How would i find the CR of these fissile isotopes

[hhhnain]

I used a MOX fuel with reactor grade plutonium vector.
I want the conversion ratio but don’t know how to. I thought it was the sum of fissile at the end divided by sum of fissile at start but doesn’t work

[paulromano]

@hhhnain See my response here:

How to find the conversion ratio?

Yes, on second thought, I think you’re better off calculating conversion rate using a a ratio of reaction rates as suggested by @gridley. Namely, the numerator (fissile material produced) can be calculated by summing the tallied (n,gamma) reaction rates for each fissionable nuclide, and the denominator (fissile material destroyed) can be calculated by summing the tallied absorption reaction rates for each fissionable nuclide.

[mortennygaard]

Hi Paul. Could you elaborate on which RR you would include? I want BR for a SFR in U Pu fuel cycle. Is this not enough?:

BR = RR_(n,gamma)_U238 / (RR_fission_U235 + RR_fission_Pu239 + RR_fission_Pu241)?

Would you include RR_(n,gamma)_Pu240 in numerator?

I’m worried what I have now will overestimate BR since some of RR_(n,gamma)_U238 will lead to MA production rather than production of fissile nuclides.

Should I just have the sum of (n,gamma) RR for all fertile nuclides in numerator and the sum of fission RR of all fissile nuclides in the denominator?

E.g. from fig. 12 in Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2and MOX Spent Fuels