The zig-zag announcements regarding unit #1 fuel status is probably due to data available to TEPCO before and after they regained access to the control room. John Timmer at Ars Technica summarized the latest TEPCO release yesterday, covering much of the same ground as Will Davis (that I linked yesterday). But also including some info that was new to me:
The new analysis was enabled by the recent installation of air purifiers that let personnel reenter the reactor control room for the first time. Once inside, they were able to recalibrate some of the instruments that have been monitoring the reactor core; the revised numbers have enabled TEPCO to better understand what happened in the wake of the tsunami.
Timmer also linked the new TEPCO slide deck. That presentation is worth a careful read. Note the “Temperatures around RPV” chart at the end with diagram of sensor locations.
TEPCO says the bottom line is this:
1. RPV cooling water leak is likely
2. RPV significant bottom damage unlikely (inferred from temp/pressure data)
3. The corium on bottom of RPV “considered to be sufficiently cooled inside the RPV”
Not discussed are the leak(s) from the PCV, where the contaminated water is going, and what they are going to do next. In particular how are they going to achieve recirculation cooling? The following thumbnail is the temperature data from the PDF slide deck: