(n,t) Reaction Rate in Void material

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1

Hello,

I am using OpenMC to simulate a point source and I am trying a test case. I’m using a mesh tally for tritium production and i have a spherical shell of FLiBe with the outside boundary condition as vacuum and the inside of the sphere as VOID. When plotting the data I get data for tritium production within the VOID material which should not exist. Any suggestions?

Test Sphere.py (2.7 KB)

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image1611×979 70.7 KB

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image1602×968 83 KB

2

Hi Travis, welcome back to the community.
I think the value that existed on the void region in the middle of your sphere came from how you defined your mesh,

mesh.dimension = [500, 500, 1]
mesh.lower_left = [-75, -75, -75]
mesh.upper_right = [75, 75, 75]

you are creating an XYZ mesh with a size of [500, 500, 1], and the region its cover is -75 to +75 from all x-axis, y-axis, and z-axis. The problem is you are summing all tally scores in the z-axis into 1 Z mesh. So it is basically a 3D XYZ distribution/mesh plotted on a 2D XY mesh and the score on the top region and bottom region of the sphere will be summed on a specific XY coordinate mesh.
Then the value on the void region is simply the tally value for your sphere region at the top and bottom of this void region (z-axis). Same as when you see this tally above the sphere, we will see some flux (other tallies) that came from the nearest side to the sphere to you and the other sides of the sphere.

if you use another mesh definition, like if you only want a slice of your sphere in origin with a 1cm thickness

mesh1cmZ.dimension = [500, 500, 1]
mesh1cmZ.lower_left = [-75, -75, -0.5]
mesh1cmZ.upper_right = [75, 75, 0.5]

then you will get the tally for this slice of your sphere, and as predicted, the void region will be empty because at the origin, with only a 1 cm slice, then other tally scores at the top and bottom side of the sphere will not be reported.
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sorry, I am not that good at English, but I hope you understand what I mean.

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3

Yes thank you, this is what I was thinking after I brainstormed it for a little bit but never got back to changing the code. Thank you for the clarification!

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