My comments are based upon observations of several years of visiting, and speaking with scores of people that work/live in the Exclusion Zone. Anecdotally, large Animal sightings of things like Moose are rare enough that even people who have visited hundreds of times, over decades, will stop, get very excited, take photos, and then chat about the last time it happened.
Edit: this report agrees with what I have found (in real life)
https://academic.oup.com/jhered/article/105/5/704/2961808
"All major taxonomic groups investigated (i.e., birds, bees, butterflies, grasshoppers, dragonflies, spiders, mammals) displayed reduced population sizes in highly radioactive parts of the Chernobyl Exclusion Zone."
Isn't this what should be expected? Even in ordinary wilderness like Maine or Canada where moose are indigenous, you could spend a year in the woods and never see one.