NISA nor any government agency asked for the report, but TEPCO apparently volunteered. The voluminous data is supposed to refute the claim by certain researchers that the melted fuel at the bottom of the RPV in Reactor 3 may have been re-melted on March 21 and went through the RPV and dropped on the floor of the Containment Vessel, releasing a huge amount of radioactive materials as evidenced by large spikes in air radiation throughout Tohoku and Kanto on that day.
According to TEPCO, there was no re-melt, because their data shows that the amount of water into Reactor 3 RPV was more than adequate, and the spikes in air radiation was simply because of the rain, and had nothing to do with what was happening in Fukushima I Nuclear Power Plant.
The 565-page report also covers the other reactors.
I think I know what this is all about. It's TEPCO's defense and counterattack against the former Kan administration officials like Cabinet Secretary Edano and Prime Minister Kan himself, who, upon resigning, immediately started the media blitz to spread their versions of the event, painting themselves as selfless heroes worried for the humanity and TEPCO as the sole villain.
TEPCO's report on September 9 in Japanese:
http://www.tepco.co.jp/cc/press/betu11_j/images/110909m.pdf
The company promises it will upload the English translation as soon as it is done.
In the press conference on September 9, TEPCO released these charts as part of the evidence that there was no re-melt. TEPCO's translation is just as bad as the man who pointed finger at TEPCO livecam, but I hope the charts speak volume:
