> I thought thought radioactivity was harmful to all life forms
The ambient levels of radioactivity are very "livable" in the surroundings of Chernobyl nowadays, plus you have to consider that it's not because radioactivity is detrimental that it prevents animals from breeding and surviving. Only very high levels of radioactivity are known to be fast killers, moderate levels will likely cause more cancers, and low levels are heavily debated (some people saying it causes harm, some others saying it has protective effects on the body as it kills a number of microorganisms).
The ambient levels of radioactivity are very "livable" in the surroundings of Chernobyl nowadays, plus you have to consider that it's not because radioactivity is detrimental that it prevents animals from breeding and surviving. Only very high levels of radioactivity are known to be fast killers, moderate levels will likely cause more cancers, and low levels are heavily debated (some people saying it causes harm, some others saying it has protective effects on the body as it kills a number of microorganisms).