Fukushima Daiichi nuclear disaster (Unit 3 Reactor)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Fukushima Daiichi nuclear disaster (Unit 3 Reactor)
Fukushima I by Digital Globe.jpg
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 (About this sound 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]

Unit 3 Reactor[edit]

Reactor Unit 3 (right) and Unit 4 (left) on 16 March.
Three of the reactors at Fukushima Daiichi overheated, causing meltdowns which released large amounts of radioactive material into the air.
Pipes are the direction of the ocean.[36]

Unlike the other five reactor units, reactor 3 ran on mixed core, containing both uranium fuel and mixed uranium and plutonium oxide, or MOX fuel (with the core comprising ~6% MOX fuel[37]), during a loss of cooling accident in a subcritical reactor MOX fuel will not behave differently from UOX fuel. The key difference between plutonium-239 and uranium-235 is that plutonium emits fewer delayed neutrons than uranium when it undergoes fission.[38]

While water-insoluble forms of plutonium such as plutonium dioxide are very harmful to the lungs, this toxicity is not relevant during a Loss Of Coolant Accident (LOCA) because plutonium is very involatile and unlikely to leave the reactor in large amounts. Plutonium dioxide has a very high boiling point. The toxic effect of the plutonium to the public under these conditions is much less than that of iodine-131 and caesium. During a loss of cooling accident, the fuel is not subject to such intense mechanical stresses, so the release of radioactivity is controlled by the boiling-point of the different elements present.[39]

Cooling problems[edit]

Following the reactor SCRAM, operators activated the reactor core isolation cooling system (RCIC) and the residual heat removal system and core spray systems were made available to cool the suppression pool; whether they were activated prior to the tsunami has not been made clear. The RHRS and CS pumps were knocked out of commission by the tsunami. With DC battery power remaining, the RCIC continued to keep the water level stable, and the operators switched to the high pressure coolant injection (HPCI) system when water level began to drop. On 13 March, the HPCI system failed, the reason for which is not completely clear due to instrumentation not being available. It is believed to be either due to loss of DC power due to depletion of batteries or to reactor pressure dropping below the level at which it can operate. Operators were unable to restart it as batteries were exhausted. After this the operators were unable to start the RCIC system and began injecting seawater. Although it was not clear at the time, some of the fuel in Reactor 3 apparently melted around sixty hours after the earthquake (the night of the 12th to 13th).[40]

Early on 13 March an official of the Japan Nuclear and Industrial Safety Agency (NISA) told at a news conference that the emergency cooling system of Unit 3 had failed, spurring an urgent search for a means to supply cooling water to the reactor vessel to prevent a meltdown of its reactor core.[41] At 05:38 there was no means of adding coolant to the reactor, owing to loss of power. Work to restore power and to vent excessive pressure continued.[42] At one point, the top three meters of the uranium/mixed oxide (MOX) fuel rods were not covered by coolant.[43]

At 07:30 JST, TEPCO prepared to release radioactive steam, indicating that "the amount of radiation to be released would be small and not of a level that would affect human health"[44] and manual venting took place at 08:41 and 09:20.[45] At 09:25 JST on 13 March, operators began injecting water containing boric acid into the primary containment vessel (PCV) via the pump of a fire truck.[46][47] When water levels continued to fall and pressure to rise, the injected water was switched to seawater at 13:12.[42] By 15:00 it was noted that despite adding water the level in the reactor did not rise and radiation had increased.[48] A rise was eventually recorded but the level stuck at 2 m below the top of reactor core. Other readings suggested that this could not be the case and the gauge was malfunctioning.[45]

Injection of seawater into the primary containment vessel (PCV) was discontinued at 01:10 on 14 March because all the water in the reserve pool had been used up. Supplies were restored by 03:20 and injection of water resumed.[47] On the morning of 15 March, Secretary Edano announced that according to TEPCO, at one location near reactor Units 3 and 4, radiation at an equivalent dose rate of 400 mSv/h was detected.[3][49][50] This might have been due to debris from the explosion in Unit 4.[51]


At 12:33 JST on 13 March, the chief spokesman of the Japanese government, Yukio Edano said hydrogen gas was building up inside the outer building of Unit 3 just as had occurred in Unit 1, threatening the same kind of explosion.[citation needed] At 11:15 JST on 14 March, the envisaged explosion of the building surrounding Reactor 3 of Fukushima 1 occurred, owing to the ignition of built up hydrogen gas.[52][53] The Nuclear and Industrial Safety Agency of Japan (NISA) reported, as with Unit 1, the top section of the reactor building was blown apart, but the inner containment vessel was not breached. The explosion was larger than that in Unit 1 and felt 40 kilometers away. Pressure readings within the reactor remained steady at around 380 kPa at 11:13 and 360 kPa at 11:55 compared to nominal levels of 400 kPa and a maximum recorded of 840 kPa. Water injection continued. Dose rates of 0.05 mSv/h were recorded in the service hall and of 0.02 mSv/h at the plant entrance.[54]

Eleven people were reported injured in the blast.[55] TEPCO and NISA announced that four TEPCO employees, three subcontractor employees, and four Self-Defence-Force soldiers were injured.[56][57][58] Six military personnel from the Ground Self Defense Force's Central Nuclear Biological Chemical Weapon Defense Unit, led by Colonel Shinji Iwakuma, had just arrived outside the reactor to spray it with water and were exiting their vehicles when the explosion occurred. Iwakuma later said that TEPCO had not informed them that there was a danger of a hydrogen explosion in the reactor, adding, "Tokyo Electric was desperate to stabilize (the plant), so I am not angry at them. If there is a possibility of an explosion, I would be reluctant to send my men there."[59]

Possibility of criticality in the spent fuel pool[edit]

TEPCO claimed that there was a small but non-zero probability that the exposed fuel assemblies could reach criticality.[60][61] The BBC commented that criticality would never mean a nuclear explosion, but could cause a sustained release of radioactive materials.[60] Criticality is usually considered highly unlikely, owing to the low enrichment level used in light water reactors.[62][63][64] American nuclear engineer Arnold Gundersen, noting the much greater power and vertical debris ejection compared to the Unit 1 hydrogen blast, has theorized that the Unit 3 explosion involved a prompt criticality in the spent fuel pool material, triggered by the mechanical disruption of an initial, smaller hydrogen gas explosion in the building.[65]

On 11 May, TEPCO released underwater robotic video from the spent fuel pool. The video appears to show large amounts of debris contaminating the pool. Based on water samples analysed, unnamed experts and TEPCO reported that the fuel rods were left "largely undamaged",[66][67] and that it appears that the Unit 3 explosion was entirely related to hydrogen buildup within the building from venting of the reactor.

Cooling efforts[edit]

Around 10:00 JST on 16 March, NHK helicopters flying 30 km away videotaped white fumes rising from the Fukushima I facility. Officials suggested that the Reactor 3 building was the most likely source, and said that its containment systems may have been breached.[68] The control room for Reactors 3 and 4 was evacuated at 10:45 JST but staff were cleared to return and resume water injection into the reactor at 11:30 JST.[69] At 16:12 JST, Self Defence Force (SDF) Chinook helicopters were preparing to pour water on Unit 3, where white fumes rising from the building was believed to be water boiling away from the fuel rod cooling pond on the top floor of the reactor building, and on Unit 4 where the cooling pool was also short of water. The mission was cancelled when helicopter measurements reported radiation levels of 50 mSv.[70][71] At 21:06 pm JST, the government reported that major damage to Reactor 3 was unlikely but that it nonetheless remained their highest priority.[72]

Early on 17 March, TEPCO requested another attempt by the military to put water on the reactor using a helicopter[73] and four helicopter drops of seawater took place around 10:00 JST.[74] The riot police used a water cannon to spray water onto the top of the reactor building and then were replaced by members of the SDF with spray vehicles. On 18 March, a crew of firemen took over the task with six fire engines each spraying 6 tons of water in 40 minutes. 30 further hyper rescue vehicles were involved in spraying operations.[75] Spraying continued each day to 23 March because of concerns the explosion in Unit 3 may have damaged the pool (total 3,742 tonnes of water sprayed up to 22 March) with changing crews to minimise radiation exposure.[3] Lighting in the control room was restored on 22 March after a connection was made to a new grid power supply and by 24 March it was possible to add 35 tonnes of seawater to the spent fuel pool using the cooling and purification system.[76] On 21 March grey smoke was reported to be rising from the southeast corner of Unit 3 – where the spent fuel pool is located. Workers were evacuated from the area. TEPCO claimed no significant change in radiation levels and the smoke subsided later the same day.[77]

On 23 March, black smoke billowed from Unit 3, prompting another evacuation of workers from the plant, though Tokyo Electric Power Co. officials said there had been no corresponding spike in radiation at the plant. "We don't know the reason for the smoke", Hidehiko Nishiyama of the Nuclear Safety Agency said.[78]

On 24 March, three workers entered the basement of the turbine building and were exposed to radiation when they stepped into contaminated water. Two of them were not wearing high boots and received beta ray burns. They were hospitalized but their injuries were not life-threatening.[79]

From 25 March, the source of water being injected into the core was switched from seawater to freshwater.[80]

In August, TEPCO began considering changing the core injection method for the no. 3 reactor as it was requiring a much larger quantity of water to cool and the temperatures remained relatively high compared to the nos. 1 and 2 reactors which required far less water. TEPCO has hypothesized that this may be because some fuel is still present above the core support plate inside the pressure vessel of the no. 3 reactor in addition to the fuel that has fallen to the bottom of the pressure vessel. The fuel on the bottom would be easily cooled by the existing method, but as the pressure vessel is leaking, any fuel located on the support plate was likely only being cooled due to the steam generated by the cooling of the melted fuel at the bottom. TEPCO began considering utilizing the reactor's core spray system pipes as an additional path of water injection and then reduce the amount of water through the existing feedwater piping system. A team of workers were sent inside the reactor building to inspect the core spray system pipes and it was found that the piping was undamaged. Hoses were then run from the temporary injection pumps located outside the building and connected to the core spray system piping. On 1 September, TEPCO began injecting water using the new route. The new injection method has been considerably effective in lowering the temperature of the reactor to below 100 degrees Celsius. As of 27 September, most of the no. 3 reactor's temperature readings are between 70–80 degrees Celsius. Later, TEPCO began utilizing the same method in the no. 2 reactor; it has not had as significant effect on the no. 2 reactor as it did on the no. 3.[81]

Further developments[edit]

Unit 3 reactor temperatures, 19 March to 28 May

On 25 March 2011, officials announced the reactor vessel might be breached and leaking radioactive material. High radiation levels from contaminated water prevented work.[82] Japan Nuclear and Industrial Safety Agency (NISA) reiterated concerns about a Unit 3 breach on 30 March.[83] NHK World reported the NISA's concerns as "air may be leaking", very probably through "weakened valves, pipes and openings under the reactors where the control rods are inserted", but that "there is no indication of large cracks or holes in the reactor vessels".[83] As with the other reactors, water was transferred from condenser reservoirs to the suppression pool surge tanks so that condensers could be used to hold radioactive water pumped from the basement.[84]

On 17 April, remote control robots were used to enter the Reactor Building and performed a series of inspections.[80] On 27 April, TEPCO revised its estimate of damaged fuel in Unit 3 from 25% to 30%.[85] Radiation measurements of the water in the Unit 3 spent fuel pool were reported at 140 kBq of radioactive caesium-134 per cubic centimeter, 150 kBq of caesium-137 per cubic centimeter, and 11 kBq per cubic centimeter of iodine-131 on 10 May.[67]

On 15 May, TEPCO revealed that the pressure vessel that holds nuclear fuel "is likely to be damaged and leaking water at Units 2 and 3", which meant most of the thousands of tons of water pumped into the reactors had leaked.[86] On 23 May, TEPCO reported that Reactor 3 had suffered a meltdown some sixty hours after the earthquake.[40]

On 9 June, staff entered the Reactor Building to conduct radiation surveys.[80] On 25 June and the following day boric acid dissolved in 90 tons of water was pumped into the spent fuel pool of Reactor 3. Concrete debris from the March hydrogen explosion of the reactor building have been detected in the spent fuel pool. In June TEPCO discovered that the water in the pool was strongly alkaline: the pH had reached a value of 11.2. Leaching of calcium hydroxide (portlandite) or calcium silicate hydrate (CSH) from the concrete could have caused this. The alkaline water could accelerate the corrosion of the aluminium racks holding the spent fuel rods. If the fuel assemblies would fall, this could lead to re-criticality. In the mean time preparative works began to install a recirculation cooling system at the fuel pool, that should be operational in the first weeks of July.[87]

On 14 July, TEPCO began injecting nitrogen into the containment vessel, which was expected to reduce the likelihood of further hydrogen explosions.[80] On 1 July, the spent fuel pool was switched from the water-injection cooling system, to a circulatory cooling system.[80] After 2 July, the Reactor was cooled using fresh water treated by the on-site water treatment plant.[80]

On 11 January 2012, radioactive contaminated water was found in two underground tunnels. On 12 January, TEPCO admitted that around 300 cubic meters of water had accumulated in an underground tunnel near reactor No.3, with electric cables. Radioactive caesium was measured in concentrations varying from 49 to 69 becquerels per cubic centimeter. Smaller amounts of contaminated water with lower concentrations caesium was found in a tunnel near reactor no.1. How the water could accumulate at these places was under examination.[88]

In a study that began two months after the earthquake and tsunami, mutant butterflies were found and are considered a possible reaction to the Fukushima nuclear disaster. Some of the butterflies had abnormalities in their legs, antennae, and abdomens, and dents in their eyes.[89]

In the morning of 18 July 2013 at 8:20 a.m. (2320 GMT) small amounts of steam escaped from the reactor building. Video images made by a subcontractor, filming the destroyed building and preparing to remove rubble from the place, showed some vapors rising, but it was unclear where it came from. Although there was no change in the afternoon, TEPCO said that radiation levels did not change, and the reactor was still cooled.[90] According to TEPCO rain could have found its way to the primary containment of the reactor, and because this vessel was still hot, it could cause the steam.[91] The next day at 7:55 a.m. the steam was gone. Because the radiation levels were too high all work to remove rubble was done by remote control. Operations stopped after the steam was found. According to TEPCO the rain on 17 and 18 July was to blame.[92] On 18 July the actual dosage measurement was 562 millisieverts per hour, therefore the NRA ordered TEPCO to make further investigations. On 23 July at 9:05 the steam was seen again coming out of the fifth floor just above the reactor containment. The night before a rain shower did hit the building, and water might have reached the - 38C - reactor container lid, or might have reached hot fuel left behind in the reactor vessel. At that moment the ambient temperature was 20.3 C and the humidity was 91.2 percent. All work removing rubble from the place was halted.[93] During the last event, radiation levels were measured at 24 locations around the fifth floor of the reactor building. The dosage ranged between 137 millisieverts and 2,170 millisieverts per hour.[94]

See also[edit]



  1. ^ Negishi, Mayumi (12 April 2011). "Japan raises nuclear crisis severity to highest level". Reuters. 
  2. ^ "Fukushima accident upgraded to severity level 7". IEEE Spectrum. 12 April 2011. 
  3. ^ a b c "IAEA Update on Japan Earthquake". 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. 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. 
  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."
  8. ^ Black, Richard (15 March 2011). "Reactor breach worsens prospects". BBC Online. 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. Retrieved 13 July 2011. 
  11. ^ "'Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown". Yomiuri. 8 June 2011. Retrieved 8 June 2011. 
  12. ^ "Fukushima nuclear accident update log, updates of 15 March 2011". IAEA. 15 March 2011. Retrieved 8 May 2011. 
  13. ^ Hydrogen explosions Fukushima nuclear plant: what happened?
  14. ^ Stricken reactors may get power Sunday, The Wall Street Journal, 19 March 2011
  15. ^ Justin McCurry. Japan raises nuclear alert level to seven. The Guardian. 12 April 2011
  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. 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. 
  20. ^ a b 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.  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
  23. ^ Justin McCurry in Osaka (23 March 2010). "Tokyo water unsafe for infants after high radiation levels detected". The Guardian (London). Retrieved 23 March 2011. 
  24. ^ "TEPCO puts radiation release early in Fukushima crisis at 900 PBq". Kyodo News. 24 May 2012. Retrieved 24 May 2012. 
  25. ^ Kevin Krolicki (24 May 2012). "Fukushima radiation higher than first estimated". Reuters. Retrieved 24 May 2012. 
  26. ^ "Trauma, Not Radiation, Is Key Concern In Japan". NPR. 2012-03-09. Retrieved 15 April 2012. 
  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. Retrieved 1 October 2013. 
  29. ^ "Japan PM says Fukushima nuclear site finally stabilised". BBC Online. 16 December 2011. 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. Retrieved 9 July 2012. 
  31. ^ "UPDATE: Government panel blasts lack of 'safety culture' in nuclear accident". The Asahi Shimbun. 23 July 2012. Retrieved 29 July 2012. 
  32. ^ Fackler, Martin (12 October 2012). "Japan Power Company Admits Failings on Plant Precautions". The New York Times. Retrieved 13 October 2012. 
  33. ^ Sheldrick, Aaron (12 October 2012). "Fukushima operator must learn from mistakes, new adviser says". Reuters. Retrieved 13 October 2012. 
  34. ^ Yamaguchi, Mari (12 October 2012). "Japan utility agrees nuclear crisis was avoidable". Associated Press. Boston.com. Retrieved 13 October 2012. 
  35. ^ "Japanese nuclear plant operator admits playing down risk". CNN Wire Staff. CNN. 12 October 2012. Retrieved 13 October 2012. 
  36. ^ Martin Fackler (1 June 2011). "Report Finds Japan Underestimated Tsunami Danger". The New York Times. 
  37. ^ "What fuel mix was in use at Fukushima and was that a factor in the accident? Does the United States use MOX fuel?". Nuclear Energy Institute. 25 July 2011. 
  38. ^ {{X. Li, R. Henkelmann and F. Baumgärtner, Rapid determination of uranium and plutonium content in mixtures through measurement of the intensity-time curve of delayed neutrons, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 2004, volume 215, issue 1–2, pages 246–251}}
  39. ^ J.-P. Hiernaut, T. Wiss, D. Papaioannou, R.J.M. Konings, V.V. Rondinella, Journal of Nuclear Materials, 2008, volume 372, pages 215 to 225
  40. ^ a b "Tepco confirms extra partial fuel rod meltdown at plant". BBC. 24 May 2011. Retrieved 27 May 2011. 
  41. ^ "Japan's Fukushima nuclear plant faces new reactor problem". Reuters. 12 March 2011. Retrieved 12 March 2011. 
  42. ^ a b "Seismic Damage Information(the 20th Release)" (PDF). Nuclear and Industrial Safety Agency. 13 March 2011. Retrieved 12 April 2011. 
  43. ^ "Meltdowns may have occurred in two Japan reactors". Channel NewsAsia. Agence France-Presse. 2011. Retrieved 13 March 2011. 
  44. ^ Takenaka, Kiyoshi (12 March 2011). "Japan's TEPCO preparing to release radiation from second reactor". Reuters. Retrieved 12 March 2011. 
  45. ^ a b "Efforts to manage Fukushima Daiichi 3, update 2". World Nuclear News. 13 March 2011. Retrieved 13 March 2011. 
  46. ^ "TEPCO press release 8". Tepco (Press release). 13 March 2011. 
  47. ^ a b "Seismic damage information (the 22nd release)" (PDF). Nuclear and Industrial Safety Agency. 14 March 2011. Retrieved 12 April 2011. 
  48. ^ "press release 10". Tepco (Press release). 13 March 2011. 
  49. ^ 放射線、福島原発で400ミリシーベルト=「人体に影響及ぼす可能性」-官房長官. jiji press (in Japanese). 15 March 2011. Retrieved 15 March 2011. 
  50. ^ "Radiation levels spike at Japanese nuclear plant". CNN. 15 March 2011. Retrieved 15 March 2011. 
  51. ^ "Radiation leak feared at spent fuel pool, water injection ordered". Kyodo News. 15 March 2011. Retrieved 15 March 2011. 
  52. ^ "Urgent: Hydrogen blast occurs at Fukushima nuke plant's No. 3 reactor: agency". Kyodo News Agency. Retrieved 14 March 2011. 
  53. ^ "180,000 flee as Japan's nuclear crisis intensifies". MSNBC. Retrieved 13 March 2011. 
  54. ^ "Second explosion rocks Fukushima Daiichi". World-nuclear-news.org. Retrieved 15 March 2011. 
  55. ^ "An explosion caused by hydrogen at Unit 3 of Fukushima Dai ichi NPS (3rd release)" (PDF). Nuclear and Industrial Safety Agency. 14 March 2011. 
  56. ^ "News Release" (PDF). Nuclear and Industrial Safety Agency. 14 March 2011. Retrieved 22 March 2011. 
  57. ^ 福島第一3号機爆発 自衛隊員ら11人ケガ. NNN News 24 (in Japanese). 14 March 2011. Retrieved 22 May 2011. 
  58. ^ 「有事並み」10万人態勢の救援活動 震災害と原発事故の「二正面作戦」に挑む. The Mainichi Shimbun (in Japanese). 11 May 2011. Retrieved 25 May 2011. [dead link]
  59. ^ Kyodo News, "GSDF colonel recounts fearing for life in Fukushima reactor blast", Japan Times, 7 June 2011, p. 2.
  60. ^ a b Black, Richard (16 March 2011). "Surprise 'critical' warning raises nuclear fears". BBC. Retrieved 26 March 2011. 
  61. ^ McCurry, Justin (16 March 2011). "Fukushima nuclear plant evacuated after radiation spikes". The Guardian (London). The No 4 reactor is an increasing cause for concern. Tepco believes that the storage pool may be boiling, raising the possibility that exposed rods will reach criticality. "The possibility of re-criticality is not zero", a TEPCO spokesman said. 
  62. ^ "Criticality Safety in the Waste Management of Spent Fuel from NPPs, Robert Kilger" (PDF). Retrieved 24 April 2011. 
  63. ^ "Nondestructive assay of nuclear low-enriched uranium spent fuels for burnup credit application". Cat.inist.fr. Retrieved 24 April 2011. 
  64. ^ Wikibooks:Radioactive Waste Management/Spent Nuclear Fuel
  65. ^ "Gundersen postulates Unit 3 explosion may have been prompt criticality in fuel pool". Fairewinds Associates. 26 April 2011. Retrieved 27 April 2011. 
  66. ^ Underwater robot captures Fukushima wreckage, The Telegraph, 11 May 2011
  67. ^ a b "Radiation high at No.3 reactor pool". NHK. 10 May 2011. Retrieved 2 June 2011. 
  68. ^ "Japan says 2nd reactor may have ruptured with radioactive release", The New York Times 16 March 2010.
  69. ^ "Seismic damage information (the 26th release)" (PDF). Nuclear and Industrial Safety Agency. 16 March 2011. Retrieved 12 April 2011. 
  70. ^ "Video: Helicopters attempt to cool Fukushima nuclear plant from the air". Telegraph (London). 16 March 2011. Retrieved 18 March 2011. 
  71. ^ "SDF gives up on dousing No.3 reactor". NHK. 16 March 2011. Retrieved 2 June 2011. 
  72. ^ "Major damage unlikely at Japan nuke plant's No.3 reactor – Kyodo | Energy & Oil". Af.reuters.com. 9 February 2009. Retrieved 18 March 2011. 
  73. ^ "Tokyo Elec: want military chopper to try again to douse Reactor | Energy & Oil". Af.reuters.com. 9 February 2009. Retrieved 18 March 2011. 
  74. ^ Helicopter starts spraying water on Japan nuclear plant Reuters 17 March 2011
  75. ^ "Seismic Damage Information (the 30th Release)" (PDF). Nuclear and Industrial Safety Agency. 18 March 2011. Retrieved 12 April 2011. 
  76. ^ "Seismic Damage Information (the 46th Release)" (PDF). Nuclear and Industrial Safety Agency. 23 March 2011. Retrieved 12 April 2011. 
  77. ^ "Grey smoke from No.3 reactor subsided". Retrieved 21 March 2011. 
  78. ^ "Tokyo tap water tests higher for radiation; smoke prompts new evacuation of leaking nuke plant". StarTribune.com. 23 March 2011. Retrieved 29 March 2011. 
  79. ^ Kanako Takahara and Kazuaki Nagata (26 March 2011). "Level of iodine-131 in seawater off chart". Japan Times. Retrieved 27 March 2011. 
  80. ^ a b c d e f "Records from March 11, 2011 to 31 July 2011" (PDF). TEPCO (Press release). Retrieved 22 August 2011. 
  81. ^ "Plant status of Fukushima Daiichi nuclear power station" (Press release). Retrieved 27 September 2011. 
  82. ^ "Japan reactor core may be leaking radioactive material, official says". CNN. 25 March 2011. Retrieved 26 March 2011. 
  83. ^ a b "Air may be leaking from reactors No. 2 and 3". NHK WORLD English. 30 March 2011. Retrieved 2 June 2011. 
  84. ^ "Press Release | Status of TEPCO's Facilities and its services after the Tohoku-Taiheiyou-Oki Earthquake(as of 10:00 pm)". TEPCO (Press release). 30 March 2011. Retrieved 7 April 2011. 
  85. ^ TEPCO revises nuclear fuel damage ratios, NHK, 27 April 2011
  86. ^ Mitsuru Obe (16 May 2011). "Cores damaged at three reactors". The Wall Street Journal. 
  87. ^ Boric acid added to spent fuel pool of Unit 3.
  88. ^ The Mainichi Daily news (13 January 2012) 300 tons of tainted water found near No. 3 unit at Fukushima plant[dead link]
  89. ^ "Mutant butterflies a result of Fukushima nuclear disaster, researchers say". CNN. Retrieved 14 August 2012. 
  90. ^ The Mainichi Shimbun (18 July 2013) TEPCO sees steam but no crisis at nuclear plant
  91. ^ The Asahi Shimbun (18 July 2013) Steam rising from reactor building in Fukushima
  92. ^ The Mainichi Shimbun (19 July 2013) Steam coming out from Fukushima reactor building disappeared: TEPCO
  93. ^ The Mainichi Shimbun (23 July 2013) Steam again seen at No. 3 reactor building at Fukushima Daiichi plant,
  94. ^ The Asahi Shimbun (24 July 2013)High radiation levels found near area where steam spotted at Fukushima plant

External links[edit]