Investigations into the Fukushima Daiichi nuclear disaster

Investigations into the Fukushima Daiichi nuclear disaster

Satellite image on 16 March 2011 of the four damaged reactor buildings
Date 11 March 2011 (2011-03-11)
Location Ōkuma, Fukushima, Japan
Coordinates 37°25′17″N 141°1′57″E / 37.42139°N 141.03250°E / 37.42139; 141.03250
Outcome INES Level 7 (ratings by Japanese authorities as of 11 April)[1][2]
Non-fatal injuries 37 with physical injuries,[3]
2 workers taken to hospital with radiation burns[4]
External video
24 hours live camera for Fukushima Daiichi nuclear disaster on YouTube, certified by Tokyo Electric Power Co. Inc.

The Fukushima Daiichi nuclear disaster (福島第一原子力発電所事故 Fukushima Dai-ichi ( pronunciation) genshiryoku hatsudensho jiko) was a series of equipment failures, nuclear meltdowns, and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the Tōhoku earthquake and tsunami on 11 March 2011.[5][6] It is the largest nuclear disaster since the Chernobyl disaster of 1986.[7]

The plant comprises 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 quake, Reactor 4 had been de-fueled while 5 and 6 were in cold shutdown for planned maintenance.[8] Immediately after the earthquake, the remaining reactors 1-3 shut down automatically, and emergency generators came online to control electronics and coolant systems. However the tsunami following the earthquake quickly flooded the low-lying rooms in which the emergency generators were housed. The flooded generators failed, cutting power to the critical pumps that must continuously circulate coolant water through a nuclear reactor for several days in order to keep it from melting down after being shut down. As the pumps stopped, the reactors overheated due to the normal high radioactive decay heat produced in the first few days after nuclear reactor shutdown (smaller amounts of this heat normally continue to be released for years, but are not enough to cause fuel melting).

At this point, only prompt flooding of the reactors with seawater could have cooled the reactors quickly enough to prevent meltdown. Salt water flooding was delayed because it would ruin the costly reactors permanently. Flooding with seawater was finally commenced only after the government ordered that seawater be used, and at this point it was already too late to prevent meltdown.[9]

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.[10][11]

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.[12][13]

Concerns about the repeated small explosions, the atmospheric venting of radioactive gasses, and the possibility of larger explosions led to a 20 km (12 mi)-radius evacuation around the plant. During the early days of the accident workers were temporarily evacuated at various times for radiation safety reasons. At the same time, sea water that had been exposed to the melting rods was returned to the sea heated and radioactive in large volumes for several months until recirculating units could be put in place to repeatedly cool and re-use a limited quantity of water for cooling. The earthquake damage and flooding in the wake of the tsunami hindered external assistance. Electrical power was slowly restored for some of the reactors, allowing for automated cooling.[14]

Japanese officials initially assessed the accident as Level 4 on the International Nuclear Event Scale (INES) despite the views of other international agencies that it should be higher. The level was later raised to 5 and eventually to 7, the maximum scale value.[15][16] The Japanese government and TEPCO have been criticized in the foreign press for poor communication with the public and improvised cleanup efforts.[17][18][19] On 20 March, the Chief Cabinet Secretary Yukio Edano announced that the plant would be decommissioned once the crisis was over.

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.[20] 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,[21] leading the government to ban the sale of food grown in the area. Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants.[22][23] 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.[24][25]

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[26] to 100[27] to a non-peer-reviewed "guesstimate"[28] of 1,000.[20] 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.[29] On 5 July 2012, the parliament appointed The Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) submitted its inquiry report to the Japanese parliament,[30] while the government appointed Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company submitted its final report to the Japanese government on 23 July 2012.[31] 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.[32][33][34][35]

Investigations

Position of Japanese atomic plants and spreading of tsunami

On 7 June 2011 a government-appointed committee of 10 people convened to investigate the accident. The panel was headed by Yotaro Hatamura, professor emeritus of the University of Tokyo, and included Yukio Takasu, Michio Furukawa, the mayor of Kawamata, Fukushima, and author Kunio Yanagida, considered an expert on crisis management.[36][37]

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.[38]

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.

From these documents could be concluded:

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.[39]

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. Their first remarks were:

According to professor Tadashi Narabayashi of the Hokkaido University Graduate School, plant operators should arrange emergency power supplies with other utilities. These discussion should be completed in March 2012, to be able to implement their conclusions into the new safety-regulations by the new nuclear safety agency to be launched in April 2012.[40]

The Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company was formed 7 June 2011 by the Japanese government as an independent body to investigate the Fukushima Daiichi disaster.[41] The Investigation Committee issued an interim report in December 2011, and is expected to issue its final report summer, 2012. The interim report was "a scathing assessment of the response to the Fukushima disaster", in which the investigative panel "blamed the central government and the Tokyo Electric Power Co., saying both seemed incapable of making decisions to stem radiation leaks as the situation at the coastal plant worsened in the days and weeks after the disaster".[42]

In February 2012, an independent investigation into the accident by the Rebuild Japan Initiative Foundation said that "In the darkest moments of last year's nuclear accident, Japanese leaders did not know the actual extent of damage at the plant and secretly considered the possibility of evacuating Tokyo, even as they tried to play down the risks in public". The government was preparing for the possibility of having to evacuate Tokyo while assuring its millions of residents that everything was under control.[43]

Officials revealed in interviews that they were grappling the possibility of a "demonic chain reaction": If Fukushima collapsed and released enough radiation, it was possible that other nearby nuclear power plants would have to be abandoned and could also collapse, thereby necessitating the evacuation of one of the world's largest cities.[44]

A 2012 report in The Economist said that the response to Fukushima has, so far, been inadequate, as many questions remain. One of the more worrying is how much damage the earthquake did to the reactors:[45]

It is claimed that they weathered the quake, but some experts, such as Masashi Goto, a retired nuclear engineer, argue that there is evidence of significant damage that speeded up the subsequent meltdown. Analysis of the spread of fallout suggests that the first releases came very soon after the tsunami hit, if not before. With quakes a more constant threat than monster tsunamis, these are the sort of lessons that Japan’s "nuclear village" needs to learn.[45]

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.[46][47]

TEPCO released its final internal investigation report on 20 June 2012. 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."[48]

On 5 July 2012, the National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission released an executive summary report[49] of The Fukushima Nuclear Accident. The report "blames Japanese culture for the fundamental causes of the disaster."[50][51][52][53] The panel is due to deliver its final report at the end of July.[50]

See also

Notes

    References

    1. ↑ Negishi, Mayumi (12 April 2011). "Japan raises nuclear crisis severity to highest level". Reuters. Archived from the original on 2013-11-12.
    2. ↑ "Fukushima accident upgraded to severity level 7". IEEE Spectrum. 12 April 2011. Archived from the original on 2014-03-11.
    3. ↑ "IAEA Update on Japan Earthquake". Archived from the original on 2011-03-12. 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.
    4. ↑ "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.
    5. ↑ "Japan's unfolding disaster 'bigger than Chernobyl'". New Zealand Herald. 2 April 2011.
    6. ↑ "Explainer: What went wrong in Japan's nuclear reactors". IEEE Spectrum. 4 April 2011. Archived from the original on 2011-07-04.
    7. ↑ "Analysis: A month on, Japan nuclear crisis still scarring" 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 18 April 2011 at WebCite
    8. ↑ Black, Richard (15 March 2011). "Reactor breach worsens prospects". BBC Online. Archived from the original on 2011-03-16. Retrieved 23 March 2011.
    9. ↑ F. Tanabe, Journal of Nuclear Science and Technology, 2011, volume 48, issue 8, pages 1135 to 1139
    10. ↑ "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.
    11. ↑ "'Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown". Yomiuri. 8 June 2011. Archived from the original on 2011-06-15. Retrieved 8 June 2011.
    12. ↑ "Fukushima nuclear accident update log, updates of 15 March 2011". IAEA. 15 March 2011. Archived from the original on 2011-04-09. Retrieved 8 May 2011.
    13. ↑ Hydrogen explosions Fukushima nuclear plant: what happened? Archived December 2, 2013, at the Wayback Machine.
    14. ↑ Stricken reactors may get power Sunday, The Wall Street Journal, 19 March 2011 Archived May 10, 2013, at the Wayback Machine.
    15. ↑ Justin McCurry. Japan raises nuclear alert level to seven. The Guardian. 12 April 2011 Archived March 11, 2013, at the Wayback Machine.
    16. ↑ '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.
    17. ↑ Wagner, Wieland (15 March 2011). "Problematic public relations: Japanese leaders leave people in the dark". Der Spiegel. Archived from the original on 2011-04-15. Retrieved 19 March 2011.
    18. ↑ "China urges Japan's openness amid panic buying of salt". Channel NewsAsia. Agence France-Presse. 17 March 2011. Retrieved 17 March 2011.
    19. ↑ Veronika Hackenbroch, Cordula Meyer and Thilo Thielke (5 April 2011). "A hapless Fukushima clean-up effort". Der Spiegel. Archived from the original on 2011-04-06.
    20. 1 2 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 2011-12-20. Check date values in: |date= (help)
    21. ↑ "Caesium fallout from Fukushima rivals Chernobyl". New Scientist. Archived from the original on 30 March 2011. Retrieved 30 March 2011.
    22. ↑ Japan mulls Fukushima food ban: IAEA, Reuters, 19 March 2011 Archived 19 March 2011 at WebCite
    23. ↑ Justin McCurry in Osaka (23 March 2010). "Tokyo water unsafe for infants after high radiation levels detected". The Guardian. London. Archived from the original on 2011-04-08. Retrieved 23 March 2011.
    24. ↑ "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.
    25. ↑ Kevin Krolicki (24 May 2012). "Fukushima radiation higher than first estimated". Reuters. Archived from the original on 2013-10-15. Retrieved 24 May 2012.
    26. ↑ "Trauma, Not Radiation, Is Key Concern In Japan". NPR. 2012-03-09. Archived from the original on 2014-03-09. Retrieved 2012-04-15.
    27. ↑ Caracappa, Peter F. (28 June 2011), "Fukushima Accident: Radioactive Releases and Potential Dose Consequences" (PDF), ANS Annual Meeting, retrieved 13 September 2011
    28. ↑ "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.
    29. ↑ "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.
    30. ↑ National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission. "国会事故調 | 東京電力福島原子力発電所事故調査委員会のホームページ". National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission. Archived from the original on 2013-01-19. Retrieved 9 July 2012.
    31. ↑ "UPDATE: Government panel blasts lack of 'safety culture' in nuclear accident". The Asahi Shimbun. 23 July 2012. Archived from the original on 2014-04-13. Retrieved 29 July 2012.
    32. ↑ 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.
    33. ↑ 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.
    34. ↑ Yamaguchi, Mari (12 October 2012). "Japan utility agrees nuclear crisis was avoidable". Boston.com. Associated Press. Archived from the original on 2013-10-05. Retrieved 13 October 2012.
    35. ↑ "Japanese nuclear plant operator admits playing down risk". CNN Wire Staff. CNN. 12 October 2012. Archived from the original on 2014-03-09. Retrieved 13 October 2012.
    36. ↑ Ito, Masami, "Official probe begins into nuclear disaster", Japan Times, 8 June 2011, p. 1. Archived 7 June 2011 at WebCite
    37. ↑ Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company Archived 11 July 2011 at WebCite
    38. ↑ Jiji Press, "Tepco must submit reactor accident manuals without deleted portions", Japan Times, 28 September 2011, p. 2.
    39. ↑ NHK-world (24 October 2011) Parts of TEPCO's accident manuals made public. Archived 24 June 2011 at WebCite
    40. ↑ NKH-world (24 October 2011)Nuke energy experts discuss technological issues. Archived August 12, 2011, at the Wayback Machine.
    41. ↑ Ito, Masami, "Official probe begins into nuclear disaster", Japan Times, 8 June 2011, p. 1. Archived 7 June 2011 at WebCite
    42. ↑ "Report: U.S. nuclear renaissance unlikely after Fukushima". LA Times. 28 December 2011. Archived from the original on 2014-01-24.
    43. ↑ Martin Fackler (27 February 2012). "Japan Weighed Evacuating Tokyo in Nuclear Crisis". The New York Times. Archived from the original on 26 June 2012.
    44. ↑ Krista Mahr (29 February 2012). "Fukushima Report: Japan Urged Calm While It Mulled Tokyo Evacuation". Time. Archived from the original on 2012-05-30.
    45. 1 2 "Blow-ups happen: Nuclear plants can be kept safe only by constantly worrying about their dangers". The Economist. 10 March 2012. Archived from the original on 2014-04-12.
    46. ↑ 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.
    47. ↑ 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.
    48. ↑ Nagata, Kazuaki, "Tepco lashes prime minister's office", Japan Times, 21 June 2012, p. 1 Archived November 1, 2012, at the Wayback Machine.
    49. ↑ The Fukushima Nuclear Accident - Executive summary (PDF). Fukushima Nuclear Accident Independent Investigation Commission (Report). The National Diet of Japan. July 2012. Archived from the original (PDF) on 10 July 2012. Retrieved 5 July 2012.
    50. 1 2 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: |access-date= (help)
    51. ↑ Tabuchi, Hiroko (5 July 2012). "Inquiry Declares Fukushima Crisis a Man-Made Disaster". The New York Times. Retrieved 5 July 2012.
    52. ↑ Hiyama, Hiroshi (7/5/2012). "Japan's Fukushima nuclear disaster 'man-made,' probe decides". The Globe and Mail. Toronto. Archived from the original on 2012-07-05. Retrieved 7/5/2012. Check date values in: |access-date=, |date= (help)
    53. ↑ Inajima, Tsuyoshi (07/5/2012). "Fukushima Disaster Was Man-Made, Investigation Finds". Bloomberg News. Archived from the original on 2014-05-06. Retrieved 07/5/2012. Check date values in: |access-date=, |date= (help)
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