What was the fukushima disaster?

Answer 1

The Fukushima disaster is a series of three meltdowns at the Fukushima Daiichi Nuclear Power Plant in Fukushima prefecture, Japan.

The plant at Fukushima was built with its emergency equipment in the basement, because this was the safest place in the building. Unfortunately, no one thought to protect this equipment from flooding.

This error was compounded by the fact that the plant was protected from being flooded by a tsunami by a 5.7 meter seawall, which was clearly inadequate on a coast that is regularly hit by tsunamis of much greater wave height. The tsunami that it had a wave height of 14 meters at the plant, but the wave was 38.9 meters on a part of the coast closer to the epicenter of the earthquake.

When the wave struck, it went right over the seawall and swamped the plant, filling the basements with water, and rendering the equipment useless. The earthquake, which had a magnitude of 9.0 at the epicenter and about 6.6 at the plant, wrecked roads, power lines, and other infrastructure, making it impossible to bring emergency equipment to the plant.

Both the reactors and the spent fuel pools require constant cooling. Because there was no electrical power, and no pumps to circulate water, the reactors overheated, and the fuel began to melt.

When the fuel melts, it can burn through its containment, and reacts chemically with steam to produce hydrogen. The hydrogen mixed with the air in the reactor buildings. Vents that were supposed to move the hydrogen out failed to operate, and the hydrogen-air mixture exploded in three of the buildings, two that were in operation at the time of the earthquake, and one that was not.

Three reactors melted down, and the spent fuel pool of one reactor that was out of service appears to have had fuel melting problems. The containments were breached, and radioactive materials were able to get out. Since there was no way to circulate water, and cooling was needed, a constant flow of fresh or salt water was pumped into the reactors and spent fuel pools to prevent further damage. This created a huge inventory of highly radioactive water.

Radioactive material was blown as far as 1.6 kilometers (1 mile) from the plant by the explosions, but other materials worsened the contamination, and large areas of Japan have been evacuated. Small particles, called "fuel fleas" have been carried thousands of miles by the wind, and these increase the chances of people who inhale them of getting cancer.

After 100 days, the situation is still not under complete control, and there is some worry that it can get worse again. With changes in the prevailing winds, which had been pushing most of the pollution out to sea, there is some chance of greater areas having to be evacuated. It is regarded as unlikely that any major areas will have to be evacuated, but we will not know for some time how things will play out.

The cause of the failure is clearly inadequate engineering based on a misjudgment of the potential for tsunami in the area of the plant. Because the engineering was altered at the Fukushima Daini plant, preventing the plant from being similarly destroyed, we can know that the problems were understood at some time after the plant was built, but were not corrected at the plant; this indicates a serious failure of the regulatory system in place.