The Fukushima Daiichi nuclear power plant, located in the towns of Futaba and Ohkuma, 250km north of Tokyo, Japan, was operational from 1979 until it was damaged by the Great East Japan Earthquake in March 2011.
Fukushima Daiichi was the first nuclear power plant to be constructed and operated entirely by Tokyo Electric Power Company (TEPCO). It is now being decommissioned, which is expected to take at least 30 years for completion.
Fukushima Daiichi nuclear power plant make-up
The 4,696MW Fukushima Daiichi nuclear power station was equipped with six GE-designed boiling water reactor (BWR) units.
The unit one, with an installed capacity of 460MW, was commissioned in 1971. It was scheduled for closure in 2011, but was granted an extension of further ten years by the Japanese regulators in February 2011.
Units two, three, four and five had 784MW installed capacity each. Units two and three were commissioned in 1974 and 1976 respectively, whereas units four and five were brought into operation in 1978.
The unit six, with an installed capacity of 1,100MW, was commissioned in 1979.
The containment structure for units 1 to 5 was of Mark I configuration, whereas unit six featured Mark II containment structure.
The unit one reactor core contained 400 fuel assemblies, while the units two, three, four and five were operated with 548 fuel assemblies, whereas the unit 6 reactor core contained 764 fuel assemblies.
The reactor fuel used by all units was low enriched uranium (LEU), except for unit three, which used plutonium mixed-oxide (MOx) fuel from 2010 onwards.
The power station fed electricity to the national grid via the 500kV Shin-Fukushima substation.
Contractors involved with the Fukushima Daiichi nuclear power plant
GE provided the reactor design for all six generating units of the nuclear power plant.
The architectural design for all the reactor units was provided by Ebasco.
GE supplied the units one, two and six, whereas units three and five were supplied by Toshiba and unit 4 by Hitachi.
Kajima was responsible for the construction of the nuclear complex.
Fukushima Daiichi boiling water reactor (BWR) details
The boiling water reactor (BWR) technology was introduced by General Electric (GE) in the 1960s.
BWRs work as direct cycle reactors, which pass the steam generated inside the reactor directly to the turbine for power generation, unlike pressurised water reactors (PWR).
Jointly developed by Hitachi and GE, the generation III+ BWRs, known as advanced boiling water reactors (ABWR), have been designed to higher levels of safety to prevent and mitigate consequences of severe accidents.
GE Hitachi Nuclear Energy, a global nuclear alliance created by General Electric and Hitachi in June 2007, is the leading manufacturer of ABWRs.
As of August 2018, a total of 75 boiling water reactor units were in operation worldwide and four units (two in Taiwan and two in Japan) were under construction, with several new nuclear power plants, including the Wylfa Newydd nuclear power plant in the UK, proposed to use ABWR technology.
Fukushima Daiichi nuclear disaster details
The Fukushima Daiichi nuclear disaster was triggered by the 9.1 magnitude Great East Japan Earthquake and the resulting 15m-high tsunami on the afternoon of 11 March 2011.
The power station, built approximately 10m above sea level, was flooded with tsunami. The units 1, 2 and 3, which were in operation at the time of the disaster, were automatically shut down.
The supply of off-site power to the Fukushima Daiichi nuclear power plant was cut off meanwhile, while emergency diesel generators located at the basement of the turbine building, roughly 5m above the sea level, which are intended to provide back-up electricity to the plant's cooling system, were disabled by tsunami flooding.
The absence of cooling led to melt down of units 1, 2 and 3 within the following three days.
The unit 1 suffered a massive hydrogen explosion on 12 March 2011, which caused extensive damage to the 1m-thick reactor building walls.
It was followed by another hydrogen explosion at the unit 3 reactor on 14 March 2011, which led to the explosion of unit 4 with gas flowing from unit 3 into the unit 4 reactor.
The hydrogen explosions at the plant led to massive release of radioactive Iodine-131 and Caesium-137, with radiation levels rising to 1015 microsievert.
More than 80,000 residents within 30 km radius from the power plant were evacuated after the disaster.
In December 2011, TEPCO along with the government officially announced the cold shutdown (below 100oC) of all six reactor units.