Warning while reading from ENDF/B-VII.1

User Support
1

Hi,
I was running a simple depletion problem on jupyter notebook.I didn’t finish running it.After starting the depletion calculation,I opened my terminal and I saw these two types of warning

  1. negative values found on the probability table
  2. Maximum neutron energy is below 20Mev.This may bias the results

This is the file I was trying to run:

I am running OpenMC version 0.12 and the data library I am using is ENDF/B-VII.1.I have never seen these warnings when I run only transport calculation using openmc.run().
Thanks in advance

2

Sorry,I uploaded the wrong file but the same warning is still present

3

These are both data-related issues. Probability tables are used for unresolved resonance region cross sections to account for energy self-shielding effects. These tables are generated by NJOY and should not have negative probabilities, but this does sometimes occur. OpenMC will zero out those values, but it is telling you that the data produced by NJOY may be suspect.

The second message about the maximum neutron energy is due to an erroneous evaluation of Be7 in ENDF/B-VII.1 that has an upper limit on energy of 8.1 MeV. For most problems, this actually isn’t something you should be that worried about because very few particles will have energies exceeding 8 MeV. If you were trying to simulate, say, a D-T fusion with neutrons being produced at 14 MeV, this would obviously be a bigger problem. If you’re really concerned about this, I would suggest removing Be7 from the depletion chain file, which will prevent it from getting inserted in the simulation.

2 Likes
4

Thank you for your response.After seeing your comment, I ran a depletion simulation yestarday.I know the timesteps I used is too long but after the run particle_83_1515.h5 file was created along with other files.I have run depletion before but never got this.Is this because of wrong timesteps?
Files:
https://drive.google.com/drive/folders/1lZrghMEEbGQiyXWAS9hxq5BCAkhl3-o4?usp=sharing

5

Any particle_*.h5 files that are created are particle restart files, which are generated when a particle becomes lost in your geometry. This could be indicative of a problem with how your geometry is defined, but occasionally even geometries that are correct can result in lost particles due to numerical precision. I would recommend looking at the user’s guide section that discusses geometry debugging. Note that OpenMC has cutoff values for the fraction of lost particles that it considers acceptable. If you reach this cutoff, your simulation will abort altogether.