# Higher k\_eff at 0 depletion step

**URL:** <https://openmc.discourse.group/t/higher-k-eff-at-0-depletion-step/3469>\
**Category:** Validation and Verification\
**Created:** [September 28, 2023, 8:07pm UTC](https://openmc.discourse.group/t/higher-k-eff-at-0-depletion-step/3469 "2023-09-28T20:07:50Z")\
**Posts on this page:** 1\
**Showing post:** 1

<div class="post-metadata">

**Author:** ![scaleuser](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/scaleuser/32/2904_2.png) [@scaleuser](https://openmc.discourse.group/u/scaleuser)\
**Post date:** [September 28, 2023, 8:07pm UTC](https://openmc.discourse.group/t/higher-k-eff-at-0-depletion-step/3469/1 "2023-09-28T20:07:50Z")

</div>

![openmcvsSCALE](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/7/7c8906e1ed1af04f27841718c61f49e833693bde.png)

Hello,  
I’m observing some strange behavior where the 0 step depletion k in OpenMC is higher than the eigenvalue simulation:  
1.03869058e+00 +/- 3.76492873e-04 (depletion) vs. 1.03693 +/- 0.00021 (eigenvalue)  
For comparison, SCALE is giving:  
1.03683 +/- 0.00023 vs. 1.03701 +/- 0.00019  
I have checked the material.xml file atom densities at step 0 with the SCALE output values and they appear to be the same.  
Graphite moderated Molten Salt (FLiBe w/~20% enriched U) reactor core. Using CECMIntegrator.  
Any ideas?

---

_[View the full topic](https://openmc.discourse.group/t/higher-k-eff-at-0-depletion-step/3469)._