Zircaloy-4 activation with JEFF33 depletion chain (Nb97_m1)

Validation and Verification
1

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 (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
image1244×474 19.7 KB

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
image1244×474 19.7 KB

2

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 (119.7 KB)

3

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
FP_vs_OMC_JEFF33964×738 33.2 KB