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This is a timeline of events leading up to and after the explosions and partial meltdowns at the Fukushima nuclear power plant. On March 11 2011, a 9.0 magnitude earthquake struck off the coast of Japan, off the island of Honshu. This earthquake triggered a tsunami warning for over 20 countries, including the States of Hawaii, Oregon, and California in the United States. This earthquake also shut down the Fukushima power plant's nuclear reactor units, the subsequent tsunami shut down the plant's backup diesel generators. They are believed to be the blame for the explosions and partial meltdowns at the same power plant.

Times are given in Japan Standard Time (JST), unless noted.

Timeline at Fukushima I

Friday, 11 March

1446

An 9.0 magnitude earthquake strikes of the coast of Honshu Island at a depth of about 24km. Fukushima I power plant's nuclear rectors 1,2 and 3 are automatically shut down by the shake. Nuclear reactors 4, 5, and 6, were undergoing routine maintenance and were not operating. The tremble causes the power plant to be cut off from the Japanese electricity grid. Tokyo Electric Power Co (TEPCO), the plant's operator, find that units 1 and 2 are not operating correctly and notify the proper officials.

1600

The Nuclear and Industrial Safety Agency of Japan initiates an emergency headquarters in an attempt to gather information on the 55 nuclear reactors in Japan.

1930

Prime Minister Naoto Kan declares a nuclear emergency status. This is announced by Yukio Edano, Chief Cabinet officer in Japan. Japanese government officials try to comfort the people of Japan by telling them that the proper procedure are being undertaken. They also announce that no radioactive materials have been located.

2100

An evacuation order is issued by the government to persons within a 3km radius of the Fukushima station. Those within a 10km radius are told that they can remain in their homes and carry on with regular activities until told otherwise.

The emergency generators fail subsequently causing the cooling system to fail before the pressure in the nuclear units build up. This pressure build up is the result of residual decay heat causing the coolant, which is not being circulated, to evaporate. The coolant circuit pressure increase is controlled by pressure release valves which leads to a pressure increase within the containment chamber at the reactor building.

TEPCO announces that pressure inside reactor unit 1 is more than twice normal levels.

Saturday, 12 March

0530

In an attempt to release pressure within the reactor unit, a consensus is reached upon to vent steam out of the unit, which contains some traces of radioactive material, into the air.

1009

TEPCO confirms that a small amount of vapor has been released into the air to release tension in the reactor unit.

1058

Tensions are high with pressure still remaining inside the 2nd reactor. In order to alleviate some of this pressure, A consensus is reached to, once more, vent radioactive vapor into the air.

1536

Unit 1 at Fukushima I: A massive event is caught on cameras. These cameras document an explosion on the outer structure of one of four buildings at the plant. It also documents the structure collapsing. TEPCO announces that four persons who are employed at the power plant have been injured. (The explosion was a hydrogen explosion)

2000

A cloud of uncertainty surrounds the actual cause of the blast and the damage caused.

Yukio Edano announces that the concrete building surrounding the steel reactor container has collapsed as a result of the explosion however no damage has been inflicted on the reactor itself.

Monday, 14 March

1115

The building surrounding Reactor 3 of Fukushima I exploded, presumably due to the ignition of built up hydrogen gas. No health risk reported, though 600 people have been ordered to stay indoors.

1120 (approximate)

It was reported that the outer reactor building was blown apart, but the inner containment vessel was not breached. TEPCO stated that one worker was injured and seven missing.

2100 (approximate)

Fuel rods at the reactor #2 of the Fukushima nuclear plant were fully exposed. TEPCO earlier said the cooling system had been lost and began injecting seawater into the reactor to cool it down.

2116

Yukio Edano affirms that the reactor number 2 is unlikely to explode. In addition, he stated that there is ongoing work to cool down the reactor

Timeline at Fukushima II

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Unit 1

Friday, 11 March

1448

Unit 1 At Fukushima II is shut down automatically and reactor water level is stable. Offsite power is available.

Saturday, 12 March

0348

Injection by Make-up Water Condensate System begins.

0522

The temperature of the suppression chamber exceeds 100 degrees. As the reactor pressure suppression function was lost, at 5:22AM, it was determined that a specific incident stipulated in article 15, clause 1 has occurred.

0819

A special alarm, which alerts that the position of one control rod (used to halt the reactor) is unclear, is sounded. Whether it is fully inserted into the reactor or outside the reactor, allowing it to continue generating heat.

0943

Plant workers prepare to reduce the pressure of the reactor containment vessel (partial discharge of air containing radioactive materials) in order to fully secure safety.

1043

The control rod alarm is shut off and all rods are confirmed as being fully inserted.

1808

An increase in reactor containment vessel pressure is reported, apparently due to leakage of reactor coolant. However, we do not believe there is leakage of reactor coolant in the containment vessel at this moment.

Unit 2

1448

Unit 2 At Fukushima II is shut down automatically and reactor water level is stable. Offsite power is available.

• Control rods are fully inserted (reactor is in subcritical status)
• Status of main steam isolation valve: closed
• Injection of water into the reactor had been done by the Reactor Core Isolation Cooling System, but at 4:50AM, injection by Make-up Water Condensate System begun.
• We do not believe there is leakage of reactor coolant in the containment vessel.
• At 5:22AM, the temperature of the suppression chamber exceeded 100 degrees. As the reactor pressure suppression function was lost, at 5:22AM, it was determined that a specific incident stipulated in article 15, clause 1 has occurred.
• We decided to prepare implementing measures to reduce the pressure of the reactor containment vessel (partial discharge of air containing radioactive materials) in order to fully secure safety. This preparation work commenced at around 10:33AM and completed at 10:58AM.

Unit 3

1448

Unit 3 At Fukushima II is shut down automatically and reactor water level is stable. Offsite power is available.

• Control rods are fully inserted (reactor is in subcritical status)
• Status of main steam isolation valve: closed
• Reactor Core Isolation Cooling System is turned off. Currently, injection of water into the reactor is done by Make-up Water Condensate System.
• We do not believe there is leakage of reactor coolant in the containment vessel.
• We decided to prepare implementing measures to reduce the pressure of the reactor containment vessel (partial discharge of air containing radioactive materials) in order to fully secure safety. This preparation work commenced at around 12:08PM and completed at 12:13AM.
• At 12:15PM, the reactor achieved cold shut down.

Unit 4

1448

Unit 4 At Fukushima II is shut down automatically and reactor water level is stable. Offsite power is available.

• Control rods are fully inserted (reactor is in subcritical status)
• Status of main steam isolation valve: closed
• Reactor Core Isolation Cooling System is turned off. Currently, injection of water into the reactor is done by Make-up Water Condensate System.
• We do not believe there is leakage of reactor coolant in the containment vessel.
• In order to cool down the reactor, injection of water into the reactor had been done by the Reactor Core Isolation Cooling System, however, At 6:07AM, the temperature of the suppression chamber exceeded 100 degrees. As the reactor pressure suppression function was lost, at 6:07AM, it was determined that a specific incident stipulated in article 15,clause 1 has occurred.
• We decided to prepare implementing measures to reduce the pressure of the reactor containment vessel (partial discharge of air containing radioactive materials) in order to fully secure safety. This preparation work commenced at around 11:44AM and completed at 11:52AM.

References

1. "URGENT: Hydrogen blast occurs at Fukushima nuke plant's No. 3 reactor: agency". Kyodo News Agency. Retrieved 14 March 2011.
2. "180,000 flee as Japan's nuclear crisis intensifies". MSNBC.com. Retrieved 13 March 2011.
3. Yuji Okada and Shigeru Sato (13 March 2011). "Fukushima No.3 Reactor Container Intact After Hydrogen Blast". Bloomberg Businessweek. Retrieved 14 March 2011.
4. KyodoNews (14 March 2011). "URGENT: Fuel rods at No. 2 reactor of Fukushima No. 1 nuke plant fully exposed". KyodoNews. Retrieved 14 March 2011.
5. KyodoNews (14 March 2011). "Ongoing work to cool No. 2 reactor hoped to stabilize situation". KyodoNews. Retrieved 14 March 2011.

• Current events from March 2011
• 2011 Sendai earthquake and tsunami
• Civilian nuclear power accidents
• Fukushima Prefecture
• History of Japan