TEPCO has concluded that most of the fuel in the Unit 1 reactor is damaged. The original estimate of 55% core damage was low based on the data now available. The fuel is at the bottom of the reactor vessel and the heat from the molten mass melted holes through the bottom of the vessel at welded seams. The damaged fuel is being cooled by the continuous water injection into the vessel and is being maintained below 100°C. On Sunday the injection was increased from 8 to 10 tons/hour (2100 – 2600 gal/hr) to quantify the cooling affects. The increased flow decreased the temperature of the fuel at the bottom of the vessel by 15° C. The plan to submerge the fuel by filling the reactor containment has been scuttled because of the leaking water. Two alternate plans are being considered. Both will continue to inject water into the reactor vessel, but the first would circulate the water already in the reactor containment through a heat exchanger and then into the reactor. The second would draw the water from the flooded reactor building which has accumulated over 12 feet of water in the basement.
Radioactivity in water samples from the inlet bay near Unit 3 are on the rise again indicating leakage from the plant. Radioactive cesium was measured to be 2400 times above the allowable limits. TEPCO also reported Iodine-131 in water samples taken near the Unit 2 intake at 2,100 times the legal limits. We will be watching for an explanation of this sample because the radioactive iodine from the fuel should have decayed to negligible amounts since the March 11 earthquake shutdown the reactors.
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