Flooding caused by the tsunami rendered emergency power equipment inoperable thereby rendering cooling equipment useless. As a result, the water inside the pressure vessels of Units 1~3 evaporated causing water levels to drop.
In conjunction with the drop in water level, fuel rods (rods filled with nuclear fuel such as uranium) began exposed from the water surface, and hydrogen was generated by the chemical reaction between the fuel rods and water vapor. This hydrogen that accumulated inside the reactor buildings and caused hydrogen explosions at Units 1 and 3 that blew off the ceiling and walls of the reactor buildings.
At Unit 4, hydrogen flowed into the reactor building through joint ventilation pipes used to expel air from inside the Unit 3 containment vessel and accumulated in the reactor building where we assume an explosion occurred.
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The Development of and Lessons from the Fukushima Daiichi Nuclear AccidentNot found
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