Fukushima Daiichi nuclear disaster
(From Wikipedia) The plant comprised six separate
boiling water reactors originally designed by
General Electric (GE) and maintained by the
Tokyo Electric Power Company (TEPCO). At the time of the earthquake, reactor 4 had been de-fueled and reactors 5 and 6 were in cold
shutdown for planned maintenance.
[18] Immediately after the earthquake, following government regulations, the remaining reactors 1–3 shut down their sustained
fission reactions automatically, inserting
control rods in what is termed the
SCRAM event, following this, emergency generators came online to power electronics and coolant systems, which operated right up until the tsunami. The tsunami arrived some 50 minutes after the initial earthquake. The 13
meter tall tsunami overwhelmed the plant's
seawall, which was only 10 m high,
[6] with the moment of the tsunami striking being caught on camera.
[19] The tsunami water quickly flooded the low-lying rooms in which the emergency generators were housed.
[20] With the flooded
diesel generators failing soon afterwards, cutting power to the critical pumps that must continuously circulate
coolant water through a
Generation II reactor to keep the
fuel rods from melting down following the
SCRAM event, the rods remained hot enough to melt themselves down as no adequate
cold sink was available. After the secondary emergency pumps (run by back-up electrical
batteries) ran out, one day after the tsunami, 12 March,
[21] the water pumps stopped and the
reactors began to overheat due to the high
decay heat produced in the first few days after the
SCRAM (diminishing amounts of this decay heat continue to be released for years, but with time it is not enough to cause fuel rod melting).
TEPCO admitted for the first time on October 12, 2012 that it had failed to take stronger measures to prevent disasters for fear of inviting lawsuits or protests against its nuclear plants. There are no clear plans for decommissioning the plant, but some estimates extend to thirty or forty years.
On 22 July 2013, more than two years after the incident, it was revealed that the plant is leaking radioactive water into the Pacific Ocean. This had been denied by TEPCO.
[30] The report prompted Japanese Prime Minister
Shinzō Abe to order the government to step in.
[31] On 20 August, in a further incident, it was announced that 300
metric tons of heavily radioisotope-contaminated water had leaked from a storage tank.
[32] On 26 August, the government took charge of emergency measures to prevent further radioactive water leaks.