# High temperature cross sections

**URL:** <https://openmc.discourse.group/t/high-temperature-cross-sections/1384>\
**Category:** User Support\
**Created:** [August 18, 2021, 12:30pm UTC](https://openmc.discourse.group/t/high-temperature-cross-sections/1384 "2021-08-18T12:30:15Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![LukeLabrie](https://avatars.discourse-cdn.com/v4/letter/l/c37758/32.png) [@LukeLabrie](https://openmc.discourse.group/u/LukeLabrie)\
**Post date:** [August 18, 2021, 12:30pm UTC](https://openmc.discourse.group/t/high-temperature-cross-sections/1384/1 "2021-08-18T12:30:15Z")

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Hello,

With a sodium material at ~ 977K, the model I’m running is throwing the following error:

`RuntimeError: Nuclear data library does not contain cross sections for Na23 at or near 977.59440 K.`

According to this post ([Using high temperature cross-sections in OpenMC - #5 by Julien](https://openmc.discourse.group/t/using-high-temperature-cross-sections-in-openmc/249/5)), this error can come from using HDF5 data that was produced using an older version of OpenMC than the running version. As far as I know, I’m using the latest version of both OpenMC and the nuclear data (see below), so I’m not sure what the issue is. Thoughts?

OpenMC version: 0.13.0-dev  
Nuclear data: [https://openmc.org/official-data-libraries/](https://openmc.org/official-data-libraries/) (ENDF/B-VII.1)

I will also try running with the other available libraries.

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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:** [August 18, 2021, 12:50pm UTC](https://openmc.discourse.group/t/high-temperature-cross-sections/1384/2 "2021-08-18T12:50:34Z")

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By default, OpenMC will look for cross sections that are within some tolerance of the temperature specified rather than interpolating between cross sections at adjacent temperatures. If you want interpolation, you need to specify:

```auto
settings = openmc.Settings()
settings.temperature = {'method': 'interpolation'}

```

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**Author:** ![LukeLabrie](https://avatars.discourse-cdn.com/v4/letter/l/c37758/32.png) [@LukeLabrie](https://openmc.discourse.group/u/LukeLabrie)\
**Post date:** [August 18, 2021, 12:59pm UTC](https://openmc.discourse.group/t/high-temperature-cross-sections/1384/3 "2021-08-18T12:59:45Z")

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That worked. Thanks!