« Thus the more dangerously radioactive stuff decays a lot quicker. » If it decays very quickly, yes, it's less of a threat (except in case of a spill from the

« Thus the more dangerously radioactive stuff decays a lot quicker. » If it decays very quickly, yes, it's less of a threat (except in case of a spill from the reactor, where people would get exposed to fresh material.) If it decays very slowly... well, the damage just might be spread out over time. I think a case could be made for that, at least... But it's more complicated than that, anyway. Strontium, for instance, is a particular problem because it is similar to calcium, so people's bodies incorporate it into bones. Having it stick around in the body rather than flushing out makes it more dangerous than it would otherwise be. Similar for iodine, which is why nuclear meltdown preparedness programs involve having potassium iodide pills on hand—to try to saturate the body with non-radioactive iodine. So the bioaccumulation potential must be considered as well, because what matters is how long people are in contact with radioisotopes.