Some of the key “milestone” events surrounding the Fukushima disaster. For a more comprehensive timeline, see this related Wikipedia page.
March 11, 2011
At 2:46 PM, a 9.0 magnitude earthquake strikes off Honshu island. Reactors 1,2 and 3 at the Fukushima Daiichi plant automatically shut down, reactors 4,5,6 were already offline for maintenance at the time. Plant was initially being cooled by backup generators.
An hour later, a 46 ft Tsunami hits, overfowing the 19′ seawall, inundating the plant, and disabling all but 1 (underground) generator. Most of the emergency core cooling system fails, the only portion still in operation being a steam and battery system which hadn’t been tested or used in 40 years.
At 9 PM, an evacuation order is issued for people within 1.9 miles of the plant.
March 12, 2011
Emergency backup battery for reactor 3 runs out and the fuel rods are exposed. Some steam is released into the air. As the situation in the 3 reactors worsens, the evacuation zone is extended – first to 10 km (6.2 mi) then to 20 km (12.4 mi)
March 13, 2011
The situation at Unit 1 is declared an INES level 4. Core damage begins in unit 3, unit 2 is thought to be stable.
March 14, 2011
A major explosion in the building for reactor 3 damages the cooling system for reactor 2, triggering core damage in that unit. The INES level for the situation is escalated to 5 and there’s talk or raising it to 6
March 15, 2011
An explosion severely damages reactor 4. Another explosion takes place in unit 3. A fire starts in unit 4. Radiation near reactor 3 measured at 400 mSv/h (millisieverts per hour.)
March 17, 2011
Construction begins to hook up an external power source to all 6 units. Helicopters are brought in to drop water on spent fuel pools in units 3 and 4.
March 18, 2011
30 fire engines from Tokyo Fire COmpany arrive and begin spraying water on the afflicted reactors.
March 20, 2011
Power is successfully connected to unit 2. A generator providing power for units 5 and 6 is repaired, allowing them both to be brought to a cold shutdown state.
March 22, 2011
White smoke can be seen rising from reactors 2 and 3.
March 25, 2011
A breach in reactor 3’s containment vessel is suspected. US Navy sends a barge with 500,000 gallons of fresh water to the scene. Voluntary evacuation zone is extended to a radius of 19 miles.
March 27, 2011
An aerial video taken by the Ground Self4/2 Defense Force shows the first detailed images of the overall damage to the plant.
March 30, 2011
TEPCO Chairman admits it is”unclear” how the issue will be resolved. In the USA, the EPA finds traces of radioactive iodine in milk.
April 2, 2011
Contaminated water from reactor 2 is found to be flowing into the sea.
April 3, 2011
Two missing workers are found dead, apparently from injuries sustained in the Tsunami.
April 4, 2011
TEPCO begins dumping radioactive water from storage tanks into the Pacific.
April 5, 2011
Levels of iodine-131 in seawater near the plant are measured to be 7.5 million times the legal limit.
April 7, 2011
A 7.1 magnitude aftershock strikes, workers are evacuated but no additional damage is incurred.
April 12, 2011
The INES level of the incident is raised to 7 – the same level as Chernobyl. It is determined by nuclear experts to be the most complicated accident of its kind ever to occur.
April 19, 2011
Two iRobot PackBot robots enter units 1 and 3 to assess the conditions. They report radiation levels of 1120 Msv/h inside unit 1, the highest to date.
May 5, 2011
Workers in protective gear are allowed to re-enter unit 1 for very short periods of time.
May 14, 2011
A 3rd TEPCO employee dies, reportedly from a heart attack.
May 20, 2011
TEPCO president Masataka Shimizu resigns
June 14, 2011
A large unexplained release of steam is observed coming from unit 3.
June 15, 2011
Trial of a new treatment program for the radioactive water begins.
July 3, 2011
Contaminated water is no longer being generated. Recycled water is being used for cooling.
August 10, 2011
A new closed circulation cooling system is completed. However there are ongoing problems with the water decontamination system, which is only working at 66% of its anticipated capability.
October 8, 2011
High levels of plutonium and other radioactive particles are found outside the 30km evacuation zone.
November 17, 2011
A shipment of rice from a nearby farm is banned by the government, after it is found to contain illegal amounts of cesium.
December 15, 2011
A timetable for decommissioning the reactors is announced – with an anticipated end date of the year 2052.
December 16, 2011
TEPCO and the Japanese government announce that all reactors are now in a stage of cold shutdown. However questions about the temperatures at the bottom of the containment vessels and the state of the fuel rods remain.
December 18, 2011
230 tons of highly radioactive water are found in a tunnel beneath a building storing contaminated water.
December 20, 2011
The US Nuclear Regulatory Commission confirms that the reactors are now stable – some 9 months after the initial incident.
December 26, 2011
An interim report concludes that poor communication on the part of the government and procedural errors by TEPCO employees contributed to the severity of the disaster.
January 19, 2012
Another 1100 tons of water with radioactive cessium found in two sites near reactors 2 and 3.
February 22, 2012
TEPCO begins pouring concrete on the ocean floor to try to abate contaminated sediment
December 12, 2012
TEPCO for the first time, admits fault in the disaster.
Ongoing issues with contaminated water continue to plague the disaster site.
November 18, 2013
Workers begin removing fuel rods from the Unit 4 reactor building – a dangerous and delicate operation expected to take a year to complete.
March 11, 2014
In cities throughout Japan, thousands protest on the 3rd anniversary of the disaster.
American company Kurion is awarded a contract to treat contaminated tank water.
July 7, 2014
TEPCO begins construction to create an ice wall in the ground around the reactors to control contaminated water.
September 20, 2014
TEPCO begins testing a new and improved water decontamination system, in hopes of doubling the amount of water processed daily from 750 to 1500 tons.
October 1, 2014
The Japanese government further narrowed the size of the evacuation zone around the disaster site, allowing 275 people in 139 households to return to their homes. It is unclear whether they will actually do so, due to living conditions in the area.