# Lattice Code Error

**URL:** <https://openmc.discourse.group/t/lattice-code-error/3798>\
**Category:** User Support\
**Created:** [January 3, 2024, 11:38pm UTC](https://openmc.discourse.group/t/lattice-code-error/3798 "2024-01-03T23:38:04Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Jarret](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/jarret/32/4075_2.png) [@Jarret](https://openmc.discourse.group/u/Jarret)\
**Post date:** [January 3, 2024, 11:38pm UTC](https://openmc.discourse.group/t/lattice-code-error/3798/1 "2024-01-03T23:38:05Z")

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Hello everyone,

I am modelling a CANDU reactor using Openmc, and I was able to get one working with a k-eff of 1.15, but it was a very rudimentary one without reactivity devices. I have tried to make some channels with control rods in it, which have been completed below,

As you can see, I was able to plot the individual universes and see everything, but when I implement it into my matrix,

It removes the fuel sections of the new adjuster rod universe, but the rest of the reactor is fine. I have also switched my normal fuel channels with the ones with the adjuster and they suddenly had their fuel sections again. Is there a limit to the number of different universes that can be used within a matrix? If anyone could help me, this seems very fickle and random to me, making me think something is glitching.

 ![image](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/0/07fbb4231ed1fac308f7829ede48ba41fefa0491.jpeg)

Single Image as I am a new account.

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<div class="post-metadata">

**Author:** ![Jarret](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/jarret/32/4075_2.png) [@Jarret](https://openmc.discourse.group/u/Jarret)\
**Post date:** [January 3, 2024, 11:47pm UTC](https://openmc.discourse.group/t/lattice-code-error/3798/2 "2024-01-03T23:47:36Z")

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![image](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/7/7bdd8b26024063d3214f7034a35c30e243a41059.png)  
Here is an image of my reactor without the control rods, this was made using only two different universes for the matrix, one with a fuel channel, one completely moderator.

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<div class="post-metadata">

**Author:** ![Jarret](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/jarret/32/4075_2.png) [@Jarret](https://openmc.discourse.group/u/Jarret)\
**Post date:** [January 5, 2024, 11:30pm UTC](https://openmc.discourse.group/t/lattice-code-error/3798/3 "2024-01-05T23:30:21Z")

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So I figured it out myself after learning more about the code. I was unaware that you could not reuse cells in multiple universes, therefore, I had to use the command,

cell1\_copy = cell.clone(clone\_materials=False, clone\_regions=False)

for each of the cells that were being used by multiple universes. I’m kind of shocked that Openmc cannot reuse cells, but now that I know it’s not the biggest issue.