Unlike Units 2 & 3, Unit 4 didn't erupt in a violent explosion(s) and is relatively intact so workers can approach for short periods of time without being totally irradiated. Anyway, TEPCO's guessing the amount of water covering the melted core was off by about 25'. This besides that some of the melted radioactive fuel is still shown in the Pressure Vessel and some has fallen below unto the floor of the Primary Containment. This leads to the question of how can cooling take place when the water level is so low that it leaves the upper portion of the melted fuel exposed? It is no wonder that gauge and sensor readings report high heat levels at the bottom of the Pressure Vessel when cooling water being constantly pumped in can only shower down as it passes by the upper areas falling to a water level shown in the picture. In other words, TEPCO couldn't flood to keep the melted fuel underwater at all times if they wanted to due to massive leaks. Besides any water that comes in contact with the melted fuel becomes radioactively contaminated.
posted on 03/27/2012 9:32:01 AM PDT
The reaction is over.
All that remains is decay heat.
Since it has already melted through the reactor vessel, there is no longer any need to add any more water.
posted on 03/27/2012 11:30:33 AM PDT
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