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Timeline: How Japan's nuclear crisis unfolded

By Bryony Jones, for CNN
Japan's quake and tsunami sparked a major emergency at one of the country's nuclear power stations, amid meltdown fears.
Japan's quake and tsunami sparked a major emergency at one of the country's nuclear power stations, amid meltdown fears.
  • Tsunami resulting from magnitude 9.0 earthquake damages nuclear power plant in north-east Japan
  • The plants has suffered three explosions and two fires since the crisis began Friday March 11
  • IAEA says two workers are missing at the site and at least 20 have fallen ill due to possible radiation contamination

(CNN) -- Authorities in Japan are battling to resolve a series of crises at the nuclear power plant at Fukushima Daiichi, which was badly hit by the devastating earthquake and tsunami that struck over a week ago.

Here's a look at efforts to contain the damage and avert a potential nuclear meltdown. (all times and dates are local).

Friday, March 11

2.46 p.m. (0.46 a.m. ET/5.46 a.m. GMT): A magnitude 9.0 earthquake strikes an area 370 kilometers (230 miles) northeast of Tokyo, Japan, at a depth of 24.5 kilometers.

The offshore quake, the fifth largest worldwide since records began, sparks a major tsunami warning across the Pacific. Within an hour a wall of water up to 9 meters (30 feet) high hits the Japanese coast, sweeping away towns and villages in its path.

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The quake causes serious damage at Tokyo Electric Power Company's (TEPCO) Fukushima Daiichi nuclear power plant, about 65 kilometers south of Sendai. Three of the plant's six reactors, which came into service between 1970 and 1979, were already shut down for inspection at the time the disaster struck. Those still in operation are designed to also shut down in the event of a quake, with diesel generators pumping water around the reactors to keep them cool.

But when the tsunami hits, flood water swamps the generators, causing them to fail. The reactors begin to heat up.

8.15 p.m.: The Japanese government declares an emergency at Fukushima Daiichi power plant.

10.30 p.m.: Authorities reveal the cooling system at the plant is not working, and admit they are "bracing for the worst."

Saturday, March 12

2.06 a.m.: Radiation levels in the No.1 reactor at Fukushima are reported to be rising.

3.24 a.m.: Japanese trade minister Banri Kaieda warns that a small radiation leak could occur at the plant.

6.45 a.m.: TEPCO says radioactive substances may have leaked at Fukushima.

Japan's Nuclear and Industrial Safety Agency says radiation near the plant's main gate is more than eight times the normal level.

4.19 p.m.: Japan's Nuclear and Industrial Agency reveals a small amount of radioactive cesium has escaped from the power plant, possibly caused by a fuel rod melting.

EXPLOSION: 6.22 p.m.: A hydrogen explosion at Fukushima's reactor No.3 blows the roof off the containment structure around the No.1 reactor and injures four people -- two plant workers and two subcontractors.

8.18 p.m.: Residents living within 20 kilometers of the plant are told to evacuate the area. Some 200,000 people leave.

8.54 p.m.: Authorities insist no harmful gases were emitted as a result of the explosion at the Fukushima plant, blaming the blast on "water vapor that was part of the cooling process."

10.35 p.m.: Radiation levels around the plant fall as officials prepare to flood the containment structure around the reactor with sea water to cool it. Meanwhile, authorities prepare to distribute iodide tablets to residents near the damaged nuclear plant to prevent radiation poisoning.

Sunday, March 13

3.20 a.m.: Three people randomly selected from a group of 90 test positive for radiation exposure in Fukushima prefecture.

5.37 a.m.: Japanese authorities say Saturday's explosion at the Fukushima Daiichi plant occurred outside the primary containment vessel, adding that the vessel's integrity has not been compromised.

4.46 p.m.: Chief Cabinet Secretary Yukio Endo warns of the possibility that a second explosion could happen at the No.3 reactor.

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Monday, March 14

EXPLOSION: 11 a.m.: Hydrogen explosion at the No.3 reactor damages the cooling system at the No.2 reactor and injures 11 people, including employees, subcontractors and four civil defense workers.

A wall at the plant collapses as a result of the blast, but officials say the containment vessel surrounding the reactor remains intact.

Authorities begin pumping a mixture of sea water and boron into the No.2 reactor to cool its nuclear fuel rods.

Those residents living within 20 kilometers of the plant who have so far ignored evacuation orders are warned to stay indoors.

Up to 2.7 meters of the No.2 reactor's control rods are left uncovered because the pump which keeps them cool has run low on fuel after being left unattended. It causes them to heat up generating radioactive steam.

Tuesday, March 15

EXPLOSION: 6 a.m.: An "explosive impact" rocks the No.2 reactor -- the third blast at the plant in four days -- and damages its suppression pool.

7 a.m.: The U.S. Navy begins repositioning ships and planes after detecting low-level "airborne radioactivity" in the region. Three people on the U.S.S. Ronald Regan earlier tested positive for low levels of radiation.

8.30 a.m.: Chief Cabinet Secretary Yukio Edano says he cannot rule out the possibility of a meltdown at all three of the plant's damaged reactors.
He says radiation levels at the plant have increased to "levels that can impact human health", and warns anyone living within 20 and 30 kilometers of the plant to remain indoors.

Almost all of the plant's staff, about 800 people, are evacuated from the site, with just 50 remaining to carry out emergency operations.

FIRE: 8.54 am: Fire breaks out in a cooling pond used for nuclear fuel at the No.4 reactor -- which had been shut down before Friday's quake.

Japanese Prime Minister Naoto Kan warns that "there is still a very high risk of further radioactive material coming out," but urges the public to remain calm.

The government imposes a no-fly zone within a 30-kilometer radius of the plant.

11 a.m.: The fire in No.4 reactor is reported to have been extinguished.

The International Atomic Energy Agency reveals that radiation levels at the plant have been recorded at 167 times the average annual dose of radiation, but that level is expected to drop quickly.

11.10 p.m.: The IAEA reports that Monday's blast at reactor No.2 "may have affected the integrity of its primary containment vessel."

11.45 p.m.: TEPCO says it plans to use helicopters to pour water onto reactor No.4 in order to cool the nuclear fuel rods.

Wednesday, March 16

FIRE: 7 a.m.: The second fire in two days is discovered in the building of the No. 4 reactor at Fukushima Daiichi. This one is in the northeastern corner of the building, an official with TEPCO says.

Thursday, March 17

4.35 a.m.: The U.S. Nuclear Regulatory Commission recommends that U.S. residents within 80 kilometers of the Fukushima reactors evacuate the area.

5.00 a.m.: Gregory Jaczko, head of the NRC, tells U.S. Congress spent fuel rods in the No. 4 reactor have been exposed because there "is no water in the spent fuel pool," resulting in the emission of "extremely high" levels of radiation.

Japanese Defense Minister Toshimi Kitazawa says a decision has been taken to address the crisis from the air and the ground -- despite concerns about exposing workers to radiation -- with efforts to cool down the No.3 reactor the top priority.

"We could not delay the mission any further, therefore we decided to execute it," Kitazawa said.

9.48 a.m.: Helicopters operated by Japan's Self-Defense Forces begin dumping tonnes of seawater scooped from the Pacific Ocean on to the No.3 and No.4 reactors to try to reduce overheating.

But hours later, TEPCO tells Japan's Kyodo News the operation does not appear to have lowered radiation levels in the area.

10.15 a.m.: The IAEA says two people are missing at Fukushima Daiichi, and another has suffered significant exposure to radioactive material.

Based on information supplied by Japanese authorities, it says two TEPCO workers have been injured, along with two subcontractors, and that at least 20 people have fallen ill due to possible radiation contamination.

12.00 p.m.: TEPCO officials deny claims the spent fuel pool has run dry. "We have been able to confirm that there is water in the spent nuclear fuel pool," a Tokyo Electric spokesman said. "But we do not know how much water."

3.00 p.m.: Australia urges its citizens living within 80 kilometers of the Fukushima plant to evacuate.

7.30 p.m.: Japanese Defense Ministry uses five water cannon trucks to shoot water into reactor No.3 in another effort to prevent it overheating. The operation ends forty minutes later.

Friday, March 18

9.30 a.m
.: Japan's nuclear and industrial safety agency raises the crisis level from four to five, putting it on a par with the 1979 nuclear incident at Three Mile Island in Pennsylvania.

The International Nuclear Events Scale says a level five incident means there is a likelihood of a release of radioactive material, several deaths from radiation and severe damage to the reactor core.

Saturday, March 19

9.00 a.m.: As searches for survivors continued, police in Japan said more than 7,100 people had died since the monster earthquake and ensuing tsunami struck. On Saturday morning 7,197 people were confirmed dead, according to Japan's National Police Agency. Another 10,905 people were missing and 2,611 were injured, the agency said.

1.00 p.m.: Efforts accelerated Saturday to restore power to nuclear reactors' cooling systems at the stricken Fukushima Daiichi plant. Officials said workers hope to fully restore power by day's end Saturday to plant's Nos. 1, 2, 5 and 6 reactors, and to get power up and running Sunday for the Nos. 3 and 4 reactors.

7.27 p.m.: Japan's National Police Agency says 7,348 people are now confirmed dead and 10,947 are missing. The agency said 2,603 people have been injured.

Sunday, March 20

9.00 a.m.: Crews struggling to bring the crippled Fukushima Daiichi nuclear plant under control had some success Sunday as cooling systems at two of the facility's reactors were working, Kyodo News reported. Earlier, workers had connected electric cables needed to power up cooling systems in the damaged reactors. The plan is to get power up and running for the Numbers 1, 2, 3 and 4 reactors soon.

1.00 p.m.: The pressure in the containment vessel of reactor No. 3 at the Fukushima Daiichi nuclear plant is increasing, Japan's nuclear safety agency said Sunday. The agency said officials are planning an operation to reduce pressure in the vessel -- the steel and concrete shell that insulates radioactive material inside.

2.00 p.m.: Japan's National Police Agency said Sunday that 8,199 people are confirmed dead and 12,722 have been reported missing following the March 11 quake and tsunami. The agency said 2,612 people have been injured.

The CNN Wire contributed to this report

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