I admittedly didn't think anything happened at chernobyl in 30 Years... why is it being seized?
the whole of ukraine is being seized. chernobyl is in ukraine. ergo...
the russians are taking control of all infrastructure: airports, power stations, water treatment, communications... chernobyl is noteworthy because of the risk, and historical memories, it represents. just raises a lot of alarms. the russians have taken the workers there hostage since the invaders don't know how to run the joint anymore.