Jump to content

Fukushima nuclear accident (Unit 3 Reactor)

Add links
From Wikipedia, the free encyclopedia

Fukushima Daiichi (Unit 3 Reactor)
Unit 3 after the explosion on 15 March 2011
Map
General information
StatusSeverely damaged
TypeReactor
LocationŌkuma and Futaba, Fukushima, Japan
Coordinates37°25′17″N 141°1′57″E / 37.42139°N 141.03250°E / 37.42139; 141.03250
Construction started28 December 1970[1]
Completed10 October 1971[1]
Opened27 March 1976[1]
Closed19 May 2011
(shutdown)[1]
External videos
video icon 24 hours live camera for Fukushima Daiichi nuclear disaster on YouTube, certified by Tokyo Electric Power Co. Inc.

The Fukushima Daiichi (Unit 3) reactor, was 1 out of 4 reactors seriously affected during the Fukushima Daiichi nuclear disaster (福島第一原子力発電所事故, Fukushima Dai-ichi) on 11 March 2011.[2][3] Overall, the plant had 6 separate boiling water reactors originally designed by General Electric (GE), and maintained by the Tokyo Electric Power Company (TEPCO). In the aftermath, Unit 3 experienced hydrogen gas explosions and suffered a partial meltdown, along with the other two reactors (1 & 2) in operation at the time the tsunami struck. Reactor 4 had been de-fueled while 5 and 6 were in cold shutdown for planned maintenance.[4]

Background

[edit]

The Fukushima Daiichi Nuclear Power Plant consists of six separate boiling water reactors originally designed by General Electric (GE), and maintained by the Tokyo Electric Power Company (TEPCO). 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 being approximately 6% MOX fuel[5]), 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.[6]

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.[7]

At the time of the quake, Reactor 4 had been de-fueled while 5 and 6 were in the 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).

Disaster

[edit]

Cooling problems

[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.[9]

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).[10]

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.[11] 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.[12] At one point, the top three meters of the uranium/mixed oxide (MOX) fuel rods were not covered by coolant.[13]

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"[14] and manual venting took place at 08:41 and 09:20.[15] 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.[16][17] When water levels continued to fall and pressure to rise, the injected water was switched to seawater at 13:12.[12] By 15:00 it was noted that despite adding water the level in the reactor did not rise and radiation had increased.[18] 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.[15]

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.[17] 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.[19][20][21] This might have been due to debris from the explosion in Unit 4.[22]

Explosion

[edit]

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.[23][24] 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.[25]

Eleven people were reported injured in the blast.[26] TEPCO and NISA announced that four TEPCO employees, three subcontractor employees, and four Self-Defence-Force soldiers were injured.[27][28][29] 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."[30]

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.[31] 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.[32] 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.[33][34] At 21:06 pm JST, the government reported that major damage to Reactor 3 was unlikely but that it nonetheless remained their highest priority.[35]

Early on 17 March, TEPCO requested another attempt by the military to put water on the reactor using a helicopter[36] and four helicopter drops of seawater took place around 10:00 JST.[37] 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.[38] 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.[19] 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.[39] 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.[40]

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.[41]

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.[42]

From 25 March, the source of water being injected into the core was switched from seawater to freshwater.[43]

In August, TEPCO began considering changing the core injection method for the no. 3 reactor as it required 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 more 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 and 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.[44]

Aftermath

[edit]

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 in the Unit 4 reactor could reach criticality.[45][46] The BBC commented that criticality would never mean a nuclear explosion, but could cause a sustained release of radioactive materials.[45] Criticality is usually considered highly unlikely, owing to the low enrichment level used in light water reactors.[47][48][49] 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.[50]

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",[51][52] and that it appears that the Unit 3 explosion was entirely related to hydrogen buildup within the building from venting of the reactor.

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.[53] Japan Nuclear and Industrial Safety Agency (NISA) reiterated concerns about a Unit 3 breach on 30 March.[54] 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".[54] 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.[55]

On 17 April, remote control robots were used to enter the Reactor Building and performed a series of inspections.[43] On 27 April, TEPCO revised its estimate of damaged fuel in Unit 3 from 25% to 30%.[56] 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.[52]

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.[57] On 23 May, TEPCO reported that Reactor 3 had suffered a meltdown some sixty hours after the earthquake.[10]

On 9 June, staff entered the Reactor Building to conduct radiation surveys.[43] 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 has 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 meantime preparative works began to install a recirculation cooling system at the fuel pool, that should be operational in the first weeks of July.[58]

On 14 July, TEPCO began injecting nitrogen into the containment vessel, which was expected to reduce the likelihood of further hydrogen explosions.[43] On 1 July, the spent fuel pool was switched from the water-injection cooling system to a circulatory cooling system.[43] After 2 July, the Reactor was cooled using fresh water treated by the on-site water treatment plant.[43]

On 11 January 2012, radioactively contaminated water was found in two tunnels. On 12 January, TEPCO admitted that around 300 cubic meters of water had accumulated in a 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.[59]

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.[60]

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.[61] 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.[62] 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.[63] 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.[64] 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.[65]

See also

[edit]

References

[edit]
  1. ^ a b c d "Japan: Nuclear Power Reactors". Power Reactor Information System – PRIS. IAEA. Archived from the original on 28 May 2011. Retrieved 14 March 2011.
  2. ^ "Japan's unfolding disaster 'bigger than Chernobyl'". The New Zealand Herald. 2 April 2011. Archived from the original on 30 March 2020. Retrieved 30 January 2013.
  3. ^ "Explainer: What went wrong in Japan's nuclear reactors". IEEE Spectrum. 4 April 2011. Archived from the original on 21 August 2011.
  4. ^ Black, Richard (15 March 2011). "Reactor breach worsens prospects". BBC Online. Archived from the original on 16 March 2011. Retrieved 23 March 2011.
  5. ^ "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. Archived from the original on 28 October 2013. Retrieved 30 January 2013.
  6. ^ Li, X.; Henkelmann, R.; Baumgärtner, F. (January 2004). "Rapid determination of uranium and plutonium content in mixtures through measurement of the intensity–time curve of delayed neutrons". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. 215 (1–2): 246–251. Bibcode:2004NIMPB.215..246L. doi:10.1016/S0168-583X(03)01822-6.
  7. ^ Hiernaut, J.-P.; Wiss, T.; Papaioannou, D.; Konings, R.J.M.; Rondinella, V.V. (January 2008). "Volatile fission product behaviour during thermal annealing of irradiated UO2 fuel oxidised up to U3O8". Journal of Nuclear Materials. 372 (2–3): 215–225. Bibcode:2008JNuM..372..215H. doi:10.1016/j.jnucmat.2007.03.174.
  8. ^ Black, Richard (15 March 2011). "Reactor breach worsens prospects". BBC Online. Retrieved 23 March 2011.
  9. ^ Martin Fackler (1 June 2011). "Report Finds Japan Underestimated Tsunami Danger". The New York Times.
  10. ^ a b "Tepco confirms extra partial fuel rod meltdown at plant". BBC. 24 May 2011. Retrieved 27 May 2011.
  11. ^ "Japan's Fukushima nuclear plant faces new reactor problem". Reuters. 12 March 2011. Retrieved 12 March 2011.
  12. ^ a b "Seismic Damage Information(the 20th Release)" (PDF). Nuclear and Industrial Safety Agency. 13 March 2011. Archived from the original (PDF) on 9 April 2011. Retrieved 12 April 2011.
  13. ^ "Meltdowns may have occurred in two Japan reactors". Channel NewsAsia. Agence France-Presse. 2011. Archived from the original on 22 October 2012. Retrieved 13 March 2011.
  14. ^ Takenaka, Kiyoshi (12 March 2011). "Japan's TEPCO preparing to release radiation from second reactor". Reuters. Retrieved 12 March 2011.
  15. ^ a b "Efforts to manage Fukushima Daiichi 3, update 2". World Nuclear News. 13 March 2011. Retrieved 13 March 2011.
  16. ^ "TEPCO press release 8". Tepco (Press release). 13 March 2011.
  17. ^ a b "Seismic damage information (the 22nd release)" (PDF). Nuclear and Industrial Safety Agency. 14 March 2011. Archived from the original (PDF) on 9 April 2011. Retrieved 12 April 2011.
  18. ^ "press release 10". Tepco (Press release). 13 March 2011.
  19. ^ a b "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 .... because of this detected value, the 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.
  20. ^ 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. Archived from the original on 10 April 2014. Retrieved 15 March 2011.
  21. ^ "Radiation levels spike at Japanese nuclear plant". CNN. 15 March 2011. Retrieved 15 March 2011.
  22. ^ "Radiation leak feared at spent fuel pool, water injection ordered". Kyodo News. 15 March 2011. Archived from the original on 20 March 2011. Retrieved 15 March 2011.
  23. ^ "Urgent: Hydrogen blast occurs at Fukushima nuke plant's No. 3 reactor: agency". Kyodo News Agency. Archived from the original on 13 May 2011. Retrieved 14 March 2011.
  24. ^ "180,000 flee as Japan's nuclear crisis intensifies". NBC News. 13 March 2011. Retrieved 13 March 2011.
  25. ^ "Second explosion rocks Fukushima Daiichi". World-nuclear-news.org. Retrieved 15 March 2011.
  26. ^ "An explosion caused by hydrogen at Unit 3 of Fukushima Dai ichi NPS (3rd release)" (PDF). Nuclear and Industrial Safety Agency. 14 March 2011. Archived from the original (PDF) on 28 March 2012.
  27. ^ "News Release" (PDF). Nuclear and Industrial Safety Agency. 14 March 2011. Archived from the original (PDF) on 22 March 2011. Retrieved 22 March 2011.
  28. ^ 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.
  29. ^ 「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]
  30. ^ Kyodo News, "GSDF colonel recounts fearing for life in Fukushima reactor blast", Japan Times, 7 June 2011, p. 2.
  31. ^ "Japan says 2nd reactor may have ruptured with radioactive release", The New York Times 16 March 2010.
  32. ^ "Seismic damage information (the 26th release)" (PDF). Nuclear and Industrial Safety Agency. 16 March 2011. Archived from the original (PDF) on 9 April 2011. Retrieved 12 April 2011.
  33. ^ "Video: Helicopters attempt to cool Fukushima nuclear plant from the air". The Telegraph. London. 16 March 2011. Archived from the original on 17 March 2011. Retrieved 18 March 2011.
  34. ^ "SDF gives up on dousing No.3 reactor". NHK. 16 March 2011. Archived from the original on 19 March 2011. Retrieved 2 June 2011.
  35. ^ "Major damage unlikely at Japan nuke plant's No.3 reactor – Kyodo | Energy & Oil". Af.reuters.com. 9 February 2009. Archived from the original on 26 April 2011. Retrieved 18 March 2011.
  36. ^ "Tokyo Elec: want military chopper to try again to douse Reactor | Energy & Oil". Af.reuters.com. 9 February 2009. Archived from the original on 26 April 2011. Retrieved 18 March 2011.
  37. ^ Helicopter starts spraying water on Japan nuclear plant Reuters 17 March 2011
  38. ^ "Seismic Damage Information (the 30th Release)" (PDF). Nuclear and Industrial Safety Agency. 18 March 2011. Archived from the original (PDF) on 9 April 2011. Retrieved 12 April 2011.
  39. ^ "Seismic Damage Information (the 46th Release)" (PDF). Nuclear and Industrial Safety Agency. 23 March 2011. Archived from the original (PDF) on 9 April 2011. Retrieved 12 April 2011.
  40. ^ "Grey smoke from No.3 reactor subsided". Archived from the original on 11 May 2011. Retrieved 21 March 2011.
  41. ^ "Tokyo tap water tests higher for radiation; smoke prompts new evacuation of leaking nuke plant". StarTribune.com. 23 March 2011. Retrieved 29 March 2011.
  42. ^ Kanako Takahara; Kazuaki Nagata (26 March 2011). "Level of iodine-131 in seawater off chart". The Japan Times. Retrieved 27 March 2011.
  43. ^ a b c d e f "Records from March 11, 2011 to 31 July 2011" (PDF). TEPCO (Press release). Retrieved 22 August 2011.
  44. ^ "Plant status of Fukushima Daiichi nuclear power station" (Press release). Retrieved 27 September 2011.
  45. ^ a b Black, Richard (16 March 2011). "Surprise 'critical' warning raises nuclear fears". BBC. Retrieved 26 March 2011.
  46. ^ 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.
  47. ^ "Criticality Safety in the Waste Management of Spent Fuel from NPPs, Robert Kilger" (PDF). Archived from the original (PDF) on 11 May 2011. Retrieved 24 April 2011.
  48. ^ Lebrun, Alain; Bignan, Gilles (September 2001). "Nondestructive Assay of Nuclear Low-Enriched Uranium Spent Fuels for Burnup Credit Application". Nuclear Technology. 135 (3): 216–229. Bibcode:2001NucTe.135..216L. doi:10.13182/NT01-A3217. S2CID 94259786. INIST 1068367.
  49. ^ Wikibooks:Radioactive Waste Management/Spent Nuclear Fuel
  50. ^ "Gundersen postulates Unit 3 explosion may have been prompt criticality in fuel pool". Fairewinds Associates. 26 April 2011. Archived from the original on 23 April 2012. Retrieved 27 April 2011.
  51. ^ Underwater robot captures Fukushima wreckage, The Telegraph, 11 May 2011
  52. ^ a b "Radiation high at No.3 reactor pool". NHK. 10 May 2011. Archived from the original on 10 May 2011. Retrieved 2 June 2011.
  53. ^ "Japan reactor core may be leaking radioactive material, official says". CNN. 25 March 2011. Retrieved 26 March 2011.
  54. ^ a b "Air may be leaking from reactors No. 2 and 3". NHK WORLD English. 30 March 2011. Archived from the original on 11 May 2011. Retrieved 2 June 2011.
  55. ^ "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.
  56. ^ TEPCO revises nuclear fuel damage ratios, NHK, 27 April 2011
  57. ^ Mitsuru Obe (16 May 2011). "Cores damaged at three reactors". The Wall Street Journal.
  58. ^ "Boric acid added to spent fuel pool of Unit 3". Archived from the original on 2 April 2012. Retrieved 30 January 2013.
  59. ^ The Mainichi Daily news (13 January 2012) 300 tons of tainted water found near No. 3 unit at Fukushima plant Archived 15 January 2012 at the Wayback Machine
  60. ^ "Mutant butterflies a result of Fukushima nuclear disaster, researchers say". CNN. Archived from the original on 2 January 2013. Retrieved 14 August 2012.
  61. ^ The Mainichi Shimbun (18 July 2013) TEPCO sees steam but no crisis at nuclear plant Archived 21 July 2013 at the Wayback Machine
  62. ^ The Asahi Shimbun (18 July 2013) Steam rising from reactor building in Fukushima Archived 24 July 2013 at the Wayback Machine
  63. ^ The Mainichi Shimbun (19 July 2013) Steam coming out from Fukushima reactor building disappeared: TEPCO Archived 19 July 2013 at archive.today
  64. ^ The Mainichi Shimbun (23 July 2013) Steam again seen at No. 3 reactor building at Fukushima Daiichi plant Archived 24 July 2013 at archive.today,
  65. ^ The Asahi Shimbun (24 July 2013)High radiation levels found near area where steam spotted at Fukushima plant Archived 28 July 2013 at the Wayback Machine
[edit]
Retrieved from "https://wiki.riteme.site/w/index.php?title=Fukushima_nuclear_accident_(Unit_3_Reactor)&oldid=1245212717"