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How Japan’s 2011 nuclear disaster unfolded

By Takehiko Kambayashi –

TOKYO — The following is a chronology of what happened during Japan’s 2011 nuclear disaster:

March 11: A magnitude-9 earthquake and tsunami strikes northeastern Japan at 2:46 pm (0546 GMT). Less than an hour later, a tsunami hits the Fukushima Daiichi Nuclear Power Station, 250 kilometers (155 miles) northeast of Tokyo, knocking out power and leading to the failure of the cooling systems at reactors 1 to 4 at the six-reactor plant.

The government declares a nuclear emergency and orders residents to evacuate from a 3-kilometre radius of the plant.

March 12: Soon after then-prime minister Naoto Kan flies to the plant for an inspection, radioactive steam is vented from reactor 1. A hydrogen explosion occurs in the building of reactor 1.

The government expands the evacuation zone to a 10-kilometer (6-mile) radius of the plant and later to 20 kilometers (12.5 miles).

March 14: A hydrogen explosion strikes the building housing reactor 3.

March 15: An explosion is heard near the suppression chamber of reactor 2. The building of reactor 4 is also damaged.

March 17: Military helicopters dump 30 tons of seawater over the building of overheating reactor 3, and firefighters also douse the reactor from the ground.

March 20: A cold shutdown is achieved at reactors 5 and 6, the plant’s operator, the Tokyo Electric Power Company (Tepco), says.

April 2: Highly radioactive water is confirmed to be flowing into the Pacific Ocean through a crack in a pit near reactor 2.

April 4: Tepco starts to dump relatively low-level radioactive water into the sea.

April 12: The government raises the accident level to 7, on par with the 1986 Chernobyl disaster in Ukraine.

June 7: The government concedes core meltdowns occurred at three of the plant’s six reactors.

June 27: Tepco starts a water treatment system to cool the overheating reactors. The system is designed to decontaminate radioactive water and use it to cool the reactors. But Tepco stops the system several times because of leaks and other problems.

September 28: Water temperatures at the bottom of pressure vessels at reactors 1 to 3 fall below 100 degrees Celsius for the first time since the start of the crisis, Tepco says.

November 4: The government decides to provide 900 billion yen (US$11.9 billion) to help Tepco meet compensation payments.

December 2: An interim company report concludes that the larger-than-expected tsunami was the direct cause of the disaster.

December 16: Prime Minister Yoshihiko Noda declares that a cold shutdown is achieved at the plant, meaning no nuclear reactions are occurring and little radiation is leaking into the environment.

The declaration marks an end to the emergency phase of the disaster and the start of the clean-up and scrapping of the reactors.

December 26: A government-commissioned independent investigation into the accident blasts Tepco and the government for mistakes made before and after the incident, saying they were unprepared, proper response mechanisms weren’t in place and those that were weren’t always implemented.

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