1. Fukushima Daiichi
Jourdan Robbins
12/6/ /16/16

2. WHEN DID IT HAPPEN Friday, March 11th, 2011 at 2:46 pm
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WHEN DID IT HAPPEN
Friday, March 11th, 2011 at 2:46 pm

3. WHAT HAPPENED
An earthquake, with a recorded magnitude of 9.0, gave a lot of damage to the northern part of Japan, especially in the prefectures of Fukushima, Miyagi and Iwate. 
After the earthquake, a tsunami also hit the plant. 
The Fukushima Daiichi nuclear power station, located in the Pacific Ocean coast, received a lot of damage by the earthquake and tsunami. 
The piping facility in the building, the facilities for the external power supply and backup power were destroyed. 

4. The next day, in the early morning, the leakage of radioactive materials had been found in front of the main gate of the nuclear power plant. 
The steam was filled in the building by the core melt down caused by the dysfunction of the cooling system. Lots of radioactive materials were scattered in the environment through “vent” to reduce the internal pressure and the hydroponic explosions of the nuclear reactors. 
The amount of radioactive materials released into the air were 770,000 tera Bq until beginning of Apr.11,2011, and still going on with high risk. 
It is said that this amount is about 20% of the Chernobyl accident. 
On April 12th, 2011, Nuclear and Industrial Safety Agency raised the rate of the accident from level 5 to the level 7, the same level as Chernobyl.  

5. Evacuation orders
The government issued an evacuation instruction for residents within 3km radius in the beginning. Eventually it was expanded to within 20km, and the residents of a range of 20km -30km were instructed to stay indoors. The movement of the radioactive plume and the information in the radiation dose was not released immediately.
The residents of the region lost the access to the supply of daily necessities such as foods, medicine, gasoline, etc. Though the distribution of the iodine tablet after the nuclear accident is the conventional means for reducing the risk of thyroid cancer. 
There were also cities that did not put out evacuation orders even though high level of radiation had been measured there.
The wide ranges of contamination had been identified through the Tohoku and Kanto region during 14th midnight to 15th.

6. Inside the reactors
Inside unit 1 the water level dropped to the top of the fuel around 6 pm and the bottom of the fuel 1.5 hours later. The temperature of the exposed fuel rose to some 2800°C so that the central part started to melt after a few hours.
In unit 2, water injection using the steam-driven back-up water injection system failed on Monday 14th, and it was about six hours before a fire pump started injecting seawater into the RPV. Before the fire pump could be used RPV pressure had to be relieved via the wetwell, which required power and nitrogen, hence the delay. Meanwhile the reactor water level dropped rapidly after back-up cooling was lost. , so that core damage started about 8 pm.

7. Inside the reactors
In Unit 3, the main back-up water injection system failed at about 11 am on Saturday 12th and early on Sunday 13th, water injection using the high pressure system failed also and water levels dropped dramatically. RPV pressure was reduced by venting steam into the wetwell, allowing injection of seawater using a fire pump from just before noon. 
In defuelled unit 4, at about 6 am on Tuesday 15 March, there was an explosion which destroyed the top of the building and damaged unit 3's superstructure further. This was apparently from hydrogen arising in unit 3 and reaching unit 4 by backflow in shared ducts when vented from unit 3.

8. Present situation
Work towards the decommissioning has been accelerated by conducting rubble removal at the site concurrently with cooling down. 
The plan of the dismantling of the facility will be terminated over years, but the decommissioning work has been hampered by difficulties in the very high radioactivity.
The radioactive materials from the Fukushima Daiichi nuclear power plant are still leaking. Of course, the amount is small compared with at the time of the accident. 
Most of radioactive materials are leaking from Unit 1-3 because of lack of the confinement function at the collapsed reactor building from Units 1-3. 

9. Video

10. SOURCES