Hello, I’m currently working on a validation project for a full core TRIGA. I have experimental data which expresses reactivity in dollars so I need both the delayed neutron fraction and effective delayed neutron fraction. I read on past posts about this topic that currently there is no direct way of computing these. I was just wondering about the ‘delayed-nu-fission’, ‘prompt-nu-fission’ and ‘nu-fission’ tallies, can’t I use those on the full core to compute beta? If this is the case, can’t I apply an Energy Filter and limit my calculations to the thermal range to get beta_effective?

Hi @Lorenzo_Mazzocco. Unfortunately there is no way to properly get the effective delayed neutron fraction from our basic tallies. If you’re willing to make a patch to the code, you can calculate an estimate of beta-effective using the “prompt method”. See the discussion on a previous topic:

The prompt method is described in a paper by Meulekamp and var der Marck. The way it works is as follows. First, you would calculate k using a normal version of OpenMC, and then you’d calculate k using the patched version (call it k’), which gives you k-effective accounting only for prompt neutrons rather than prompt+delayed. The prompt method approximation is then βeff = 1 - k’ / k.

Sorry for asking in this QA section after 2 years of being closed. I just want to ask, is there any update on the openMC since Q1 2022 to 2024 regarding the calculation of kinetic parameters such as beta (delayed neutron fraction), neutron generation time, and prompt neutron lifetime? Is there any new feature for calculating these parameters using IFP, Nauchi, or other adjoint weighted methods but with a simpler call or command from pythonAPI? Not some sort of modifying the source code and recompiling to get the prompt version of k-eigenvalue which is then compared to the prompt+delayed version of k.

Thank you,

Wahid

Yes, it is possible to calculate it using the method Paul mentions. You can calculate k_prompt using the create_delayed_neutrons=False attribute in the Settings class, and then calculate beta_effective using the formula 1 - k_prompt/k.

k_prompt is the same as k’ in Paul’s post.

Okay Yuri, so from what you said, we still didn’t have any built in feature to calculate adjoint weighted kinetic parameter in openmc right? just to make sure that the prompt method it our best method to calculate betaeff today. Thank you Yuri

Sorry for the late reply. Haven’t been here for a long time…

I don’t know about the adjoint flux weighting. Maybe someone more experienced knows.

Thank you Yuri.

Have a great day