We are using the data/generate_endf.py at master · openmc-dev/data · GitHub to generate the cross-section ENDF/B-VII.1. We have a problem in producing cross-sections at 0 Kelvin. When the 0 K is added to the temperature list, it reports always: “Command ‘njoy’ returned non-zero exit status 1”. We have succeeded to produce the cross-sections with other temperatures. Thanks for help.
This means that NJOY is crashing when trying to generate cross sections at 0 K. As suggested here, you may want to just give it a temperature of 0.1 K instead of exactly 0 K.
One other thing to note – if you just need 0 K elastic scattering cross sections for the sake of using a resonance elastic scattering treatment, that is automatically included in our data files when you run IncidentNeutron.from_njoy (which is what the linked script relies on).