Can't use multipole temperature method

User Support
1

Hi there,

I get an error when attempting to use the multipole method with the following line:

settings.temperature = {'method': 'interpolation'}

The error is:

ValueError: Unable to set "temperature method" to "multipole" since it is not in "['nearest', 'interpolation']"

I’m using the ENDF 7.1 database which includes the windowed multipole library according to this link: https://docs.openmc.org/en/stable/usersguide/cross_sections.html#windowed-multipole-data

2

@MrReactorMan Welcome to the community! To use multipole data, you need to set:

settings.temperature = {'multipole': True}

Generally you should also set the temperature method to interpolation (which is still needed outside of the resolved resonance range), so together this would look like:

settings.temperature = {
    'method': 'interpolation',
    'multipole': True
}
3

Thank you Paul! That worked great.

I’m now having an issue of the temperatures I would like to use being lower than the ENDF 7.1 database supports. Specifically Hydrogen and Zirconium. What is the best way to get properties at temperatures below 293 K?

4

Starting from the ENDF files for the isotopes of H and Zr you’re interested in, you can use our data API to call NJOY under the hood to generate data at whatever temperature you desire. This would look like:

zr90 = openmc.data.IncidentNeutron.from_njoy('Zr90.endf', temperatures=[200., 293., 600., ...])
zr90.export_to_hdf5('Zr90.h5')

Then you can add this file to an existing cross_sections.xml file.

1 Like
5

Hi Paul,

Thanks for the response. I attempted that method however I’m getting the following error:
“FileNotFoundError: [Errno 2] No such file or directory: ‘njoy’: ‘njoy’”

Is this a package I need to import, or something within the ENDF folders?

6

I ended up not having the NJOY application installed. Here’s the link to the installation instructions for anyone that needs it: https://docs.njoy21.io/install.html

I was advised to use NJOY2016, I’m unsure if this fix will work for 21. After installing it I had to change line 180 in “openmc-0.12.2/python3.6/openmc/data/njoy.py” to have the variable ‘njoy_exec’ include my path to NJOY file. For me it was: “/home/shared/NJOY2016/bin/njoy”.

7

@MrReactorMan You actually don’t need to modify the OpenMC source in order to specify the NJOY executable. This can be done as follows:

openmc.data.IncidentNeutron.from_njoy(..., njoy_exec="/home/shared/NJOY2016/bin/njoy")
8

Hi Paul, thanks for adding that that’s definitely easier.

I’m getting a weird warning now:

 WARNING: Windowed multipole functionality is turned on, but no multipole
          libraries were found. Make sure that windowed multipole data is
          present in your cross_sections.xml file.

I added the newly generated .h5 files to the endf library and modified the cross_sections file to point to their new paths, is there another step I missed?

9

Multipole data has to be specially processed – right now the only library available that contains multipole data is the ENDF/B-VII.1 one that you can find here: Official Data Libraries | OpenMC

If you’re processing your own data, you could add multipole library with something like:

multipole_library_filenames = [
    '/path/to/wmp/001001.h5',
    '/path/to/wmp/001002.h5',
    ...
]
lib = openmc.data.DataLibrary.from_xml(<existing cross_sections.xml file>)
for path in multipole_library_filenames:
    lib.register_file(path)
lib.export_to_xml('new_cross_sections.xml')