unity of kappa-fission

User Support
1

Hi everybody I calculate the maximal power released by a bar of fuel by using Kappa-fission Anybody Can anyone tell me the exact unity of kappa-fission declared in the tallies.out file? Thank you in advance

2

Hi Mohamed,

First some details – the kappa-fission tally is equal to the fission rate multiplied by the “psuduo Q value” for fission. The pseudo Q value is the total recoverable energy per fission MeV/fission and includes the energy from fission fragments, prompt and delayed neutrons, prompt and delayed gammas, and delayed betas. All this energy is assumed to be deposited locally, which is not physically accurate since photons are transported away from the fission site. Also neglected is energy from gammas emitted from subsequent neutron capture. Nevertheless, it’s the easiest approximation to make in order to get something that is close to power production.

So, to answer your question, the units of the tally would be MeV per source neutron.

Best regards,
Paul

1 Like
3

thank you very much Paul

4

Hi all,

just have a question:

I would like to learn how to convert kappa-fission parameter.

Prompt energy release per fission=5.1E-10 J/fission
Fission cross-section=3.2E-2 1/cm
Kappa-Fission= ??

Thank you in advance

6 Haziran 2015 Cumartesi 06:29:19 UTC-6 tarihinde Mohamed Lahdour yazdı:

5

Hi Sabahattin,

Sorry I missed your message until now. In OpenMC, when you ask for the “kappa-fission” score, it uses the “pseudo” Q-value of fission which is equal to the recoverable energy release. The recoverable energy release is defined by ENDF as the total energy release (prompt + delayed) minus the neutrino energy. As one example, this amounts to about 193.4 MeV for fission of U235 which is 13 MeV higher than the prompt energy alone. Hope this helps.

Best,
Paul