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Friday, May 13, 2011

Fukushima Daiichi No. 1: Meltdown?

Note: Blogger.com has been down for almost an entire day, preventing any new posts and actually removing, temporarily I'm told, some of the posts made between Wednesday and now. This was due to data corruption during a site software update. Read more at this link from the official Blogger Buzz blog.

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

4 comments:

  1. Thank you for this insightful comment.
    You are the first blogger to raise the salt issue, afaik, yet it seems a very important factor.
    Salt has many virtues as a nuclear packing material, so much so that Germany planned to store its nuclear waste in salt mines.
    Here the salt may be preventing the loose fuel pellets from collecting together, thereby averting a meltdown.
    That might imply that more salt should be added to the cores.
    Is there any analysis on this topic in the public domain?

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  2. The salt issue has been overlooked. Good point.

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  3. netudiant, the pellets "collecting together" is not a determining factor in meltdown, if you have in mind the misconception that there is a critical mass problem. There is not; there is only a moderated reaction potential, and for that the fuel needs to be in a carefully controlled and measured geometry with a moderator, not collected in a heap. Decay heat will continue to be produced; now at signficantly lower rates than in March, of course, but still easily enough to boil water. Roughly, it will now be one-thousandth of the thermal output of the reactor at full power - say 1500kW @1 and 2500kW @2 & 3.

    The meltdown, such as it was, has already happened; the strong likelihood of fuel melt was acknowledged much earlier in the process.

    I am grateful for will's diligence, and this is not the first time that salt clogging has been mentioned on this blog - remarks early in the process may well have been some of the first - an example from April.

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  4. Overlooked ,yes!!!the salt issue was ignored&recklessly handled,I ,in this blog I commented to a post at the time period when Seawater was flown into the reactor,i wrote clearly that at high temperatures rapdid Salt deposit and scale formation is a must happening process,which would lead to cracks and breakages in core and pipes that would make more leakages .leading to total collapse of the reactor.And thats happening now, so bad.Why was this not thought by Scientists outside Japan,that such a problem would arise with Sea water? i asked the same question to the author of this bog.

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