timeline of the Fukushima Daiichi nuclear disaster

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timeline of the Fukushima Daiichi nuclear disaster
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{{Use dmy dates|date=October 2012}}(File:Fukushima I Nuclear Powerplant site close-up (wotext).PNG|thumb|Fukushima Daiichi I nuclear powerplant site close-up.)(File:Fukushima I nuclear accidents diagram.svg|thumb|Schematic representation of the Fukushima Daiichi nuclear accidents.)File:Fukushima I by Digital Globe.jpg|thumb|Following the 2011 Japanese Fukushima nuclear disaster, authorities shut down the nation's 54 nuclear power plants. As of 2013, the Fukushima site remains highly radioactive, with some 160,000 evacuees still living in temporary housing, and some land will be unfarmable for centuries. The difficult cleanup job will take 40 or more years, and cost many tens of billions of dollars, with total economic costs estimated at $250–$500 billion.NEWS,weblink Two years on, America hasn't learned lessons of Fukushima nuclear disaster, Richard Schiffman, 12 March 2013, The Guardian, London, NEWS,weblink Report Finds Japan Underestimated Tsunami Danger, Martin Fackler, June 1, 2011, New York Times, WEB,weblink The Staggering Costs to Clean Up Fukushima,, Tyler Falk, 12 November 2013, 21 January 2014, ]]Fukushima Dai-ichi (dai-ichi means "#1"), is a multi-reactor nuclear power site in the Fukushima Prefecture of Japan. The Fukushima Daiichi nuclear disaster occurred after a 9.0 magnitude Tōhoku earthquake and subsequent tsunami on 11 March 2011, only 14 days before the reactor was to be shut down. This offshore earthquake, near the island of Honshu,WEB,weblink Magnitude 9.0 – near the East coast of Honshu, Japan,, 17 March 2011, yes,weblink" title="">weblink 13 March 2011, dmy-all,
produced a large tsunami in Japan, and a tsunami warning for over 20 countries within and around the Pacific Rim.
The earthquake triggered a scram shut down of the three active reactors at the Fukushima I Nuclear Power Plant (Fukushima Dai-Ichi). The ensuing tsunami crippled the site, stopped the Fukushima I backup diesel generators, and caused a station blackout. The subsequent lack of cooling led to explosions and meltdowns at the Fukushima I facility, with problems at three of the six reactors and in one of the six spent-fuel pools.Times are given in Japan Standard Time (JST), unless noted, which is (UTC+09:00|UTC plus nine hours).{{TOC limit|}}

March 2011

Monday, 7 March

Tokyo Electric Power Company (TEPCO) submits a report to Japan's nuclear safety agency which predicts the possibility of a tsunami up to 10.2 metres high at the Fukushima Daiichi nuclear plant in the event of an earthquake similar to the magnitude 7.2 earthquake with accompanying tsunami that devastated the area in 1896. TEPCO actually made this prediction in 2008 but delayed in submitting the report because they "did not feel the need to take prompt action on the estimates".WEB,weblink Earthquake report No. 224, JAIF, 4 October 2011, 4 October 2011, yes,weblink" title="">weblink 28 October 2011, dmy-all,

Friday, 11 March

{{wikinews|8.9 magnitude earthquake hits Japan, causes tsunami}}
  • 14:46: A 9.1 magnitude earthquake strikes off the coast of Honshu Island at a depth of about {{convert|24|km|mi}}. The Fukushima I power plant's nuclear reactors 1, 2, and 3 are automatically shut down by the tremor. Nuclear reactors 4, 5, and 6 were undergoing routine maintenance and were not operating (reactor 4 was defueled in November 2010). The tremor also cut the power plant off from the Japanese electricity grid; however, backup diesel generators kicked in to continue cooling.
  • 14:52: Reactor 1's emergency cooling system, which was capable of running without external power, turned on automatically.WEB,weblink Earthquake Report No. 91, JAIF, 25 May 2011, 23 June 2017, yes,weblink" title="">weblink 3 January 2012, dmy-all,
  • 15:03: Reactor 1's emergency cooling system was manually shut down to avoid reactor damage (temperature was not critical at this point).
  • 15:27: The first tsunami struck the plant.WEB, TEPCO details tsunami damage,weblinkweblink" title="">weblink yes, 10 April 2011, The Yomiuri Shimbun, 24 April 2011, dmy-all,
  • 15:30: The emergency condenser designed to cool the steam inside the pressure vessel of the No. 1 reactor fails.The Mainichi Daily News {{Webarchive|url= |date=20 May 2011 }} TEPCO admits nuclear meltdown occurred at Fukushima reactor 16 hours after quake
  • 15:46 (approximate): A {{convert|14|m|adj=on}} tsunami, unleashed by the earthquake, overtops the seawall designed to protect the plant from a tsunami of {{convert|5.7|m}}, inundating the Fukushima facility and disabling the backup diesel generators – all but one of which were housed underground – and washing away their fuel tanks.NEWS,weblink The Telegraph, Japan nuclear crisis: tsunami study showed Fukushima plant was at risk, 19 March 2011, 5 May 2011, London, Richard, Gray, With the loss of all electrical power supply, the low-pressure core spray, the residual heat removal and low-pressure coolant injection system main pumps, and the automatic depressurization systems all failed (most of the emergency core cooling system). Only the steam-powered pump systems (isolation condenser in reactor 1, high-pressure coolant injection and reactor core isolation cooling system in reactors 2 and 3) remained available. A subsequent investigation by NHK would later reveal that the isolation condenser units had not been tested or operated in over 40 years. Later, as the temperature rose, a system started that used steam-powered pumps{{Failed verification|date=May 2011}} and battery-powered valves.WEB,weblink Fukushima faced 14-metre tsunami, 23 March 2011, World Nuclear News, 24 March 2011, NEWS,weblink Fukushima: What happened – and what needs to be done, 10 April 2011, BBC, 22 April 2011,
According to a report in the New York Times, "... at the start of the crisis Friday, immediately after the shattering earthquake, Fukushima plant officials focused their attention on a damaged storage pool for spent nuclear fuel at the No. 2 reactor at Daiichi, said a nuclear executive who requested anonymity ... The damage prompted the plant’s management to divert much of the attention and pumping capacity to that pool, the executive added. The shutdown of the other reactors then proceeded badly, and problems began to cascade."NEWS, In stricken fuel-cooling pools, a danger for the longer term,weblink New York Times, 14 March 2011, William J., Broad, Hiroko, Tabuchi, 14 March 2011,
  • 16:00: The Nuclear and Industrial Safety Agency of Japan (NISA) initiates an emergency headquarters {{Clarify|date=August 2016|reason=Is headquarters the correct word to use?}} in an attempt to gather information on the 55 nuclear reactors in Japan.NEWS,weblink Timeline: Japan power plant crisis, 15 March 2011, 13 March 2011, BBC News, There is no report that radiation was detected outside power-plant borders.WEB, Earthquake report 2,weblink JAIF, 11 March 2011, yes,weblink" title="">weblink 22 July 2011, dmy-all,
  • 18:00: The falling water level in reactor 1 reaches the top of the fuel, and the core temperature starts climbing.WEB,weblink TEPCO, Reactor core status of Fukushima Daiichi nuclear power station Unit 1, 15 May 2011, 20 May 2011,
  • 18:18: Reactor 1's emergency cooling system is once again back on.
  • 19:03: Prime Minister Naoto Kan declares a nuclear emergency statusWEB, Declaration of nuclear emergency,weblink Cabinet Secretariat, Cabinet Public Relations Office, 14 March 2011, announced by Yukio Edano, Chief Cabinet officer in Japan. Japanese government officials try to comfort the people of Japan by telling them that the proper procedures are being undertaken. They also announce that no radioactive leaks have been detected.
  • 19:30: The fuel in reactor 1 becomes fully exposed above the water surface, and fuel damage in the central core begins soon after.
  • 21:00: An evacuation order is issued by the government to persons within a radius of {{convert|3|km|mi}} from the Fukushima I station. Those within a radius of {{convert|10|km|mi}} are told that they can remain in their homes, and carry on with regular activities, until told otherwise. TEPCO announces that the pressure inside reactor unit 1 of Fukushima I is more than twice normal levels.

Saturday, 12 March

(File:Fukushima accidents overview map.svg|thumb|right|Overview map showing evacuation and other zone progression and selected radiation levels.)
  • 02:44: Emergency battery power for the high pressure core-flooder system (HPCFS) for reactor 3 runs out.
  • 04:15: Fuel rods in reactor 3 are exposed.
  • 05:30: Despite the high risk of hydrogen (produced from the water in the containment vessel) igniting after combining with oxygen from water or in the atmosphere, and in order to release some of the pressure inside the reactor at Fukushima I unit 1, the decision is taken to vent some of the steam (which contained a small amount of radioactive material) into the air.
  • 05:50: Fresh water injection into reactor 1 is started.
  • 06:50: Although unknown at the time, the core of reactor 1 has now completely melted and falls to the bottom of the reactor pressure vessel.
  • 10:09: TEPCO confirms that a small amount of vapor has been released into the air to release pressure in reactor unit 1 at Fukushima I.NEWS,weblink Timeline: Japan power plant crisis, BBC News, 15 March 2011, 13 March 2011,
  • 10:58: Pressure still remains too high inside reactor unit 2 at Fukushima I. In order to alleviate some of this pressure, a consensus is reached to once more vent radioactive vapor into the air.
  • 14:50: Fresh water injection into reactor 1 is halted.
  • 15:30: Evacuation of residents within 3 km of Fukushima II and within 10 km of Fukushima I are underway.WEB,weblink IAEA update on Japan earthquake, IAEA, March 2011,
  • 15:36: There is a massive explosion in the outer structure of unit 1. The concrete building surrounding the steel reactor vessel collapses as a result of the explosion; however no damage is believed to have been sustained to the reactor itself. Four workers are injured. {{Citation needed|date=October 2013}}
  • 19:00: Seawater injection into reactor 1 is started. TEPCO orders Daiichi to cease seawater injection at 19:25, but Daiichi plant boss Masao Yoshida orders workers to continue with the seawater injection.Kyodo News, "Disregard Tepco order, boss told plant workers", Japan Times, 30 November 2011, p. 1.
  • 21:40: The evacuation zone around Fukushima I is extended to 20 km, while the evacuation zone around Fukushima II is extended to 10 km.
To release pressure within reactor unit 1 at Fukushima I, steam is released out of the unit into the air. This steam contains water vapor, hydrogen, oxygen and some radioactive material.TEPCO engineers decided to directly inject seawater inside the pressure vessel of the reactors by means of the mobile trucks of the firemen. The pressure relief was also necessary to allow the firemen to inject seawater into the reactors vessels.

Sunday, 13 March

  • 02:42: The high pressure coolant injection system for reactor 3 stops and, shortly thereafter, the water level within the reactor starts falling.WEB,weblink Status of cores at Units 2 and 3 in Fukushima Daiichi nuclear power station, TEPCO, 23 May 2011, 6 June 2011,
  • 05:10: Fukushima I Unit 1 is declared as an INES Level-4 "accident with local consequences" event.
  • 07:00 (approximate): The water level in reactor 3 reaches the top of the fuel.
  • 09:00: Core damage starts occurring in reactor 3.
A partial meltdown was reported to be possible at unit 3.NEWS,weblink Partial meltdown possible at Japan nuclear plant as death toll estimates rise to 10,000, Fox News, 7 April 2010, 29 March 2011, At 13:00 JST reactors 1 and 3 are vented to release overpressure and then re-filled with water and boric acid for cooling, and to inhibit further nuclear reactions.WEB,weblink Press release 8, 13 March 2011, TEPCO, 13 March 2011, Unit 2 was possibly suffering a lower than normal water level, but was thought to be stable; although pressure inside the containment vessel was high. The Japan Atomic Energy Agency announced that it was rating the situation at unit 1 as level 4 (an accident with local consequences) on the International Nuclear and Radiological Event Scale.NEWS,weblink Japan rates quake less serious than Three Mile Island, Chernobyl, Maeda, Risa, 12 March 2011, Reuters, 12 March 2011,

Monday, 14 March

{{wikinews|Japan suffers second reactor explosion, cooling issue at third reactor}}
  • 11:01: The unit 3 reactor building explodes, injuring six workers.NEWS, Justin McCurry,weblink Explosion at Japanese nuclear plant, The Guardian, London, 14 March 2011, According to TEPCO there was no release of radioactive material beyond that already being vented, but blast damage affected the water supply to unit 2.PRESS RELEASE, White smoke around the Fukushima Daiichi Nuclear Power Station unit 3 (2nd release), Tokyo Electric Power Company, 14 March 2011,weblink
  • 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.
  • 15:00: A major part of the fuel in reactor 3 drops to the bottom of the reactor pressure vessel.
  • 18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.
  • 20:00: Core damage starts occurring in reactor 2.
The president of the French nuclear safety authority, Autorité de sûreté nucléaire (ASN), said that the accident should be rated as a 5 (an accident with wider consequences) or even a 6 (a serious accident) on INES. Reuters UK 15 March 2011

Tuesday, 15 March

{{wikinews|Third explosion at Fukushima Daiichi nuclear power plant}}
  • approx. 06:00 According to TEPCO, an explosion damaged the 4th floor area above the reactor and spent-fuel pool of the Unit 4 reactor.
PRESS RELEASE,weblink Damage to the Unit 4 Nuclear Reactor Building at Fukushima Dai-ichi Nuclear Power Station, Tokyo Electric Power Company, 15 March 2011, 26 February 2013,
  • 11:00: A second explosion of reactor 3 (according to The World Meteorological Organization report)
  • 20:00: A majority of the fuel in reactor 2 drops to the bottom of the reactor pressure vessel.
Damage to the temporary cooling systems on unit 2 from the explosion in unit 3, plus problems with its venting system, meant that water could not be added to the extent that unit 2 was in the most severe condition of the three reactors.NEWS, Hiroko Tabuchi, Keith Bradsher, Matt Wald,weblink Japan faces prospect of nuclear catastrophe as workers leave plant, The New York Times, 14 March 2011, An explosion in the "pressure suppression room" causes some damage to unit 2’s containment system.Radiation shoots up at Fukushima nuke plant after blast heard Kyodo News 15 March 2010 A fire breaks out at unit 4. Radiation levels at the plant rise significantly but subsequently fall.NEWS, Container damaged, radiation leak feared at Fukushima No.2 reactor, Kyodo News, 15 March 2011,weblink Radiation equivalent dose rates of 400 millisieverts per hour (400 mSv/h) are observed at one location in the vicinity of unit 3.WEB,weblink IAEA update on Japan earthquake, As reported earlier, a 400 millisieverts (mSv) per hour radiation dose observed at Fukushima Daiichi occurred between Units 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., 16 March 2011, NEWS,weblinkweblink" title="">weblink yes, 10 April 2014, ja: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, Japanese, jiji press, 15 March 2011, 15 March 2011, NEWS,weblink Radiation levels spike at Japanese nuclear plant, CNN, 15 March 2011, 15 March 2011,

Wednesday, 16 March

{{wikinews|Fukushima reactor suffers multiple fires, radiation leak confirmed}}At approximately 14:30 TEPCO announces its belief that the fuel rod storage pool of unit 4 – which is located outside the containment areaNEWS, Black, Richard,weblink Japanese emperor 'deeply worried' BBC News, BBC News, 16 March 2011, 23 March 2011, — may have begun boiling, raising the possibility that exposed rods could reach criticality. By midday NHK TV is reporting white smoke rising from the Fukushima I plant, which officials suggest is likely coming from reactor 3. Shortly afterwards all but a small groupNEWS, Mackey, Robert,weblink Latest updates on Japan's nuclear crisis and earthquake aftermath, Japan, The New York Times, 15 March 2011, 18 March 2011, of remaining workers at the plant are placed on standby because of the radiation rising to a dangerous level of up to 1 Sv/h.NEWS, CBS/AP,weblink Radiation spike hinders work at Japan nuke plant, CBS News, 15 March 2011, 18 March 2011, WEB,weblink Japan suspends work at stricken nuclear plant,, 26 June 2011, yes,weblink" title="">weblink 11 June 2011, dmy-all, TEPCO temporarily suspended operations at the facility.NEWS, Richard Black,weblink Fukushima workers withdraw after radiation spikes, BBC News, 16 March 2011, 18 March 2011, A TEPCO press release states that workers had been withdrawn at 06:00 JST because of abnormal noises coming from one of the reactor pressure suppression chambers.WEB,weblink Press release: Transfer of Fukushima Dai-ichi power station workers, TEPCO, 18 March 2011, Late in the evening Reuters reports that water is being poured into reactors 5 and 6.NEWS,weblink Fukushima operator: pouring water into No. 5, 6 reactors, Reuters, 16 March 2011, 18 March 2011, {{Dubious|date=September 2011}}

Thursday, 17 March

During the morning Self-Defense Force helicopters drop water four times on the spent-fuel pools of units 3 and 4.WEB,weblink 北沢防衛相「自衛隊ヘリの水投下、4回実施」, Yomiuri Shimbun, Japan, 23 March 2011, They measure radiation field of 3.75 Sv/h above Unit 3weblink In the afternoon it is reported that the unit 4 spent-fuel pool was filled with water and none of the fuel rods were exposed.NEWS, ja:4号機プール内に大量の水、自衛隊ヘリ確認, Japanese, Yomiuri Shimbun, 17 March 2011,weblink Construction work is started to supply a working external electrical power source to all six units of Fukushima I.NEWS, ja:冷却装置回復へ、原発に送電線引き込み工事開始, Japanese, Yomiuri Shimbun, 16 March 2011,weblink Starting at 7 pm, police and fire water trucks attempt to spray water into the unit 3 reactor with high pressure hoses.Takahara, Kanako, and Alex Martin, "Copters, trucks try to cool fuel rod pool", Japan Times, 18 March 2011, p. 1. Japanese authorities inform the IAEA that engineers are laying an external grid power line cable to unit 2. After watching the helicopter effort on TV Kazunori Hasegawa, president of Chuo Construction, calls the government and offers the use of his two truck-mounted concrete boom pumps to spray water directly into the reactors. TEPCO did not respond for three days, and then stated it would wait for the arrival of similar pumps obtained elsewhere.Higgins, Andrew, "Early disorder intensified Japan’s crisis", Washington Post, 19 April 2011. Retrieved 21 April 2011.

Friday, 18 March

{{wikinews|IAEA Clarifies: Fukushima nuclear cable has not been completed}}Tokyo Fire Department dispatches thirty fire engines with 139 fire-fighters and a trained rescue team at approximately 03:00 JST, including a fire truck with a 22-metre water tower.WEB,weblink NHK WORLD English,, 18 March 2011, For the second consecutive day, high radiation levels are detected in an area {{convert|30|km|mi}} northwest of the damaged Fukushima I nuclear plant at 150 Î¼Sv/h.WEB,weblink NHK WORLD English,, 18 March 2011, yes,weblink" title="">weblink 25 March 2011, dmy-all, Japanese authorities upgrade INES ratings for cooling loss and core damage at unit 1 to level 5, and issue the same rating for units 2 and 3. The loss of fuel pool cooling water at unit 4 is classified as a level 3. In a 24-hour period ending at 11 am local time, radiation levels near the plant decline from 351.4 to 265 Î¼Sv/h, but it is unclear if the water spraying efforts were the cause of the decrease.Takahara, Kanako, and Kazuaki Nagata, "Workers battle against time", Japan Times, 19 March 2011, p. 1.

Saturday, 19 March

A second group of 100 Tokyo and 53 Osaka firefighters replaces the previous team. They use a vehicle that projects water from a height of 22 meters to cool spent nuclear fuel in the storage pool inside the reactor of unit 3.WEB,weblink More Tokyo firefighters join the battle, 19 March 2011, NHK, yes,weblink" title="">weblink 14 April 2011, dmy-all, weblink" title="">放水支援で大阪市消防局部隊, Sankei newspaper 19 March 2011 Water is sprayed into the reactor for a total of 7 hours during the day. TEPCO reports that the water was effective in lowering the temperature around the spent fuel rods to below 100 Â°C.NHK (Evening news broadcast), 19 March 2011, 19:00.{{Verify source|date=March 2011}}

Sunday, 20 March

External power is reconnected to unit 2, but work continues to make the equipment operational. Repaired diesel generators at unit 6 provide power to restart the cooling on units 5 and 6, both of which are returned to cold shutdown and their fuel cooling ponds returned to normal operating temperatures.WEB,weblink Stabilisation at Fukushima Daiichi, update 2, World Nuclear News, 20 March 2011, WEB, JAIF,weblink Earthquake Report 15 (Chief Cabinet Secretary's Press briefing on March 20), 20 March 2011, TEPCO announces that the pressure in reactor 3's containment vessel is rising, and that it might be necessary to vent air containing radioactive particles to relieve pressure, as reported by Japanese broadcaster NHK at 1:06. The operation is later aborted as TEPCO deems it unnecessary. While joining in a generally positive assessment of progress toward overall control, Japanese chief cabinet secretary Edano confirms, for the first time, that the heavily damaged and contaminated complex will be closed once the crisis is over.NEWS,weblink Japan makes progress at nuclear reactors, but contamination spreads, The New York Times, 20 March 2011, Hiroko, Tabuchi, Norimitsu, Onishi,

Monday, 21 March

Ongoing repair work is interrupted by a recurrence of grey smoke from the south-east side of unit 3 (the general area of the spent-fuel pool) seen at 15:55 and dying down by 17:55. Employees are evacuated from unit 3, but no changes in radiation measurements or reactor status are seen. No work was going on at the time (such as restoring power) which might have accounted for the fire. White smoke, probably steam, is also seen coming from unit 2 at 18:22 JST, accompanied by a temporary rise in radiation levels. A new power line is laid to unit 4 and unit 5 is transferred to its own external power from a transmission line instead of sharing the unit 6 diesel generators.WEB,weblink Archived copy, 2011-04-12, yes,weblink" title="">weblink 1 May 2011, dmy-all, WEB,weblink Work to restore power delayed as smoke seen at Fukushima reactors, Kyodo News,, 23 March 2011, Officials learn that the crisis will not end with power recovery as the cooling pumps are damaged beyond repair and must be replaced. An emergency order was placed for new pumps for unit 2 which had suffered less damage than units 1 and 3.WEB,weblinkweblink" title="">weblink yes, 18 July 2012, More trouble at Fukushima,, 24 April 2011, WEB,weblink Fukushima reactor 2 cooling fails: Pump must be replaced,, 24 April 2011,

Tuesday, 22 March

Smoke is still rising from units 2 and 3, but is less visible, and is theorized to be steam following operations to spray water onto the buildings. Repair work resumes, after having been halted because of concerns over the smoke; it is felt safe because no significant changes in radiation levels have occurred. Work continues to restore electricity, and a supply cable is connected to unit 4. Injection of seawater into units 1–3 continues.WEB,weblink Archived copy, 2011-04-12, yes,weblink" title="">weblink 22 March 2011, dmy-all, External power cables are reported to be connected to all six units and lighting is back on again in the control room of unit 3.Hogg, Chris Stop-start work at Japan reactors BBC News Asia-Pacific, 22 March 2011, 15:44 GMT. Retrieved 22 March 2011Marin, Alex, "All reactors linked to outside power", Japan Times, 23 March 2011, p. 1.

Wednesday, 23 March

Smoke again starts belching from reactor 3 in the late afternoon, this time black and grey smoke, causing another evacuation of workers from around the area. Aerial video from the plant shows what appears to be a small fire at the base of the smoke plumes in the heavily damaged reactor building. Feed water systems in unit 1 are restored allowing an increase in the rate water that can be added to the reactor.WEB,weblink Press release: Plant status of Fukushima Daiichi nuclear power station (as of 11:00 pm Mar 22nd), TEPCO, 26 March 2011, The Japanese Chief Cabinet Secretary also advises that high levels of radioactivity have been found in Tokyo's drinking water and that it should not be used to reconstitute baby formula as it is around twice the legal limit for children.Coren, Anna "Bottled water scarce after Japan's tap water shown unsafe for infants", CNN, 24 March 2011. Retrieved 24 March 2011.

Thursday, 24 March

Seawater injection to units 1, 2 and 3 continues,WEB,weblink Press release, 24 March 2011, TEPCO, and radiation levels near the plant decline to 200 μSv/h,WEB,weblink Press release, TEPCO, 24 March 2011, while lighting is restored to the unit 1 control room.WEB, Martin, Alex,weblink No. 3 cooling pump test-run readied, The Japan Times, Japan, 25 March 2011, 1, Three workers are exposed to high levels of radiation which cause two of them to require hospital treatment, after radioactive water seeps through their protective clothes.NEWS,weblink 3 Japan nuclear workers exposed to radiation, CBS News, 24 March 2011, NEWS,weblink 2 Japanese nuclear workers hospitalized for radiation exposure, LA Times, 24 March 2011, Thomas H., Maugh II, The workers are exposed to an estimated equivalent dose of 2–6 Sv to the skin below their ankles.NEWS,weblink Japan raises possibility of breach in reactor vessel, The New York Times, The injured workers’ dosimeters suggested exposure to 170 millisieverts of radiation. But the institute said that the actual amount of radiation the workers are thought to have been exposed to in the water is 2 to 6 sievert. Even 2 sievert is eight times the 250 millisievert annual exposure limit set for workers at Daiichi., 25 March 2011, Hiroko, Tabuchi, Keith, Bradsher, David, Jolly, 25 March 2011, They were not wearing protective boots, as their employing firm's safety manuals "did not assume a scenario in which its employees would carry out work standing in water at a nuclear power plant".NEWS,weblink 2 of 3 radiation-exposed workers suffer internal exposure, Kyodo News, Japan, 25 March 2011, yes,weblink 17 May 2011, dmy-all, The activity concentration of the water is about 3.9 GBq/L. Infra-red surveys of the reactor buildings, obtained by helicopter, show that the temperatures of units 1, 2, 3 and 4 continue to decrease, ranging from 11–17 Â°C, and the fuel pool at unit 3 is recorded at 30 Â°C.NEWS,weblink Surface temps of reactors continue to fall, NHK, 24 March 2011, Reactor temperatures as of 24 March 2011: No 1- 13, No 2- 13, No 3- 11, and No 4- 17 degrees, yes,weblink" title="">weblink 11 May 2011, dmy-all,

Friday, 25 March

NISA announces a possible breach in the containment vessel of the unit 3 reactor, though radioactive water in the basement might alternatively have come from the fuel storage pool.NEWS, Reactor core may be breached at damaged Fukushima plant,weblink Bloomberg, 25 March 2011, Go Onomitsu and Takashi Hirokawa, 25 March 2011, NEWS, High radiation leak suggests damage to No. 3 reactor vessel,weblink Kyodo, 25 March 2011, Highly radioactive water is also found in the turbine buildings of units 1 and 2.NEWS, Japan reactor core may be leaking radioactive material, official says,weblink 25 March 2011, Kyodo News Network, 25 March 2011, Tokyo, The US Navy sends a barge with {{convert|1890|m3|gal}} of fresh water, expected to arrive after two days.WEB,weblink US Navy to provide 500,000 gallons of fresh water to Fukushima power plant, 25 March 2011,, Japan announces transportation will be provided in a voluntary evacuation zone of {{convert|30|km|mi}}. Tap water is reported to be safe for infants in Tokyo and Chiba by Japanese authorities, but still exceeds limits in Hitachi and Tokaimura.NEWS,weblink Japan encourages voluntary evacuations near stricken nuclear plant, CNN, 25 March 2011, Iodine-131 in the ocean near the plant measures 50,000 Bq/L, 1,250 times normal levels.WEB,weblink Radioactive seawater in Japan raises new fears of reactor crack,, 27 March 2011,

Saturday, 26 March

Fresh water becomes available again for use instead of seawater to top up reactor water levels.WEB,weblink Press Release (Mar 26, 2011) Plant status of Fukushima Daiichi nuclear power station (as of 10:30 am 26 Mar) (TEPCO press release),, 26 March 2011, The fresh water is provided by two United States Navy barges holding a total of 2,280 metric tons of fresh water which were towed by the Japan Maritime Self-Defense Force from the United States Fleet Activities Yokosuka Naval Base to Fukushima."Water-laden U.S. barge heading for Fukushima," Yomiuri Shimbun (Japan). 27 March 2011. Radiation levels near the plant decline to a still relatively high 170 Î¼Sv/h.WEB,weblink Monitoring data by a monitoring car at Fukushima Daiichi nuclear power station, measurement date: 03/26/2011 (TEPCO), PDF, 26 March 2011,

Sunday, 27 March

Levels of "over 1000" and 750 mSv/h are reported from water within unit 2 (but outside the containment structure) and 3 respectively. A statement that this level in unit 2 is "ten million times the normal level" were later retracted and attributed to incorrectly high levels of iodine-134 (which is later reported to be below the limit by TEPCO).WEB,weblink Contaminated pools to be drained, 27 March 2011, World Nuclear News, NEWS,weblink Officials retract reports of extremely high radiation at Fukushima plant, 27 March 2011, Los Angeles Times, Julie, Makinen, Kenji, Hall, WEB,weblink Results of contamination check of water in the basement at the turbine building of Unit 2 of Fukushima Daiichi power station, 29 March 2011, TEPCO, NEWS, Officials: Big spike at Japan nuke plant an error,weblink AP, Yahoo! News, 27 March 2011, Yuri Kageyama and Mari Yamaguchi, 27 March 2011, yes,weblink" title="">weblink 5 April 2011, Japan's Nuclear and Industrial Safety Agency indicate that "The level of radiation is greater than 1,000 millisieverts. It is certain that it comes from atomic fission ... But we are not sure how it came from the reactor."WEB, Nagata, Kazuaki, Radioactive pools block reactor repairs: 1 sievert readings in Unit No. 2 signal fission under way,weblink The Japan Times, 27 March 2011, The high radiation levels cause delays for technicians working to restore the water cooling systems for the troubled reactors.Nagata, Kazuaki, "Wild radiation spike in Unit No. 2 proves false", Japan Times, 28 March 2011. Retrieved 28 March 2011. USAF technicians at Yokota AB complete the fabrication of compatibility valves to allow the connection of deployed pump systems to the existing infrastructure at Fukushima.WEB, Staff Sgt. J.G. Buzanowski,weblink Yokota AB airmen play vital role in cooling Fukushima power plant,, 29 March 2011,weblink" title="">weblink 16 July 2012, yes, dmy-all, An aerial video recorded by a Ground Self-Defense Force helicopter reveals, according to NHK, the clearest and most detailed view of the damaged plant to date. Significant observations include:NEWS, Latest Fukushima plant video released,weblink 27 March 2011, NHK (Japan Broadcasting Company), 27 March 2011, yes,weblink" title="">weblink 9 August 2011, dmy-all,
* White vapour, possibly steam, emanating from the buildings of reactors 2, 3, and 4. * The roof of the reactor 2 building has been badly damaged but is still intact.

Monday, 28 March

The Japanese Nuclear Safety Commission states that it "assumed" melted fuel rods in unit 2 have released radioactive substances into the coolant water, which subsequently leaked out through an unknown route to the unit 2 turbine building basement. To reduce the amount of leaking water, TEPCO reduced the amount of water pumped into the unit 2 reactor, from 16 tons per hour to 7 tons per hour, which could lead to higher reactor temperatures. The highly radioactive water halts work on restoring the cooling pumps and other powered systems to reactors 1–4.Nagata, Kazuaki, and Kanako Takahara, "Radioactive water keeps workers out", Japan Times, 29 March 2011, p. 1. TEPCO confirms finding low levels of plutonium in five samples during 21 and 22 March.NEWS, the CNN Wire Staff,weblink TEPCO says plutonium found on quake-damaged plant grounds, CNN, 7 April 2011, 28 March 2011, Enriched levels of Plutonium-238, relative to Plutonium-239 and Plutonium-240, at two of the sites in the plant (solid waste area and field) indicate that contamination has occurred at those sites due to the "recent incident". Nonetheless, the overall levels of plutonium for all samples are about the same as background Pu levels resulting from atmospheric nuclear bomb testing in the past.WEB,weblink Press Release (Mar 28, 2011) Detection of radioactive material in the soil in Fukushima Daiichi Nuclear Power Station,, 28 March 2011, 7 April 2011, However, these weapons did not use fuel that has decayed significantly. Such nuclear accidents as this one are a potent source of biologically accumulating isotopes of transuranic elements such as curium and americium which are incorporated into bones, complexed into the Ca/PO4 hydroxide.{{Citation needed|date=April 2012}}

Tuesday, 29 March

TEPCO continues to spray water into reactors 1–3 and discovers that radioactive runoff water is beginning to fill utility trenches outside the three reactor buildings. The highly radioactive water in and around the reactor buildings continues to limit progress of the technicians in restoring the cooling and other automated systems to the reactors.Matsutani, Minoru, "Plutonium traces point to core leak", Japan Times, 30 March 2011, p. 1.

Wednesday, 30 March

At a news conference TEPCO Chairman Tsunehisa Katsumata announces that it is unclear how the problems at the plant will be resolved. An immediate difficulty is the removal of large quantities of radioactive water in the basement buildings, but also salt build up inside the reactors, from using seawater for cooling, will need to be removed. Building concrete walls to enclose the reactors in a shield is being considered, as had been done at Chernobyl.WEB,weblink TEPCO chief shows no road map to end nuke accident, NHK WORLD English, 30 March 2011, 7 April 2011, yes,weblink" title="">weblink 2 April 2011, dmy-all, The Environmental Protection Agency (EPA) finds radioactive iodine in milk in the United States.NEWS,weblink Traces of radioactive iodine found in Washington state milk, 9 April 2011, yes,weblink" title="">weblink 4 April 2011, dmy-all,

Thursday, 31 March

Workers pump radioactive water from a utility trench near reactor 1 into a storage tank near reactor 4.Takahara, Kanako, and Kazuaki Nagata, "High radiation found outside no-go zone", Japan Times, 1 April 2011, p. 1. Water in the condensers for reactors 2 and 3 is shifted to outside storage tanks so that the condensers can remove more contaminated water from inside the reactors.Asahi Shimbun, "TEPCO testing new ways to stop radioactive pollution from Fukushima", 1 April 2011. The world's largest concrete pumping truck is shipped from the United States to Fukushima.WEB, Pavey, Rob,weblink SRS pump will head to Japan,, 7 April 2011, The truck has been slightly modified to be able to pump cooling water initially, then will later possibly to be used to pump concrete for any eventual permanent containment structure.WEB,weblink Concrete pumps to Fukushima,, 1 April 2011, 7 April 2011, A 62-metre-tall pumping truck, donated by Chinese manufacturer SANY is also used.WEB, 寄給朋友,weblink zh:雅虎香港新聞 : 中國62米泵車助日射水 2011年3月21日,, Chinese, 7 April 2011, yes,weblink" title="">weblink 23 March 2011, dmy-all,

April 2011

Friday, 1 April

TEPCO says that groundwater near unit 1 contains radioiodine at levels 10,000 times normal, but NISA later disputes the numbers.WEB,weblink Iodine 131 found in groundwater, The Japan Times, 1 April 2011, 7 April 2011, NEWS,weblink CNN, Status report: Reactor-by-reactor at the Fukushima Daiichi plant, 2 April 2011, The Japanese government is reported to be considering injecting nitrogen into the reactor vessels.WEB,weblink Gov't eyes injecting nitrogen into reactor vessels to prevent blasts,, 7 April 2011, WEB,weblink Absorbent used to soak up radioactive water, 2 found dead at nuke plant,, 7 April 2011, Two more concrete pumping trucks, used initially to pump cooling water, are shipped to Japan from the Putzmeister factory in Germany.

Saturday, 2 April

TEPCO observes for the first time that contaminated water from the unit 2 is flowing into the sea.NEWS,weblink The New York Times, Ken, Belson, Hiroko, Tabuchi, Japan struggles to plug leak as radioactive water seeps into the sea, 2 April 2011, Workers discover a crack about 20 cm (8 inches) wide in the maintenance pit, which lies between the reactor 2 and the sea, and holds cables used to power seawater pumps. Workers were preparing to pour concrete into the crack to stop the water, which was emitting radiation at 1 Sv/h.NEWS,weblink Radioactive water from Japan nuclear plant leaks in sea, BBC News, 2 April 2011, 7 April 2011, WEB,weblink IAEA briefing on Fukushima nuclear accident (2 April 2011, 12:00 UTC), 3 April 2011,

Sunday, 3 April

The attempt to plug the leak near unit 2 fails when the concrete fails to set. TEPCO then reattempts to plug up the trench that leads to the damaged storage pit with a combination of superabsorbent polymer, sawdust and shredded newspaper, which also fails.Takahara, Kanako, "Two missing Tepco workers found dead", Japan Times, 4 April 2011, p. 1. Radioactive water continues to leak into the sea. Radiation levels around the plant are estimated at 1 Sv/h and continue to decrease.NHK, "Radiation levels gradually decreasing", 3 April 2011.NHK, "Radiation levels drop or remain flat", 4 April 2011.TEPCO confirms the first deaths at the Fukushima facility, two workers who had been missing since 11 March and appear to have died in the basement of reactor 4 from bleeding due to multiple injuries inflicted by the tsunami.NEWS, Makinen, Julie,weblink Two workers' bodies recovered at Fukushima nuclear plant, Los Angeles Times, 3 April 2011, 5 July 2011, Japanese government officials say the Daiichi plant may continue to release dangerous radiation into the air for several months.NEWS,weblink Japanese utility dumps radioactive water into Pacific to ease storage woes, The Washington Post, 24 April 2011, 5 April 2011, Joel, Greenberg,

Monday, 4 April

TEPCO begins dumping water from storage tanks tainted with low levels of radioactivity into the Pacific Ocean on Monday night. Officials say this is needed to make room in a central waste facility to store water with a higher radioactive level. This more highly radioactive water is preventing workers from making progress on restoring the cooling and other systems to reactors 1–4.Takahara, Kanako, "Tepco dumps toxic water into sea", Japan Times, 5 April 2011, p. 1.NHK, "Discharge of radioactive water into sea continues", 5 April 2011. Samples of seawater near the plant reveal radioactive caesium at 1.1 million times the legal limit.Hall, Kenji and Makinen, Julie, "weblink", "Los Angeles Times", 5 April 2011.The company says it could release up to 11,500 tons of radioactive water into the sea. A spokeswoman for Japan’s Nuclear and Industrial Safety Agency says the less-contaminated water must be disposed of so that workers can secure a place to store more highly contaminated water on the site.Engineers consider plans to inject inert nitrogen gas into the containment buildings of units 1, 2 and 3 to expel atmospheric oxygen and to dilute accumulated hydrogen, which combine explosively.Japanese nuclear plant continues its radioactive spill into ocean, Los Angeles Times.

Tuesday, 5 April

It is determined that the leak into the cable storage pit from unit 2 was likely due to a faulty joint where the pit meets a duct. The pit leads to a gravel layer beneath, resulting in highly radioactive water pouring directly into the sea.WEB,weblink IAEA Update on Fukushima Nuclear Accident (6 April 2011, 8:15 UTC) : IAEA Alert Log: Fukushima Daiichi Nuclear Accident,, 24 April 2011, Japan nuclear plant operator reports some success on leak, Los Angeles Times.Levels of radioactive iodine-131 in seawater near the facility are found to be 7.5 million times the legal limit. TEPCO drills a hole into the pit near reactor 2, from which highly radioactive water is leaking, and injects water glass (sodium silicate) into the pit to prevent further leaking.NHK, "Radioactive water leak at Fukushima plant stops", 6 April 2011.

Wednesday, 6 April

TEPCO announces that an injection of {{convert|6000|L|gal}} of polymer coagulant into the pit mitigated the leaking;"Out flow of fluid containing radioactive materials to the ocean from areas near intake channel of Fukushima Daiichi Nuclear Power Station Unit 2," TEPCO Press Release. 6 April 2011. Retrieved 8 April 2011. however, the IAEA and others credit additional factors."IAEA Update (6 April 2011, 8:15 UTC)," retrieved 8 April 2011; "Fukushima leak plugged; nitrogen approved," World Nuclear News (UK). 6 April 2011. Retrieved 8 April 2011. Sodium silicate ("water glass") and additives are injected into the ground in order to stop the leakage of radioactive water.Daily Mail Reporter. "Liquid glass successfully plugs radioactive leak at crippled Fukushima nuclear plant", Daily Mail (UK). 6 April 2011. Retrieved 8 April 2011. The residual heat carried by the water used for cooling the damaged reactors accelerates the setting of the injected mixture.Despite protests from the South Korean government, Russian scientists, and Japanese fishermen, Japan authorizes the release of {{convert|11500|tonne}} of less radioactive water into the ocean to make room to store the more highly contaminated water.WEB,weblink Japan defends radical decision to dump toxic water in Pacific, The Japan Times, 6 April 2011, 24 April 2011, Iodine-131 levels reach 7.5 million times the legal limit in a seawater sample taken near the facility.TEPCO announces that the leak of highly radioactive water from the utility pit near reactor 2 has stopped. According to U.S. Representative Ed Markey, the Nuclear Regulatory Commission says that the core of unit 2 has become so hot that part of it has melted through the reactor pressure vessel;Rampton, Roberta and Rascoe, Ayesha."weblink" "Reuters", "Japan No 2 core melted through reactor vessel: Rep. Markey", 6 April 2011. however, a NRC spokesperson says, "That's not clear to us, nor is it clear to us that the reactor has penetrated the vessel."WEB, Rampton, Roberta,weblink NRC says not clear that Japan reactor has melted vessel – Yahoo! News,, 7 April 2011, TEPCO begins injection of nitrogen into unit 1 to lower the possibility of hydrogen explosions.NEWS,weblink Japan nuclear crisis: Workers focus on preventing more hydrogen explosions, Huffington Post, USA from AP, 6 April 2011, 6 April 2011, Yamaguchi Mari, yes,weblink" title="">weblink 7 April 2011, dmy-all,

Thursday, 7 April

Nitrogen injection into the pressure containment vessel of unit 1 commences at 01:31.WEB,weblink Plant Status of Fukushima Daiichi Nuclear Power Station (as of 7:00 pm, April 7), TEPCO, 7 April 2011, Workers are evacuated following a magnitude 7.1 aftershock off the north-eastern coast of Japan, 118 kilometers from the plant. TEPCO reports communications and power were not affected and no additional damage was observed as a result.NEWS, the CNN Wire Staff,weblink Fresh aftershock in Japan rouses fear, kills 2, CNN, 24 April 2011, 8 April 2011, WEB,weblink Magnitude 7.1 – Near the East coast of Honshu, Japan,, 24 April 2011, yes,weblink" title="">weblink 14 April 2011, dmy-all, A tsunami warning is also issued, but is lifted after 90 minutes. Most of the workers at the nuclear plant were evacuated.{{Citation needed|date=April 2011}}Official measures at Fukushima I reactor unit 1, however, show a rise in temperature following the aftershock and a spiking amount of radiation in the Dry Well, which exceeds the instrument maximum of 100 Sv/h.WEB,weblink Unit 1 nuclear power plant Fukushima Radiation, TEPCO, 8 April 2011, yes,weblink" title="">weblink 8 April 2011, dmy-all, Gauge B, in the meantime, records a steady increase in pressure for the previous ten days in the same reactor.WEB,weblink Unit 1 nuclear power plant Fukushima Pressure, TEPCO, 8 April 2011, yes,weblink" title="">weblink 10 April 2011, dmy-all, Reporting the rise to 100 Sv/h from the earlier 30 Sv/h, TEPCO declares that the "validity of the measurement is questioned" both for radiation levels and pressure.

Friday, 8 April

Before the crisis evaluation was elevated by Japanese authorities to level 7, the highest level, experts already recognized that Fukushima is the most complicated nuclear accident.DiSavino, Scott. "Analysis: A month on, Japan nuclear crisis still scarring," Reuters (UK). 8 April 2011. Retrieved 26 March 2017.
{| class="wikitable collapsible collapsed plainrowheaders" style="border-bottom: 3px solid gray;"! scope="col" style="border-right: 3px solid gray; width: 16%;" |! scope="col" style="width: 14%;" | Unit 1! scope="col" style="width: 14%;" | Unit 2! scope="col" style="width: 14%;" | Unit 3! scope="col" style="width: 14%;" | Unit 4! scope="col" style="width: 14%;" | Unit 5! scope="col" style="width: 14%;" | Unit 6
| Fuel integrity
Damaged (70% estimated)}}Damaged (30% estimated)}}Damaged (25% estimated)}}Spent fuel possibly damaged}}Not damaged}}Not damaged}}
| Reactor pressure vessel integrity
Unknown}}Unknown}}Unknown}}Not damaged (defueled)}}Not damaged}}Not damaged}}
| Containment integrity
Not damaged (estimation)}}Damage and leakage suspected}}Not damaged (estimation)}}Not damaged}}Not damaged}}Not damaged}}
| Core cooling system 1 (ECCS/RHR)
Not functional}}Not functional}}Not functional}}Not necessary (defueled)}}Functional}}Functional}}
| Core cooling system 2 (RCIC/MUWC)
Not functional}}Not functional}}Not functional}}Not necessary (defueled)}}Functional (in cold shutdown)}}Functional (in cold shutdown)}}
Building integritySeverely damaged due to hydrogen explosion|style=border-bottom:3px solid gray;}}Slightly damaged, also panel removed to prevent hydrogen explosion|style=border-bottom:3px solid gray;}}Severely damaged due to hydrogen explosion|style=border-bottom:3px solid gray;}}Severely damaged due to hydrogen explosion|style=border-bottom:3px solid gray;}}Panel removed to prevent hydrogen explosion|style=border-bottom:3px solid gray;}}Panel removed to prevent hydrogen explosion|style=border-bottom:3px solid gray;}}
| Pressure vessel, water level
Fuel exposed partially or fully}}Fuel exposed partially or fully}}Fuel exposed partially or fully}}Safe (defueled)}}Safe (in cold shutdown)}}Safe (in cold shutdown)}}
| Pressure vessel, pressure (Two instrument trains)
Increasing to 0.456 MPa absolute (Train A) / 0.836 MPa absolute (Train B – suspected faultyHTTP://WWW.IAEA.ORG/PRESS/?P=1988>TITLE=IAEA BRIEFING ON FUKUSHIMA NUCLEAR ACCIDENT (7 APRIL 2011, 18:00 UTC)ACCESSDATE=8 APRIL 2011, Stable at 0.090 MPa absolute (Train A) / 0.083 MPa absolute (Train B) at 7 April 02:00 JST}}Stable at 0.103 MPa absolute (Train A) / 0.022 MPa absolute (Train C) at 7 April 02:00 JST}}Safe (defueled)}}Safe (in cold shutdown)}}Safe (in cold shutdown)}}
| Pressure vessel, temperature
Stable at 224 °C on 7 April}}HTTP://WWW.IAEA.ORG/PRESS/?P=1988>TITLE=IAEA BRIEFING ON FUKUSHIMA NUCLEAR ACCIDENT (7 APRIL 2011, 18:00 UTC), 8 April 2011, Stable at 143 °C on 7 April}}Stable at 115 °C on 7 April}}Safe (defueled)}}Safe (in cold shutdown)}}Safe (in cold shutdown)}}
Containment pressureStable at 0.150 MPa (absolute) at 7 April 02:00 JST|style=border-bottom:3px solid gray;}}Stable at atmospheric pressure on 6 April|style=border-bottom:3px solid gray;}}Stable at 0.1071 MPa (absolute) at 7 April 02:00 JST|style=border-bottom:3px solid gray;}}Safe|style=border-bottom:3px solid gray;}}Safe|style=border-bottom:3px solid gray;}}Safe|style=border-bottom:3px solid gray;}}
| Seawater injection into core
Continuing (switched to freshwater 25 March)}}Continuing (switched to freshwater 26 March)}}Continuing (switched to freshwater 25 March)}}Not necessary (defueled)}}Not necessary}}Not necessary}}
| Seawater injection into containment vessel
To be decided}}To be decided}}To be decided}}Not necessary}}Not necessary}}Not necessary}}
Containment ventingTemporarily stopped|style=border-bottom:3px solid gray;}}Temporarily stopped|style=border-bottom:3px solid gray;}}Temporarily stopped|style=border-bottom:3px solid gray;}}Not necessary|style=border-bottom:3px solid gray;}}Not necessary|style=border-bottom:3px solid gray;}}Not necessary|style=border-bottom:3px solid gray;}}
International Nuclear Event Scale>INESLevel 5}}Level 5}}Level 5}}Level 3}}–}}–}}
| Environmental effect
  • Radiation levels:

* South side of office building: 650 ÂµSv/hour at 8 April 15:00 JST * Main gate: 94 ÂµSv/hour at 8 April 15:00 JST * West gate: 40 ÂµSv/hour at 8 April 15:00 JST
  • Levels of radioactive iodine 4,385 times higher than regulatory limits were detected in seawater samples on 30 March
  • Levels of radioactive iodine 7.5 million times higher than regulatory limits were detected in seawater samples near the unit 2 water intake on 2 April
  • On 2 April highly radioactive (over 1 Sv/hour) water was discovered leaking from a concrete structure housing electrical cables into the sea through cracks in the concrete wall; as of 6 April this leakage has been stopped
  • On 4 April the release of 10,000 tons of low-level radioactive waste water began in order to make room for the highly radioactive water discovered on 2 April
  • Radioactive material was detected in underground water sampled near the turbine buildings on 30 March
  • Radioactive material has been detected in milk and agricultural products from Fukushima and neighboring prefectures, prompting government limits on shipments (21 March) and intake (23 March) for some products
  • Radioactive iodine was found in tap water in some prefectures between 21 and 27 March, prompting government warnings not to drink the water in those regions; as of 2 April these warnings have been lifted
  • Levels of radioactive caesium above regulatory limits were detected in small fish caught off the coast of Ibaraki on 4 April
Evacuation radius 20 km from the nuclear power station, but 30 km should consider leaving as of 25 March 11:30 JSTHTTP://WWW.LATIMES.COM/NEWS/NATIONWORLD/WORLD/LA-FGW-JAPAN-NUCLEAR-PLANT-20110326,0,5763742.STORY>TITLE=JAPAN STEPS UP NUCLEAR PLANT PRECAUTIONS; KAN APOLOGIZESWORK=L.A. TIMESLAST=MAKINEN,
| General status from all sources regarding reactor cores
Stabilized by injecting sea water and boron}}Stabilized by injecting sea water and boron}}Stabilized by injecting sea water and boron; pressure elevated on 20 March}}Defueled}}Cold shutdown on 20 March 14:30 JST}}Cold shutdown on 20 March 19:27 JST}}
| General status from all sources regarding Spent-Fuel Pools
Sprayed freshwater injection started, 60 °C on 20 March by infrared helicopter measurement}}Freshwater injection continues, 71.0 °C on 5 April 06:00 JSTSEISMIC DAMAGE INFORMATION (THE 75TH RELEASE) (AS OF 16:00 APRIL 5TH, 2011)>URL=HTTP://WWW.NISA.METI.GO.JP/ENGLISH/FILES/EN20110408-1-1.PDFACCESSDATE=8 APRIL 2011DEADURL=YESARCHIVEDATE=23 MAY 2011, dmy-all, }}Sprayed freshwater injection continues, 60 °C on 20 March by infrared helicopter measurement}}Sprayed freshwater injection continues after hydrogen explosion from pool on 15 March 40 °C on 20 March by infrared helicopter measurementL'Institut de radioprotection et de sûreté nucléaire (IRSN, the French "Radioprotection and Nuclear Safety Institute"). Retrieved 11 April 2011.}}Cooling system restored, 34.8 °C on 4 April 13:00 JST}}Cooling system restored, 27.5 °C on 4 April 13:00 JST}}
!colspan="7" | Information sources
WEB, Status of nuclear power plants in Fukushima as of 19:00 JST on 16 March,weblink JAIF, 16 March 2011, 16 March 2011, yes,weblink" title="">weblink 13 May 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 09:00 JST on 17 March,weblink JAIF, 17 March 2011, 17 March 2011, yes,weblink" title="">weblink 12 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 16:00 JST on 17 March,weblink JAIF, 17 March 2011, 17 March 2011, yes,weblink" title="">weblink 12 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 22:00 JST on 17 March,weblink JAIF, 17 March 2011, 17 March 2011, yes,weblink" title="">weblink 13 May 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 10:00 JST on 18 March,weblink JAIF, 18 March 2011, 18 March 2011, {{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }}

WEB, Status of nuclear power plants in Fukushima as of 22:00 JST on 18 March,weblink JAIF, 18 March 2011, 18 March 2011, yes,weblink" title="">weblink 22 March 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 10:00 JST on 19 March,weblink JAIF, 19 March 2011, 19 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 10:00 JST on 20 March,weblink JAIF, 20 March 2011, 20 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 22:00 JST on 21 March,weblink JAIF, 21 March 2011, 21 March 2011, yes,weblink" title="">weblink 21 March 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 22 March,weblink JAIF, 22 March 2011, 22 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 23 March,weblink JAIF, 23 March 2011, 23 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 16:00 JST on 25 March,weblink JAIF, 25 March 2011, 25 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all,

WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 25 March,weblink JAIF, 25 March 2011, 25 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all,
WEB, Status of nuclear power plants in Fukushima as of 20:00 JST on 26 March,weblink JAIF, 26 March 2011, 26 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 10:00 JST on 27 March,weblink JAIF, 27 March 2011, 27 March 2011, yes,weblink" title="">weblink 13 May 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 20:00 JST on 28 March,weblink JAIF, 28 March 2011, 28 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 20:00 JST on 29 March,weblink JAIF, 29 March 2011, 29 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 30 March,weblink JAIF, 30 March 2011, 30 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 31 March,weblink JAIF, 31 March 2011, 31 March 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 1 April,weblink JAIF, 1 April 2011, 1 April 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 18:00 JST on 2 April,weblink JAIF, 2 April 2011, 2 April 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 18:00 JST on 3 April,weblink JAIF, 3 April 2011, 3 April 2011, yes,weblink" title="">weblink 9 April 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 21:00 JST on 4 April,weblink JAIF, 4 April 2011, 4 April 2011, {{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }}WEB, Status of nuclear power plants in Fukushima as of 20:00 JST on 5 April,weblink JAIF, 5 April 2011, 5 April 2011, WEB, Status of nuclear power plants in Fukushima as of 20:00 JST on 7 April,weblink JAIF, 7 April 2011, 7 April 2011, yes,weblink" title="">weblink 13 May 2011, dmy-all, WEB, Status of nuclear power plants in Fukushima as of 20:00 JST on 8 April,weblink JAIF, 8 April 2011, 8 April 2011, yes,weblink" title="">weblink 13 May 2011, dmy-all,

Saturday, 9 April

Japan still struggles to keep water on the reactors to cool them and prevent further meltdown. Russian Antonov An-124 cargo planes fly out of Atlanta and Los Angeles, each carrying a huge concrete boom pump. The two 95-ton boom pumps, which TEPCO purchased for $2million each, can be operated from two miles away by remote control. Each boom pump can direct focused streams of water into the damaged reactors.Longbottom, Wil. "Massive cargo plane transports £2m remote-controlled concrete pump to stricken Japanese nuclear plant," Daily Mail (UK). 9 April 2011. Retrieved 11 April 2011; "World's largest concrete boom pumps en route to Japan to help cool nuclear reactors", The Street (US). 9 April 2011. Retrieved 11 April 2011.TEPCO does not plan to take a Chernobyl approach to resolving the nuclear power plant crisis by entombing the radioactive material in concrete."TEPCO won't take Chernobyl approach to resolving nuclear power plant crisis," Mainichi Shimbun (Japan). 8 April 2011. Retrieved 11 April 2011. If this decision were to change, the boom pumps could be retrofitted to deliver concrete for that purpose.Prior to the elevation to level 7 by the Japanese authorities James Acton, Associate of the Nuclear Policy Program at the Carnegie Endowment for International Peace, was of the opinion that "Fukushima is not the worst nuclear accident ever but it is the most complicated and the most dramatic, {{sic|This}} was a crisis that played out in real time on TV. Chernobyl did not."weblink" title="">"Analysis: A month on, Japan nuclear crisis still scarring," International Business Times (Australia). 9 April 2011. Retrieved 12 April 2011.A survey of radiation in seawater outside unit 2 shows radioactive isotope concentrations (iodine-131, caesium-134 and caesium-137) falling for the third consecutive day since the leak was plugged. However, the levels are still high at several thousand times legal levels. Other nuclides are being investigated, but Japanese regulator NISA has flagged up problems with TEPCO's sampling methodology.WEB,weblink Nuclear Engineering International,, 12 April 2011, 24 April 2011, yes,weblink" title="">weblink 19 March 2012, dmy-all,

Monday, 11 April

Coolant injection into reactors 1 and 3 is interrupted for 50 minutes due to a loss of power after a strong earthquake.NEWS,weblink Restoration work at Fukushima plant suffers setback in Monday quake, Kyodo News, 11 April 2011, Workers plan to pump water into turbine condensers, but need to pump water out of them first. Work to transfer water from the unit 2 and unit 1 condensers to a central storage tank was completed on 9 and 10 April. Workers have also knocked holes through the turbine hall buildings of units 2 and 4 to accommodate hoses for the water transfer. At unit 3, work continues to make space for water in the turbine condenser by pumping existing water into other tanks. Japanese news wire NHK reports that workers are laying hoses to transfer water to an LLW waste processing facility, which continues to be inspected. TEPCO says that it cannot start work switching on emergency systems on site until the turbine hall is dry. NHK also reported that radioactive water filling a tunnel near unit 2 has risen 12 cm since a leak in a trench was stopped on Wednesday 6 April.

Tuesday, 12 April

Japan officially raises Fukushima to INES Level 7, the same as Chernobyl.NEWS,weblink Nuclear accident level raised to maximum, NHK World, 12 April 2011, 12 April 2011, yes,weblink" title="">weblink 14 March 2011, dmy-all, WEB, Fukushima Accident Upgraded to Severity Level 7,weblink IEEE Spectrum, 12 April 2011, This new rating considers the accidents as a single event and uses estimated total release to the atmosphere as a justification.WEB, IAEA,weblink Fukushima Nuclear Accident Update Log, 12 April 2011, 13 April 2011, Following the hydrogen explosion in the reactor 1 building on 12 March and releases from the reactor 3 building, the equivalent of 190,000 terabecquerels of radioactive iodine had been released from the reactor buildings by 15 March, according to calculations by the Nuclear Safety Commission of Japan. A terabecquerel is equivalent to 1 trillion becquerels. The high level meant that by 15 March the Fukushima plant accident had already reached the worst level 7 on the International Nuclear and Radiological Event Scale, matching the assessment given to the 1986 Chernobyl nuclear disaster.NEWS, High radiation levels detected at Fukushima grounds a month after explosions, 26 April 2011,weblink Since that time the Fukushima reactors have continued to emit radiation; including atmospheric, water, and gamma ray releases.At Chernobyl, approximately 10 times the amount of radiation was released into the atmosphere as was released from Fukushima I through 12 April 2011.NEWS, Tran, Mark,weblink Nuclear crises: How do Fukushima and Chernobyl compare?, The Guardian, UK, 12 April 2011, 13 April 2011, The total amount of radioactive material still stored at Fukushima is about 8 times that stored at Chernobyl, and leakage at Fukushima continues.After cooling efforts at spent-fuel pool 4 were halted, due to an erroneous warning about the pool filling up,WEB, Japan Plant Emits More Radiation After Cooling Lapse,weblink NTI, 17 April 2011, the temperature of the pool rises to 90 Â°C and the dose rate 6 meters above the pool spikes at 84 mSv/h.WEB, Radiation surges above 4's fuel pool,weblink The Japan Times, 17 April 2011,

Friday, 15 April

Nuclear fuel is reported to have melted and fallen to the lower containment sections of reactors 1, 2 and 3. The melted material is not expected to breach a container (which might cause a massive radiation release). Instead, the melted fuel is thought to have dispersed fairly uniformly across the lower portions of the containers of the three reactors, which would make the resumption of the fission process, to the extent of a recriticality accident, 'most unlikely';WEB,weblink Japan plant fuel melted partway through reactors: Report,, 15 April 2011, 24 April 2011, however, it is only during future dismantling of the three damaged reactors that it would be possible to verify this hypothesis and to know what really occurred inside the reactor cores.

Saturday, 16 April

Plans are announced for a large-scale study on the environmental and health effects of radioactive contamination from the nuclear plant. Academics and researchers from across Japan will work with the Fukushima Prefectural Government starting in May.WEB,weblink Scholars eye extensive study on nuclear crisis, Tokyo Times (Japan), 16 April 2011, 16 April 2011,

Monday, 18 April

The Associated Press reports that two PackBot ground robots from iRobot have entered unit 1 and unit 3 of the crippled Fukushima nuclear power plant and performed temperature, pressure, and radioactivity measurements. The remote-controlled robots entered the two reactors over the preceding weekend. The devices opened closed doors and explored the insides of the reactor buildings, coming back with radioactivity readings of up to 49 mSv/h inside unit 1 and up to 57 mSv/h inside unit 3. TEPCO officials say that the radiation data from the robots do not change their plans for shutting down the plant by the end of this year. Though more robots will be used, a TEPCO official, Takeshi Makigami, says that robots are limited in what they can do, and eventually "people must enter the buildings".WEB,weblink Robots enter Fukushima reactors, detect high radiation – IEEE Spectrum,, 24 April 2011, Robots also entered unit 2, but the probe was hindered by fogging of the robot's camera lens from the high humidity, over 90%, inside the building.WEB,weblink Earthquake Report No. 85, JAIF, 18 May 2011, 18 May 2011, yes,weblink" title="">weblink 11 October 2011, dmy-all, Test spraying of an "anti-scattering agent" on the ground to prevent further spread of radioactive materials from the site is carried out over an area of about 1200 m2.WEB,weblink Seismic damage information (the 100th Release) (as of 15:00 April 18th, 2011), TEPCO, 18 April 2011, yes,weblink" title="">weblink 28 April 2011, dmy-all,

Tuesday, 19 April

TEPCO begins transferring excess radioactive cooling water from the reactor 2's basement and maintenance tunnels to a waste processing facility.Bradsher, Keith and Hiroko Tabuchi. "Water pumping begins at Japan nuclear reactor" New York Times (US). 20 April 2011, retrieved 2011; "Transfer of highly contaminated water begins", NHK (Japan). 19 April 2011.  Operations to pump radioactive water in the basements of buildings of units 1, 2, 3 and their associated tunnels start with unit 2.NEWS,weblink JAIF, 2 May 2011, {{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }}

Friday, 22 April

Japanese Prime Minister Naoto Kan states additional towns might be asked to evacuate, which largely involves agricultural lands.NEWS, Williams, Martyn, Japan expands evacuation zone around nuclear plant,weblink 22 April 2011,, 22 April 2011,   The government also plans to build 30,000 temporary homes by the end of May, and an additional 70,000 will follow.The president of the Tokyo Electric Power Company (TEPCO), Masataka Shimizu, formally apologizes at the prefectural government office in Fukushima to the Fukushima Governor Yuhei Sato for the nuclear crisis following the 11 March 2011 earthquake and tsunamis.NEWS, TEPCO president apologizes to Fukushima governor for nuke crisis,weblink 22 April 2011, People's Daily Online (Xinhua), 22 April 2011, In response, the Governor requests better working conditions for the workers.

Tuesday, 26 April

To prevent the proliferation of dust, TEPCO initiates spraying a synthetic resin to contain contaminated dust.

Wednesday, 27 April

Junichi Matsumoto, a general manager at Tokyo Electric Power Co., reports that radiation readings taken by two iRobot PackBot robots inside the reactor 1 building are as high as 1120 mSv/h, the highest level disclosed to date.NEWS, Radiation readings in Fukushima reactor rise to highest since crisis began,weblink 27 April 2011, Bloomberg, 27 April 2011, Tsuyoshi, Inajima, Michio, Nakayama,

May 2011

Monday, 2 May

T. Matsui of the University of Tokyo Institute of Physics releases a scientific paper analysing the ratio of iodine-131 to caesium-137 taken from water samples, which concludes that a recriticality may have occurred at least 10–15 days after the attempted shutdown.JOURNAL, 1105.0242, Deciphering the measured ratios of Iodine-131 to Cesium-137 at the Fukushima reactors, 2 May 2011, Matsui, 10.1143/PTP.126.1167, 126, 6, Progress of Theoretical Physics, 1167–1176, 2011PThPh.126.1167M,

Thursday, 5 May

Workers enter the reactor 1 building. This is the first time since the start of the crisis that a reactor building in the plant is visited by a human being. The workers will connect a ventilation system that should absorb radiation inside the building for the next 4–5 days, allowing them to start installation of the cooling system replacement. Because of protective gear, the workers are only exposed to a small amount of radiation (about 2 mSv).Tomoka A Hosaka (2011)Workers Enter Fukushima Reactor Building. TIME. TEPCO expects to bring the plant into a cold shutdown within six to nine months. IAEA releases a briefing.WEB,weblink Summary of reactor unit status – 5 May 2011, International Atomic Energy Agency, 18 February 2015,

Tuesday, 10 May

In a press release,WEB, 10 May 2011, TEPCO Press Release (May 10, 2011): Results of nuclide analyses of (radioactive materials in the) water in spent-fuel pool of unit 3 at Fukushima Daiichi nuclear power station,weblink TEPCO reports that levels of caesium-134, caesium-136, caesium-137, and iodine-131 (half-life of ~ 8 days), had spiked since last sampled on 2 March 2011, when these four nuclides were below detection limits. TEPCO's reportTEPCO Press Release (10 May 2011): Results of nuclide analyses of radioactive materials in the water in the spent-fuel pool of unit 3 at Fukushima Daiichi Nuclear Power Station:weblink gives the newly measured concentration (Bq/cm3) of each nuclide as of sampling date, 8 May.

Thursday, 12 May

TEPCO engineers confirm that a meltdown occurred, with molten fuel having fallen to the bottom of the reactor's containment vessel.NEWS,weblink Nuclear meltdown at Fukushima plant, 12 May 2011, Julian Ryall, The Daily Telegraph, London, The utility says fuel rods of the No. 1 reactor are fully exposed with the water level 1 meter (3.3 feet) below the base of the fuel assembly. The government and TEPCO are described as "consistently appeared to be underestimating the severity of the situation." According to a Japanese press report, there are holes in the base of the pressure vessel, and most of the fuel has likely melted. The nuclear fuel has possibly leaked into the containment vessel, which was damaged by an explosion during the crisis.NEWS,weblink Japan Reactor-Core Damage Worse Than Thought, 12 May 2011, Joe Carroll and Michio Nakayama, Bloomberg, However, the Nuclear Energy Institute, a nuclear lobbying firm, states that the situation "is in no way alarming. It was anticipated that there was fuel damage in reactors 1, 2 and 3. This is confirmation."NEWS,weblink CNN, 12 May 2011, Low reactor water level may have caused fuel rods to melt,

Saturday, 14 May

A third TEPCO (contractor) employee dies, after falling ill at 06:50, being brought to the plant's medical room unconscious.  The likely cause of death is a heart attack.NEWS,weblink Fukushima death not from radiation: TEPCO, UPI,   TEPCO says he was exposed to 0.17 millisieverts of radiation on Saturday. NEWS,weblink Reuters, Third worker dies at Japan's troubled nuclear plant,

Sunday, 15 May

A robot sent to the first floor of unit 1 records a radiation level of 2,000 mSv/h. At this level, workers would only be allowed to stay in the area for 8 minutes. In addition, the reactor's containment vessel is leaking large amounts of water into the basement. A TEPCO worker is able to peer into the basement and determines that the 11 m deep basement is approximately half full of water.NEWS,weblink Reuters, Japan readies new tactics for Fukushima after setback, 15 May 2011, 22 May 2011, TEPCO releases a report on the core status of reactor 1, revealing that fuel elements had become exposed above the water just 4 hours after the earthquake and SCRAM, and had fully melted after 16 hours.

Wednesday, 18 May

Four workers in protective suits and SCBA enter unit 2 for the first time since the 15 March explosion, to check on radiation levels and other conditions inside the building. The workers receive a dose of between 3 and 4 mSv each.

Friday, 20 May

TEPCO president Masataka Shimizu resigns after reporting the largest financial losses in the company's history.NEWS,weblink Tepco president resigns over Japan nuclear crisis, Telegraph, 20 May 2011, 29 June 2011, London,

Sunday, 22 May

TEPCO reports that reactor 3 leaked at least 250 tons of radioactive water into the Pacific Ocean over a period of 41 hours beginning on 10 May 2011.WEB,weblink Japan reports more radiation leakage,, 22 May 2011, 22 May 2011,

Tuesday, 24 May

On the eve of the arrival in Tokyo of a delegation from the International Atomic Energy Agency, TEPCO admits that the cores of reactor 2 and reactor 3 also melted down in the days immediately following the earthquake in mid-March 2011.NEWS,weblink Japan nuclear plant confirms meltdown of two more reactors; Fukushima Daiichi operator accused of delaying announcement of meltdowns in reactors 2 and 3 as IAEA inspectors arrive, The Guardian, 24 May 2011, 24 May 2011, London, Justin, McCurry, 16 hours after the earthquake and SCRAM, the fuel rods of reactor 1 had "mostly melted and fallen into a lump at the bottom of the pressure vessel – a state that TEPCO officials have described as a 'meltdown'".NEWS,weblink Fuel Rods at Japan Nuke Plant Mostly Melted, AP, Shino Yuasa, Time, 24 May 2011, 24 May 2011, A TEPCO spokesman Yoshimi Hitosugi stated last night, "The situation inside two and three is almost the same." TEPCO further stated that the fuel in reactor three took about 60 hours to melt and that the reactor melted down 100 hours after the magnitude nine quake struck.NEWS, McNeill, David, Fukushima plant suffered triple meltdown,weblink 25 May 2011, Irish Times, 25 May 2011,

Wednesday, 25 May

TEPCO informs the Nuclear and Industrial Safety Agency and the government of Fukushima Prefecture of the results of soil tests for plutonium ({{SimpleNuclide2|plutonium|238}}, {{SimpleNuclide2|plutonium|239}} and {{SimpleNuclide2|plutonium|240}}) carried out around the Fukushima Daiichi plant. While the levels were comparable to the fallout in Japan from atmospheric nuclear testing, TEPCO deemed that the plutonium had originated from the accidents.WEB,weblink Detection of radioactive materials in the soil in Fukushima Daiichi Nuclear Power Station (12th release), TEPCO, 25 May 2011, 28 May 2011,

Saturday, 28 May

TEPCO informs the Nuclear and Industrial Safety Agency and the government of Fukushima Prefecture of the results of soil tests for uranium ({{SimpleNuclide2|Uranium|234}}, {{SimpleNuclide2|Uranium|235}} and {{SimpleNuclide2|Uranium|238}}) carried out around the Fukushima Daiichi plant. The uranium found was considered to be natural, as its isotope ratios were consistent with the natural abundance.WEB,weblink Detection of radioactive materials in the soil in Fukushima Daiichi Nuclear Power Station (13th release), TEPCO, 28 May 2011, 28 May 2011, At 21:14 a cooling pump at reactor five stops. At 08:12 the next day, work began on a spare pump, and cooling was restored at 12:49.WEB,weblink Status of TEPCO's Facilities and its services after the Tohoku-Chihou-Taiheiyou-Oki Earthquake(as of 4:00 pm, May 29), TEPCO, 29 May 2011, 29 May 2011, The reactor temperature had risen to 92.2 Â°C. The cause of the outage is suspected to be motor failure.WEB,weblink Earthquake News No. 96, JAIF, 29 May 2011, 29 May 2011, yes,weblink" title="">weblink 11 October 2011, dmy-all,

Sunday, 29 May

It is reported that 22 out of 23 radiation monitoring systems around the Fukushima plants were disabled by the earthquake and tsunami. Some were directly damaged, but most were disabled due to communication and power lines being cut. Even monitors equipped with backup satellite links failed, probably due to antenna damage. In Miyagi prefecture, 4 out of 7 were disabled by the tsunami, with the remaining three stopping after three hours. In Ibaraki, some 40 monitors stopped working for three hours until power could be restored.NEWS, Kyodo, Power outages, downed communication lines knocked out most radiation monitoring systems in disaster areas,weblink 29 May 2011, The Japan Times, 29 May 2011, The first of the typhoons of the season is due to strike the area, while Japan states radiation levels at the seabed are several hundreds of times above normal levels off the coast of Fukushima. "The Science Ministry announced late on Friday highly radioactive materials were detected in a 300-km north-south stretch from Kesennuma in Miyagi Prefecture to Choshi in Chiba Prefecture, the Kyodo news agency reported."NEWS, Japan detects radiation,weblink 29 May 2011, Oman Daily Observer, 29 May 2011, yes,weblink" title="">weblink 1 June 2011, dmy-all, TEPCO reports that cooling has been restored for spent-fuel pools 1 to 4.

Tuesday, 31 May

An oil spill near reactors 5 and 6 is detected at 8:00 am, as well as an explosion heard at 2:30 pm near reactor 4.NEWS, Japanese nuclear plant hit by explosion and oil spill,weblink 31 May 2011, Guardian News and Media Limited 2011, 31 May 2011, London, NEWS, Press Release (Jun 01,2011), Status of TEPCO's Facilities and its services after the Tohoku-Chihou-Taiheiyou-Oki Earthquake(as of 9:00 am, June 1),weblink Tokyo Electric Power Company, 1 June 2011, 4 June 2011, TEPCO reports that the explosion was the bursting of an oxygen cylinder damaged by unmanned machinery during debris removal.WEB,weblink Earthquake Report No. 99, JAIF, 1 June 2011, 1 June 2011, yes,weblink" title="">weblink 3 April 2012, dmy-all, TEPCO states that there was a temporary oil leak into the sea near the plant, from an oil pipe that may have been damaged in the March disaster. It is stated as being an extremely small leak, possibly caused by recent rainy weather from Typhoon Songda. TEPCO says that the leak has stopped and oil fences have been installed to prevent the liquid from spreading into the Pacific Ocean.WEB, TEPCO starts system to cool spent-fuel pool at Fukushima plant,weblink 1 June 2011, THE MAINICHI DAILY NEWS, 3 June 2011, yes,weblink" title="">weblink 3 June 2011, dmy-all, NEWS, Storm suspends work at Japan Fukushima nuclear plant,weblink BBC News Asia-Pacific, 30 May 2011, 4 June 2011, WEB, TEPCO starts system to cool spent-fuel pool at nuclear plant,weblink Japan Today, 1 June 2011, 4 June 2011,

June 2011

Friday, 3 June

The first case is confirmed where radiation levels in humans have exceeded limits since the accident at the plant.WEB,weblink Earthquake Report No. 102, JAIF, 4 June 2011, 4 June 2011, yes,weblink" title="">weblink 19 April 2012, dmy-all, One worker in his thirties received 678 mSv, while another one in his forties received 643 mSv.WEB,weblink Earthquake Report No. 109, JAIF, 11 June 2011, 11 June 2011, yes,weblink" title="">weblink 16 November 2011, dmy-all, Before the accident the limit for emergency situations was 100 mSv, but it was raised by the government to 250 mSv just after the accident. The two TEPCO workers were on duty in the central control rooms of reactors Nos. 3 and 4 and told the health and labor ministry that they didn't remember whether they wore protective masks or not when a hydrogen explosion occurred at reactor No. 1 on 12 March.

Saturday, 4 June

Air radiation readings of up to 4000 millisieverts per hour are recorded in the reactor 1 building.WEB,weblink No. 1 plant's air radiation highest measured so far, The Japan Times, 4 June 2011, 7 June 2011,

Monday, 6 June

Japan's Nuclear and Industrial Safety Agency (NISA) gives new estimates of the times at which the reactor pressure vessels were damaged and possibly dropped fuel into the containment vessels: 5 hours after the initial earthquake for reactor 1 (20:00 March 11); 80 hours for reactor 2 (22:50 March 14); and 79 hours for reactor 3 (22:10 March 14).WEB,weblink 'Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown, Yomiuri Shimbun, 8 June 2011, 8 June 2011, In addition, NISA more than doubles its original estimate of radiation that escaped into the atmosphere in the first six days, from 370,000 terabecquerels to 770,000 terabecquerels.Japan says fuel may have melted through 3 reactorsweblink

Wednesday, 8 June

The ministry of education says that strontium {{SimpleNuclide2|Strontium|89}} and {{SimpleNuclide2|Strontium|90}} have been detected in soil samples collected from late March to early May and 22–62 km away from the Fukushima Daiichi plant. The highest values are reported in Namie town at 1,500 Bq/kg of strontium {{SimpleNuclide2|Strontium|89}}, and 250 Bq/kg of strontium {{SimpleNuclide2|Strontium|90}}.WEB,weblink Strontium detected in soil more than 20 km away from Fukushima Daiichi plant, Yomiuri Shimbun, 8 June 2011, 8 June 2011, yes,weblink" title="">weblink 26 November 2011, dmy-all, The Japanese government's report on the Fukushima disaster to IAEAWEB, Report of Japanese government to the IAEA ministerial conference on nuclear safety – The accident at TEPCO's Fukushima nuclear power stations,weblink is described in an article in the Yomiuri newspaper. The government report states that nuclear fuel has possibly melted through the base of the pressure vessels in the first three reactors. With data from the government report, the newspaper compares the March timelines provided by TEPCO and by NISA, which had performed further analysis; there were differences in the theoretical timing of events of up to 29 hours in the days following the tsunami.'Melt-through' at Fukushima? / Govt. suggests situation worse than meltdownweblink

Thursday, 9 June

A spokesman for TEPCO says the company is revising its earlier road-map for bringing the plant under control, including the time expected to achieve cold shutdown.Nuclear fuel has melted through base of Fukushima plantweblink

Tuesday, 14 June

From 00:44 to 02:35 there is a massive steam and smoke release from unit 3, recorded by the TEPCO live cam.WEB,weblink 2011.06.14 00:00–01:00 / 福島原発ライブカメラ (Live Fukushima Nuclear Plant Cam), Tepco weblink, 14 June 2011, 2 July 2011, yes,weblink" title="">weblink 19 July 2011, dmy-all, WEB,weblink 2011.06.14 01:00–02:00 / 福島原発ライブカメラ (Live Fukushima Nuclear Plant Cam), Tepco weblink, 14 June 2011, 2 July 2011, No explanation has been given yet by TEPCO officials.

Wednesday, 15 June

TEPCO begins a trial run of a radioactive water treatment system in an effort to break away from the vicious cycle of injecting water into reactors to cool them and ending up with more contaminated water.TEPCO starts up water treatment system, but massive radioactive waste feared {{webarchive|url= |date=19 June 2011 }} While contaminated water is treated, the system is expected to produce about 2,000 cubic meters of radioactive sludge by the end of 2011.

Saturday, 18 June

The radioactive water treatment system is forced to shut down because a filter exceeds its radioactivity limit. The separation unit, which removes caesium from the water, had been expected to last about a month before its cartridge required replacing—at a radiation level of 4 millisieverts per hour. The radiation levels near the filter cartridge replacement valves reach 4.7 millisieverts per hour after just 5 hours of operation, reportedly due to oil and sludge in the water which contained more radioactivity than expected.WEB,weblink After five hours, accumulated radiation forces TEPCO to stop water treatment, Nuclear Street, 20 June 2011, 23 June 2011, WEB,weblink TEPCO plays down decontamination failure, The Japan Times, 20 June 2011, 20 June 2011,

Sunday, 19 June

Radiation in some areas of Tsukidate, 50 km NW of the Fukushima 1 plant, exceeds the legal limit. The government plans to help households in designated areas to evacuate, raising concern among residents. Although the Tsukidate elementary school has not detected radiation levels in excess of the legal limit, about 80 parents and teachers thoroughly wash windows and verandas with high-pressure water jets and brushes and the school suspends activities on the playground in response to concern by parents.WEB,weblink Earthquake Report No. 117, JAIF, 19 June 2011, 19 June 2011, yes,weblink" title="">weblink 3 April 2012, dmy-all,

Tuesday, 21 June

A radiation reading of 430 millisieverts per hour is recorded in a mezzanine between the first floor and basement of reactor 2. This is the highest level measured up to this point in the reactor 2 building, and marks the first time that workers have entered the basement of this building since the beginning of the crisis.WEB,weblink TEPCO cuts back on water due to expected rains, Yomiuri, 23 June 2011, 23 June 2011, yes,weblink" title="">weblink 22 June 2011, dmy-all,

Monday, 27 June

Although the radioactive water treatment system has not yet started full-scale operation, a total of 1,850 tons of radioactive water has been processed during test runs of the system. Today this decontaminated water is used to cool the reactors for the first time. TEPCO states that it will continue injecting 16 tons of water per hour for cooling the 3 reactors, and that 13 tons of this will be made up from the decontaminated water.WEB,weblink Earthquake Report No. 125, JAIF, 27 June 2011, 27 June 2011, yes,weblink" title="">weblink 11 October 2011, dmy-all, The recycling system operates for only 90 minutes before it is halted due to a burst connection which leaks about one ton of water.WEB,weblink Earthquake Report No. 126, JAIF, 28 June 2011, 28 June 2011, yes,weblink" title="">weblink 1 October 2011, dmy-all,

Wednesday, 29 June

TEPCO reports that tellurium-129m is found at 720 becquerels per litre of seawater collected on 4 June, detected near the water intake for the reactor 1; about 2.4 times safe levels. Though tellurium-129m has a short half-life of about 34 days, TEPCO denied that its detection indicated the possibility of a new leak of radioactive water into the sea.WEB,weblink TEPCO denies new leak at Fukushima plant, Asahi Shimbun, 1 July 2011,

Thursday, 30 June

The Itabashi Ward Office announces that a concentration of caesium-134 at 2,700 becquerels per kilogram – in excess of the government's provisional limit – was detected in tea processed from leaves picked on 9 May in Tokyo.WEB,weblink Radioactive cesium detected in tea leaves grown in Tokyo, The Mainichi Daily News, 1 July 2011, yes,weblink" title="">weblink 3 July 2011, dmy-all,

July 2011

Sunday, 3 July

The water decontamination and water recycling systems are now both functional. 100% recycled water is now used for reactor cooling, and no additional volume of contaminated water is being generated.WEB,weblink Earthquake report No. 131, JAIF, 3 July 2011, 4 July 2011, yes,weblink" title="">weblink 16 November 2011, dmy-all,

Monday, 4 July

Radioactive caesium-137 is found in Tokyo's tap water for the first time since April.NEWS,weblinkweblink" title="">weblink yes, 4 July 2011, Cesium is found in Tokyo tap water for first time since April, Bloomberg, 3 July 2011, Radioactive caesium from Fukushima was expected to enter the Japanese seafood supply, and was projected to reach the US West Coast in 5 years.WEB,weblink Radioactive cesium from Fukushima expected to reach US West coast in 5 years, Mainichi Daily News, 27 June 2011, yes,weblink" title="">weblink 30 June 2011, dmy-all,

Wednesday, 13 July

The Japanese Nuclear Safety Commission publishes a report dated 11 June 1993, (Heisei 5) whose title literally translates to The event of entire alternating current station blackout on the nuclear power plant (原子力発電所における全交流電源喪失事象について) conducted by a working group. This reports the results of an evaluation of the regulations to prevent and handle an occurrence of the full loss of alternating current (Station Blackout or SBO) in nuclear power plants in Japan and other countries. It concludes that further discussion is needed on methods to avoid or recover from such accidents. It also reports that the probability of an SBO in Japan is lower than in other countries.WEB,weblink ja:原子力発電所における全交流電源喪失事象について, 1993-06-11, Japanese Nuclear Safety Commission, Japanese, The event of entire Alternating Current station blackout on the nuclear power plant,weblink" title="">weblink 17 August 2011, 2011-07-18, yes, dmy-all, 1. NEWS, ja:18年前、全電源喪失検討 安全委 幻の報告書,weblink Tokyo Shimbun, 14 July 2011 ver.11 Page 2, 2011-07-18, Japanese, 18 years ago, SBO was discussed by Japanese Nuclear Safety Commission, but it is a phantom report., yes,weblink" title="">weblink 16 July 2011, dmy-all, 2. NEWS, ja:東日本大震災:福島第1原発事故「全電源喪失は考慮不要」93年、安全委が国追認,weblink Mainichi Shimbun, 14 July 2011 ver.14新Page 1, 2011-07-18, Japanese, Aftermath of the 2011 Tōhoku earthquake and tsunami; Fukushima Daiichi nuclear disaster, "reported in 1993, No need to consider SBO", Japanese Nuclear Safety Commission had followed to acknowledge governments regulation., yes,weblink" title="">weblink 15 July 2011, dmy-all, 3. NEWS, ja:18年前に電源喪失対策検討「重大性低い」安全委結論,weblink Asahi Shimbun, 14 July 2011 Ver. 13 Page 1, 2011-07-18, Japanese, Japanese Nuclear Safety Commission concluded "Low seriousness" on discussed SBO 18 years ago., 4. NEWS, ja:原発の電源喪失、安全委93年に検討…公表せず,weblink Yomiuri Shimbun, 15 July 2011, 2011-07-18, Japanese, SBO in nuclear power plant, Japanese Nuclear Safety Commission discussed in 1993, ..... but no disclosure.,

Thursday, 14 July

The number of people actively working at the Fukushima Daiichi nuclear plant is about 3,000. NISA orders TEPCO to boost the number of safety managers to support this large number of workers.WEB,weblink Earthquake report No. 142, JAIF, 14 July 2011, 14 July 2011, yes,weblink" title="">weblink 21 May 2013, dmy-all, The water decontamination systems continue to be plagued by leaks and filter problems. Over the last week they had been operating at an average of 73% capacity, below the target of 90% which is required to meet the current timetable.WEB,weblink Earthquake report No. 143, JAIF, 15 July 2011, 15 July 2011, yes,weblink" title="">weblink 1 October 2011, dmy-all,

Saturday, 16 July

In a joint assessment the Japanese government and TEPCO say they have completed the first step of a 3-month plan outlined in mid-April for a complete cold shutdown. Reactors 1, 2 and 3 have been cooled down to a stable level and nitrogen has been injected into their containment vessels to prevent hydrogen explosions; however, the assessment admits that contaminated water has leaked out of storage tanks, and that water level settings at its water purification facilities were incorrect.WEB,weblink Earthquake report No. 144, JAIF, 16 July 2011, 16 July 2011, yes,weblink" title="">weblink 18 August 2011, dmy-all,

August 2011

Monday, 1 August

A radiation level of 10 sieverts per hour is read at a ventilation shaft between reactors 1 and 2. The area is subsequently sealed.NEWS,weblinkweblink" title="">weblink yes, 3 August 2011, Japan utility seals area with high radiation level,, 23 August 2011, The reading of 10 Sv is the maximum for many Geiger counters, including those used for these readings. One official states that it is entirely possible that the radiation readings were higher since the counter was reading its maximum. Radiation has been impeding attempts to replace cooling systems.NEWS,weblink Tepco Reports Second Deadly Radiation Reading at Fukushima Plant, Bloomberg, 3 August 2011, 3 August 2011, Tsuyoshi, Inajima, Kari, Lundgren, These are the highest readings logged indoors since the initial March 2011 explosions.NEWS,weblink Tepco Detects Hotspots At Fukushima Site, No Delay Expected For Recovery Plan, Wall Street Journal, 2 August 2011, 3 August 2011, {{dead link|date=September 2016|bot=medic}}{{cbignore|bot=medic}}

Tuesday, 2 August

On Tuesday, 2 August, a radiation level of 5 sieverts per hour is detected on the second floor of the turbine building in reactor 1.WEB,weblink Place where high radiation dose was detected on the 2nd floor of Turbine Building, Unit1, at Fukushima Daiichi Nuclear Power Station, TEPCO, 23 August 2011, The radioactivity rates detected on 2 and 1 August are considered lethal for even brief human exposures, an exposure of 0.1 Sv being the normal accepted workplace exposure over 5 yearsWEB, World nuclear Association,weblink Nuclear Radiation and Health Effects, 2011-08-22, and 8 Sv or 8 Gray (8Gy){{Elucidate|reason=Absorbed dose (Gray) or dose equivalent (Sv)?|date=October 2015}} being a 100% lethal dose.WEB, Radiation Contamination and Exposure,weblink The Merck Manual, Merck, 2011-08-22,

Wednesday, 10 August

Installation of the new, closed circulation cooling system is finished for all four damaged reactors (1–4), reactor 1 being the last.weblink" title="">Earthquake Report – JAIF, No. 170 (englisch, pdf). JAIF / NHK, 8. August 2011, archived from Original, fetched 14. August 2011. Previously, cooling was achieved with water injection by giant pump trucks.The water decontamination system is not working as well as expected, operating at roughly 66% of expected performance and suffering from numerous malfunctions. The system is necessary to decontaminate the large amount of radioactive water that remains on the site.

September 2011

Thursday, 8 September

The Japan Atomic Energy Agency calculates that a total of 15,000 terabecquerels of radiation has been released into the sea from the crippled Fukushima Daiichi power plant.WEB,weblink Radioactive release into sea estimated triple, NHK, 8 September 2011, 20 September 2011, yes,weblink" title="">weblink 24 September 2011, dmy-all,

Friday, 16 September

Research indicates that the meltdown of reactor number 2 could have been avoided if water was injected to cool the reactor 4 hours earlier. Water injection was started at 8 pm on 14 March after the cooling system failed at 1 pm that day. The meltdown could have been avoided if injection had started by 4 pm.WEB,weblink Earthquake report No. 206, JAIF, 16 September 2011, 16 September 2011, yes,weblink" title="">weblink 19 April 2012, dmy-all,

Wednesday, 21 September

Typhoon Roke brings strong winds and up to 42 cm of rain to some areas of NE Japan. At the same time a magnitude 5.3 earthquake strikes just south of Fukushima. No significant problems are reported at the Fukushima Daiichi plant.NEWS,weblink Typhoon-ravaged Japan also hit by earthquake, CBC, 21 September 2011, 22 September 2011, yes,weblink" title="">weblink 21 September 2011,

Thursday, 29 September

The measured core temperature falls below 100 degrees Celsius for all 3 damaged reactors with reactor number 2 finally achieving this status; reactors 1 and 3 had been below 100 degrees since August.WEB,weblink Earthquake report No. 219, JAIF, 29 September 2011, 29 September 2011, yes,weblink" title="">weblink 28 October 2011, dmy-all, Hydrogen is found at concentrations of 61 to 63 percent in pipes connected to the reactor 1 containment vessel. Plans are made to check for hydrogen in the pipes of all reactors and flush if necessary to prevent the possibility of another explosion.

October 2011

Saturday, 8 October

The Economist reports that high levels of radioactive particles, including plutonium have been found in an extended irregular zonweblink map that extends well outside the 30 km evacuation radius around the Fukushima Dai-ichi nuclear power plant.NEWS,weblink Radiation in Japan, Hot spots and blind spots, The mounting human costs of Japan’s nuclear disaster, 8 October 2011, The Economist,

Monday, 31 October

A French studyWEB, Synthèse actualisée des connaissances relatives à l’impact sur le milieu marin des rejets radioactifs du site nucléaire accidenté de Fukushima Dai-ichi,weblink by the Institute for Radiological Protection and Nuclear Safety revealed that the Fukushima nuclear disaster caused the biggest discharge of radioactive material into the ocean in history. The radioactive caesium that flowed into the sea from the Fukushima Dai-Ichi nuclear plant was 20 times the amount estimated by its owner, Tokyo Electric Power Co.NEWS, Beth Thomas, Fukushima Plant Released Record Amount of Radiation Into Ocean,weblink Bloomberg, 31 October 2011, Atmospheric releases were cited as amounting to 35,800 terabecquerels of caesium-137 by the Atmospheric Chemistry and Physics journal—an estimate about 42 percent of that released into the atmosphere in the Chernobyl explosion in 1986. Caesium-137 has a half-life of 30 years.

November 2011

Tuesday, 1 November

TEPCO reports the completion of a cover for the reactor unit 1, which is 54 metres high, 47 metres wide and 42 metres deep. The cover has a built-in ventilation system that is supposed to filter radioactive material.WEB,weblink Tepco Completes Installation Of Cover at Fukushima-Daiichi Unit 1, 1 November 2011, WEB,weblink Unit1 of Fukushima Daiichi Nuclear Power Station Construction work of cover panels around,

Wednesday, 2 November

Boric acid is injected into reactor number 2 after the discovery of xenon in its containment vessel. The presence of xenon may be an indication that a self-sustained fission reaction has been occurring.WEB,weblink Earthquake report No. 253, JAIF, 2 November 2011, 2 November 2011, yes,weblink" title="">weblink 21 May 2013, dmy-all,

Friday, 4 November

TEPCO retracts Wednesday's statement about a possible self-sustained fission reaction, and now claims that the xenon was a result of the normal decay of radioisotopes in the fuel.WEB,weblink Earthquake report No. 255, JAIF, 4 November 2011, 4 November 2011, yes,weblink" title="">weblink 3 January 2012, dmy-all,

Thursday, 17 November

The Japanese government bans shipments of rice from a farm near the Fukushima Dai-ichi nuclear plant. 630 becquerels of caesium per kilogram was found in the rice, over the 500 becquerels of caesium per kilogram allowed for human consumption. (From hundreds of spots tested around Fukushima, none had previously exceeded the limit.)Japan bans rice grown near crippled nuke plant

Tuesday, 29 November

TEPCO now claims that there was no explosion at reactor number 2 on 15 March as previously reported, and that instead the explosion occurred at reactor number 4. However, TEPCO has no explanation for the observed rise in radioactive emissions from reactor 2 at this time.WEB,weblink Earthquake report No. 276, JAIF, 29 November 2011, 29 November 2011, yes,weblink" title="">weblink 16 May 2013, dmy-all,

Wednesday, 30 November

TEPCO reports that a new computer simulation of the meltdown shows nuclear fuel rod material melting through the pressure vessel and deep inside the concrete of the primary containment vessel, within a foot of breaching it fully in Reactor No. 1. In the pessimistic scenario, all of the fuel of Reactor No. 1 has escaped the pressure vessel, as well as a majority of the fuel for Reactor No. 2 and 3.WEB,weblink Containment vessels held: simulation test, The Japan Times Online, 5 December 2011, 1 December 2011,

December 2011

Saturday, 3 December

Forty-five tons of highly radioactive water leaked from the apparatus being used to decontaminate the water at the plant. Plant workers attempted to contain the leak, but it was unknown if any of the water escaped into the water table or the ocean.Matsutani, Minoru, "Fukushima plant springs new water leak", Japan Times, 6 December 2011, p. 1.

Thursday, 15 December

A long-range timetable is announced for the decommissioning of the Fukushima Daiichi reactors.WEB,weblink Earthquake report No. 291, JAIF, 15 December 2011, 15 December 2011, yes,weblink" title="">weblink 3 January 2012, dmy-all, The plan is to repair the damaged containment vessels and determine the condition of the melted fuel by the end of 2021, then begin the retrieval of this fuel in 2022. The full duration of the schedule is 40 years, with the decommissioning work to be completed by 2052.

Friday, 16 December

In a joint statement by TEPCO and the Japan government it is announced that the reactors have achieved a state of cold shutdown. Temperatures in the containment vessels were 38.9 degrees Celsius for reactor one, 67.5 degrees for reactor two, and 57.4 degrees for reactor 3.NEWS, Nagata, Kazuaki, Officials: Cold shutdown has been achieved,weblink 16 December 2011, Japan Times, 16 December 2011, This announcement failed to lay to rest substantial concerns arising from TEPCO's inability to directly measure temperatures at the bottoms of the containment vessels, and the fact that the site is too radioactive for visual confirmation of the fuel rods' status.NEWS, Skeptics cast doubt on Fukushima status, even as Japan declares nuclear reactors 'stable', Arthur, Bright, 16 December 2011, 17 December 2011,weblink NEWS, Japan’s Prime Minister Declares Fukushima Plant Stable, Hiroko Tabuchi, 16 December 2011, 17 December 2011,weblink The New York Times,

Sunday, 18 December

230 tons of highly radioactive water is discovered in a tunnel below a building that stores contaminated water, raising questions about TEPCO's inspection and management capabilities.WEB,weblink Earthquake report No. 295, JAIF, 19 December 2011, 20 December 2011, yes,weblink" title="">weblink 21 May 2013, dmy-all, TEPCO admits that this radioactive water may be mixing with the ground water, yet claims that the tunnel is not connected to the sea.

Tuesday, 20 December

US Nuclear Regulatory Commission Chairman Gregory Jaczko, visiting Japan, confirmed that the Daiichi reactors were stable. Said Jaczko, "The temperatures have decreased significantly, the amount of heat that's being produced from the reactor fuel itself is very, very low now. So it simply doesn't have the kind of energy, if you will, that's needed to have any kind of off-site releases of radiation. I feel very comfortable with the (government's cold shutdown) decision."Kyodo News, "Fukushima 'stable': U.S. nuke chief", Japan Times, 22 December 2011, p. 2.

Monday, 26 December

An interim report was issued by the investigative panel headed by Yotaro Hatamura. In the report, the panel concluded that poor internal communication by the Japanese government and faulty knowledge and actions by TEPCO employees contributed to the disaster. The Japanese cabinet was not informed of the government's System for Prediction of Environmental Emergency Dose Information, which could have told them of the wind direction's effect on the spread of radiation, which would have allowed them to make better decisions on which areas to evacuate around Fukushima Daiichi. TEPCO workers mistakenly believed that the isolation condenser for reactor No. 1 was still working, when it was not, delaying efforts to try other methods to cool the reactor. TEPCO workers turned off an emergency cooling system on reactor No. 3 for seven hours to try to switch to another system that was not working, allowing the reactor to overheat more quickly.Nagata, Kazuaki, "Report blasts government's crisis response", Japan Times, 27 December 2011, p. 1.


19 January

An attempt is made to view the state of the melted fuel in reactor 2 using a fibre-optic endoscope, however clear images of the water level and fuel location could not be obtained, probably due to the harsh environment inside the containment vessel.NEWS, New video of Fukushima nuclear reactor interior,weblink BBC, 20 January 2012, 20 January 2012, After radioactive water was discovered in a tunnel under reactor 2 on 18 December, the government directed TEPCO to survey the plant's underground facilities and check for more accumulation of radioactive water. TEPCO finds an additional 500 tons of water containing 16,200 Bq/cm3 of radioactive caesium in a pit near reactor 2, and 600 tons of 860 Bq/cm3 water near reactor 3.WEB,weblink Earthquake report No. 323, JAIF, 20 January 2012, 20 January 2012, yes,weblink" title="">weblink 16 May 2013, dmy-all,

22 February

TEPCO begins pouring a 60-centimetre-thick layer of concrete over 70,000 square metres of the ocean seabed near the Fukushima Daiichi power plant in an effort to contain contaminated sediments.WEB,weblink Earthquake report No. 354, JAIF, 22 February 2012, 22 February 2012, yes,weblink" title="">weblink 21 May 2013, dmy-all,

27 March

TEPCO measures atmospheric radiation at several points inside the containment vessel of reactor 2 for the first time, and reports values of 31.1 and 72.9 Sv/h. The utility states that radiation is too high for robots, endoscopes, and other devices to work properly.WEB,weblink The Japan Times, Reactor 2 radiation too high for access, Minoru Matsutani, 29 March 2012, 1 April 2012,

5 April

For the second time in 10 days highly radioactive wastewater is accidentally discharged into the sea. About 12 tons of wastewater leaks from a disconnected joint, a large portion of which flows into the sea through a drainage ditch.WEB,weblink Earthquake report No. 394, JAIF, 5 April 2012, 5 April 2012, yes,weblink" title="">weblink 21 May 2013, dmy-all,

5 May

Japan's last remaining active nuclear reactor goes offline. Since the Fukushima Daiichi incident, nuclear reactors have not been allowed to restart after being shut down for maintenance or safety checks. One by one the number of active nuclear reactors has steadily decreased until the last of Japan's 54 nuclear reactors is finally taken offline.WEB, Japan switches off final nuclear reactor,weblink Japan Today, 6 May 2012, 7 May 2012,

22 May

Japanese scientists report that the water depth inside reactor No. 1 is only 40 cm; much lower than expected, and low enough to expose some fuel. From this observation, it is concluded that a 2 cm hole may exist in a pipe that is 40 cm from the bottom of the vessel.WEB,weblink Earthquake report No. 427, JAIF, 23 May 2012, 24 May 2012, yes,weblink" title="">weblink 21 May 2013, dmy-all,

24 May

TEPCO releases new estimate of 900,000 terabecquerels for the total amount of radioactive material released from this facility into the environment.WEB,weblink Earthquake report No. 429, JAIF, 25 May 2012, 25 May 2012, yes,weblink" title="">weblink 10 November 2012, dmy-all,

5 July

Japan once again has a working nuclear reactor as the number 3 reactor at the Ohi nuclear plant begins generating power.WEB,weblink Earthquake report No. 459, JAIF, 5 July 2012, 5 July 2012, yes,weblink" title="">weblink 21 May 2013, dmy-all, This is the first reactor to be restarted since the tsunami, and marks the end of two months without nuclear power for Japan.

12 October

TEPCO admits for the first time that it had failed to take stronger measures to prevent disasters for fear of inviting lawsuits or protests against its nuclear plants.NEWS, Fackler, Martin, Japan Power Company Admits Failings on Plant Precautions,weblink 13 October 2012, The New York Times, 12 October 2012, NEWS, Sheldrick, Aaron, Fukushima operator must learn from mistakes, new adviser says,weblink Reuters, 13 October 2012, 12 October 2012, TEPCO's internal reform task force, led by company President Naomi Hirose, said in a report TEPCO had feared efforts to better protect nuclear facilities from severe accidents such as tsunamis would trigger anti-nuclear sentiment, interfere with operations or increase litigation risks. TEPCO could have mitigated the impact of the accident if it had diversified power and cooling systems by paying closer attention to international standards and recommendations, the report said. TEPCO also should have trained employees with practical crisis management skills rather than conduct obligatory drills as a formality, it said.NEWS, Yamaguchi, Mari, Japan utility agrees nuclear crisis was avoidable,weblink Associated Press,, 13 October 2012, 12 October 2012, In the internal report TEPCO said that before the accident it had been afraid to consider the risk of such a large tsunami as the one in March 2011 which hit Fukushima, fearing admissions of risk could result in public pressure to shut plants down. "There were concerns that if new countermeasures against severe accidents were installed, concern would spread in host communities that the current plants had safety problems," the report said. TEPCO said in the report that "severe accident measures" were taken in 2002, which included "containment venting and power supply cross-ties between units," but additional measures were never put in place.NEWS, Japanese nuclear plant operator admits playing down risk,weblink CNN Wire Staff, CNN, 13 October 2012, 12 October 2012, TEPCO added that taking such measures could also add to "public anxiety and add momentum to anti-nuclear movements."


(File:IAEA Experts at Fukushima (02813336).jpg|thumb|IAEA Experts at Fukushima Daiichi Nuclear Power Plant Unit 4, 2013)

18 March

Public trust in TEPCO takes another hitWEB, Govt. tells TEPCO to add multiple power sources,weblink NHK World, 21 March 2013, 21 March 2013, {{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }} as cooling systems for several spent-fuel pools go down for more than 29 hoursNEWS, Fukushima Plant Hit by Power Outage,weblink Mitsuru Obe, The Wall Street Journal, 21 March 2013, 19 March 2013, after a power interruption that may have been caused by a rat in a switchboard.NEWS, Fukushima: Rat linked to outage at Japan nuclear plant,weblink BBC, 21 March 2013, 20 March 2013,

9 July

Levels of caesium in groundwater from monitoring wells around the reactors jumps by 90 times compared with the levels 3 days earlier. The contamination is now measured at 9,000 becquerels of caesium-134 and 18,000 becquerels of caesium-137 per litre of water.WEB, Cesium levels soar in Fukushima plant groundwater,weblink NHK World, 10 July 2013, 9 July 2013, yes,weblink" title="">weblink 10 July 2013, dmy-all, As well, tritium levels in seawater from the port next to the plant have been increasing since May, and a water sample taken on 3 July showed 2,300 becquerels per litre, the highest measurement since the start of the nuclear crisis in March 2011.WEB, Level of radioactive tritium rising in harbor at Fukushima plant,weblink Japan Times, 10 July 2013, 25 June 2013,

10 July

Japanese government admits Fukushima Daiichi may have been leaking radioactive water into ground water and into the ocean since 2011.NEWS,weblink The New York Times, Hiroko, Tabuchi, Japanese Nuclear Plant May Have Been Leaking for Two Years, 10 July 2013,

22 July

TEPCO admits that since the 2011 reactor breaches, radioactive water has continued to leak from the plant into groundwater, making the groundwater radioactive, with implications for drinking water and for the Pacific.NEWS,weblink Japan's Fukushima operator acknowledges contaminated water flowing into sea, Takenaka, Kiyoshi, Reuters, 2013-07-22, 2013-07-23, NEWS,weblink The New York Times, Martin, Fackler, Japan: Nuclear Plant Admits Leaks, 22 July 2013,

19 August

It is discovered that 300 tonnes of highly contaminated water (80 MBq/LWEB,weblink ‘Serious’: Japan hikes Fukushima radiation danger level,, 2013-08-21, 2013-08-22, ) had leaked from a storage tank and seeped into the ground.WEB,weblink Fukushima operator reveals leak of 300 tonnes of highly contaminated water,, 2013-08-20, 2013-08-22,

21 August

Japan's Nuclear Regulation Authority raises the severity of the contaminated water leaks at Fukushima to INES level 3 "serious incident".NEWS,weblink Japan nuclear agency upgrades Fukushima alert level, BBC, 2013-08-21, 2013-08-22,

26 August

The Japanese government takes charge in dealing with the contaminated water situation. Trade minister Toshimitsu Motegi says "We’ve allowed Tokyo Electric to deal with the contaminated water situation on its own and they’ve essentially turned it into a game of Whack-a-Mole".NEWS,weblink Tepco ‘Whack-a-Mole’ Means Government Takeover in Fukushima, Bloomberg, 2013-08-26, 2013-08-27, Yuji, Okada, Takashi, Hirokawa, Jacob, Adelman,

15 September

Japan is once again nuclear free as its only working reactor goes offline for refuelling and maintenance.NEWS,weblink Japan goes nuclear-free indefinitely, Associated Press, CBC, 2013-09-15, 2013-10-28, Shizuo, Kambayashi,

18 November

Workers begin removing fuel rods from a storage pond at the Unit 4 reactor building. About 1,500 rods, some of them damaged, must be removed in a risky and dangerous operation set to take a year. Removed rods will then be moved into a more secure storage.WEB,weblink BBC News – Japan's Fukushima nuclear plant begins fuel rod removal, BBC News, 18 February 2015,


6 February

The reanalysis of a groundwater sample taken from a well in July 2013 updates its measurement from 900,000 Bq/L total beta radioactivity to a record-high 5 MBq/L of strontium-90 only (corresponding to about 10 MBq/L total beta radioactivity), after a problem with the measuring devices was found in October.WEB, Record-high strontium-90 in past Fukushima plant groundwater sample,weblink Kyodo News, 7 February 2014,

13 February

It is revealed that TEPCO had concealed for months the increase in measured groundwater radioactivityweblinkweblink Tepco took months to release record strontium readings at Fukushima, Reuters, 18 February 2015, 13 February 2014,

21 May

TEPCO begins operation to bypass groundwater flow around the reactor by pumping upstream groundwater to storage tanks, then discharging directly to the sea after measuring the contamination levels.WEB,weblink BYPASS OF CLEAN GROUNDWATER TO OCEAN STARTS, TEPCO, 2014-05-21, 2014-05-22,

3 June

TEPCO begins to construct facilities to establish an ice wall within the ground around the reactors to prevent contaminated water to mix with groundwater flowing under the area.WEB,weblink CONSTRUCTION OF WATER-BLOCKING ICE WALL STARTS AT FUKUSHIMA, TEPCO, 2014-06-03, 2014-06-28,

7 July

TEPCO has switched off the cooling system at reactor 5 due to a 3mm leak near a flow valve. Approximately 1,300 litre of water has spilled. They have approximately 9 days to repair it before water temperature reaches 65 degrees CelsiusWEB,weblink Fukushima has 9 days to prevent unsafe overheating, TEPCO, 2014-07-07, 2014-07-07,

17 July

TEPCO launches another campaign to contain the spread of contaminated sediments in the sea near the power plant, this time coating 180,000 square meters of sea floor with cement.WEB,weblink TEPCO Begins Coating Bottom of Sea in Port near Fukushima Daiichi to Prevent Spread of Contaminated Materials, JAIF, 2014-07-28, 2014-07-29, {{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }}

20 December

TEPCO reports that all spent fuel rods have now been safely removed from the storage pool at reactor 4.WEB,weblink Fuel Rods Are Removed From Damaged Fukushima Reactor Building, 2015-10-12,


10 January

TEPCO begins operation of a new reverse-osmosis system to remove strontium from contaminated water. The new system was built to treat 500 to 900 cubic metres of water per day, and reduce the strontium levels in the water by a factor of 100 to 1000.WEB,weblink TEPCO Starts Removing Strontium from Contaminated Water at Fukushima Daiichi NPS, JAIF, 2015-01-19, 2015-01-20, {{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }}

10 April

A robot designed to withstand intense heat and radiation is sent into Reactor 1 to locate the melted fuel. It covers 14 of 18 locations before it stops functioning and has to be abandoned.WEB,weblink Fukushima robot stranded after stalling inside reactor, McCurry, Justin, 2015-04-13, the Guardian, 2016-06-02,

5 September

The evacuation order is lifted for Naraha Town in Fukushima Prefecture.WEB,weblink Lifting of Evacuation Order for Naraha Town Marks Step Forward toward Reconstruction of Fukushima, JAIF, 2015-09-09, 2015-09-11,

10 September

The Sendai-1 nuclear reactor resumes commercial operation for the first time since the earthquake in May 2011. This ends almost 2 years with no Japan nuclear power plants in commercial operation since Ohi-1 was halted on 15 September 2013.WEB,weblink Kyushu Electric Power Starts Up Sendai-1, Ending 23-month Hiatus in Japanese NPP Operation, JAIF, 2015-08-11, 2015-08-12, WEB,weblink Sendai-1 NPP Returns to Commercial Operation: First to Do So under Japan’s New Nuclear Regulatory Standards, JAIF, 2015-09-11, 2015-09-11, WEB,weblink Shutdown of Japan’s Last Nuclear Reactor Raises Power Concerns, 2013-09-15, 2015-09-11,

26 October

After a 3-1/2 year construction project, TEPCO completes a 780 m seaside shielding wall to reduce the amount of contaminated water leaking into the sea.WEB,weblink TEPCO Completes Seaside Shielding Wall at Fukushima Daiichi, Greatly Reducing Risk of Contaminated Water Leakage, JAIF, 2015-10-29, 2015-10-29,


16 February

TEPCO estimates that 749,000 cubic metres of contaminated debris from Fukushima Daiichi will be produced by the year 2027, and releases a plan for incineration and storage of this waste.WEB,weblink TEPCO: Total Debris from Fukushima Daiichi to Reach 749,000 Cubic Meters by 2027, JAIF, 2016-02-16, 2016-02-16,


03 February

TEPCO said the radiation level in the containment vessel of reactor 2 at the crippled Fukushima No. 1 power plant was 530 sieverts per hour, the highest recorded level since the triple core meltdown in March 2011. This is however the first measurement of the radiation level within the reactor area and as such is likely lower than in the initial period after the meltdown. TEPCO also announced that there is a 2-meter hole under the pressure vessel in the reactor’s primary containment vessel.WEB,weblink Highest radiation reading since 3/11 detected at Fukushima No. 1 reactor, The Japan Times, 2017-02-03, 2017-02-03,

20 June

A recent investigation by TEPCO using temperature measurements has determined the probable location of the cores for reactors 1–3. They believe that most of the core debris has breached the pressure vessel and lays at the bottom of the containment vessel for reactors 1 and 3, although some debris seems to be lodged in the control rod drive mechanism for reactor 1. However, they believe that most debris may remain at the bottom of the pressure vessel for reactor 2.WEB,weblink New Data Obtained on Debris Locations Based on Temperature Changes Using Reduced Injections of Water, JAIF, 2017-06-20, 2017-06-21,

19–21 July

A remote operated robot takes the first pictures of the melted core of reactor 3.WEB,weblink Fuel Debris at Fukushima Daiichi Unit 3 Apparently Located under Pressure Vessel and at Bottom of PCV, JAIF, 2017-07-25, 2017-07-27, Some melted material hangs from the control-rod insertion mechanism under the pressure vessel, and there are piles of rocky objects at the bottom of the PCV that are thought to be melted core.

26 September

A revised decommissioning roadmap has the removal of fuel rods from reactor 3 storage pool starting in 2018, but the removal of fuel rods from the reactor 1 and 2 storage pools will be delayed until 2023.WEB,weblink 3-year delay in removal of fuel rods from Fukushima plant, The Asahi Shimbun, Chikako Kawahara, 2017-09-26, 2018-05-09, Removal of melted fuel debris from one of the reactors is expected to begin by 2021.


15 February

A robot with two "fingers" makes first contact with the fuel debris in the primary containment vessel (PCV) of reactor 2.WEB,weblink TEPCO Makes Contact with Debris at Fukushima Daiichi-2, JAIF, Noriyuki Ishii, 2019-02-15, 2019-02-22, The robot was able to move loose debris at 7 of the 10 locations probed, providing hope that it may be possible to remove these deposits from the PCV.

See also




  • Wang, John X. and Marvin L. Roush (2000) What every engineer should know about risk engineering and management. London: CRC Press. {{ISBN|9781420026962}}; {{OCLC|5030452}}
  • BOOK, 東日本大震災の記録 −原子力事故と計画停電−, 電気新聞, (社)日本電気協会新聞部, June 2011, 2011.6, (Japanese)

External links

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