If the Russians cause a meltdown, it will almost certainly be more like Three Mile Island than Chernobyl. i.e. the radioactive mess will be completely contained inside the giant lead impregnated concrete box that surrounds the giant steel pressure chamber that contains the reactor.

That was the lesson of Chernobyl, build a giant ass containment system to soak up an internal explosion. This is why the plant has survived being shelled by the Russian multiple times.

So no, there won’t be a giant cloud of radioactive material. There’s a containment vessel to keep it all inside, and more importantly, reactors are designed to not explode anymore. Turns out you can design them to just melt instead.

It’s still going to be a bitch to clean up, but unless the Russians specifically plant bombs in and around the containment vessel, and then trigger those bombs after a melt down is in progress, the plant will likely contain all radioactive material.

The worst effects on the region as a whole will be the loss of power, and a site that cannot be used to rebuild a plant without tearing the entire thing to the ground and starting over, with added clean up needed at every step of the process.