Documents released by the Tokyo Electric Power Co. this week show the panic that struck the utility when the March 11 earthquake and tsunami hit, The New York Times reports.
The venting system, built by General Electric, used the same power source as the rest of the plant, backup generators in basements that were vulnerable to tsunamis. The earthquake also may have damaged the valves, Tepco said.
When the vents failed at Fukushima, the hydrogen gas fueled explosions that spewed radioactive materials into the atmosphere.
U.S. officials had said American reactors would be spare such disasters by new and stronger venting systems. But Tepco now says Fukushima installed the same vents years ago, the Times reported.
"Japan is going to teach us lessons," said David Lochbaum of the Union of Concerned Scientists. "If we're in a situation where we can't vent where we need to, we need to fix that."