TEPCO / NISA ASSUME ALMOST TOTAL CORE MELT AT FUKUSHIMA DAIICHI NO. 1
Hidehiko Nishiyama of NISA has been quoted at a press conference clearly indicating that it is the present assumption that the core material in No. 1 reactor is melted and at the bottom of the pressure vessel. The material is still inside the pressure vessel, according to NISA and TEPCO. Nishiyama has also indicated that (obviously, to this writer) the full flood of the dry well is no longer required, or helpful. Instead, TEPCO is preparing alternate plans. Meanwhile, all indications are that the core material is being cooled adequately in whatever configuration it is in at the bottom of the pressure vessel, according to NISA and TEPCO.
The assumption at this time by all official parties appears to be that the core is most likely totally destroyed. The assumption also appears to be there was not a total, catastrophic failure of the pressure vessel.
This writer wonders about the early statements by GE, and the NRC, that there might be as much as 50 tons of salt accumulated inside the pressure vessel at No. 1 plant. This seems to have been either forgotten or omitted in much of the present commentary. Given that most scenarios for long-term SBO include failure of the core support and dropping of the core to the bottom of the vessel, it's certainly plausible that this has happened. Perhaps, though, we should begin to wonder if this melted fuel material is encased in salt.. or sitting in a large mass of salt at the bottom of the pressure vessel. Perhaps, in fact, early core melt did actually cause some failures at the lower vessel head which was then plugged by the salt deposits. All of this is highly speculative.
What remains unclear, even with the finding of a number of failed "welded pipes" at the bottom head of the reactor, is the total number of leak paths for all this injected water out of the pressure vessel... and then the leak paths for this water out of the primary containment. We already know where it's ended up.
Another development regarding No. 1 plant... TEPCO has released the first exterior three dimensional view of the first type enclosure to be placed around No. 1 reactor building. Work to level the ground and gain full access to construct it is either underway at this time or about to start. Identical ones will follow for the other reactor buildings. Later, heavy concrete and steel buildings will be erected that will allow protection for workers engaged in dismantling the reactor plants during the decommissioning process. Below is the first type (fabric) enclosure.
2:40 PM Eastern Friday 5/13
ATOMIC POWER REVIEW
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