So from the look of it, the IFP method within OpenMC might only be included within development branches. The documentation for it is version 0.15.3.dev29+ga7d1ceba3 which is not the newest main stable version of 0.15.2, and seems to be a newer dev version. I can’t find anything on IFP method within the 0.15.2 documentation. Previous development branches developed by individuals using the code were discussed in these previous user support threads here,
I don’t know if they have formally been consolidated into the main branch. I tried to play around with it on my pc running 0.15.2, and I was able to get the tallies to be exported to XML, but I don’t know how to run the IFP simulation, and the documentation doesn’t state how to actually run the simulation. I tried defining ifp_n_generation in the settings to try to have it run the sim but that didn’t seem to work. Therefore, it might be in the newest version, the tally definition is at least, but I don’t know if the full process is integrated. @paulromano can probably give a confirmation if it has been implemented.