# Reflective boundary could not reflecting particles

**URL:** <https://openmc.discourse.group/t/reflective-boundary-could-not-reflecting-particles/1754>\
**Category:** User Support\
**Created:** [March 2, 2022, 4:24pm UTC](https://openmc.discourse.group/t/reflective-boundary-could-not-reflecting-particles/1754 "2022-03-02T16:24:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![lz152](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/lz152/32/1547_2.png) [@lz152](https://openmc.discourse.group/u/lz152)\
**Post date:** [March 2, 2022, 4:24pm UTC](https://openmc.discourse.group/t/reflective-boundary-could-not-reflecting-particles/1754/1 "2022-03-02T16:24:32Z")

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Hi everyone,  
When I run a simulation, the OpenMC interrupted unexpectedly.  
And echo the Warning means Reflective boundary could not reflecting particles.  
At first, I thought it was an accident. But secondly the Warning appears, the simulation broke down.  
Has anyone ever encountered this？  
Any answer will be appreciate!

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#Update#

 ![20220303ERROR](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/c/c67252f79e1089ce83abf9e96759ed389d5a5e94.png)  
Same particles, same warning, same result.(surface 4 is reflective boundary)

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Best regards!  
Zhuangli

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**Author:** ![YimingZ](https://avatars.discourse-cdn.com/v4/letter/y/f19dbf/32.png) [@YimingZ](https://openmc.discourse.group/u/YimingZ)\
**Post date:** [March 4, 2022, 1:47am UTC](https://openmc.discourse.group/t/reflective-boundary-could-not-reflecting-particles/1754/2 "2022-03-04T01:47:57Z")

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Hi Zhuang,

Is there only surface 4 is reflective in your model? Maybe you can try to change other surfaces to be reflective and see what will happen.

Best wishes,  
Yiming

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<div class="post-metadata">

**Author:** ![lz152](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/lz152/32/1547_2.png) [@lz152](https://openmc.discourse.group/u/lz152)\
**Post date:** [March 4, 2022, 1:55am UTC](https://openmc.discourse.group/t/reflective-boundary-could-not-reflecting-particles/1754/3 "2022-03-04T01:55:59Z")

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Hi Yiming,  
Good morning!  
There are 4 reflective surfaces of my case.Now I have dealt with the issue with more particles, But I have no idea what’s happen!

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Best regards!  
Zhuangli

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<div class="post-metadata">

**Author:** ![YimingZ](https://avatars.discourse-cdn.com/v4/letter/y/f19dbf/32.png) [@YimingZ](https://openmc.discourse.group/u/YimingZ)\
**Post date:** [March 4, 2022, 5:40am UTC](https://openmc.discourse.group/t/reflective-boundary-could-not-reflecting-particles/1754/4 "2022-03-04T05:40:15Z")

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Hi Zhuang,

I find your model is named the singleonePin\_test. So I assume the four reflective surfaces are rectangular box surfaces. Trying the other way to model is cell. Such as:  
box = openmc.rectangular\_prism(width=pitch, height=pitch,  
boundary\_type=‘reflective’)  
type(box)

If still appear the same problem, I feel you should check the surface of the fuel rod cylinder.

Ps: Do you have WeChat?

Best wishes,  
Yiming