Hello all,
I’m trying to setup a depletion model for validation with experimental Neutron Activation Analysis data and I’m getting significantly lower activities compared to the experimental data that I have.
For context, this depletion model uses a CAD model of a RSR Tube with a test sample inside and is surrounded by a slightly larger cylindrical source which contains energy and probability bins comparable to what may be seen in the rotary specimen rack of a TRIGA MK II reactor.
energy_bins = [
1.0000E-09, 5.0000E-09, 1.0000E-08, 3.0000E-08, 7.0000E-08, 1.0000E-07, 1.5230E-07, 2.0000E-07,
4.1399E-07, 6.0000E-07, 8.0000E-07, 1.1253E-06, 3.0590E-06, 5.0435E-06, 8.3153E-06, 1.3710E-05,
2.2603E-05, 3.7266E-05, 6.1442E-05, 1.0130E-04, 1.6702E-04, 2.7536E-04, 3.5358E-04, 4.5400E-04,
5.8295E-04, 7.4852E-04, 9.6112E-04, 1.0891E-03, 1.2341E-03, 1.3984E-03, 1.5846E-03, 1.7956E-03,
2.0347E-03, 2.3056E-03, 2.6126E-03, 2.9604E-03, 3.3546E-03, 3.8013E-03, 4.3074E-03, 4.8810E-03,
5.5308E-03, 6.2673E-03, 7.1017E-03, 8.0473E-03, 9.1188E-03, 1.0333E-02, 1.1709E-02, 1.3268E-02,
1.5034E-02, 1.7036E-02, 1.9304E-02, 2.1875E-02, 2.4788E-02, 2.6058E-02, 2.8088E-02, 3.1828E-02,
4.0868E-02, 5.2475E-02, 6.7379E-02, 8.6517E-02, 1.1109E-01, 1.4264E-01, 1.8316E-01, 2.3518E-01,
3.0197E-01, 3.8774E-01, 4.3937E-01, 4.9787E-01, 5.6416E-01, 6.3928E-01, 7.2440E-01, 8.2085E-01,
9.3014E-01, 1.0540E+00, 1.1943E+00, 1.3534E+00, 1.7377E+00, 2.2313E+00, 2.8651E+00, 3.6788E+00,
4.7237E+00, 6.0653E+00, 7.7880E+00, 1.0000E+01, 1.1912E+01, 1.3499E+01, 1.4918E+01, 1.6905E+01,
2.0000E+01
]
probabilities = [
2.3372E-04, 6.2347E-03, 1.7621E-02, 1.1596E-01, 2.0149E-01, 7.5095E-02, 4.9570E-02, 1.5053E-02,
2.0904E-02, 8.2432E-03, 6.5604E-03, 7.1269E-03, 2.0287E-02, 9.9576E-03, 9.7193E-03, 9.6311E-03,
9.7966E-03, 1.0127E-02, 9.4954E-03, 1.0271E-02, 9.7238E-03, 1.0113E-02, 5.0014E-03, 5.3494E-03,
5.0541E-03, 5.2070E-03, 4.9424E-03, 2.6686E-03, 2.5196E-03, 2.8925E-03, 2.4813E-03, 2.7874E-03,
2.6408E-03, 2.5222E-03, 2.6105E-03, 2.4430E-03, 2.4992E-03, 2.6212E-03, 2.7000E-03, 3.0312E-03,
2.8721E-03, 2.6108E-03, 2.9806E-03, 2.8157E-03, 2.8732E-03, 2.7703E-03, 2.6580E-03, 3.1954E-03,
3.0565E-03, 3.0714E-03, 3.0785E-03, 3.1391E-03, 3.3095E-03, 1.2780E-03, 1.7935E-03, 4.0324E-03,
5.8039E-03, 7.1491E-03, 7.8652E-03, 8.8356E-03, 8.1467E-03, 1.0375E-02, 9.3798E-03, 1.0993E-02,
1.2509E-02, 1.2874E-02, 6.3160E-03, 7.4020E-03, 8.2228E-03, 8.0082E-03, 8.4470E-03, 8.7870E-03,
8.6618E-03, 8.5806E-03, 8.9805E-03, 9.6753E-03, 1.9410E-02, 1.9372E-02, 1.7459E-02, 1.1045E-02,
8.1418E-03, 5.4196E-03, 2.4563E-03, 7.5463E-04, 1.3263E-04, 4.5278E-05, 2.6936E-05, 5.1245E-06,
0.0000E+00
]
TRIGA = openmc.IndependentSource()
TRIGA.space = openmc.stats.CylindricalIndependent(
openmc.stats.Uniform(0.5, 1),
openmc.stats.Uniform(0, 6.28318530718),
openmc.stats.Uniform(0, 14),
origin=[0, 0, 0]
)
TRIGA.angle = openmc.stats.Isotropic()
TRIGA.energy= openmc.stats.Discrete(energy_bins,probabilities)
TRIGA.particle = "neutron"
In the experiment, the 100 mg sample is irradiated for 1 hour and then allowed to rest for 20 days and is then taken to a detector for counting. I’ve attempted to replicate that here by setting up 6 10min time steps with a source rate of 2e12 n/cm2/s and the rest of the 20 day timesteps as 0 for the source rate. I also set up an unstructured mesh tally to verify the flux the values.
Once the model is finished running, I execute my post processing script only to find that the activities are very low and the right isotopes are not showing up. Furthermore, the flux tallies don’t record anything going through.
Be8: 1.4063284546168917e-23 Bq
Rb87: 0.029995661047714735 Bq
Hf174: 1.0952007896725205e-09 Bq
Ta180: 7.383388569970425e-11 Bq
W180: 3.056857070978273e-15 Bq
Ir180: 3.662565239016263e-13 Bq
Total Activity: 0.029995662217118725 Bq
Flux values from tally:
[]
Mesh volumes: []
Sum of mesh volumes: 0.0
[]
Traceback (most recent call last):
File "/home/haider/NAA/NAA_infor.py", line 71, in <module>
umesh.write_data_to_vtk("flux_distribution", data_dict)
File "/home/haider/miniforge3/envs/openmc-env/lib/python3.12/site-packages/openmc/mesh.py", line 2420, in write_data_to_vtk
raise ValueError(f'Cannot apply dataset "{name}" with '
ValueError: Cannot apply dataset "Flux 0 - 1 MeV" with shape (0, 1, 1) to mesh 1 with dimensions (0,)
What’s even more strange is when I increase the source rate value to something absurd like 2e56, the output remains unchanged. I suspect it might have to do with how the the Cylindrical Source is setup (the intention is for the particles to move towards the sample). Kindly have a look at the attached relevant files. I’ve also attached a screenshot of how the RSR Tube looks like.
NAA.Coupled.py (6.9 KB)
NAA_Post.py (1.8 KB)
Unfortunately, the post isn’t allowing me to upload the TubeAndSample.h5m file but any comments and suggestions are welcome.