The muon scan of the Unit 1 reactor vessel at Fukushima has been completed. No nuclear fuel was fuel in it. No surprise.
According to this article at Simply Info,
TEPCO published the results of the muon scan done by IRID and their cooperating partners. No fuel was found in the reactor vessel of unit 1 Fukushima Daiichi… This was as expected by many (including us) who have been documenting the other evidence that indicated this was the likely case… Also noted on these images was the lack of detectable solid vessel in the bottom head area. The center lower section of the reactor vessel appears to be missing. The uniform dark outline of the reactor vessel is noticeably missing…
The corium has burned through the vessel and has melted through to the basemat and drywell floor. The question is whether it burned through that too, into the soil underneath. I would say this is very likely.
From this long Sandia pdf,
The drywell floor is subdivided into three regions (i.e., cavities) for the purposes of modeling molten-core/concrete interactions (see Figure 20). The first region, which receives core debris exiting the reactor vessel, corresponds to the reactor pedestal floor and sump areas (CAV 0).
Debris that accumulates in CAV 0 can flow out through a doorway in the pedestal wall to a second region representing a 90 degree sector of the drywell floor (CAV 1). If debris accumulates in this region to a sufficient depth, it can spread further around the annular drywell floor into the third region (CAV 2). This discrete representation of debris spreading is illustrated in Figure 20. (p. 64)
It was already assumed that the molten fuel had interacted with the concrete:
The three accidents (i.e., the accidents in Units 1, 2, and 3), while similar in many ways in terms of SBO accident progression, each proceeded to different degrees of core damage, with Unit 1 believed to be the most severely damaged of the three. It is believed that the Unit 1 core damage proceeded to the point of lower vessel head failure that released core materials to the containment cavity where core-concrete interactions likely initiated. Units 2 and 3 are believed to be less damaged. Collectively, the accidents likely reflect varying degrees of core/reactor damage and are therefore an invaluable source of information that can validate/confirm our current understanding of severe reactor accidents and provide new understanding not currently realized in our body of knowledge. (p. 18)
I was already talking about the corium-concrete reaction when I was still posting at the Japan Earthquake scribble. This must have been in early 2011. The corium-concrete reaction liberates all sorts of radionuclides that wouldn’t have been released otherwise, and the concrete particles help spread the radioactive particles into the wind.
Note high levels of Ba-140 and La-140 on March 15-16. Lanthanum-140 is the daughter product of Barium-140… If a TMI-style meltdown occurred, using Dr. Saji’s inventory figures (below), there would have been a 23:1 ratio of I-131 to Te-129m released. The Takasaki figures indicate a 1:2 ratio. The data do not support this scenario…
“This study describes the increase in iodine activity released to the atmosphere during a severe accident due to the radioactive decay of tellurium precursors… here it is seen that the iodine activity in the atmosphere is due disproportionately to I-132. Unlike the longer-lived isotopes, most I-132 (half-life of 2.30 hr.) existing early in the accident will decay before the significant atmospheric releases which follow reactor vessel failure. However, the supply is replenished by the decay of Te-132, which is released in large quantities from the drywell rubble.”
Takasaki is almost 100 miles from the Fukushima plant. Thus most of the I-132 which was released would be decayed. The large amounts of I-132 detected must have come from the decay of Te-132.
From p. 533, “Upon contact, the molten core material (the so-called “corium”) starts to react with the material of the basemat concrete… when the reaction zone is flooded with sump water… the highest temperatures might be reached… the molten-core – concrete interaction is the principal source of the release of the low-volatility fission products to the containment. The volatilization of these elements, such as barium, strontium, lanthanum, and cerium, is strongly supported by the gas bubbles which penetrate through the molten zone.”
Note again the high concentrations of barium and lanthanum, and that of tellurium.
Conclusion: The emissions observed at Takasaki were not due to a TMI-style accident, but one in which corium interacted with concrete and water. This released significant concentrations of barium, lanthanum, and strontium into the atmosphere.
Well, it’s about time they did this scan. It’s only been 4 years.
FUKU+4 HEALTH NOTE: Really nasty hand-foot-mouth rash on my hands and feet. This is from a disseminated enterovirus infection, from a virus I caught almost a year ago. I don’t know what strain or type of enterovirus it is. It has infected the neurons in the brain and spinal cord (thus it is myalgic encephalomyelitis). Minor improvement today… I did a technical thing, added a Mid-p feature to my Fisher’s exact test program for large samples. It is good to know that I can do math and scientific programming again. Things are still dire, though.