Station Blackout: All Power Lost to Reactor Cooling

With AC and DC power lost on Units 1–4, operators at Fukushima Daiichi faced a station blackout (SBO)—a condition the plant was not adequately designed to handle for extended duration. Reactor Isolation Cooling (RCIC) systems on Units 2 and 3 operated briefly on residual steam, but without power for sustained injection. Unit 1's IC (Isolation Condenser) was operated intermittently; the full extent of its operation was later disputed. Fuel heating began almost immediately after shutdown.