Pretty wild to think about how something we take for granted as never changing in daily life can actually change in human lifespans to things as fundamental as atoms and isotopes. Sure, there's radioactive decay but few interact with this.

It's really like a big mess of uncontrolled alchemy of matter shifting around at chernobyl. I know it's a actually a giant mess of nuclear chemistry going on with all sorts of unknown distributions and spatial proximities of various atoms but wild to think about.

Typically this stuff is well controlled and reactor configurations are well established as are the types of reactions and byproducts produced with fairly high certainty. Take those very detailed designs away and you have no idea what sort of materials are shifting states in these globs of materials. They have designs and can reason basic percentages of what may have ended up where but lots of guesswork and lots of those are not highly refined materials I'm sure, which means a bunch of impurities are incorporated in as well.