- Station Manager Yoshida decides to use seawater as a cooling source, but TOEPCO headquarters tells him to wait for authorization from the administration.
- Maejima is able to stop Kinoshita and Tateno just before they are about to enter the reactor unit 1 building.
Turns out the white smoke was only water vapor from the nuclear reactor. The compressor attached by Yoshida to open the valve from outside worked and hence vented the reactor as planned. It is around 2:30 PM and the pressure in the primary containment vessel is already at 610 Kpa and dropping.
On the evening of March 12th, the debris outside the unit 1 turbine building is cleared. The voltage truck cannot be connected to the switchboard and the fire engines are to be connected to the fire prevention system instead to spray cold water inside the reactor chamber to cool down the nuclear fuel. The process took 4 hours as the injection point for the fire prevention system was hidden under the debris.
Power was restored to unit 1 (and 2) using a mobile generator at 15:30 on March 12. It is evening of March 12th 3:36 PM. As the fire trucks are out of fresh water, Yoshida makes the decision to start injecting sea water into the reactors. This is when the entire plant is rocked by a large explosion. A hydrogen explosion had damaged the secondary confinement structure (the RB) of Unit 1. A large plume of dust rose, and the explosion injured almost all the workers working outside of the buildings. After the initial panic the radiation was measured at 6 MSV outside the buildings, which could not be so low if the actual containment structure had blown apart.
The debris produced by the explosion damaged the mobile emergency power generator and the seawater injection lines. And the containment vessel of unit 1 is exposed to open air. Since the freshwater is out, Yoshida asks the Fire Department team led by Hayami to lay down the injection lines to the ocean, but the ocean is too far away. They find a backwash valve pit which is 9 meters by 66 meters. It is full of seawater due to the tsunami and much closer to the injection point for Unit 1. The seawater injection lines were repaired and put back into operation at 19:04 on March 12th.
With seawater, there is a chance of Recriticality as seawater is not pure. At the Cabinet meeting for crisis management, nobody can say for sure if there is a real threat of Recriticality. Japan faces a power shortage. Murukami informs the Cabinet that by 6 PM on 13th March, the country will have to resort to load shedding to manage the grid. He is instructed by Chief Cabinet Secretary Sano to ask large companies to cut down power usage, so hospital and home care patients continue to receive power.
Meanwhile Yoshida is ordered by Murukami (VP of TOEPCO) to stop injecting seawater into the reactor and use as much fresh water as he can. Yoshida overrules the order and continues to inject sea water into the reactor. Yoshida is disgusted that the people from SDF and his own team are risking their lives to save the power plant, and yet the orders are being given by people who have no clue about the condition on the ground and the side consequences of their decisions. No keeping the reactor cool will lead to fuel meltdown and nuclear fuel can eat through the containment vessel and seep into the ground.
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