# Zircaloy-4 activation with JEFF33 depletion chain (Nb97\_m1)

**URL:** <https://openmc.discourse.group/t/zircaloy-4-activation-with-jeff33-depletion-chain-nb97-m1/4932>\
**Category:** Validation and Verification\
**Created:** [November 5, 2024, 3:57pm UTC](https://openmc.discourse.group/t/zircaloy-4-activation-with-jeff33-depletion-chain-nb97-m1/4932 "2024-11-05T15:57:49Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![KUNG](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/kung/32/3725_2.png) [@KUNG](https://openmc.discourse.group/u/KUNG)\
**Post date:** [November 5, 2024, 3:57pm UTC](https://openmc.discourse.group/t/zircaloy-4-activation-with-jeff33-depletion-chain-nb97-m1/4932/1 "2024-11-05T15:57:49Z")

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Hi everybody,  
I am looking into the activation of the cladding in a PWR pincell and compare the cladding transmutation results from OpenMC with FISPACT-II (using the tallied cladding spectra from OpenMC in FP as an input). To perform such a comparison has quite some challenges, e.g. self-shielding of the “material lump” in the inventory code, having available the same nuclear data, different numerical solvers for the depletion step, (n,2n) reactions…

For the comparison I have generated a depletion chain based on JEFF33 (fission yield, decay and neutron files). Also the default isomeric branching ratios from Serpent were added to the chain (see attached chain file).  
[chain\_jeff33.xml](https://openmc.discourse.group/uploads/short-url/xgh50TFuwoWbJsWdgxZ8UBfAQfu.xml) (7.2 MB)

Looking at the activity values of Zr97, Nb97 and Nb97\_m1 in OpenMC directly at the end of the irradiation cycle (3 cycles with two decay breaks) leaves me a bit puzzled since the Nb97\_m1 activity should be around 95% of the Zr97 activity (the decay branching ratio to Nb97\_m1 is ~0.95 while the rest goes to Nb97 directly). However, I come up with ~85% of Zr97 activity.

This is peculiar since I performed the same OpenMC simulation also with the ENDF/B-VII.1 chain for which the ratios are plausible (see below).

**Does anybody have an idea where this discrepancy comes from? I could not spot any error with the JEFF33 depletion chain. Are metastable states (\_m1) well tracked in the depletion module?**

_Note: both chain files provide very similar half lifes for Nb97, Zr97 and Nb97\_m1 and branching ratios for Zr97 decay, both simulations were run with 70 batches (50 active ones) with 20k particles per batch, for depletion I used the CELIIntegrator_

**OpenMC Cladding Activity (Bq/cm) - JEFF33 depletion chain**

- Nb97: 2.995600e+10 (half life ~1 h)
- Zr97: 2.994710e+10 (half life ~17 h)
- Nb97\_m1: 2.556226e+10 (half life ~1 min) → ~85% of Zr97 !?

**Zr97 production rate JEFF33**

 ![image](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/d/dfa279e25f3aa1b191a0b5968c2946bd5ec780e0.png)

**OpenMC Cladding Activity (Bq/cm) ENDF/B-VII.1 depletion chain**

- Nb97: 3.233517e+10
- Zr97: 3.233514e+10
- Nb97\_m1: 3.073337e+10 → ~95% of Zr97

**Zr97 production rate ENDF/B-VII.1**

 ![image](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/b/bc26148ca31034c66aadcc93c4b7cdffad9c1625.png)

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<div class="post-metadata">

**Author:** ![KUNG](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/kung/32/3725_2.png) [@KUNG](https://openmc.discourse.group/u/KUNG)\
**Post date:** [November 6, 2024, 2:26pm UTC](https://openmc.discourse.group/t/zircaloy-4-activation-with-jeff33-depletion-chain-nb97-m1/4932/2 "2024-11-06T14:26:37Z")

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Here is a Juypter Notebook with outputs using the JEFF33 file for depletion. Nb97\_m1 activity is roughly 85% of Zr97 although it should be 95%.  
[pincell\_depletion\_jeff33.ipynb](https://openmc.discourse.group/uploads/short-url/fLh1FIfB5JRq7tBymimiWAA4m7H.ipynb) (119.7 KB)

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<div class="post-metadata">

**Author:** ![KUNG](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/kung/32/3725_2.png) [@KUNG](https://openmc.discourse.group/u/KUNG)\
**Post date:** [November 8, 2024, 3:29pm UTC](https://openmc.discourse.group/t/zircaloy-4-activation-with-jeff33-depletion-chain-nb97-m1/4932/3 "2024-11-08T15:29:45Z")

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Here is the comparison between FP and OpenMC (Top 10 nuclides for activtiy) for JEFF33:

This is where I noted Nb97m not following Zr97.

 ![FP_vs_OMC_JEFF33](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/d/d9e821123aa3ff98429adc9f33814db894b638d8.png)