Liked it, though the premise was absurd

Spoilers of course.

I've always felt that a good horror film gives you JUST ONE crazy pill to swallow, then does its best to play things realistically, apart from that one element.

The "mutants" are obviously the crazy pill here. Apparently hundreds of people have been transformed into feral, yet cunning cannibal freaks by the radiation at Chernobyl.

(There are also the mutant leg-biting fish, but they're a minor problem.)

Here are the problems with that, though I do not want to give the impression that this wholly ruined it for me.

We pretty well know what radiation does to a living human, that's not a mystery.
It basically gives them sunburn through much of their bodies, not only skin. It damages tissue and damages DNA. The initial symptoms are burn-like (skin sloughing, for instance - including from places like the stomach lining).

The DNA damage - it's important to understand - is wholly random on a per-cell basis. Even in the unlikely case that ONE of your cells' DNA was corrupted in just the right way that the new genes would produce a person with (let's say) enhanced strength, superior night vision, or an insatiable craving for human flesh - that doesn't mean YOU would gain those properties. Having just ONE altered cell isn't enough to change how your whole body operates, and your other cells would be corrupted in different, entirely random ways.

So - the nocturnal cannibals in CD cannot be people who were adults at the time of the nuclear accident.

Now, if an adult with radiation-corrupted DNA conceives a child, and either the sperm or egg contains a DNA corruption, then every cell in the baby's body will have that mutation. So - if a baby was conceived in Pripyat shortly after the Chernobyl incident in April 1986 (or shortly before, during the embryo's very early development) THEN you could end up with an entire individual who was a mutant - every cell in his or her body containing the identical radiation-induced alteration.

In that way you could perhaps end up with ONE complete, feral, light-fearing cannibal mutant.

But CD has hundreds.

Well, Chernobyl's reactor exploded on 26 April, 1986. If a child was conceived that very day, it would have been born around January 1987. If we assume this story takes place in (let's say) June 2012 that child would be 27 years old.

That's old enough for a second generation of mutants to be conceived (if we assume that all the mutant traits were genetically dominant, such that just one mutant parent was needed to breed more mutants) and that second generation might have grown to the age of, at most, say 14.

This is, of course, assuming that the original cannibal mutant was both able and willing to impregnate someone (or alternately, to become pregnant) rather than simply eating anyone who tried to copulate with them.

That's still not enough to populate Pripyat with hundreds of fully-grown mutants.
The only way it might work out is if the mutations ALSO include an intense sex drive and rapid maturation.

And... we'd have to assume that for some reason the Russian authorities were either allowing the mutants to breed, or were somehow unable to stop them.

When you think it all out, it's a lot to swallow.