Normalization of Fission reaction rates

User Support
1

Hi , i’m trying to find cell average fission reaction rates using DistribcellFilter which gives the value in reactions/source . By multiplying it with the normalization factor (Pnu)/(Qk) which has the unit source/sec i’m able to get the reaction rates value in fission reactions/s.But here,

P= power in J/s
nu=nu-fission/fission (neutrons/fission)
Q=200MeV (3.2e-11J/fission)
k=eigenvalue obtained by running the simulation (neutrons/source)

so, by multiplying it with fission score i get the value in fission/sec. but if R is the normalized fission reaction rate & f is the scored fission rate then

R=f*(Pnu)/(Qfk)
=> R= (Pnu)/(Q*k) [f got eliminated]

So, To find the fission rates i’m not using the fission reaction rate score at all. Is this correct? But the value i obtained doesn’t match with the existing solution? Can anyone clear my doubt?

1 Like
2

I generally don’t recommend using (Pν)/(Qk) as a normalization factor. Please see the user’s guide section on tally normalization that describes a better approach based on the heating or heating-local score.

3

@paulromano thank you for your reply. If the power produced by core is unknown (in case it’s not in operating state) then what value should be used for P here?

4

If the power produced by the core is unknown, then it’s also not physically possible to know what the absolute fission reaction rates are either.

5

@paulromano i got it. Thank you.

6

hi @paulromano can you tell me if there is a way to get the isometric plot
of the flux density plot mentioned is this example? https://nbviewer.org/github/openmc-dev/openmc-notebooks/blob/main/post-processing.ipynb

Best Regards
Imtiaj

7

@imtiaj_hossain I’m not aware of any easy way to do that. @pshriwise has been working on some capabilities to take mesh tallies and export them to VTK files, which could them be visualized in 3D using ParaView or a similar program, so that might be an option in the future.