# Reflective Boundary Hexagonal Multigroup problem **URL:** \ **Category:** User Support\ **Created:** [April 9, 2022, 1:16pm UTC](https://openmc.discourse.group/t/reflective-boundary-hexagonal-multigroup-problem/1914 "2022-04-09T13:16:30Z")\ **Posts on this page:** 1\ **Showing post:** 10
**Author:** ![pshriwise](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/pshriwise/32/3863_2.png) [@pshriwise](https://openmc.discourse.group/u/pshriwise)\ **Post date:** [October 20, 2022, 5:30am UTC](https://openmc.discourse.group/t/reflective-boundary-hexagonal-multigroup-problem/1914/10 "2022-10-20T05:30:30Z")
My reply in the post that @paulromano provided above might be useful here. @jerrylizy I think some of the same issues might show up in your model too. > [@The mesh tally outputs are broken by the ''reflective" boundary type planes](https://openmc.discourse.group/t/the-mesh-tally-outputs-are-broken-by-the-reflective-boundary-type-planes/2312/3): > > Hi @YimingZ, A very interesting problem! It took a bit for me to sort out what is going on here. I pulled your model (thanks for providing it!) and pulled it up in the [plotter](https://github.com/openmc-dev/plotter). This allowed me to look at the containing cell definition more clearly. It looked correct to me. But of course when I ran the problem I saw the same issue as you: So I stared at it for a bit and then broke the cell region definition up into 4 cells (one for each quadrant): This helped me… --- _[View the full topic](https://openmc.discourse.group/t/reflective-boundary-hexagonal-multigroup-problem/1914)._