Accidents, Paradoxes and the Epistemic Future of Nuclear Policy

On March 11, 2011, at 2:46 pm Japan Standard Time an earthquake measuring 8.9 struck just off the east coast of Japan. At the time of the earthquake, three reactors were in operation at the Tokyo Electric Power Company (TEPCO) owned Fukushima Daiichi site. Three others were shut down and undergoing scheduled inspections. All six reactors at the site were boiling water reactors based on American General Electric designs. The peak ground acceleration resulting from the earthquake caused the three operating reactors at the Fukushima Daiichi plant to shut down automatically.

The earthquake also damaged the transmission towers with an immediate loss of offsite power supply to the plant. Following this loss of power, the Emergency Diesel Generators (EDGs) at each of the three operating reactor units started up automatically to remove the decay heat from the recently shut down reactors as well as to cool the spent fuel pools.

A tsunami caused by the earthquake arrived at the Fukushima Daiichi plant site approximately 45 minutes after the earthquake. The maximum wave height of the tsunami, 49 feet (15 meters), exceeded the height of the 16 foot (5 meter) sea wall around the plant. Seawater surged over the seawall, submerged and damaged the EDGs and units 1 through 5 lost AC power. The tsunami water also disabled two out of three EDGs at unit 6 (but the remaining EDG, which was air-cooled and located at a slightly higher elevation, supplied emergency AC power to reactor units 5 and 6.)

Despite efforts to depressurize the reactors and inject water into the core, fuel temperatures began to rise in reactor units 1, 2 and 3. The overheating caused the zirconium in the fuel cladding and the steam to react and produce hydrogen.

On March 12, a hydrogen explosion in the Unit 1 reactor destroyed the reactor building.

Hydrogen explosions also occurred on March 14 at Unit 3, and at Unit 4 on March 15.

Overheating of the fuel ultimately led to fuel melting in units 1, 2 and 3. The accident was rated at level 7, which is the maximum possible level on the International Atomic Energy Agency’s International Nuclear Event Scale. While estimates of the damages caused by the accident vary, they are upwards of ¥20 trillion Japanese yen or close to $200 billion American dollars. Yet even these estimates do little to capture the massive human displacements and resettlements caused by the accident.

I am a nuclear engineer by training, albeit one with a sociological imagination. I work at the intersection of technology and policy, and attempt also to work at the intersection of engineering and the social sciences. Specifically, in my work, I have studied how designers of nuclear reactors make decisions in the foundational early stages of design – particularly how they think about risk and safety.

When accidents, particularly nuclear accidents, occur, there is a desire, even an imperative almost, to identify the ‘root causes’ of that particular accident. This is not entirely surprising because such accidents cause existential crises sector-wide or industry-wide that reflect the desire to never repeat the mistakes that led to such a severe outcome. However, identifying the root causes of an accident is seldom possible. The causes of an accident are typically large in number and complex in relationship to each other.