Investigations into the Fukushima Daiichi nuclear disaster

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Investigations into the Fukushima Daiichi nuclear disaster
Fukushima I by Digital Globe.jpg
Satellite image on 16 March 2011 of the four damaged reactor buildings
Date11 March 2011 (2011-03-11)
LocationFutaba-machi and Okuma-machi, Futaba-gun, Fukushima Prefecture, Japan
OutcomeINES Level 7 (ratings by Japanese authorities as of 11 April)[1]
Non-fatal injuries37 with physical injuries,[2]
2 workers taken to hospital with radiation burns[3]

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]


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[edit]

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[edit]

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]


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 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]

See also[edit]

Investigation Committees

Notes and references[edit]

  1. ^ "Fukushima accident upgraded to severity level 7". IEEE Spectrum. 12 April 2011. Archived from the original on 2014-03-11.
  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.
  3. ^ "Radiation-exposed workers to be treated at Chiba hospital". Kyodo News. 25 March 2011. Archived from the original on 2013-02-17. Retrieved 17 April 2011.
  4. ^ Fukushima Daiichi Nuclear Accident (福島第一原子力発電所事故, Fukushima Dai-ichi ( About this soundpronunciation ) 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.
  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.
  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. Check date values in: |date= (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 2012-05-24. Retrieved 24 May 2012.
  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
  14. ^ Kevin Krolicki (24 May 2012). "Fukushima radiation higher than first estimated". Reuters. Archived from the original on 2013-10-15. Retrieved 24 May 2012.
  15. ^ "Trauma, Not Radiation, Is Key Concern In Japan". NPR. 2012-03-09. Archived from the original on 2014-03-09. Retrieved 2012-04-15.
  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". 2012-03-15. Archived from the original on 2014-05-05. Retrieved 2012-04-15.
  18. ^ "Japan PM says Fukushima nuclear site finally stabilised". BBC Online. 16 December 2011. Archived from the original on 2014-02-20. Retrieved 7 January 2012.
  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 2014-04-14. Retrieved 13 July 2011.
  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.
  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.
  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)
  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. Check date values in: |accessdate= (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 2014-01-24.
  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.
  32. ^ Nagata, Kazuaki, "Tepco lashes prime minister's office", Japan Times, 21 June 2012, p. 1 Archived November 1, 2012, at the Wayback Machine.
  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.
  34. ^ Sheldrick, Aaron (12 October 2012). "Fukushima operator must learn from mistakes, new adviser says". Reuters. Archived from the original on 2014-03-09. Retrieved 13 October 2012.
  35. ^ Yamaguchi, Mari (12 October 2012). "Japan utility agrees nuclear crisis was avoidable". Associated Press. Archived from the original on 2013-10-05. Retrieved 13 October 2012.
  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. ^ 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
  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.


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

External links[edit]