Fukushima 1 Nuclear Accident Day 2: Saturday, 12 March

Emergency battery power for the High Pressure Core Flooder System for #3 ran out.
Fuel rods in #3 are exposed.
Officials declare a heightened state of alert for Fukushima II (Dai-ni). Officials declare a state of nuclear emergency for Fukushima I (Dai-ichi).
Despite the high risk of the hydrogen ignited after combining with oxygen in water or the atmosphere, 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 in the concrete container building surrounding the unit.
TEPCO confirms that a small amount of vapor has been released into the air to release pressure in reactor unit 1 (Fukushima I).
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.
Evacuation of residents within 3 km of Fukushima II underway. Evacuation of residents within 10 km of Fukushima I underway.
Unit 1 at Fukushima I: cameras document a massive hydrogen explosion on the outer structure of one of four buildings at the plant. It also documents the outer structure collapsing. TEPCO 3 hrs later announces that four persons who are employed at the power plant have been injured.
18:36 (approximately)
TEPCO announces that four persons who are employed at the power plant have been injured in the unit one explosion.
Uncertainty surrounds the actual cause of the blast at Fukushima I (later identified as a hydrogen explosion) and the damage caused.
Yukio Edano announces that the concrete building surrounding the steel reactor container at unit 1 in Fukushima I has collapsed as a result of the explosion; however no damage has been inflicted on the reactor itself.
Evacuation zone around Fukushima I extended to 20 km. Evacuation zone around Fukushima II extended to 10 km.
To release pressure within the 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 16N.

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