# RuntimeError: Could not find nuclide N7 in the nuclear data library

**URL:** <https://openmc.discourse.group/t/runtimeerror-could-not-find-nuclide-n7-in-the-nuclear-data-library/6298>\
**Category:** User Support\
**Created:** [April 20, 2026, 7:04pm UTC](https://openmc.discourse.group/t/runtimeerror-could-not-find-nuclide-n7-in-the-nuclear-data-library/6298 "2026-04-20T19:04:23Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![rayjbryant](https://avatars.discourse-cdn.com/v4/letter/r/6de8d8/32.png) [@rayjbryant](https://openmc.discourse.group/u/rayjbryant)\
**Post date:** [April 20, 2026, 7:04pm UTC](https://openmc.discourse.group/t/runtimeerror-could-not-find-nuclide-n7-in-the-nuclear-data-library/6298/1 "2026-04-20T19:04:23Z")

</div>

Hello Everyone,

I’m trying to run a simple simulation of a TRISO fuel cylinder with a neutron flux tally but get the following error:

RuntimeError: Could not find nuclide N7 in the nuclear data library.

Initially, I thought this was because I had an “air” material specified in my code and there was an issue with the nitrogen element I was adding to that material. However, since then I’ve tried running the code without any instance of nitrogen and I still get the error.

I’ve tried using both endfb-vii.1-hdf5 and endfb-viii.1-hdf5 cross-section XML files with no success.

Here is how I am calling the cross-sections into my project:

```auto
openmc.config['cross_sections'] = 'Absolute Path'

```