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Wednesday, November 30, 2011

TEPCO reporting on vessel failure

NHK has carried the distilled result of information it has obtained from TEPCO regarding the possible amount of fuel damage, and melt, and vessel failure, and fuel melt into the dry well at Fukushima Daiichi No. 1.

To summarize the report (and we should note this is all preliminary) TEPCO feels that the melted core material that exited the pressure vessel may in the worst case, or in other words if the worst postulated case exists, have eaten about 2/3 of the way into the bottom structure of the dry well.

No exit of the material from the dry well structure is supposed.

TEPCO does not feel the material could have gotten below the structure, or into the actual basement, or come in contact with the floor or the ground. The material is not in the earth below the plant. Such reports as this are circulating, leading to a widely hysterical supposition on one site of a "hydrovolcanic explosion." That is about the worst - and certainly the least intelligent - hyperbole this author has ever read. I only mention it here because TEPCO's initial analysis released to NHK today (and about which I'm sure we'll see more) is timely in relation to that story.

Readers of this blog are all too well aware of this likelihood. In fact, let's take a look at a post from way back -- below is a link to a post I made on May 14th, 2011 when details were still far from clear about the plant conditions.

Fukushima Daiichi No. 1: Core melt / exit of pressure vessel speculated by TEPCO, NISA (post from May 14, 2011)

Readers may recall, a couple of months back, repeated attempts by TEPCO to indirectly assess the conditions of the lower vessel heads at the three reactor plants. None of these was successful - no useful data was obtained. What was clear though was that the electrical equipment in the lower head area was very heavily deranged, and not just in one zone or area, it appeared. TEPCO would like very much to get a handle on the actual condition and location of core material at each plant (and each is different in this respect) but so far has been really unable to directly assess this. The new study results that NHK is quoting come from a variety of data TEPCO has accumulated which don't require direct vision or detection. This is probably the best we'll have for a while.

Sharp readers also may recall the days in which the JAIF was continuously posting updates; that organization's last given estimate of core damage at No. 1 plant was, I believe, 70%. I should add though that all the data JAIF was using to attempt to estimate core damage percentages was very rough and some of JAIF's revisions of core damage percentages were taken directly from TEPCO. (Of course, all of JAIF's news items now are from NHK -- it has stopped making its own statements or assessments, at least in public.)

When TEPCO releases the full detail of this report, I'll put those details here.

9:15 AM Eastern Wednesday November 30, 2011


The NHK report indicates a melt depth of about 2.1 feet. The distance to the ground is roughly eighteen times this depth from the dry well interior floor to grade. Below is a drawing from WASH-1082 which I've marked to show the distance from the dry well floor to the grade outside, which on the particular plant shown is 39' 0". I do not presently know the exact measurement at Fukushima Daiichi No. 1 but it is likely within ten percent of this measurement... meaning that in the worst case that TEPCO is describing, by its own data, the core material may have melted only about as much as 5% of the distance to the grade.


  1. It's useful to know worst case - did they sepculate on median likelihood and minimum damage cases too?

  2. @joffan: If they did, I'm not yet aware of it. I believe that the assumptions I made in the May 14th post still hold, as do the others I've made on the blog over time. These briefly are that the cores at all three are seriously damaged or totally demolished, that penetrations or possibly some sections of head material in the lower vessel head are damaged and possibly some other pipes are broken or valves stuck open, that there is core material in the dry well of each but that it's not melted through the dry well to its exterior. This seems to be the consensus of official, official but not publicly stated (and don't ask what those are) and unofficial but well-informed sources.

  3. Will,

    An AP article is now making the rounds with the usual end-of-the-world prognosis by the anti's and the spreaders of FUD even though the news release is about TEPCO's simulation not actual data.

    The AP article is stating the fuel came within 12" of breaching the "crucial steel barrier". Looking at your diagram it appears this would be the dry well. Is that a correct interpretation?


  4. @will rodgers: I would imagine you are correct. However, I am not so sure I'd label the dry well itself at that level as the only barrier to release to the outside world, as you can see in the diagram I've provided. The AP is good for FUD nowadays; it sells papers.

  5. Will- Do you have information regarding how the cooling water is flowing from the drywells/wetwells and into the turbine buildings? I know the containments were overpressurized during the meltdowns. Is there a working theory on which parts of the containments failed?

  6. @t. This is another of those $64,000 questions that we'd all like an answer to. There are a couple of working theories. First is that the earthquake compromised the integrity of the structure so that when the melt occurred and vessel damage occurred, water could then get out of the drywell. Another theory is that the hydrogen blasts may have had something to do with it, although frankly there's water in No. 2 plant turbine building and now we know there was no blast at that plant at all. Further possibilities include broken piping or piping used in vain attempts to restore cooling. We are not going to know fully until probably some time from now, maybe several months. This is one of the most important things to figure out coming out of this accident because it's clearly unexpected. As I posted many times on this blog, many simulations, calculations and models predict core melt in long term SBO .. so on and so forth.. but you never expect the wide spread of the coolant with entrained core material outside the reactor buildings. You could make a case that this spread of water is probably the worst UNPREDICTED event in the entire accident scenario as we understand it now.

  7. Will, Fukushima was hit with an over design basis earthquake and tsunami, and yet we are assuming that the structure itself remains monolithic, there are no cracks, no settlement (even some areas of Honshu are now underwater at high tide that never were before). Also report of steam rising from ground, AND no pictures of the Corium.

    Not to mention repeated lies and misinformation, lack of using radiation spread software and instead just concentric circles, and a host of other reasons (like smile and you won't be affected by radiation) that really discredit the entire system.

    In light of this, why do you believe any information that is "provided to us"

  8. @steveo: Who assumed that the containment has no failures? I've been saying that there were clearly problems with the containment for a long time... otherwise, how did water get into the turbine buildings? I have not seen steam rising from the ground at Fukushima Daiichi at all, and we tried to substantiate those reports a couple months back when they first hit the net and could not. There's plain little about Fukushima Daiichi I cannot find out. How do you expect anyone to get into the high rad field to photograph the drywell interior at this point?

    Further, I have seen no lies. Mistakes, yes, in estimation and calculation and reporting by TEPCO before it had all the facts but no lies. No one says "smile and you won't be affected" - most of us that write (responsibly) about the accident have been occupationally exposed to radiation and know the limits and risks.

    I believe the information provided by TEPCO, NISA and the Japanese government bodies as best I can believe it when released. If I don't believe it I say I don't believe it. No one gets a free pass on this blog - and that also includes, by the way, the anti-nuclear crowd.