Our favorite analysis tool is the Pivot Chart in MS Excel. Its basic charts aren’t very artistic, so we pretty them up a bit. Visitors who have Excel can reproduce some of these from the View235 download. However, View235 lost its link to the elements table, so it’s not the source of the first chart.
The Colored Elements Chart
“Decay Chain Stacks” is our favorite IFFY chart, partly because a data-mining instructor once said he’d never seen a stacked bar chart that he liked. The stacks represent each decay chain, with highly unstable isotopes at the bottom. Each nucleus climbs one of these stacks to become a stable isotope at the top. The most popular fission products inhabit the tallest stacks. From left to right the decay chains get heavier. In this chart the stacks are layered as differing elemental populations. Each element is assigned a different color, basically by Bill Gates. The bands for Krypton and Xenon are highlighted in red.
The most obvious phenomenon is the bi-modal distribution, with a Sparse Valley between. The double-hump reflects that when you split an atom, it hardly ever splits in half. A more “normal” split is 1/3rd and 2/3rds.
Xenon is a popular fission product from atomic weights 136-140. 136-Xe is the most popular stable/primordial isotope, which shows up more obviously in the TimeStep 0 chart below.
Aging the Waste
The next four charts show the decreasing proportion of really hot isotopes over time.
The first shows the dominance of isotopes with very short half-lives in hot colors. This is the state of the reactor one second after startup. This sort of activity happens every second, but these nuclides cool quickly.
The tall purple segment is 136-Xe. 96-Zr is the only other stable isotope with an initial yield over 1%. Switching back and forth between the NuDat options reveals why.
This is the Initial Yields option, showing the Light and Heavy Hills, with the Sparse Valley between. It also shows the Stable Valley cells outlined in black. 136-Xe and 96-Zr “intrude” farthest into the hills, so have the highest initial yield of all the stable isotopes. 140-Ce and 100-Mo, also “farthest right” of the Cerium and Molybdenum stable isotopes, occasionally approach 1%.
By Timestep 10, a thousand seconds later (17 min), the reds have cooled to orange and yellow. The most recent fission event looks like the above, but 999 older events dominate. The older fission fragments have migrated from the 0_Zero and 1_Second time-bins to nuclides with half-lives measured in minutes or more. At atomic weights 96, 98, 100, and 136 the first long-lived daughter in the chain is stable or nearly so.
At TimeStep 20, aka a MegaSec (12 days), the short-lived isotopes – in yellow – represent only about 1.5% of the population.
Well over 50% of the waste is stable by Timestep 30, 34 years after reactor startup.
The serious radioactivity will come from (green) 90-Sr and 137-Ce for the next 300 years. After that, the radioactivity comes from the long-lived fission products 93-Zr, 99-Tc, and 135-Cs (the blue stacks).