Doppler Broadening

User Support
1

Hey guys, I just stumbled upon OpenMC and am considering using it in my thesis. It sure beats using the ancient code in the “A Monte Carlo Primer”. Everything I’ve seen so far looks great. However, I do not quite understand how, if at all, OpenMC handles doppler broadening. I noticed that there is a doppler broadening module within the development branch on github, but that it is currently not being used. How hard would it be to modify OpenMC to use the doppler broadening module present in the development branch? I’m not adverse to modifying the source myself, I’d just need to know which module I’d need to modify to broaden the microscopic set.

Thanks in advance.

-Alex

2

Hi Alex,

Glad to hear you may be interested in using OpenMC. Currently (and despite the presence of a doppler.F90 module), OpenMC does not do any Doppler broadening of cross sections, so you are limited to the temperatures of whatever data you have available in your ACE format cross sections. In the future, there will likely be some type of on-the-fly Doppler broadening, but it is an active R&D topic and it’s hard to say when exactly it would make it into the code.

You could in theory do Doppler broadening on-the-fly using the algorithm that is there. Essentially, you would need to modify the cross_section.F90 module to use the Doppler broadening routine from doppler.F90. The subroutine in doppler.F90 does the broadening for all energies, but you would want to limit it to only the energy at which the particle is at. Anecdotally, I’ve heard of people trying this approach using the algorithm that is in doppler.F90 (known as SIGMA1, also implemented in NJOY) and the performance degradation is quite severe, possibly up to two orders of magnitude. As to how hard it would be to actually do this, I’d say it’s not trivial but not terribly complicated either.

Best regards,
Paul

3

hye Alex,

i am also interested in using this Doppler broadening at this time. Have you implemented the changes in source to incorporate Doppler broadening in the code?. if yes, can i get a copy of that :slight_smile: