Monday, 14 March ,2011,Fukushima Daiichi Nuclear Disaster
1. 11:01: The unit 3 reactor building explodes, injuring six workers.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.
2. 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.
3. 15:00: A major part of the fuel in reactor 3 drops to the bottom of the reactor pressure vessel.
4.18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.
5. 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.
Tuesday, 15 March ,2011,Fukushima Daiichi Nuclear Disaster
1. 11:00: A second explosion of reactor 3 (according to The World Meteorological Organization report.
2. 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. An explosion in the "pressure suppression room" causes some damage to unit 2’s containment system. A fire breaks out at unit 4. Radiation levels at the plant rise significantly but subsequently fall. Radiation equivalent dose rates of 400 millisieverts per hour (400 mSv/h) are observed at one location in the vicinity of unit 3.
Wednesday, 16 March ,2011,Fukushima Daiichi Nuclear Disaster
At approximately 14:30 TEPCO announces its belief that the fuel rod storage pool of unit 4 — which is located outside the containment area — 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 group 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. TEPCO temporarily suspended operations at the facility. A TEPCO press release states that workers had been withdrawn at 06:00 JST because of abnormal noises coming from one of the reactor pressure suppression chambers. Late in the evening Reuters reports that water is being poured into reactors 5 and 6.
Thursday, 17 March ,2011,Fukushima Daiichi Nuclear Disaster
During the morning Self-Defense Force helicopters drop water four times on the spent fuel pools of units 3 and 4. 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. Construction work is started to supply a working external electrical power source to all six units of Fukushima I. Starting at 7 pm, police and fire water trucks attempt to spray water into the unit 3 reactor with high pressure hoses. 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.
Friday, 18 March ,2011,Fukushima Daiichi Nuclear Disaster
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. For the second consecutive day, high radiation levels are detected in an area 30 kilometres (19 mi) northwest of the damaged Fukushima I nuclear plant at 150 μSv/h. 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.
Saturday, 19 March ,2011,Fukushima Daiichi Nuclear Disaster
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. 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 °C.
Sunday, 20 March ,2011,Fukushima Daiichi Nuclear Disaster
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. 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.
Monday, 21 March ,2011,Fukushima Daiichi Nuclear Disaster
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 is 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.
Tuesday, 22 March ,2011,Fukushima Daiichi Nuclear Disaster
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. 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.
Wednesday, 23 March ,2011,Fukushima Daiichi Nuclear Disaster
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. 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.
Thursday, 24 March ,2011,Fukushima Daiichi Nuclear Disaster
Seawater injection to units 1, 2 and 3 continues and radiation levels near the plant decline to 200 μSv/h, while lighting is restored to the unit 1 control room. 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. The workers are exposed to an estimated equivalent dose of 2–6 Sv to the skin below their ankles. 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". 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 °C, and the fuel pool at unit 3 is recorded at 30 °C.
Friday, 25 March ,2011,Fukushima Daiichi Nuclear Disaster
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. Highly radioactive water is also found in the turbine buildings of units 1 and 2. The US Navy sends a barge with 1,890 cubic metres (500,000 USgal) of fresh water, expected to arrive after two days. Japan announces transportation will be provided in a voluntary evacuation zone of 30 kilometres (19 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. Iodine-131 in the ocean near the plant measures 50,000 Bq/L, a "relatively high" 1,250 times normal levels.
Saturday, 26 March ,2011,Fukushima Daiichi Nuclear Disaster
Fresh water becomes available again for use instead of seawater to top up reactor water levels. 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. Radiation levels near the plant decline to a still relatively high 170 μSv/h.
Sunday, 27 March ,2011,Fukushima Daiichi Nuclear Disaster
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). 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." The high radiation levels cause delays for technicians working to restore the water cooling systems for the troubled reactors. USAF technicians at Yokota AB complete the fabrication of compatibility valves to allow the connection of deployed pump systems to the existing infrastructure at Fukushim.
Monday, 28 March ,2011,Fukushima Daiichi Nuclear Disaster
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. TEPCO confirms finding low levels of plutonium in five samples during 21 and 22 March.
Tuesday, 29 March ,2011,Fukushima Daiichi Nuclear Disaster
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.
Wednesday, 30 March ,2011,Fukushima Daiichi Nuclear Disaster
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. The Environmental Protection Agency (EPA) finds radioactive iodine in milk in the United States.
Thursday, 31 March ,2011,Fukushima Daiichi Nuclear Disaster
Workers pump radioactive water from a utility trench near reactor 1 into a storage tank near reactor 4. 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. The world's largest concrete pumping truck is shipped from the United States to Fukushima. 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. A 62 metre-tall pumping truck, donated by Chinese manufacturer SANY is also used.
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