In response to the early events of this accident, Japanese government declared a nuclear emergency situation and established the Nuclear Emergency Response Headquarters (NERHQ), which instructed the Fukushima Prefectural Governor and relevant local governments to issue an evacuation order to citizens from the nearby Fukushima Daiichi NPS.[12]
Significant amounts of radioactive material have also been released into ground and ocean waters. Measurements taken by the Japanese government 30–50 km from the plant showed
caesium-137 levels high enough to cause concern, leading the government to ban the sale of food grown in the area.[13][14]
A few of the plant's workers were severely injured or killed by the disaster conditions resulting from the earthquake. There were no immediate deaths due to direct radiation exposures, but at least six workers have exceeded lifetime legal limits for radiation and more than 300 have received significant radiation doses. Predicted future cancer deaths due to accumulated radiation exposures in the population living near Fukushima have ranged from none[15] to 100[16] to a non-peer-reviewed "guesstimate"[17] of 1,000. On 16 December 2011, Japanese authorities declared the plant to be stable, although it would take decades to decontaminate the surrounding areas and to decommission the plant altogether.[18]
A process overview of the accident
At the Fukushima Daiichi NPS, all the off-site power supply was lost due to the earthquake.
Later, the subsequent arrival of the tsunami caused flooding of many cooling seawater pumps, emergency diesel generators (EDGs), and power panels which were housed in low-lying rooms.[19]
This resulted in the total loss of AC power at Units 1 through 5.
As
nuclear reactor coolant systems stopped for a long time from cutting power, the
reactors overheated due to the normal high radioactive
decay heat produced[20] in the first few days after nuclear reactor shutdown.[21]
As the water boiled away in the reactors and the water levels in the
fuel rod pools dropped, the reactor fuel rods began to overheat severely, and to melt down. In the hours and days that followed, Reactors 1, 2 and 3 experienced full
meltdown.[22][23]
In the intense heat and pressure of the melting reactors, a reaction between the nuclear fuel metal cladding and the remaining water surrounding them produced explosive hydrogen gas. As workers struggled to cool and shut down the reactors, several
hydrogen-air chemical explosions occurred.[24][25]
Investigation Groups
National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission
On 5 July 2012, NAIIC released an executive summary report[27] of The Fukushima Nuclear Accident. The panel is due to deliver its final report at the end of July.[28]
Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company
On 2 December 2011, ICANPS issued an interim report.[30] On 23 July 2012, the government appointed the committee submitted its final report to the Japanese government.[31]
TEPCO Internal Investigation
On 20 June 2012, TEPCO released its final internal investigation report. In the report, TEPCO complained that top politicians, including the prime minister, interfered with recovery efforts during the initial stages of the disaster by making specific requests that were out of touch with what was actually taking place at the plant. TEPCO concluded that the direct cause of the accident was the tsunami which knocked out the reactors' cooling system. TEPCO also admitted that it was at fault in not being prepared for the situation, but said that its workers did the best they could "amid unprecedented circumstances."[32]
As part of the government inquiry, the
House of Representatives of Japan's special science committee directed TEPCO to submit to them its manuals and procedures for dealing with reactor accidents. TEPCO responded by submitting manuals with most of the text blotted out. In response, the
Nuclear and Industrial Safety Agency ordered TEPCO to resubmit the manuals by 28 September 2011 without hiding any of the content. TEPCO replied that it would comply with the order.[36]
On 24 October
NISA published a large portion of Tokyo Electric Power Company's procedural manuals for nuclear accidents. These were the manuals that the operator of the Fukushima Daiichi nuclear power plant earlier did send to the Lower House with most of the contents blacked out, saying that this information should be kept secret to protect its intellectual property rights, and that disclosure would offer information to possible terrorists. NISA ordered TEPCO to send the manuals without any redaction, as the law orders. 200 pages were released from the accident procedural manuals used for Fukushima Daiichi nuclear power plant. All their contents were published, only the names of individuals were left out.[37]
The agency said, the decision to publish the manuals was taken, for transparency in the search what caused the nuclear accident in Fukushima and also to establish better safety measures for the future.[38]
On 24 October 2011 the first meeting was held by a group of 6 nuclear energy specialists invited by
NISA to discuss the lessons to be learned from the accidents in Fukushima.[39]
On 28 February 2012, the Independent Investigation Commission on the Fukushima Nuclear Accident by the Rebuild Japan Initiative Foundation announced an investigation report.[40]
Oregon's
United States SenatorRon Wyden toured the plant and issued a statement that the situation was "worse than reported." He sent a letter to Japanese Ambassador Ichiro Fujisaki urging Japan to seek international help to relocate spent fuel rods stored in unsound structures and prevent leakage of dangerous nuclear material.[41][42]
^"IAEA Update on Japan Earthquake".
Archived from the original on 14 March 2011. Retrieved 16 March 2011. As reported earlier, a 400 millisieverts (mSv) per hour radiation dose observed at Fukushima Daiichi occurred between 1s 3 and 4. This is a high dose-level value, but it is a local value at a single location and at a certain point in time. The IAEA continues to confirm the evolution and value of this dose rate .... because of this detected value, non-indispensable staff was evacuated from the plant, in line with the Emergency Response Plan, and that the population around the plant is already evacuated.
^
The Japanese government estimates the total amount of radioactivity released into the atmosphere was approximately one-tenth as much as was released during the Chernobyl disaster.
^In May 2012, TEPCO reported that at least 900
PBq had been released "into the atmosphere in March last year [2011] alone" although it has been said staff may have been told to lie, and give false readings to try and cover up true levels of radiation.
^
The accident was initially assessed by Japanese officials as Level 4 on the
International Nuclear Event Scale (INES).
Later, the level was raised to 5 and eventually to 7, the maximum scale value.
^Immediately after the earthquake, the remaining Units 1-3
shutdown automatically, and emergency generators came online to control electronics and coolant systems.
By the way, Units 1-3 were operating at the time of the accident; Units 4, 5 and 6 were in planned shutdown.
IAEA(2015) p.1
^smaller amounts of this heat normally continue to be released for years, but are not enough to cause fuel melting.
^F. Tanabe, Journal of Nuclear Science and Technology, 2011, volume 48, issue 8, pages 1135 to 1139
TEPCO did not make sufficient preparations to cope with critical nuclear accidents.
After the batteries and power supply boards were inundated on 11 March, almost all electricity sources were lost
TEPCO did not envision such a power failure or any kind of prolonged power loss.
TEPCO thought that in a serious incident, venting pressure in the reactor containment vessels or carrying out other safety procedures would still be possible, because emergency power sources would still be available.