# Simulation always stops after exactly 50 batches and writes statepoint.50.h5

**URL:** <https://openmc.discourse.group/t/simulation-always-stops-after-exactly-50-batches-and-writes-statepoint-50-h5/6223>\
**Category:** User Support\
**Created:** [February 14, 2026, 3:27am UTC](https://openmc.discourse.group/t/simulation-always-stops-after-exactly-50-batches-and-writes-statepoint-50-h5/6223 "2026-02-14T03:27:13Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![cmkang](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@cmkang](https://openmc.discourse.group/u/cmkang)\
**Post date:** [February 14, 2026, 3:27am UTC](https://openmc.discourse.group/t/simulation-always-stops-after-exactly-50-batches-and-writes-statepoint-50-h5/6223/1 "2026-02-14T03:27:13Z")

</div>

Summary

I have a very simple Godiva bare-sphere model (HEU metal, radius ~8.71 cm, density 18.74 g/cm³) written in Python using the OpenMC API.No matter what I set for settings.batches, settings.inactive, settings.particles, settings.no\_batch\_limit = True, settings.trigger\_max\_batches = 1000, or settings.trigger = None, the simulation always stops after exactly 50 batches and writes statepoint.50.h5. The final combined k-eff is printed, but only ~30–40 active batches are performed (depending on inactive count).Key observations so far

1. Maximum batch is always 50

2. Same behavior in multiple versions

3. k-effective estimate at batch 50 is identical

4. Changing parameters has no visible effect on early batches

---

<div class="post-metadata">

**Author:** ![Jarret](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/jarret/32/4075_2.png) [@Jarret](https://openmc.discourse.group/u/Jarret)\
**Post date:** [February 18, 2026, 1:10am UTC](https://openmc.discourse.group/t/simulation-always-stops-after-exactly-50-batches-and-writes-statepoint-50-h5/6223/2 "2026-02-18T01:10:03Z")

</div>

Hi,

There is no such thing, you should be able to adjust these values freely. I would suggest you are either not properly updating the settings.xml file within you settings declaration, or you have a model within the folder you are operating out of. If there is a model it always runs first when you are calling openmc.run, therefore possibly rerunning a model that has batches set to 50 and gens set to 1. You can verify easily by looking into the folder you are operating out of, or by looking at the top of the outputs when running openmc.run and see if it states that there is a model.xml that its reading. If either or these are not the issue, I would post your settings declaration section and I can take a closer look.