Rail cars that should have been full arrived empty, and an operatorerror threw a network carrying 200, 000 of them into gridlock, snarling traffic along the east coast.
The passive feature means they rely less on electrically driven pumps and valves, for safety, and more on systems designed to shut down plants safely in emergencies and to prevent operatorerror.
It isn't known if operatorerror played a role, as it did three decades ago at Three Mile Island, but it's clear the earthquake exceeded the level for which the plant was designed.