In the first post on the subject, I translated what NHK reported:
It has been discovered by TEPCO's analysis that the significant amount of Reactor 1's melted fuel pierced through the steel Reactor Pressure Vessel and dropped onto the Containment Vessel, then melted the concrete at the bottom of the CV. It is estimated that the melted fuel may have eaten into the concrete to maximum 65 centimeters deep.
Maximum 65 centimeters deep from the bottom of the concrete floor, right?
Well no. It's 65 centimeters from the bottom of the deep groove on the concrete floor.
And neither NHK nor TEPCO would bother to tell you how deep the groove is.
At least, NHK Kabun (NHK's last remaining conscience, as far as I'm concerned) tweeted and gave the link to its blog post, where NHK's analysis of the concrete-eating corium is shown with the screenshots from the program:
The text below the screen says: "In the worst case, it [the corium] may have reached 65 centimeters from the surface of the concrete. Where the concrete is the thinnest, it may have reached within 37 centimeters from the steel plate [of the Containment Vessel].
The "surface of the concrete" turns out to be the surface of the bottom of the groove that is X centimeter deep.
It's one thing for TEPCO's Matsumoto to say "surface of the concrete" (as we've gotten used to hearing technically correct explanations from him), but for NHK to say so while showing the graphics indicating it is the surface of the bottom of the groove is at once deceptive and covering its behind. NHK can now say "We showed it in the graphics that it was 65 centimeters from the bottom of the groove, and people should have paid attention."
(I'm asking NHK Kabun if they know the depth of the groove, but does anyone know or have access to a schematic diagram with measurement?)
Well, it does look like the Institute of Applied Energy is more right than TEPCO in saying the corium has eaten 2 meters into the concrete. And perhaps people like Hiroaki Koide of Kyoto University and the engineers who designed the reactors at Fukushima I Nuke Plant may be more right than the Institute of Applied Energy, and the corium has indeed escaped the Containment Vessel long time ago.
As the wiki entry on "corium" states, the corium can eat into the concrete 1 meters in the first one hour, and several centimeters per hour afterwards:
The fast erosion phase of the concrete basemat lasts for about an hour and progresses into about one meter depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about 1100 °C). Complete melt-through can occur in several days even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools and solidifies. During the interaction between corium and concrete, very high temperatures can be achieved.