# S(a,b) for U-Zr/H fuel material

**URL:** <https://openmc.discourse.group/t/s-a-b-for-u-zr-h-fuel-material/49>\
**Category:** User Support\
**Created:** [December 10, 2013, 1:01am UTC](https://openmc.discourse.group/t/s-a-b-for-u-zr-h-fuel-material/49 "2013-12-10T01:01:11Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Tarek\_El\_Bardouni1](https://avatars.discourse-cdn.com/v4/letter/t/dec6dc/32.png) [@Tarek\_El\_Bardouni1](https://openmc.discourse.group/u/Tarek_El_Bardouni1)\
**Post date:** [December 10, 2013, 1:01am UTC](https://openmc.discourse.group/t/s-a-b-for-u-zr-h-fuel-material/49/1 "2013-12-10T01:01:11Z")

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Good evening,  
I’ve just compiled OpenMC and use it for the first time. It run properly with examples provided with the package.  
I have constructed an example to treat a Triga reactor cell. The fuel is U-Zr/H, and I need to use S(a,b) for H in ZrH and Zr in ZrH.  
In MCNP I’am familiar with this and use the entry: mt2 h/Zr.10t Zr/h.10t  
When I tried the same for OpenMC it crashes with the following error: ERROR: S(a,b) table zr/h.10t did not match any nuclide on material 2  
Material 2 has been defined as:  
  
  
  
  
  
  
  
  
  
  
  
  
  
and all cross section tables have been loaded successfully. They are taken from MCNP package (ENDF-B7).  
When I comment the second \<sab “z/h” …\> line it works properly.

Did any one meet this problem before.

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**Author:** ![Adam\_Nelson](https://avatars.discourse-cdn.com/v4/letter/a/8edcca/32.png) [@Adam\_Nelson](https://openmc.discourse.group/u/Adam_Nelson)\
**Post date:** [December 10, 2013, 10:09am UTC](https://openmc.discourse.group/t/s-a-b-for-u-zr-h-fuel-material/49/2 "2013-12-10T10:09:58Z")

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Good morning,

It seems as if you have found a bug! Sorry about that. What was going on here is that the zr/h table (and many S(a,b) tables) list multiple options for which nuclides the data can be applied to. OpenMC is currently only using the first of these nuclides to check for existence of the nuclide in the material when it should have been using them all.

I have created an issue on GitHub so that the other developers are aware of the bug; you can track the progress of its completion at this link: [https://github.com/mit-crpg/openmc/issues/227](https://github.com/mit-crpg/openmc/issues/227)

Thanks again, and we should get through this bug pretty quickly!  
Adam

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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:** [December 12, 2013, 3:33am UTC](https://openmc.discourse.group/t/s-a-b-for-u-zr-h-fuel-material/49/3 "2013-12-12T03:33:31Z")

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Just as an update – this bug was fixed by Adam and merged in to the develop branch of OpenMC. It will be included in the next release.

Paul