As a fact movie 10/10.

As a Cold War Movie 10/10.

As a movie based on true facts, I think many of them were pure fiction. I have never read about moon rovers in Chernobyl!. Also, the dialogues between the Soviet Union members and the Scientists is a reminiscece of 1980s Cold War Movies (The Great USA and the stupid and bad USSR). Of course people back then, had no idea about what was going to happen. We are talking about the first falulty nuclear reactor. In every dissaster of such magnitude always the chaos govern everything, but HBO tried to put some politics in this.