Loss of coolant can have effects on the reactor and/or the spent fuel pool or container if there is such in the facilities. Any of these could go critical very quickly and ignite/explode.

But based on what happened in Fukushima, critical electrical/cooling systems and backups would have to be damaged in order to pose catastrophic risk.

While this is unlikely I'll probably lose some hours of sleep on this.

I very much doubt the Russians would do this on purpose (fallout would risk the whole operation and possibly Russian territory too) although the fighting around there is incredibly stupid.