.Universe(
    cells=[fuel_cube,
           empty_cell]
)
geom = openmc.Geometry(root)
geom.export_to_xml()

sets = openmc.Settings()
sets.run_mode = 'plot'
sets.export_to_xml()

colors = {
    fuel_cube : 'blue',
    empty_cell : 'green'
}

plot = openmc.Plot()
plot.color_by = 'cell'
plot.colors = colors
plots = openmc.Plots([plot])
plots.export_to_xml()

openmc.run()

```

![plot_1](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/b/bc02cf1697765163bf1255030172937cbdca2406.png)

---

<div class="post-metadata">

**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\
**Post date:** [July 15, 2023, 6:26pm UTC](https://openmc.discourse.group/t/plot-behavior-for-cells-with-no-region/3106/2 "2023-07-15T18:26:32Z")

</div>

Hi @LukeSeifert. When you specify no region for a cell, it means “there are no bounds”, i.e., the cell extends over all space. If you want a cell that occupies _no_ space, the easiest way I can think of is to take the intersection of two half spaces that don’t overlap, e.g., `+openmc.XPlane(1) & -openmc.XPlane(-1)`