The last time I checked, being Russian doesn't make you immune to radiation. Controlling land is pretty pointless if you've poisoned it into uninhabitability for the next few generations or so.
What makes you think that what they're doing has significant risk of making the land uninhabitable? All we know is that there's a fire at the perimeter. That's it. It could be that what they're doing has little risk. From reading the twitter threads, seen elsewhere in this comment section, that seems to be the case. Not surprisingly, nuclear power plants are made pretty well.
I don't think there's any evidence that they're acting irrationally, from within their context. Making the land uninhabitable would be irrational, for everything we know of their context.