Group Analysis

This analysis groups fission fragment populations with an odd kluge of aggregation methods.  The first group consists of the nine half-life bins, Time_Bins 0-8.  The numbers for these exclude isomers and shadow-side nuclides, which are listed separately.  The shadowed numbers include isomers, so the given isomer values are for the main decay chains only.

Contribution by Group

GroupIsotopesYield (atoms)Contribution (%)
Yield & Contribution per TimeBin + Shadowed (Rung>9) & Isomers (Level>0)
Yields for Timestep 20 (12 days), 235-U/Slow with capture


There are a total of 2,097,152 (2Meg) atoms in the waste stream at Snapshot 20. About 45% 0f those are stable by then, and 16% are primordial.


The contribution of shadow-side nuclides increases with neutron capture.  Some stable isotope can capture a neutron and move to the right on the NuDat chart.  This can place them on an Isolated Island.  From there, a B- decay will move them to the second sink.


Evolution Charts

After 12 Days

The evolution of the waste stream becomes apparent when we analyze the relative contribution of groups of isotopes over time.  The Time_Bin characteristic aggregates the 1322 nuclides into nine groups.  Here’s an Excel chart that shows the composition of the waste getting proportionally more stable as the reactor gets older.  After a MegaSec, the hot isotope population (HL < 1 day) is no longer growing.  Their proportional contribution to the whole (normalized yield) is dropping.  Their population has leveled out,  but their daughters continue to grow.  Stable isotopes will only grow in population, unless they capture neutrons.

The Mass is 2Meg atoms at MSec and 2Gig atoms at GSec.  “Mass” is approximate.

Yikes! A bit of sensitivity testing— Average AtWt varies a lot!

  • Day: 122
  • Year: 129
  • Millenia: 111
  • Primordial: 123
  • Stable: 118

Guess I should change the Y-axis title to Population, or rather relative population.

The Full Span

The chart above focuses on the last ten (eleven) time steps.  A chart of the entire sim run is more colorful.

Evolution to Stability

Each chart is tailored to color the shorter-lived isotopes in hot colors, fading to black as the nuclei become stable.

These charts are still in development.  The y-axis isn’t quite right yet.  Normalized Yield runs from 0 to 2.0 atoms, not 0-100%.  The x-axis of the upper chart is more descriptive but,

  1. Not all of the TimeSteps have names, and
  2. They wouldn’t fit if they did.

Rung Analysis

IFFY introduces a new characteristic of isotopes, the Rung.  To mix three metaphors, the end of a decay chain is the bottom of the energy ladder, and the sink into which unstable nuclei drain.  The sink for the major decay chains is given a Rung value of Zero.  This is a stable isotope, which means it has the “proper” proportion of protons and neutrons.  Isotopes with too many neutrons have Rung values from one to nine, one for each excess neutron.

The table below shows how rapidly excess neutrons make the nucleus unstable.

Isotopes @ Rung per Time_Bin

Rungs 7, 8, 9 have only Zero bin isotopes
No shadowed isotopes or Isomers


  • All Rung 0 isotopes are stable or as good as stable for this analysis.
  • At Rung 3, there are no isotopes with half-lives longer than a day.
  • At Rung 4, there are no isotopes with half-lives longer than an hour.
  • At Rung 5, there are no isotopes with half-lives over a minute.
  • At Rung 6, there is just one isotope with a half-life over a second.