# Materials.xml \<element\> Problem

**URL:** <https://openmc.discourse.group/t/materials-xml-element-problem/58>\
**Category:** User Support\
**Created:** [April 17, 2014, 7:15pm UTC](https://openmc.discourse.group/t/materials-xml-element-problem/58 "2014-04-17T19:15:58Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![timoore](https://avatars.discourse-cdn.com/v4/letter/t/c4cdca/32.png) [@timoore](https://openmc.discourse.group/u/timoore)\
**Post date:** [April 17, 2014, 7:15pm UTC](https://openmc.discourse.group/t/materials-xml-element-problem/58/1 "2014-04-17T19:15:58Z")

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Hi all, I believe I found a bug in the materials.xml file while using the attribute. While using the attribute, if I try to specify a xs identifier, it will not be able to find the nuclide in the cross section data. An example of the error I get is as follows ERROR: Could not find nuclide 13027.Mo-100 in cross\_sections.xml file!. An example of the difference between the two:

**Working:**

**Not Working:**

I’ve attached the two different materials.xml files, one that works and the other that doesn’t if you’d like to see the full file.

Thanks,

Tim

[materialsworking.xml](https://openmc.discourse.group/uploads/short-url/zSKnkrw3Ldhh1PUzx69BcrqWrD2.xml) (1.14 KB)

[materialsnotworking.xml](https://openmc.discourse.group/uploads/short-url/nfb9pV6sroQqqCMJMl0F54OfKAF.xml) (1.16 KB)

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**Author:** ![Bryan\_Herman](https://avatars.discourse-cdn.com/v4/letter/b/9dc877/32.png) [@Bryan\_Herman](https://openmc.discourse.group/u/Bryan_Herman)\
**Post date:** [April 17, 2014, 9:07pm UTC](https://openmc.discourse.group/t/materials-xml-element-problem/58/2 "2014-04-17T21:07:49Z")

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I ran in to the same problem I will look into it.

-Bryan

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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:** [April 17, 2014, 9:10pm UTC](https://openmc.discourse.group/t/materials-xml-element-problem/58/3 "2014-04-17T21:10:58Z")

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Already fixed!  
[https://github.com/mit-crpg/openmc/issues/269](https://github.com/mit-crpg/openmc/issues/269)

Also note that I will be improving the natural element expansion capability in the near future so that you can specify what cross section set you’re using since different sets have different nuclides available. See [https://github.com/mit-crpg/openmc/issues/253](https://github.com/mit-crpg/openmc/issues/253)