Japan’s Nuclear Crisis: Timeline of Events

Issue 6 and Volume 115.

Southwest side of the Fukushima Daiichi Nuclear Power Station Unit 4 on April 20. Photo courtesy TEPCO.

By Brian Wheeler, Associate Editor, and Sharryn Dotson, Online Editor

The strongest earthquake ever recorded in Japan at a magnitude of 9.0 struck the country on March 11. Below is a timeline of events following the earthquake and tsunami and the effect on nuclear power plants in Japan. An up-to-date timeline, plus ongoing nuclear industry coverage, is at


  • Fukushima Daiichi reactor No. 1 is leaking water from the center of the reactor, which may delay plans to stabilize the unit, according to Reuters. Tokyo Electric Power Co. (TEPCO) repaired a gauge in the No. 1 reactor when workers noticed water levels dropped 16 feet below targeted levels to cover the fuel under normal operating conditions.
  • “The fuel pellets likely melted and fell, and in the process may have damaged … the pressure vessel itself and created a hole,” Junichi Matsumoto, a general manager at the plant, was quoted as saying.
  • Based on the amount of water remaining, Matsumoto said it is likely that at one point following the earthquake and tsunami, the rods had been entirely exposed to the air. Officials said they will review its timetable for stabilizing the plant on May 17 and that initial progress targets could change.


  • Japan’s Prime Minister Naoto Kan said the country would abandon plans for new nuclear reactors and “start from scratch” in creating a new energy policy.
  • Japan currently has 54 reactors and had a plan to build 14 more by 2030 and increase the share of nuclear power in the country’s energy mix to 50 percent.
  • PM Kan said Japan would keep nuclear and fossil fuels as energy sources but will add renewable energy and conservation.
  • TEPCO asked the Japanese government for support in paying compensation for damages caused by the disaster at the Fukushima Daiichi plant, according to the Wall Street Journal. TEPCO said it is having fundraising difficulties and will continue restructuring efforts and selling assets.
  • TEPCO may report a net loss of more than 1 trillion yen ($12.46 billion) for fiscal year 2010 because of the nuclear crisis, according to Reuters. The company estimated the cost of decommissioning at $7.4bn and it plans to book the amount as an extraordinary loss. The government will provide TEPCO with $1.4bn in support under a nuclear accident insurance program.
  • A new body including TEPCO and eight other regional electric companies with nuclear reactors will be formed to support TEPCO with loans and, if necessary, buy preferred shares in the company.


  • Chubu Electric Co. agreed to shut down the five reactors at the Hamaoka nuclear power plant southwest of Tokyo after the Japanese government asked Chubu to do so. Two of the reactors are being decommissioned, one is undergoing inspection and two more are operational.
  • Japanese Prime Minister Naoto Kan asked Chubu to shut down the plant until earthquake and tsunami protections can be built.
  • Kan said the plant’s location on the Pacific Coast makes it vulnerable and can lead to damage similar to the crisis at the Fukushima Daiichi nuclear power plant.
  • Chubu agreed to build a 40-foot seawall over the next two years.


  • A dozen workers entered the damaged reactor building of Unit 1 at the Fukushima Daiichi power plant for the first time since the March 11 earthquake. The workers were trying to install a ventilator to help lower radiation levels inside the reactor building. If the ventilator works as expected, workers should be able to enter the rest of the building within three days to install a new cooling system which was damaged in a hydrogen explosion March 12.
  • TEPCO must install cooling systems at three of the six reactors to stay on its current timetable of stabilizing the plant within six to nine months.


  • Eight workers are scheduled to enter Unit 1 at the Fukushima Daiichi nuclear power plant on Thursday for the first time since a hydrogen explosion damaged the building, according to TEPCO. The workers are part of a plan to cool the reactor by filling the containment vessel with water.
  • Workers must first verify that the water gauge in the pressure vessel and the pressure gauge in the containment vessel are working properly and radiation must be filtered from the air.
  • TEPCO then plans to set up air coolers outside the reactor building to cool the water in the containment vessel before replacing the old cooling system. Once the new system is in place and working as planned, TEPCO said the temperature will drop to under 100 degrees in several days, achieving cold shutdown.


  • TEPCO said it detected high levels of radioactive substances in seabed samples gathered April 29 between 9 and 12 miles from the Fukushima Daiichi nuclear power plant, according to The Japan Times. At a location 9 miles north of the plant, 1,400 becquerels/kg of cesium-137 and 1,300 becquerels/kg of cesium-134 were detected, more than 1,000 times higher than what is considered normal. About 190 becquerels/kg of radioactive iodine was also detected.


  • TEPCO will not have a limit placed on the amount of compensation paid over the crisis at the Fukushima Daiichi nuclear power plant, according to Reuters.
  • Workers were preparing to install air decontamination equipment in the turbine building of Unit 1 at the power plant. The four purifiers are expected to be ready by Thursday and should remove 95 percent of the radioactive substances in the air of the turbine building.
  • Robots found radiation levels in the pump room of 1,120 millisieverts per hour, indicating a possible leak from the reactor core, according to TEPCO.


  • An official at the Korea Electric Power Corp. (KEPCO) told Reuters that the disaster at the Fukushima Daiichi nuclear power plant could set the nuclear power reactor market back two to three years.
  • “Japan’s crisis may affect the market in the next two to three years but in a few decades nuclear power demand will rise due to a lack of alternative energy,” Byun Jun-yeon, executive vice president and chief nuclear project officer at state-run utility KEPCO, told Reuters in an interview.


  • Hitachi and Mitsubishi Heavy Industries have started discussions on sharing specific roles and defining actual procedures for jointly implementing measures to support recovery efforts at the Fukushima Daiichi nuclear power plant.
  • Immediately following the March 11 earthquake, MHI established as “Emergency Operation Centre,” which included provisions of emergency supplies such as radiation shields and conversion work on the Mega-Sloat to be used to store large volumes of contaminated water. MHI also proposed medium- and long-term plans that include a contaminated water treatment system, cooling system and measure to enclose the plant buildings.
  • Concurrently, Hitachi established a 24-hour “Emergency Response Center for Nuclear Power,” which has dispatched nearly 500 engineers and other workers to the Fukushima site.


  • TEPCO said it will cut the total remuneration of its president, chairman and other top executives by half and will cut the annual salary of general employees by 20 percent in order to provide compensation to those affected by the nuclear disaster at the Fukushima Daiichi nuclear power plant. The government will be sharing responsibility for compensation with the utility. As part of a broader restructuring of the company, job cuts and asset sales are also expected.
  • Dai-ichi Mutual Life Insurance Co., TEPCO’s largest shareholder, said it expects to fall 62 percent short of net profit estimates for the year ended in March because of a roughly $2 billion valuation loss on its share portfolio, including a write down of TEPCO Holding by $1.2 billion.
  • Standard & Poor’s downgraded three Japanese electric power companies’ outlooks from stable to negative. The companies are Chubu Electric, Shikoku Electric and Electric Power Development. The companies either own nuclear power plants that are functioning normally or are building a nuclear power plant.
  • Standard & Poor’s said that Japanese power companies “face increased operational and financial risks in building, operating and maintaining nuclear power plants” in light of the nuclear disaster, according to


  • The Japanese government made it illegal to enter a 20 km (12 mile) evacuation zone around the Fukushima Daiichi nuclear power plant. People were urged to leave the area after the earthquake and tsunami hit but the order was not enforced by law.
  • The BBC reports that brief re-entry will be allowed to the area’s 80,000 former residents to collect belongings.


  • TEPCO accepted a solution from Areva to treat most of the contaminated water from the Fukushima Daiichi nuclear power plant. The solution is based on a co-precipitation concept that uses special chemical reagents to separate and recover the radioactive elements. The treated water could then be reused in the plant’s cooling systems.
  • Areva also will be working with Veolia Water to deliver a large-capacity treatment plant equipped with the co-precipitation process to the Daiichi plant.


  • TEPCO said it would take up to nine months to bring the six nuclear reactors at the Fukushima Daiichi power plant into cold shutdown. The goals are part of a two-part blueprint for controlling the reactors and improving safety conditions at the plant.
  • The first part of the plan is expected to take three months, and would include building a new cooling system and filling the containment vessels of units 1 and 3 with water to stabilize their reactor cores. TEPCO then plans to cover three badly damaged reactor buildings and install filters to reduce contamination being released into the air over the next nine months. The company also plans to seal the containment vessel of the No. 2 reactor by filling damaged parts with stucky cement.
  • The government announced that residents who were forced to evacuate near the plant will be able to return in six months after the land is decontaminated.


  • Japan ordered TEPCO to pay compensation to 48,000 families who lived within 18 miles of the Fukushima Daiichi plant. Provisionally, one household will receive 1 million yen ($12,000).
  • JP Morgan Chase has estimated that TEPCO may face claims of up to 2 trillion yen ($24 billion) by the end of the year.
  • Engineers continue to pump water into three reactors to cool fuel rods.
  • Water must still be removed from the basements of reactors 1, 2 and 3 before vital work on the cooling systems can begin.


  • TEPCO said reactors at the Fukushima Daiichi nuclear power plant will take at least until June to stabilize, according to Bloomberg. The company said it will soon present a schedule for dealing with the crisis.
  • Engineers at the plant have rejected a proposal to flood reactors at the plant, which could lower the temperature in days instead of months, to avoid increasing the amount of contaminated water that could flow into the ocean. Instead, they are opting to “feed and bleed,” a method in which they pump in water and vent off the steam.
  • Decommissioning and clean up of the plant could take decades and cost more than $12 billion.
  • Water levels inside reactor No. 1., the primary danger, dropped Wednesday, leaving 1.65 meters of fuel rods exposed to air, where they can heat up and melt and release radiation into the pressure vessel. TEPCO’s data shows that pumping efforts have failed to raise the water level more than 20 cm in the 35 days since the crisis started.


  • Because of an ongoing release of radiation from the plant, Japanese authorities notified the International Atomic Energy Agency of their decision to raise the rating of the nuclear crisis from Level 5 to Level 7, the same level as the Chernobyl disaster in 1986. Level 7 ranks as a “major accident.”
  • A batch of eight safety-related incidents was recorded on the International Nuclear Event Scale (INES) in the days after the earthquake and tsunami at both the Daiichi and Daiini plants. They include the overall effect on the nuclear plants (Level 3), two losses of cooling function (Level 5), one covering radiological release (Level 5), one on loss of cooling to a fuel pool (Level 3) and three more on loss of reactor cooling (Level 3).
  • EPA’s RadNet radiation monitoring program shows there are very small amounts of iodine, cesium and tellurium in air samples in the U.S. The largest amounts were found in Alaska on March 19 and 24, 2011 but they are still below levels of concern
  • Drinking water samples taken at various locations throughout the U.S. during the week of April 4, 2011 ranged from non-detects to 1.6 picocuries per liter of iodine-131. Early precipitation samples indicate low levels of radioactivity, and milk samples taken March 28, 2011 in Phoenix and Los Angeles detected 3 pCi/L of iodine-131, more than 1,500 times lower than the Derived Intervention Level set by the U.S. Food and Drug Administration.


  • The Japanese government said it will widen the evacuation area around the Fukushima Daiichi power plant outside the current 20 km (12 mile) zone within one month, according to AFP.


  • The 7.1-magnitude earthquake that struck off the coast of Japan on April 7 caused water to slosh out of spent fuel pools at the Onagawa nuclear power plant, according to Reuters. Plant owners Tohoku Electric Power Co. said water leaked out of units 1, 2 and 3 at the plant, which had been shut down after the 9.0-magnitude earthquake on March 11. Company officials also said two out of three lines supplying off-site power to the plant were lost Thursday.
  • Cooling operations of spent pool fuels resumed after they stopped due to the quake and there was still an emergency backup generator to fall back on.


  • A 7.1-magnitude aftershock hits 90 miles from Fukushima and 25 miles underwater, triggering new tsunami warnings for waves up to 3 feet. There were no reports of additional damage at the plant.
  • TEPCO officials said an operation to reduce the risk of a hydrogen explosion at Fukushima Daiichi’s nuclear reactor No. 1 by injecting it with nitrogen has been a success.
  • Workers continue to dump low-level radioactive water into the Pacific Ocean to make room for more highly radioactive water. Officials said most of the water will be released by Thursday and the remaining amount will be discharged by Saturday.


  • TEPCO officials said they have plugged a leak that was sending radioactive water into the Pacific Ocean, according to the Associated Press. Workers injected 400 gallons of sodium silicate, or “water glass,” into the crack in a maintenance pit to close it.
  • Officials said they will begin injecting nitrogen into the reactors to stem a buildup of hydrogen gas that previously caused several explosions at the plant.


  • TEPCO visually confirmed they had slowed the leak of radioactive water from Unit 2, according to Reuter’s. Samples of the water used to cool reactor 2 were shown to be 5 million times the legal limit of radioactivity.
  • The Japanese government says it is considering radioactivity restrictions on seafood. India has banned food imports from anywhere in Japan.


  • Power supply to the temporary electric pumps for water supply to the reactor pressure vessels of units 1, 2 and 3 was switched from the temporary mobile power supply to the off-site power supply.
  • Polymer was poured into a trench where a leak was found near Unit 2.
  • TEPCO said it would start releasing 11,500 tonnes of low-level radioactive seawater into the ocean to make room for more highly contaminated water. The process is expected to take 5 days.


  • According to the International Atomic Energy Agency (IAEA), an external power supply is being used to power units 1, 2 and 3 and the pumps at the Fukushima Daiichi nuclear power plant. Some lighting has also been reactivated in the turbine buildings of the three units as well.
  • TEPCO said they may have found a leakage path from the turbine building of Unit 2 via a series of tunnels and trenches used to provide power to the sea water intake pumps. Pouring of the concrete ended as there was no visible difference observed. There is a plan to inject polymer in an attempt to stop the leak.
  • Most of the imposed recommendations on drinking water have been lifted.
  • TEPCO reported that two employees missing since the earthquake hit on March 11 were found dead in the -1 Level of Unit 4’s turbine building.


  • A crack was found in the sidewall of a pit that houses cables near Unit 2 at the Fukushima Daiichi nuclear power plant in Japan. Water has been leaking from the crack directly into the sea. TEPCO plans to use concrete to try and fill the crack and stop the leakage.


  • Japan considers widening exclusion zone around the Fukushima Daiichi nuclear power plant after the IAEA found high radiation levels in a village 25 miles away. Levels ranged from 0.2 to 25 megabecquerels per square meter for iodine-131, and from 0.02 to 3.7 megabecquerels per square meter for caesium-137 in soil samples of between 15 and 36 miles away.
  • Recent measurements of radionuclides in tap water are below Japanese emergency limits, according to the IAEA. However, concentrations of several radionuclides remain far beyond normal regulatory limits at measuring posts near the plant discharge canals.


  • TEPCO said it would decommission reactor units 1-4 at the Fukushima Daiichi nuclear power plant.
  • TEPCO is considering whether to cover the reactor buildings to stem the spread of radioactive substances.


  • Japan’s Prime Minister Naoto Kan said the government is on “maximum alert” over the Fukushima Daiichi nuclear power plant.
  • Plutonium has been discovered in soil around the facility and radioactive water has leaked from a reactor building.
  • The government is also considering temporarily nationalizing TEPCO.


  • Fatal radiation levels were detected outside of reactor buildings for the first time. Water in an underground trench had levels exceeding 1 sievert an hour, according to a spokesman with TEPCO. A partial meltdown of fuel rods in Unit 2 probably caused a jump in the readings.


  • Work resumes at reactor 3 of the Fukushima Daiichi nuclear power plant after black smoke was seen coming from the reactor. Officials with TEPCO said they were unsure what caused the black smoke and there was no fire. Radiation levels in the vicinity did not rise, officials said.
  • Two workers at reactor 3 were taken to the hospital after being exposed to radiation.


  • Black smoke rising out of Unit 3 halts work at the nuclear power plant. A radiation spike at Unit 2 forces workers to evacuate.
  • Power cables have been connected to all six reactors, and lighting at Unit 3 has been restored. TEPCO says restoring power to all of the reactors could take weeks or even months.
  • Officials said tap water in Tokyo is unfit for babies to drink after radiation was found.


  • Electricity has been restored to three reactors at the Fukushima Daiichi plant. However, the cooling systems are not yet operating.
  • Residents near the plant have been warned not to drink tap water due to higher levels of radioactive iodine.
  • Some workers were evacuated after smoke was seen rising from Unit 3.


  • Authorities raise the alert level at the nuclear power plant to a level 5 on a seven-point international scale of nuclear accidents. The move places the plant two levels below the Chernobyl disaster in Ukraine in 1986. The head of the IAEA said the crisis was a “race against the clock.”


  • Engineers laid an external grid power line cable to Unit 2, which will allow cooling pumps to be restarted.


  • Another fire breaks out in Unit 4 at the crippled Fukushima Daiichi power plant. Power plant workers say Unit 3 is the “priority,” but the situation at Unit 4 is “not so good.”
  • Water is now being pumped into Units 5 and 6, which indicates that the entire nuclear plant is in danger of overheating.


  • Radiation leaks from Fukushima Daiichi No. 2 after a third explosion at the plant and a fire in a storage pond for used nuclear fuel.
  • About 200,000 people have been evacuated within a 12-mile radius of the plant.
  • A 6.1 magnitude earthquake aftershock shakes the eastern part of Japan, although authorities are reportedly not anticipating significant damage and the risk of another tsunami is low.
  • The IAEA said that all units at Fukushima Daini, Onagawa and Tokai nuclear plants are in a “safe and stable” condition.
  • Implementation of rolling blackouts for periods of up to three hours each.


  • TEPCO reports a rise in radiation levels at its Fukushima Daiichi nuclear power plant to government officials.
  • A hydrogen explosion occurred at Unit 3 at 11:01 am local Japan time at the Fukushima Daiichi nuclear power complex and reportedly has not damaged the plant’s No. 3 reactor vessel.
  • The IAEA says Japan reported the hydrogen explosion at the No. 3 reactor at the Fukushima Daiichi nuclear plan did not damage the primary containment vessel.
  • Jiji news agency says Japanese authorities have safely cooled down two nuclear reactors at the 4,400 MW Fukushima Daini nuclear plant. Fukushima Daini houses four boiling water reactors supplied by Toshiba and Hitachi.
  • TEPCO says water levels inside the Fukushima Daiichi complex’s No. 2 reactor are almost empty.
  • Cooling systems at Units 1, 2 and 3 of the Fukushima Daiichi plant fail adding concern over a possible meltdown.
  • Restoration work in reactor cooling function that was conducted to achieve reactor cold shutdown has been completed and cooling of the reactor has been commenced at 7:13 am local time, March 14th at Unit 2 at Fukushima Daini Nuclear Power Station, which makes it the third reactor at this plant to cool down.
  • Earthquake upgraded from an 8.9 to a 9.0-magnitude.


  • Risk of an explosion at a building housing the Fukushima Daiichi complex where an explosion March 12 blew the roof off another reactor building.
  • TEPCO begins injecting sea water into the No.1 and No. 3 units at Fukushima Daiichi to cool down the reactors and reduce pressure inside reactor container vessels. TEPCO prepares to pump sea water into the No.2 reactor at its Fukushima Daiichi nuclear power plant.


  • TEPCO begins releasing pressure from the 460 MW No. 1 reactor at Fukushima Daiichi nuclear plant, the Trade Ministry says.
  • Chief Cabinet Secretary Yukio Edano confirms an explosion (apparently hydrogen) and radiation leak at Fukushima Daiichi.
  • TEPCO plans to fill the leaking reactor with sea water to cool it and reduce pressure in the unit.


  • Earthquake takes place at roughly 2:46 p.m. local time. The epicenter is located about 130 kilometers off the east coast of the island.
  • Eleven reactors shut down in the quake-affected area.
  • Cooling problem reported at TEPCO’s 4,600 MW Fukushima Daiichi nuclear plant on the northeast coast of Japan. Fukushima Daiichi is a six-reactor plant that uses GE, Hitachi and Toshiba boiling water reactor technology. TEPCO confirms water levels are falling inside reactors at the plant and says it is trying to avert the exposure of nuclear fuel rods by restoring power to its emergency power system so that it can pump water inside the reactors.
  • Fire reported at Tohoku Electricity Co.’s 2,100 MW Onagawa nuclear plant, which has since been extinguished. The Onagawa consists of three boiling water reactor units.
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