Someone at Yomiuri Shinbun who was made to read the TEPCO's report to the Nuclear and Industrial Safety Agency (NISA), the government overseer, found this bit of information in the main report (225 pages, in Japanese; English translation is on-going at TEPCO): Containment Vessels were damaged within 24 hours of the quake.
It is not in the summary slides (10 slides, in Japanese), which I did read. In the TEPCO's press conferences since May 15, Matsumoto never admitted to the Containment Vessel damage but he didn't deny it either. He specifically said in a press conference I watched that he "cannot deny the possibility of the Containment Vessel having been damaged." (I will link my post reporting that if I ever retrieve it; Google deleted it in their "maintenance".)
Looks like a fun reading. I will report back when I see the exact words from TEPCO on the subject.
It's also amusing to see the Japan's MSMs now use the word "core meltdown (炉心溶融) quite often, which was a taboo word for 2 months until TEPCO officially admitted it on May 15.
Yomiuri Shinbun (9:53PM JST 5/24/2011):
It's been revealed that the steel Containment Vessels of the Reactors 1, 2 and 3 that house the Reactor Pressure Vessels (RPV) may have been damaged within 24 hours after the earthquake on March 11, according to the detailed analysis of the core meltdown at Fukushima I Nuclear Power Plant by TEPCO.
The result of the analysis was compiled into a report and submitted to the Ministry of Economy and Industry's Nuclear and Industrial Safety Agency on May 23.
The detailed calculation of the reactors' operation data after the earthquake revealed that the bottom of the Reactor 1 RPV was broken after 15 hours after the earthquake because the emergency core cooling system didn't function well and the fuel started to melt down. There are many openings through which the control rods and the neutron measurement device goes through. The welded parts at the bottom, which do not have the same strength as the other part of the RPV, broke, and highly contaminated water that included the melted fuel may have leaked from there, according to the report.
I've been thinking about the "Level 7" designation of the Fukushima I Nuke Plant accident. When the NISA announced "Level 7", they were still publicly (at least) assuming that the majority of the fuel rods were more or less intact and inside the RPVs; that the RPVs were intact, and the Containment Vessels were intact, except for the Reactor 2 (the Suppression Chamber was damaged).
So, is it more likely now, that far more radioactive materials have escaped the reactors than the NISA or the Nuclear Safety Commission calculated? "Don't worry it's only 1/10 of Chernobyl" was another lie?
Or, were their calculations based on the secret knowledge that the RPVs and Containment Vessels were broken in the very early stage of the accident?