Daniel D'Addario Chief TV CriticThe partial meltdown at the nuclear power plant at Three Mile Island in Pennsylvania in 1979 was a perfect coalescing of factors in two senses. First, a series of cascading mechanical and human errors brought the plant close to a catastrophe that would have potentially made much of the East Coast uninhabitable, we’re told in the new documentary “Meltdown: Three Mile Island.” Second, coming as it did both within memory of the height of Cold War paranoia and days after the release of the film “The China Syndrome,” the disaster was perfectly primed to set off anxieties about the danger of atomic energy.“Meltdown: Three Mile Island,” a new four-part documentary on Netflix, does an elegant job of braiding those two truths — that Three Mile Island was a narrowly averted nightmare scenario and that it lives on in the public imagination as an argument against nuclear energy.