The Fukushima Daiichi nuclear disaster was a catastrophic failure at the Fukushima Daiichi Nuclear Power Plants on 11 March 2011. The nuclear power plant was located on a 3.5-square-kilometre site in the towns of Okuma and Futaba in the Futaba District of Fukushima Prefecture, Japan. There were altogether 10 nuclear reactors, with 5 reactors using old designs and the rest using new designs.
All the Fukushima plants, including the newer plants, were all based on General Electric(GE) designs. A lucrative contracts had been made between General Electric and Tokyo Electric Power Co (Tepco) to service the GE nuclear plants in Japan. General Electric is an American multinational conglomerate corporation incorporated in Schenectady, New York and operates through four divisions: Energy, Technology Infrastructure, Capital Finance and Consumer and Industrial.
The oldest Fukushima nuclear reactor was built at 1960s. Unit 1-5 reactors were built with the older design, GE(General Electric) Mark 1 design. To keep the reactors compact and economical, the Mark 1 design had its reactor buildings small. Instead of putting the generators inside the reactor buildings, they are put into neighbouring structures that house turbines. Unfortunately, the turbine buildings were far less sturdy, especially their doors. On the other hand, the reactor buildings were built strong and stable, with thick concrete walls and dual sets of sturdy doors. However, even though the reactor building itself had strong protection, backup power generators are critical safety equipment and it should have been put inside the reactor buildings. The cooling systems of the nuclear plants run on electricity which pulled from the nation's power grid. For situation when the power grid fails, on-site diesel generators have to kick in and run the cooling system.
Tepco engineers were very dissatisfied with Mark 1 design because of the limited space inside the reactor buildings. Hence, from no.6 to no.10 nuclear reactors, Mark II design was used. With Mark II design, the reactor buildings are large enough to accommodate the backup generators. The last 4 reactors that started building at Fukushima Daini complex about seven miles away in the late 1970s also further improved its design on Mark II, and had better protection against earthquakes and tsunamis.
Over the years, Japanese governement had tightened the standards for earthquake preparedness a few times and updated the plants. The older reactors with Mark I design were rated Class B for a lower earthquake-preparedness rating while the new reactors with Mark II design were graded Class S. According to the interviews after the Fukushima nuclear disaster, the Tepco's top engineers that guided the company's nuclear division were all well aware of the inconsistent placement of the diesel generators at Fukushima Daiichi between reactor No.6 and the older reactors 1 through 5. However, they didn't point out the vulnerable Mark I design and...