An early tipoff that Japanese authorities felt that events at Fukushima were very serious was the ordering of an evacuation within a couple of hours of the earthquake. Though the area was small and the evacuation was called “precautionary”, the fact is that ordering several thousand more people into motion during the immediate aftermath of a major earthquake and tsunami is something that no government would do if it could possibly help it.
Neither Three Mile Island nor Chernobyl were accompanied by natural disasters. Even then, authorities were loathe to evacuate, in part because evacuations are themselves dangerous and in part because they are admissions of a major failure. But with natural disasters you have many people moving about in panic anyway. They have no place to go. Traffic lights aren’t working. Roads are closed. Transport is disrupted. Police have other responsibilities. Many are seeing to their own families. Only gravest danger would justify an evacuation at such a moment.
The viability of US emergency plans at densely populated reactor sites may have to be reexamined to determine whether they can be implemented in the context of a nuclear accident precipitated by a natural disaster. This was always a theoretical possibility. Now it’s real.
Update: 50,000 people and 12 miles have been evacuated from the vicinity of the destabilized nuclear plants.