Investigations into the Fukushima nuclear accident: Difference between revisions

Investigations into the Fukushima nuclear accident
	Satellite image on 16 March 2011 of the four damaged reactor buildings
Date	11 March 2011
Location	Futaba-machi and Okuma-machi, Futaba-gun, Fukushima Prefecture, Japan
Outcome	INES Level 7 (ratings by Japanese authorities as of 11 April)
Non-fatal injuries	37 with physical injuries,; 2 workers taken to hospital with radiation burns

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Investigations into the Fukushima Daiichi Nuclear Disaster (or Accident)^[4] began on March 11, 2011 when a series of equipment failures, core melt and down, and releases of radioactive materials occurred at the Fukushima Daiichi Nuclear Power Station from the 2011 off the Pacific coast of Tohoku Earthquake and tsunami on the same day.^[5]^[6]

Introduction

In Japan, the 2011 off the Pacific coast of Tohoku Earthquake occurred at 14:46 on 11 March 2011.^[7] At the Fukushima Daiichi Nuclear Power Station (Fukushima Daiichi NPS),^[8] operated by the Tokyo Electric Power Company (TEPCO), the earthquake and tsunami caused the compound accident (hereinafter called Fukushima Daiichi Nuclear Accident) consisting of Station BlackOut (SBO) incident, Unit 1, 2, 3 severe core damage accidents, Unit 1, 2, 4 hydrogen explosion accidents, radioactive releases^[9]^[10] and so on.^[11]

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 Unit1 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

The National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) was established by the National Diet of Japan as the first independent investigation commission on December 8, 2011.^[26]

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

The Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company (ICANPS) was established by the Cabinet decision on May 24, 2011.^[29]

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]

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.^[33]^[34]^[35]

Others

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 a investigation report.^[40]

Oregon's United States Senator Ron 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]

Notes and References

^ "Fukushima accident upgraded to severity level 7". IEEE Spectrum. 12 April 2011. Archived from the original on 11 March 2014. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "IAEA Update on Japan Earthquake". Archived from the original on 12 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. It should be noted that 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. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "Radiation-exposed workers to be treated at Chiba hospital". Kyodo News. 25 March 2011. Archived from the original on 17 February 2013. Retrieved 17 April 2011. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Fukushima Daiichi Nuclear Accident (福島第一原子力発電所事故, Fukushima Dai-ichi ( pronunciation ) genshiryoku hatsudensho jiko)
^ "Explainer: What went wrong in Japan's nuclear reactors". IEEE Spectrum. 4 April 2011. Archived from the original on 4 July 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ It is the largest nuclear disaster since the Chernobyl disaster of 1986.
"Japan's unfolding disaster 'bigger than Chernobyl'". New Zealand Herald. 2 April 2011.
"Analysis: A month on, Japan nuclear crisis still scarring" Archived 18 April 2011 at WebCite International Business Times (Australia). 9 April 2011, retrieved 12 April 2011; excerpt, According to James Acton, Associate of the Nuclear Policy Program at the Carnegie Endowment for International Peace, "Fukushima is not the worst nuclear accident ever but it is the most complicated and the most dramatic...This was a crisis that played out in real time on TV. Chernobyl did not." "Archived copy". Archived from the original on 18 April 2011. Retrieved 18 April 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)CS1 maint: archived copy as title (link)
^ This name of the earthquake is chosen by Japan Meteorological Agency(JMA). By a cabinet decision, the Japanese government has approved the use of expression "Great East Japan Earthquake" in reference to the disaster, including the Fukushima Daiichi nuclear disaster, caused by this earthquake. ICANPS(2011) p.19
^ The power station has six boiling water reactors (BWRs) originally designed by General Electric (GE) and Toshiba.
^ 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.
Frank N. von Hippel (September/October 2011 vol. 67 no. 5). "The radiological and psychological consequences of the Fukushima Daiichi accident". Bulletin of the Atomic Scientists. pp. 27–36. Archived from the original on 20 December 2011. {{cite web}}: Check date values in: |date= (help); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ 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.
"TEPCO puts radiation release early in Fukushima crisis at 900 PBq". Kyodo News. 24 May 2012. Archived from the original on 24 May 2012. Retrieved 24 May 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ 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.
Justin McCurry. Japan raises nuclear alert level to seven. The Guardian. 12 April 2011 Archived March 11, 2013, at the Wayback Machine

'Now radiation in Japan is as bad as radiation level is raised to 7 for only the second time in history' Daily Mail 12 April 2011.
^ ICANPS(2011) p.303
^ Japan mulls Fukushima food ban: IAEA, Reuters, 19 March 2011 Archived 19 March 2011 at WebCite
^ Kevin Krolicki (24 May 2012). "Fukushima radiation higher than first estimated". Reuters. Archived from the original on 15 October 2013. Retrieved 24 May 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "Trauma, Not Radiation, Is Key Concern In Japan". NPR. 9 March 2012. Archived from the original on 9 March 2014. Retrieved 15 April 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Caracappa, Peter F. (28 June 2011), "Fukushima Accident: Radioactive Releases and Potential Dose Consequences" (PDF), ANS Annual Meeting, retrieved 13 September 2011
^ "The Cost of Fear: The Framing of a Fukushima Report". 15 March 2012. Archived from the original on 5 May 2014. Retrieved 15 April 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "Japan PM says Fukushima nuclear site finally stabilised". BBC Online. 16 December 2011. Archived from the original on 20 February 2014. Retrieved 7 January 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ 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
^ "3 nuclear reactors melted down after quake, Japan confirms". CNN. 7 June 2011. Archived from the original on 14 April 2014. Retrieved 13 July 2011. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "'Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown". Yomiuri. 8 June 2011. Archived from the original on 15 June 2011. Retrieved 8 June 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "Fukushima nuclear accident update log, updates of 15 March 2011". IAEA. 15 March 2011. Archived from the original on 9 April 2011. Retrieved 8 May 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Hydrogen explosions Fukushima nuclear plant: what happened? Archived December 2, 2013, at the Wayback Machine
^ A profile description in the NAIIC top page.
^ NAIIC_summary(2012)
^ Wakatsuki, Yoko. "Japanese parliament report: Fukushima nuclear crisis was 'man-made'". CNN. Archived from the original on 2014-02-03. Retrieved 7/5/2012. {{cite news}}: Check date values in: |accessdate= (help); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ ICANPS_summary(2011) p.1
^ "Report: U.S. nuclear renaissance unlikely after Fukushima". LA Times. 28 December 2011. Archived from the original on 24 January 2014. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "UPDATE: Government panel blasts lack of 'safety culture' in nuclear accident". The Asahi Shimbun. 23 July 2012. Archived from the original on 13 April 2014. Retrieved 29 July 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Nagata, Kazuaki, "Tepco lashes prime minister's office", Japan Times, 21 June 2012, p. 1 Archived November 1, 2012, at the Wayback Machine
^ Fackler, Martin (12 October 2012). "Japan Power Company Admits Failings on Plant Precautions". The New York Times. Archived from the original on 6 October 2014. Retrieved 13 October 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Sheldrick, Aaron (12 October 2012). "Fukushima operator must learn from mistakes, new adviser says". Reuters. Archived from the original on 9 March 2014. Retrieved 13 October 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Yamaguchi, Mari (12 October 2012). "Japan utility agrees nuclear crisis was avoidable". Boston.com. Associated Press. Archived from the original on 5 October 2013. Retrieved 13 October 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ Jiji Press, "Tepco must submit reactor accident manuals without deleted portions", Japan Times, 28 September 2011, p. 2.
^
From these documents could be concluded:
- 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.
^ NHK-world (24 October 2011) Parts of TEPCO's accident manuals made public. Archived 24 June 2011 at WebCite
^
Their first remarks were:
- Japanese nuclear power plants should have multiple power sources
- plants should be able to maintain electricity during an earthquake or other emergencies
- TEPCO should examine why the equipment failed to work and should take appropriate actions to prevent such failures in the future
^ The Independent Investigation Commission on the Fukushima Nuclear Accident
^ Phred Dvorak, Fukushima Daiichi’s Achilles Heel: Unit 4′s Spent Fuel?, Wall Street Journal, 17 April 2012. Archived March 12, 2014, at the Wayback Machine
^ After Tour of Fukushima Nuclear Power Station, Wyden Says Situation Worse than Reported, from Office of United States Senator Ron Wyden, 16 April 2012. Archived April 4, 2014, at the Wayback Machine

Sources

National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) [国会事故調]

NAIIC (2012). Executive summary (PDF).
NAIIC (2012). Main Report.

Investigation Committee on the Accident at Fukushima Nuclear Power Stations of Tokyo Electric Power Company (ICANPS) [政府事故調]

ICANPS (2011). Executive Summary of the Interim Report.
ICANPS (2011). Interim Report (Main text).
- 淵上正朗; 笠原直人; 畑村洋太郎 (2012). 福島原発で何が起こったか政府事故調技術解説. 日刊工業新聞社. (Technical Commentary)
- 畑村洋太郎; 安部誠治; 淵上正朗 (2013). 福島原発事故はなぜ起こったか政府事故調核心解説. 講談社. (Essential Commentary)

Tokyo Electric Power Company Internal Investigation (TEPCO) [東電社内事故調]

TEPCO (2011). Fukushima Nuclear Accident Analysis Report (Interim Report) (PDF).
- 石川迪夫 (2014). 考証福島原子力事故炉心溶融・水素爆発はどう起こったか. 日本電気協会新聞部. (Unofficial Report)
- Michio Ishikawa (2015). A Study of the Fukushima Daiichi Nuclear Accident Process. Springer. (the improved above in English)

International Investigations

IAEA (2015). The Fukushima Daiichi Accident Report by The Director General (PDF).
NEA (2016). Five Years after the Fukushima Daiichi Accident: Nuclear Safety Improvements and Lessons Learnt (PDF).

External links

Reports published by investigation committees, the Japanese government and TEPCO
IAEA Update on Japan Earthquake
In graphics: Fukushima nuclear alert - Fukushima report: Key points in nuclear disaster report
TerraFly Timeline Aerial Imagery of Fukushima Nuclear Reactor after 2011 Tsunami and Earthquake
PreventionWeb Japan: 2011 Fukushima Daiichi nuclear disaster
"What should we learn from the severe accident at the Fukushima Dai-ichi Nuclear Power Plant?" by Kenichi Ohmae, Team H2O Project. 28 October 2011
Act on Special Measures Concerning Nuclear Emergency Preparedness (Japanese Law Translation)

[1] "Fukushima accident upgraded to severity level 7". IEEE Spectrum. 12 April 2011. Archived from the original on 11 March 2014. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[IAEAtsunami1-2] "IAEA Update on Japan Earthquake". Archived from the original on 12 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. It should be noted that 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. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[3] "Radiation-exposed workers to be treated at Chiba hospital". Kyodo News. 25 March 2011. Archived from the original on 17 February 2013. Retrieved 17 April 2011. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[4] Fukushima Daiichi Nuclear Accident (福島第一原子力発電所事故, Fukushima Dai-ichi ( pronunciation^ⓘ ) genshiryoku hatsudensho jiko)

[5] "Explainer: What went wrong in Japan's nuclear reactors". IEEE Spectrum. 4 April 2011. Archived from the original on 4 July 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[6] It is the largest nuclear disaster since the Chernobyl disaster of 1986.
"Japan's unfolding disaster 'bigger than Chernobyl'". New Zealand Herald. 2 April 2011.
"Analysis: A month on, Japan nuclear crisis still scarring" Archived 18 April 2011 at WebCite International Business Times (Australia). 9 April 2011, retrieved 12 April 2011; excerpt, According to James Acton, Associate of the Nuclear Policy Program at the Carnegie Endowment for International Peace, "Fukushima is not the worst nuclear accident ever but it is the most complicated and the most dramatic...This was a crisis that played out in real time on TV. Chernobyl did not." "Archived copy". Archived from the original on 18 April 2011. Retrieved 18 April 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)CS1 maint: archived copy as title (link)

[7] This name of the earthquake is chosen by Japan Meteorological Agency(JMA). By a cabinet decision, the Japanese government has approved the use of expression "Great East Japan Earthquake" in reference to the disaster, including the Fukushima Daiichi nuclear disaster, caused by this earthquake. ICANPS(2011) p.19

[8] The power station has six boiling water reactors (BWRs) originally designed by General Electric (GE) and Toshiba.

[9] 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.
Frank N. von Hippel (September/October 2011 vol. 67 no. 5). "The radiological and psychological consequences of the Fukushima Daiichi accident". Bulletin of the Atomic Scientists. pp. 27–36. Archived from the original on 20 December 2011. {{cite web}}: Check date values in: |date= (help); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[10] 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.
"TEPCO puts radiation release early in Fukushima crisis at 900 PBq". Kyodo News. 24 May 2012. Archived from the original on 24 May 2012. Retrieved 24 May 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[11] 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.
Justin McCurry. Japan raises nuclear alert level to seven. The Guardian. 12 April 2011 Archived March 11, 2013, at the Wayback Machine

'Now radiation in Japan is as bad as radiation level is raised to 7 for only the second time in history' Daily Mail 12 April 2011.

[12] ICANPS(2011) p.303

[13] Japan mulls Fukushima food ban: IAEA, Reuters, 19 March 2011 Archived 19 March 2011 at WebCite

[Kevin_Krolicki-14] Kevin Krolicki (24 May 2012). "Fukushima radiation higher than first estimated". Reuters. Archived from the original on 15 October 2013. Retrieved 24 May 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[15] "Trauma, Not Radiation, Is Key Concern In Japan". NPR. 9 March 2012. Archived from the original on 9 March 2014. Retrieved 15 April 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[Caracappa-ANS-16] Caracappa, Peter F. (28 June 2011), "Fukushima Accident: Radioactive Releases and Potential Dose Consequences" (PDF), ANS Annual Meeting, retrieved 13 September 2011

[17] "The Cost of Fear: The Framing of a Fukushima Report". 15 March 2012. Archived from the original on 5 May 2014. Retrieved 15 April 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[18] "Japan PM says Fukushima nuclear site finally stabilised". BBC Online. 16 December 2011. Archived from the original on 20 February 2014. Retrieved 7 January 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[19] 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

[20] smaller amounts of this heat normally continue to be released for years, but are not enough to cause fuel melting.

[21] F. Tanabe, Journal of Nuclear Science and Technology, 2011, volume 48, issue 8, pages 1135 to 1139

[22] "3 nuclear reactors melted down after quake, Japan confirms". CNN. 7 June 2011. Archived from the original on 14 April 2014. Retrieved 13 July 2011. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[23] "'Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown". Yomiuri. 8 June 2011. Archived from the original on 15 June 2011. Retrieved 8 June 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[IAEA15March-24] "Fukushima nuclear accident update log, updates of 15 March 2011". IAEA. 15 March 2011. Archived from the original on 9 April 2011. Retrieved 8 May 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[25] Hydrogen explosions Fukushima nuclear plant: what happened? Archived December 2, 2013, at the Wayback Machine

[26] A profile description in the NAIIC top page.

[27] NAIIC_summary(2012)

[Wakatsuki-28] Wakatsuki, Yoko. "Japanese parliament report: Fukushima nuclear crisis was 'man-made'". CNN. Archived from the original on 2014-02-03. Retrieved 7/5/2012. {{cite news}}: Check date values in: |accessdate= (help); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[29] ICANPS_summary(2011) p.1

[30] "Report: U.S. nuclear renaissance unlikely after Fukushima". LA Times. 28 December 2011. Archived from the original on 24 January 2014. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[Asahi20120723-31] "UPDATE: Government panel blasts lack of 'safety culture' in nuclear accident". The Asahi Shimbun. 23 July 2012. Archived from the original on 13 April 2014. Retrieved 29 July 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[32] Nagata, Kazuaki, "Tepco lashes prime minister's office", Japan Times, 21 June 2012, p. 1 Archived November 1, 2012, at the Wayback Machine

[NYT20121012-33] Fackler, Martin (12 October 2012). "Japan Power Company Admits Failings on Plant Precautions". The New York Times. Archived from the original on 6 October 2014. Retrieved 13 October 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[34] Sheldrick, Aaron (12 October 2012). "Fukushima operator must learn from mistakes, new adviser says". Reuters. Archived from the original on 9 March 2014. Retrieved 13 October 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[Yamaguchi20121012-35] Yamaguchi, Mari (12 October 2012). "Japan utility agrees nuclear crisis was avoidable". Boston.com. Associated Press. Archived from the original on 5 October 2013. Retrieved 13 October 2012. {{cite news}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[36] Jiji Press, "Tepco must submit reactor accident manuals without deleted portions", Japan Times, 28 September 2011, p. 2.

[37] From these documents could be concluded:
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.

[38] TEPCO did not make sufficient preparations to cope with critical nuclear accidents.

[39] After the batteries and power supply boards were inundated on 11 March, almost all electricity sources were lost

[40] TEPCO did not envision such a power failure or any kind of prolonged power loss.

[41] 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.

[38] NHK-world (24 October 2011) Parts of TEPCO's accident manuals made public. Archived 24 June 2011 at WebCite

[39] Their first remarks were:
Japanese nuclear power plants should have multiple power sources

plants should be able to maintain electricity during an earthquake or other emergencies

TEPCO should examine why the equipment failed to work and should take appropriate actions to prevent such failures in the future

[44] Japanese nuclear power plants should have multiple power sources

[45] ts should be able to maintain electricity during an earthquake or other emergencies

[46] TEPCO should examine why the equipment failed to work and should take appropriate actions to prevent such failures in the future

[40] The Independent Investigation Commission on the Fukushima Nuclear Accident

[41] Phred Dvorak, Fukushima Daiichi’s Achilles Heel: Unit 4′s Spent Fuel?, Wall Street Journal, 17 April 2012. Archived March 12, 2014, at the Wayback Machine

[42] After Tour of Fukushima Nuclear Power Station, Wyden Says Situation Worse than Reported, from Office of United States Senator Ron Wyden, 16 April 2012. Archived April 4, 2014, at the Wayback Machine

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 {{nihongo|Fukushima Daiichi Nuclear Accident|福島第一原子力発電所事故|[[Fukushima Daiichi Nuclear Power Station|Fukushima Dai-ichi]] ( {{Audio|Fukushima daiichi.ogg|pronunciation|lang=ja|help=no}} ) genshiryoku hatsudensho jiko}}
 </ref> began on March 11, 2011 when a series of [[Nuclear and radiation accidents#Equipment failure|equipment failures]], [[nuclear meltdown|core melt and down]], and [[Nuclear and radiation accidents#Radiation accidents|releases of radioactive materials]] occurred at the [[Fukushima Daiichi Nuclear Power Station]]
-from the [[Great East Japan Earthquake|2011 off the Pacific coast of Tohoku Earthquake and tsunami]] on the same day.<ref>{{cite web|title=Explainer: What went wrong in Japan's nuclear reactors|url=http://spectrum.ieee.org/tech-talk/energy/nuclear/explainer-what-went-wrong-in-japans-nuclear-reactors|work=IEEE Spectrum|date=4 April 2011| archiveurl = http://www.webcitation.org/5zujk3oQL | archivedate = 2011-07-04| deadurl=no}}
+from the [[Great East Japan Earthquake|2011 off the Pacific coast of Tohoku Earthquake and tsunami]] on the same day.<ref>{{cite web|title=Explainer: What went wrong in Japan's nuclear reactors |url=http://spectrum.ieee.org/tech-talk/energy/nuclear/explainer-what-went-wrong-in-japans-nuclear-reactors |work=IEEE Spectrum |date=4 April 2011 |archiveurl=http://www.webcitation.org/5zujk3oQL?url=http://spectrum.ieee.org/tech-talk/energy/nuclear/explainer-what-went-wrong-in-japans-nuclear-reactors |archivedate=4 July 2011 |deadurl=no |df=dmy-all }}
 </ref><ref>It is the largest nuclear disaster since the [[Chernobyl disaster]] of 1986.<br />
-{{cite news|url=http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=10716671|title=Japan's unfolding disaster 'bigger than Chernobyl'|work=[[New Zealand Herald]]|date=2 April 2011}}<br />
+{{cite news|url=http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=10716671 |title=Japan's unfolding disaster 'bigger than Chernobyl' |work=[[New Zealand Herald]] |date=2 April 2011 }}<br />
-[http://in.ibtimes.com/articles/132391/20110409/japan-nuclear-crisis-radiation.htm "Analysis: A month on, Japan nuclear crisis still scarring"] ''International Business Times'' (Australia). 9 April 2011, retrieved 12 April 2011; excerpt, According to [[James M. Acton|James Acton]], Associate of the Nuclear Policy Program at the Carnegie Endowment for International Peace, "Fukushima is not the worst nuclear accident ever but it is the most complicated and the most dramatic...This was a crisis that played out in real time on TV. Chernobyl did not." {{webarchive |url=http://www.webcitation.org/5y2agYEQZ?url=http://in.ibtimes.com/articles/132391/20110409/japan-nuclear-crisis-radiation.htm |date=18 April 2011 }}
+[http://in.ibtimes.com/articles/132391/20110409/japan-nuclear-crisis-radiation.htm "Analysis: A month on, Japan nuclear crisis still scarring"] {{webarchive|url=http://www.webcitation.org/5y2agYEQZ?url=http%3A%2F%2Fin.ibtimes.com%2Farticles%2F132391%2F20110409%2Fjapan-nuclear-crisis-radiation.htm |date=18 April 2011 }} ''International Business Times'' (Australia). 9 April 2011, retrieved 12 April 2011; excerpt, According to [[James M. Acton|James Acton]], Associate of the Nuclear Policy Program at the Carnegie Endowment for International Peace, "Fukushima is not the worst nuclear accident ever but it is the most complicated and the most dramatic...This was a crisis that played out in real time on TV. Chernobyl did not." {{cite web|url=http://in.ibtimes.com/articles/132391/20110409/japan-nuclear-crisis-radiation.htm |title=Archived copy |accessdate=2011-04-18 |deadurl=yes |archiveurl=http://www.webcitation.org/5y2agYEQZ?url=http://in.ibtimes.com/articles/132391/20110409/japan-nuclear-crisis-radiation.htm |archivedate=18 April 2011 |df=dmy-all }}
 </ref>
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 radioactive releases<ref>
 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.
-: {{cite web |url=http://bos.sagepub.com/content/67/5/27.full |title=The radiological and psychological consequences of the Fukushima Daiichi accident |author= Frank N. von Hippel |date= September/October 2011 vol. 67 no. 5 |work= Bulletin of the Atomic Scientists |pages= 27–36 | archiveurl = http://www.webcitation.org/643mZ4JGx | archivedate = 2011-12-20| deadurl=no}}
+: {{cite web|url=http://bos.sagepub.com/content/67/5/27.full |title=The radiological and psychological consequences of the Fukushima Daiichi accident |author=Frank N. von Hippel |date=September/October 2011 vol. 67 no. 5 |work=Bulletin of the Atomic Scientists |pages=27–36 |archiveurl=http://www.webcitation.org/643mZ4JGx?url=http://bos.sagepub.com/content/67/5/27.full |archivedate=20 December 2011 |deadurl=no |df=dmy-all }}
 </ref><ref>In May 2012, TEPCO reported that at least 900 [[Petabecquerel|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.
 : {{cite web|url=http://english.kyodonews.jp/news/2012/05/159960.html|title=TEPCO puts radiation release early in Fukushima crisis at 900 PBq|work=[[Kyodo News]]|date=24 May 2012|accessdate=24 May 2012| archiveurl = https://web.archive.org/web/20120524191342/http://english.kyodonews.jp/news/2012/05/159960.html | archivedate = 2012-05-24| deadurl=yes}}
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 </ref> in the first few days after nuclear reactor shutdown.<ref>F. Tanabe, Journal of Nuclear Science and Technology, 2011, volume 48, issue 8, pages 1135 to 1139</ref>
-As the water boiled away in the reactors and the water levels in the [[Spent nuclear fuel|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 [[Nuclear meltdown|meltdown]].<ref>{{cite news|url=http://edition.cnn.com/2011/WORLD/asiapcf/06/06/japan.nuclear.meltdown/index.html?iref=NS1 |title=3 nuclear reactors melted down after quake, Japan confirms |work=CNN|date= 7 June 2011|accessdate=13 July 2011| archiveurl = https://web.archive.org/web/20140414115531/http://edition.cnn.com/2011/WORLD/asiapcf/06/06/japan.nuclear.meltdown/index.html?iref=NS1 | archivedate = 2014-04-14| deadurl=no}}</ref><ref>{{cite web|url=http://www.yomiuri.co.jp/dy/national/T110607005367.htm |title='Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown |work=Yomiuri |date=8 June 2011 |accessdate=8 June 2011|archiveurl = http://www.webcitation.org/5zSkWxIIC |archivedate = 2011-06-15|deadurl=yes}}</ref>
+As the water boiled away in the reactors and the water levels in the [[Spent nuclear fuel|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 [[Nuclear meltdown|meltdown]].<ref>{{cite news|url=http://edition.cnn.com/2011/WORLD/asiapcf/06/06/japan.nuclear.meltdown/index.html?iref=NS1 |title=3 nuclear reactors melted down after quake, Japan confirms |work=CNN|date= 7 June 2011|accessdate=13 July 2011| archiveurl = https://web.archive.org/web/20140414115531/http://edition.cnn.com/2011/WORLD/asiapcf/06/06/japan.nuclear.meltdown/index.html?iref=NS1 | archivedate = 2014-04-14| deadurl=no}}</ref><ref>{{cite web|url=http://www.yomiuri.co.jp/dy/national/T110607005367.htm |title='Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown |work=Yomiuri |date=8 June 2011 |accessdate=8 June 2011 |archiveurl=http://www.webcitation.org/5zSkWxIIC?url=http://www.yomiuri.co.jp/dy/national/T110607005367.htm |archivedate=15 June 2011 |deadurl=yes |df=dmy-all }}</ref>
 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 safety|hydrogen-air]] chemical explosions occurred.<ref name="IAEA15March"/><ref>[http://www.hyer.eu/news/regional-news/hydrogen-in-nuclear-accidents-what-is-the-role-of-the-gas-in-fukushima Hydrogen explosions Fukushima nuclear plant: what happened?] {{webarchive |url=https://web.archive.org/web/20131202235552/http://www.hyer.eu/news/regional-news/hydrogen-in-nuclear-accidents-what-is-the-role-of-the-gas-in-fukushima |date=December 2, 2013 }}</ref>
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 {{reflist|refs=
-<ref name="IAEA15March">{{cite web |url=http://www.iaea.org/newscenter/news/2011/fukushima150311.html |title=Fukushima nuclear accident update log, updates of 15&nbsp;March&nbsp;2011 |work=IAEA |date=15 March 2011 |accessdate=8 May 2011| archiveurl = http://www.webcitation.org/5xoqS3dVJ | archivedate = 2011-04-09| deadurl=no}}</ref>
+<ref name="IAEA15March">{{cite web|url=http://www.iaea.org/newscenter/news/2011/fukushima150311.html |title=Fukushima nuclear accident update log, updates of 15&nbsp;March&nbsp;2011 |work=IAEA |date=15 March 2011 |accessdate=8 May 2011 |archiveurl=http://www.webcitation.org/5xoqS3dVJ?url=http://www.iaea.org/newscenter/news/2011/fukushima150311.html |archivedate=9 April 2011 |deadurl=no |df=dmy-all }}</ref>
 <!-- <ref name="TEPCO12-3:00">{{cite press release |url=http://www.tepco.co.jp/en/press/corp-com/release/11031203-e.html |title=Press Release &#124; Plant Status of Fukushima Daiichi Nuclear Power Station (as of 0&nbsp;am 12 March) |work=TEPCO |date=12 March 2011 |accessdate=23 March 2011| archiveurl = http://www.webcitation.org/5yZvLHSV7 | archivedate = 2011-05-10| deadurl=no}}</ref> -->
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 <!-- <ref name="WNN1">{{cite news|url=http://www.world-nuclear-news.org/RS_Battle_to_stabilise_earthquake_reactors_1203111.html |title=Battle to stabilise earthquake reactors |author=World Nuclear News |work=World Nuclear News |date=12 March 2011 |accessdate=12 March 2011| archiveurl = http://www.webcitation.org/5x8MU5e7u | archivedate = 2011-03-12| deadurl=no}}</ref> -->
-<ref name="IAEAtsunami1">{{cite web|url=http://www.iaea.org/newscenter/news/tsunamiupdate01.html|title=IAEA Update on Japan Earthquake|quote=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. It should be noted that 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.|accessdate=16 March 2011| archiveurl = http://www.webcitation.org/5x8gJ8rN2 | archivedate = 2011-03-12| deadurl=no}}</ref>
+<ref name="IAEAtsunami1">{{cite web|url=http://www.iaea.org/newscenter/news/tsunamiupdate01.html |title=IAEA Update on Japan Earthquake |quote=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. It should be noted that 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. |accessdate=16 March 2011 |archiveurl=http://www.webcitation.org/5x8gJ8rN2?url=http://www.iaea.org/newscenter/news/tsunamiupdate01.html |archivedate=12 March 2011 |deadurl=no |df=dmy-all }}</ref>
 <!-- <ref name="cnn-status-0324">{{cite news|url=http://www.cnn.com/2011/WORLD/asiapcf/03/24/japan.nuclear.status/ |title=Status report: Reactor-by-reactor at the Fukushima Daiichi plant |work=CNN |date=24 March 2011|accessdate=26 March 2011| archiveurl = https://web.archive.org/web/20140414113959/http://www.cnn.com/2011/WORLD/asiapcf/03/24/japan.nuclear.status/ | archivedate = 2014-04-14| deadurl=no}}</ref> -->
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 <!-- <ref name="BBCConfirmMelt">{{cite news |url=http://www.bbc.co.uk/news/business-13497656 |title=Tepco confirms extra partial fuel rod meltdown at plant |work=BBC |date=24 May 2011 |accessdate=27 May 2011| archiveurl = https://web.archive.org/web/20130118120003/http://www.bbc.co.uk/news/business-13497656 | archivedate = 2013-01-18| deadurl=no}}</ref> -->
-<ref name="Asahi20120723">{{cite news|title=UPDATE: Government panel blasts lack of 'safety culture' in nuclear accident|url=http://ajw.asahi.com/article/0311disaster/fukushima/AJ201207230081|accessdate=29 July 2012|newspaper=The [[Asahi Shimbun]]|date=23 July 2012| archiveurl = https://web.archive.org/web/20140413220232/http://ajw.asahi.com/article/0311disaster/fukushima/AJ201207230081 | archivedate = 2014-04-13| deadurl=no}}</ref>
+<ref name="Asahi20120723">{{cite news|title=UPDATE: Government panel blasts lack of 'safety culture' in nuclear accident |url=http://ajw.asahi.com/article/0311disaster/fukushima/AJ201207230081 |accessdate=29 July 2012 |newspaper=The [[Asahi Shimbun]] |date=23 July 2012 |archiveurl=https://web.archive.org/web/20140413220232/http://ajw.asahi.com/article/0311disaster/fukushima/AJ201207230081 |archivedate=13 April 2014 |deadurl=yes |df=dmy-all }}</ref>
 <ref name="Kevin Krolicki">{{cite news|url=http://in.reuters.com/article/2012/05/24/nuclear-japan-radiation-fukushima-idINDEE84N0CR20120524|title=Fukushima radiation higher than first estimated|work=[[Reuters]]|author=Kevin Krolicki|date=24 May 2012|accessdate=24 May 2012| archiveurl = https://web.archive.org/web/20131015040840/http://in.reuters.com/article/2012/05/24/nuclear-japan-radiation-fukushima-idINDEE84N0CR20120524 | archivedate = 2013-10-15| deadurl=no}}</ref>