Negative branching ratios in JEFF-3.3 chain

[nplinden]

Hi,
generating a JEFF-3.3 depletion chain using this script results in 5 isotope having negative decay branching ratios, namely:

• Cd99
• Cs119
• Cs120
• Cs120-m1
• Bk249

Manually inspecting the corresponding decay files, it seems the sum of branching ratios for these isotopes' decay add up to more than one.

For instance Cs120 has the following decay modes:

• ec/beta+ br = 1.0
• ec/beta+,alpha br = 2e-7
• ec/beta+,p br = 7e-8

This adds up to 1.00000027. When generating the chain using OpenMC, line 399 to 404 in this file tweak the last BR to ensure that the sum is equal to one. Four our five nuclides, this results in the last BR becoming negative.

Though having BRs adding up to more that one is weird, I am not sure tweaking the last one is the right approach, as it leads to unphysical effects. Why not renormalize all BRs by dividing them by the total?

I'm creating an issue on this repo because it hosts a generate_jeff_chain script which creates a (slightly) broken chain, but I'll create the same one on the official OpenMC repo since the responsible code is from there.

[shimwell]

Thanks for letting me know. I should regenerate the chain file with the newest version of openmc. renormalize all BRs by the total sounds like the way to go from my point of view but lest us see what the openmc people say

[shimwell]

With the recent merge into openmc dev branch of this PR openmc-dev/openmc#3080 (comment)

The chain files can be updated #todo