Day 3 of the inspections inside the unit 3 pedestal have been concluded. TEPCO did not report if the ROV unit (Sunfish) is still operable or if it had been abandoned inside unit 3.
They were able to move the ROV into the pedestal and obtain photos of the areas around the melt hole in the upper grate and also into the basement level of the pedestal. We have an archive of images from unit 5 for these same areas for comparison.
The three images for the lower area of the pedestal all appear to show what may be a debris bed of melted materials. These look somewhat like known types of corium including both brown and pumice type. It would require sampling these materials to know for sure.
The photos from the lower areas of the pedestal lack the light colored thick smooth blobs seen higher up in the pedestal and in the areas of the containment structure at the same general height.
This diagram roughly indicates where the splattered materials have been seen vs. the assumed debris bed.
TEPCO has not publicly admitted sampling any of these substances to date. The lighter colored substances may be some form of byproduct from the reaction caused between the concrete and the molten fuel (corium). A molten corium concrete reaction (MCCI) is a well know process where the molten fuel and reactor materials decompose the concrete and integrate it into the fuel mass. Both limestone and the constituent materials of portland cement are known to be able to become molten themselves at high enough temperatures. Yet substances like those found inside unit 3 have not been found in any previous reactor meltdown or corium research conducted in a lab setting that we are aware of. Sampling of these residues would be the best way to determine what they are actually made of. That would likely be sufficient to trace the cause of the splattered substances.
TEPCO had not released video of either the 2nd or 3rd inspections and the completed muon scan for unit 3 has also not been made public. No radiation readings have been provided for this work inside unit 3. This may be due to the scandal in the media after similar work in unit 2. A number of major media outlets incorrectly described a high radiation reading found inside unit 2 containment as being a reading “at the plant”. This caused public concern that there was a new radiation leak to the environment at the disaster site. The radiation readings from inside unit 3 containment are still significant and important information that should be released to the public.
TEPCO and IRID may continue to analyze the data collected from this work. We will update if more information is made public.
Our image archive for this series of inspections can be found here.
Images below are the original images from TEPCO plus an enhanced copy. Images with our watermark are the modified versions.
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