Account for capture branching ratios in depletion chains (#1237) · Issues · Shikhar Kumar / openmc

Account for capture branching ratios in depletion chains

Created by: paulromano

This is mentioned in #977 and was originally discussed here, but I thought it deserves its own issue. The depletion chains that we have generated so far (full ENDF/B-VII.1, CASL chain) don't have any capture branching ratios. This leads to wrong isotopic concentrations for higher actinides (since we miss Am241 and Am243 capture branching) as well as Ag110m.

Upon looking at our deplete module, there is nothing that inherently stops us from having multiple <reaction>s with the same type but different targets. In fact, we already have the data structures set up to take a branching ratio on a reaction.

The main questions are:

What branching ratios to use? For starters, we can use the values that Serpent uses. These were computed in a typical LWR spectrum, but generally the spectral effects will probably be small.
In a reduced chain (e.g., our CASL 255 nuclide chain), what should we do when the metastable product from capture is not in the chain already? The easiest thing to do is to just have it still go to ground, but this will definitely be wrong in some cases. To be more accurate, we should really look at the decay files for the missing product to see what would have happened and adjust the target accordingly.

*Created by: paulromano*

This is mentioned in #977 and was originally discussed [here](https://github.com/mit-crpg/opendeplete/issues/33), but I thought it deserves its own issue. The depletion chains that we have generated so far (full ENDF/B-VII.1, CASL chain) don't have any capture branching ratios. This leads to wrong isotopic concentrations for higher actinides (since we miss Am241 and Am243 capture branching) as well as Ag110m.

Upon looking at our deplete module, there is nothing that inherently stops us from having multiple `<reaction>`s with the same type but different targets. In fact, we already have the data structures set up to take a branching ratio on a reaction.

The main questions are:
- What branching ratios to use? For starters, we can use the values that [Serpent uses](http://serpent.vtt.fi/mediawiki/index.php/Default_isomeric_branching_ratios). These were computed in a typical LWR spectrum, but generally the spectral effects will probably be small.
- In a reduced chain (e.g., our CASL 255 nuclide chain), what should we do when the metastable product from capture is not in the chain already? The easiest thing to do is to just have it still go to ground, but this will definitely be wrong in some cases. To be more accurate, we should really look at the decay files for the missing product to see what would have happened and adjust the target accordingly.