# Memory errors. Particles getting lost? (or some other problem) **URL:** \ **Category:** User Support\ **Created:** [September 25, 2014, 6:45pm UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108 "2014-09-25T18:45:33Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Kaur\_Tuttelberg](https://avatars.discourse-cdn.com/v4/letter/k/a587f6/32.png) [@Kaur\_Tuttelberg](https://openmc.discourse.group/u/Kaur_Tuttelberg)\ **Post date:** [September 25, 2014, 6:45pm UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108/1 "2014-09-25T18:45:33Z")
Hi, I have a problem running a model and I’m not really sure what the issue is, sorry about the subject line. I run the code and get ` … … Loading ACE cross section table: 73181.09c WARNING: Negative value(s) found on probability table for nuclide 73181.09c Creating unionized energy grid… Initializing source particles… [geometry.xml](https://openmc.discourse.group/uploads/short-url/3bhMl0MVLFswrDiEB0KYaFbIiEn.xml) (5.07 KB) [materials.xml](https://openmc.discourse.group/uploads/short-url/kRGxzw97efcpROLTDiklVp0k8Pz.xml) (916 Bytes) [settings.xml](https://openmc.discourse.group/uploads/short-url/f5ltY1ABPye2C0D9j8okHaoqXFE.xml) (529 Bytes) ---
**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:** [September 25, 2014, 10:06pm UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108/2 "2014-09-25T22:06:24Z")
Hi Kaur, What cross sections are you using for your simulations? When I switch cross sections to use the [NNDC-distributed cross sections](http://www.nndc.bnl.gov/endf/b7.1/acefiles.html), it seems to work fine. I’ve confirmed you don’t have any syntax errors in the XML files. FYI- hexagonal lattices will likely be in OpenMC version 0.7. See this [pull request](https://github.com/mit-crpg/openmc/pull/313). Best, Paul ---
**Author:** ![Kaur\_Tuttelberg](https://avatars.discourse-cdn.com/v4/letter/k/a587f6/32.png) [@Kaur\_Tuttelberg](https://openmc.discourse.group/u/Kaur_Tuttelberg)\ **Post date:** [September 26, 2014, 6:46am UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108/3 "2014-09-26T06:46:29Z")
Hi, I’m using ENDF/B-VII ace cross section data distributed with an older version of Serpent. Here’s the header of one of the files: 1001.12c 0.999167 1.0341E-07 09/03/09 ENDFB-VII Data for Serpent 1.1.7 (1001 at 1200.00K) I’m going to try the ones from NNDC later. Cheers, Kaur ---
**Author:** ![Kaur\_Tuttelberg](https://avatars.discourse-cdn.com/v4/letter/k/a587f6/32.png) [@Kaur\_Tuttelberg](https://openmc.discourse.group/u/Kaur_Tuttelberg)\ **Post date:** [September 26, 2014, 1:35pm UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108/4 "2014-09-26T13:35:04Z")
Thanks. It’s enough to take the Ta-181 cross sections from the NNDC library to make it run. I suppose OpenMC is having some trouble with that ace file for Ta-181 at 900K. The same model was also run in Serpent so I don’t think it’s the data itself. Kaur ---
**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:** [September 26, 2014, 1:41pm UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108/5 "2014-09-26T13:41:18Z")
Thanks for the observation Kaur. I think I have a copy of that Serpent data sitting around somewhere so I’ll see if I can dig to the bottom of it. Best, Paul ---
**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:** [October 2, 2014, 1:28am UTC](https://openmc.discourse.group/t/memory-errors-particles-getting-lost-or-some-other-problem/108/6 "2014-10-02T01:28:30Z")
It looks like the root cause of the problem is the fact that the unresolved resonance probability tables for Ta-181 have values that can result in a negative total cross section. This is not really OpenMC’s problem, but it’s reasonable to expect OpenMC to still run. I’m going to try to get a fix in the next release which should be out within a few weeks. Thanks, Paul