Monday, 7 March Timeline of the Fukushima Daiichi nuclear disaster
Tokyo Electric Power ( Fukushima Newclear Power Plant ) Company (TEPCO) submits a report to Japan's nuclear safety agency which predicts the possibility of a tsunami up to 10.2 metres high at the Fukushima Daiichi nuclear plant in the event of an earthquake similar to the magnitude 7.2 earthquake with accompanying tsunami that devastated the area in 1896. TEPCO actually made this prediction in 2008 but delayed in submitting the report because they "did not feel the need to take prompt action on the estimates".
Friday, 11 March Timeline of the Fukushima Daiichi nuclear disaster
1. 14:46: A 9.0 magnitude earthquake strikes off the coast of Honshu Island at a depth of about 24 kilometres (15 mi). The Fukushima I power plant's nuclear reactors 1, 2, and 3 are automatically shut down by the tremor. Nuclear reactors 4, 5, and 6 were undergoing routine maintenance and were not operating, (reactor 4 was defueled in November 2010). The tremor has the additional effect of causing the power plant to be cut off from the Japanese electricity grid, however, backup diesel generators kick in to continue cooling. Tokyo Electric Power Company (TEPCO), the plant's operator, finds that units 1 and 2 are not operating correctly and notifies the proper officials.
2. 14:52: Reactor 1's emergency cooling system, which is capable of running without external power, turns on automatically.
3. 15:03: Reactor 1's emergency cooling system is manually shut down.
4. 15:27: The first tsunami strikes the plant.
5. 15:30: The emergency condenser designed to cool the steam inside the pressure vessel of the No. 1 reactor fails.
6. 15:46 (approximate): A 14-metre (46 ft) tsunami, unleashed by the earthquake, overtops the seawall designed to protect the plant from a tsunami of 5.7 metres (19 ft), inundating the Fukushima facility and disabling the backup diesel generators – all but one of which were housed underground – and washing away their fuel tanks. With the loss of all electrical power supply, the low-pressure core spray, the residual heat removal and low-pressure coolant injection system main pumps, and the automatic depressurization systems all failed (most of the emergency core cooling system). Only the steam-powered pump systems (isolation condenser in reactor 1, high-pressure coolant injection and reactor core isolation cooling system in reactors 2 and 3) remained available. Later, as the temperature rose, a system started that used steam-powered pumps[not in citation given] and battery-powered valves.
According to a report in the New York Times, "... at the start of the crisis Friday, immediately after the shattering earthquake, Fukushima plant officials focused their attention on a damaged storage pool for spent nuclear fuel at the No. 2 reactor at Daiichi, said a nuclear executive who requested anonymity.
1. 16:00: The Nuclear and Industrial Safety Agency of Japan (NISA) initiates an emergency headquarters in an attempt to gather information on the 55 nuclear reactors in Japan. There is no report that radiation was detected outside power-plant borders.
2.18:00: The falling water level in reactor 1 reaches the top of the fuel, and the core temperature starts climbing.
3. 18:18: Reactor 1's emergency cooling system is once again back on.
4.19:03: Prime Minister Naoto Kan declares a nuclear emergency status 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 procedures are being undertaken. They also announce that no radioactive leaks have been detected.
4.19:30: The fuel in reactor 1 becomes fully exposed above the water surface, and fuel damage in the central core begins soon after.
5.21:00: An evacuation order is issued by the government to persons within a radius of 3 kilometres (1.9 mi) from the Fukushima I station. Those within a radius of 10 kilometres (6.2 mi) are told that they can remain in their homes, and carry on with regular activities, until told otherwise. TEPCO announces that the pressure inside reactor unit 1 of Fukushima I is more than twice normal levels.
March, Saturday, 12 March
1. 02:44: Emergency battery power for the high pressure core-flooder system (HPCFS) for reactor 3 runs out.
2.04:15: Fuel rods in reactor 3 are exposed and 05:30: Despite the high risk of hydrogen (produced from the water in the containment vessel) igniting after combining with oxygen from water or in the atmosphere, and in order to release some of the pressure inside the reactor at Fukushima I unit 1, the decision is taken to vent some of the steam (which contained a small amount of radioactive material) into the air within the metal container building surrounding the unit.
3. 05:50: Fresh water injection into reactor 1 is started .
4. 06:50: Although unknown at the time, the core of reactor 1 has now completely melted and falls to the bottom of the reactor pressure vessel.
5. 10:09: TEPCO confirms that a small amount of vapor has been released into the air to release pressure in reactor unit 1 at Fukushima I.
6. 10:58: Pressure still remains too high inside reactor unit 2 at Fukushima I. In order to alleviate some of this pressure, a consensus is reached to once more vent radioactive vapor into the air.
7. 14:50: Fresh water injection into reactor 1 is halted.
8. 15:30: Evacuation of residents within 3 km of Fukushima II and within 10 km of Fukushima I are underway.
9. 15:36: There is a massive explosion in the outer structure of unit 1. The concrete building surrounding the steel reactor vessel collapses as a result of the explosion; however no damage is believed to have been sustained to the reactor itself. Four workers are injured.
10. 19:00: Sea water injection into reactor 1 is started. TEPCO orders Daiichi to cease seawater injection at 19:25, but Daiichi plant boss Masao Yoshida orders workers to continue with the seawater injection.
11. 21:40: The evacuation zone around Fukushima I is extended to 20 km, while the evacuation zone around Fukushima II is extended to 10 km.
To release pressure within reactor unit 1 at Fukushima I, steam is released out of the unit into the air. This steam contains water vapor, hydrogen, oxygen and some radioactive material, mostly tritium and nitrogen-16.
TEPCO engineers decided to directly inject sea water inside the pressure vessel of the reactors by means of the mobile trucks of the firemen. The pressure relief was also necessary to allow the firemen to inject seawater into the reactors vessels.
Sunday, 13 March Timeline of the Fukushima Daiichi nuclear disaster
1. 02:42: The high pressure coolant injection system for reactor 3 stops and, shortly thereafter, the water level within the reactor starts falling.
2. 07:00 (approximate): The water level in reactor 3 reaches the top of the fuel.
3. 09:00: Core damage starts occurring in reactor 3.
A partial meltdown was reported to be possible at unit 3. At 13:00 JST reactors 1 and 3 are vented to release overpressure and then re-filled with water and boric acid for cooling, and to inhibit further nuclear reactions.[20] Unit 2 was possibly suffering a lower than normal water level, but was thought to be stable; although pressure inside the containment vessel was high. The Japan Atomic Energy Agency announced that it was rating the situation at unit 1 as level 4 (an accident with local consequences) on the International Nuclear.
Timeline of the Fukushima Daiichi nuclear disaster
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