Hi Zeqin Zhang, welcome to the openmc community.
Sorry if I am not giving a proper response, but if you want to know which methods fit your case scenario, then I think you could check with some benchmark cases which has the reference beta-eff value and within the same type of case scenario that you are doing.
Or if you are using another production code like serpent or mcnp, then you could compare your calculated results between each code.
Then regarding the methods, I think basically the 1st and 2nd approaches that you already mentioned are the same since both methods use the same tally score, delayed-nu-fission and decay-rate. So if you want to add more methods, then you could try the prompt methods that have been mentioned in this discussion
scores for delayed-nu-fission and decay-rate
Actually, thank you for mentioning Joffrey Dorville’s works for IFP. I didn’t know that that script existed before you mentioned it. However, I think Joffrey is still doing some tests with benchmark cases to make sure that the implementation in openmc was consistent with benchmark data. I hope this feature can be merged into the openmc main channel soon after the benchmark tests. IFP is one method that takes into account the adjoint weighted neutron flux, so it will be different from the prompt methods but honestly, I don’t know how much the difference will be, is it still below 50 pcm? Don’t know, I hope other experienced members will give their comments here.