Fukushima Daiichi nuclear disaster

Blamed on the wave. The backup generators sat in the basement, below a seawall long known to be too low.

Tightly coupled systems where one small fault cascades and takes down the whole machine.

Room: Q3 Engineered
Year: 2011
Impact: 159,128 evacuated
Sector: Nuclear power
Region: Asia-Pacific
Category: Environmental

Why this room

The engineered-failure classification rests on common-cause defeat of redundancy: a single external event removed every layer of the backup at once. Ten of the thirteen emergency diesel generators were water-cooled and sited in basement levels of the turbine and reactor buildings, so the inundation that overtopped the site took out AC power, seawater pumps and instrumentation simultaneously, and station blackout propagated to loss of core cooling, meltdown in three units and hydrogen explosions. The site's design basis tsunami was 5.7 m (itself revised up from 3.1 m in 2002) against run-up of roughly 15 m. Redundancy that shares a location and a failure mode is not redundancy, which is the q3 lesson.

The record

The NAIIC concluded the accident 'cannot be regarded as a natural disaster. It was a profoundly manmade disaster - that could and should have been foreseen and prevented', and that 'the direct causes of the accident were all foreseeable prior to March 11, 2011'.certain
The NAIIC found that since 2006 the regulators and TEPCO were aware that a total loss of electricity at Fukushima Daiichi could occur if a tsunami reached the level of the site, and were aware of core-damage risk from loss of seawater pumps, but no regulations were created and TEPCO took no protective steps.certain
The plant's design basis tsunami height was 5.7 m (revised upward from an original 3.1 m in 2002); the 11 March 2011 tsunami reached roughly 15 m at the site, following a magnitude 9.0 earthquake.high
A total of 146,520 residents were evacuated under government evacuation orders; the NAIIC puts the total evacuated in response to the accident at approximately 150,000. Fukushima Prefecture records a peak of about 160,000 evacuees in May 2012, and 23,410 still displaced as of 1 February 2026.certain
An estimated 167 workers were exposed to more than 100 millisieverts while dealing with the accident, and as much as 1,800 square kilometres of Fukushima Prefecture was contaminated at a cumulative dose of 5 mSv/year or higher.certain

Sources

The book

This entry is one of 111 in the register. The full story, and what it cost the people who lived it, is in Risky Business by Claudia Zeisberger, David Munro and Joanna Reijgersberg-Siew.

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