How to get the decay constant and the fraction of six delayed neutron precursor by OpenMC？

User Support
1

Hi all,
I wanna get the decay constant and the fraction of six delayed neutron precursor by OpenMC and I found there is a “decay-rate” tally in the user’s guide. However, the specification of this tally is that: “The delayed-nu-fission-weighted decay rate”. I don’t know what does “the delayed nu-fission-weighted” means. Shortly, I don’t know how to use it to get the real decay constant of six delayed neutron precursor.
Besides, there is a “openmc. DelayedGroupFilter” in the python API specification. If I make a tally, whose score is the “nu-fission” and filter is the openmc. DelayedGroupFilter. Does it means that the result of this tally is the fraction of six delayed neutron？
Any reply will be appreciated!

Best regards!
Benjamin

2

Hi Benjamin,

You are right, you will want to tally the delayed-nu-fission and the decay-rate, each with a DecayGroupFilter. Then, the decay rate you want is the decay-rate score, divided by the delayed-nu-fission.

You can alternatively use the MGXS Python API which can handle this for you (https://docs.openmc.org/en/stable/pythonapi/generated/openmc.mgxs.DecayRate.html#openmc.mgxs.DecayRate) as shown in this example problem:
https://docs.openmc.org/en/stable/examples/mdgxs-part-i.html and/or
https://docs.openmc.org/en/stable/examples/mdgxs-part-ii.html

Hope this helps!
Adam

3

Hi Adam, the last two links you shared with us are no longer available, is there a way to get them back?

Thanks in advance,
Mohammad

4

Hi Zouzou M.
I think that’s the same example from openmc notebooks and you could find it at

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