# Discrepancy in Photon Heating Values

**URL:** <https://openmc.discourse.group/t/discrepancy-in-photon-heating-values/6019>\
**Category:** User Support\
**Created:** [September 25, 2025, 6:26pm UTC](https://openmc.discourse.group/t/discrepancy-in-photon-heating-values/6019 "2025-09-25T18:26:07Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![alwonj7](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@alwonj7](https://openmc.discourse.group/u/alwonj7)\
**Post date:** [September 25, 2025, 6:26pm UTC](https://openmc.discourse.group/t/discrepancy-in-photon-heating-values/6019/1 "2025-09-25T18:26:07Z")

</div>

I am running a few cases for nuclear heating using the same geometry and materials, then comparing it to MCNP values. My values are:

1. OpenMC run with heating-local: 10.09682 MeV/sp
2. OpenMC run with heating (n,p): 9.1556 MeV/sp
  - n: 9.30226 MeV
  - p: 0.0025368 MeV

3. OpenMC run with heating (n,p,e,e+): 10.57913 MeV/sp
  - n: 9.15309 MeV
  - p: 0.002536 MeV
  - e-: 1.284695 MeV
  - e+: 0.138812 MeV

4. MCNP run with heating (mode n,p): 10.571 MeV/sp
  - n: 9.79 MeV
  - p: 0.781 MeV

My questions are:

1. Shouldn’t the heating-local be a more conservative estimate as the photon transport is also included in ‘heating’ simulations whereas in ‘heating-local’ all photon energy deposited + charged particles are deposited locally?
2. As far as I know OpenMC does not run charged particle transport, so why do the numbers for change between #2 and #3 cases above? Am I double counting contribution if I add up all the numbers in #3 to compare to the MCNP value?

Thank you

---

<div class="post-metadata">

**Author:** ![yrrepy](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/yrrepy/32/2365_2.png) [@yrrepy](https://openmc.discourse.group/u/yrrepy)\
**Post date:** [September 25, 2025, 10:27pm UTC](https://openmc.discourse.group/t/discrepancy-in-photon-heating-values/6019/2 "2025-09-25T22:27:39Z")

</div>

There are no charged particles in OpenMC, it is all photon and neutron Kerma.

I never use heating-local, I believe it pertains to lumping the secondary photons from fission into the Kerma. Though the wording/documentations is a bit fuzzy and implies all photon secondaries.

#3 is the correct way.  
It’s to do with how OpenMC accounts for different interactions.  
This is a frequent hang-up in OpenMC

> [@Photon heating](https://openmc.discourse.group/t/photon-heating/619/):
>
> Hi, I’m interested in studying heating in a reactor core. I ran my model in dev version (0.12.0) twice, with two different commits: A. From Jan 17 - after the correction of delayed gamma energy ([#1449](https://github.com/openmc-dev/openmc/pull/1449)). B. From Feb 4 - after the correction of photon energy, including separation into photon/electron/positron ([#1462](https://github.com/openmc-dev/openmc/pull/1462)). See tallies below. My questions are: In Case B (Feb 4) I observe negative positron energy, why is that? While neutron heating are same in both cases, when I compare heati…

> [@Absorbed dose rate discrepancy between OpenMC & TRIPOLI](https://openmc.discourse.group/t/absorbed-dose-rate-discrepancy-between-openmc-tripoli/4057):
>
> Hi, I am trying to compare the absorbed dose rate on a cylinder due to a punctual source with both neutron and photon emissions between 3 Monte-Carlo codes: TRIPOLI-4, RayXpert and OpenMC. Both TRIPOLI-4 and RayXpert gives the same results (around 10% discrepancy, mostly due to some simplification in the TRIPOLI modelling). However, my OpemnMC input should be identical to the TRIPOLI one but I have a discrepancy factor of 10 000. Here are the results: Here is my python script for …