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Comments by T. Fronte
        Fukushima BWR General Electric                
                 
 
                                                                                                               
                                                                                                                                                                                             
      Cooling corium at Fukushima                          
                                                                         
         
         
         
             
             
             
         
         
         
             
             
                                                                         
        Cooling the "corium"         The Fukusmima case              
                                                                                                                                                                                                       
       

In many normal operating cases, should the coolant stop flowing through a reactor , the fuel rods become insufficiently cooled and the rise of their temperature may within minutes initiate a meltdown. Even if the coolant flow is fully restored , some paths may have been restricted by molten or distorted parts ; the spots which can’t any more be reached by the needed rate of coolant will suffer more overheating and the disorder may expand in the reactor core.

A molten core, also known as “corium”, is an heterogeneous jumble of radioactive fuel , metallic structures and casings ; depending on the shape and the location of this disparate conglomerate, it may prove very difficult or impossible to cool or to remove .

The cost and the time frame of the deactivation are largely unpredictable . For instance, the “official end of clean up” at the unit 2 of Three Mile Island occurred 14 years after the 1979 accident . At Chernobyl , the case is still on going , although the accident occurred tens of years ago, in 1982.



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Most likely , the cores of the reactors started to meltdown in the early stages of the accident, in march 2011 ; this is consistent with the releases of products of radioactive fission - iodine-131 and caesium - which suggest that the radioactive fuel was escaping from overheated and cracked rods. In addition, the hydrogen responsible for several explosions is the product of water interacting with overheated zirconium fuel assemblies.

Two months after the incident, officials have confirmed the meltdowns of the reactors 1 to 3; in addition they have reported that some reactor vessels and containments are breached.

The efforts are first of all aimed at preventing the coolant from flowing through many unidentified leaks; pending this goal, part of the coolant which is sprayed or injected in the molten reactors reaches the environment ; an other part is stored , waiting for later decontamination process.

The amount of coolant released in the environment can hardly be evaluated.

The highly contaminated coolant which has been collected and stored for more than two mounts could be in the scale of 100.000 tons. It’s about the capacity of 40 average Olympic swimming pools, 2500 m3 each .

This is a facet of the disaster.

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2008-2011