A wave the seawall could not stop
The disaster at Fukushima Daiichi began with the magnitude 9.0 earthquake of 11 March 2011, which triggered automatic shutdowns at the plant’s reactors as designed. The greater threat arrived roughly fifty minutes later, when a tsunami reported at thirteen to fourteen metres struck the site and overtopped the plant’s seawall, flooding the turbine buildings that housed critical backup systems. This flooding destroyed ten of the plant’s thirteen emergency diesel generators along with DC battery backups in three of the reactor units, eliminating the power needed to keep reactor cooling systems running once the earthquake had already cut off the plant’s normal electricity supply from the grid.
Three reactors melt down in four days
Without power for cooling, the reactors began to fail in sequence over the following days. Unit 1 lost all AC and DC power by mid-afternoon on 11 March, and after roughly twelve hours without effective cooling, fuel melting began, culminating in a hydrogen explosion that damaged the reactor building on 12 March. Unit 2 maintained a form of steam-driven cooling longer before that system failed after some sixty-eight hours, with an explosion following on 15 March. Unit 3 saw its DC power partially restored using replacement batteries on 13 March, but its cooling system failed after twenty and a half hours regardless, producing a hydrogen explosion on 14 March. Units 5 and 6 avoided meltdown and reached cold shutdown by 20 March.
The worst release since Chernobyl
The radioactive material released into the atmosphere during these events was substantial, including an estimated seven to twenty petabecquerels of caesium-137, one hundred to four hundred petabecquerels of iodine-131, and six thousand to twelve thousand petabecquerels of xenon-133. The United Nations Scientific Committee on the Effects of Atomic Radiation has characterised Fukushima as the worst nuclear accident since the 1986 Chernobyl disaster, a comparison based on the scale of radioactive material released rather than on any equivalence in the human casualties directly caused by radiation exposure, which the two accidents’ records differ on considerably.
A hundred and sixty-four thousand people displaced
The practical human consequence of the accident was a mass evacuation covering a wide area around the damaged plant. Approximately 164,000 residents were displaced at the evacuation’s peak in June 2012, a figure that captures the scale of communities uprooted by exclusion zones established around Fukushima Daiichi as officials worked to limit public exposure to radioactive contamination spreading from the site. This evacuation removed entire towns from ordinary habitation for years, with some areas remaining restricted long after the immediate crisis at the plant itself had been brought under control, reflecting the slow pace at which radioactive contamination in soil and infrastructure could be meaningfully reduced to levels considered safe for permanent return.
The evacuation killed more than the radiation did
The evacuation itself, rather than radiation exposure, proved to be the accident’s most immediately lethal consequence. At least fifty-one deaths are attributed directly to the evacuation process, with the toll falling disproportionately on elderly hospital patients who were relocated without adequate ongoing medical support during the disruption. This finding highlights a genuinely difficult tension in disaster response: the same evacuation ordered specifically to protect the population from radiation exposure ended up causing more documented deaths, at least in this immediate accounting, than the radiation itself has been confirmed to cause, a pattern relevant to how future nuclear emergency planning weighs the risks of relocation against the risks of remaining in place.
No confirmed radiation deaths, but a decade of displacement
Longer-term health assessments from the UN Scientific Committee have found no adverse health effects among Fukushima residents that can be directly attributed to radiation exposure, a notably firm official conclusion given the scale of public concern the accident generated worldwide. One worker who died of lung cancer four years later, following recorded exposure of 74 millisieverts, remains a disputed case regarding causation, and six other workers developed cancer or leukaemia following the accident. The recovery has proven expensive and prolonged regardless of the radiation findings: cleanup costs are estimated at roughly twenty trillion yen, around 180 billion dollars, with fuel removal and contaminated water treatment still ongoing, and more than 41,000 people remained living as evacuees a full decade after the accident occurred.