The strongest earthquake ever recorded in Japan at a magnitude of 8.9 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.
FRIDAY, APRIL 8
- 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.
THURSDAY, APRIL 7
- 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 say 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.
WEDNESDAY, APRIL 6
- 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.
TUESDAY, APRIL 5
- Tepco visually confirmed they had slowed the leak of radioactive water from Unit 2, according to Reuters news service. 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.
MONDAY, APRIL 4
- 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.
SUNDAY, APRIL 3
- According to the 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.
SATURDAY, APRIL 2
- 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.
THURSDAY, MARCH 31
- 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 metre for iodine-131, and from 0.02 to 3.7 megabecquerels per square metre 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.
WEDNESDAY, MARCH 30
- Tokyo Electric Power Co. (TEPCO) said the company 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.
TUESDAY, MARCH 29
- 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 the Tokyo Electric Power Co.
MONDAY, MARCH 28
- 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.
THURSDAY, MARCH 24
- 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.
WEDNESDAY, MARCH 23
- 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.
MONDAY, MARCH 21
- 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.
FRIDAY, MARCH 18
- 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."
THURSDAY, MARCH 17
- Engineers laid an external grid power line cable to Unit 2, which will allow cooling pumps to be restarted.
WEDNESDAY, MARCH 16
- 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.
TUESDAY, MARCH 15
- 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 International Atomic Energy Agency has 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.
MONDAY, MARCH 14
- 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 International Atomic Energy Agency 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.
SUNDAY, MARCH 13
- 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.
SATURDAY, MARCH 12
- 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
FRIDAY, MARCH 11
- The earthquake took place at roughly 2:46 p.m. locally. The epicenter was located about 130 kilometers off the east coast of the island.
- Eleven reactors shut down in the quake effected area
- Cooling problem 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 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.
We will have continuing updates on the events in Japan at PowerGenWorldwide.com