# Cylindrical\_shell for pack\_spheres()

**URL:** <https://openmc.discourse.group/t/cylindrical-shell-for-pack-spheres/3103>\
**Category:** User Support\
**Created:** [June 15, 2023, 8:41pm UTC](https://openmc.discourse.group/t/cylindrical-shell-for-pack-spheres/3103 "2023-06-15T20:41:19Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![tintin](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@tintin](https://openmc.discourse.group/u/tintin)\
**Post date:** [June 15, 2023, 8:41pm UTC](https://openmc.discourse.group/t/cylindrical-shell-for-pack-spheres/3103/1 "2023-06-15T20:41:19Z")

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Hi everyone,  
How to fill a cylindrical shell with `openmc.model.triso.pack_spheres()`?  
For now, the only admitted regions are ‘rectangular prism, cylinder, sphere, and spherical shell’ ([cf doc](https://docs.openmc.org/en/stable/_modules/openmc/model/triso.html#create_triso_lattice))  
_(by ‘cylindrical shell’, I mean the region between two co-axial ZCylinders, the ZPlane(z0=0.) and Zplane(z0=1.) for instance)_  
Thanks a lot!

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**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:** [June 15, 2023, 8:59pm UTC](https://openmc.discourse.group/t/cylindrical-shell-for-pack-spheres/3103/2 "2023-06-15T20:59:47Z")

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Unfortunately right now it’s not possible. If you wanted to take a stab at implementing this though, it would only require changes to this class:

> <https://github.com/openmc-dev/openmc/blob/787b3e0308e3470c86155f82ae048a533095470a/openmc/model/triso.py#L417-L632>

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<div class="post-metadata">

**Author:** ![tintin](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@tintin](https://openmc.discourse.group/u/tintin)\
**Post date:** [June 15, 2023, 10:25pm UTC](https://openmc.discourse.group/t/cylindrical-shell-for-pack-spheres/3103/3 "2023-06-15T22:25:50Z")

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Ok, thanks @paulromano

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**Author:** ![am4020](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@am4020](https://openmc.discourse.group/u/am4020)\
**Post date:** [January 25, 2024, 4:38pm UTC](https://openmc.discourse.group/t/cylindrical-shell-for-pack-spheres/3103/4 "2024-01-25T16:38:10Z")

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Hi,  
I’m facing the same issue, were you able to edit this to pack TRISOs in the region or make your own function to pack the spheres?  
Thanks!