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Overview of Current Status of the Accidents
Editorís view of what are not reported (3/19)
In the past few days, the water sprinkling by the fire fighters and Japanese Defense Army has been reported frequently but no significant reports have been released on the conditions of the reactor cores that have been damaged. Also, no reports have been made regarding the spent fuels in No1 and No.2 reactors.
The editorís view on these issues are as follows:
In Reactor No.1, the fuel rods were exposed without water for some period of time. Since fuel rods cannot sustain for long when no cooling is available, some portion of the fuel rods should have been damaged.† Damage of the fuel rods means that zirconium alloy cladding of the fuel rods are broken and consequently the fuel pellets (uranium oxide of approximately 1 cm diameter and 1 cm high) are no longer contained in the cladding tubes but fell toward the bottom of the reactor core or possibly to the bottom of the pressure vessel.
In reactor No.2, an explosion in the pressure suppression pool was reported on 3/15.† The cause of the explosion must be burning of the hydrogen gas generated inside the reactor core, that is, the zirconium alloy cladding reacted with water under the condition that no water covered the fuel rods.† This must be a severe damage of the fuel rods.† A significant fraction of the core, possible the almost entire fuel rods, collapsed and fell downward in the form of pellets. The fuel pellets may be stuck in the middle of the control rods assembly or have fallen to the bottom of the pressure vessel.† The only mechanism to prevent from melt-down of the uranium oxide is the cooling effect of the water in the bottom of the pressure vessel.† This condition is very dire, as the core material can melt forming a molten mass that can penetrate the pressure vessel bottom.
In Reactor No.3, the fuel rods were exposed without water for some period of time. The condition inside the reactor core seems to be similar to that of No.1.† Damage of the fuel rods means that zirconium alloy cladding of the fuel rods are broken and consequently the fuel pellets are no longer contained in a rod form but fell toward the bottom of the reactor core or possibly to the bottom of the pressure vessel.
Spent fuel pool of No.1 reactor.† When the hydrogen explosion at the top portion of the reactor building occurred, where the hydrogen came from was not known, or at least not reported.† However the explosions at No3. reactor and No.4 reactor are very similar to that of No.1 reactor. Therefore, we must conclude that the spent fuels were overheated and generated hydrogen gas that ignited in No.1 plant. Therefore the spent fuels are in a similar condition as in No.3 and No.4 although no effort to supply water to the spent fuel storage pool has been made.†
The condition of the spent fuel pool of No.2 reactor is not known. No effort to supply water to the spent fuel pool has been made.† However, we must concern about it.††