Timeline of the Fukushima I nuclear accidents
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Fukushima Dai-ichi (dai-ichi means "number one"), is a disabled nuclear power plant. The Fukushima I nuclear accidents occurred after the 9.0 magnitude 2011 Tohoku earthquake and tsunami on 11 March. This offshore earthquake near the island of Honshu[1] produced a large tsunami in Japan, and a tsunami warning for over 20 countries. The earthquake triggered the shut down of the three active reactors at the Fukushima I Nuclear Power Plant (Fukushima Dai-Ichi). The subsequent tsunami stopped Fukushima I station's backup diesel generators, causing a station blackout. The subsequent lack of cooling led to explosions and partial meltdowns at the Fukushima I facility, with problems at all six reactor units and the central spent fuel pool.
Contents |
[edit] Timeline
Times are given in Japan Standard Time (JST), unless noted, which is UTC plus nine hours.
[edit] March event tree
The nuclear accident event tree[2] developed quickly in the early weeks after the earthquake and tsunami caused a number of accident sequences to begin.
[edit] First week
[edit] 11 March
14:46: A 9.0 magnitude earthquake strikes off the coast of Honshu Island at a depth of about 24 kilometres (15 mi). The Fukushima I power plant's nuclear reactors 1, 2, and 3 are automatically shut down by the shake. Nuclear reactors 4, 5, and 6 were undergoing routine maintenance and were not operating, (reactor 4 was defueled in November 2010). The tremor has the additional effect of causing the power plant to be cut off from the Japanese electricity grid, however, backup diesel generators kick in to continue cooling. Tokyo Electric Power Company (TEPCO), the plant's operator, finds that units 1 and 2 are not operating correctly and notifies the proper officials.[3]
15:01 (approximate): A 14-metre (46 ft) tsunami unleashed by the earthquake overtops the seawall designed to protect the plant from a tsunami of 5.7 metres (19 ft), inundating the Fukushima facility and disabling the backup generators whose electricity was then required to operate controls and cool the reactors.[4]
According to a report in the New York Times, "[A]t 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 Fukushima I, 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."[5]
16:00: The Nuclear and Industrial Safety Agency of Japan (NISA) initiates an emergency headquarters in an attempt to gather information on the 55 nuclear reactors in Japan.[6] There is no report that radiation was detected outside plant borders.[7]
19:03: Prime Minister Naoto Kan declares a nuclear emergency status.[8] This is 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.[6]
21:00: An evacuation order is issued by the government to persons within a 3 kilometres (1.9 mi) radius of the Fukushima I station. Those within a 10 kilometres (6.2 mi) radius are told that they can remain in their homes and carry on with regular activities until told otherwise.[6]
At Fukushima I, the ongoing lack of electricity is causing the cooling system to fail, and the pressure within the nuclear units build up. This pressure buildup is the result of residual decay heat causing the coolant, which is not being circulated, to evaporate.[9] There is no confirmation of radiation leaking from the reactor.[10] TEPCO announces that pressure inside reactor unit 1 of Fukushima I is more than twice normal levels.[6]
[edit] 12 March
02:44: Emergency battery power for the High Pressure Core Flooder System for Reactor 3 runs out.
04:15: Fuel rods in Reactor 3 are exposed.
05:30: Despite the high risk of the hydrogen igniting after combining with oxygen from water or in the atmosphere, 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 in the metal container building surrounding the unit.
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.[11]
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 once more reached to vent radioactive vapor into the air.[11]
15:30: Evacuation of residents within 3 km of Fukushima II and within 10 km of Fukushima I are underway.[12]
15:36: At reactor unit 1 at Fukushima I cameras document a massive hydrogen explosion on the outer structure of one of four buildings at the plant. It also documents the outer structure collapsing.
18:36 (approximately): TEPCO announces that four people who are employed at the power plant have been injured in the unit 1 explosion.
20:00: Uncertainty surrounds the actual cause of the blast at Fukushima I (later identified as a hydrogen explosion) and the damage caused.
Yukio Edano announces that the concrete building surrounding the steel reactor vessel at unit 1 in Fukushima I has collapsed as a result of the explosion; however no damage is believed to have been sustained by the reactor itself.
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.[12]
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, mostly tritium and nitrogen-16.
TEPCO engineers decided to directly inject sea water inside the pressure vessel of the reactors by means of the mobile trucks of the firemen, a brilliant ideas which avoided the situation to worsen. The pressure relief was also necessary to allow the firemen to inject seawater into the reactors vessels.
[edit] 13–17 March
- 13 March: A partial meltdown was reported to be possible at unit 3.[13] As of 13:00 JST, both reactors 1 and 3 were being vented to release overpressure and re-filled with water and boric acid for cooling and inhibition of further nuclear reactions.[14] Unit 2 was possibly suffering lower than normal water level but was thought to be stable, although pressure inside the containment vessel was high.[14] The Japan Atomic Energy Agency announced that it was rating the situation at unit 1 as level 4 (accident with local consequences) on the International Nuclear and Radiological Event Scale.[15][16]
- 14 March: The reactor building for unit 3 exploded[17] injuring eleven people. There was no release of radioactive material beyond that already being vented but blast damage affected water supply to unit 2.[18] The president of the French nuclear safety authority, Autorité de sûreté nucléaire (ASN), said that the accident should be rated as a 5 (accident with wider consequences) or even a 6 (serious accident) on INES.[19]
- 15 March: Damage to temporary cooling systems on unit 2 by 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.[20] An explosion in the "pressure suppression room" caused some damage to unit 2’s containment system.[20][21] A fire broke out at unit 4 involving spent fuel rods from the reactor, which are normally kept in the water-filled spent fuel pool to prevent overheating. Radiation levels at the plant rose significantly but subsequently fell back.[22] Radiation equivalent dose rates at one location in the vicinity of unit 3 recorded 400 millisieverts per hour (400 mSv/h).[15][23][24]
- 16 March: At approximately 14:30 on 16 March, TEPCO announced its belief that the fuel rod storage pool of unit 4—which is located outside the containment area[25]—may have begun boiling, raising the possibility that exposed rods could reach criticality. By midday, NHK TV was reporting white smoke rising from the Fukushima I plant, which officials suggested was likely coming from reactor 3. Shortly afterward, all but a small group[26] of remaining workers at the plant had been placed on standby because of the dangerously rising levels of radiation up to 1 Sv/h.[27][28] TEPCO had temporarily suspended operations at the facility due to radiation spikes and had pulled all their employees out.[29] A TEPCO press release stated that workers had been withdrawn at 06:00 JST because of abnormal noises coming from one of the reactor pressure suppression chambers.[30] Late in the evening, Reuters reported that water was being poured into reactors 5 and 6.[31]
- 17 March: During the morning, Self-Defense Force helicopters dropped water four times on the spent fuel pools of units 3 and 4.[32] In the afternoon it was reported that the unit 4 spent fuel pool was filled with water and none of the fuel rods were exposed.[33] Construction work was started to supply a working external electrical power source to all six units of Fukushima I.[34] Starting at 7 pm, police and fire water trucks with high pressure hoses attempted to spray water into the unit 3 reactor.[35] Japanese authorities informed the IAEA that engineers were laying an external grid power line cable to unit 2.[15]
[edit] Second week
[edit] 18–24 March
- 18 March: Tokyo Fire Department dispatched thirty fire engines with 139 fire-fighters and a trained rescue team at approximately 03:00 JST. These included a fire truck with a 22 m water tower.[36] For the second consecutive day, high radiation levels had been detected in an area 30 kilometers (18.6 miles) northwest of the damaged Fukushima I nuclear plant. The reading was 150 microsieverts per hour.[37] Japanese authorities upgraded INES ratings for cooling loss and core damage at unit 1 to level 5 and issued the same rating for units 2 and 3.[15] The loss of fuel pool cooling water at unit 4 was classified as level 3.[15] In a 24-hour period ending at 11 am local time, radiation levels near the plant had declined from 351.4 to 265 µSv/h, but it was unclear if the water spraying efforts were the cause of the decrease.[38]
- 19 March: A second group of 100 Tokyo and 53 Osaka firefighters replaced the previous team. They used a vehicle that projected water from a height of 22 meters for cooling spent nuclear fuel storage pool inside the reactor of unit 3.[39][40] Water was sprayed into the reactor for a total of 7 hours during the day. TEPCO reported afterward that the water had been effective in lowering the temperature around the spent fuel rods to below 100 °C.[41][verification needed]
- 20 March: External power was reconnected to unit 2 but work continued to make equipment operational. Repaired diesel generators at unit 6 provided power to restart cooling on units 5 and 6 which were returned to cold shutdown and their fuel cooling ponds returned to normal operating temperatures.[42][43] TEPCO announced that pressure in reactor 3's containment vessel was rising, and that it might be necessary to vent air containing radioactive particles to relieve pressure, Japanese broadcaster NHK reported at 1:06.[42] The operation was later aborted as TEPCO deemed it unnecessary.[42] While joining in a generally positive assessment of progress toward overall control, chief cabinet secretary Edano confirmed for the first time that the heavily damaged and contaminated complex would be closed once the crisis was over.[44]
- 21 March: Ongoing repair work was 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 were evacuated from unit 3 but no changes in radiation measurements or reactor status were seen. No work was going on at the time (such as restoring power) which might have accounted for the fire. White smoke, probably steam, was also seen coming from unit 2 at 18:22 JST, and this was accompanied by a temporary rise in radiation levels. A new power line was laid to unit 4 and unit 5 was transferred to its own external power from transmission line instead of sharing the unit 6 diesel generators.[45][46]
- 22 March: Smoke was still rising from units 2 and 3 but was less visible and was theorized to be steam following operations to spray water onto the buildings. Repair work resumed after having been halted because of concerns over the smoke, but no significant changes in radiation levels occurred so it was felt safe to resume work. Work continued to restore electricity, and a supply cable was connected to unit 4. Injection of seawater into units 1–3 continued.[47] External power cables were reported to be connected to all six units. Lighting was back on again in the control room of unit 3.[48][49]
- 23 March: In the late afternoon, smoke again started belching from reactor 3, this time black and grey smoke, causing another evacuation of workers from around the area. Aerial video from the plant showed what looked like a small fire at the base of the smoke plumes from within the heavily damaged reactor building. Feed water systems in unit 1 were restored increasing the rate water could be added to the reactor.[50] The Japanese Chief Cabinet Secretary also advised that high levels of radioactivity (around twice the legal limit for children) had been found in Tokyo's drinking water and that it should not be used to reconstitute baby formula.[51]
- 24 March: Seawater injection to units 1, 2 and 3 continued,[52] and radiation levels near the plant declined to 200 µSv/h.[53] Lighting was restored to the unit 1 control room.[54] Three workers were exposed to high levels of radiation which caused two of them to require hospital treatment after radioactive water seeped through their protective clothes.[55][56] The workers were exposed to an estimated equivalent dose of 2–6 Sv to the skin below their ankles.[57][58] 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".[57] The amount of the radioactivity of the water was about 3.9 MBq/ml. Infra-red surveys of the reactor buildings by helicopter showed that temperatures of units 1, 2, 3 and 4 continued to decrease, ranging 11–17 °C, and the fuel pool at unit 3 recorded 30 °C.[59]
[edit] Third week
[edit] 25–31 March
- 26 March: Fresh water became available instead of seawater to top up reactor water levels.[66] The fresh water was 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 Yokosuka Naval Base to Fukushima.[67] Radiation levels near the plant had declined to a still high 170 µSv/h.[68]
- 27 March: Levels of "over 1000" and 750 mSv/h were reported from water within unit 2 (but outside the containment structure) and 3 respectively. A statement that this level was "ten million times the normal level" in unit 2 was later retracted and attributed to incorrectly high levels of iodine-134 (which was later reported to be below the limit by TEPCO).[69][70][71][72] Japan's Nuclear and Industrial Safety Agency indicated 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."[73] The high radiation levels delayed technicians working to restore the water cooling systems for the troubled reactors.[74] USAF technicians at Yokota AB completed the fabrication of compatibility valves to allow the connection of deployed pump systems with the existing infrastructure at Fukushima.[75] An aerial video recorded by a Ground Self-Defense Force helicopter revealed according to NHK the clearest and most detailed view of the damaged plant to date. Significant observations included:[76]
-
- 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.
- The reactor 3 building is largely uncovered, its roof blown off in a hydrogen explosion over two weeks prior.
- The walls of the reactor 4 building have also collapsed.
- 28 March: The Japanese Nuclear Safety Commission stated that it "assumed" melted fuel rods in unit 2 have released radioactive substances into cooling water which subsequently leaked out through an unknown route to the unit 2 turbine building basement. To reduce the amount of water subject to leaking, TEPCO reduced the amount of water pumped into unit 2 reactor from 16 tons per hour to 7 ton per hour, which could lead to higher reactor temperatures. The highly radioactive water halted work on restoring the cooling pumps and other powered systems to reactors 1–4.[77] TEPCO confirmed finding low levels of plutonium in five samples from 21 March and 22 March.[78] Enriched levels of Pu238 relative to Pu239 and Pu240 at two of the sites in the plant (solid waste area and field), indicated that contamination had occurred at those sites due to the “recent incident”. Nonetheless, the overall levels of Pu for all samples were about the same as background Pu levels resulting from atmospheric nuclear bomb testing in the past.[79]
- 29 March: TEPCO continued to spray water into reactors 1–3 and discovered that radioactive runoff water was beginning to fill utility trenches outside the three reactor buildings. The highly radioactive water in and around the reactor buildings continued to limit progress by technicians in restoring the cooling and other automated systems to the reactors.[80]
- 30 March: TEPCO Chairman Tsunehisa Katsumata announced at a news conference that it was presently unclear how the problems at the plant would be resolved. An immediate difficulty was the removal of large quantities of radioactive water in basement buildings, but also salt built up inside the reactors from using seawater for cooling needed to be removed. Building new concrete walls around the reactors was being considered as had been done at Chernobyl.[81] The EPA (Environmental Protection Agency) found radioactive iodine in milk in the United States.[82]
- 31 March: Workers pumped radioactive water from a utility trench near reactor No. 1. into a storage tank near reactor No. 4.[83] Water in the condensers for the No. 2 and No. 3 reactors was shifted to outside storage tanks so that the condensers could receive more contaminated water from the reactors.[84] The world's largest concrete pumping plant was shipped from the United States to Fukushima.[85] The pumping truck was slightly modified to be able to pump cooling water initially, then later possibly to be used to pump concrete for any eventual permanent radiative-materials containment structure.[85][86] A 62m-tall pumping truck, donated by Chinese manufacturer SANY was used.[87]
[edit] April event tree
The nuclear accident event tree continued to evolve in the second month after the earthquake and tsunami caused the accident sequence to begin.
[edit] Fourth week
[edit] Saturday, 2 April
TEPCO observed for the first time that contaminated water from the unit 2 was flowing into the sea.[88] Workers discovered 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.
[edit] Sunday, 3 April
The radioactive water leaked into the sea by unit 2 continued despite concrete pumped Saturday evening. Workers injected a mixture of a water-absorbing polymer, sawdust and shredded paper.[89] Radiation levels in the water were estimated at 1 Sv/h.
TEPCO announced that the bodies of two workers killed by the tsunami were discovered on 30 March.[90]
On Sunday, April 3, Japanese government officials said the Daiichi plant may continue to release dangerous radiation into the air for several months.[91]
[edit] Monday, 4 April
TEPCO began dumping water tainted with low levels of radioactivity into the Pacific Ocean on Monday night, 4 April, so that a central waste facility could be used to store more dangerously radioactive water, officials said. The company said it could release up to 11,500 tons of radioactive water into the sea. A spokeswoman for Japan’s Nuclear and Industrial Safety Agency said the less-contaminated water must be disposed of so that workers can secure a place to store more highly contaminated water on the site.[92]
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.[93]
[edit] Tuesday, 5 April
It was determined that the leak in the cable storage pit by unit 2 was likely due to a faulty joint where the pit meets a duct, leading to a gravel layer beneath, resulting in highly radioactive water pouring directly into the sea.[94][95]
[edit] Wednesday, 6 April
TEPCO announced that an injection of 6,000 litres (1,600 USgal) of polymer coagulant into the pit mitigated the leaking;[96] however, the IAEA and others credit additional factors.[97] Sodium silicate, also known as "water glass", and additives were injected into the ground in order to stop the leakage of radioactive water.[98] The residual heat carried by the water used for cooling the damaged reactors accelerated the setting of the injected mixture.
Despite protests from the South Korean government, Russian scientists, and Japanese fishermen, Japan authorized the release of the 11,500 tonnes (12,700 tons) of less radioactive water into the ocean to make room to store more highly contaminated water.[95][99]
Iodine-131 levels reached 7.5 million times the legal limit in a seawater sample taken near the facility.[95]
[edit] Thursday, 7 April
Nitrogen injection into the pressure containment vessel of unit 1 was commenced at 01:31.[100]
A large aftershock, later downgraded from a 7.4 to a 7.1 by USGS, occurred. A tsunami warning was also issued but lifted after 90 minutes. Most of the workers at the nuclear plant were evacuated. TEPCO reported that no further damage to the nuclear plant was detected after this earthquake.[citation needed]
Official measures at Fukushima I reactor unit 1, however, showed a rise in temperature consecutive to the aftershock and a spiking amount of radiation in the Dry Well which exceeded the instrument maximum of 100 Sv/h.[101] Gauge B, in the meantime, has recorded a steady increase of the pressure for the previous ten days, in the same reactor.[102] Reporting the rise to 100 Sv/h up from the earlier 30 Sv/h TEPCO declared that the "validity of the measurement is questioned" both for radiation levels and pressure.
[edit] Summary
- Distilling significance, 1–7 April
- 1 April: TEPCO said that groundwater near unit 1 contained radioiodine at levels 10,000 times normal, but NISA later disputed the numbers.[103][104] The Japanese government was reported to be considering injecting nitrogen into reactor vessels.[105][106] Two more concrete pumping trucks, used initially to pump cooling water, were shipped to Japan from Germany.[86]
- 2 April: A crack leaking radioactive water into the ocean was discovered in pit housing electrical cables near the unit 2 seawater inlet. Workers were preparing to pour concrete into the 20-centimetre (7.9 in) long crack to stop the water, emitting radiation at 1 Sv/h.[107][108]
- 3 April: TEPCO confirmed the first deaths at the Fukushima facility, two workers who had been missing since 11 March and who appear to have died in the basement of reactor No. 4 from bleeding from multiple injuries inflicted by the tsunami.[106][109] The attempt to plug the leak near unit 2 failed when the concrete failed to set and TEPCO then reattempted to plug up the trench leading to the damaged storage pit with a combination of superabsorbent polymer, sawdust and shredded newspaper, which also failed.[110] Measured radiation levels in the area around the plant continues to decrease.[111][112]
- 4 April: TEPCO begun to release 10,000 metric tons of lightly radioactive water from storage tanks into the ocean. This is claimed as necessary in order to make room for more highly radioactive water which is preventing workers from making progress on restoring the cooling and other systems to reactors 1–4.[113][114] Samples of seawater near the plant revealed radioactive cesium at 1.1 million times the legal limit.[115]
- 5 April: Levels of radioactive iodine-131 in seawater near the facility were found to be 7.5 million times the legal limit.[115] TEPCO drilled a hole into the pit near reactor No. 2 from which highly radioactive water was leaking and injected water glass (sodium silicate) into the pit to prevent further leaking.[116]
- 6 April: TEPCO announced that the leak of highly radioactive water from the utility pit near reactor No. 2 has stopped.[116] According to U.S. Representative Ed Markey, the Nuclear Regulatory Commission says that the core of unit 2 has gotten so hot that part of it has melted through the reactor pressure vessel,[117] however a NRC spokesperson said, "That's not clear to us, nor is it clear to us that the reactor has penetrated the vessel."[118] TEPCO begins injection of nitrogen into unit 1 to lower the possibility of hydrogen explosions.[119]
[edit] Fifth week
[edit] Friday, 8 April
-
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 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 integrity Severely damaged due to hydrogen explosion Slightly damaged, also panel removed to prevent hydrogen explosion Severely damaged due to hydrogen explosion Severely damaged due to hydrogen explosion Panel removed to prevent hydrogen explosion Panel removed to prevent hydrogen explosion 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 faulty[122]) at 7 April 02:00 JST[123] Stable at 0.090 MPa absolute (Train A) / 0.083 MPa absolute (Train B) at 7 April 02:00 JST[123] Stable at 0.103 MPa absolute (Train A) / 0.022 MPa absolute (Train C) at 7 April 02:00 JST[123] Safe (defueled) Safe (in cold shutdown) Safe (in cold shutdown) Pressure vessel, temperature Stable at 224°C on 7 April[124] Stable at 143°C on 7 April[124] Stable at 115°C on 7 April[124] Safe (defueled) Safe (in cold shutdown) Safe (in cold shutdown) Containment pressure Stable at 0.150 MPa (absolute) at 7 April 02:00 JST[123] Stable at atmospheric pressure on 6 April[124] Stable at 0.1071 MPa (absolute) at 7 April 02:00 JST[123] Safe Safe Safe Seawater injection into core Continuing (switched to freshwater 25 March)[66] Continuing (switched to freshwater 26 March)[66] Continuing (switched to freshwater 25 March)[66] 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 venting Temporarily stopped Temporarily stopped Temporarily stopped Not necessary Not necessary Not necessary INES Level 5 Level 5 Level 5 Level 3 – – Environmental effect - Radiation levels:
-
- South side of office building: 650 µSv/hour at 8 April 15:00 JST
- Main gate: 94 µSv/hour at 8 April 15:00 JST
- West gate: 40 µSv/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 JST[125] 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[126] Freshwater injection continues, 71.0°C on 5 April 06:00 JST[127] Sprayed freshwater injection continues, 60°C on 20 March by infrared helicopter measurement[126] Sprayed freshwater injection continues after hydrogen explosion from pool on 15 March, 40°C on 20 March by infrared helicopter measurement[126] Cooling system restored, 34.8°C on 4 April 13:00 JST[127] Cooling system restored, 27.5°C on 4 April 13:00 JST[127] Information sources[128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153]
[edit] Saturday, 9 April
Japan is still struggling to keep water on the reactors to cool them and prevent further meltdown. Russian Antonov An-124 cargo planes flew 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.[154]
Currently TEPCO does not plan to take a Chernobyl approach to resolving nuclear power plant crisis by entombing the radioactive material in concrete.[155] If this decision were to change, the boom pumps could be retrofitted to deliver concrete for that purpose.[154]
[edit] Monday, 11 April
Coolant injection into reactors 1 and 3 was interrupted for 50 minutes due to a loss of power after a strong earthquake.[156]
[edit] Tuesday, 12 April
Japan officially raises Fukushima to INES Level 7, the same as Chernobyl.[157][158] This new rating considers the accidents as a single event and uses estimated total release to the atmosphere as a justification.[159] At Chernobyl, approximately 10 times the amount of radiation was released into the atmosphere as was released from Fukushima I through April 12, 2011.[160]
After cooling efforts at spent fuel pool 4 were halted due to an erroneous warning about the pool filling up[161], the temperature of the pool rose to 90 °C and the dose rate 6 meters above the pool spiked at 84 mSv/h.[162]
[edit] Summary
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 ever.[163]
- Distilling significance, 8–14 April
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 ... This was a crisis that played out in real time on TV. Chernobyl did not."[164]
A 9 April survey of radiation in seawater outside unit 2 shows radioactive isotope concentrations (iodine-131, caesium-134 and caesium-137) falling for the third straight day since the leak was plugged. However, the levels are still high, at several thousand times legal levels. Other nuclides are being investigated, but Japan regulator NISA has flagged up problems with TEPCO's sampling methodology.[165]
(April 11) Workers plan to pump the water into turbine condensers, but need to pump water out of them first. Work to transfer water from the unit 2 and 1 condenser to a central storage tank was completed on 9 and 10 April. Also, workers have 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 operations in other tanks. Japanese news wire NHK reports that workers are laying hoses to transfer water to a 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.[166]
[edit] Sixth week
Plans were 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.[167]
Nuclear fuel was reported to have melted and fallen to the lower containment sections of three reactors, including reactor three. The melted material was not expected to breach a container (which might cause a massive radiation release). Instead, the melted fuel was thought to have dispersed fairly uniformly across the lower portions of the containers of reactors No. 1, No. 2 and No. 3, which would make the resumption of the fission process, to the extent of a recriticality accident, most unlikely.[168] 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.
[edit] Monday, 18 April
The Associated Press is reporting 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 weekend. The devices opened closed doors and explored the insides of the reactor buildings, coming back with radioactivity readings of up to 49 millisieverts per hour inside Unit 1 and up to 57 millisieverts per hour inside Unit 3. TEPCO officials said that the radiation data from the robots don't change their plans for shutting down the plant by the end of this year. And though more robots will be used, a TEPCO official, Takeshi Makigami, said that robots are limited in what they can do and eventually "people must enter the buildings." [169]
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.[170]
[edit] Tuesday, 19 April
TEPCO began transferring excess, radioactive cooling water from the reactor No. 2's basement and maintenance tunnels to a waste processing facility.[171]
[edit] See also
- 2011 Japanese nuclear incidents
- Fukushima I nuclear accidents
- 2011 Tohoku earthquake and tsunami
- List of civilian nuclear incidents (2010s)
- Lists of nuclear disasters and radioactive incidents
- Nuclear safety
[edit] Notes
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- ^ "Status of nuclear power plants in Fukushima as of 18:00 JST on 2 April". JAIF. 2 April 2011. http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1301737920P.pdf. Retrieved 2 April 2011.
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- ^ http://www.neimagazine.com/story.asp?sectionCode=72&storyCode=2059373
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[edit] References
- Wang, John X. and Marvin L. Roush. (2000). What Every Engineer Should Know About Risk Engineering and Management. London: CRC Press. 13-ISBN 9781420026962/10-ISBN 1420026968; OCLC 5030452
[edit] External links
- Webcam Fukushima nuclear power plant I
- TEPCO News Releases, Tokyo Electric Power Company
- TEPCO near real-time radiation sensor data in English and Japanese; brief instructions for English-speaking readers on how to interpret the Japanese table data
- NISA Information update, Nuclear and Industrial Safety Agency, the nuclear safety authority of Japan
- JAIF Information update, Japan Atomic Industrial Forum
- JAEA Information update, Japan Atomic Energy Agency
- IAEA Update on Japan Earthquake, International Atomic Energy Agency
- Nature Journal – Specials: Japan earthquake and nuclear crisis
- Japanese Nuclear Emergency: EPA's Radiation Air Monitoring
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Coordinates: 37°25'17?N 141°1'57?E? / ?37.42139°N 141.0325°E
