In the control room where operators managed reactor 1, the alarms went silent. The overhead lights blinked off, and the indicator lights on the instrument panels faded away. The floodwaters had even knocked out the control room's batteries, the power source of last resort. The operators would have to respond to the emergency without working instruments. [...]
As the operators surveyed the damage, they quickly realized that the diesel generators couldn't be salvaged and that external power wouldn't be restored anytime soon. In the plant's parking lots, workers raised car hoods, grabbed the batteries, and lugged them back to the control rooms. They found cables in storage rooms and studied diagrams. If they could connect the batteries to the instrument panels, they could at least determine the water levels in the pressure vessels.
The rest of Fukushima Dai-ichi now faced a cataclysmic scenario that nuclear power plant operators have long feared but never experienced: a complete station blackout.